Ultimate length and capacity of production heading with regard to gas content,considering nonuniform air flow

Procedures for calculating permissible length and capacity of a fully mechanized production heading with regard to gas content and considering nonuniform air flow across and along longwall are described. Nonlinear relations are derived for methane concentrations and air leakage into mined-out area. It is proposed to assess a production heading capacity based on the gas-related permissible length of the heading and the coal cutting chart with a shearer. It is found that the increased gas content of coal and higher air leakage into mined-out area results in reduction of gas-related length and capacity of production headings.     

Brush-Wear Reduction in High-Altitude Direct-Current Motors

The factors of increased wear of current-carrying brushes in direct-current motors designed for high-altitude operation are considered. The results of testing six motors with different degrees of airtightness are presented. It is found out that increased airtightness makes the lacquer film less resistive (thinner) and increases the brush wear. A method of decreasing the wear of current-carrying brushes at standard and high altitudes is proposed that consists in installing a DMS-140 molybdenum disulfide lubricating brush. The lubricating brush is installed in an auxiliary brush holder or in a pocket structurally connected with the current-carrying brush holder on the header runway. The effect of the collector profile material (copper, cadmium bronze, chromium bronze) on the wear of current-carrying brushes is studied, as well as the efficiency of installing lubricating brushes for standard and high-altitude operations. The effect of lubricating brushes on the performance of a 5-W motor is considered as well as the results of testing seven 5-W motors equipped with lubricating brushes in conformity with the machine and warranty service specifications. Information is given on the results of long-term storage (for 1 and 1.9 years) of four motors with different capacities equipped with lubricating brushes, as well as in thermal vacuum tests of 10-W motors under p = 10^–5–10^–6 mm Hg.     

Anisotropy of Wetting and Spreading in Binary Cu-Pb Metallic System: Experimental Facts and MD Modeling

Contact angle for millimeter-size drops of lead on {100} and {110} surfaces of monocrystalline copper and on polycrystalline copper was determined by means of dispensed drop technique at 450 °C under He-H₂ atmosphere. It was demonstrated that the wetting anisotropy (a difference between contact angles on differently oriented substrates) is not exceed a few degrees. Spreading kinetics was found to be different for the first and second drops deposited on each substrate. This result was interpreted as an effect of a lead precursor film formation on the substrate surface. Molecular dynamics simulations of the lead drop spreading over {111}, {100}, and {110} surfaces of monocrystalline copper confirm the weak anisotropy of equilibrium contact angle and a formation of lead precursor film on copper surface in front of wetting line.     

Photoluminescence of erbium ions in heterostructures with silicon nanocrystals

Photoluminescence properties of erbium-doped silicon dioxide layers containing silicon nanocrystals with 1.5–4.5 nm average size are investigated. It is found that the intensity and mean lifetime of the Er³⁺-ion photoluminescence depend on the nanocrystal size, optical pump intensity, and temperature. The results obtained are explained both by the effect of the local environment on Er³⁺ ions and by the manifestation of nonradiative deexcitation of ions caused by the transfer of energy back into the solid-state matrix and the Auger processes.     

New biodegradable antifriction grease

The paper presents the composition and the process of production of the new grease containing exclusively environmentally safe biodegradable components such as rape oil, vegetable oil tar, inedible fat as well as natural and artificial silicates. The grease is operable within 0–160°C and intended for friction units of light and food industry equipment.     

Kinetics of scattered fracture in structural metals under elastoplastic deformation

The paper presents a procedure whereby the damage accumulation kinetics in structural materials, such as steel 45, stainless steel 12Kh18N10T, aluminum alloy D16T, and titanium alloy VT22, under elastoplastic deformation is studied based on variation parameters of elastic modulus and resistivity. For complex stress conditions, a continuum model for damage accumulation is proposed which relates the damage parameter to the intensity of accumulated plastic strains. The data calculated by the proposed continuum model are compared to the experimental findings of the investigation of the damage accumulation kinetics for some structural metals. __________ Translated from Problemy Prochnosti, No. 3, pp. 23–34, May–June, 2007.     

A mixture of tris(propenyl)phosphinoxides: A new effective collector reagent for copper-nickel ore flotation

The properties of a new collector reagent (SF-239) based on a mixture of tris(propenyl)phosphinoxides have been studied with respect to the flotation of copper-nickel ores. For the flotation of chalcopyritecubanite ores, the new collector gives a 1.82% increase in copper yield into the concentrate as compared to a butyl aeroflot collector.     

Calcinated hydrotalcite—a sorbent for purifying uraniferous waters

The Mg-, Al sorbent with a structure of hydrotalcite Mg₄Al₂(OH)₁₂ · CO₃ · nH₂O was synthesized and its thermoactivated form Mg₄Al₂O₇ was investigated in sorption processes. Physicochemical investigations demonstrated that the resultant sorbent (Mg₄Al₂O₇) displays high sorption selectivity with respect to anionic forms of U(VI). Complexation ligands characteristic of natural and waste waters virtually do not affect sorption of U(VI). Based on sorption isotherms we calculated static and dynamic exchange capacities of the Mg-, Al-sorbent by U(VI). The demonstrated results make it possible to recommend the obtained sorbent for efficient removal of anionic forms of uranium from aqueous media.     

Photoluminescence properties of cadmium-selenide quantum dots embedded in a liquid-crystal polymer matrix

The photoluminescence properties of cadmium-selenide (CdSe) quantum dots with an average size of ～3 nm, embedded in a liquid-crystal polymer matrix are studied. It was found that an increase in the quantum-dot concentration results in modification of the intrinsic (exciton) photoluminescence spectrum in the range 500–600 nm and a nonmonotonic change in its intensity. Time-resolved measurements show the biexponential decay of the photoluminescence intensity with various ratios of fast and slow components depending on the quantum-dot concentration. In this case, the characteristic lifetimes of exciton photoluminescence are 5–10 and 35–50 ns for the fast and slow components, respectively, which is much shorter than the times for colloidal CdSe quantum dots of the same size. The observed features of the photoluminescence spectra and kinetics are explained by the effects of light reabsorption, energy transfer from quantum dots to the liquid-crystal polymer matrix, and the effect of the electronic states at the CdSe/(liquid crystal) interface.     

Preparation of blast-furnace Coke at PAO AKKhZ. Part 1

The preparation of blast-furnace coke in coke shop 1 at PAO Avdeevskii Koksokhimicheskii Zavod (AKKhZ) is analyzed. The content of the >80 mm class cannot be reduced to the required values without special crushing equipment. Initial data for the selection and design of screening and crushing equipment are obtained. On that basis, the coke-preparation system in coke shop 1 is reconstructed.