alloy & solid solution

7/28/2019 Alloy & Solid Solution

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Alloy & Solid Solution


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solid-statesolution of one or more solutes in a solvent.

Such a mixture is considered a solution rather than a compound when the crystalstructure of the solvent remains unchanged by addition of the solutes, and whenthe mixture remains in a single homogeneousphase.

The solute may incorporate into the solvent crystal latticesubstitutionally, byreplacing a solvent particle in the lattice, orinterstitially, by fitting into the spacebetween solvent particles.

Both of these types of solid solution affect the properties of the material bydistorting the crystal lattice and disrupting the physical and electrical homogeneityof 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 forany twosubstances to form a solid solution is a complicated matter involving the chemical,crystallographic, and quantum properties of the substances in question.

Solid solutions, in accordance with the Hume-Rothery rules, may form if the soluteand solvent have:

Similaratomic radii (15% or less difference)

Same crystal structure

Similarelectronegativities

Similarvalency
http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Phase_%28matter%29http://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solublehttp://en.wikipedia.org/wiki/Solventhttp://en.wikipedia.org/wiki/Crystal_structurehttp://en.wikipedia.org/wiki/Crystal_structurehttp://en.wikipedia.org/wiki/Mixturehttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Crystal_structurehttp://en.wikipedia.org/wiki/Crystal_structurehttp://en.wiktionary.org/wiki/Homogeneoushttp://en.wikipedia.org/wiki/Phase_%28matter%29http://en.wikipedia.org/wiki/Crystal_latticehttp://en.wikipedia.org/wiki/Substitutionhttp://en.wikipedia.org/wiki/Interstitialhttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Crystallographyhttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Hume-Rothery_ruleshttp://en.wikipedia.org/wiki/Atomic_radiushttp://en.wikipedia.org/wiki/Crystallitehttp://en.wikipedia.org/wiki/Electronegativityhttp://en.wikipedia.org/wiki/Valence_%28chemistry%29http://en.wikipedia.org/wiki/Image:Eutektikum.gifhttp://en.wikipedia.org/wiki/Valence_%28chemistry%29http://en.wikipedia.org/wiki/Electronegativityhttp://en.wikipedia.org/wiki/Crystallitehttp://en.wikipedia.org/wiki/Atomic_radiushttp://en.wikipedia.org/wiki/Hume-Rothery_ruleshttp://en.wikipedia.org/wiki/Hume-Rothery_ruleshttp://en.wikipedia.org/wiki/Hume-Rothery_ruleshttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Crystallographyhttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Interstitialhttp://en.wikipedia.org/wiki/Substitutionhttp://en.wikipedia.org/wiki/Crystal_latticehttp://en.wikipedia.org/wiki/Phase_%28matter%29http://en.wiktionary.org/wiki/Homogeneoushttp://en.wikipedia.org/wiki/Crystal_structurehttp://en.wikipedia.org/wiki/Crystal_structurehttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Mixturehttp://en.wikipedia.org/wiki/Solventhttp://en.wikipedia.org/wiki/Solublehttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Phase_%28matter%29http://en.wikipedia.org/wiki/Solid


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Hume-Rothery (1899-1968) was a metallurgist who studied thealloying of metals. His research was conducted at Oxford Universitywhere in 1958, he was appointed to the first chair in metallurgy.

His research led to some simple and useful rules on the extent towhich an element might dissolve in a metal . The rules that hederived are paraphrased here. The rules are still used widely. Forexample, the miscibility gap in Au-Ni is correlated with the fact thatthe lattice parameter of Au is 1.15 times that of Ni, thus actingmaximally according to Hume-Rothery .

If a solute differs in its atomic size by more than about 15% from thehost, then it is likely to have a low solubility in that metal. The size

factoris said to be unfavourable. If a solute has a large difference in electronegativity (or

electropositivity) when compared with the host, then it is more likelyto form a compound. Its solibility in the host would therefore belimited.

A metal with a lower valency is more likely to dissolve in one which

has a higher valency, than vice versa.


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The phase diagram in Fig. 1 displaysan alloy of two metals which forms asolid solution at all relativeconcentrations of the two species. Inthis case, the pure phase of eachelement is of the same crystalstructure, and the similar properties ofthe two elements allow for unbiasedsubstitution through the full range ofrelative concentrations.

Solid solutions have importantcommercial and industrialapplications, as such mixtures oftenhave superior properties to purematerials. Many metal alloys are solidsolutions. Even small amounts ofsolute can affect the electrical andphysical properties of the solvent.
http://en.wikipedia.org/wiki/Phase_diagramhttp://en.wikipedia.org/wiki/Alloyhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Concentrationhttp://upload.wikimedia.org/wikipedia/commons/c/cb/Solid_solution.jpghttp://upload.wikimedia.org/wikipedia/commons/c/cb/Solid_solution.jpghttp://en.wikipedia.org/wiki/Image:Eutektikum.gifhttp://upload.wikimedia.org/wikipedia/commons/c/cb/Solid_solution.jpghttp://upload.wikimedia.org/wikipedia/commons/c/cb/Solid_solution.jpghttp://en.wikipedia.org/wiki/Image:Eutektikum.gifhttp://en.wikipedia.org/wiki/Image:Eutektikum.gifhttp://en.wikipedia.org/wiki/Concentrationhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Alloyhttp://en.wikipedia.org/wiki/Phase_diagram


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The binary phase diagram in Fig. 2at right shows

the phases of amixture of two substances in varyingconcentrations, alpha and beta. Theregion labeled "alpha" is a solid

solution, with beta acting as thesolute in a matrix of alpha. On theother end of the concentration scale,the region labeled "beta" is also asolid solution, with alpha acting asthe solute in a matrix of beta. Thelarge solid region in between thealpha and beta solid solutions,labeled "solid alpha and beta", is nota solid solution. Instead, anexamination of the microstructure ofa mixture in this range would revealtwo phases solid solution alpha-in-beta and solid solution beta-in-alpha
http://en.wikipedia.org/wiki/Phase_diagramhttp://en.wikipedia.org/wiki/Microstructurehttp://en.wikipedia.org/wiki/Microstructurehttp://en.wikipedia.org/wiki/Phase_diagram


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Hume-Rothery rules

The Hume-Rothery rules are a set of basic rules describing the conditionsunder which an element could dissolve in a metal, forming a solid solution.There are two sets of rules, one which refers to substitutional solid

solutions, and another which refers to interstitial solid solutions.

Substitutional Solid Solution Rule for substitutional solid solutions,

the Hume-Rothery rules are: 1. The atomic radii of the solute and solvent atoms must differ by no more than

15%:

2. The crystal structures of solute and solvent must match. 3. Maximum solubility occurs when the solvent and solute have the same

valency. Metals with lower valency will tend to dissolve metals with highervalency.

4. The solute and solvent should have similar electronegativity. If theelectronegativity difference is too great, the metals will tend to formintermetallic compounds instead of solid solutions.

Interstitial Solid Solution Rules

For interstitial solid solutions, the Hume-Rothery rules are: 1. Solute atoms must be smaller than the pores in the solvent lattice.

2. The solute and solvent should have similar electronegativity.
http://en.wikipedia.org/wiki/Solid_solutionhttp://en.wikipedia.org/wiki/Atomic_radiihttp://en.wikipedia.org/wiki/Atomic_radiihttp://en.wikipedia.org/wiki/Solid_solution


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