Effect of Er(NO3)3 content on the thermal decomposition kinetics of kaolinite

This study investigated the thermal decomposition process of kaolinite mixed with different Er(NO3)(3) contents by means of a comprehensive thermal analysis (TG-DTG). HTXRD, SEM-EDS, TEM, AFM and Al-27 MAS NMR analyses were used; the activation energy, controlling mechanism function and pre-exponential factor of the thermal decomposition kinetics for kaolinite were obtained through the Coats-Redfern integral and Achar differential methods; and the Ozawa method was used to verify the activation energy. The results showed that as the Er(NO3)(3) content increased, the controlling mechanism function of the thermal decomposition kinetics of kaolinite transformed from chemical reaction model F-3 to F-2, whereas the activation energy and pre-exponential factors decreased rapidly before stabilizing. The corresponding temperature at the maximum reaction rate decreased significantly as the Er(NO3)(3) content increased for higher heating rates (>= 25 degrees C.min(-1)), promoting the thermal decomposition reaction of kaolinite. The Al-27 MAS NMR spectra indicated that increasing the Er(NO3)(3) content accelerated the transformation of A1(VI) to Al-V as part of the thermal decomposition reaction of kaolinite. Er(NO3)(3) in the sample was first converted to ErONO3 and was then dispersed evenly as Er2O3 nanoparticles.