1.
Wetting
–
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting is determined by a balance between adhesive and cohesive forces. Wetting deals with the three phases of materials, gas, liquid, and solid and it is now a center of attention in nanotechnology and nanoscience studies due to the advent of many nanomaterials in the past two decades. Wetting is important in the bonding or adherence of two materials, Wetting and the surface forces that control wetting are also responsible for other related effects, including capillary effects. There are two types of wetting, non-reactive wetting and active wetting, adhesive forces between a liquid and solid cause a liquid drop to spread across the surface. Cohesive forces within the cause the drop to ball up. The contact angle, as seen in Figure 1, is the angle at which the liquid–vapor interface meets the solid–liquid interface, the contact angle is determined by the result between adhesive and cohesive forces. As the tendency of a drop to spread out over a flat, solid surface increases, thus, the contact angle provides an inverse measure of wettability. A contact angle less than 90° usually indicates that wetting of the surface is very favorable, contact angles greater than 90° generally means that wetting of the surface is unfavorable, so the fluid will minimize contact with the surface and form a compact liquid droplet. For water, a surface may also be termed hydrophilic. Superhydrophobic surfaces have contact angles greater than 150°, showing almost no contact between the drop and the surface. This is sometimes referred to as the Lotus effect, the table describes varying contact angles and their corresponding solid/liquid and liquid/liquid interactions. For nonwater liquids, the term lyophilic is used for low contact angle conditions, similarly, the terms omniphobic and omniphilic apply to both polar and apolar liquids. Liquids can interact with two types of solid surfaces. Traditionally, solid surfaces have been divided into high-energy solids and low-energy types, the relative energy of a solid has to do with the bulk nature of the solid itself. Solids such as metals, glasses, and ceramics are known as hard solids because the bonds that hold them together are very strong. Thus, it takes an input of energy to break these solids. Most molecular liquids achieve complete wetting with high-energy surfaces, the other type of solids is weak molecular crystals where the molecules are held together essentially by physical forces
2.
Soldering
–
Soldering, is a process in which two or more items are joined together by melting and putting a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces, in brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated use of alloys for electronics. There is evidence that soldering was employed as early as 5000 years ago in Mesopotamia, soldering and brazing are thought to have originated very early in the history of metal-working, probably before 4000 BC. Sumerian swords from ~3000 BC were assembled using hard soldering, soldering was historically used to make jewelry items, cooking ware and tools, as well as other uses such as in assembling stained glass. Soldering is used in plumbing, electronics, and metalwork from flashing to jewelry, jewelry components, machine tools and some refrigeration and plumbing components are often assembled and repaired by the higher temperature silver soldering process. Small mechanical parts are often soldered or brazed as well, soldering is also used to join lead came and copper foil in stained glass work. Electronic soldering connects electrical wiring and electronic components to printed circuit boards, soldering filler materials are available in many different alloys for differing applications. In electronics assembly, the alloy of 63% tin and 37% lead has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications, a eutectic formulation has advantages when applied to soldering, the liquidus and solidus temperatures are the same, so there is no plastic phase, and it has the lowest possible melting point. Having the lowest possible melting point minimizes heat stress on electronic components during soldering, and, having no plastic phase allows for quicker wetting as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as the temperature drops through the liquidus and solidus temperatures, any movement during the plastic phase may result in cracks, resulting in an unreliable joint. Common solder formulations based on tin and lead are listed below and they are also suggested anywhere young children may come into contact with, or for outdoor use where rain and other precipitation may wash the lead into the groundwater. Unfortunately, most lead-free solders are not eutectic formulations, melting at around 250 °C, alloying silver with other metals changes the melting point, adhesion and wetting characteristics, and tensile strength. Of all the brazing alloys, silver solders have the greatest strength, specialty alloys are available with properties such as higher strength, the ability to solder aluminum, better electrical conductivity, and higher corrosion resistance. The purpose of flux is to facilitate the soldering process, one of the obstacles to a successful solder joint is an impurity at the site of the joint, for example, dirt, oil or oxidation. The impurities can be removed by mechanical cleaning or by chemical means and this effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the workpiece. One of the earliest forms of flux was charcoal, which acts as a reducing agent, some fluxes go beyond the simple prevention of oxidation and also provide some form of chemical cleaning
3.
Corrosion
–
Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
4.
Wear
–
Wear is related to interactions between surfaces and specifically the removal and deformation of material on a surface as a result of mechanical action of the opposite surface. In materials science, wear is erosion or sideways displacement of material from its derivative, Wear of metals occurs by the plastic displacement of surface and near-surface material and by the detachment of particles that form wear debris. The size of the particles may vary from millimeter range down to an ion range. This process may occur by contact with metals, nonmetallic solids, flowing liquids. Secondary stage or mid-age process, where a rate of ageing is in motion. Most of the operational life is comprised in this stage. Tertiary stage or old-age period, where the components are subjected to rapid failure due to a rate of ageing. The secondary stage is shortened with increasing severity of conditions such as higher temperatures, strain rates, stress. Note that, wear rate is influenced by the operating conditions. Specifically, normal loads and sliding speeds play a role in determining wear rate. In addition, tribo-chemical reaction is important in order to understand the wear behavior. Different oxide layers are developed during the sliding motion, the layers are originated from complex interaction among surface, lubricants, and environmental molecules. In general, a plot, namely wear map. Demonstrating wear rate under different loading condition is used for operation and this graph also represents dominating wear modes under different loading conditions. Surface engineering and treatments are used to wear and extend the components working life. The study of the processes of wear is part of the discipline of tribology, the complex nature of wear has delayed its investigations and resulted in isolated studies towards specific wear mechanisms or processes. Impact-, cavitation-, diffusive- and corrosive- wear are all such examples and these wear mechanisms, however, do not necessarily act independently and wear mechanisms are not mutually exclusive. Industrial Wear are commonly described as incidence of multiple wear mechanisms occurring in unison, another way to describe Industrial Wear is to define clear distinctions in how different friction mechanisms operate, for example distinguish between mechanisms with high or low energy density
5.
Hardness
–
Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials are harder than others, Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of matter are ceramics, concrete, certain metals, and superhard materials. There are three types of hardness measurements, scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales, for practical reasons conversion tables are used to convert between one scale and another. Scratch hardness is the measure of how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object, the principle is that an object made of a harder material will scratch an object made of a softer material. When testing coatings, scratch hardness refers to the necessary to cut through the film to the substrate. The most common test is Mohs scale, which is used in mineralogy, one tool to make this measurement is the sclerometer. Another tool used to make these tests is the pocket hardness tester and this tool consists of a scale arm with graduated markings attached to a four-wheeled carriage. A scratch tool with a rim is mounted at a predetermined angle to the testing surface. In order to use it a weight of mass is added to the scale arm at one of the graduated markings. The use of the weight and markings allows a known pressure to be applied without the need for complicated machinery. Indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from an object, they are primarily used in engineering. The tests work on the premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter. Common indentation hardness scales are Rockwell, Vickers, Shore, rebound hardness, also known as dynamic hardness, measures the height of the bounce of a diamond-tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity, the device used to take this measurement is known as a scleroscope. Two scales that measures rebound hardness are the Leeb rebound hardness test, there are five hardening processes, Hall-Petch strengthening, work hardening, solid solution strengthening, precipitation hardening, and martensitic transformation. Hardness in the elastic range—a small temporary change in shape for a given force—is known as stiffness in the case of a given object and they exhibit plasticity—the ability to permanently change shape in response to the force, but remain in one piece
6.
Electrical resistivity and conductivity
–
Electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ, the SI unit of electrical resistivity is the ohm-metre. Electrical conductivity or specific conductance is the reciprocal of electrical resistivity and it is commonly represented by the Greek letter σ, but κ or γ are also occasionally used. Its SI unit is siemens per metre and CGSE unit is reciprocal second, many resistors and conductors have a uniform cross section with a uniform flow of electric current, and are made of one material. All copper wires, irrespective of their shape and size, have approximately the same resistivity, every material has its own characteristic resistivity – for example, resistivity of rubber is far larger than coppers. If the pipes are the size and shape, the pipe full of sand has higher resistance to flow. Resistance, however, is not solely determined by the presence or absence of sand and it also depends on the length and width of the pipe, short or wide pipes have lower resistance than narrow or long pipes. The above equation can be transposed to get Pouillets law, R = ρ ℓ A, the resistance of a given material increases with length, but decreases with increasing cross-sectional area. From the above equations, resistivity has the SI unit ohm metre, the formula R = ρ ℓ / A can be used to intuitively understand the meaning of a resistivity value. For example, if A = 7000100000000000000♠1 m2 ℓ = 7000100000000000000♠1 m, Conductivity, σ, is defined as the inverse of resistivity, σ =1 ρ. Conductivity has SI units of siemens per metre, the above definition was specific to resistors or conductors with a uniform cross-section, where current flows uniformly through them. A more basic and general definition starts from the fact that a field inside a material makes electric current flow. Conductivity is the inverse, σ =1 ρ = J E, for example, rubber is a material with large ρ and small σ—because even a very large electric field in rubber makes almost no current flow through it. On the other hand, copper is a material with small ρ, according to elementary quantum mechanics, electrons in an atom do not take on arbitrary energy values. Rather, electrons only occupy discrete energy levels in an atom or crystal. When a large number of such allowed energy levels are spaced close together —i. e. have similar energies— we can talk about these energy levels together as an energy band. There can be many such bands in a material, depending on the atomic number
7.
Friction
–
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest. The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity, temperature and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
8.
Mill finish
–
Mill finish refers to the surface texture of metal after it exits a rolling mill, extrusion die, or drawing processes, including sheet, bar, plate, or structural shapes. This texture is rough and lacks lustre, it may have spots of oxidation or contamination with mill oil. Most mill finish surfaces are machined or treated with polishing, industrial etching, the quality and characteristics of mill finish can vary widely from one mill to another, and even from one lot to another. Hot rolled parts are dark and dull, their surface oxidized from being hot worked. Extruded products may have die marks running the length of the stock, other mill finishes are surprisingly smooth and uniform. It is possible for a mill to influence the finish of produced stock, architectural Metals, A Guide to Selection, Specification, and Performance
9.
Surface finish
–
Surface finish, also known as surface texture or surface topography, is the nature of a surface as defined by the three characteristics of lay, surface roughness, and waviness. It comprises the small deviations of a surface from the perfectly flat ideal. Surface texture is one of the important factors that control friction, considerable efforts have been made to study the influence of surface texture on friction and wear during sliding conditions. Surface textures can be isotropic or anisotropic, sometimes, stick-slip friction phenomena can be observed during sliding depending on surface texture. Each manufacturing process produces a surface texture, the process is usually optimized to ensure that the resulting texture is usable. If necessary, a process will be added to modify the initial texture. Lay is the direction of the predominant surface pattern ordinarily determined by the method used. Surface roughness commonly shortened to roughness, is a measure of the finely spaced surface irregularities, in engineering, this is what is usually meant by surface finish. Waviness is the measure of surface irregularities with a greater than that of surface roughness. These usually occur due to warping, vibrations, or deflection during machining, surface finish may be measured in two ways, contact and non-contact methods. Contact methods involve dragging a measurement stylus across the surface, these instruments are called profilometers, non-contact methods include, interferometry, confocal microscopy, focus variation, structured light, electrical capacitance, electron microscopy, and photogrammetry. In the United States, surface finish is specified using the ASME Y14. 36M standard. The other common standard is International Organization for Standardization 1302, many factors contribute to the surface finish in manufacturing. In forming processes, such as molding or metal forming, surface finish of the die determines the finish of the workpiece. In machining the interaction of the edges and the microstructure of the material being cut both contribute to the final surface finish. In general, the cost of manufacturing a surface increases as the surface finish improves, any given manufacturing process is usually optimized enough to ensure that the resulting texture is usable for the parts intended application. If necessary, a process will be added to modify the initial texture. The expense of additional process must be justified by adding value in some way—principally better function or longer lifespan
10.
Burnishing (metal)
–
Burnishing is the plastic deformation of a surface due to sliding contact with another object. Visually, burnishing smears the texture of a surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the strength of the material. To understand burnishing, first look at the case of a hardened ball on a flat plate. If the ball is pressed directly into the plate, stresses develop in both objects around the area where they contact, as this normal force increases, both the ball and the plates surface deform. The deformation caused by the ball is different depending on the magnitude of the force pressing against it. If the force on it is small, when the force is released both the ball and plates surface will return to their original, undeformed shape. In this case, the stresses in the plate are always less than the strength of the material. Since it was given that the plate is softer than the ball. If a larger force is used, there also be plastic deformation. A bowl-shaped indentation will be left behind, surrounded by a ring of raised material that was displaced by the ball, the stresses between the ball and the plate are described in more detail by Hertzian stress theory. Now consider what happens if the force on the ball drags it across the plate. In this case, the force on the ball can be decomposed into two component forces, one normal to the surface, pressing it in, and the other tangential. As the tangential component is increased, the ball will start to slide along the plate, at the same time, the normal force will deform both objects, just as with the static situation. If the normal force is low, the ball will rub against the plate, the rubbing action will create friction and heat, but it will not leave a mark on the plate. However, as the force increases, eventually the stresses in the plates surface will exceed its yield strength. When this happens the ball will plow through the surface and create a trough behind it, the plowing action of the ball is burnishing. Even the smoothest of surfaces will have imperfections if viewed at a high enough magnification, the imperfections that extend above the general form of a surface are called asperities, and they can plow material on another surface just like the ball dragging along the plate
11.
Calender
–
A calender is a series of hard pressure rollers used to form or smooth a sheet of material such as paper or plastic film. In a principal application, the calender is located at the end of a papermaking process. Those that are used separately from the process are also called supercalenders, the purpose of a calender is to make the paper smooth and glossy for printing and writing, as well as of a consistent thickness for capacitors that use paper as their dielectric membrane. The calender section of a paper machine consists of a calender and other equipment, the paper web is run between in order to further smooth it out, which also gives it a more uniform thickness. The pressure applied to the web by the rollers determines the finish of the paper, the first is Machine Finish, or, MF Paper and it can range from a Rough/ Matt, look to a Smooth high quality finish. The second is called a Supercalendered Finish or, MG Paper which is Glossy/ Glazed suitable for a high degree fine-screened halftone printing. A special finish such as a finish would be achieved by placing a piece of linen between the plate and the sheet of paper, or else an embossed steel roll might be used. After calendering, the web has a content of about 6%. It is wound onto a roll called a tambour, and stored for final cutting and shipping, the word calender itself is a derivation of the word κύλινδρος kylindros, the Greek word that is also the source of the word cylinder. In 1836, Edwin M. Chaffee, of the Roxbury India Rubber Company, Chaffee worked with Charles Goodyear with the intention to produce a sheet of rubber laminated to a fabric base. Calenders were also used for paper and fabrics long before later applications for thermoplastics, with the expansion of the rubber industry the design of calenders grew as well, so when PVC was introduced the machinery was already capable of processing it into film. In the past, for paper, sheets were worked on with a hammer or pressed between polished metal sheets in a press. With the continuously operating paper machine it became part of the process of rolling the paper, the pressure between the rollers, the nip pressure, can be reduced by heating the rolls and/or moistening the paper surface. This helps to keep the bulk and the stiffness of the web paper which is beneficial for its later use, modern calenders have hard heated rollers made from chilled cast iron or steel, and soft rollers coated with polymeric composites. The soft roller is slightly non-cylindrical, tapered in diameter toward both ends, to widen the working nip and distribute the pressure on the paper more evenly. A supercalender is a stack of calenders consisting of alternating steel and fiber-covered rolls through which paper is passed to increase its density and it is similar to a calender except that alternate chilled cast iron and softer rolls are used. The rolls used to supercalender uncoated paper usually consist of cast iron and highly compressed paper, while the used for coated paper are usually cast iron. The finish produced varies according to the raw material used to make the paper and the pressure exerted on it, and ranges from the highest English finish to a highly glazed surface
12.
Case-hardening
–
For iron or steel with low carbon content, which has poor to no hardenability of its own, the case-hardening process involves infusing additional carbon into the surface layer. The term face hardening is used to describe this technique. Because hardened metal is more brittle than softer metal, through-hardening is not always a suitable choice for uses where the metal part is subject to certain kinds of stress. In such circumstances, case-hardening can provide a part that will not fracture, early iron smelting made use of bloomeries, which produced two layers of metal, one with a very low carbon content that is worked into wrought iron, and the rest a high carbon cast iron. Since the high carbon iron is hot short, meaning it fractures and crumbles when forged, the wrought iron, with nearly no carbon in it, was very malleable and ductile but not very hard. Case-hardening involves packing the low-carbon iron within a high in carbon. This forms a surface layer of higher carbon steel, with the carbon content gradually decreasing deeper from the surface. The resulting product combines much of the toughness of a steel core, with the hardness. This carburizing package is then heated to a high temperature but still under the point of the iron. The longer the package is held at the temperature, the deeper the carbon will diffuse into the surface. The resulting case-hardened part may show distinct surface discoloration, if the material is mixed organic matter as described above. The steel darkens significantly, and shows a pattern of black, blue and purple, caused by the various compounds formed from impurities in the bone. This oxide surface works similarly to bluing, providing a degree of corrosion resistance, case colouring refers to this pattern and is commonly encountered as a decorative finish on firearms. Case-hardened steel combines extreme hardness and extreme toughness, something which is not readily matched by homogeneous alloys, carbon itself is solid at case-hardening temperatures and so is immobile. Transport to the surface of the steel was as gaseous carbon monoxide, generated by the breakdown of the carburising compound and this takes place with pure carbon but too slowly to be workable. Although oxygen is required for this process it is re-circulated through the CO cycle, the sealing is necessary to stop the CO either leaking out or being oxidised to CO2 by excess outside air. It is a common fallacy that case-hardening was done with bone. Although bone was used, the main donor was hoof
13.
Ceramic glaze
–
Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a ceramic body through firing. Glaze can serve to color, decorate or waterproof an item, glazing renders earthenware vessels suitable for holding liquids, sealing the inherent porosity of terracotta, the term we now use for basic unglazed earthenware. It also gives a tougher surface, glaze is also used on stoneware and porcelain. In addition to their functionality, glazes can form a variety of finishes, including degrees of glossy or matte finish. Glazes may also enhance the design or texture either unmodified or inscribed, carved or painted. Most pottery produced in recent centuries has been glazed, tiles are almost always glazed, and modern architectural terracotta is very often glazed architectural terra-cotta. Domestic sanitary ware is invariably glazed, as are many used in industry. The most important groups of traditional glazes, named after their main ceramic fluxing agent, are, Lead-glazed earthenware, is shiny and transparent after firing, used for about 2,000 years around the Mediterranean, in Europe and China. Tin-glazed pottery, which coats the ware with a white glaze. Known in the Ancient Near East and then important in Islamic pottery, includes faience, maiolica, majolica and Delftware. Ash glaze, important in East Asia, simply made from wood or plant ash, modern materials technology has invented new vitreous glazes that do not fall into these traditional categories. Glazes need to include a ceramic flux which functions by promoting partial liquefaction in the clay bodies, fluxes lower the high melting point of the glass formers silica, and sometimes boron trioxide. These glass former may be included in the materials, or may be drawn from the clay beneath. Raw materials of ceramic glazes generally include silica, which will be the glass former. Various metal oxides, such as sodium, potassium and calcium, alumina, often derived from clay, stiffens the molten glaze to prevent it from running off the piece. Colorants, such as oxide, copper carbonate or cobalt carbonate. Most commonly, glazes in aqueous suspension of various powdered minerals, other techniques include pouring the glaze over the piece, spraying it onto the piece with an airbrush or similar tool, or applying it directly with a brush or other tool. Small marks left by these spurs are sometimes visible on finished ware, decoration applied under the glaze on pottery is generally referred to as underglaze
14.
Cladding (metalworking)
–
Cladding is the bonding together of dissimilar metals. It is different from fusion welding or gluing as a method to fasten the metals together, cladding is often achieved by extruding two metals through a die as well as pressing or rolling sheets together under high pressure. The United States Mint uses cladding to manufacture coins from different metals and this allows a cheaper metal to be used as a filler. In roll bonding, two or more layers of different metals are cleaned and passed through a pair of rollers under sufficient pressure to bond the layers. The pressure is enough to deform the metals and reduce the combined thickness of the clad material. Heat may be applied, especially when metal are not ductile enough and this is used to make heat exchangers for refrigeration equipment. In explosive welding, the pressure to bond the two layers is provided by detonation of a sheet of chemical explosive, no heat-affected zone is produced in the bond between metals. The explosion propagates across the sheet, which tends to expel impurities and oxides from between the sheets, pieces up to 4 x 16 metres can be manufactured. The process is useful for cladding metal sheets with a corrosion-resistant layer and it is often used to improve mechanical properties or increase corrosion resistance, repair worn out parts, and fabricate metal matrix composites. The powder used in laser cladding is normally of a metallic nature, the interaction of the metallic powder stream and the laser causes melting to occur, and is known as the melt pool. This is deposited onto a substrate, moving the substrate allows the pool to solidify. This is the most common technique, however some processes involve moving the assembly over a stationary substrate to produce solidified tracks. The motion of the substrate is guided by a CAD system which interpolates solid objects into a set of tracks, a great deal of research is now being concentrated on developing automatic laser cladding machines. However, many groups are focusing their attention on developing sensors to measure the process online, such sensors monitor the clads geometry, metallurgical properties, and temperature information of both the immediate melt pool and its surrounding areas. With such sensors, control strategies are being designed such that constant observation from a technician is no longer required to produce a final product, further research has been directed to forward processing where system parameters are developed around specific metallurgical properties for user defined applications. Best technique for coating any shape => increase life-time of wearing parts, most suited technique for graded material application. Low dilution between track and substrate (unlike other welding processes and strong metallurgical bond, low deformation of the substrate and small heat affected zone. High cooling rate => fine microstructure, built part is free of crack and porosity
15.
Corona treatment
–
Corona treatment is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. The corona plasma is generated by the application of voltage to an electrode that has a sharp tip. The plasma forms at the tip, a linear array of electrodes is often used to create a curtain of corona plasma. Materials such as plastics, cloth, or paper may be passed through the corona plasma curtain in order to change the energy of the material. All materials have an inherent surface energy, surface treatment systems are available for virtually any surface format including dimensional objects, sheets and roll goods that are handled in a web format. Corona treatment is a widely used treatment method in the plastic film, extrusion. The corona treatment was invented by the Danish engineer Verner Eisby in 1951, Verner had been asked by one of his customers if he could find a solution which would make it possible to print on plastic. Verner found that there were already a couple of ways to accomplish this, one was a gas flame method and the other was a spark generating method, both of which were crude and uncontrollable and did not produce a homogeneous product. Verner came up with the theory that a high frequency corona discharge would provide both an efficient and controllable method to treat the surface. Exhaustive experiments proved him to be correct, verners company, Vetaphone, obtained patent rights for the new corona treatment system. Although results are invisible to the eye, surface treating modifies surfaces to improve adhesion. Polyethylene, polypropylene, nylon, vinyl, PVC, PET, metalized surfaces, foils, paper and it is safe, economical, and delivers high line speed throughput. Corona treatment is suitable for the treatment of injection and blow molded parts. Corona discharge equipment consists of a power generator, a high-voltage transformer, a stationary electrode. Standard utility electrical power is converted into higher frequency power which is supplied to the treater station. The treater station applies this power through ceramic or metal electrodes over an air gap onto the material’s surface, two basic corona treater stations are used in extrusion coating applications. On a Bare Roll treater station the dielectric encapsulates the electrode, on a Covered Roll station it encapsulates the treater base roll. The treater consists of an electrode and a roll in both stations
16.
Carburizing
–
The intent is to make the metal harder. Depending on the amount of time and temperature, the area can vary in carbon content. Longer carburizing times and higher temperatures increase the depth of carbon diffusion.25 inches. In some cases it serves as a remedy for undesired decarburization that happened earlier in a manufacturing process, carburization of steel involves a heat treatment of the metallic surface using a source of carbon. Carburization can be used to increase the hardness of low carbon steel. Early carburization used an application of charcoal packed around the sample to be treated. For applications where control over gas composition is desired, carburization may take place under very low pressures in a vacuum chamber. Plasma carburization is increasingly used to improve the characteristics of various metals. It also provides a treatment of components with complex geometry. The process of carburization works via the diffusion of atoms into the surface layers of a metal. If the carbon remains in solution, the steel is then heat treated to harden it. Both of these mechanisms strengthen the surface of the metal, the former by forming pearlite or martensite, both of these materials are hard and resist abrasion. Gas carburizing is normally carried out at a temperature within the range of 900 to 950 °C, in oxy-acetylene welding, a carburizing flame is one with little oxygen, which produces a sooty, lower-temperature flame. It is often used to anneal metal, making it malleable and flexible during the welding process. A main goal when producing carburized workpieces is to ensure contact between the workpiece surface and the carbon-rich elements. In gas and liquid carburizing, the workpieces are often supported in mesh baskets or suspended by wire, in pack carburizing, the workpiece and carbon are enclosed in a container to ensure that contact is maintained over as much surface area as possible. Pack carburizing containers are made of carbon steel coated with aluminum or heat-resisting nickel-chromium alloy. There are different types of elements or materials that can be used to perform this process, a few typical hardening agents include carbon monoxide gas, sodium cyanide and barium carbonate, or hardwood charcoal
17.
Nitriding
–
Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-carbon, low-alloy steels and they are also used on medium and high-carbon steels, titanium, aluminium and molybdenum. The processes are named after the medium used to donate, the three main methods used are, gas nitriding, salt bath nitriding, and plasma nitriding. In gas nitriding the donor is a nitrogen gas, usually ammonia. When ammonia comes into contact with the work piece it dissociates into nitrogen and hydrogen. The nitrogen then diffuses onto the surface of the creating a nitride layer. This process has existed for nearly a century, though only in the last few decades has there been an effort to investigate the thermodynamics and kinetics involved. Recent developments have led to a process that can be accurately controlled, the thickness and phase constitution of the resulting nitriding layers can be selected and the process optimized for the particular properties required. The advantages of gas nitriding over the other variants are, Precise control of potential of nitrogen in the nitriding atmosphere by controlling gas flow rate of nitrogen and oxygen. Also, care must be taken when heating in the presence of oxygen to reduce the risk of explosion In salt bath nitriding the nitrogen donating medium is a salt such as cyanide salt. The salts used also donate carbon to the surface making salt bath a nitrocarburizing process. The temperature used is typical of all nitrocarburizing processes, 550–570 °C, the advantages of salt nitriding is that it achieves higher diffusion in the same period time compared to any other method. This is one of the most significant reasons the process has fallen out of favor in recent decades, in plasma nitriding, the reactivity of the nitriding media is not due to the temperature but to the gas ionized state. In this technique intense electric fields are used to generate ionized molecules of the gas around the surface to be nitrided, such highly active gas with ionized molecules is called plasma, naming the technique. The gas used for plasma nitriding is usually pure nitrogen, since no spontaneous decomposition is needed, there are hot plasmas typified by plasma jets used for metal cutting, welding, cladding or spraying. There are also cold plasmas, usually generated inside vacuum chambers, usually steels are beneficially treated with plasma nitriding. This process permits the close control of the microstructure, allowing nitriding with or without compound layer formation. Not only the performance of metal parts is enhanced, but working lifespans also increase, and so do the strain limit, for instance, mechanical properties of austenitic stainless steel like resistance to wear can be significantly augmented and the surface hardness of tool steels can be doubled
18.
Electroplating
–
Electroplating is a process that uses electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode. The term is used for electrical oxidation of anions onto a solid substrate. Electroplating is primarily used to change the properties of an object. The process used in electroplating is called electrodeposition and it is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit, in one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that it comprises, at the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they plate out onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, in this manner, the ions in the electrolyte bath are continuously replenished by the anode. Other electroplating processes may use a non-consumable anode such as lead or carbon, in these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution. The most common form of electroplating is used for creating coins such as pennies, the cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, for example, for copper plating, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42− in the solution to form copper sulfate, at the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the transfer of copper from the anode source to a plate covering the cathode. The plating is most commonly a metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder, many plating baths include cyanides of other metals in addition to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level, additionally, non-metal chemicals such as carbonates and phosphates may be added to increase conductivity. When plating is not desired on certain areas of the substrate, typical stop-offs include tape, foil, lacquers, and waxes. The ability of a plating to cover uniformly is called throwing power, initially, a special plating deposit called a strike or flash may be used to form a very thin plating with high quality and good adherence to the substrate
19.
Galvanization
–
Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in parts are submerged in a bath of molten zinc. Galvanizing protects the metal in three ways, It forms a coating of zinc which, when intact, prevents corrosive substances from reaching the underlying steel or iron. The zinc serves as a sacrificial anode so that if the coating is scratched. The zinc protects its base metal by corroding before iron, for better results, application of chromates over zinc is also seen as an industrial trend. The earliest known example of galvanized iron was encountered by Europeans on 17th-century Indian armor in the Royal Armouries Museum collection and it was named in English via French from the name of Italian scientist Luigi Galvani. Originally in the 19th century, the term galvanizing was used to describe the administration of electric shocks and this usage is the origin of the metaphorical use of the verb galvanize, such as to galvanize into action meaning stimulating a complacent person or group to take action. In modern usage, the term galvanizing has largely come to be associated with zinc coatings, galvanic paint, a precursor to hot-dip galvanizing, was patented by Stanislas Sorel, of Paris, in December 1837. Hot-dip galvanizing deposits a thick robust layer of iron alloys on the surface of a steel item. In the case of bodies, where additional decorative coatings of paint will be applied. The hot-dip process generally does not reduce strength on a measurable scale and this deficiency is a consideration affecting the manufacture of wire rope and other highly-stressed products. The protection provided by hot-dip galvanizing is insufficient for products that will be exposed to corrosive materials such as acids. For these applications, more expensive stainless steel is preferred, some nails made today are galvanized. Nonetheless, electroplating is used on its own for many applications because it is cheaper than hot-dip zinc coating. Another reason not to use hot-dip zinc coating is that for bolts and nuts of size M10 or smaller, the thick hot-dipped coating fills in too much of the threads, the size of crystallites in galvanized coatings is a visible and aesthetic feature, known as spangle. Visible crystallites are rare in other engineering materials, even though they are usually present, thermal diffusion galvanizing, or Sherardizing, provides a zinc diffusion coating on iron- or copper-based materials. Parts and zinc powder are tumbled in a rotating drum. Around 300 °C, zinc will diffuse into the substrate to form a zinc alloy, the advance surface preparation of the goods can be carried out by shot blasting
20.
Gilding
–
The term gilding covers a number of decorative techniques for applying fine gold leaf or powder to solid surfaces such as wood, stone, or metal to give a thin coating of gold. A gilded object is described as gilt. Where metal is gilded, it was silver in the West, to make silver-gilt objects, but gilt-bronze is commonly used in China. Methods of gilding include hand application and glueing, chemical gilding, and electroplating, parcel-gilt objects are only gilded over part of their surfaces. This may mean that all of the inside, and none of the outside, of a chalice or similar vessel is gilded, herodotus mentions that the Egyptians gilded wood and metals, and many such objects have been excavated. Certain Ancient Greek statues of great prestige were chryselephantine, i. e. made of gold and ivory, extensive ornamental gilding was also used in the ceiling coffers of the Propylaea. But he adds that luxury advanced on them so rapidly that in very little time you see all, even private and poor people, gild the walls, vaults. Owing to the thickness of the gold leaf used in ancient gilding. Fire-gilding of metal goes back at least to the 4th century BC, in Europe, silver-gilt has always been more common than gilt-bronze, but in China the opposite has been the case. The ancient Chinese also developed the gilding of porcelain, which was taken up by the French. Modern gilding is applied to numerous and diverse surfaces and by various processes, mechanical gilding includes all the operations in which gold leaf is prepared, and the processes to mechanically attach the gold onto surfaces. The process is completed by cold burnishing, overlaying or folding or hammering on gold foil or gold leaf is the simplest and most ancient method, and is mentioned in Homers Odyssey and the Old Testament. The Ram in a Thicket of about 2600–2400 BCE from Ur uses this technique on wood, the next advances involved two simple processes. The first involves gold leaf, which is gold that is hammered or cut very thin sheets. If gilding on canvas or on wood, the surface was often first coated with gesso, gesso is a substance made of finely ground gypsum or chalk mixed with glue. Other gilding processes involved using the gold as pigment in paint, then the gold was applied in the same way as with any paint. Sometimes, after either gold-leafing or gold-painting, the artist would heat the piece enough to melt the gold slightly and these techniques remained the only alternatives for materials like wood, leather, and the vellum pages of illuminated manuscripts. Chemical gilding embraces those processes in which the gold is at some stage of chemical combination and these include, In this process the gold is obtained in a state of extremely fine division, and applied by mechanical means
21.
Knurling
–
Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is cut or rolled into the material. The operation is performed for producing indentations on a part of a workpiece, Knurling allows hands or fingers to get a better grip on the knurled object than would be provided by the originally smooth metal surface. Occasionally, the pattern is a series of straight ridges or a helix of straight ridges rather than the more-usual criss-cross pattern. Knurling may also be used as a method, because a rolled-in knurled surface has raised-up areas surrounding the depressed areas. As auto parts have become less expensive, knurling has become less prevalent than it once was, Knurling can also be used when a component will be assembled into a low precision component, for example a metal pin into a plastic molding. The outer surface of the pin is knurled so that the raised detail bites into the plastic irrespective of whether the size of the hole in the plastic closely matches the diameter of the pin. Tool handles, mechanical pencils, barbell bars, and the knobs on electronic equipment are frequently knurled. Knurling is also used on the grips of darts and the footpegs of BMX bicycles, aside from adding functionality to an object, knurling also adds a decorative pattern to the material. The knurled nut is one application, which uses a knurled finish instead of hexagonal or square edges which helps in tightening or loosening the nut without the use of a tool. The knurled surfaces provide enough grip to hold the nut between the thumb and forefinger, hence it is also called a thumb nut. It is mainly used on small diameter bolts, knurled nuts are typically used in electrical components, musical instruments and in automobiles. More common than knurl cutting, knurl rolling is usually accomplished using one or more very hard rollers that contain the reverse of the pattern to be imposed. It is possible for a straight knurl to be pressed with a roller, however the material needs to be supported adequately to avoid deformation. A criss-cross pattern can be accomplished using any of, A single roller that contains the reverse of the desired pattern. The integer number of knurls for any given diameter typically varies by three repetitions from the bottom to the top of the pattern. By comparison, for cut knurls, the spacing of the cuts is not preset and these resemble pipecutters but contain knurling wheels rather than cutting wheels. Usually, three wheels are carried by the tool, two left-handed wheels and one right-handed wheel or vice versa, Annular rings Frequently used when the mating part is plastic. Rings allow for easy mating but ridges make it difficult to pull the components apart, Linear knurl Used with mating plastic pieces, the Linear Knurl allows greater torsion between components
22.
Paint
–
Paint is any liquid, liquefiable, or mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture to objects, Paint can be made or purchased in many colors—and in many different types, such as watercolor, synthetic, etc. Paint is typically stored, sold, and applied as a liquid, in 2001 and 2004, South African archeologists reported finds in Blombos Cave of a 100, 000-year-old human-made ochre-based mixture that could have been used like paint. Further excavation in the cave resulted in the 2011 report of a complete toolkit for grinding pigments. Cave paintings drawn with red or yellow ochre, hematite, manganese oxide, ancient colored walls at Dendera, Egypt, which were exposed for years to the elements, still possess their brilliant color, as vivid as when they were painted about 2,000 years ago. The Egyptians mixed their colors with a substance, and applied them separately from each other without any blending or mixture. They appear to have used six colors, white, black, blue, red, yellow and they first covered the area entirely with white, then traced the design in black, leaving out the lights of the ground color. They used minium for red, and generally of a dark tinge, pliny mentions some painted ceilings in his day in the town of Ardea, which had been done prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries, Paint was made with the yolk of eggs and therefore, the substance would harden and adhere to the surface it was applied to. Pigment was made from plants, sand, and different soils, Most paints used either oil or water as a base. The process was done by hand by the painters and exposed them to lead poisoning due to the white-lead powder, in 1718, Marshall Smith invented a Machine or Engine for the Grinding of Colours in England. It is not known precisely how it operated, but it was a device that increased the efficiency of pigment grinding dramatically. By the proper onset of the Industrial Revolution, paint was being ground in steam-powered mills, interior house painting increasingly became the norm as the 19th century progressed, both for decorative reasons and because the paint was effective in preventing the walls rotting from damp. Linseed oil was also used as an inexpensive binder. In 1866, Sherwin-Williams in the United States opened as a large paint-maker and it was not until the stimulus of World War II created a shortage of linseed oil in the supply market that artificial resins, or alkyds, were invented. Cheap and easy to make, they held the color well. The vehicle is composed of the binder, or, if it is necessary to thin the binder with a diluent like solvent or water, it is the combination of binder + diluent. In this case, once the paint has dried or cured very nearly all of the diluent has evaporated, thus, an important quantity in coatings formulation is the vehicle solids, sometimes called the resin solids of the formula
23.
Passivation (chemistry)
–
Passivation, in physical chemistry and engineering, refers to a material becoming passive, that is, less affected or corroded by the environment of future use. As a technique, passivation is the use of a coat of a protective material, such as metal oxide. Passivation can occur only in conditions, and is used in microelectronics to enhance silicon. The technique of passivation strengthens and preserves the appearance of metallics, other proprietary systems to avoid electrode passivation, several discussed below, are the subject of ongoing research and development. When exposed to air, many metals naturally form a hard, relatively inert surface, in the case of other metals, such as iron, a somewhat rough porous coating is formed from loosely adherent corrosion products. In this case, an amount of metal is removed. There has been much interest in determining the mechanisms that govern the increase of thickness of the oxide layer over time, boundaries between micro grains, if the oxide layer is crystalline, form an important pathway for oxygen to reach the unoxidized metal below. For this reason, vitreous oxide coatings – which lack grain boundaries – can retard oxidation, the conditions necessary for passivation are recorded in Pourbaix diagrams. Some corrosion inhibitors help the formation of a layer on the surface of the metals to which they are applied. Some compounds, dissolving in solutions form non-reactive and low solubility films on metal surfaces, schönbein named the first state the active condition and the second the passive condition. If passive iron is touched by active iron, it becomes active again, in 1920, Ralph S. Lillie measured the effect of an active piece of iron touching a passive iron wire and found that a wave of activation sweeps rapidly over its whole length. In the area of microelectronics, the formation of a strongly adhering passivating oxide is important to the performance of silicon. In the area of photovoltaics, a surface layer such as silicon nitride. Aluminium alloys, however, offer protection against corrosion. There are three ways to passivate these alloys, alclading, chromate conversion coating and anodizing. Alclading is the process of bonding a thin layer of pure aluminium to the aluminium alloy. Chromate conversion coating is a way of passivating not only aluminum, but also zinc, cadmium, copper, silver, magnesium. Anodizing forms an oxide coating
24.
Anodizing
–
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called anodizing because the part to be treated forms the anode electrode of an electrical circuit, anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does. Anodizing is also used to prevent galling of threaded components and to make films for electrolytic capacitors. Anodic films are most commonly applied to aluminium alloys, although processes also exist for titanium, zinc, magnesium, niobium, zirconium, hafnium. Carbon flakes or nodules in iron or steel with carbon content may cause an electrolytic potential. Ferrous metals are commonly anodized electrolytically in nitric acid or by treatment with red fuming nitric acid to form hard black ferric oxide and this oxide remains conformal even when plated on wire and the wire is bent. Anodizing changes the texture of the surface and the crystal structure of the metal near the surface. Thick coatings are normally porous, so a process is often needed to achieve corrosion resistance. Anodized aluminium surfaces, for example, are harder than aluminium but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are much stronger and more adherent than most types of paint and metal plating. This makes them likely to crack and peel from aging and wear. Anodizing was first used on a scale in 1923 to protect Duralumin seaplane parts from corrosion. This early chromic acid–based process was called the Bengough–Stuart process and was documented in British defence specification DEF STAN 03-24/3 and it is still used today despite its legacy requirements for a complicated voltage cycle now known to be unnecessary. Variations of this soon evolved, and the first sulfuric acid anodizing process was patented by Gower. Sulfuric acid soon became and remains the most common anodizing electrolyte, oxalic acid anodizing was first patented in Japan in 1923 and later widely used in Germany, particularly for architectural applications. Anodized aluminium extrusion was an architectural material in the 1960s and 1970s. The phosphoric acid processes are the most recent major development, so far only used as pretreatments for adhesives or organic paints, aluminium alloys are anodized to increase corrosion resistance and to allow dyeing, improved lubrication, or improved adhesion. However, anodizing does not increase the strength of the aluminium object, aluminium alloys typically form a thicker oxide layer, 5–15 nm thick, but tend to be more susceptible to corrosion
25.
Bluing (steel)
–
Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is a conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite. Black oxide provides minimal protection against corrosion, unless treated with a water-displacing oil to reduce wetting. A distinction can be made between traditional bluing and some more modern black oxide coatings, although bluing is a subset of black oxide coatings. In comparison, rust, the red oxide of iron, undergoes a large volume change upon hydration, as a result. Cold, Hot, Rust Blue and Fume Blue are oxidizing processes simply referred to as bluing, cold bluing is generally a selenium dioxide based compound that colours steel black, or more often a very dark grey. It is a product to apply evenly, offers minimal protection and is generally best used for small fast repair jobs. The Hot process is a salt solution, referred to as Traditional Caustic Black. This method was adopted by larger companies for large scale. It does provide good rust resistance which is improved with the use of oil, Rust Bluing and Fume Bluing provide the best rust and corrosion resistance as the process continually converts any metal that is capable of rusting into magnetite. Treating with an oiled coating enhances the protection offered by the bluing and this process is also the only process safely used to re-blue vintage shotguns. Many double barrelled shotguns are soft soldered / silver brazed together, the higher temperatures of the other processes as well as their caustic nature will weaken the soldered joints and make the gun hazardous to use. Bluing can also be done in a furnace, for example for a sword or other item traditionally made by a blacksmith or specialist such as a weaponsmith. Blacksmith products to this day may occasionally be made from blued steel by traditional craftsmen in cultures. Bluing is most commonly used by gun manufacturers, gunsmiths, and gun owners to improve the appearance of. It was also used by machinists, who protected and beautified tools made for their own use, Bluing also helps to maintain the metal finish by resisting superficial scratching, and also helps to reduce glare to the eyes of the shooter when looking down the barrel of the gun. All blued parts still need to be oiled to prevent rust. Bluing, being a conversion coating, is not as robust against wear and corrosion resistance as plated coatings
26.
Chromate conversion coating
–
Chromate conversion coating is a type of conversion coating used to passivate steel, aluminum, zinc, cadmium, copper, silver, magnesium, and tin alloys. It is primarily used as an inhibitor, primer, decorative finish. The process is named after the found in chromic acid, also known as hexavalent chromium. However, hexavalent chromium is toxic, thus, highly regulated, so new, Chromate conversion coatings are commonly applied to everyday items such as hardware and tools, and can usually be recognized by their distinctively iridescent, greenish-yellow color. Chromate conversion coatings on a substrate are known by the following terms, chemical film, yellow iridite. It is also used on aluminum alloy parts in the aircraft industry. Iridite NCP is a type of conversion coating for aluminium substrates. The most commonly referred-to standard for applying chromate conversion coating to aluminium is MIL-DTL-5541 in the US, Alodine may also refer to chromate-coating magnesium alloys. Chromate conversion coatings can be applied over phosphate conversion coatings used on ferrous substrates, the process is used to enhance the phosphate coating. Chromating is often performed on galvanized parts to them more durable. The chromate coating acts as paint does, protecting the zinc from white corrosion, thus making the part considerably more durable, steel and iron cannot be chromated directly. Chromating zinc plated steel does not enhance zincs cathodic protection of the steel from rust. The protective effect of chromate coatings on zinc is indicated by color, progressing from clear/blue to yellow, gold, olive drab, darker coatings generally provide more corrosion resistance. However, the color can also be changed with dyes. ISO4520 specifies chromate conversion coatings on electroplated zinc and cadmium coatings, ASTM B633 Type II and III specify zinc plating plus chromate conversion on iron and steel parts. The composition of chromate conversion solutions varies greatly, depending on the material to be coated, Iridite 14-2, a chromate conversion coating for aluminum, contains chromium oxide, barium nitrate, sodium silicofluoride and ferricyanide. Chromate coatings are soft and gelatinous when first applied, but harden, curing can be accelerated by heating up to 70 °C, but higher temperatures will gradually damage the coating. Yellow and green chromating chemistry on aluminium MIL-C-17711B, Chromate conversion coating specification for zinc and zinc alloy casting and hot dipped galvanized parts
27.
Parkerizing
–
Parkerizing is commonly used on firearms as a more effective alternative to bluing, which is an earlier-developed chemical conversion coating. It is also used extensively on automobiles to protect unfinished metal parts from corrosion, the Parkerizing process cannot be used on non-ferrous metals such as aluminium, brass, or copper. It similarly cannot be applied to steels containing an amount of nickel. Passivation can be used for protecting other metals, the process involves submerging the metal part into a phosphoric acid solution whose key ingredient is often zinc or manganese, with varying additional amounts of nitrates, chlorates, and copper. In one of the processes that have been developed, the solution is heated to a temperature of 88–99 °C for a period ranging between 5 and 45 minutes. A stream of bubbles is emitted from the metal part as the process takes place, when the bubbling stops. The Parkerizing reaction equation in a metal-phosphate-solution is as follows,2 Fe + Fe3+ +3 H2PO4− →3 FePO4 +3 H2 Zinc phosphating results in a non-reflective, manganese phosphating produces a medium- to dark-gray or black finish. Iron phosphating produces a black or dark gray finish similar to manganese phosphating, the grain size of the zinc phosphating is usually the smallest among the three processes, providing a more appealing cosmetic appearance in many applications. Many firearms that are Parkerized turn to a light greenish-gray color within a few years, as the coating ages, cosmoline, especially, interacting with Parkerizing, can cause the greenish-gray patina to develop on firearms that are stored in armories. Manganese and iron phosphating coatings are usually the thickest electrochemical conversion coatings, a heavy oil coating is unnecessary and undesirable for achieving a positive grip on Parkerized metal parts. Alternatively, the Parkerized surface may be painted over with an epoxy or molybdenum finish for added wear resistance, development of the process was started in England and continued by the Parker family in the United States. The process was first used on a scale in the manufacture of firearms for the United States military during World War II. The earliest work on phosphating processes was developed by British inventors William Alexander Ross, British patent 3119, in 1869, Coslett, of Birmingham, England, subsequently filed a patent based on this same process in America in 1907, which was granted U. S. It essentially provided an iron phosphating process, using phosphoric acid. S, Clark W. Parker acquired the rights to Cosletts and Richards U. S. patents, and experimented in the family kitchen with these and other rust-resisting formulations. The ultimate result was that Clark W. Parker, along with his son Wyman C, Parker, working together, set up the Parker Rust-Proof Phosphating Company of America in 1915. Colquhoun of the Parker Rust-Proof Phosphating Company of America then filed another improved phosphating patent application in 1919 and this patent was issued in 1919 as U. S. Patent 1,311,319, for an improved manganese phosphating technique and this patent was issued as U. S. Manganese phosphating, even with these improvements, still required the use of expensive
28.
Plasma electrolytic oxidation
–
Plasma electrolytic oxidation, also known as electrolytic plasma oxidation or microarc oxidation, is an electrochemical surface treatment process for generating oxide coatings on metals. It is similar to anodizing, but it employs higher potentials, so that discharges occur and this process can be used to grow thick, largely crystalline, oxide coatings on metals such as aluminium and titanium. Because they can present high hardness and a barrier, these coatings can offer protection against wear. The coating is a conversion of the substrate metal into its oxide. Because it grows inward into the substrate, it has excellent adhesion to the substrate metal, a wide range of substrate alloys can be coated, including all wrought aluminum alloys and most cast alloys, although high levels of silicon can reduce coating quality. Metals such as aluminum naturally form an oxide layer which provides moderate protection against corrosion. The layer is strongly adherent to the surface, and it will regrow quickly if scratched off. In conventional anodizing, this layer of oxide is grown on the surface of the metal by the application of electrical potential, in plasma electrolytic oxidation, higher potentials are applied. For example, in the electrolytic oxidation of aluminum, at least 200 V must be applied. This locally exceeds the breakdown potential of the growing oxide film. These discharges result in localized plasma reactions, with conditions of temperature and pressure which modify the growing oxide. Processes include melting, melt-flow, re-solidification, sintering and densification of the growing oxide, one of the most significant effects, is that the oxide is partially converted from amorphous alumina into crystalline forms such as corundum which is much harder. As a result, mechanical properties such as wear resistance and toughness are enhanced, the part to be coated is immersed in a bath of electrolyte which usually consists of a dilute alkaline solution such as KOH. Potentials of over 200 V are applied between two electrodes. These may be continuous or pulsed direct current, or alternating pulses where the stainless steel counter electrode might just be earthed, plasma electrolytic oxide coatings are generally recognized for high hardness, wear resistance, and corrosion resistance. However, the properties are highly dependent on the substrate used, as well as on the composition of the electrolyte. Even on aluminium, the properties can vary strongly according to the exact alloy composition. Extensive work is being pursued by Prof. T. W. List of plasma articles Introduction to plasma electrolytic oxidation
29.
Peening
–
Peening is normally a cold work process. It tends to expand the surface of the metal, thereby inducing compressive stresses or relieving tensile stresses already present. Peening can also encourage strain hardening of the surface metal, plastic deformation from peening induces a residual compressive stress in a peened surface, along with tensile stress in the interior. This stress state resembles the one seen in toughened glass, and is useful for similar reasons, surface compressive stresses confer resistance to metal fatigue and to some forms of corrosion, since cracks will not grow in a compressive environment. The benefit comes at the expense of higher tensile stresses deeper in the part, however, the fatigue properties of the part will be improved, since the stresses are normally significantly higher at the surface in part due to surface imperfections and damage. Cold work also serves to harden the materials surface and this makes cracks less likely to form at the surface and provides resistance to abrasion. When a metal undergoes strain hardening its yield strength increases but its ductility decreases, strain hardening actually increases the number of dislocations in the crystal lattice of the material. Plastic deformation from peening can be useful in stretching the surface of an object, the manual method uses a hand held peening hammer and is a form of planishing. There are also machine assisted methods that use a version of a hammer to peen the sheet metal. Another use of the process is to flatten sheet metal and is specifically used as a primary technique to flatten steel belts used in industrial conveying and pressing operations. The peening of steel belts is usually achieved by a shot peening process, using specialized equipment, when peening is used to induce residual stress or work harden an object, care needs to be taken with thin parts not to stretch the workpiece. Where stretching is unavoidable then allowances may need to be made in the design or process application. Hand peening may also be performed after welding to help relieve the stresses that develop on cooling in the welded metal. The level of reduction in stress is minimal and only occurs on or near to the weld surface. Other methods, like heat spots, help reduce residual tensile stresses, peening will induce a higher hardness into the weld and this is something that should be avoided. For this reason, peening is not normally accepted by the majority of codes, any peening that is carried out on a weld should have been carried out on the weld procedure qualification test piece. The welding procedure qualification test piece replicates all of the variables that will be used in production welding. These mechanical properties must, as a minimum, match the properties of the materials that have been welded together
30.
Shot peening
–
Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals and composites. It entails impacting a surface with shot with force sufficient to create plastic deformation, in machining, shot peening is used to strengthen and relieve stress in components like steel automobile crankshafts and connecting rods. In architecture it provides a finish to metal. Shot peening is similar to sandblasting, except that it operates by the mechanism of plasticity rather than abrasion, in practice, this means that less material is removed by the process, and less dust created. Peening a surface spreads it plastically, causing changes in the properties of the surface. Its main application is to avoid the propagation of microcracks from a surface, such cracks do not propagate in a material that is under a compressive stress, shot peening can create such a stress in the surface. Shot peening is often called for in aircraft repairs to relieve stresses built up in the grinding process. Depending on the geometry, part material, shot material, shot quality, shot intensity. Plastic deformation induces a residual stress in a peened surface. Surface compressive stresses confer resistance to fatigue and to some forms of stress corrosion. The tensile stresses deep in the part are not as problematic as tensile stresses on the surface cracks are less likely to start in the interior. A study done through the SAE Fatigue Design and Evaluation Committee showed what shot peening can do for welds compared to welds that didnt have this operation done and this is part of the reason that shot peening is a popular operation with aerospace parts. However, the beneficial prestresses can anneal out at higher temperatures, intensity is a key parameter of the shot peening process. After some development of the process, an analog was needed to measure the effects of shot peening, john Almen noticed that shot peening made the side of the sheet metal that was exposed begin to bend and stretch. He created the Almen strip to measure the compressive stresses in the created by the shot peening operation. One can obtain what is referred to as the intensity of the blast stream by measuring the deformation on the Almen strip that is in the shot peening operation. As the strip reaches a 10% deformation, the Almen strip is then hit with the intensity for twice the amount of time. If the strip deforms another 10%, then one obtains the intensity of the blast stream, another operation to gauge the intensity of a shot peening process is the use of an Almen round, developed by R. Bosshard
31.
Thermal spraying
–
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The feedstock is heated by electrical or chemical means, thermal spraying can provide thick coatings, over a large area at high deposition rate as compared to other coating processes such as electroplating, physical and chemical vapor deposition. Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and they are fed in powder or wire form, heated to a molten or semimolten state and accelerated towards substrates in the form of micrometer-size particles. Combustion or electrical arc discharge is used as the source of energy for thermal spraying. Resulting coatings are made by the accumulation of numerous sprayed particles, the surface may not heat up significantly, allowing the coating of flammable substances. Coating quality is assessed by measuring its porosity, oxide content, macro and micro-hardness, bond strength. Generally, the coating quality increases with increasing particle velocities, media supply – gases or liquids for the generation of the flame or plasma jet, gases for carrying the powder, etc. Oxygen and fuel are fed into the barrel along with a charge of powder, a spark is used to ignite the gas mixture, and the resulting detonation heats and accelerates the powder to supersonic velocity through the barrel. A pulse of nitrogen is used to purge the barrel after each detonation and this process is repeated many times a second. The high kinetic energy of the hot powder particles on impact with the results in a buildup of a very dense. In plasma spraying process, the material to be deposited — typically as a powder, sometimes as a liquid, suspension or wire — is introduced into the plasma jet, emanating from a plasma torch. In the jet, where the temperature is on the order of 10,000 K, there, the molten droplets flatten, rapidly solidify and form a deposit. Commonly, the deposits remain adherent to the substrate as coatings, there are a large number of technological parameters that influence the interaction of the particles with the plasma jet and the substrate and therefore the deposit properties. These parameters include feedstock type, plasma gas composition and flow rate, energy input, torch offset distance, substrate cooling, the deposits consist of a multitude of pancake-like splats called lamellae, formed by flattening of the liquid droplets. Between these lamellae, there are voids, such as pores, cracks. As a result of this structure, the deposits can have properties significantly different from bulk materials. These are generally mechanical properties, such as strength and modulus, higher strain tolerance. Also, due to the rapid solidification, metastable phases can be present in the deposits and this technique is mostly used to produce coatings on structural materials
32.
Powder coating
–
Powder Coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is cured under heat to allow it to flow. The powder may be a thermoplastic or a thermoset polymer and it is usually used to create a hard finish that is tougher than conventional paint. Powder coating is used for coating of metals, such as household appliances, aluminum extrusions, drum hardware. Newer technologies allow other materials, such as MDF, to be powder coated using different methods, because no carrier fluid evaporates away, the coating process emits few volatile organic compounds. Finally, several powder colors can be applied before curing them all together, allowing color blending, while it is relatively easy to apply thick coatings which cure to smooth, texture-free coating, it is not as easy to apply smooth thin films. As the film thickness is reduced, the film more and more orange peeled in texture due to the particle size. For such powder coatings, film build-ups of greater than 50 μ may be required to obtain an acceptably smooth film, the surface texture which is considered desirable or acceptable depends on the end product. There are very specialized operations where powder coatings of less than 30 micrometres or with a Tg below 40 °C are used in order to produce thin films. For garage-scale jobs, small rattle can spray paint are less expensive, at the professional scale, the capital expense and time required for a powder coat gun, booth and oven are similar to a spray gun system. Powder coatings have an advantage in that the overspray can be recycled. However, if multiple colors are being sprayed in a spray booth. Powder coatings contain no solvents and releases negligible amounts of Volatile Organic Compounds into the atmosphere, powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging. Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items, the wide range of specialty effects are easily accomplished using powder coatings that would be impossible to achieve with other coating processes. There are two categories of powder coating, thermosets and thermoplastics. The thermosetting variety incorporates a cross-linker into the formulation, when the powder is baked, it reacts with other chemical groups in the powder to polymerize, improving the performance properties. The thermoplastic variety does not undergo any additional actions during the baking process, the most common polymers used are polyester, polyurethane, polyester-epoxy, straight epoxy and acrylics. is essential prior to the powder coating process
33.
Thin-film deposition
–
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. The controlled synthesis of materials as thin films is a step in many applications. A familiar example is the mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once used to produce mirrors. It is also being applied to pharmaceuticals, via thin-film drug delivery, a stack of thin films is called a multilayer. In addition to their applied interest, thin films play an important role in the development and study of materials with new, examples include multiferroic materials, and superlattices that allow the study of quantum confinement by creating two-dimensional electron states. The act of applying a thin film to a surface is thin-film deposition – any technique for depositing a film of material onto a substrate or onto previously deposited layers. Thin is a term, but most deposition techniques control layer thickness within a few tens of nanometres. Molecular beam epitaxy and atomic layer deposition allow a single layer of atoms to be deposited at a time and it is useful in the manufacture of optics, electronics, packaging, and in contemporary art. Deposition techniques fall into two categories, depending on whether the process is primarily chemical or physical. Here, a fluid precursor undergoes a change at a solid surface. An everyday example is the formation of soot on an object when it is placed inside a flame. Chemical deposition is further categorized by the phase of the precursor, Plating relies on liquid precursors, some plating processes are driven entirely by reagents in the solution, but by far the most commercially important process is electroplating. It was not commonly used in processing for many years. Chemical solution deposition or chemical bath deposition uses a liquid precursor and this is a relatively inexpensive, simple thin film process that is able to produce stoichiometrically accurate crystalline phases. This technique is known as the sol-gel method because the sol gradually evolves towards the formation of a gel-like diphasic system. The speed at which the solution is spun and the viscosity of the sol determine the thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired, thermal treatment is often carried out in order to crystallize the amorphous spin coated film
34.
Chemical vapor deposition
–
Chemical vapor deposition is a chemical process used to produce high quality, high-performance, solid materials. The process is used in the semiconductor industry to produce thin films. In typical CVD, the wafer is exposed to one or more volatile precursors, frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. Microfabrication processes widely use CVD to deposit materials in various forms, including, monocrystalline, polycrystalline, amorphous and these materials include, silicon, carbon, fluorocarbons, filaments, tungsten, titanium nitride and various high-k dielectrics. CVD is practiced in a variety of formats and these processes generally differ in the means by which chemical reactions are initiated. Classified by operating pressure, Atmospheric pressure CVD – CVD at atmospheric pressure, low-pressure CVD – CVD at sub-atmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer, ultrahigh vacuum CVD – CVD at very low pressure, typically below 10−6 Pa. Note that in other fields, a division between high and ultra-high vacuum is common, often 10−7 Pa. Most modern CVD is either LPCVD or UHVCVD and this technique is suitable for use with non-volatile precursors. Direct liquid injection CVD – CVD in which the precursors are in liquid form, liquid solutions are injected in a vaporization chamber towards injectors. The precursor vapors are then transported to the substrate as in classical CVD and this technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique, classified by type of substrate heating, Hot wall CVD - CVD in which the chamber is heated by an external power source and the substrate is heated by radiation from the heated chamber walls. Cold wall CVD - CVD in which only the substrate is directly heated either by induction or by passing current through the substrate itself or a heater in contact with the substrate, the chamber walls are at room temperature. Plasma methods, Microwave plasma-assisted CVD Plasma-Enhanced CVD – CVD that utilizes plasma to enhance chemical reaction rates of the precursors, PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors. The lower temperatures also allow for the deposition of coatings, such as plasma polymers. Remote plasma-enhanced CVD – Similar to PECVD except that the substrate is not directly in the plasma discharge region. Removing the wafer from the region allows processing temperatures down to room temperature. Atomic-layer CVD – Deposits successive layers of different substances to produce layered, Combustion Chemical Vapor Deposition – Combustion Chemical Vapor Deposition or flame pyrolysis is an open-atmosphere, flame-based technique for depositing high-quality thin films and nanomaterials
35.
Electrophoretic deposition
–
A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and this includes materials such as polymers, pigments, dyes, ceramics and metals. The process is useful for applying materials to any electrically conductive surface, the materials which are being deposited are the major determining factor in the actual processing conditions and equipment which may be used. Due to the utilization of electrophoretic painting processes in many industries. However, non-aqueous electrophoretic deposition applications are known, applications of non-aqueous EPD are currently being explored for use in the fabrication of electronic components and the production of ceramic coatings. Non-aqueous processes have the advantage of avoiding the electrolysis of water and this process is industrially used for applying coatings to metal fabricated products. Thick films produced this way allow cheaper and more rapid synthesis relative to sol-gel thin-films, in the fabrication of solid oxide fuel cells EPD techniques are widely employed for the fabrication of porous ZrO2 anodes from powder precursors onto conductive substrates. EPD processed have a number of advantages which have made such methods widely used The process applies coatings which generally have a uniform coating thickness without porosity. Complex fabricated objects can easily be coated, both inside cavities as well as on the outside surfaces, applicability to wide range of materials Easy control of the coating composition. The process is automated and requires less human labor than other coating processes. Highly efficient utilization of the coating materials result in lower costs relative to other processes, the aqueous process which is commonly used has less risk of fire relative to the solvent-borne coatings that they have replaced. Modern electrophoretic paint products are more environmentally friendly than many other painting technologies. Thick, complex ceramic pieces have been made in research laboratories. Furthermore, EPD has been used to produce customized microstructures, such as gradients and laminates. The first patent for the use of painting was awarded in 1917 to Davey. Since the 1920s, the process has used for the deposition of rubber latex. In the 1930s the first patents were issued which described base neutralized, the first commercial anodic automotive system began operations in 1963. The first patent for a cathodic EPD product was issued in 1965, PPG Industries, Inc. was the first to introduce commercially cathodic EPD in 1970
36.
Mechanical plating
–
Mechanical plating, also known as peen plating, mechanical deposition, or impact plating, is a plating process that imparts the coating by cold welding fine metal particles to a workpiece. Mechanical galvanization is the process, but applies to coatings that are thicker than 0.001 in. It is commonly used to overcome hydrogen embrittlement problems, commonly plated workpieces include nails, screws, nuts, washers, stampings, springs, clips, and sintered iron components. The process involves tumbling the workpieces with a mixture of water, metal powder, media, common coating materials are zinc, cadmium, tin, copper, and aluminium. Invented by the Tainton Company in the 1950s, it was developed by the 3M company. The process begins with a descaling and removing soil from the workpiece and this can be done in the tumbler or in a separate cleaning system. After cleaning, the parts are prepared by combining them with water, medium, the surface conditioner lightly coats the workpiece in copper, while the medium removes any residual mill scale or oxides. Finally, accelerators, promoters and metal powder are added to the mix, the accelerators and promoters provide the proper chemical environment for the plating to occur, such as the maintenance of a pH level of 1 to 2 to prevent oxidation and promote adhesion. The medium that is already in the mixture cold welds the metal powder to the workpiece through impacts that are induced by the action of the tumbler. At this point the surface finish is typically matte to a semi-bright finish, the time required for the above process is approximately 50 minutes. For some thinly coated workpieces a chromate passivation is necessary, finally, the workpiece, whether passivated or not, is dried. The medium material is usually soda lime glass or a ceramic and it is usually spherical in form, but angular shapes are also used. For plating, medium usage is usually 1 part medium for every workpiece, but for galvanization the ratio is 2,1. However, various sized media are used in batch with a typical batch consisting of 50% 4–5 in sized beads, 25% 2–2.5 in sized beads. The smaller media are omitted when the workpiece has a cavity that the medium can get caught in, note that the medium is reused many times. This process works if the workpieces surface finish is slightly rough. The most important piece of equipment in the process is the tumbler and it is constructed of steel or stainless steel and lined with an acid and abrasion resistant material, such as neoprene, polypropylene, and polybutylene. The barrel sizes range from 0. 04–1.13 m3, for most plating applications the tumbler is rotated at 60 RPM, however it can vary
37.
Sputter deposition
–
Sputter deposition is a physical vapor deposition method of thin film deposition by sputtering. This involves ejecting material from a target that is a source onto a substrate such as a silicon wafer, resputtering is re-emission of the deposited material during the deposition process by ion or atom bombardment. Sputtered atoms ejected from the target have an energy distribution. The sputtered ions can ballistically fly from the target in straight lines, the entire range from high-energy ballistic impact to low-energy thermalized motion is accessible by changing the background gas pressure. The sputtering gas is often an inert gas such as argon, reactive gases can also be used to sputter compounds. The compound can be formed on the surface, in-flight or on the substrate depending on the process parameters. The availability of many parameters that control sputter deposition make it a complex process, one of the earliest widespread commercial applications of sputter deposition, which is still one of its most important applications, is in the production of computer hard disks. Sputtering is used extensively in the industry to deposit thin films of various materials in integrated circuit processing. Thin antireflection coatings on glass for optical applications are deposited by sputtering. Because of the low temperatures used, sputtering is an ideal method to deposit contact metals for thin-film transistors. Another familiar application of sputtering is low-emissivity coatings on glass, used in double-pane window assemblies, the coating is a multilayer containing silver and metal oxides such as zinc oxide, tin oxide, or titanium dioxide. A large industry has developed around tool bit coating using sputtered nitrides, such as titanium nitride, Sputtering is also used as the process to deposit the metal layer during the fabrication of CDs and DVDs. Hard disk surfaces use sputtered CrOx and other sputtered materials, Sputtering is one of the main processes of manufacturing optical waveguides and is another way for making efficient photovoltaic solar cells. Sputter coating in scanning electron microscopy is a deposition process to cover a specimen with a thin layer of conducting material, typically a metal. A conductive coating is needed to prevent charging of a specimen with a beam in conventional SEM mode. While metal coatings are useful for increasing signal to noise ratio. For this reason when using X-ray spectroscopy a carbon coating is preferred, Sputter deposited films have a composition close to that of the source material. The difference is due to different elements spreading differently because of their different mass, sputtered films typically have a better adhesion on the substrate than evaporated films
38.
Physical vapor deposition
–
Physical vapor deposition describes a variety of vacuum deposition methods which can be used to produce thin films and coatings. PVD is characterized by a process in which the material goes from a phase to a vapor phase. The most common PVD processes are sputtering and evaporation, PVD is used in the manufacture of items which require thin films for mechanical, optical, chemical or electronic functions. Examples include semiconductor devices such as thin film panels, aluminized PET film for food packaging and balloons. Besides PVD tools for fabrication, special tools have been developed. Common industrial coatings applied by PVD are titanium nitride, zirconium nitride, chromium nitride, the source material is unavoidably also deposited on most other surfaces interior to the vacuum chamber, including the fixturing used to hold the parts. Cathodic Arc Deposition, In which an electric arc discharged at the target material blasts away some into highly ionized vapor to be deposited onto the workpiece. Evaporative deposition, In which the material to be deposited is heated to a vapor pressure by electrical resistance heating in high vacuum. Pulsed laser deposition, In which a high-power laser ablates material from the target into a vapor, sputter deposition, In which a glow plasma discharge bombards the material sputtering some away as a vapor for subsequent deposition. Sublimation sandwich method, Used for creating man-made crystals, most coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable that protective topcoats are almost never necessary. Ability to utilize any type of inorganic and some organic coating materials on an equally diverse group of substrates and surfaces using a wide variety of finishes. More environmentally friendly than traditional coating processes such as electroplating and painting, more than one technique can be used to deposit a given film. Specific technologies can impose constraints, for example, line-of-sight transfer is typical of most PVD coating techniques, some PVD technologies typically operate at very high temperatures and vacuums, requiring special attention by operating personnel. Requires a cooling system to dissipate large heat loads. As mentioned previously, PVD coatings are used to improve hardness, wear resistance
39.
Vacuum deposition
–
Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmospheric pressure, the deposited layers can range from a thickness of one atom up to millimeters, forming freestanding structures. Multiple layers of different materials can be used, for example to form optical coatings, the process can be qualified based on the vapor source, physical vapor deposition uses a liquid or solid source and chemical vapor deposition uses a chemical vapor. Vacuum deposition describes the family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface and these processes operate at pressures well below atmospheric pressure. The deposited layers can range from a thickness of one atom up to millimeters, multiple layers of different materials can be used, for example to form optical coatings. There are subcategories of the process, based on the source, Physical vapor deposition uses a liquid or solid source. A plasma environment aids in activating gaseous species and in decomposition of chemical vapor precursors, when the vapor source is a liquid or solid the process is called physical vapor deposition. When the source is a chemical vapor precursor, the process is called chemical vapor deposition, the latter has several variants, low-pressure chemical vapor deposition, Plasma-enhanced chemical vapor deposition, and plasma-assisted CVD. Often a combination of PVD and CVD processes are used in the same or connected processing chambers, electrical conduction, metallic films, transparent conductive oxides, superconducting films & coatings Semiconductor devices, semiconductor films, electrically insulating films Solar cells. Ion plating Sputter deposition Cathodic arc deposition Spin coating Metallised film
40.
Vitreous enamel
–
Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C. The powder melts, flows, and then hardens to a smooth, durable vitreous coating on metal, so in technical terms fired enamelware is an integrated layered composite of glass and metal. Enamelling is an old and widely adopted technology, for most of its history mainly used in jewelry, enamelled and enamelling are the preferred spellings in British English, while enameled and enameling are preferred in American English. The term enamel is most often restricted to work on metal, enamelled glass is also called painted, and overglaze decoration to pottery is often called enamelling. The word enamel comes from the Old High German word smelzan via the Old French esmail, or from a Latin word smaltum, used as a noun, an enamel is usually a small decorative object coated with enamel. Since the 19th century the term also to industrial materials and many metal consumer objects, such as some cooking vessels, dishwashers, laundry machines, sinks. The ancient Egyptians applied enamels to stone objects, pottery, and sometimes jewellery, the ancient Greeks, Celts, Georgians, and Chinese also used enamel on metal objects. Enamel powder could be produced in two ways, either by powdering coloured glass, or by mixing colourless glass powder with pigments such as a metallic oxide, designs were either painted freehand or over the top of outline incisions, and the technique probably originated in metalworking. Once painted, enamelled glass vessels needed to be fired at a high enough to melt the applied powder. Ancient Persians used this method for colouring and ornamenting the surface of metals by fusing over it brilliant colours that are decorated in an intricate design and called it Meenakari. Gold has been used traditionally for Meenakari Jewellery as it holds the enamel better, lasts longer, initially, the work of Meenakari often went unnoticed as this art was traditionally used as a backing for the famous kundan or stone-studded jewellery. This also allowed the wearer to reverse the jewellery as also promised a special joy in the secret of the hidden design, the Byzantine enamel style was widely adopted by the barbarian peoples of Migration Period northern Europe. The Byzantines then began to use cloisonné more freely to create images, the champlevé technique was considerably easier and very widely practiced in the Romanesque period. In Gothic art the finest work is in basse-taille and ronde-bosse techniques, from either Byzantium or the Islamic world, the cloisonné technique reached China in the 13-14th centuries. The first written reference to cloisonné is in a book from 1388, cloisonné remained very popular in China until the 19th century and is still produced today. Starting from the century, the Japanese also produced large quantities of very high technical quality. A resurgence in enamel-based art took place near the end of the 20th century in the Soviet Union, led by artists like Alexei Maximov, in Australia, abstract artist Bernard Hesling brought the style into prominence with his variously sized steel plates. Enamel was first applied commercially to sheet iron and steel in Austria, industrialization increased as the purity of raw materials increased and costs decreased
41.
Abrasive blasting
–
A pressurized fluid, typically compressed air, or a centrifugal wheel is used to propel the blasting material. The first abrasive blasting process was patented by Benjamin Chew Tilghman on 18 October 1870, there are several variants of the process, using various media, some are highly abrasive, whereas others are milder. The most abrasive are shot blasting and sandblasting, moderately abrasive variants include glass bead blasting and media blasting with ground-up plastic stock or walnut shells and corncobs. In addition, there are alternatives that are barely abrasive or nonabrasive, such as ice blasting and dry-ice blasting. One of the pioneers of the wet abrasive process was Norman Ashworth who found the advantages of using a wet process a strong alternative to sandblasting—which is banned in many countries. g. Removal of asbestos, radioactive, or other products from components. The process is available in all formats including hand cabinets, walk-in booths, automated production machinery. Process speeds can be as fast as conventional dry sand blasting when using the equivalent size, however the presence of water between the media and the substrate being processed creates a lubricating cushion that can protect both the media and the surface from excess damage. This has the advantage of lowering media breakdown rates and preventing impregnation of foreign materials into the surface. Subsequent coating or bonding operations are always better after wet blasting than dry blasting because of the levels achieved. The lack of surface recontamination also allows the use of equipment for multiple blasting operations—e. g. Stainless steel and carbon steel items can be processed in the equipment with the same media without problems. Bead blasting is the process of removing surface deposits by applying fine glass beads at a high pressure without damaging the surface and it is used to clean calcium deposits from pool tiles or any other surfaces, remove embedded fungus, and brighten grout color. It is also used in auto body work to remove paint, in removing paint for auto body work, bead blasting is preferred over sand blasting, as sand blasting tends to invite rust formation under re-painted surfaces. Its additionally used in cleaning mineral specimens, most of which have a Mohs hardness of 7 or less, in wheel blasting, a spinning wheel propels the abrasive against an object. It is typically categorized as an airless blasting operation because there is no propellant used, a wheel machine is a high-power, high-efficiency blasting operation with recyclable abrasive. Specialized wheel blast machines propel plastic abrasive in a cryogenic chamber, the size of the wheel blast machine, and the number and power of the wheels vary considerably depending on the parts to be blasted as well as on the expected result and efficiency. The first blast wheel was patented by Wheelabrator in 1932, hydro-blasting, commonly known as water blasting, is commonly used because it usually requires only one operator
42.
Chemical-mechanical planarization
–
Chemical mechanical polishing/planarization is a process of smoothing surfaces with the combination of chemical and mechanical forces. It can be thought of as a hybrid of chemical etching, the process uses an abrasive and corrosive chemical slurry in conjunction with a polishing pad and retaining ring, typically of a greater diameter than the wafer. The pad and wafer are pressed together by a dynamic polishing head, the dynamic polishing head is rotated with different axes of rotation. This removes material and tends to even out any irregular topography and this may be necessary to set up the wafer for the formation of additional circuit elements. For example, CMP can bring the surface within the depth of field of a photolithography system. Typical depth-of-field requirements are down to Angstrom levels for the latest 22 nm technology, typical CMP tools, such as the ones seen on the right, consist of a rotating and extremely flat plate which is covered by a pad. The wafer that is being polished is mounted upside-down in a carrier/spindle on a backing film, the retaining ring keeps the wafer in the correct horizontal position. During the process of loading and unloading the wafer onto the tool, a slurry introduction mechanism deposits the slurry on the pad, represented by the slurry supply in Figure 1. Both the plate and the carrier are then rotated and the carrier is kept oscillating, a downward pressure/down force is applied to the carrier, pushing it against the pad, typically the down force is an average force, but local pressure is needed for the removal mechanisms. Down force depends on the area which, in turn, is dependent on the structures of both the wafer and the pad. Typically the pads have a roughness of 50 µm, contact is made by asperities and, as a result, in CMP, the mechanical properties of the wafer itself must be considered too. If the wafer has a slightly bowed structure, the pressure will be greater on the edges than it would on the center, in order to compensate for the wafer bow, pressure can be applied to the wafers backside which, in turn, will equalize the centre-edge differences. The pads used in the CMP tool should be rigid in order to polish the wafer surface. However, these pads must be kept in alignment with the wafer at all times. Therefore, real pads are often just stacks of soft and hard materials that conform to wafer topography to some extent. Generally, these pads are made from polymeric materials with a pore size between 30-50 µm, and because they are consumed in the process, they must be regularly reconditioned. In most cases the pads are very much proprietary, and are referred to by their trademark names rather than their chemical or other properties. Before about 1990 CMP was viewed as too dirty to be included in high-precision fabrication processes, since abrasion tends to create particles, since that time, the integrated circuit industry has moved from aluminium to copper conductors
43.
Electropolishing
–
Electropolishing, also known as electrochemical polishing, anodic polishing or electrolytic polishing, is an electrochemical process that removes material from a metallic workpiece. It is used to polish, passivate, and deburr metal parts and it is often described as the reverse of electroplating. It may be used in lieu of abrasive fine polishing in microstructural preparation, a current passes from the anode, where metal on the surface is oxidised and dissolved in the electrolyte, to the cathode. At the cathode, a reaction occurs, which normally produces hydrogen. Electrolytes used for electropolishing are most often concentrated acid solutions having a high viscosity, such as mixtures of sulphuric acid, other electropolishing electrolytes reported in the literature include mixtures of perchlorates with acetic anhydride and methanolic solutions of sulphuric acid. To achieve electropolishing of a surface, the protruding parts of a surface profile must dissolve faster than the recesses. This process, referred to as anodic levelling, can be subject to incorrect analysis when measuring the surface topography, anodic dissolution under electropolishing conditions deburrs metal objects due to increased current density on corners and burrs. Electropolishing has many applications in the finishing industry because of its simplicity. Typical examples are electropolished stainless steel drums of washing machines and stainless steel surgical devices, ultra high vacuum components are typically electropolished in order to have a smoother surface for improved vacuum pressures, out-gassing rates, and pumping speed. Electropolishing also provides a clean and smooth surface that is easier to sterilise, while improving the finish by levelling micro-peaks. This methodology is able to polish areas that are inaccessible by other polishing methods, another benefit of electropolishing is that it removes a small amount of material from the surface of the parts, while also removing small burrs or high spots. It can be used to reduce the size of parts when necessary. The results of electropolishing are considered to be aesthetically pleasing by many people, Electropolishing The Then & Now of Electropolishing by Anopol Limited/Surface World
