Thermal Expansion of Alkali Sulphate Mixtures

The linear thermal expansivities of polycrystalline samples of mixtures of L i 2 S 0 4 with K 2 S 0 4 and with N a 2 S 0 4 have been measured with a "Fused-Quarz T u b e " apparatus Phase transitions are accompanied by changes in the expansion coeff icient and also by volume changes. The observed expansion coeff icient is constant over wide temperature intervals. Simple crystal structures show higher expansivities than more complex structures. The "pre-melt ing" phenomenon in L i 2 S 0 4 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.