M. I. Alymov

Preparation of nanostructured composite ceramic materials and products under conditions of a combination of combustion and high-temperature deformation (SHS extrusion)

The results of studies showing the possibility of obtaining long products from composite ceramic nanomaterials by self-propagating high-temperature synthesis (SHS) extrusion have been presented, combining the combustion process of the initial components of the exothermic mixture and the high-temperature deformation of the combustion products. It is found that the production of nanoscale elements of the structure of the material is regulated by regime parameters of the technological process and a special choice of the initial composition of the initial exothermic mixture. The experimental results of studies of the microstructure and properties of the resulting nanostructured composite are discussed. The regularities of the influence of shear plastic deformation during the SHS extrusion on the microstructure and the size of the structural components of the synthesized ceramic composite have been studied in comparison with other methods: SHS without the application of external forces, free SHS compression, free SHS compression followed by quenching, and SHS pressing.

Influence of mechanical activation mode on morphology and phase composition of Al-2Mg-nC nanostructured composite material

This article discusses peculiar features of formation of the structure and phase composition of powdered nanostructured aluminum matrix composite materials reinforced by graphene-like structures obtained by combined mechanical activation. The morphology of the powders has been studied and a neural network model has been developed which describes the dynamics of crystallite disintegration upon mechanical activation as a function of processing time and concentration of carbon nanostructures.

Synthesis of Titanium Carbide Nanopowders and Production of Porous Materials on Their Basis

A technology for the synthesis of titanium carbide nanopowders with a narrow particle-size distribution and a small concentration of impurities has been developed. Conditions for pressing and sintering titanium carbide powders, which served as a basis for the creation of a porous material with an open porosity of up to 50%, have been determined. The ultimate bending strength of the porous material tended to decrease as the sintering temperature increased from 1250 to 1550°C, but it was still in the range of 66 to 95 MPa.

Specific Features of the Densification of Hydroxyapatite Nanopowders upon Pressing

In this work we study the pressing and subsequent sintering of hydroxyapatite powders prepared by two methods, i.e., precipitation from aqueous solutions (I) and heterophase synthesis (II). The particle size of powders I and II does not exceed 50 and 100 nm, respectively. In the optimum pressing mode, the relative density of billets reaches 60%. The pressing of powders with preevacuation contributes to the formation of a more homogeneous structure of ceramics. The strength of the ceramics prepared without and with evacuation is 25 ± 1 MPa and 20 ± 1 MPa, respectively; the decrease is attributed to higher open porosity.

Coagulation of gold nanoparticles in thin amorphous films under irradiation with a fast electron beam

Results of in situ studies into the coagulation of gold nanoparticles in amorphous carbon and silicon dioxide films exposed to an electron beam are presented. Special attention is paid to the final stage of coagulation (nanoparticle merging). The results clearly demonstrate the possibility of modifying the structure in a local film region by exposing it to an electron beam. Binary interparticle collisions are prevalent in the studied films. It is found that the rate of nanoparticle aggregation depends on the difference in their diameters and the orientation relationship at the moment of contact between the merging nanoparticles. It is also found that some nanoparticles are enlarged much in the same way as is done under recrystallization, i.e., via the migration of nanocrystal boundaries.

Sintering mechanisms for crystalline powders: Comparative analysis

234 As is known, the process of sintering plays a key role in structuring of SHS products in post processes [1, 2]. Free sintering is usually treated as the diffusion assisted creeping under the action of surface tension forces [3a–c], while sintering under applied pressure is regarded as diffusion mediated extrusion of voids out of crystals [3c]. It is normally thought that the neck between particles (figure) may grow by mecha nisms schematically indicated in figure. In this communication, we the report on some comparative analysis concerning relative importance of different mechanisms of sintering. According to Frenkel [4], the sintering process can be described in terms of plastic flow. Accordingly, the neck growth (see figure) is associated with the action of capillary forces and given [5] by the expression:

Sintering diagrams of gold powders

The sintering diagrams of the gold powders with different particle sizes are plotted. The dominant mechanisms of the sintering of the gold at a specified temperature, powder particle size, and neck size are identified.

Formation of an Ensemble of Gold Clusters in a Thin Amorphous Carbon Film by Electron Beam

The origination and evolution processes of gold clusters in a three-layer carbon-(gold + carbon)-carbon system have been observed in situ in the column of a transmission electron microscope. It has been shown that the sizes of the gold nanoclusters depend on the duration of the impact of a fast electron beam. Under long-term exposure (about 2 h) with an electric current density of 1.2 A/cm2, nanocrystallites with a maximum size reaching 4.5 nm are formed in the central region of the film. It is found that the average size of nanoclusters decreases with an increase in the distance from the center of the heat source; nanoclusters are not formed outside the impact area of the electron beam. The change in the nanocrystal sizes in this region correlates with the intensity profile of the electron beam. It is established that the coarsening of nanoclusters is achieved both through the mechanism of coalescence and the mechanism of coagulation.

Sintering diagram of titanium carbide powders

Sintering diagrams, which determine the dominating mechanism of powder sintering at a given temperature, the size of powder grains, and the neck between the grains, may be used to explain the experiments on sintering and solve some practical problems concerning the sintering of metals and ceramics. In this work we have built sintering diagrams for titanium carbide powders of various dispersities. Using such diagrams, we have established that the dominating mechanisms of sintering titanium carbide micro- and nanopowders are the surface and grain-boundary diffusion of substance to the neck between the particles. It is found that the contribution of sintering basic mechanisms in the case of titanium carbide does not depend on the dispersity of powders.

Influence that cobalt hydroxide reduction regimes have on dispersion and reduction degree of cobalt nanopowders

The influence that regimes of the hydrogen reduction of cobalt hydroxide have on the reduction degree, dispersion, and structural composition of cobalt powders is studied. It is established that, with an increase in the reduction temperature from 320 to 420°C, the specific surface of cobalt nanopowder decreases from 4.96 to 3.39 m2/g. If the reduction temperature changes from 150 to 320°C, the reduction degree increases from 5 to 100 vol %.