Mechanism and Kinetics of Thermal Decomposition of Yttrium Oxide Precursor

The thermal decomposition process and kinetics of yttrium oxide precursor of yttrium carbonate and yttrium oxalate were analyzed by means of thermogravimetric-differential thermal analysis, and the experimental data were processed by the methods of Kissinger, Ozawa and Coast-Redfern. The results showed that there are four steps for thermal decomposition of yttrium oxalate, the first two steps are the dehydration process, the following two steps are the decomposition process, and the activation energy Ec corresponding to the four-step reaction are 64.24, 59.48, 146.20 and 112.37 kJ•mol-1, the preexponential factors Ac are 4.09×108, 3.83×105, 6.86×1010 and 6.18×105, respectively. The mechanism functions of each step are 1-(1-α)1/2=kt, 1-(1-α)1/3=kt, [(1-α)-2-1]/2=kt and [-ln(1-α)]1/3=kt. The thermal decomposition of yttrium carbonate includes two steps, the first step is the taking off of three H2O and one CO2 molecules', the second step is giving off two CO2 molecules' and then generating yttrium oxide. The activation energy Ec corresponding to the two steps are 88.29 and 116.53 kJ•mol-1, their preexponential factors Ac are 1.5×1013 and 9.4×107, respectively. The mechanism functions are (1-α)-1-1=kt and [1-(1-α)1/3]2=kt. The precursor of yttrium carbonate is more easily decomposed than yttrium oxalate to produce yttrium oxide, and the speed controlling step of the thermal decomposition of the two precursors is the last step. © 2019, Editorial Office of Journal of the Chinese Society of Rare Earths. All right reserved.