Thermal behaviour of layered double hydroxides studied by emanation thermal analysis

Thermal behaviour of the Mg-Al, Co-Al, and Ni-Al hydrotalcite-like compounds was studied during heating in air in the temperature range 20-1100 degreesC using the emanation thermal analysis (ETA), which is based on the measurement of the radon release rate from the samples previously labeled. The release of interlayer water followed by the dehydroxylation of hydroxide layers and decomposition of interlayer carbonate anions were observed during samples heating. Thermal decomposition of samples was accompanied by the sharp increase of surface area and radon release rate, which then decreased with increasing temperature as crystallization of formed oxides took place. The ETA results were in a good agreement with results of thermal analysis (TG, DTA, EGA), X-ray diffraction and BET surface area measurements.