X線回折法によるジルコニア結晶化過程に対する金属イオン添加効果の検討

　ジルコニア担持酸化タングステン触媒の強酸性発現機構を解明するための予備検討として，水酸化ジルコニウムが873 -1073 K で焼成後に準安定正方晶を取り得る条件を探索するため，12 種類の金属イオンおよび硫酸イオンを添加した試料を調製し，結晶相の存在比率および格子面間隔をXRDにて検討した．種々のイオンを添加することでジルコニア結晶相の準安定正方晶を形成しうる温度領域が広がり，またその程度は添加金属種により異なった．水酸化ジルコニウムに金属イオンを添加した場合，準安定正方晶が存在しうる焼成温度範囲が狭い元素群のみ，773 K で焼成した際に観察される正方晶(101)面の格子面間隔が小さく，またそのイオン半径がジルコニウムイオンと近かった．

　Twelve kinds of metal-ion added zirconium oxide catalyst materials were prepared by impregnation of 10 mol% metal salt (Ca, V, Cr, Fe, Ni, Cu, Zn, Mo, W, Y and Ce) or sulfate ion onto amorphous zirconium hydroxide followed by calcination at 673-1273 K. Crystallization process of zirconium oxide, fraction of the tetragonal phase and d-spacing of the tetragonal (101) reflection were investigated by XRD as a function of calcination temperature. The addition of metal ion stabilized meta-stable tetragonal and/or cubic phase, and suppressed phase transition to thermodynamically stable monoclinic phase. The added elements were classified into four groups by degree of stabilization. In cases for Fe, Ni, Cu and Zn-ion added zirconium oxides, the meta-stable phase could exist at the calcination temperature till 873 K. The d (101) spacing for corresponding to tetragonal ZrO2 phase in the four samples calcined at 773 K were smaller than that for non modified ZrO2, and ion radii of the added elements were close to that of Zr4+.

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