Abstract: The lattice parameters a and the molar volumes V_m of Pb-based a-phase solid solutions in the Pb-Sn-Cd ternary system were determined by means of X-ray diffraction. The lattice parameters a vary linearly with the molar fractions, the molar volumes show a positive deviation from the ideal solution behaviour, and the contribution of the solute Cd to the excess molar volumes V_m is much larger than that of the solute Sn. According to Vegard' s law orsub-regular solution model, the relationship between the experimental data of a or V_m andthe compositions of alloy is obtained by the mathematic regressive method, the prediction precisions of the both formulae are within the limits of experiment error.

Key words: Alloy solid solution, Lattice parameter, Molar volume, Excess molar volume