几种铈盐的热分解过程及非等温热分解动力学研究

Thermal Decomposition and Their Non-Isothermal Kinetics Parameters of Carbonate,Oxalate and Nitrate of Cerium

利用TG-DTG-DTA热分析技术研究了二水合碳酸亚铈、九水合草酸亚铈、六水合硝酸亚铈三种铈盐的热分解过程.发现二水合碳酸亚铈在75-180℃下脱去2 mol水生成无水碳酸亚铈,后者在220 300℃下分解脱去CO2生成CeO2;九水合草酸亚铈在100 180℃下脱去9 mol水生成无水草酸亚铈,后者在290-380℃下分解并同时脱去CO和CO2生成CeO2;而六水合硝酸亚铈在60-80℃下首先脱去3.5 mol水生成含2.5个结晶水的硝酸亚铈,后者在190-250℃下脱去2.5 mol结晶水生成无水硝酸亚铈,在258-310℃下硝酸亚铈热分解脱去NO2和O2并生成CeO2.采用外推法研究了九水合草酸亚铈两步热分解过程的动力学,由不同升温速率下的热分析曲线及外推β→0获得了相应的固相热分解反应所遵循的分解机理及动力学参数.发现九水合草酸亚铈脱水过程遵循球形对称的三维扩散机理,即Jander方程G(α)=G(α)=[1-(1-α)1/3]2,动力学参数E=180.9 kJ/m ol、lnA=63.5 s-1;而脱CO和CO2过程遵循成核和生长机理,即Avram i-Erofeev方程G(α)=[-ln(1-α)]1/1.5,动力学参数E=115.4 kJ/m ol,lnA=22.0 s-1.

Thermal decomposition processes of hydrated carbonate, oxalate and nitrate of cerium have been studied by TG-DTG-DTA thermal analysis techniques. The results show that Ce2 （CO3）3 · 2H2O first dehydrates to obtain Ce2 （CO3 ）3 at 75-180 ℃and then Ce2 （CO3 ）3 decomposes to CeO2 at 220-300 ℃, respectively. For Ce2 （C2O4）3 · 9H2O, 9 mol waters are first lost to form Ce2 （C2O4）3 at 100-180 ℃ and the latter decomposes to CeO2 with sending out carbon monoxide and carbon dioxide at 290-380 ℃. For Ce（NO3）3 · 6H2O, 3.5 mol adsorbed waters and 2.5 mol crystal waters are first released to Ce（NO3）3 at 60-80 ℃ and at 190-250 ℃, respectively, and then Ce （NO3 ）3 decomposes to CeO2 with giving out nitrogen oxide and oxygen at 258-310 ℃. A extrapolate method was used to determine the non-isothermal kinetic parameters of two thermal decomposition processes of Ce2 （C2O4）3 · 9H2O. The thermal decomposition function of the first step is found to follow Jander equation G（α） = [ 1 - （ 1 -α）^1/3] ^2 and its kinetic parameter is E = 180.9 kJ/mol and lnA =63.5 s^-1. The second step abides by Avrami-Erofeev equation [ G（α） = [ In（ 1 - α ） ] 1/1.5 ] and its kinetic parameter is E = 115.4 kJ/mol and lnA = 22.0 s^-1.