Thermal decomposition of solid sodium sesquicarbonate, Na2CO3·NaHCO3·2H2O

Abstract

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.