Patent ID: 8506919

Claim:
A method for the production of a fine powder of single crystalline diamond particles, comprising: (1) impact crushing a raw material of single crystalline diamond particles that is a product of a conversion from non-diamond carbon under static ultrahigh pressure, to prepare starting minute diamond particles; (2) oxidizing the surfaces of said starting minute diamond particles to chemically attach hydrophilic atoms or functional groups to the surfaces of diamond particles and thus to impart thereto hydrophilic quality; (3) preparing a slurry by dispersing the hydrophilic diamond particles in a water medium, wherein said slurry is set and kept weakly alkaline (by addition of an alkaline substance thereto); (4) subjecting said slurry to a wet-mode preliminary particle size grading process, in order to remove by sedimentation from said slurry a top particle size fraction of the diamond particles, said top particle size fraction having a D 50 size of 60 nm or more; (5) adding, in a slurry supply tank, de-ionized water to a remainder of said slurry, which has been removed of said top particle size fraction, to a diamond concentration of 0.1% by weight or less; (6) subjecting said remainder of the slurry to a centrifugal grading process, whereby to separate and remove a coarser particle size fraction, in primary and secondary state, wherein the water medium is taken out of the centrifugal grading process and is received and held in an intermediate tank as a first intermediate slurry that contains a fraction of diamond particles of an average particle size that has been decreased, and whereby said coarser diamond particles are condensed as a solid mass, removed from the slurry, returned to said slurry supply tank, and dispersed in de-ionized water to form a second intermediate slurry for another cycle of said centrifugal grading, whereby fine particles in said second slurry are loosened, dispersed, and integrated into said first slurry; (7) repeating once or more an operation of the step (6) above with said second intermediate slurry, wherein a flow rate of the slurry into the centrifugal grading process is adjusted each time the centrifugal grading process is repeated and whereby a coarser particle size fraction of the diamond particles is separated by condensation and removed as a solid mass from the slurry, until a target set of parameters have been achieved with the diamond particles contained in said mass: a D 50 size of 50 nm or less and ratios of D 10 size to D 50 size and D 90 size to D 50 size of 50% or more and 200% or less, respectively, said slurry effluent from the centrifugal process containing a fraction of diamond particles having a smaller average particle size; and (8) recovering from said slurry the diamond particles as having a minimal average particle size by precipitating into a solid mass.