Thermal decomposition of solid wegscheiderite, Na2CO3· 3NaHCO3

Abstract

The thermal decomposition of solid wegscheiderite, Na₂CO₃· 3NaHCO₃, has been studied over the temperature range 350–465 K in atmospheres of pure nitrogen and pure carbon dioxide. At high temperatures, in both gases, the decomposition is controlled by a phase-boundary process having an activation energy of ca. 30 kJ mol^–1. The frequency factor for this process is very low in both gases. At low temperatures, nucleation-and-growth processes control the decomposition; in nitrogen the reaction follows Avrami–Erofeyev kinetics with n= 2, with an activation energy of 64 kJ mol^–1, while in carbon dioxide a first-order mechanism is rate-controlling, with an activation energy of 94 kJ mol^–1. Electron micrographs are presented which generally support the suggested mechanisms. Comparisons are made with the decomposition of sodium hydrogencarbonate.