Melting and Polymorphism of Potassium Cyanide and Thiocyanate to 44 kbar

Abstract
The phase diagrams of KCN and KSCN were studied by means of differential thermal analysis. Bridgman's KCN II appears to be metastable. The transition line between cubic KCN I and orthorhombic KCN V runs from −60°C at 1 bar to the I/IV/V triple point at 20.0 kbar, 41°C. The KCN III/IV transition line lies at slightly higher temperatures than found by Bridgman. The melting curve of KCN is similar to that of KCl, with the III/I/liquid triple point at 22.2 kbar, 823°C. The phase behavior and the probable structures of the high-pressure phases of KCN and also of KNO2 can be simply explained as a combination of coordinational polymorphism and disordering. Three new solid phases of KSCN were found, and the melting curves and transition lines were followed to 44 kbar. There was no evidence of premelting in KSCN.

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