Solid Solution

The solid concept of solution is a thermodynamic concept. it is a mixture of pure substances forming a homogeneous solid .

For a Liquid, the concept of solution is rather intuitive: when a body is in solution, one cannot distinguish it in the Solvant even with the optical Microscope. If not, one speaks about Précipité or emulsion.

For a solid, the case is a little different: in certain cases of solutions, one can distinguish from the different phases.

Solid solution and crystallography

Specific defects

In the general case, the solid solution in a crystalline solid is done by two mechanisms:

substitution: the foreign atoms take the place of the native atoms of the crystal;
insertion: the foreign atoms slip between the native atoms, in sites known as “interstitial”.

In both cases, they are specific defects. These mechanisms were particularly studied by William Hume-Rothery in first half of the 20th century on iron and copper, money alloys like on the intermetallic compounds.

Eutectics and eutectoids

The Eutectic case of the S and the Eutectoïde S is different. In these cases, it is formed two different phases, a phase of each pure substance has and B, but the two phases are closely dependant within a grain. For example, one will have a succession of plates (eutectic lamellate) pretense to form a Cristallite with the defined joints, or the fiber formation (sticks, needles, acicular eutectic) or aligned globules (eutectic globular) of a phase in crystallites of the other.

The material is then homogeneous with the macroscopic, but heterogeneous scale on a mesoscopic scale (scale of crystallite). However, it behaves thermodynamically like only one phase.

Metallurgy

In the Steel, the Carbone is in solid solution in the matrix of Fer. The Cémentite is an eutectic iron/carburizes iron Fe₃C.

Mineralogy

It is said that two or several mineral phases form a solid solution when one passes gradually from the one to the other by substitutions of their chemical elements.

Examples:

plagioclases constitute a solid solution continues whose composition varies since the sodic term Albite (Si₃AlO₈) Na, until the calcic term Anorthite (Si_{2Al _{2O₈) Ca}}
the alkaline feldspars constitute a solid solution between the potassic term Orthose, (Si₃AlO₈) K, and the sodic term Albite (Si₃AlO₈) Na, unstable at low temperature.
olivine constitutes a solid solution between the ferrous term Fayalite (Fe₂SiO₄) and the magnesian term Forstérite (Mg₂SiO₄).

The poles (pure substances) pass from a liquid behavior to solid without transition.

The intermediate materials are entirely liquid at very high temperatures. The reduction in the temperature is marked by the passage in a field of transition and the appearance of the first crystals. This field is characterized by the curves of the liquiduses and solidi of a Diagramme of phase.

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