Question

Which of the following is an example for interstitial solid solution?
(a) SiC
(b) TiC
(c) $L{{i}_{2}}{{C}_{2}}$ (d)$A{{l}_{4}}{{C}_{3}}$

Answer 1

As we know that interstitial solid solution is a type of solid solution where the solute atom is small enough to fit at interstitial sites between the solvent atoms. For this to happen, the solute atoms must be very small that belong to the second period of the periodic table and there must be a huge difference in the atomic size of solute and solvent.

Complete step-by-step answer: Let us begin with the understanding of solid solutions:-
-A solid solution tells us about the family of materials and compounds which have a varying range of compositions and a single crystal structure. It is a phase where two or more elements (solid at room temperature) are completely soluble in each other.
Depending on the ratio of the solvent (also called as matrix) metal atom size and solute element atom size, there are two types of solid solutions: substitution and interstitial.
-Substitution solid solution: If the atoms of the solvent metal and solute element are of almost similar sizes i.e., they do not have a difference of more than 15% then they form substitution solid solution. In this solution, a part of the solvent atoms are substituted by atoms of the alloying element or solute.

-Interstitial solid solution: If the atoms of the alloying elements are considerably smaller as compared to the atoms of the matrix metal (solvent), formation of interstitial solid solution takes place, where the small solute atoms are located in the spaces between large solvent atoms (in the voids).
Now let us check the difference in the elements’ atomic size of the compounds given the option as follows:
(a) SiC: We know that silicon and carbon just belongs to the adjacent periods due to which they do not have much difference in their atomic sizes and hence it is not an interstitial solid solution
(b) TiC: As we know that titanium belongs to the fourth period whereas carbon belongs to the second period of periodic table due to which they have sufficient amount of atomic size difference that they qualify to be an interstitial solid solution.
(c) $L{{i}_{2}}{{C}_{2}}$: Here, lithium and carbon just belongs to the adjacent periods due to which they do not have much difference in their atomic sizes and hence it is not an interstitial solid solution (d)$A{{l}_{4}}{{C}_{3}}$: In here, aluminum and carbon just belongs to the adjacent periods due to which they do not have much difference in their atomic sizes and hence it is also not an interstitial solid solution

Therefore (b) TiC is an example of interstitial solid solution.

Note: -Always remember that whenever the solubility of a solute element in interstitial solution is exceeded, a complete phase of intermediate compound is formed. These compounds such as TiN, WC etc. play important role in strengthening of alloys such as steels.
-Formation of solid solution is usually done to increase of electrical resistance, mechanical strength and decrease of plasticity of the alloy.