Synthesis and properties of single phase diamond ceramics

We report on the synthesis of single phase diamond ceramics and its microst ructural and physical characterization. The most relevant physical properti es are listed and are compared to natural diamond. The ceramic solid has be en fabricated from chemically treated micro crystalline diamond powder, whe re oxy-functional groups have been attached to the surface. The special sur face treatment is considered essential to achieve direct atomic bonding bet ween adjacent grains. The hot isostatic pressing method (HIP) has been appl ied for materials processing that pertains to the stability region of the r elated carbon phase diagram. No further additives have been used for prepar ation. Transmission and scanning electron microscopy, energy dispersive X-r ay analysis, X-ray diffraction and Raman spectroscopy have been used for th e micro structural analysis. The achievable density is close to that of nat ural diamond, revealing porosity values of <3%. The micro structural analys es indicated the presence of small amounts of isolated diamond micro crysta ls, embedded into a matrix of polycrystalline diamond with a very small gra in size. The grains are much smaller than the originally used micro crystal line source material, indicating crystal break-up and atomic rebonding duri ng the sintering process. Also traces of sp(2)-hybridized carbon have been identified, located primarily at grain boundaries. Fracture of the material appears mostly transgranular. Relevant physical properties as thermal and electrical conductivity, hardness and Young's modulus approach those of nat ural diamond. (C) 1999 Elsevier Science S.A. All rights reserved.