Features of the interaction of molecular oxygen with the condensation surface in the plasma of a low-pressure arc discharge

A model has been developed for studying the features of the thermal interaction of molecular oxygen in the near-surface condensation layer in the plasma of a low-pressure arc discharge. It was found that the input power and pressure of the gas mixture exert the main influence on the electron temperature and on the density of positive ions (O_2^+ and O+). It is shown that at a fixed pressure, the ion density increases with an increase in the power of the system, and vice versa.

Vacuum-arc synthesis of metal-organic framework structures based on ZrO2

The vacuum-arc synthesis of nanopowders based on zirconium oxide and metal-organic framework structures was carried out using a low-pressure arc discharge plasma. The obtained material was studied by several methods (XRF, IR, TEM, DTA). The TEM method showed that Zr-MOK is a highly agglomerated particle of an almost spherical shape. The image clearly shows the crystalline ordering of nanoparticles with a large (about 2 nm) lattice parameter. Particle sizes range from 5 to 30 nm. Average particle size 9.4 nm. XRD showed that the proportion of ZrO relative to Zr-MOK, calculated from the most intense lines of the diffractogram, is 65%. XRF results are in good agreement with IR studies. The DTA curve demonstrates a continuous exothermic process associated with a number of features of the plasma-chemical synthesis and morphology of the resulting nanoparticles, which is in full agreement with studies using transmission microscopy.

Ceramics based on powders synthesized from ammonium hydrophosphate and acetates of calcium and magnesium

Ceramics the phase composition of which included tricalcium phosphate, calcium magnesium ortophosphate and magnesium pyrophosphate has been produced from nanosized powders synthesized by chemical deposition from 1M aqueous solutions of ammonium hydrogen phosphate and calcium and / or magnesium acetates. According to XRD analysis the phase composition of the powder synthesized from calcium acetate included calcium hydroxyapatite Ca5(PO4)3(OH), octacalcium phosphate Ca8H2(PO4)6·5H2O and brushite CaHPO4·2H2O. The phase composition of the powder synthesized from magnesium acetate included struvite MgNH4PO4·6H2O. And the phase composition of the powder synthesized from solution containing calcium and magnesium acetates at the cation ratio Са: Mg = 9: 1 included hydroxyapatite Ca5(PO4)3(OH), whitlockite Ca18Mg2H2(PO4)14, and struvite MgNH4PO4·6H2O. Ceramic materials containing the bioresorbable and biocompatible phases of calcium and / or magnesium phosphates can be used to make bone implants for treatment of bone tissue defects. Keywords: tricalcium phosphate, calcium magnesium orthophosphate, magnesium pyrophosphate, whitlockite, octacalcium phosphate, hydroxyapatite, brushite, struvite, ceramics.

FEATURES OF STRUCTURE FORMATION IN NI-C, AL-C AND NI-AL-C SYSTEMS UNDER HIGH-TEMPERATURE HEATING

The high-temperature treatment of powder mixtures of Ni-C, Al-C and Ni-Al-C (5% wt C (soot)) has been carried out up to the melting temperature of the metals. It was found that melt particles coagulate with the formation of spherical particles of Ni, Al, and the intermetallic compound NiAl, respectively. Ni particles are characterized by the almost perfect spherical shape and a multilayer graphite coating. NiAl particles have a thin graphene (graphite) coating.

Plasma-chemical synthesis of YBa2Cu3O7–y / CuO granular composites

The possibility of synthesizing HTSC ceramics in the reaction chamber of a plasma-chemical reactor is shown. The method allows one to significantly reduce the process of solid-phase synthesis and obtain modified HTSC ceramics with a given content of non-superconducting additives that act as pinning centers.

Structure formation of alloys of tin — zinc system during high-rapid solidification

The results of a study of the structure parameters of rapidly solidified foil of a hypoeutectic, eutectic, hypereutectic Sn—Zn system alloys containing 4.4; 8.8 and 15 mas. % Zn are presented Rapidly solidified foil consists of equiaxed zinc particles and a supersaturated tin solid solution. Zinc particles are distributed uniformly in the foil, that is caused by the formation of a supercooled and supersaturated liquid solution and its subsequent spinodal decomposition. The areas of the liquid solution enriched with tin and zinc are transformed into nuclei of crystalline phases. With an increase in the zinc concentration in the studied alloys, the volume fraction of zinc particles, the average chord of random secant sections at the sections of zinc particles, and the specific surface of the interphase formed by zinc and tin increase. The foil of Sn—Zn alloys has a microcrystalline structure in which the predominant grain orientation is observed. The formation of the texture of (100) tin and (0001) zinc occurs. Rapidly solidified alloy foils are in an unstable state, that results in the decomposition of a tin solid solution, the dissolution of small particles and the growth of large particles. Annealing at 180 °C for 22 hours causes an increase in the average chord of sections of zinc particles, volume of zinc particles and a decrease in the specific surface of the interface.

Investigation of structure and properties of elemental carbon fibers with metal coating

Four types of metal coatings made of stainless steel, silver, titanium and copper were deposited on the surface of unidirectional carbon tape by the magnetron sputtering technology. The experimental evaluation results of strength of elemental carbon fibers with the metal coatings and strength of carbon-filled plastics based on them during the interlaminar displacement are presented. When producing the carbon-filled plastics an epoxy binder and the vacuum infusion technology were used. It has been found out that all the used metal coatings lead to an increase in strength of the carbon-filled plastics during the interlaminar displacement. The carbon tape with the stainless steel coating has the highest strength increase (by 50%). However, during long-term storage, the coating effectiveness of the metalized carbon tapes decreases.

Thermochemical synthesis of tribotechnical coatings based on molybdenum diselenide MoSe2 on structural steels

The study results of the influence of parameters of the process of chemical-thermal treatment in selenium vapor during the preparation of solid lubricating coatings from molybdenum diselenide on specimens of structural steels with a plasma Mo-coating are presented. An empirical mathematical model of the temperature-time parameters of the Mo selenization process is proposed, which makes possible to control the quality of the obtained coatings depending on requirements for their tribotechnical properties. An assessment of their tribotechnical characteristics in air and in vacuum in the temperature range 20—600 °С has been carried out.