Synthesis and spark plasma sintering of sub-micron HfB2: Effect of various carbon sources

The present work describes a simple process to synthesise HfB2 powder with sub-micron sized particles. Hafnium chloride and boric acid were used as the elemental sources whilst several carbon sources including sucrose, graphite, carbon black, carbon nanotubes and liquid and powder phenolic resin were used. The carbon sources were characterised using thermogravimetric analysis and transmission electron microscope. The mechanism by which the structure of the carbon source used, affects the size and morphology of the resultant HfB2 powder was studied; the HfB2 powders were characterised using X-ray diffraction and scanning and transmission electron microscopy. The powder synthesised using powder phenolic resin had a surface area of 21 m2 g−1 and a particle size distribution between 30 and 150 nm. This was sintered using SPS to a relative density of 94% of theoretical density (TD) at 2100 °C and 50 MPa pressure without the help of any sintering aids.