Question:

# If An alloy is an example of what kind of solution?

## An Alloy is a solid solution with mixed metals in a single homogeneous phase.

Laves phases are intermetallic phases that have composition AB2 and are named for Fritz Laves who first described them. The phases are classified on the basis of geometry alone. There are three different classification classes: cubic MgCu2 (C15), hexagonal MgZn2 (C14), and hexagonal MgNi2 (C36). The latter two classes are unique forms of the hexagonal arrangement, but share the same basic structure. In general, the A atoms are ordered as in diamond, hexagonal diamond, or a related structure, and the B atoms form tetrahedra around the A atoms for the AB2 structure. Laves phases are of particular interest in modern metallurgy research because of their abnormal physical and chemical properties. Many hypothetical or primitive applications have been developed. However, little practical knowledge has been elucidated from Laves phase study so far. A characteristic feature is the almost perfect electrical conductivity, but they are not plastically deformable at room temperature. In each of the three classes of Laves phase, if the two types of atom were perfect spheres with a size ratio of $\sqrt{3/2} \approx 1.225$, the structure would be topologically tetrahedrally close-packed. At this size ratio, the structure has an overall packing volume density of 0.710 Compounds found in Laves phases typically have an atomic size ratio between 1.05 and 1.67. Analogues of Laves phases can be formed by the self assembly of a colloidal dispersion of two sizes of sphere.
Solid in which components are compatible and form a unique phase. Note 1: The definition “crystal containing a second constituent which fits into and
is distributed in the lattice of the host crystal” given in refs., is not general
and, thus, is not recommended. Note 2: The expression is to be used to describe a solid phase containing
more than one substance when, for convenience, one (or more) of the substances,
called the solvent, is treated differently from the other substances, called solutes. Note 3: One or several of the components can be macromolecules. Some of
the other components can then act as plasticizers, i.e., as molecularly dispersed
substances that decrease the glass-transition temperature at which the amorphous
phase of a polymer is converted between glassy and rubbery states. Note 4: In pharmaceutical preparations, the concept of solid solution is often
applied to the case of mixtures of drug and polymer. Note 5: The number of drug molecules that do behave as solvent (plasticizer)
of polymers is small. A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase. This often happens when the two elements (generally metals) involved are close together on the periodic table; conversely, a chemical compound is generally a result of the non-proximity of the two metals involved on the periodic table. The solid solution need to be distinguished from a mechanical mixture of powdered solids like two salts, sugar and salt, etc. The mechanical mixtures have total or partial miscibility gap in solid state. Examples of solid solutions include cristalyzed salts from their liquid mixture, metal alloys, moist solids. In the case of metal alloys intermetallic compounds occur frequently. The solute may incorporate into the solvent crystal lattice substitutionally, by replacing a solvent particle in the lattice, or interstitially, by fitting into the space between solvent particles. Both of these types of solid solution affect the properties of the material by distorting the crystal lattice and disrupting the physical and electrical homogeneity of the solvent material. Some mixtures will readily form solid solutions over a range of concentrations, while other mixtures will not form solid solutions at all. The propensity for any two substances to form a solid solution is a complicated matter involving the chemical, crystallographic, and quantum properties of the substances in question. Substitutional solid solutions, in accordance with the Hume-Rothery rules, may form if the solute and solvent have: The phase diagram in Fig. 1 displays an alloy of two metals which forms a solid solution at all relative concentrations of the two species. In this case, the pure phase of each element is of the same crystal structure, and the similar properties of the two elements allow for unbiased substitution through the full range of relative concentrations. Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials. Many metal alloys are solid solutions. Even small amounts of solute can affect the electrical and physical properties of the solvent. The binary phase diagram in Fig. 2 shows the phases of a mixture of two substances in varying concentrations, $A$ and $B$. The region labeled "$\alpha$" is a solid solution, with $B$ acting as the solute in a matrix of $A$. On the other end of the concentration scale, the region labeled "$\beta$" is also a solid solution, with $A$ acting as the solute in a matrix of $B$. The large solid region in between the $\alpha$ and $\beta$ solid solutions, labeled "$\alpha$ + $\beta$", is not a solid solution. Instead, an examination of the microstructure of a mixture in this range would reveal two phases — solid solution $A$-in-$B$ and solid solution $B$-in-$A$ would form separate phases, perhaps lamella or grains. In the phase diagram, at three different concentrations, the material will be solid until it's heated to its melting point, and then (after adding the heat of fusion) become liquid at that same temperature: At other proportions, the material will enter a mushy or pasty phase until it warms up to being completely melted. The mixture at the dip point of the diagram is called a eutectic alloy. Lead-tin mixtures formulated at that point (37/63 mixture) are useful when soldering electronic components, particularly if done manually, since the solid phase is quickly entered as the solder cools. In contrast, when lead-tin mixtures were used to solder seams in automobile bodies a pasty state enabled a shape to be formed with a wooden paddle or tool, so a 70-30 lead to tin ratio was used. (Lead is being removed from such applications owing to its toxicity and consequent difficulty in recycling devices and components that include lead.) When a solid solution becomes unstable — due to a lower temperature, for example — exsolution occurs and the two phases separate into distinct microscopic to megascopic lamellae. This is mainly caused by difference in cation size. Cations which have a large difference in radii are not likely to readily substitute. Take the alkali feldspar minerals for example, whose end members are albite, NaAlSi3O8 and microcline, KAlSi3O8. At high temperatures Na+ and K+ readily substitute for each other and so the minerals will form a solid solution, yet at low temperatures albite can only substitute a small amount of K+ and the same applies for Na+ in the microcline. This leads to exsolution where they will separate into two separate phases. In the case of the alkali feldspar minerals, thin white albite layers will alternate between typically pink microcline.
The liquidus temperature, TL or Tliq, is mostly used for glasses, alloys and rocks. It specifies the maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium. Above the liquidus temperature the material is homogeneous and liquid at equilibrium. Below the liquidus temperature more and more crystals may form in the melt if one waits a sufficiently long time, depending on the material. However, even below the liquidus temperature homogeneous glasses can be obtained through sufficiently fast cooling, i.e., through kinetic inhibition of the crystallization process. The crystal phase that crystallizes first on cooling a substance to its liquidus temperature is termed primary crystalline phase or primary phase. The composition range within which the primary phase remains constant is known as primary crystalline phase field. The liquidus temperature is important in the glass industry because crystallization can cause severe problems during the glass melting and forming processes, and it also may lead to product failure. The liquidus temperature can be contrasted to the solidus temperature. The solidus temperature quantifies the point at which a material completely solidifies (crystallizes). The liquidus and solidus temperatures do not necessarily align or overlap; if a gap exists between the liquidus and solidus temperatures, then within that gap, the material consists of solid and liquid phases simultaneously (like a slurry). For pure substances, e.g. pure metal, pure water, etc. the liquidus and solidus are at the same temperature, and the term "melting point" may be used. For impure substances, e.g. alloys, tap water, coca cola, ice cream, etc. the melting point broadens into a melting interval instead. If the temperature is within the melting interval, one may see "slurries" at equilibrium, i.e. the slurry will neither fully solidify nor melt. This is why new snow of high purity either melts or stays solid, while dirty snow on the ground tend to become slushy at certain temperatures. Weld melt pools containing high levels of sulfur, either from melted impurities from the base metal or from the welding electrode, typically have very broad melting intervals, which leads to increased risk of hot cracking.
Homogeneous as a term in physical chemistry and material science refers to substances and mixtures which are in a single phase. This is in contrast to a substance that is heterogeneous. The definition of homogeneous strongly depends on the context used. Generally it refers to smooth variation of properties with no discontinuities or jumps. In Chemistry, a homogeneous suspension of material means that when dividing the volume in half, the same amount of material is suspended in both halves of the substance. However, it might be possible to see the particles under a microscope. An example of a homogeneous mixture is air. Air can be more specifically described as a gaseous solution (oxygen and other gases dissolved in the major component, nitrogen). Since interactions between molecules play almost no role, dilute gases form rather trivial solutions. In part of the literature, they are not even classified as solutions. In Chemistry, some mixtures are homogeneous. In other words, mixtures have the same proportions throughout a given sample or multiple samples of different proportion to create a consistent mixture. However, two homogeneous mixtures of the same pair of substances may differ widely from each other and can be homogenized to make a constant. Homogeneous mixtures have always the same composition. Mixtures can be characterized by being separable by mechanical means e.g. A solution is a special type of homogeneous mixture. Solutions are homogeneous because, the ratio of solute to solvent remains the same throughout the solution even if homogenized with multiple sources, and stable because, the solute will not settle out, no matter how long the solution sits, and it cannot be removed by a filter or a centrifuge. This type of mixture is very stable, i.e., its particles do not settle, or separate. As a homogeneous mixture, a solution has one phase (liquid) although the solute and solvent can vary: for example, salt water. In chemistry, a mixture is a substance containing two or more elements or compounds that are not covalently bound to each other and which retain their own chemical and physical identities; – a substance which has two or more constituent physical substances. Mixtures, in the broader sense, are two or more substances physically in the same place, but these are not chemically combined, and therefore ratios are not necessarily considered.
Intermetallic or intermetallic compound is a term that is used in a number of different ways. Most commonly it refers to solid-state phases involving metals. There is a "research definition" adhered to generally in scientific publications, and a wider "common use" term. There is also a completely different use in coordination chemistry, where it has been used to refer to complexes containing two or more different metals. Although the term intermetallic compounds, as it applies to solid phases, has been in use for many years, its introduction was regretted, for example by Hume-Rothery in 1955. Note that many intermetallic compounds are often simply called 'alloys', although this is somewhat of a misnomer. Both are metallic phases containing more than one element, but in alloys the various elements substitute randomly for one another in the crystal structure, forming a solid solution with a range of possible compositions; in intermetallic compounds, different elements are ordered into different sites in the structure, with distinct local environments and often a well-defined, fixed stoichiometry. Complex structures with very large unit cells can be formed. Schulze in 1967, defined intermetallic compounds as solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents. Under this definition the following are included The definition of a metal is taken to include: Alloys, which are homogeneous solid solutions of metals, and interstitial compounds such as the carbides and nitrides are excluded under this definition. However, interstitial intermetallic compounds are included as are alloys of intermetallic compounds with a metal. In common use, the research definition, including poor metals and metalloids, is extended to include compounds such as cementite, Fe3C. These compounds, sometimes termed interstitial compounds can be stoichiometric, and share similar properties to the intermetallic compounds defined above. The term intermetallic is used to describe compounds involving two or more metals such as the cyclopentadienyl complex Cp6Ni2Zn4. Intermetallic compounds are generally brittle and have a high melting point. They often offer a compromise between ceramic and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice some toughness and ease of processing. They can also display desirable magnetic, superconducting and chemical properties, due to their strong internal order and mixed (metallic and covalent/ionic) bonding, respectively. Intermetallics have given rise to various novel materials developments. Some examples include alnico and the hydrogen storage materials in nickel metal hydride batteries. Ni3Al, which is the hardening phase in the familiar nickel-base superalloys, and the various titanium aluminides have also attracted interest for turbine blade applications, while the latter is also used in very small quantities for grain refinement of titanium alloys. Silicides, intermetallics involving silicon, are utilized as barrier and contact layers in microelectronics. The formation of intermetallics can cause problems. Intermetallics of gold and aluminium can be a significant cause of wire bond failures in semiconductor devices and other microelectronics devices. There are five intermetallic compounds in the binary phase diagram of Al–Au. AuAl2 is known as "purple plague". Au5Al2 is known as "white plague". Examples of intermetallics through history include: German type metal is described as breaking like glass, not bending, softer than copper but more fusible than lead. The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one.
Solid solution strengthening is a type of alloying that can be used to improve the strength of a pure metal. The technique works by adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal). The alloying element diffuses into the matrix, forming a solid solution. In most binary systems, when alloyed above a certain concentration, a second phase will form. When this increases the strength of the material, the process is known as precipitation strengthening, but this is not always the case. Depending on the size of the alloying element, a substitutional solid solution or an interstitial solid solution can form. In both cases, the overall crystal structure is essentially unchanged. Substitutional solid solution strengthening occurs when the solute atom is large enough that it can replace solvent atoms in their lattice positions. According to the Hume-Rothery rules, solvent and solute atoms must differ in atomic size by less than 15% in order to form this type of solution. Because both elements exist in the same crystalline lattice, both elements in their pure form must be of the same crystal structure. Examples of substitutional solid solutions include the Cu-Ni and the Ag-Au FCC binary systems, and the Mo-W BCC binary system. When the solute atom is equal to or slightly smaller and can fill the interstices of the solvent atoms, an interstitial solid solution forms. The atoms crowd into the interstitial sites, causing the bonds of the solvent atoms to compress and thus deform.Elements commonly used to form interstitial solid solutions include H, Li, Na, N, C, and O. Carbon in iron (steel) is one example of interstitial solid solution. The strength of a material is dependent on how easily dislocations in its crystal lattice can be propagated. These dislocations create stress fields within the material depending on their character. When solute atoms are introduced, local stress fields are formed that interact with those of the dislocations, impeding their motion and causing an increase in the yield stress of the material, which means an increase in strength of the material. This gain is a result of both lattice distortion and the modulus effect. When solute and solvent atoms differ in size, local stress fields are created. Depending on their relative locations, solute atoms will either attract or repel dislocations in their vicinity. This is known as the size effect. This allows the solute atoms to relieve either tensile or compressive strain in the lattice, which in turn puts the dislocation in a lower energy state. In substitutional solid solutions, these stress fields are spherically symmetric, meaning they have no shear stress component. As such, substitutional solute atoms do not interact with the shear stress fields characteristic of screw dislocations. Conversely, in interstitial solid solutions, solute atoms cause a tetragonal distortion, generating a shear field that can interact with both edge, screw, and mixed dislocations. The attraction or repulsion of the dislocation centers to the solute particles increase the stress it takes to propagate the dislocation in any other direction. Increasing the applied stress to move the dislocation increases the yield strength of the material. The energy density of a dislocation is dependent on its Burgers vector as well as the modulus of the local atoms. When the modulus of solute atoms differs from that of the host element, the local energy around the dislocation is changed, increasing the amount of force necessary to move past this energy well. This is known as the modulus effect. Meanwhile, in the specific case of a lattice distortion, the difference in lattice parameter leads to a high stress field around that solute atom that impedes dislocation movement. Surface carburizing, or case hardening, is one example of solid solution strengthening in which the density of solute carbon atoms is increased close to the surface of the steel, resulting in a gradient of carbon atoms throughout the material. This provides superior mechanical properties to the surface of the steel. Solid solution strengthening increases yield strength of the material by increasing the stress $\tau$ to move dislocations: $\Delta \tau =Gb \epsilon^\tfrac 3 2 \sqrt c$ where c is the concentration of the solute atoms, G is the shear modulus, b is the magnitude of the Burger's vector, and $\epsilon$ is the lattice strain due to the solute. This is composed of two terms, one describing lattice distortion and the other local modulus change. $\epsilon = | \epsilon_a - \beta \epsilon_G |$ Here, $\epsilon_a$ is the lattice distortion term, $\beta$ a constant dependent on the solute atoms and $\epsilon_G$ the term that captures the local modulus change. The lattice distortion term can be described as: $\epsilon_a = \dfrac {\Delta a}{a\Delta c}$, where a is the lattice parameter of the material. Meanwhile, the local modulus change is captured in the following expression: $\epsilon_G = \dfrac {\Delta G}{G\Delta c}$, where G is shear modulus of the solute material, In order to achieve noticeable material strengthening via solute solution strengthening one should alloy with solutes of higher shear modulus, hence increasing the local shear modulus in the material. In addition, one should alloy with elements of different equilibrium lattice constants. The greater the difference in lattice parameter, the higher the local stress fields introduced by alloying. Alloying with elements of higher shear modulus or of very different lattice parameters will increase the stiffness and introduce local stress fields respectively. In either case, the dislocation propagation will be hindered at these sites, impeding plasticity and increasing yield strength proportionally with solute concentration. Solid solution strengthening depends on:
- Concentration of solute atoms
- Shear modulus of solute atoms
- Size of solute atoms
- Valency of solute atoms (for ionic materials) Nevertheless, one should not add so much solute as to precipitate a new phase. This occurs if the concentration of the solute reaches a high critical point given by the binary system phase diagram. This critical concentration therefore puts a limit to the amount of solid solution strengthening a material can have, as the material cannot be infinitely strengthened.
Alloys

Solid in which components are compatible and form a unique phase.

Note 1: The definition “crystal containing a second constituent which fits into and
is distributed in the lattice of the host crystal” given in refs., is not general
and, thus, is not recommended.

Solution Phase

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering and quenching. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

In printing, type metal (sometimes called hot metal) refers to the metal alloys used in traditional typefounding and hot metal typesetting. Lead is the main constituent of these alloys. Antimony and tin are added to make the character produced durable and tough while reducing the difference between the coefficients of expansion of the matrix and the alloy.

Chemistry Metallurgy

Materials science, also commonly known as materials engineering, is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This relatively new scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates elements of applied physics and chemistry. With significant media attention focused on nanoscience and nanotechnology in recent years, materials science is becoming more widely known as a specific field of science and engineering. It is an important part of forensic engineering (Forensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property.) and failure analysis, the latter being the key to understanding, for example, the cause of various aviation accidents. Many of the most pressing scientific problems that are currently faced today are due to the limitations of the materials that are currently available and, as a result, breakthroughs in this field are likely to have a significant impact on the future of human technology.

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