Synthesis and densification of zirconium diboride prepared by carbothermal reduction

Using boron powder as additive, the preparation of zirconium diboride (ZrB₂) by carbothermal reduction was investigated. The results show that the carbothermal reduction cannot be completely done until the temperature is more than 1900 °C. The ZrB₂ particles prepared without boron (B) additive at 1900 °C for 3 h are rodlike and show a preferential grain growth along [001] direction. B additive changes the heat effect of the raw materials. With B additive, the morphology of ZrB₂ particles turns to be regular shape. The average particle size is about 3.6 μm with 2.5 wt% B additives. With more B additive, the shape of particles turns to be round like and the average particle size is decreased to 2.3 μm when 5 wt% B is added. The existence of oxides in grain boundary is a key factor to keep ZrB₂ ceramic from deep densification. Using ZrB₂ powder prepared with 5 wt% B additives, by controlling carbon content in ZrB₂ powder, ZrB₂ ceramic with 93% relative density is hot-pressed.