Synthesis of alumina-bonded polycrystalline diamond by detonation

In this study, nanodiamond, aluminum isopropoxide, and hexogen (RDX) were used as starting materials to synthesize alumina-bonded polycrystalline diamond materials under high-temperature and high-pressure conditions generated by the detonation of the explosive. During detonation, the surface of the nanodiamond is coated with boron, silicon, and chromium through vacuum diffusion. Carbides of boron, silicon, and chromium referred as “bridges” are formed at the diamond/metal interface during the carbonization reaction. The "bridge" formed between diamond and nanoalumina considerably reduced the possibility of oxidation of nanodiamond as well as its graphitization during the detonation reaction. The phase, morphology, microstructure, and elemental composition of the detonation products were characterized by X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The results revealed that the explosion causes alumina and diamond to bond tightly to form alumina-bonded polycrystalline diamond composites. The thermal stabilities of the nanodiamond particles coated with boron, silicon, and chromium were found to be markedly higher, and the diamond phase remained intact even after heating at elevated temperatures. Thus, boron, silicon, and chromium reduced the wetting angle of diamond and alumina and improved the degree of bonding between them. Furthermore, boron facilitated the bonding between nanodiamond and alumina. In contrast, the bond was weaker in the case of silicon. Chromium also aided the bonding of the nanodiamond and alumina but introduced a large amount of oxygen into the composite.