An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different from ambient air pressure. Autoclaves are used in medical applications to perform sterilization and in the chemical industry to cure coatings and vulcanize rubber and for hydrothermal synthesis. Industrial autoclaves are used in industrial applications regarding composites. Many autoclaves are used to sterilize equipment and supplies by subjecting them to pressurized saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents; the autoclave was invented by Charles Chamberland in 1884, although a precursor known as the steam digester was created by Denis Papin in 1679. The name comes from Greek auto- meaning self, Latin clavis meaning key, thus a self-locking device. Sterilization autoclaves are used in microbiology, podiatry, body piercing, veterinary medicine, funerary practice and prosthetics fabrication, they vary in size and function depending on the media to be sterilized and are sometimes called retort in the chemical and food industries.
Typical loads include laboratory glassware, other equipment and waste, surgical instruments, medical waste. A notable recent and popular application of autoclaves is the pre-disposal treatment and sterilization of waste material, such as pathogenic hospital waste. Machines in this category operate under the same principles as conventional autoclaves in that they are able to neutralize infectious agents by using pressurized steam and superheated water. A new generation of waste converters is capable of achieving the same effect without a pressure vessel to sterilize culture media, rubber material, dressings, etc, it is useful for materials which cannot withstand the higher temperature of a hot air oven. Autoclaves are widely used to cure composites and in the vulcanization of rubber; the high heat and pressure that autoclaves generate help to ensure that the best possible physical properties are repeatable. The aerospace industry and sparmakers have autoclaves well over 50 feet long, some over 10 feet wide.
Other types of autoclaves are used to grow crystals under high pressures. Synthetic quartz crystals used in the electronics industry are grown in autoclaves. Packing of parachutes for specialist applications may be performed under vacuum in an autoclave, which allows the chutes to be warmed and inserted into their packs at the smallest volume, it is important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a poor medium for achieving sterility. Steam at 134 °C can achieve in three minutes the same sterility that hot air at 160 °C can take two hours to achieve. Methods of air removal include: Downward displacement: As steam enters the chamber, it fills the upper areas first as it is less dense than air; this process compresses the air to the bottom, forcing it out through a drain which contains a temperature sensor. Only when air evacuation is complete does the discharge stop. Flow is controlled by a steam trap or a solenoid valve, but bleed holes are sometimes used in conjunction with a solenoid valve.
As the steam and air mix, it is possible to force out the mixture from locations in the chamber other than the bottom. Steam pulsing: air dilution by using a series of steam pulses, in which the chamber is alternately pressurized and depressurized to near atmospheric pressure. Vacuum pumps: a vacuum pump sucks air or air/steam mixtures from the chamber. Superatmospheric cycles: achieved with a vacuum pump, it starts with a vacuum followed by a steam pulse followed by a vacuum followed by a steam pulse. The number of pulses depends on the particular cycle chosen. Subatmospheric cycles: similar to the superatmospheric cycles, but chamber pressure never exceeds atmospheric pressure until they pressurize up to the sterilizing temperature. A medical autoclave is a device; this means that all bacteria, viruses and spores are inactivated. However, such as those associated with Creutzfeldt–Jakob disease, some toxins released by certain bacteria, such as Cereulide, may not be destroyed by autoclaving at the typical 134 °C for three minutes or 121 °C for 15 minutes.
Although a wide range of archaea species, including Geogemma barosii, can survive and reproduce at temperatures above 121 °C, no archaea are known to be infectious or otherwise pose a health risk to humans. Autoclaves are found in many medical settings and other places that need to ensure the sterility of an object. Many procedures today employ single-use items rather than reusable items; this first happened with hypodermic needles, but today many surgical instruments are single-use rather than reusable items. Autoclaves are of particular importance in poorer countries due to the much greater amount of equipment, re-used. Providing stove-top or solar autoclaves to rural medical centers has been the subject of several proposed medical aid missions; because damp heat is used, heat-labile products cannot be sterilized this way or they will melt. Paper and other products that may be damaged by steam must be sterilized another way. In all autoclaves, items should always be separated to allow the ste
Laser-heated pedestal growth
Laser-heated pedestal growth or laser floating zone is a crystal growth technique. A narrow region of a crystal is melted with a powerful YAG laser; the laser and hence the floating zone, is moved along the crystal. The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it; this technique for growing crystals from the melt is used in materials research. The main advantages of this technique are the high pulling rates and the possibility of growing materials with high melting points. In addition, LHPG is a crucible-free technique, which allows single crystals to be grown with high purity and low stress; the geometric shape of the crystals, the low production cost, make the single-crystal fibers produced by LHPG suitable substitutes for bulk crystals in many devices those that use high melting point materials. However, single-crystal fibers must have equal or superior optical and structural qualities compared to bulk crystals to substitute for them in technological devices.
This can be achieved by controlling the growth conditions. Until 1980, laser-heated crystal growth used; this condition generated a high radial thermal gradient in the molten zone, making the process unstable. Increasing the number of beams to four did not solve the problem, although it improved the growth process. An improvement to the laser-heated crystal growth technique was made by Fejer et al. who incorporated a special optical component known as a reflaxicon, consisting of an inner cone surrounded by a larger coaxial cone section, both with reflecting surfaces. This optical element converts the cylindrical laser beam into a larger diameter hollow cylinder surface; this optical component allows radial distribution of the laser energy over the molten zone, reducing radial thermal gradients. The axial temperature gradient in this technique can go as high as 10000 °C/cm, high when compared to traditional crystal growth techniques. A feature of the LHPG technique is its high convection speed in the liquid phase due to Marangoni convection.
It is possible to see that it spins fast. When it appears to be standing still, it is in fact spinning fast on its axis
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of an O2 -- atom. Metal oxides thus contain an anion of oxygen in the oxidation state of −2. Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide. Materials considered pure elements develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further corrosion. Individual elements can form multiple oxides, each containing different amounts of the element and oxygen. In some cases these are distinguished by specifying the number of atoms as in carbon monoxide and carbon dioxide, in other cases by specifying the element's oxidation number, as in iron oxide and iron oxide. Certain elements can form many different oxides, such as those of nitrogen.
Due to its electronegativity, oxygen forms stable chemical bonds with all elements to give the corresponding oxides. Noble metals are prized because they resist direct chemical combination with oxygen, substances like gold oxide must be generated by indirect routes. Two independent pathways for corrosion of elements are oxidation by oxygen; the combination of water and oxygen is more corrosive. All elements burn in an atmosphere of oxygen or an oxygen-rich environment. In the presence of water and oxygen, some elements— sodium—react to give the hydroxides. In part, for this reason and alkaline earth metals are not found in nature in their metallic, i.e. native, form. Cesium is so reactive with oxygen that it is used as a getter in vacuum tubes, solutions of potassium and sodium, so-called NaK are used to deoxygenate and dehydrate some organic solvents; the surface of most metals consists of hydroxides in the presence of air. A well-known example is aluminium foil, coated with a thin film of aluminium oxide that passivates the metal, slowing further corrosion.
The aluminum oxide layer can be built to greater thickness by the process of electrolytic anodizing. Though solid magnesium and aluminum react with oxygen at STP—they, like most metals, burn in air, generating high temperatures. Finely grained powders of most metals can be dangerously explosive in air, they are used in solid-fuel rockets. In dry oxygen, iron forms iron oxide, but the formation of the hydrated ferric oxides, Fe2O3−x2x, that comprise rust requires oxygen and water. Free oxygen production by photosynthetic bacteria some 3.5 billion years ago precipitated iron out of solution in the oceans as Fe2O3 in the economically important iron ore hematite. Oxides have a range of different structures, from individual molecules to polymeric and crystalline structures. At standard conditions, oxides may range from solids to gases. Oxides of most metals adopt polymeric structures; the oxide links three metal atoms or six metal atoms. Because the M-O bonds are strong and these compounds are crosslinked polymers, the solids tend to be insoluble in solvents, though they are attacked by acids and bases.
The formulas are deceptively simple. Many are nonstoichiometric compounds; some important gaseous oxides. Examples of molecular oxides are carbon monoxide. All simple oxides of nitrogen are molecular, e.g. NO, N2O, NO2 and N2O4. Phosphorus pentoxide is a more complex molecular oxide with a deceptive name, the real formula being P4O10; some polymeric oxides depolymerize when heated to give molecules, examples being selenium dioxide and sulfur trioxide. Tetroxides are rare; the more common examples: ruthenium tetroxide, osmium tetroxide, xenon tetroxide. Many oxyanions are known, such as polyoxometalates. Oxycations are rarer, some examples being nitrosonium and uranyl. Of course many compounds are known with other groups. In organic chemistry, these include many related carbonyl compounds. For the transition metals, many oxo complexes are known as well as oxyhalides. Conversion of a metal oxide to the metal is called reduction; the reduction can be induced by many reagents. Many metal oxides convert to metals by heating.
Metals are "won" from their oxides by chemical reduction, i.e. by the addition of a chemical reagent. A common and cheap reducing agent is carbon in the form of coke; the most prominent example is that of iron ore smelting. Many reactions are involved, but the simplified equation is shown as: 2 Fe2O3 + 3 C → 4 Fe + 3 CO2Metal oxides can be reduced by organic compounds; this redox process is the basis for many important transformations in chemistry, such as the detoxification of drugs by the P450 enzymes and the production of ethylene oxide, converted to antifreeze. In such systems, the metal center transfers an oxide ligand to the organic compound followed by regeneration of the metal oxide by oxygen in the air. Metals that are lower in the reactivity series can be reduced by heating alone. For example, silver oxide decomposes at 200 °C: 2 Ag2O → 4 Ag + O2 Metals that are more reactive displace the oxide of the metals that are less reactive. For example, zinc is more reactive than copper, so it displaces copper oxide to form zinc oxide: Zn + CuO → ZnO + Cu Apart from metals, hydrogen can displace metal oxides to form hydrogen oxide
Ammonium chloride is an inorganic compound with the formula NH4Cl and a white crystalline salt, soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of the mineralogical form of ammonium chloride; the mineral is formed on burning coal dumps from condensation of coal-derived gases. It is found around some types of volcanic vents, it is used as fertilizer and a flavouring agent in some types of liquorice. It is the product from the reaction of hydrochloric ammonia, it is a product of the Solvay process used to produce sodium carbonate: CO2 + 2 NH3 + 2 NaCl + H2O → 2 NH4Cl + Na2CO3In addition to being the principal method for the manufacture of ammonium chloride, that method is used to minimize ammonia release in some industrial operations. Ammonium chloride is prepared commercially by combining ammonia with either hydrogen chloride or hydrochloric acid: NH3 + HCl → NH4ClAmmonium chloride occurs in volcanic regions, forming on volcanic rocks near fume-releasing vents.
The crystals deposit directly from the gaseous state and tend to be short-lived, as they dissolve in water. Ammonium chloride appears to sublime upon heating but decomposes into ammonia and hydrogen chloride gas. NH4Cl → NH3 + HClAmmonium chloride reacts with a strong base, like sodium hydroxide, to release ammonia gas: NH4Cl + NaOH → NH3 + NaCl + H2OSimilarly, ammonium chloride reacts with alkali metal carbonates at elevated temperatures, giving ammonia and alkali metal chloride: 2 NH4Cl + Na2CO3 → 2 NaCl + CO2 + H2O + 2 NH3A 5% by weight solution of ammonium chloride in water has a pH in the range 4.6 to 6.0. Some of ammonium chloride's reactions with other chemicals are endothermic like its reaction with barium hydroxide and its dissolving in water; the dominant application of ammonium chloride is as a nitrogen source in fertilizers such as chloroammonium phosphate. The main crops fertilized this way are wheat in Asia. Ammonium chloride was used in pyrotechnics in the 18th century but was superseded by safer and less hygroscopic chemicals.
Its purpose was to provide a chlorine donor to enhance the green and blue colours from copper ions in the flame. It had a secondary use to provide white smoke, but its ready double decomposition reaction with potassium chlorate producing the unstable ammonium chlorate made its use suspect. Ammonium chloride galvanized or soldered, it works as a flux by cleaning the surface of workpieces by reacting with the metal oxides at the surface to form a volatile metal chloride. For that purpose, it is sold in blocks at hardware stores for use in cleaning the tip of a soldering iron, it can be included in solder as flux. Ammonium chloride is used as an expectorant in cough medicine, its expectorant action is caused by irritative action on the bronchial mucosa, which causes the production of excess respiratory tract fluid, easier to cough up. Ammonium salts may induce nausea and vomiting. Ammonium chloride is used as a systemic acidifying agent in treatment of severe metabolic alkalosis, in oral acid loading test to diagnose distal renal tubular acidosis, to maintain the urine at an acid pH in the treatment of some urinary-tract disorders.
Ammonium chloride, under the name sal ammoniac or salmiak is used as food additive under the E number E510, working as a yeast nutrient in breadmaking and as an acidifier. It is a feed supplement for cattle and an ingredient in nutritive media for yeasts and many microorganisms. Ammonium chloride is used to spice up dark sweets called salmiak, in baking to give cookies a crisp texture, in the liquor Salmiakki Koskenkorva for flavouring. In Iran, India and Arab countries it is called "Noshader" and is used to improve the crispness of snacks such as samosas and jalebi. Ammonium chloride has been used to produce low temperatures in cooling baths. Ammonium chloride solutions with ammonia are used as buffer solutions including ACK lysis buffer. In paleontology, ammonium chloride vapor is deposited on fossils, where the substance forms a brilliant white removed and harmless and inert layer of tiny crystals; that covers up any coloration the fossil may have, if lighted at an angle enhances contrast in photographic documentation of three-dimensional specimens.
The same technique is applied in archaeology to eliminate reflection on glass and similar specimens for photography. In organic synthesis saturated NH4Cl solution is used to quench reaction mixtures. Giant squid and some other large squid species maintain neutral buoyancy in seawater through an ammonium chloride solution, found throughout their bodies and is less dense than seawater; this differs from the method of flotation used by most fish, which involves a gas-filled swim bladder. The solution tastes somewhat like salmiakki and makes giant squid unattractive for general human consumption. Ammonium chloride is used in a ~5% aqueous solution to work on oil wells with clay swelling problems, it is used as electrolyte in zinc–carbon batteries. Other uses include in hair shampoo, in the glue that bonds plywood, in cleaning products. In hair shampoo, it is used as a thickening agent in ammonium-based surfactant systems such as ammonium lauryl sulfate. Ammonium chloride is used in the textile and leather industry, in dyeing, textile printing and cotton clustering.
Around the turn of the 20th Century, Ammonium Chloride was used in aqueous solution as the electrolyte in
Crystallization is the process by which a solid forms, where the atoms or molecules are organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more deposition directly from a gas. Attributes of the resulting crystal depend on factors such as temperature, air pressure, in the case of liquid crystals, time of fluid evaporation. Crystallization occurs in two major steps; the first is nucleation, the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth, the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface lodge themselves into open inconsistencies such as pores, etc; the majority of minerals and organic molecules crystallize and the resulting crystals are of good quality, i.e. without visible defects. However, larger biochemical particles, like proteins, are difficult to crystallize.
The ease with which molecules will crystallize depends on the intensity of either atomic forces, intermolecular forces or intramolecular forces. Crystallization is a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering, crystallization occurs in a crystallizer. Crystallization is therefore related to precipitation, although the result is not amorphous or disordered, but a crystal; the crystallization process consists of two major events and crystal growth which are driven by thermodynamic properties as well as chemical properties. In crystallization Nucleation is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale, that become stable under the current operating conditions; these stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size; such critical size is dictated by many different factors.
It is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal, although those are a result of the internal crystal structure. The crystal growth is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by Ksp. Depending upon the conditions, either nucleation or growth may be predominant over the other, dictating crystal size. Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism.
Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature. There are many examples of natural process. Geological time scale process examples include: Natural crystal formation. Human time scale process examples include: Snow flakes formation. Crystal formation can be divided into two types, where the first type of crystals are composed of a cation and anion known as a salt, such as sodium acetate; the second type of crystals are composed for example menthol. Crystal formation can be achieved by various methods, such as: cooling, addition of a second solvent to reduce the solubility of the solute, solvent layering, changing the cation or anion, as well as other methods.
The formation of a supersaturated solution does not guarantee crystal formation, a seed crystal or scratching the glass is required to form nucleation sites. A typical laboratory technique for crystal formation is to dissolve the solid in a solution in which it is soluble at high temperatures to obtain supersaturation; the hot mixture is filtered to remove any insoluble impurities. The filtrate is allowed to cool. Crystals that form are filtered and washed with a solvent in which they are not soluble, but is miscible with the mother liquor; the process is repeated to increase the purity in a technique known as recrystallization. For biological molecules in which the solvent channels continue to be present to retain the three dimensional structure intact, microbatch crystallization under oil and vapor diffusion methods have been the common methods. Equipment for the main industrial processes for crystallization. Tank crystallizers. Tank crystallization is an old method still used in some specialized cases.
Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquo