Vapour pressures of some inorganic sulphates at high temperatures

Abstract

The vapour pressures of some inorganic sulphates at high temperatures were determined by the combined use of the Knudsen effusion, transpiration, and matrix isolation methods. After a detailed comparison with the results of other investigators, it is concluded that the principal vapour species in the case of K₂SO₄, Rb₂SO₄, and Cs₂SO₄ are the undecomposed sulphate molecules themselves, and in the case of Li₂SO₄ the decomposition products, Li, SO₂, and O₂. The sodium salt also decomposes to some extent into Na, SO₂, and O₂, but it is deduced that the vapour concentration of the species Na₂O₄ is probably greater than was formerly supposed. The decomposition of alkaline earth sulphates is also discussed, especially in the light of the dependence of the Knudsen effusion results upon the size of the orifice used. On the basis of the vapour constitutions deduced, thermodynamic functions for the important species present are tabulated up to 1400 K or above. Reference is also made to the function of sodium sulphate in the glass-making industry and to the possible mechanism of its corrosive action on furnace walls.