Precursor effects on ZrW2O8 formation kinetics

The synthesis of ZrW2O8 from different kinds of mixtures containing ZrO2–WO3, ZrO(NO3)2·2H2O–WO3, ZrCl2O·8H2O–WO3, and ZrO2–(NH4)10W12O41·5H2O was investigated, and the kinetics was analyzed using JMA equation. It was found that ZrO(NO3)2·2H2O, ZrCl2O·8H2O H2O and (NH4)10W12O41·5H2O that were used as inorganic precursors formed ZrO2 and WO3 after firing above 500 °C. The content of ZrW2O8 obtained by firing the mixtures is influenced by the kinds of precursors as well as mixing methods. The formation rate of ZrW2O8 depends on homogeneity related to mixing methods as well as the particle size of starting powders. Phase-pure ZrW2O8 is obtained from the ZrCl2O·8H2O–WO3 mixtures at 1200 °C for 4 h, which is much shorter time than in the case of conventional ZrO2–WO3 mixtures. In the reaction kinetics of ZrO2–WO3 system, the Avrami exponent (n) is ∼0.5 above 1175 °C, indicating that the reaction is controlled by the diffusion-controlled reaction.