Polymorphism and Melting of Sodium Cyanide and Thiocyanate to 40 kbar

The phase diagrams of NaCN and NaSCN were studied to 40 kbar by means of differential thermal analysis. The NaCN orthorhombic/cubic transition line can be expressed as t(°C) = 15.3 + 5.42 P − 0.0426 P2 (P in kilobars). The melting curve of cubic NaCN is very similar to the melting curve of NaCl, and can be fitted by the Simon parameters A = 18.55 kbar, c = 2.224. NaSCN is orthorhombic, space-group Pnma, with a0 = 13.45 Å, b0 = 4.10 Å, c0 = 5.66 Å. It has no polymorphism in the range studied. The melting curve can be fitted by Simon parameters A = 8.808 kbar, c = 6.938.