A think-tank of Russian physicists, employed at several science and research institutions of Moscow and Moscow region, currently develops production conditions for a new composite material with diamond matrix and prepares to investigate its properties. Said material is a result of baking of nanodiamonds with cobalt under conditions of high pressure and high temperature.

Microcrystalline diamond powder is a common material for providing various processing tools with diamond coating, however, scientists also suggest using nanodiamonds, produced by means of so-called “detonation technique”, for this purpose. Hardness of mentioned nanodiamonds is nearly the same that natural diamond monocrystals have. Diamond coating is generated by simple baking of nanoparticles, but special coatings (a hyperfine film with appropriate mechanical properties, for instance) often require an activating additive. Researchers claim cobalt, commonly used in production of two-layered diamond carbide blades, is great as an activating additive.

 

 

Nanodiamonds are polycrystalline particles, which size does not exceed twenty nanometers. Physicists placed said particles together with cobalt into a high pressure chamber, and when pressure reached 8 GPa, reagents were steadily heated, until thermometers showed 1700-1800 degrees Kelvin – this temperature caused cobalt to melt and enter diamonds, filling empty spaces in crystals. Key reagent for the experiment was following: polycrystalline nanodiamond powder with diameter of aggregates (polycrystals) about 3-4 microns, and crystallites (microcrystals) in these aggregates were as little as 10-20 nanometers. Baking time was very short and never exceeded 10 seconds. Reagent ratio was adjusted in order to prevent diamond powder from full saturation with cobalt.

 

 

Cuts were then prepared from caked samples, and researchers used them for studies of element composition of sample’s various parts. Since cobalt was entering diamond crystals in a gradual manner, various parts of the sample cut showed different concentrations of said element.

Scientists were happy to discover that presence of cobalt, which turned out to be a catalytic agent, caused effective recrystallization of nanodiamonds, which resulted in formation of a rigid diamond skeleton. Micro-hardness of the new composite material depends on cobalt concentration in said material. If one wants to get hard and firm composite materials, he should add no less cobalt than three or even four per cent by volume. Maximum hardness of the composite showed to reach 80 GPa (close to that of diamond monocrystal), when cobalt concentration in reaction mixture was between 6-8 per cent by volume.

Researchers cannot wait until preliminary studies of new composite material will be over, and innovation hits industrial kingdom, bringing even more technology to our everyday life

Source: Russian Science News

Kizilova Anna