Zr(OH)_4的热分解及ZrO_2的相变过程

Thermal Decomposition Process of Zr(OH)_4 and Phase Transition Process of ZrO_2

利用TG-TDG-DTA热分析技术研究了由Zr(OH)4热分解制备ZrO2的脱水过程,并结合X射线粉末衍射技术研究了ZrO2的相变过程.发现在82℃的吸热峰对应Zr(OH)4的脱水,而435℃附近出现的放热峰则为四方ZrO2向单斜ZrO2的晶相转变.采用外推法确定了Zr(OH)4脱水过程遵循三维扩散机理,其函数方程为g(α)=[{1/(1-α)}1/3-1]2.以实验获得的动力学参数lnA和E为基础,用最小二乘法对lnA和E进行线性拟合,得到动力学补偿效应表达式为lnA=0.437E-20.69.

Zirconia is an important promoter and support in catalysis. The thermal decomposition and phase transition processes of zirconium hydroxide Zr（OH） 4, a precursor of preparing ZrO2 material, were studied by TG-DTG-DTA thermal analysis methods in state air and X ray diffraction analysis. It is found that Zr（OH） 4 was dehydrated absolutely to tetragonal ZrO2 below 200 ℃ and subsequently the phase was changed into monoclinic phase at 435 ℃. The kinetic parameters were determined by extrapolated method and combination of Achar method and Coats-Redfern method from thermal analysis curves of Zr（OH） 4. The result indicates that the process follows Zhuralev-Lesokin-Tempelmen 3D mechanism and the kinetic equation is g（α） = [ { 1/（ 1 - α） }^1/3 - 1]^2. The mathematical expression of kinetic parameters E and ln A were derived from the kinetic compensation effects： ln A = 0. 437 E - 20.69.