Influence of the gas composition on the electron transport coefficients in helium-based gas mixtures

For several helium–isobutane and helium–methane gas mixtures the drift velocity and the longitudinal and transversal diffusion coefficients have been measured with a time of flight method using single-drift electrons. The influence of the hydrocarbon, water and nitrogen content in the gas mixture on the transport coefficients was studied in detail for concentrations typical for the operation of drift chambers.     

Effect of nonlinearity of gas mixtures on the process of their partition by thermal diffusion

Under consideration is the effect of nonideality of the components in a gas mixture on the process of their separation by thermal diffusion. It is demonstrated that in the expressions for the heat flux and the mass flux, the thermodiffusion ratio and the characteristic of diffusional thermal conductivity the effect of nonideality appears in the heat of mixing.Notation p pressure - density - length of the mean free path for molecules during transport of particles - length of the mean free path for particles during a transfer of the mean velocity - n molecule concentration - M molecular weight - I particle flux - J mass flux - m mass of a molecule - t time - D_ij coefficient of interdiffusion for a binary mixture - D _i ^T coefficient of thermal diffusion - K_T thermodiffusion ratio - _T thermodiffusion constant - x_i molar fraction of the i-th component in the mixture (r), intermolecular interaction potential - r intermolecular distance - collision integrals - T temperature - T^* referred temperature - R universal gas constant - k Boltzmann constant - Ñ Avogadro's number - v mean velocity of molecules - ¯V diffusion rate - _{i, trans} thermal conductivity associated with translatory degrees of freedom - f_i(r, v, t) velocity distribution function of molecules - viscosity - _i chemical potential of the i-th component - c_i mass fraction - _o thermal conductivity at the initial instant of time - thermal conductivity in the steady state - _DT diffusional component of thermal conductivity - g and h molar thermodynamic functions - ¯g and ¯h specific thermodynamic functions - c_p specific heat - J_q heat flux - J_q reduced heat flux - B second virial coefficient - U^* transport energy - coefficient of thermal expansion - coefficient of isothermal compression - f_i activity coefficient for the i-th mixture component Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 829–839, May, 1981.     

ZrC-C包晶固定点研制及评价

ZrC-C包晶固定点因其极高的名义相变温度(2882℃),超出了绝大多数高温加热炉的使用上限.通过改进自行设计的HT271型加热炉,使其工作温度上限提高到2900℃以上,满足了ZrC-C包晶固定点的使用要求.采用ZrC粉末和C粉末配置混合粉末,进行了ZrC-C包晶固定点的灌注和复现试验,共得到2组复现循环数据,其中第1...     

The process window for diamond deposition from the vapor phase with sulfur in the C–H–O feed gas mixtures

Theoretical predictions using a modified radical species ternary diagram for C–H–O system indicate that addition of sulfur expands the C–H–O gas phase compositional window for diamond deposition. Sulfur addition to no-growth domain increases the carbon super-saturation by binding the oxygen and the addition of sulfur to the non-diamond domain reduces the heavy carbon super-saturation by decreasing C_nH_m species concentration in the gas phase. The overall effect of sulfur addition to gas phase mixtures is characterized as that of oxygen addition to the C–H system, i.e. expansion of the compositional window over which diamond can be deposited from the gas phase. In addition, the increasing sulfur concentration to diamond domain feed gases beyond 2000 ppm did not affect the steady state gas phase composition but the quality of diamond was reduced.     

Influence of composition and process parameters on the thermal spray deposition of UHMWPE coatings

Ultra-high molecular weight polyethylene (UHMWPE) has remarkable properties in the bulk state and has substantial potential for use as a protective coating on metals. However, the molecular architecture responsible for these exceptional properties also causes difficulties in the formation of coatings by thermal spraying. This paper studies the effect of molecular weight, particle size and the influence of the addition of low-molecular weight binders on the structure and properties of combustion flame sprayed coatings. The flow of splats for each UHMWPE polymer and blends of selected polyethylenes was characterized by microstructural analysis and the performance of the resulting coatings evaluated by mechanical testing. A computational model was developed to calculate the temperature profiles of in-flight particles and to simulate the behaviour of particles during deposition. The model was applied to the polyethylene system and the experimental results show that the composition, the particle size and the process parameters are important factors in the optimization of coating quality.     

Safe growth of graphene from non-flammable gas mixtures via chemical vapor deposition

Chemical vapor deposition has emerged as the most promising technique for the growth of graphene.However, most reports of this technique use either flammable or explosive gases, which bring safety concerns and extra costs to manage risk factors. In this article, we demonstrate that continuous monolayer graphene can be synthesized via chemical vapor deposition technique on Cu foils using industrially safe gas mixtures. Important factors, including the appropriate ratio of hydrogen flow and carbon precursor,pressure, and growth time are considered to obtain graphene films. Optical measurements and electrical transport measurements indicate graphene films are with comparable quality to other reports. Such continuous large area graphene can be synthesized under non-flammable and non-explosive conditions, which opens a safe and economical method for mass production of graphene. It is thereby beneficial for integration of graphene into semiconductor electronics.     

Effect of nitrogen on diamond growth using unconventional gas mixtures

The influence of nitrogen on the growth of diamond using unconventional gas mixtures of CH₄---CO₂ by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH₄-CO₂ gas mixtures. However, most interestingly, for lower methane concentration, the addition of small amounts of nitrogen resulted in the formation of isolated diamond particles possessing a vacant “cage-like” structure with completed {100} facets This result indicates that the continued addition of nitrogen gives rise to the deterioration of {111} facets and the retention of {100} facets. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Although the amount of atomic hydrogen in the ground state decreased and CN radicals increased with increasing amounts of added nitrogen, good-quality diamond films were deposited resulting from a larger amount of atomic oxygen and the decrease in the C₂ emissions in the gas phase under optimum conditions.     

非共沸混合制冷剂组分对冷凝器换热特性的影响

为了揭示非共沸混合工质在冷凝器内的换热特性,探明非共沸混合工质组分对制冷剂和换热流体间沿程温度的影响,通过建立冷凝器换热模型,对不同沸点差的二元环保型非共沸混合工质进行了理论分析.结果表明:由于非共沸混合工质比焓值与温度的非线性关系,换热流体间的沿程传热温差出现极值点;混合工质中富含低沸点组分时,冷凝器内部存在最小传热温差;反之,存在最大传热温差;混合工质沸点差增加,滑移温度的限制条件之差增大,窄点现象增强.     

Effect of polyurethane composition and the fabrication process on scaffold properties

The microdomain structure of polyurethanes (PUR) determines their unique physical properties and makes polyurethanes attractive candidates for various tissue engineering applications. 3D scaffolds based on polyurethanes with different contents of hard segments were fabricated by a salt-leaching/polymer coagulation method. The process parameters were carefully considered, particularly the polymer solution concentration and characteristics of the polyurethane, which are the critical parameters for the control of porosity and pore size distribution. In this study, 3D polyurethane scaffolds were fabricated with interconnected pores and porosity from 64% to 80%. Pore size distribution was evaluated using quantitative image analysis and mercury intrusion porosimetry (MIP). The scaffolds fabricated from polyurethanes with 70 wt.% of hard-domain content were found to have the best compression properties.     

The prediction of the viscosity of dense gas mixtures

An extension of an earlier procedure for the evaluation of the viscosity of very dense gas mixtures is proposed. The scheme is based upon the rigid-sphere theory of dense fluids, which is modified to take into account the behavior of real gases in a self-consistent manner. In particular, it is shown that a pseudoradial distribution function for each pure gas constructed from pure component viscosity data is a smooth function of density and is well behaved in limits of both high and low density. The method proposed removes the restrictions on the range of applicability of earlier methods. Comparisons with the limited amount of experimental information available indicate that the procedure allows evaluation of the viscosity of gas mixtures to within a few percent.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Effect of longitudinal diffusion on separation of gas mixtures using semipermeable membranes

Flow of a binary gas mixture in a cylindrical channel is studied considering presence of longitudinal diffusion fluxes of the components, as occurs in separation of gas mixtures using semipermeable membranes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 916–924, December, 1986.     

Effect of heats of chemical reactions on turbulence in homogeneous gas mixtures

The effect of the heats of chemical reactions on the turbulence in a turbulent gas flow is considered. An example of the application of the obtained results to a dissociating polyatomic gas is given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 4, pp. 648–654, October, 1969.     

Effect of the composition of mineral and organomineral mixtures on the tribological properties of friction pairs

We have studied the tribological properties of friction pairs of chromium-plated steel parts after processing with geomaterials: serpentinite, a natural silicate, a mixture of serpentinite and the silicate, a polysaccharide-modified natural silicate, and a mixture of serpentine and the polysaccharide-modified silicate. The abrasive used was quartz dust ranging in particle size from 1 to 5 μm, whose concentration reached 1%. The mixtures were shown to be highly effective in producing composite coatings on friction surfaces of parts. The incorporation of the polysaccharide-modified silicate into a friction joint considerably reduces its coefficient of friction and, as a consequence, the energy level of contact interaction.     

Effect of elemental composition on phase formation during milling of multicomponent equiatomic mixtures

Using mechanochemical synthesis through milling of equiatomic multicomponent mixtures of Cr, Fe, Co, Ni, Al, Ti, Mo, and Nb metals in various combinations, we have synthesized powder alloys with different phase compositions: amorphous phase (AP), AP + BCC phase, AP + BCC phase + MO, and FCC + BCC phases. The FCC phase has been shown to be a Ni-based solid solution. The presence of aluminum in a starting mixture helps to stabilize the BCC phase owing to the formation of a disordered B2 phase. Al dissolves in both the BCC and FCC solid solutions, increasing their lattice parameters. In Al-free starting mixtures, Cr is responsible for the formation of the BCC solid solution. The formation of an AP during milling of multicomponent mixtures is favored by the presence of transition metals with a large atomic radius: Ti, Mo, and Nb.     

溅射工艺参数对BaAl2S4薄膜沉积速率、化学组成及电致发光特性的影响

BaAl2S4:Eu发光薄膜是最有希望实现彩色无机电致发光显示器的蓝色电致发光材料.用射频磁控溅射法制备了厚度在150～375nm之间的BaAl2S4:Eu薄膜,研究了溅射功率、Ar/H2S流量比和气压对其沉积速率和化学组成的影响,考察了不同退火条件下BaAl2S4:Eu薄膜的电致发光特性.并根据这些结果分析了较优的工艺条件.