SiON/SiO2复合膜层对太阳能电池阵板间电缆的表面改性及其耐空间环境性能

在空间站工作的太阳电池阵板间电缆上下表面为聚酰亚胺薄膜,在低轨运行时会受到原子氧的强烈侵蚀,需要采取措施对其进行保护。采用射频磁控溅射法在电缆表面制备了颗粒尺寸均匀、排列致密的SiO₂膜层。通过表征空间环境试验前后样品发现由于电缆表面的凸起颗粒等缺陷无法完全被SiO₂膜层覆盖,导致原子氧会对缺陷位置产生侵蚀作用。采用全氢聚硅氮烷溶液对板间电缆基底进行表面改性处理,制备的聚硅氧氮烷涂层（SiON）可以有效地覆盖电缆基底表面的凸起颗粒等缺陷,使得其上溅射的SiO₂膜层表面光滑平整。经原子氧暴露试验,SiON/SiO₂层内部没有受到其侵蚀作用,可以防止原子氧对电缆基底的破坏。经多次冷热循环试验,SiON/SiO₂复合膜层仍然具备良好的结构特性与结合性能。     

Peculiarities of vacuum annealing of nanocrystalline WC powders

The effect of vacuum annealing temperature on the phase and chemical composition, particle size, and microstrains of nanocrystalline powders of tungsten carbide WC with particles from 20 to 60 nm in size has been studied using X-ray diffraction and electron microscopy methods. It is established that nanocrystalline WC powders stored in air, contain from 1 to 2 wt.% of impurity oxygen. It is found that vacuum annealing of WC nanopowders at a temperature up to 1400 °C is accompanied by appreciable decarburization and variation in the phase composition due to carbon desorption as a result of interaction with impurity oxygen. Annealing leads to coarsening of powder particles caused by intergrowth of aggregated nanoparticles and to decreasing microstrains.     

Numerical Study of Suspension HVOF Spray and Particle Behavior Near Flat and Cylindrical Substrates

In thermal spray processes, it is demonstrated that substrate shape and location have significant effects on particle in-flight behavior and coatings quality. In the present work, the suspension high-velocity oxygen fuel (HVOF) spraying process is modeled using a three-dimensional two-way coupled Eulerian–Lagrangian approach. Flat and cylindrical substrates are placed at different standoff distances, and particles characteristics near the substrates and upon impact are studied. Suspension is a mixture of ethanol, ethylene glycol, and mullite solid powder (3Al₂O₃·2SiO₂) in this study. Suspension droplets with predefined size distribution are injected into the combustion chamber, and the droplet breakup phenomenon is simulated using Taylor analogy breakup model. Furthermore, the eddy dissipation model is used to model the premixed combustion of oxygen–propylene, and non-premixed combustion of oxygen–ethanol and oxygen–ethylene glycol. To simulate the gas phase turbulence, the realizable k–ε model is applied. In addition, as soon as the breakup and combustion phenomena are completed, the solid/molten mullite particles are tracked through the domain. It is shown that as the standoff distance increases the particle temperature and velocity decrease and the particle trajectory deviation becomes more significant. The effect of stagnation region on the particle velocity and temperature is also discussed in detail. The catch rate, which is defined as the ratio of the mass of landed particles to injected particles, is calculated for different substrate shapes and standoff distances in this study. The numerical results presented here is consistent with the experimental data in the literature for the same operating conditions.     

Optimal design of a novel cold spray gun nozzle at a limited space

Numerical analysis for the accelerating behavior of spray particles in cold spraying is conducted using a computational fluid dynamics program, FLUENT. The optimal design of the spray gun nozzle is achieved based on simulation results to solve the problem of coating for the limited inner wall of a small cylinder or pipe. It is found that the nozzle expansion ratio, particle size, accelerating gas type, operating pressure, and temperature are main factors influencing the accelerating behavior of spray particles in a limited space. The experimental results using the designed short nozzle with a whole gun length of <70 mm confirmed the feasibility of optimal design for a spray gun nozzle used in a limited space.     

Flash smelting copper concentrates

Flash smelting is a comparatively new method of smelting copper and nickel sulfide concentrates. It takes place when the concentrate, with or without additional fuel, is suspended in gases containing oxygen whereby the heat of oxidation reactions bring the suspended particles to a smelting temperature. From the suspended state the hot particles are separated and molten slag and matte are deposited on the furnace hearth.     

Investigations of the nickel promotional effect on the reduction and sintering of tungsten compounds

In this article, Ni-coated W powders were firstly prepared by a liquid-solid doping method combined with air calcination and hydrogen reduction. X-ray diffraction analysis, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and temperature programmed reduction analysis were carried out to investigate the nickel doping process in WO₃ and its influence on the reduction behaviors of tungsten oxides. It reveals that after calcinations most Ni ions would occupy the lattice sites of host W ions and decrease the interplanar spacing of WO₃. The latter is due to the promotion of oxygen vacancy generation within WO₃ rather than the changes in ionic radius. After hydrogen reduction, the doped Ni atoms precipitate onto the surface of W particles as thin metallic coatings, whereby the size and morphology of reduced W particles are varied greatly with increasing Ni addition. The presence of Ni has also been found to lower the reduction barriers for WO₃ by using first-principles calculation. Finally, W-Ni compacts were sintered at 1500 °C in hydrogen atmosphere and the accelerated densification phenomenon of W alloy upon Ni doping is discussed.     

线材表面红色浮锈成因分析及控制措施

针对线材产品表面红色浮锈问题,根据实际生产不同规格、不同钢种线材表面红色浮锈的宏观特征,统计分析了产品规格、轧制速度、终轧温度、吐丝温度、冷却水水质等工艺参数对成品线材表面红色浮锈的影响。分析得出：红色浮锈并非由后续三次氧化铁皮演变而成,是线材表面附着的氧化铁皮微粒在高温下与水和氧气的反应产物。工艺参数对线材表面红色浮锈影响的实质是影响线材表面氧化铁皮微粒与水和氧气反应的外部条件。因此,需要在减少反应物数量、减少反应时间、降低反应温度、减弱冷却水中带电离子的催化作用等方面对生产工艺进行改进。提出了通过增加二次氧化铁皮吹扫装置、改善冷却水水质、在冷却水中加入药剂以中和带电离子,以及优化轧制过程温度制度等措施来减少线材表面红色浮锈。     

亚微米SiC粉体的氧化过程

从热力学和动力学角度研究了亚微米级SiC粉体的氧化过程 ,结果表明 :当温度低于 80 0℃ ,亚微米级的SiC粉体很难在空气中氧化 ;但在较高温度下 (90 0～ 12 0 0℃ )极易氧化 ,且服从抛物线速度方程 ,受氧气通过SiO2 氧化膜的内扩散控制 ,反应的平均表观活化能为 143.4kJ/mol。     

Examination of the critical velocity for deposition of particles in cold spraying

The critical velocity of copper (Cu) particles for deposition in cold spraying was estimated both experimentally and theoretically. An experimental method is proposed to measure the critical velocity based on the theoretical relationship between deposition efficiency and critical velocity at different spray angles. A numerical simulation of particle impact deformation is used to estmate the critical velocity. The theoretical estimation is based on the critical velocity corresponding to the particle velocity at which impact begins to cause adiabatic shear instability. The experimental deposition was conducted using Cu particles of different particle sizes, velocities, oxygen contents, and temperatures. The dependency of the critical velocity on particle temperature was examined. Results show that the critical velocity can be reasonably measured by the proposed test method, which detects the change of critical velocity with particle temperature and oxygen content. The Cu particles of oxygen content 0.01 wt.% yielded a critical velocity of about 327 m/s. Experiments show that the oxygen content of powder significantly influences the critical velocity. Variations in oxygen content can explain the large discrepancies in critical velocity that have been reported by different investigators. Critical velocity is also found to be influenced by particle temperature as well as types of materials. High particle temperature causes a decrease in critical velocity. This effect is attributed to the thermal softening at elevated temperatures. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

The internal oxidation of Nb-Hf alloys

The internal oxidation of some binary Nb-Hf and several commercial Nb alloys containing Hf was studied at 1568 and 1755°C in oxygen pressures ranging from 5×10 ^–5 to 1×10^–3 torr.The reaction kinetics were linear, suggesting that diffusion of oxygen in the substrate was not rate-controlling. The dependence of the reaction rate on oxygen pressure was linear also. Well-defined reaction fronts were observed at higher pressures and the lower temperature, whereas ill-defined fronts occurred at lower pressures and at the higher temperature. The solubility product was much higher than normally encountered in Wagnerian-type behavior and gave rise to varying solute content across the internal-reaction zone. The solute-concentration profiles (EPMA/WDS) of the matrix between particles exhibited a sigmoidal shape for well-defined reaction fronts, whereas the profiles showed a gradual decrease in solute with distance near the front for ill-defined fronts, dropping fairly abruptly at the metal/gas interface. The solute concentration never reached zero at the surface for any condition studied. In contrast to classical, Wagnerian behavior, solute continued to precipitate out after the reaction zone had passed, leading to a variation in the mole fraction of oxide in the zone. SEM/EDXA and XRD showed that precipitation occurred by the formation of precursors (Hf-rich regions surrounded by Hf-depleted regions), followed by precipitation of tetragonalHfO₂,which in some cases transformed to monoclinicHfO₂ and subsequently coarsened. The precipitate morphology varied with solute concentration, temperature, oxygen pressure, and location within the reaction zone. High temperature and high oxygen pressure favored a Widmanstätten structure, whereas low temperature and low oxygen pressure favored a spheroidal precipitate structure. Widmanstätten plates were observed to spheroidize at longer times, suggesting that the interfacial energy between particles and matrix was very high. The presence of a small amount of Y (0.11 w/o in C129) always resulted in spheroidal particles. It appears that Y markedly increased the particle/matrix interfacial energy. Microhardness profiles showed decreasing values with distance into the sample for some conditions and alloys but increasing values in other cases. Hardness increases in the substrate in advance of the interface showed that oxygen activity did not reach zero at the reaction front, once again contrary to classical behavior but consistent with high solubility products of the oxide. Results are analyzed in terms of oxygen-trapping by reactive solutes as noted in the literature for both lattice-parameter measurements and oxygen diffusivity studies.     

Energy transformation in water and oxygen-containing electrolytes

The conductivity of distilled water and dilute electrolyte solutions in the presence and absence of dissolved oxygen is studied. It is found that the circuit can be implemented with equal probability as a capacitive circuit with physically different current carriers and as an inductive circuit in water and dilute aqueous solutions of oxygen-containing electrolytes. The occurrence of an inductive resistance is caused by the presence of particles with intrinsic magnetic moment, i.e., reactive oxygen species. The frequency ranges of possible pulse energy transformation in an electrochemical system that contains oxygenated water are shown. In the absence of oxygen, this circuit is not implemented.     

Behavior of Pearlitic Steels in Oxygen Containing Water

The corrosion behavior of steels in oxygen-containing water is considered. It depends on the oxygen concentration, water flow velocity, temperature, the presence of corrosive impurities, and the physico-chemical state of the metal surface. Insignificant changes in the parameters listed above favor the transition of steel into the active state. Under the conditions of neutral oxygen water operation (NOWO), the preliminary oxidation of steels allows one to make their protection more effective in several cases, namely, in an initial service period of the power plant, when the temperature of water heat carrier decreases; for heat carriers of lower quality; and for aqueous heat carriers with lowered oxygen concentration limits. Under adverse conditions of NOWO (during shut-downs of power units), potassium (sodium) nitrite should be introduced in place of oxygen.     

Influence of Spray Materials and Their Surface Oxidation on the Critical Velocity in Cold Spraying

The critical velocity is an important parameter in cold spraying, which determines the deposition efficiency under a given spray condition. The critical velocity depends not only on materials types, but also on particle temperature and oxidation conditions. In the present paper, three types of materials including copper, 316L stainless steel, Monel alloy were used to deposit coatings by cold spraying. The critical velocities of spray materials were determined using a novel measurement method. The oxygen content in the three powders was changed by isothermal oxidation at ambient atmosphere. The effect of oxygen content on the critical velocity was examined. It was found that the critical velocity in cold spray was significantly influenced by particle oxidation condition besides materials properties. The critical velocity of Cu particles changed from about 300 m/s to over 610 m/s with the change of oxygen content in powder. It is evident that the materials properties influence the critical velocity more remarkable at low oxygen content than at high oxygen content. The results suggest that with a severely oxidized powder the critical velocity tends to be dominated by oxide on the powder surface rather than materials properties.     

Warm Spray Forming of Ti-6Al-4V

Warm spray (WS) is a modification of high-velocity oxy-fuel spraying, in which the temperature of the supersonic gas flow generated by the combustion of kerosene and oxygen is controlled by diluting the combustion flame with an inert gas such as nitrogen. The inert gas is injected into the mixing chamber placed between the combustion chamber and the powder feed ports, thus the temperature of the propellant gas can be controlled from ~700 to 2,000 K. Since WS allows for higher particle temperatures in comparison to cold spray, warm sprayed particles are more softened upon impact, thus resulting in greater deformation facilitating the formation of shear instability for bonding. Recently, the combustion pressure of WS has been increased from 1 (low-pressure warm spray) to 4 MPa (high-pressure warm spray) in order to increase the velocity of sprayed particles. Effects of spray parameters on microstructure, mechanical properties, and splats formation of Ti-6Al-4V were systematically studied. Obtained coatings were examined by analyzing the coating cross-section images, microhardness as well as oxygen content. In addition, flattening ratio of splats was calculated as a function of nitrogen flow rate. It was found that the increased particle velocity caused by the increased combustion pressure had significant beneficial effects in terms of improving density and controlling the oxygen level in the sprayed Ti-6Al-4V coatings.     

The role of nanosized gold particles in adsorption and oxidation of carbon monoxide over Au/Fe2O3 Catalyst

The presence of gold is found to promote the development of weakly bonded (CO)_ad species over the surface of Au/Fe₂O₃ catalyst during interaction with carbon monoxide (CO) or a mixture of carbon monoxide and oxygen. The concentration of these species and the nature of the bonding depend on the gold particle size. No such species are formed for gold particles larger than ∼11 nm or over gold-free iron oxide. The bulk carbonate-like species, formed in the process with the involvement of the hydroxy groups of the support, are merely side products not responsible for the low temperature activity of this catalyst.     

The kinetics of the corrosion of copper containing different amounts of oxygen in 1.7 M H2SO4

The rate of corrosion of rotating copper discs was measured as a function of the concentration of oxygen in metal. It was found that the catastrophic acceleration of the corrosion of the sample occurs at 3 × 10³ ppm of oxygen in metal. In the temperature range 5–75°C, the corrosion resulting from the presence of the oxygen in the metal occurs in the regime of activational control, and it is not influenced by the oxygen dissolved in the acid. The corrosion resulting from the oxygen depolarization occurs in the activational control regime in the temperature range 5–35°C, in the mixed kinetics regime in the range 45–55°C, and in the range 65–75°C in the diffusional regime with respect to the oxygen dissolved in the acid. The overall rate of corrosion of copper containing 8 × 10³ ppm of oxygen is about 20 times greater than the rate of corrosion of copper with oxygen depolarization.     

氟化物活性TIG焊电弧特征的光谱分析

氟化物作为最为常见的A-TIG焊活性剂配方之一,在实际焊接生产中已得到了广泛的应用,然而其对电弧行为的影响机制目前仍存在争议. 为此,利用光谱诊断方法对涂覆氟化物活性剂的A-TIG焊电弧空域光谱分布进行了研究,分析了活性剂粒子、氩、铁粒子在电弧空域中的分布特征,并结合Boltzmann图法计算了电弧电子温度. 结果表明,氟化物活性剂粒子主要分布于弧柱中心区域;氟化物的引入能够使电弧中ArⅡ谱线辐射强度降低同时增强FeⅡ谱线辐射强度;氟化物对不同电弧空间区域的电子温度作用并不一致,其中使阳极区附近电弧温度大幅提升但对其它区域电弧温度的影响很小.     

Studies on morphological and electrical properties of Al incorporated combusted iron oxide

The aluminium incorporated iron oxide samples were prepared by combustion route using aluminium nitrate and ferric trichloride as precursors. The samples were characterized for their morphological, dielectrical, impedance and thermal conductivity properties as a function of temperature. A strong low frequency dielectric dispersion is found to exist in these samples; this is ascribed to the presence of the ionized space charge carriers such as oxygen ion vacancies and interfacial polarization. The room temperature dielectric constant and the loss tangent (tan δ) at 1 kHz are 315 and 0.0855 for optimized 10 at.% Al:Fe₂O₃ sample, respectively. The frequency analysis of dielectric and ac conduction properties of these samples suggests the conduction process in these samples to be via oxygen ion vacancy motion through various defect sites. Impedance spectroscopy is used to characterize the electrical behavior. Results indicate that the relaxation mechanism of the material is temperature and frequency dependent and has dominant bulk contribution in different temperature ranges.     

Corrosion of oxygen-doped tantalum by lithium

The increase in the penetration of tantalum by liquid lithium with increasing oxygen content of tantalum results from the ability of lithium to extract oxygen from tantalum oxides and/or from regions of high oxygen concentrations, accompanied by the creation of minute channels. At low oxygen concentration, oxides are present primarily at the grain boundaries and the lithium penetration is primarily intergranular. At high oxygen concentration, oxides and/or regions of high oxygen concentration are present both at the grain boundaries and within the grains; lithium penetration is both intergranular and transgranular. For a specific oxygen concentration, the severity of corrosion decreases with increasing temperature because (a) the oxygen solubility increases with temperature, decreasing the number of oxide particles and/or regions of high oxygen concentration, and (b) the diffusivity of oxygen in tantalum increases, allowing more rapid oxygen removal at the tantalum lithium interface.     

Effects of erosion on corrosion of type 430 and 316 stainless steels in aqueous environments

Abstract

The effects of erosion on the corrosion of two types of stainless steel in aqueous 0·5M NaCl and 1M NaCl environments at ambient temperature have been studied using a modified rotating cylinder electrode system. Erosion by silica particles greatly increased the passive current density for both ferritic type 430 and austenitic type 316 stainless steels. It is suggested that two factors were largely responsible for the observed effects. The impact of the eroding silica particles on the specimen surface destroyed the passive film and removed corrosion products from the specimen surface; and impact with the fast moving silica particles generated numerous microplastic deformation sites on the metal surface which were activated owing to the presence of residual stress, dislocations and defects, etc., and the emission of low energy electrons.