Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in group 6, it is a steely-grey, lustrous and brittle transition metal. Chromium boasts a high usage rate as a metal, able to be polished while resisting tarnishing. Chromium is the main additive in stainless steel, a popular steel alloy due to its uncommonly high specular reflection. Simple polished chromium reflects 70% of the visible spectrum, with 90% of infrared light being reflected; the name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored. Ferrochromium alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and aluminium. Chromium metal is of high value for hardness. A major development in steel production was the discovery that steel could be made resistant to corrosion and discoloration by adding metallic chromium to form stainless steel.
Stainless steel and chrome plating together comprise 85% of the commercial use. In the United States, trivalent chromium ion is considered an essential nutrient in humans for insulin and lipid metabolism. However, in 2014, the European Food Safety Authority, acting for the European Union, concluded that there was not sufficient evidence for chromium to be recognized as essential. While chromium metal and Cr ions are not considered toxic, hexavalent chromium is both toxic and carcinogenic. Abandoned chromium production sites require environmental cleanup. Chromium is the fourth transition metal found on the periodic table, has an electron configuration of 3d5 4s1, it is the first element in the periodic table whose ground-state electron configuration violates the Aufbau principle. This occurs again in the periodic table with other elements and their electron configurations, such as copper and molybdenum; this occurs. In the previous elements, the energetic cost of promoting an electron to the next higher energy level is too great to compensate for that released by lessening inter-electronic repulsion.
However, in the 3d transition metals, the energy gap between the 3d and the next-higher 4s subshell is small, because the 3d subshell is more compact than the 4s subshell, inter-electron repulsion is smaller between 4s electrons than between 3d electrons. This lowers the energetic cost of promotion and increases the energy released by it, so that the promotion becomes energetically feasible and one or two electrons are always promoted to the 4s subshell. Chromium is the first element in the 3d series where the 3d electrons start to sink into the inert core. Chromium is a strong oxidising agent in contrast to the tungsten oxides. Chromium is hard, is the third hardest element behind carbon and boron, its Mohs hardness is 8.5, which means that it can scratch samples of quartz and topaz, but can be scratched by corundum. Chromium is resistant to tarnishing, which makes it useful as a metal that preserves its outermost layer from corroding, unlike other metals such as copper and aluminium. Chromium has a melting point of 1907 °C, low compared to the majority of transition metals.
However, it still has the second highest melting point out of all the Period 4 elements, being topped by vanadium by 3 °C at 1910 °C. The boiling point of 2671 °C, however, is comparatively lower, having the third lowest boiling point out of the Period 4 transition metals alone behind manganese and zinc. Chromium has an unusually high specular reflection in comparison to that of other transition metals. At 425 μm, chromium was found to have a relative maximum reflection of about 72% reflectance, before entering a depression in reflectivity, reaching a minimum of 62% reflectance at 750 μm before rising again to reflecting 90% of 4000 μm of infrared waves.. When chromium is formed into a stainless steel alloy and polished, the specular reflection decreases with the inclusion of additional metals, yet is still rather high in comparison with other alloys. Between 40% and 60% of the visible spectrum is reflected from polished stainless steel; the explanation on why chromium displays such a high turnout of reflected photon waves in general the 90% of infrared waves that were reflected, can be attributed to chromium's magnetic properties.
Chromium has unique magnetic properties in the sense that chromium is the only elemental solid which shows antiferromagnetic ordering at room temperature. Above 38 °C, its magnetic ordering changes to paramagnetic.. The antiferromagnetic properties, which cause the chromium atoms to temporarily ionize and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the lattice periodicity; this is due to the fact that the magnetic moments at the cube's corners and the cube centers are not equal, but are still antiparallel. From here, the frequency-dependent relative permittivity of chromium, deriving from Maxwell's equations in conjunction with chromium's antiferromagnetivity, leaves chromium with a high infrared and visible light reflectance. Chromium metal left standing in air is passivated by oxidation, forming a th
Tungsten carbide is a chemical compound containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through a process called sintering for use in industrial machinery, cutting tools, armor-piercing rounds, other tools and instruments, jewelry. Tungsten carbide is twice as stiff as steel, with a Young's modulus of 530–700 GPa, is double the density of steel—nearly midway between that of lead and gold, it is comparable with corundum in hardness and can only be polished and finished with abrasives of superior hardness such as cubic boron nitride and diamond powder and compounds. Referred to as Wolfram, Wolf Rahm, wolframite ore discovered by Peter Woulfe was later carburized and cemented with a binder creating a composite now called "cemented tungsten carbide". Tungsten is Swedish for "heavy stone". Colloquially among workers in various industries, tungsten carbide is simply called carbide, despite the imprecision of the usage.
Among the lay public, the growing popularity of tungsten carbide rings has led to consumers calling the material tungsten. Tungsten carbide is prepared by reaction of tungsten metal and carbon at 1400–2000 °C. Other methods include a patented lower temperature fluid bed process that reacts either tungsten metal or blue WO3 with CO/CO2 mixture and H2 between 900 and 1200 °C. WC can be produced by heating WO3 with graphite: directly at 900 °C or in hydrogen at 670 °C following by carburization in argon at 1000 °C. Chemical vapor deposition methods that have been investigated include: reacting tungsten hexachloride with hydrogen and methane at 670 °C WCl6 + H2 + CH4 → WC + 6 HClreacting tungsten hexafluoride with hydrogen and methanol at 350 °C WF6 + 2 H2 + CH3OH → WC + 6 HF + H2O There are two well-characterized compounds of tungsten and carbon, WC and tungsten semicarbide, W2C. Both compounds may be present in coatings and the proportions can depend on the coating method. At high temperatures WC decomposes to tungsten and carbon and this can occur during high-temperature thermal spray, e.g. in high velocity oxygen fuel and high energy plasma methods.
Oxidation of WC starts at 500–600 °C. It is resistant to acids and is only attacked by hydrofluoric acid/nitric acid mixtures above room temperature, it reacts with fluorine gas at room temperature and chlorine above 400 °C and is unreactive to dry H2 up to its melting point. Finely powdered WC oxidizes in hydrogen peroxide aqueous solutions. At high temperatures and pressures it reacts with aqueous sodium carbonate forming sodium tungstate, a procedure used for recovery of scrap cemented carbide. Tungsten carbide has a high melting point at 2,870 °C, a boiling point of 6,000 °C when under a pressure equivalent to 1 standard atmosphere, a thermal conductivity of 110 W·m−1·K−1, a coefficient of thermal expansion of 5.5 µm·m−1·K−1. Tungsten carbide is hard, ranking about 9 on Mohs scale, with a Vickers number of around 2600, it has a Young's modulus of 530–700 GPa, a bulk modulus of 630–655 GPa, a shear modulus of 274 GPa. It has an ultimate tensile strength of 344 MPa, an ultimate compression strength of about 2.7 GPa and a Poisson's ratio of 0.31.
The speed of a longitudinal wave through a thin rod of tungsten carbide is 6220 m/s. Tungsten carbide's low electrical resistivity of about 0.2 µΩ·m is comparable with that of some metals. WC is wetted by both molten nickel and cobalt. Investigation of the phase diagram of the W-C-Co system shows that WC and Co form a pseudo binary eutectic; the phase diagram shows that there are so-called η-carbides with composition 6C that can be formed and the brittleness of these phases makes control of the carbon content in WC-Co cemented carbides important. There are two forms of WC, a hexagonal form, α-WC, a cubic high-temperature form, β-WC, which has the rock salt structure; the hexagonal form can be visualized as made up of a simple hexagonal lattice of metal atoms of layers lying directly over one another, with carbon atoms filling half the interstices giving both tungsten and carbon a regular trigonal prismatic, 6 coordination. From the unit cell dimensions the following bond lengths can be determined: the distance between the tungsten atoms in a hexagonally packed layer is 291 pm, the shortest distance between tungsten atoms in adjoining layers is 284 pm, the tungsten carbon bond length is 220 pm.
The tungsten-carbon bond length is therefore comparable to the single bond in W6 in which there is distorted trigonal prismatic coordination of tungsten. Molecular WC has been investigated and this gas phase species has a bond length of 171 pm for 184W12C. Sintered tungsten carbide - cobalt cutting tools are abrasion resistant and can withstand higher temperatures than standard high-speed steel tools. Carbide cutting surfaces are used for machining through materials such as carbon steel or stainless steel, in applications where steel tools would wear such as high-quantity and high-precision production; because carbide tools maintain a sharp cutting edge better than steel tools, they produce a better finish on parts, their temperature resistance allows faster machining. The material is called cemented carbide, solid carbide, hardmetal or tungsten-carbide cobal
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
Bischromium is the organometallic compound with the formula Cr2. It is sometimes called dibenzenechromium; the compound played an important role in the development of sandwich compounds in organometallic chemistry and is the prototypical complex containing two arene ligands. The substance is air sensitive and its synthesis requires air-free techniques, it was first prepared by Hafner and Fischer by the reaction of CrCl3, benzene, in the presence of AlCl3. This so-called reductive Friedel-Crafts method was pioneered by E. O. Fischer and his students; the product of the reaction was yellow +, reduced to the neutral complex. Idealized equations for the synthesis are: CrCl3 + 2/3 Al + AlCl3 + 2 C6H6 → AlCl4 + 2/3 AlCl3 AlCl4 + 1/2 Na2S2O4 → + NaAlCl4 + SO2Using the technique of metal vapor synthesis and many analogous compounds can be prepared by co-condensation of Cr vapor and arene. In this way, the phosphabenzene complex can be prepared. Compounds related to + had been prepared many years before Fischer's work by Franz Hein by the reaction of phenylmagnesium bromide and CrCl3.
Hein's reaction affords cationic sandwich complexes containing bi- and terphenyl, which baffled chemists until the breakthrough by Fischer and Hafner. Fischer and Seus soon prepared Hein's + by an unambiguous route, thus confirming that Hein had unknowingly discovered sandwich complexes, a half-century ahead of the work on ferrocene. Illustrating the rapid pace of this research, the same issue of Chem. Ber. describes the Mo complex. The compound reacts with carboxylic acids to give chromium carboxylates, such as chromium acetate, which have interesting structures. Oxidation affords +. Carbonylation gives chromium tricarbonyl; the compound finds limited use in organic synthesis
Mechanical alloying is a solid-state and powder processing technique involving repeated cold welding, re-welding of blended powder particles in a high-energy ball mill to produce a homogeneous material. Developed to produce oxide-dispersion strengthened nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or pre-alloyed powders; the non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases and amorphous alloys. One consideration that should be avoided is powder contamination. Mechanical alloying is akin to metal powder processing, where metals may be mixed to produce superalloys. Mechanical alloying occurs in three steps. First, the alloy materials are combined in ground to a fine powder. A hot isostatic pressing process is applied to compress and sinter the powder.
A final heat treatment stage helps remove existing internal stresses produced during any cold compaction which may have been used. This produces an alloy suitable for high heat turbine blades and aerospace components. Design parameters include type of mill, milling container, milling speed, milling time, type and size distribution of the grinding medium, ball-to-powder weight ratio, extent of filling the vial, milling atmosphere, process control agent, temperature of milling, the reactivity of the species; the process of mechanical alloying involves the production of a composite powder particles by: Using a high energy mill to favor plastic deformation required for cold welding and reduce the process times Using a mixture of elemental and master alloy powders Eliminating the use of surface-active agents which would produce fine pyrophoric powder as well as contaminate the powder Relying on a constant interplay between welding and fracturing to yield a powder with a refined internal structure, typical of fine powders produced, but having an overall particle size, coarse, therefore stable.
During high-energy milling the powder particles are flattened, cold welded and rewelded. Whenever two steel balls collide, some amount of powder is trapped in between them. Around 1000 particles with an aggregate weight of about 0.2 mg are trapped during each collision. The force of the impact plastically deforms the powder particles leading to work hardening and fracture; the new surfaces created enable the particles to weld together and this leads to an increase in particle size. Since in the early stages of milling, the particles are soft, their tendency to weld together and form large particles is high. A broad range of particle sizes develops, with some as large as three times bigger than the starting particles; the composite particles at this stage have a characteristic layered structure consisting of various combinations of the starting constituents. With continued deformation, the particles get work hardened and fracture by a fatigue failure mechanism and/or by the fragmentation of fragile flakes.
1. Bhadeshia, H. K. D. H. Recrystallisation of practical mechanically alloyed iron-based and nickel-base supperalloys, Mater. Sci. Eng. A223, 64-77 2. P. R. Soni, Mechanical Alloying: Fundamentals and Applications, Cambridge Int Science Publishing, 2000 - Science - 151 pages. Mechanical alloying, comprehensive information from University of Cambridge
A ball mill is a type of grinder used to grind and blend materials for use in mineral dressing processes, pyrotechnics and selective laser sintering. It works on the principle of impact and attrition: size reduction is done by impact as the balls drop from near the top of the shell. A ball mill consists of a hollow cylindrical shell rotating about its axis; the axis of the shell may be either horizontal or at a small angle to the horizontal. It is filled with balls; the grinding media is the balls, which may be made of stainless steel, ceramic, or rubber. The inner surface of the cylindrical shell is lined with an abrasion-resistant material such as manganese steel or rubber. Less wear takes place in rubber lined mills; the length of the mill is equal to its diameter. The general idea behind the ball mill is an ancient one, but it was not until the industrial revolution and the invention of steam power that an effective ball milling machine could be built, it is reported to have been used for grinding flint for pottery in 1870.
In case of continuously operated ball mill, the material to be ground is fed from the left through a 60° cone and the product is discharged through a 30° cone to the right. As the shell rotates, the balls are lifted up on the rising side of the shell and they cascade down, from near the top of the shell. In doing so, the solid particles in between the balls and ground are reduced in size by impact; the ball mill is used for grinding materials such as coal and feldspar for pottery. Grinding can be carried out either wet or dry but the former is performed at low speed. Blending of explosives is an example of an application for rubber balls. For systems with multiple components, ball milling has been shown to be effective in increasing solid-state chemical reactivity. Additionally, ball milling has been shown effective for production of amorphous materials. A ball mill, a type of grinder, is a cylindrical device used in grinding materials like ores, ceramic raw materials and paints. Ball mills rotate around a horizontal axis filled with the material to be ground plus the grinding medium.
Different materials are used as media, including ceramic balls, flint pebbles and stainless steel balls. An internal cascading effect reduces the material to a fine powder. Industrial ball mills can operate continuously, discharged at the other end. Large to medium-sized ball mills are mechanically rotated on their axis, but small ones consist of a cylindrical capped container that sits on two drive shafts. A rock tumbler functions on the same principle. Ball mills are used in pyrotechnics and the manufacture of black powder, but cannot be used in the preparation of some pyrotechnic mixtures such as flash powder because of their sensitivity to impact. High-quality ball mills are expensive and can grind mixture particles to as small as 5 nm, enormously increasing surface area and reaction rates; the grinding works on the principle of critical speed. Critical speed can be understood as that speed after which the steel balls start rotating along the direction of the cylindrical device. Ball mills are used extensively in the mechanical alloying process in which they are not only used for grinding but for cold welding as well, with the purpose of producing alloys from powders.
The ball mill is a key piece of equipment for grinding crushed materials, it is used in production lines for powders such as cement, refractory material, glass ceramics, etc. as well as for ore dressing of both ferrous and non-ferrous metals. The ball mill can grind other materials either wet or dry. There are two kinds of ball mill, grate type and overfall type due to different ways of discharging material. Many types of grinding media are suitable for use in a ball mill, each material having its own specific properties and advantages. Key properties of grinding media are size, density and composition. Size: The smaller the media particles, the smaller the particle size of the final product. At the same time, the grinding media particles should be larger than the largest pieces of material to be ground. Density: The media should be denser than the material being ground, it becomes a problem. Hardness: The grinding media needs to be durable enough to grind the material, but where possible should not be so tough that it wears down the tumbler at a fast pace.
Composition: Various grinding applications have special requirements. Some of these requirements are based on the fact that some of the grinding media will be in the finished product. Others are based in. Where the color of the finished product is important, the color and material of the grinding media must be considered. Where low contamination is important, the grinding media may be selected for ease of separation from the finished product. An alternative to separation is to use media of the same material as the product being ground. Flammable products have a tendency to become explosive in powder form. Steel media may spark. Either wet-grinding, or non-sparking media such as ceramic or lead must be selected; some media, such as iron, may react with corrosive materials. For this reason, stainless steel and flint grinding media may each be u
An alloy is a combination of metals and of a metal or another element. Alloys are defined by a metallic bonding character. An alloy may be a mixture of metallic phases. Intermetallic compounds are alloys with a defined crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a wide variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties. In other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, brass, duralumin and amalgams; the alloy constituents are measured by mass percentage for practical applications, in atomic fraction for basic science studies. Alloys are classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy, they can be heterogeneous or intermetallic. An alloy is a mixture of chemical elements, which forms an impure substance that retains the characteristics of a metal.
An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are considered useful. Alloys are made by mixing two or more elements, at least one of, a metal; this is called the primary metal or the base metal, the name of this metal may be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble and dissolve into the mixture; the mechanical properties of alloys will be quite different from those of its individual constituents. A metal, very soft, such as aluminium, can be altered by alloying it with another soft metal, such as copper. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its very-high strength, but still substantial toughness, its ability to be altered by heat treatment, steel is one of the most useful and common alloys in modern use.
By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel. Like oil and water, a molten metal may not always mix with another element. For example, pure iron is completely insoluble with copper; when the constituents are soluble, each will have a saturation point, beyond which no more of the constituent can be added. Iron, for example, can hold a maximum of 6.67% carbon. Although the elements of an alloy must be soluble in the liquid state, they may not always be soluble in the solid state. If the metals remain soluble when solid, the alloy forms a solid solution, becoming a homogeneous structure consisting of identical crystals, called a phase. If as the mixture cools the constituents become insoluble, they may separate to form two or more different types of crystals, creating a heterogeneous microstructure of different phases, some with more of one constituent than the other phase has.
However, in other alloys, the insoluble elements may not separate until after crystallization occurs. If cooled quickly, they first crystallize as a homogeneous phase, but they are supersaturated with the secondary constituents; as time passes, the atoms of these supersaturated alloys can separate from the crystal lattice, becoming more stable, form a second phase that serve to reinforce the crystals internally. Some alloys, such as electrum, an alloy consisting of silver and gold, occur naturally. Meteorites are sometimes made of occurring alloys of iron and nickel, but are not native to the Earth. One of the first alloys made by humans was bronze, a mixture of the metals tin and copper. Bronze was an useful alloy to the ancients, because it is much stronger and harder than either of its components. Steel was another common alloy. However, in ancient times, it could only be created as an accidental byproduct from the heating of iron ore in fires during the manufacture of iron. Other ancient alloys include pewter and pig iron.
In the modern age, steel can be created in many forms. Carbon steel can be made by varying only the carbon content, producing soft alloys like mild steel or hard alloys like spring steel. Alloy steels can be made by adding other elements, such as chromium, vanadium or nickel, resulting in alloys such as high-speed steel or tool steel. Small amounts of manganese are alloyed with most modern steels because of its ability to remove unwanted impurities, like phosphorus and oxygen, which can have detrimental effects on the alloy. However, most alloys were not created until the 1900s, such as various aluminium, titanium and magnesium alloys; some modern superalloys, such as incoloy and hastelloy, may consist of a multitude of different elements. As a noun, the term alloy is used to describe a mixture of atoms in which the primary constituent is a metal; when used as a verb, the term refers to the act of mixing a metal with other elements. The primary metal is called the matrix, or the solvent; the secondary constituents are called s