Densification of zirconium diboride with varying carbon additions

Zirconium diboride (ZrB₂) ceramics with carbon additions ranging from 0 to 1.5 wt% were densified by hot-pressing. Commercial ZrB₂ powder was the starting powder and phenolic resin was used as the carbon source. Without carbon addition, ZrB₂ can be fully densified at 2150℃ under 32 MPa resulting in an average grain size of 27.2 µm. With carbon additions to the ZrB₂, the relative density remained near 100 %, but the grain size decreased as carbon content increased. In addition to ZrB₂, small amounts of secondary phases (graphite, B₄C, and BN) were detected in the hot-pressed ceramics along grain boundaries. Thermal diffusivity, specific heat capacity, and thermal conductivity of ZrB₂ were measured as a function of carbon additions. The composition with 0.75 wt% of carbon exhibited the best combination of high relative density, small grain size, and high thermal diffusivity.