Melting and crystal structure. The mechanism of melting of group I nitrates

Abstract

Melting parameters are reviewed for the nitrates of Li, Na, K, Rb, Cs and Ag, and are com­pared with values for the corresponding halides. Previously published information has been supplemented by experiments on the viscosity of molten AgNO 3 , and on the dilatometry and electrical conductivity of AgNO 3 in the solid and melt. It is suggested that the low melting points of group I nitrates, compared with the corre­sponding halides, is due to the formation of association complexes in the nitrate melts. This process could contribute a term to the overall entropy of fusion S f without greatly increasing the heat of fusion H f . Since T f = H f / S f , this would explain the unusually low melting points. The small volume changes of fusion of nitrates, where measured, and the abnormal activation energies for the viscosities of molten nitrates, support the suggested mechanism of melting.