Phase equilibria
in the ZnCl2+KI system have been investigated by differential
thermal analysis (DTA), and by examination by X-ray powder diffraction of
solidified melts. The system evidently behaves as a simple binary, and three
congruently melting compounds are formed, viz. 2KI.ZnCl2, 2KI.3ZnCl2
and KI.4ZnC12.
Supercooled mixtures from c. 60-90 mole % ZnCl2
visibly phase separate at temperatures for the most part about 30K below the liquidus temperatures, and the phase separation
temperatures have been determined by DTA. The composition limits of the
metastable immiscibility dome have not been established, but the region of
phase separation extends at least to mixtures containing as little as 53 mole %
ZnCl2. The critical composition is approximately 80 mole % ZnCl2,
and the critical temperature 470 K. Quenching of melts containing 34-100 mole %
ZnCl2, in liquid nitrogen, yields glasses. In the region 34-43 mole
% ZnCl2 the glasses are partly crystallized. Glass transition
temperatures for the wholly glassy mixtures have been evaluated from DTA
traces, with heating rates in the range 0.11-0.25 K s-1. Two glass
transitions have been observed for mixtures of composition 53-75 mole % ZnCl2.
Growth of congruently melting gadolinium scandium gallium garnet
