Investigation on the thermal decomposition of aged La₂O₃

The thermal decomposition process of air-aged La₂O₃ in argon atmosphere was studied using nonisothermal TG-DSC. X-ray diffraction and TG-DSC analysis showed that the aged powder was composed of La(OH)₃ with small amounts of oxycarbonate. The decomposition process of air-aged La₂O₃ involves the two-step decomposition of La(OH)₃ and the decomposition of oxycarbonate. The kinetic analysis of the two-step decomposition of La(OH)₃ was carried out using Coats-Redfern and isoconversion (Ozawa) methods. The kinetics of the two-step decomposition can be described in terms of the nucleation and growth model A (m=1.5,m is the model parameter) and A (m=2.5),respectively. The apparent activation energy for the first step is 136-144 (Coats-Redfern) and 137-164 kJ/mol (isoconversion). The apparent activation energy for the second step is 191-194 (Coats-Redfern) and 186-213 kJ/mol (isoconversion).