Nanocomposites and nanomaterials

Effect of surface modification of diamond nanopowder particles on the properties of nanocomposite "diamond - tungsten carbide" sintered from them
Bochechka O.O., ChernienkoO.I, Kushch O.V., Garashchenko V.V., Lysovenko S.O., Havrylova V.S.
V. Bakul Institute for Superhard Materials, Natl. Acad. of Sci. of Ukraine. Avtozavodska, 2, Kyiv-04074, Ukraine. 
E-mail: obochechka@gmail.com

Chemical processing of diamond nanopowder of static synthesis АСМ5 0.1/0 was carried out to remove residues of the solvent metal and non-diamond carbon. The treated powder was heated at a temperature of 700 °C in a vacuum (at a residual gas pressure of 102 Pa), in an atmosphere of hydrogen and argon. Based on the study of IR absorption spectra, it was found that the surface of chemically purified diamond nanoparticles contains hydroxyl –ОН groups, carbonyl groups С=О, and С–Н groups. Annealing in vacuum and argon leads to the removal of     –ОН and С=О groups and a decrease in the number of С–Н groups. Annealing in hydrogen causes the removal of –ОН and С=О groups, an increase in the number of С–Н groups.
A study of the reaction interaction of purified diamond nanopowder with WO3 powder was carried out during simultaneous heating in vacuum, argon, in air of the indicated powders without direct contact of the reagents. In the structure of the IR spectra of diamond nanoparticles annealed at temperatures of 600 – 900 °С in vacuum and argon, there is a peak of 1250 cm-1, which is responsible for the presence of W–C bonds formed by the interaction of sublimated tungsten oxide with carbon atoms on the surface of diamond nanoparticles. The most intensely mentioned bonds are formed during annealing in vacuum at 600 °C.
Samples of the composite were sintered at a pressure of 8 GPa, a temperature of 1625–1700 оС, and a sintering time of 20 s from a mixture of ASM5 0.1/0 diamond nanopowder and tungsten trioxide powder, annealed in vacuum at a temperature of 600 °C, followed by annealing in a hydrogen atmosphere.
The study of the phase composition of the samples by X-ray diffractometry revealed the formation of tungsten carbide during sintering and the absence of non-diamond phases of carbon in the composite. Scanning electron microscopy data indicate the formation of tungsten carbide in the spaces between diamond grains and at the boundaries between them.
It was found that with an increase in the sintering temperature, the density of the composite samples increases from 4.38 to 4.40 g/cm3, the hardness, determined from the load on the Knoop indenter of 9.8 N, increases from 25 to 32 GPa.