Thermal decomposition of solid sodium sesquicarbonate, Na2CO3·NaHCO3·2H2O
The thermal decomposition of solid sodium sesquicarbonate has been studied at temperatures between 350 and 487 K in nitrogen and carbon dioxide atmospheres. In nitrogen, a single-stage decomposition to sodium carbonate occurs, following Avrami–Erofeyev kinetics (n= 2), with an inflexion at ca. 390 K. The activation energies are 24 kJ mol–1 for the high-temperature region and 58 kJ mol–1 for the low-temperature region. In carbon dioxide above 435 K, the single-stage reaction follows contracting disc kinetics with an activation energy of 29 kJ mol–1. In carbon dioxide at low temperatures, wegscheiderite (Na2CO3· 3NaHCO3) and sodium carbonate monohydrate (Na2CO3·H2O) are formed, and this reaction follows first-order kinetics, with and activation energy of 67 kJ mol–1. Microscopic evidence is also presented. Relationships between the decomposition of sesquicarbonate and other related compounds are discussed.