Vaporization behavior of Na2CO3 and K2CO3

Sodium and potassium carbonates are important components of high temperature materials. Therefore, information on gas phase is important for modelling of long term processes, where the stability of carbonates should be taken into account. In this study the vaporization behavior of Na2CO3 and K2CO3 has been studied with Knudsen Effusion Mass Spectrometry in the temperature range from 600 to 880 degrees C. It was established, that vaporization of sodium and potassium carbonates is close to congruent conditions at temperatures below 750 degrees C with the main species M, CO2 and O-2 in the gas phase. The vapor pressures of these species are in a good agreement with the calculated values within an error of +/-30%, which are based on the available thermodynamic information including formation enthalpies of M2CO3(s) and M-(g), CO2(g) and O-2(g) and corresponding thermodynamic functions. At high temperatures above 750 degrees C incongruent vaporization was observed due to a disproportional increase of the vapor pressure of CO2. On this stage also Na2O+, K2O+ and K2CO3+ ions were registered in the mass spectra. Based on the analysis of fragmentation processes of M2CO3 molecules, the sublimation enthalpy Delta H-sub degrees(298)(K2CO3) is obtained to be 360 kJ/mol.