In order to establish a set of corresponding temperatures for the much-studied molten alkali metal nitrates, estimates of the "ideal" glass transition temperatures for NaNO3 and KNO3 are made from available thermodynamic data and shown consistent with "experimental" glass transition temperatures obtained by extrapolation from binary solution (hydrate melt) data. Tg values are obtained in the same manner for the other alkali metal nitrates, Li, Rb, and CsNO3, the spread of values among the five salts found being only 18°, thereby largely justifying isothermal comparisons of their properties despite the 160° spread in melting points. The order-disorder transition in sodium nitrate is examined and the relation of this class of transition to the glass transition phenomenon is considered. Equations from a zeroth-order, order-disorder theory for the glass transition are used to give a qualitative account of the change in heat capacity at the glass transition for sodium nitrate.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry