GB1115650A - Shock-sintering of diamond - Google Patents

Abstract

<PICT:1115650/C1/1> <PICT:1115650/C1/2> <PICT:1115650/C1/3> Small diamond particles, preferably no greate than 150 microns in size and formed into a mass having a bulk density of at least 40% of the crystalline density of diamond, are shock sintered into larger agglomerates by subjecting the mass to a shock wave generated by explosive means. Impurities such as carbides, borides, nitrides, oxides and mixed amounts of metals or graphite may be present in amounts preferably less than 10% by weight. At a powder density of 40% that of the crystalline density of diamond a shock pressure of at least 600 kilobars is preferred and the projectile plate, the use of which is preferred, thus requires plate velocities of at least 2.5 km/second with certain relatively high-shock-impedance (at least 106 dyne/second/c.c.) plate materials such as aluminium or an alloy thereof and preferably steel, copper, nickel, titanium, zinc and their alloys. A shock duration of at least 0.1 microsecond is desirable and longer durations are preferred particularly when low shock pressures are employed. If a container for the powder is used the thickness of the cover between the impact surface and the powder is desirably no more than twice the thickness of the projectile plate and the cover's shock impedance is preferably at least the same as that of the projectile plate but may be lower if sufficiently thin. The cover is preferably fixed in place e.g. by welding. Fig. 5c illustrates one of the several described modifications of the apparatus used in which sample 3, overlaid with a cover 6 of uniform thickness, is fitted in container 7 which fits snugly in cavity 2 in block 1 which comprises external surrounding element 1A and supporting member 8. Further reinforcement around container 7 is provided by ring 9. Fig. 6 illustrates also a plane wave-generator, 10, initiated by blasting cap 11 and fixed to the upper flat surface of a cylindrical layer of detonating explosives 5, the lower flat surface of which rests on plate 4 which is substantially parallel to the upper surface of block 1, the impact area of the plate 4 preferably overlapping the sample. A metal confining means 13 surrounds explosive layer 5. At least the peripheral portion, the width of which should preferably be at least half the distance from the periphery of the impact area to the outside wall, and preferably all of block 1 including the base comprises one or more of the following: lead, copper, uranium and thorium. Members 6, 7, 8 and 9 should conveniently comprise steel, iron, titanium, niobium, nickel, aluminium, copper or their alloys. Exact fit of the members in the integral unit is not necessary but spaces between members should be filled with material such as grease. The shock sintered product of the process is a polycrystalline diamond having a density at least 80% that of diamond and producing an X-ray diffraction pattern as illustrated in Fig. 9 wherein the diffraction lines for diamond have a line broadening coefficient, K1, of from 4.5 x 10-2 to 7.5 x 10-4.