High temperature mass spectrometric gas-release studies of kaolinite Al2[Si2O5(OH)4] decomposition

The evolution of hydrogen together with water release during dehydroxylation kaolinite was confirmed by means of simultaneous analysis of weight loss and evolved gases during a thermal treatment of kaolinite from different locations. The evolution of hydrogen during the dehydroxylation of kaolinite supports a specific structural arrangement of OH-ions during the decomposition. A deficit in the vacuum weight loss can be explained by a degassing process at room temperature under high vacuum. Obviously approxmately 0.2 mol H2O in the kaolinite structure are more mobile than OH-combined water release. Together with the water release also carbon dioxide evolved also at the same temperature interval. The correlation to the dehydroxylation is obviously more an indication for a molecular fixation of CO2, in the kaolinite structure, like the “indigenous” carbon, than an admixture of a carbonate mineral. The hydrocarbon release is independent of the hydrogen, CO2, and water release. In any cases small quantities of OH are fixed in the meta-kaolinite structure and still escape as H2O still between 900 and 1200 °C.