Effects of starting carbon and solvent-catalyst on the reaction sintering of diamond
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Polycrystalline diamond sintered compact was prepared under high pressure and temperature conditions (7 GPa, 1700° C, 10 to 15 min) from purified natural graphite (NG) or graphitized pitch coke (GPC) using iron, cobalt or nickel as the catalytic active metal and titanium or zirconium as the solvent metal. The effects of the combinations of starting carbon and solvent-catalyst on the transformation behaviour and morphology of the converted diamond were investigated in relation to the starting powder compositions. Diamond crystals converted from NG tended to have euhedral habits, when twin crystals were occasionally found due to a relatively rapid conversion and growth rate of diamond. On the other hand, a skeletal structure of diamond was easily formed by a mild conversion from GPC in the 15 to 30 vol% (∼ 40 to 60 wt%) nickel solvent-catalyst. The degree of catalytic action in the 8A group of 3d transition metals for the GPC system was in the order: Ni ⩾ Co > Fe. The grain growth of the converted diamond was depressed by the addition of 4A transition metals (titanium or zirconium) which results in the fine-grained and homogeneous sintered microstructure.
KeywordsTitanium Zirconium Diamond Crystal Transformation Behaviour Skeletal Structure
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