Vol 39, No 2 (2017)

The effect of high pressure (7.7 GPa) and temperature (1700°C) on the phase transformations of both graphene plates with a high degree of crystallinity having less than four layers and thickness not exceeding 5 nm and powders of multilayer graphenes (of 10–20 monolayers) and 8–12 nm in thickness was experimentally studied in the presence of carbon solvents (Ni–Mn alloy, iron). Factors both contributing and inhibiting the diamond synthesis from graphene in the presence of the solvents for carbon are defined. It is shown that the transformation of multilayer graphenes into diamond at high pressure and temperature by a two-stage scheme of the diamond synthesis (i.e., after three-dimensional structural ordering of graphene at the first stage) is preferable.

The nanoindentation in the continuous stiffness measurement mode was used to investigate the onset of plasticity at the nanodeformation of cubic boron nitride (cBN). This technique allows us to reveal an elastic-plastic transition in the contact and to measure the yield strength of cBN at the nanoscale. An abrupt elastoplastic transition (a pop-in) was observed in the (111) cBN single crystal as a result of a homogeneous or heterogeneous nucleation of dislocations in the previously dislocations-free region under the contact. The analysis of the data obtained at the homogeneous nucleation of dislocations in the contact region made it possible to experimentally estimate the theoretical shear strength of cBN and its ideal (elastic) hardness. In a sample of the fine-grained cBN with a nanotwinned substructure a smooth elastoplastic transition was observed in consequence of the propagation and multiplication of already existing dislocations in the contact region.

The main results of the investigation of special features of the formation of the interface between the glass coating on the diamond and cBN powders with metals, that are bonds of grinding tools are described and generalized. It has been shown that the mutual diffusion occurring in the contact zone results in the increase of the adhesion at the interphase boundary, which ensures a strong fastening of a metal coating on a glass aggregate and the glass aggregate itself in a metal bond.

The catalytic activity of Fe–Co catalysts applied on carbon fibers of various morphologies was studied in the CO₂ methanation reaction The catalysts produced by applying the active mass on the cleaned oxygenated or cleaned reduced carbon fibers exhibited a lower activity. It was demonstrated by the SEM method that an increase of the amount of oxygen-containing functional groups on the carrier surface has a negative influence on the catalytic activity of the samples in the methanation reaction and hinders the processes of metal nitrates adjoining the carrier surface and the reduction of the active mass during the synthesis of catalysts. The sample Fe: Co = 86: 14 applied on the non-modified cleaned carbon fibers (T₆₅ = 390°C, with \({S_{C{H_4}}}\)) showed the greatest activity in the CO₂ methanation reaction.

Based on the physical-statistical model of formation of workpiece material debris particles in diamond polishing, an analysis of removal rate and form accuracy has been performed for flat surfaces of optoelectronic components made of quartz, aluminum nitride, and gallium nitride. The most efficient values of kinematic parameters of machine tool setting have been defined to achieve the required shape-generation accuracy. The paper provides some findings of the experimental verification of calculated data on the removal rate in polishing and the form deviation of the machined surfaces.

The authors put forward a method of protection of diamond electroplated coating in a dressing tool made by the electroforming process. The method consists in using diamond micron powder in the surface layer of the nickel bond in order to protect the bond surface against hydroabrasive wear. The paper provides a procedure of calculation of nickel (the basis for the diamond electroplated coating) deposition conditions, taking into account the change in the free surface area of deposition due to cross-sectional area of diamond grains of the working fraction and the micron powder. The procedure permits computing the refill-deposition rate and duration, the final thickness of the coating and its protective sublayer.

The paper addresses the detonation synthesis factors that govern the yield of nanodiamonds and diamond-containing soot, and their quality. The effect of such an important factor as the composition of armor (shell) of the explosive charge is described. The authors discuss three different methods of initiating an explosive charge, which involve the use of gas, water, or ice, respectively, and their advantages and disadvantages. The influence of the composition of mixtures of aqueous solutions of various substances (organic and inorganic) on the outcome of the detonation synthesis is shown in detail.