Precursor effects on ZrW 2O 8 formation kinetics

Abstract

The synthesis of ZrW 2O 8 from different kinds of mixtures containing ZrO 2–WO 3, ZrO(NO 3) 2·2H 2O–WO 3, ZrCl 2O·8H 2O–WO 3, and ZrO 2–(NH 4) 10W 12O 41·5H 2O was investigated, and the kinetics was analyzed using JMA equation. It was found that ZrO(NO 3) 2·2H 2O, ZrCl 2O·8H 2O H 2O and (NH 4) 10W 12O 41·5H 2O that were used as inorganic precursors formed ZrO 2 and WO 3 after firing above 500 °C. The content of ZrW 2O 8 obtained by firing the mixtures is influenced by the kinds of precursors as well as mixing methods. The formation rate of ZrW 2O 8 depends on homogeneity related to mixing methods as well as the particle size of starting powders. Phase-pure ZrW 2O 8 is obtained from the ZrCl 2O·8H 2O–WO 3 mixtures at 1200 °C for 4 h, which is much shorter time than in the case of conventional ZrO 2–WO 3 mixtures. In the reaction kinetics of ZrO 2–WO 3 system, the Avrami exponent ( n) is ∼0.5 above 1175 °C, indicating that the reaction is controlled by the diffusion-controlled reaction.