“…According to the result of XRF analysis of HfB 2 and SiC raw powders, some oxygen contamination, such as B 2 O 3 , HfO 2 , or their mixture, occurred naturally on the HfB 2 surface. This oxygen contamination could considerably hinder the densification of diborides through the reduction of boron activity 6 . The decrease in boron activity was accompanied by a reduction of the densification rate, which, in turn, promotes grain coarsening by evaporation–condensation kinetics.…”