Applications of Quantitative Thermal Analysis to Molecular Sieve Zeolites

Behavior of Kaolinite Pellets at Elevated Temperatures

“…A small step can be consistently noted in the 450-550~ region, as well as the further shrinkage that occurs above 900~ after collapse of the molecular sieve structure (Flank, 1974;Flank and Skeels, 1977). It is thus unlikely that the steps are artifacts of the pelleted clay form.…”

“…Mechanistic interpretations for this include the possible provision of a hydrolytic degradation pathway and the promotion of high-temperature silica migration by water vapor. Similar explanations for high-temperature steaming effects have been used for other materials, such as silicas and aluminosilicates (Flank, 1974).…”

“…The results of Nicholson and Fulrath (1970) were supported by a demonstration that metakaolin, from which amorphous silica had been leached by NaOH solution, did not exhibit an exotherm. It is unlikely that these workers affected significant amounts of other components in this latter experiment, since to do so would have produced a crystalline reaction product with the NaOH which would have exhibited a distinctive DTA exotherm (Flank, 1974). This exotherm occurs at about 870~ and no residual X-ray powder diffraction lines from such a product can be seen in a sample heated to 1000~ (Ambs and Flank, 1969), casting doubt on Chakraborty and Ghosh's reexamination (1977) of the work of N icholson and Fulrath (1970).…”