Provided is polycrystalline diamond having a diamond single phase as basic composition, in which the polycrystalline diamond includes a plurality of crystal grains and contains boron, at least either of nitrogen and silicon, and a remainder including carbon and trace impurities; the boron is dispersed in the crystal grains at an atomic level, and greater than or equal to 90 atomic % of the boron is present in an isolated substitutional type; the nitrogen and the silicon are present in an isolated substitutional type or an interstitial type in the crystal grains; each of the crystal grains has a grain size of less than or equal to 500 nm; and the polycrystalline diamond has a surface covered with a protective film.

Assemblies as disclosed herein for making superhard products by HPHT process comprise a first can portion for accommodating a mixture of materials therein and a second can mated with the first can portion. A leak-tight seal is provided between the first can portion and second can portion in a manner that accommodates the manufacture of relatively longer superhard products without having to change other elements or members used for HPHT processing to thereby provide improved manufacturing flexibility and cost efficiency.

The present diamond single crystal is a diamond single crystal containing nitrogen atoms, in which a concentration of the nitrogen atoms changes periodically along a crystal orientation of the diamond single crystal, and an arithmetic average value A.sub.ave, a maximum value A.sub.max, and a minimum value A.sub.min of the distance of one period along the crystal orientation satisfy the relationship expressed by the following equation (I):
(A.sub.max)/1.25(A.sub.ave)(A.sub.min)/0.75(I).

The present diamond single crystal is a diamond single crystal containing nitrogen atoms, in which a concentration of the nitrogen atoms changes periodically along a crystal orientation of the diamond single crystal, and an arithmetic average value A.sub.ave, a maximum value A.sub.max, and a minimum value A.sub.min of the distance of one period along the crystal orientation satisfy the relationship expressed by the following equation (I):
(A.sub.max)/1.25(A.sub.ave)(A.sub.min)/0.75(I).

A method of producing diamonds comprises the steps of producing a carbonaceous powder comprising nano-structured carbonaceous material and a transition metal and thermally treating the powder. The carbonaceous powder is produced by electrochemical erosion of graphite in a molten salt, the transition metal being incorporated into the carbonaceous powder during the electrochemical erosion. The step of thermally treating the carbonaceous powder is carried out in a non-oxidising atmosphere at a temperature of between 350 C. and 300 C., at a pressure of lower than 1 GPa. The method allows diamond to be produced at low pressures and low temperatures.

A container assembly for use in a high-pressure press having a central pressure cell and a method of sealing a central pressure cell. The container assembly includes a container that receives a sample to be pressed, and a gasket distinct from the container, the gasket meeting the container at an interface. The container and the gasket are dimensioned to locate the interface within the central pressure cell.

A method of making a thermally stable polycrystalline super hard construction having a plurality of interbonded super hard grains and interstitial regions disposed therebetween to form a polycrystalline super hard construction having a first thermally stable region and a second region, the first thermally stable region forming at least part of a working surface of the construction, comprises treating the polycrystalline super hard material with a leaching mixture to remove non-super hard phase material from a number of interstitial regions in the first region. The step of treating comprises masking the polycrystalline super hard construction along at least a portion of the peripheral side surface up to and/or at the working surface to inhibit penetration of the leaching mixture into the super hard construction through a peripheral side surface of the super hard construction.

A polycrystalline diamond construction comprising a body of polycrystalline diamond material formed of a mass of diamond grains exhibiting inter-granular bonding, wherein between around 50 wt % to around 99 wt % of the diamond grains in a cross-section of the body of polycrystalline diamond material taken at any orientation have a sectorial growth structure. A method of making the polycrystalline diamond construction is also disclosed.

To provide a hydrostatic pressure type high temperature and high-pressure treatment apparatus by a wet method and a dry method for efficiently mass-producing high-quality and large-sized synthetic diamond. In the treatment apparatus, a high-pressure cell prevented from the intrusion of a pressure medium into the inside is housed in a high-pressure container, and hydrostatic pressurization is performed by the liquid pressure medium. At least one pressurizing mechanism 10 for the pressure medium 6 is provided, and a pressure medium having a known compressibility and volume change rate is used. A heating mechanism for the pressure medium and a measuring means for the average temperature in the vertical direction are provided, the pressure medium is heated to a predetermined temperature to be thermally expanded, treatment is continued while maintaining the pressure even after the pressurizing mechanism is stopped, and two or more high-pressure cells 9 can be simultaneously subjected to high-temperature and high-pressure treatment at uniform pressure without directionality.

To provide a hydrostatic pressure type high temperature and high-pressure treatment apparatus by a wet method and a dry method for efficiently mass-producing high-quality and large-sized synthetic diamond. In the treatment apparatus, a high-pressure cell prevented from the intrusion of a pressure medium into the inside is housed in a high-pressure container, and hydrostatic pressurization is performed by the liquid pressure medium. At least one pressurizing mechanism 10 for the pressure medium 6 is provided, and a pressure medium having a known compressibility and volume change rate is used. A heating mechanism for the pressure medium and a measuring means for the average temperature in the vertical direction are provided, the pressure medium is heated to a predetermined temperature to be thermally expanded, treatment is continued while maintaining the pressure even after the pressurizing mechanism is stopped, and two or more high-pressure cells 9 can be simultaneously subjected to high-temperature and high-pressure treatment at uniform pressure without directionality.