Iso-conversional kinetics study on thermal degradation of Ni-Al layered double hydroxide synthesized by ‘soft chemical’ sol-gel method

Abstract

The iso-conversional kinetic parameters evaluation study from thermogravimetric analysis (TGA) data of Ni-Al-LDH was carried out under non-isothermal condition. Ni-Al-LDH was prepared by soft chemical sol-gel method using metal acetylacetonate as precursors. It was characterised by PXRD, FT-IR, TGA and SEM. Ni-Al-LDH showed three step thermal degradations where first step correspond to the loss of surface and interlayer water molecules; the second and third step correspond to the loss of intercalated water molecules and ions from the hydroxidic brucite like layers. The kinetic parameters such as activation energy (Ea), pre-exponential factor (A) and reaction order (n) were determined for the second and third step degradations by Flynn-Wall-Ozawa (FWO), Friedman, Coats-Redfern and Phadnis-Deshpande methods respectively. The activation energy obtained from Friedman method was in good agreement with the value obtained from Flynn-Wall-Ozawa method. The solid state decomposition mechanism obtained from Coats-Redfern method for the second step degradation was an A3 type nucleation and growth mechanism and for the third step a D4 type three –dimensional diffusion control mechanism which was further confirmed by Phadnis-Deshpande method.