Thermal decomposition of barium oxalate hemihydrate BaC 2O 4·0.5H 2O

Abstract

The thermal behaviour of BaC 2O 4sd0.5H 2O and BaCO 3 in carbon dioxide and nitrogen atmospheres is investigated as part of a study about the thermal decomposition of barium trioxalatoaluminate. For this purpose thermogravimetry, differential thermal analysis, differential scanning calorimetry and high temperature X-ray diffraction were used. An infrared absorption spectrum of BaC 2O 4·0.5H 2O was scanned at room temperature. At increasing temperature, in dry nitrogen, the hydrate water of BaC 2O 4· 0.5H 2O is split off, followed by the oxalate decomposition. A part of the evolved carbon monoxide disproportionates, leaving carbon behind. At higher temperatures the latter reacts with barium carbonate, previously formed. Finally the residual solid barium carbonate decomposes into barium oxide and carbon dioxide. In dry carbon dioxide atmosphere an analogous dehydration occurs, followed by oxalate decomposition. Under these conditions the carbon formation is fully suppressed, and as a consequence no secondary reaction occurs. The barium carbonate decomposition is shifted to much higher temperatures, at a low rate in the solid phase, a strongly accelerated one at the onset of melting, and a moderated one when the melt is saturated with barium carbonate. The two phase transitions of BaCO 3 are detectable in both atmospheres mentioned.