Enhancement of Oxidation Resistance via Chromium Boron Carbide on Diamond Particles

To improve the oxidation resistance of diamond, chromium boron carbide (Cr–B–C) coatings were synthesized through high temperature solid state synthesis and molten salt method on diamond particles in this paper. After holding the raw material at 900 °C for 2 h, the diamond surface was completely and uniformly covered by Cr–B–C coatings. Oxidation resistance of the diamond coated Cr–B–C was determined by the thermogravimetric analysis (TGA). The results revealed that the Cr–B–C coatings held the diamonds for 100%-mass in air atmosphere until 1151 °C, which was much better than the uncoated diamonds (720 °C) and the B4C-coated diamonds (1090 °C). When Cr–B–C-coated diamond was annealed in air, Cr2O3 and B2O3 were formed as oxygen barrier layer to protect diamond from oxidation. The formation of B2O3 with high temperature fluidity was conducive to avoiding Cr2O3 delamination due to volume expansion during oxidation in air. Furthermore, the presence of Cr2O3 provided lasting protection by reducing the evaporation of B2O3. The oxidation products (B2O3 and Cr2O3) prove a complementary functional protection on diamond particles from oxidation.