Thermal Expansion of Alkali Sulphate Mixtures

Abstract

The linear thermal expansivities of polycrystalline samples of mixtures of Li2SO4 with K2SO4 and with Na2SO4 have been measured with a “Fused-Quarz Tube” apparatus 1. Phase transitions are accompanied by changes in the expansion coefficient and also by volume changes. The observed expansion coefficient is constant over wide temperature intervals. Simple crystal structures show higher expansivities than more complex structures. The “pre-melting” phenomenon in Li2SO4 does not measurably influence the thermal expansion. A method has been devised to correct the observations for the plastic flow of the crystals close to the melting points