ИСТИНА

Tentative application of Redlikh-Kister-Muggianu model with ternary paarameters (RKMT) to the Au‐Pd‐Sn and Cu‐Pd‐Sn leads to formation of spurious miscibility gaps in calculated liquid. Wide miscibility gaps arose also when experimental thermodynamic data for the Ag‐Pd‐Sn melts were treated by us in the frame of that model. Moreover, the parameters of RKMT model obtained by authors of detailed thermodynamic investigation of the Au‐Cu‐Sn ternary [3] also give rise to immiscibility region in tin rich part, which was not noticed by authors. Such gaps clearly are artifacts of description. The Darken's stability function Ψ is calculated for the Redlich‐Kister‐Muggianu model with three ternary parameters. The signs of numerous (total of 78) parts appearing in calculated Ψ are analyzed. The negative values of Ψ (i.e. miscibility gaps) arise mainly from negative multipliers at squares of coefficients of Redlich‐Kister polynomials of bounding binaries. These results generalize the analysis of regular solutions performed long ago by Meiering. It is shown that in the case of Ag‐Pd‐Sn, in which the interactions in one of binaries (Pd‐Sn) are much stronger than in two others, spurious ternary miscibility gaps are unavoidable in the frame of RKMT model. Contrary to that, spurious miscibility gap in the Au‐Cu‐Sn ternary as modeled in [3] arise due to small incompatibility between their own data and accepted descriptions of bounding binaries.