Controlled rate thermal analysis of nontronite

The thermal decomposition of a series of nontronites and a ferruginous smectite has been studied using a combination of high-resolution thermogravimetric analysis (TGA) with a controlled heating rate and the mass spectrometry (MS) of evolved water vapour. The temperature–mass spectrum curve follows the differential TGA (DTGA) curve with precision, thus providing a second means of calculating the percentage weight loss. Three dehydration steps were observed in the controlled rate thermal analysis (CRTA) experiment at around 86, 117 and 245 °C depending on the nontronite sample. Two overlapping dehydroxylation steps were observed at approximately 350 and 400 °C with a weight loss ratio of 1:2. A comparison is made between the between the results obtained from the dynamic DTGA experiment and the CRTA experiment.