Melting and crystal structure: volume changes on mixing nitrate melts

Measurements have been made of the densities of liquid potassium nitrate containing up to 50 equivalents per cent of barium nitrate. Within the temperature range from the liquidus to 440 °C, isotherms of equivalent volume as a function of equivalent composition were found to be straight lines. The excess volume of mixing for any pair of melts in this composition range is thus zero. Partial equivalent volumes of both components are independent of composition at a given temperature, and are given by V̄ m (KNO 3 ) = 53.17 + 0.0229( t - 300), V̄ m (Ba(NO 3 ) 2 ) = 41.75 + 0.0107( t - 300), where t is the temperature in degrees centigrade. This somewhat unusual mixing behaviour is discussed in relation to possible structures for nitrate melts, and in relation to available information about excess volumes of mixing for other ionic melts and liquids generally.