Liquid potassium–antimony alloys: Investigation of some thermodynamic properties

High-temperature emf measurements of the activity of potassium in liquid K–Sb alloys were carried out at T=921 K for compositions covering the range XK=0 to 0.65. A solid electrolyte of potassium-substituted beta alumina was used in a coulometric titration technique to generate in situ potassium. The limiting slope of ln γK vs XK (γK being the activity coefficient of K) was negative, which indicates that the alkali atoms tend to form clusters, such as dimers and higher order species. An inflection point in ln γK was found at the equiatomic composition, leading to a maximum in the Darken excess stability functions. This feature, which was recently observed in equiatomic alloys formed between Na or K and Bi, Pb, or Te, can be interpreted in terms of the formation of stable species. An investigation of the enthalpies of KSb as a function of temperature showed a relatively small excess heat capacity in the temperature range T=878 to 1100 K.