Synthesis of ZrW2O8–ZrC composite powders by solid-state exothermic oxidation reaction of ZrC and WO3 powders

Abstract

In this work, ZrW₂O₈-coated ZrC composite powders are synthesized by solid-state reaction method using ZrC and WO₃ powders. Thermodynamic analysis shows that when the molar ratio of ZrC to WO₃ is larger than 5:4, ZrW₂O₈ cannot be synthesized by solid reaction of ZrC and WO₃. The favorable molar ratio of ZrC to WO₃ for solid reaction synthesis ZrW₂O₈ is 1:2. After reacted below 800°C for 8 hours, only ZrC in the ZrC and WO₃ mixture powders partially reacts with oxygen to form ZrO₂. And there is no detectable reaction between WO₃ and the formed ZrO₂ to produce ZrW₂O₈. ZrC and WO₃ can synthesize ZrW₂O₈ at 900°C. ZrW₂O₈-coated ZrC composite powders can be synthesized using powder mixtures with molar ratio of ZrC:WO₃ = 1:1.7 and ZrC:WO₃ = 1:1.9 after heat treatment at 1000°C for 4 hours. The synthesized ZrW₂O₈-coated ZrC particles show cubic shape with obvious particles growth. The exothermic oxidation reaction of ZrC leads to a significant increase in local temperature, which is believed to trigger partial reaction between ZrO₂ and WO₃ to form ZrW₂O₈.