Minute diamond powder, method for collecting the same and slurry comprisng the same in suspension

[Task to be solved] One of the principal objects of the invention is to collect minute diamond particles of D 50 of 20 nm and smaller, by MICROTRAC UPA 150, in high precision and high definition. [Means for solving the task] The minute diamond particles of the invention are recovered by a method comprising: (1) joining or combining a hydrophilic functional group with a surface of diamond powder that comprises particles of a primary particle size of 50 nm or less, so as to impart hydrophilic nature on the surface, (2) placing the hydrophilic diamond particles to hold in suspension in water to form a slurry, (3) subjecting said slurry to a hyper-centrifugal process at a centrifugal force of 4x10 3 G and at the same time a centrifugal load product of 200x10 3 G·min. or more, in order to remove by depositing a fraction of coarser particles from the slurry, said load product being defined as product of centrifugal force, loaded, in G and duration of loading in minutes, where G represents the gravitational acceleration constant; (4) adding cations to said slurry, whereby the diamond particles in suspension in the water are deposited.