catalyst solvent metal employed and selected from a list of specific materials that suppress diamond nucleation application_number US 14821480 A description one preferred form of a high pressure high temperature apparatus in which the reaction vessel of the instant invention may be employed is the subject of the aforementioned u s pat no 2 941 248 hall and is schematically illustrated in fig1 in fig1 apparatus 10 includes a pair of cemented tungsten carbide punches 11 and 11 39 and an intermediate belt or die member 12 of the same material die member 12 defines a centrally located aperture and in combination with punches 11 11 39 defines two annular volumes between punch 11 and the die 12 and between punch 11 39 and the die 12 there are included gasket insulating assemblies 13 13 39 each comprising a pair of thermally insulating and electrically non conducting pyrophyllite members 14 and 16 and an intermediate metallic gasket 17 the aforementioned assemblies 13 13 39 together with end cap assemblies 19 19 39 and electrically conductive metal end discs 21 21 39 serve to define the volume 22 occupied by reaction vessel 30 each end cap assembly comprises a pyrophyllite plug or disc 23 surrounded by an electrical conducting ring 24 reaction vessel 30 fig2 is of the general type disclosed in u s pat no 3 030 662 strong incorporated by reference modified by the addition of steel retaining rings 31 and 32 hollow cylinder 33 is preferably made of pure sodium chloride but may be made of other material such as talc broad criteria for the selection of the material for cylinder.