Question

Using the Hume-Rothery rules for the formation of substitutional solid solutions, indicate whether the following systems would be expected to exhibit solid solubility. Specifically, for each pair, indicate whether they would display: (i) a high degree of solubility; (ii) low to medium solubility; or (iii) minimal solubility.

(a) Al in Ni (d) Si in Al (g) Mn in Fe

(b)Ti in Ni (e) Li in Al (h) Cr in Fe

(c) Zn in Fe (f) Cu in Au (i) Ni in Fe

Answer 1

For substitutional solid solutions, the Hume-Rothery rules are:

1. Atomic radius of the solute and solvent atoms must differ by no more than 15%:

2.Crystal structures of solute and solvent must be comparable.

3. Complete solubility occurs when the solvent and solute have the same valency. A metal dissolves a metal of higher valency to a greater extent than one of lower valency.

4. Solute and solvent should have comparable electronegativity (EN)

(a) Al in Ni === low to medium solubility (EN, Ni = 1.91 and Al = 1.61)

(b)Ti in Ni ===  low to medium solubility (EN, Ni = 1.91 and Ti = 1.54)

(c) Zn in Fe === low to medium solubility (EN, Zn = 1.65 and Ti = 1.83)

(d) Si in Al ===  low to medium solubility (EN, Si = 1.90 and Al = 1.61)

(e) Li in Al

(f) Cu in Au

(g) Mn in Fe

(h) Cr in Fe

(i) Ni in Fe