Melting mechanisms and melt properties of alkali acetates

Abstract

Alkali salts of various univalent organic acids with melting points below 400°C have been investigated. Only a limited number of anion types yield melts which are stable. These constitute a new class of liquids, whose properties can be conveniently studied experimentally. In addition to their theoretical interest, some of these melts may have practical uses in chemical technology. The present paper deals mainly with carboxylates, and in particular with potassium and sodium acetates.

Chemical stability of the melts is found to be affected by a number of impurities; to ensure adequate stability it is important to exclude oxygen. Molar volumes of these melts have been measured to 0.1 %. Viscosities and electrical conductivities have also been measured over a range of temperatures. Binary mixtures of the acetates show a positive deviation from the ideal mixture law, similar to binary mixtures of alkali halides. Dilatometric observation of the volume of crystalline potassium acetate points to several thermal transitions in the solid below the melting point. On melting, sodium acetate expands with ΔV_f/V_s= 3.9 %, comparable to the value for sodium nitrate. Potassium acetate shows the rare behaviour of shrinkage on melting, with ΔV_f/V_s approximately –1.0 %.