Molten salt synthesis of La2Zr2O7 ultrafine powders

Abstract

Ultrafine powders of pyrochlore-type La2Zr2O7 were synthesized via a simple molten salt mediated process using zirconium oxide and lanthanum oxide as raw materials, and sodium chloride, potassium chloride and sodium fluoride to form a reaction medium. The effects of reaction temperature, salt/reactant ratio and salt type on the La2Zr2O7 formation were investigated. Among the three attempted salt assemblies (KCl–LiCl, Na2CO3–K2CO3, and NaCl–KCl–NaF), NaCl–KCl–NaF showed the best accelerating effect on the La2Zr2O7 formation. At a given temperature, the La2Zr2O7 content in the final products increased with the increase in the salt amount. Phase pure submicron sized La2Zr2O7 ultrafine powders were obtained after 3h firing at 1100°C with the salt/reactant weight ratio of 5:1 or at 1200°C with salt/reactant weight ratio of 3:1. The synthesis temperature (1100°C) was much lower than that required by the conventional solid-state mixing method or a wet chemical method. The “dissolution–precipitation” mechanism had dominated the synthesis process.