The thermal decomposition of solid sodium bicarbonate has been studied in the temperature range 360-500 K over a range of partial pressures of carbon dioxide. The effect of water vapour has also been studied. Above 440 K the reaction follows contracting-cube kinetics with an activation energy of 32 kJ mol-l and a frequency factor of lo1 s-l. In this temperature range the presence of water or carbon dioxide has little effect on the kinetics. Below 390 K the reaction follows first-order kinetics. In nitrogen, the activation energy is ca. 64 kJ m o P , the frequency factor is lo5 s-l and water vapour has little effect. High partial pressures of carbon dioxide increase the activation energy to ca. 130 kJ mol-l and the frequency factor to 1013e5 s-l.The results of microscopic examination generally confirm the kinetics but show that at low temperatures in nitrogen and carbon dioxide the processes are different in detail.A number of publications have dealt with the thermal decomposition of solid sodium bicarbonate, under various experimental conditions. These include the use of and c l o ~e d ~? ~ sample containers as well as variation in the composition of the atmosphere round the Both isothermal5? 9 9 lo and temperature-programmed heatingll, l2 regimes have been used, and several fluidised-bed studies have been

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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-' for the high-temperature region and 58 kJ mol-' 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-'. In carbon dioxide at low temperatures, wegscheiderite (Na2C0, .3NaHCO,) and sodium carbonate monohydrate (Na2C0, * H20) are formed, and this reaction follows first-order kinetics, with an activation energy of 67 kJ mot -' . Microscopic evidence is also presented. Relationships between the decomposition of sesquicarbonate and other related compounds are discussed.

has been studied in the temp. range 360‐500 K in N2 and CO2.