Synthesis of the negative thermal expansion compound ZrW_2O_8 by the spray drying technique

摘要

A novel method for the synthesis of zirconium tungstate, based on the technique of spray drying, is reported. As starting products ammonium metatungstate, zirconium oxychloride and zirconium oxynitrate were selected because of their high solubility in water. However, when mixing together these compounds in the desired stoichiometric amounts, a white slurry was obtained. Spray drying of the slurry resulted in powder with enhanced reactivity due to the thorough intermixing of the Zr- and W-phases. After a preheating step at 700℃ for 10 hours, calcination of the powder at 1180℃ during 1 hour performed in sealed quartz tubes already formed ZrW_2O_8 of high quality. Compared to zirconium tungstate prepared by a more conventional solid state reaction between ZrO_2 and WO_3, the product synthesised with the spray drying technique has a very high density and higher purity.