COMPOUND FORMATION IN SN-BASED LIQUID ALLOYS

The phenomenon of compound formation in Sn-based liquid alloys (MgSn a nd CuSn) has been discussed through the study of concentration-depende nt thermodynamic and microscopic functions such as activity, excess fr ee energy of mixing G(M)(XS), concentration fluctuations in the long-w avelength limit Scc(0) and chemical short-range order (CSRO) parameter s. The expressions for these functions have been obtained by using sta tistical mechanical theory based on compound formation. All the above- mentioned properties of mixing of MgSn and CuSn liquid alloys have bee n found to be asymmetric around equiatomic compositions. The larger ne gative values of G(M)(XS) and maximum deviation of Scc(0) from ideal v alues (Scc(0, id)) at C-Mg = 0.66 in MgSn and at C-Cu = 0.75 in CuSn s uggest that Mg2Sn and Cu3Sn compounds are formed in MgSn and CuSn syst ems, respectively. Our study of CSRO reveals that maximum order exists at compound-forming concentrations, i.e. C-Mg = 0.66 in MgSn and C-Cu = 0.75 in CuSn. It is also observed that the tendency for compound fo rmation in MgSn is greater than that of the CuSn system, although the interactions in both systems are not very strong.