GB1115648A - Synthetic diamonds - Google Patents

Abstract

Diamond is synthesized by forming an intimate mixture of graphite and a cooling medium and passing therethrough a shock wave generated by explosive means. The intensity of the shock wave must be sufficiently high to convert at least some of the graphite to diamond but sufficiently low to enable the cooling medium to cool the resulting diamond to below the rapid atmospheric graphitization temperature sufficiently rapidly e.g. in less than 0.1 second to prevent at least some of the diamond graphitizing. The product is normal cubic diamond, "hexagonal" diamond showing a hexagonal (100) reflection at a spacing of 2.186 <\>rA, a cubic (111) reflection at a spacing of 2.061 <\>rA and a hexagonal (101) reflection forming a shoulder varying from the cubic (111) reflection up to 1.895 <\>pA, or mixtures of these. The shock wave may be applied by detonating a high explosive in direct contact with the mixture, explosively driving a projectile plate against the mixture, or confining the mixture in a container and generating the shock wave in direct contact with the outside of the container using a high explosive or projectile plate. The shock wave may introduce into the mixture containing up to 60% by volume graphite a pressure between 200 and 2000 kilobars for a time between 0.1 and 10 microseconds. The cooling medium may be iron, copper, nickel, aluminium, manganese, magnesium, tungsten, titanium, niobium, steel and brass. The intimate mixture may be an integral solid that will not shatter on shocking, e.g. cast iron. Alternatively graphite and the cooling medium, both in particulate form, may be mixed and compacted, e.g. by explosive means, before passing therethrough the shock wave. The cooling medium may have a shock impedance of at least 3 x 106 dynes/sec/c.c., a heat capacity of at least 0.1 cal/g/ DEG C., a thermal conductivity at room temperature of at least 0.1 cal/sec/cm./ DEG C., a density of at least 85% of the theoretical density and reach a maximum temperature during shocking of less than 1800 DEG C. The graphite used may have a density of at least 60% of the theoretical density and the mixture an overall relative density of at least 70%. The mixture of diamond and graphite resulting from the above process may be treated in accordance with the process of Specification 1,115,649 to remove the unconverted graphite. The diamond particles recovered may be agglomerated to form larger particles using the process of Specification 1,115,650.