G. P. Shveikin

Ab-initio Calculations of the Electronic Structure and Cohesive Properties of the Orthorhombic Oxynitrides X2N2O (X = C, Si, Ge)

The full-potential LMTO method was used for the investigation of the electronic structure and chemical bonding of the silicon, germanium and hypothetical carbon oxynitrides. The isovalent substitution of Si by C allows to compare the role of Si and C in the processes of chemical bonding and cohesive properties. It was shown that doping by carbon may lead to stronger covalent bonding and therefore the new ceramic materials based on the Si-C-Al-O-N system can have improved mechanical characteristics.

Possibilities of using composite track membranes with nitride coating for fractionation of microelements in natural water

A plasma chemical procedure was developed for preparing composite track membranes with a conducting coating of titanium nitride particles having a complex hierarchic structure. Owing to oxynitride deposition on the surface of a poly(ethylene terephthalate) track membane, the membrane channels become asymmetrical and the membrane strength is enhanced. The pore opening size in composite membranes can be varied in a wide range by varying the synthesis parameters. The possibilities of directly using composite track membranes for electron-microscopic imaging of the form and composition of nonconducting mineral and biological substances and for qualitative and quantitative size fractionation of microelements in natural water by ultrafiltration were demonstrated by the example of a series of macro- (C, Al, Si, Mg, Fe, P) and microelements (Sr, U, Th).

Combined method for obtaining ultradispersed powders of vanadium oxides and carbide

New opportunity to synthesize nano- and ultradispersed powdered materials by combining of two procedures, classical liquid-phase precipitation and low-temperature microwave calcination, at a rather simple instrumentation is described. It was found in precipitation of precursors that, depending on the synthesis conditions (solution pH, amount of carbon, synthesis on the vessel surface or in the solution bulk), particles of hydrated vanadium oxide have different morphologies. It was also found that precursor powders have an insignificant microporosity, which is preserved in the final products in trace amounts upon thermal treatment of samples. Intermediate and final vanadium products were synthesized in an electromagnetic field in a flow of argon, their phase composition and structure were examined in the stages of thermolysis, reduction, and carbidization, and their lattice constants were calculated. The morphology, size, and particle size distribution in the samples under study were determined.

Supersonic plasma and wear-resistant nickel alloy coatings

Original Russian Text

New plasma ceramic coatings

107 It is expedient to use plasma methods for deposit ing protective coatings containing refractory compo nents. Plasma generators for coating deposition are selected on the basis of the composition, dispersion of initial powders, and properties that should be imparted to the coating. Wide potentialities of modern plasma generators enable the deposition of microcomposites of different types and compositions.

Fire-polished coating-steel interface structure

An important aspect of producing coatings with gradientlayer structure is the interface between the sputtered layer and the base metal. Fire polishing of selffluxing alloys is a necessary stage of treatment of sputtered layers, which ensures high adhesion of the coating to the base material. In this context, it is perti� nent to study specific features of the interaction between the coating and base materials and to deter� mine the optimal parameters of heat treatment with the consideration of the effect of the transition zone on the physicomechanical and performance proper� ties of sputtered layers.

Dissolution of monazite in humic solutions

Physicochemical analysis shows that prolonged contact (15 days) of monazite powder with solutions containing humic acids (HA) of various acidities leads to an increase by 1–2 orders of magnitude in the dissolution of heavy p, d, and f elements present in monazite. The concentration of the dissolved elements depends on the initial content of HA in solution and on pH. These factors should be taken into account when using inorganic phosphates as matrices for long-term storage of radioactive and toxic elements.

Plasma-sprayed amorphous–crystalline coatings based on TiO2, SiO2, Al2O3, and ZrO2 oxides

The results of studies of composites based on TiO2, SiO2, Al2O3, and ZrO2 oxides used as conglomerated powders (microcomposites) and plasma-sprayed coatings made therefrom have been summarized. It has been shown that, for the first time in the practice of thermal spraying, high-density gradientamorphous–crystalline ceramic coatings reinforced with ultradispersed stishovite phases were obtained. Inclusions with amorphous shells were detected. The effect of the particle size and composition of the initial microcomposites on the phase composition of the sprayed layers was investigated.

Specific features of interface formation for metal-ceramic coatings on a steel base

Mechanism of pearlite formation in the base metal in melting of coatings based on self-fluxing alloys was studied. A zone in the form of a complex carboboride (Fe, Ni, Cr, Si) (BC) in the multilayer coating-steel interface was found and studied. The effect of pore space filling by needles of carboboride phases of the solid interlayer was revealed. It was shown that the coating composition and characteristics of strengthening additives (composition and dispersity) affect the structuring of the transition zone.

Reinforcement of metal-ceramic coatings in the course of their partial fusion

Factors and mechanisms responsible for the appearance of layered structures of variable cross section in protective coatings based on self-fluxing alloys were studied. A number of structural fragments of composite coatings based on safe-fluxing PG-10K-01 and PG-SR3 alloys (initial formulations and those reinforced with oxide ceramic particles), formed by sputtering in a plasma flux and then partially fused in a furnace, by a gas-oxygen flame, and with laser and electron beams, were revealed and studied. The relationships of the element distribution across the coating layer as a whole and in separate phases were determined. The effect exerted on the chemical composition and microhardness of coatings by the size, structure, and arrangement of inclusions in the coating cross section was demonstrated.