Critical Evaluation and Calorimetric Study of the Thermodynamic Properties of Na2CrO4, K2CrO4, Na2MoO4, K2MoO4, Na2WO4, and K2WO4

Abstract

This paper evaluates crystallographic data and thermodynamic properties for sodium chromate, potassium chromate, sodium molybdate, potassium molybdate (K2MoO4), sodium tungstate, and potassium tungstate collected from the literature. A thorough literature review was carried out to obtain a good understanding of the available data, and a critical evaluation has been performed from room temperature to above the melting temperatures. Also, the solid–solid transition and melting properties of the six pure salts were measured by differential scanning calorimetry, and high-temperature x-ray powder diffraction measurements were performed to determine the crystal structures and space groups associated with the phases of K2MoO4. This work is the first step towards the development of a thermodynamic model for the Na+, K+//Cl−, SO42−, CO32−, CrO42−, Cr2O72−, MoO42−, Mo2O72−, WO42−, W2O72−, O2− system that is relevant for high temperature corrosion in atmospheres containing O–H–S–C–Cl and alkali salts.