A Method of Predicting the Elastic Characteristics of Diamond Composites

A model is considered for a representative cell, which is based on structural research on a particular composite, which consists of relatively large diamond single crystals in a relatively fine-grained SiC matrix; the elastic constants are calculated from an asymptotic averaging method.     

Optical–microphysical properties of smoke haze from Siberian forest fires in summer 2012

A comprehensive experiment on the study of dynamics of optical and microphysical characteristics of submicron aerosols in the near-ground air layer was carried out in June–August of 2012 under conditions of extremely strong smoke haze originating from vast forest fires in Siberia. Variations of the spectral angular scattering coefficients and the degree of linear polarization in the visible wavelength range are studied, as well as the mass concentrations of dry fractions of aerosol and black carbon, relative content of black carbon (BC fraction), single scattering albedo, particle size distribution function, complex refractive index of the particulate matter, and parameter of condensation activity of aerosol. Peculiarities of differences between optical and microphysical characteristics of near-ground aerosol in smoke haze and under smokeless conditions are revealed. This study is important for validation of results of remote sensing of the composition of smoke haze and background atmosphere obtained from satellite data and sun photometric measurements at the Aerosol Robotic Network (AERONET).     

Reversible Hydriding of LaNi5 − xAlx ― Pd Composites in the Presence of Carbon Monoxide

Carbon monoxide is one of the most dangerous impurities in gas mixtures involved in the hydriding of intermetallic compounds, and up to the present time the concentration limit 0.03 vol.% CO has not been surmounted. The objective of the present work was to investigate the possibility of reversibly hydriding LaNi_{5 − x} Al _x ― Pd composites in gas mixtures containing up to 5 vol.% CO. The experimental specimens were mixtures of palladium black and LaNi₅, LaNi_4.7Al_0.3, LaNi_4.5Al_0.5, LaNi_4.2Al_0.8, and LaNi₄Al powders cold pressed at 300 MPa. The intermetallics were preliminarily dispersed by hydriding and mechanical grinding. The concentration of palladium black in the powder mixtures was varied from 0 to 1.5 mass%. It was shown that it is possible to reversibly hydride LaNi_{5 − x} Al _x ― Pd composites in mixtures of hydrogen and carbon monoxide containing up to 5 vol.% CO at the temperatures 423 and 473 K. It was established that alloying LaNi₅ with aluminum in amounts which raised the stoichiometric concentration above 0.5 stabilized the absorption properties of LaNi_{5 − x} Al _x ― Pd in the presence of CO. The composition LaNi₄Al was optimal. Palladium additions to LaNi_{5 − x} Al _x ― Pd composites also increased the stability of hydrogen absorption by the intermetallic. It is noted that the effect of palladium was more positive than that of aluminum.

     

考虑轮齿修形的变厚齿轮啮合刚度数值计算

针对有限元法求解变厚齿轮时变啮合刚度的求解效率低、计算结果易不收敛等问题,基于切片法建立了一种考虑齿向修形的变厚齿轮时变啮合刚度求解模型,在综合考虑齿轮基圆与齿根圆之间关系的基础上,对现有的Weber能量法进行改进,并采用该方法计算了变厚齿轮的时变啮合刚度。通过建立变厚齿轮有限元分析模型,对其进行加载接触分析,计算其啮合刚度,并与所提方法进行比较,结果表明,所提方法可以有效提高计算精度,提升计算效率。在此基础上,采用集中参数法分析了变厚齿轮不同啮合参数和修形参数对时变啮合刚度的影响规律,为变厚齿轮的结构优化设计和系统动力学分析奠定了基础。     

High-Velocity Flame Spraying of Powder Aluminum Protective Coatings

Requirements to industrial processes for the thermal spraying of corrosion-resistant metal coatings on large-scale steel structures are formulated. The promise of high-velocity fuel·air flame spraying for this application is described. Regimes for the deposition of protective aluminum coatings by this process and their adherence characteristics were investigated. Metallographic studies including computer treatment of images of polished cross sections were carried out with the aid of the materials science software SIAMS.     

Compaction Kinetics with Liquid-Phase Sintering of W – Ni – Sn Pseudoalloys

A kinetic equation for compaction with liquid-phase sintering is found on the basis of rheological sintering theory. Kinetic coefficients of the equation are determined from physicochemical properties of a dispersed system and its components. Compaction kinetics are studied for the system W – Ni – Sn where the liquid phase is eutectic alloy Ni – Sn with the greatest nickel content. It is shown that experimental results are in good agreement with those obtained by the kinetic equation on the coordinates porosity – time. Diffusion coefficient is evaluated for tungsten in melt (67.5 mass% Ni + 32.5 mass% Sn): at 1200°C it is 0.113·10_–5 cm₂/sec for grain diameter L ₀ = 3 μm. Time dependences are also obtained for the compaction rate and viscosity of the pseudoalloys studied.     

Synthesis of high-surface-area complex zirconium phosphates via mechanochemical activation route

 High-power ball mill activation of the mixture of hydrated zirconium and lanthanum salts (oxonitrates, oxochlorides) with ammonium phosphate followed by hydrothermal treatment at temperatures not exceeding 200°C and a nearly neutral pH was found to yield crystalline dispersed phase of a cubic NH₄Zr₂(PO₄)₃ type along with admixtures of disordered orthorhombic compounds of a zirconium orthophosphate type. In the same conditions and at the same Zr/P ratio, hydrothermal treatment of gels obtained by reacting mixed zirconium and lanthanum nitrates solutions with ammonium phosphates yields no crystalline products, and only treatment in acid media generates a phase of the α-ZrPO₄(OH) type coexisting with the NH₄Zr₂(PO₄)₃ phase if polyethylene oxide is present. X-ray powder diffraction, transmission electron microscopy, ³¹MAS-NMR, FTIRS and thermal analysis were applied to elucidate factors affecting crystallization of complex zirconium phosphates in the hydrothermal conditions. The most essential factor appears to be generation of some nuclei of zirconium phosphates under high pressures developed in the course of mixed solids mechanical activation. These nuclei are embedded into matrix of such well-crystallized solid products as ammonium nitrate or chloride. Hence, metastable cubic or orthorhombic structure of the phases obtained via mechanical activation route can be assigned to the nuclei-matrix orientation relationship. Due to easily scaled-up synthesis procedure, these results appear to be very promising for manufacturing of dispersed framework zirconium phosphates as acid catalysts or fast proton conductors. Received: 18 November 1998 / Reviewed and accepted: 2 December 1998     

Reaction of Tungsten with Liquid Co ― Sn Alloys

The solubility of tungsten in Co Sn melts and the growth kinetics of a W₆Co₇ phase layer at the tungsten melt interface were studied at 1200°C. The liquid alloys composition in the three-phase equilibrium W W₆Co₇ melt was established as (at. fraction) 0.51 Co, 0.49 Sn, 2.3·10^–3 W. The solubility of tungsten in the investigated range of melt compositions is well represented by the equation lgx _W = –0.964-3.420x _Sn, where x _W and x _Sn are atomic fractions of the elements in the melt. The calculated thermodynamic properties can be used for the analysis of other systems which include cobalt and tungsten.     

Synergistic Effect in Selective Reduction of NO by Alkanes over Mechanically Mixed Oxide Catalysts

The process of selective catalytic reduction of nitrogen oxides by propane in the presence of O₂, as well as in the presence or absence of CO, was studied over series of commercial oxide catalysts used in petrochemical processes. For the first time synergistic effect was observed for catalytic systems consisting of mechanical mixtures of Cu–Zn–Ni–Al (catalyst I) + Fe–Cr (catalyst II) and Cu–Zn–Ni–Al (catalyst I) + Ni–Cr (catalyst III). The activity of these mixtures in nitrogen oxides reduction by propane was greater than that of individual components in each case. The worked-out catalytical systems showed high effectivity in the process of simultaneous removal of several toxic components: NO _x , CO, hydrocarbons – from model gas mixtures, as well as from real exhausts of automotive transport.