Nucleation of highly oriented diamond on silicon

Highly oriented diamond particles were deposited on the mirror-polished (100) silicon substrates in the belljar type microwave plasma deposition system. The diamond films were deposited by a three-step process consisting of carburization, bias-enhanced nucleation and growth. The bias-enhanced nucleation was performed under the deposition conditions such as 2-3% of methane concentration in hydrogen, 1333-2666 Pa of total pressure, the negative bias voltage below 200V and the substrate temperature of 1073 K. By adjusting the geometry of the substrate and substrate holder, very dense disc-shaped plasma was formed on the substrate when the bias voltage was below 200V. As characterized by transmission electron microscopy (TEM), almost perfectly oriented diamond particles were obtained only in this dense plasma. From the results of the optical emission spectra of disc-shaped dense plasma, it was found that the concentrations of atomic hydrogen and hydrocarbon radicals were increased with negative bias voltage. As a result, it was suggested that the highly oriented diamonds were obtained by the combination of the high dose of hydrocarbon radicals and the increased hydrogen etching effects.     

粉末冶金法制备云母/羟基磷灰石玻璃陶瓷

为了获得良好的可加工性和生物活性,采用粉末冶金法制备了云母/羟基磷灰石玻璃陶瓷.随着烧结温度的提高,材料的力学性能有所增加.在1100℃下、保温1.5 h可以获得材料的最佳力学性能,其相对密度、抗弯强度和断裂韧性分别为95%、124 MPa和2.1 MPa·m1/2.随着温度的提高,烧结过程中玻璃相的扩散速度加快并填充到剩余的孔隙中,使得材料的相对密度增加,从而提高了材料的抗弯强度.断裂韧性的提高来源于材料中高长径比的云母晶体相互交错的微观结构.     

Impact of Argumentative Negotiation on Collaborative Engineering

Engineering of complex systems involves multiple disciplinary design teams with diversified skills. The team members must work together to make joint decisions, but are often faced with difficulties when trying to reach agreements. Negotiation has been studied as a method for facilitating information exchange, mutual understanding, and joint decision-making. In our previous work, we introduced an argumentative negotiation model to support collaborative engineering. In this paper, we present an experiment study that was conducted to assess the impact of this negotiation support system on the process and the outcome of collaborative design. The results of the experiment have demonstrated the positive effects of the approach.     

纯铝等径角挤技术（I）——显微组织演化

研究了纯铝在 3种 (A、B和C)不同等径角挤工艺中的显微组织演化。结果表明 :纯铝经过等径角挤压变形后 ,其显微组织特征与加工路线有很大的关系。提出了立方元素扭转模型 ,分析了 3种不同加工路线的剪切面和剪切方向 ,较好地解释了采用 3种不同路线挤压后材料显微组织的演化规律。在路线C(各道次挤压间试样旋转 180°)中 ,每次挤压样品总是在相同的剪切面上发生剪切 ,每相邻道次之间的剪切方向相反 ,前一次变形产生的剪切应变被随后紧接着的下一次挤压所抵消 ,这导致了多余的剪切应变 ;在路线A(各道次挤压间试样不旋转 )中 ,有两个相交成 6 0°的剪切面 ,剪切交替地在两个剪切面上进行 ;在路线B(各道次挤压间试样旋转 90°)中 ,存在 4个不同的剪切面和剪切方向 ,挤压交替地在 4个剪切面上进行 ,X ,Y和Z平面上的晶粒都发生了剪切 ,这有利于等轴晶结构的形成     

Reactions at the corroding nickel electrode in molten sodium carbonate under CO/CO2 atmosphere

Anodic reactions at the CO, CO₂|Ni electrode in molten sodium carbonate at 1000°C are examined in detail. Experimental polarization curves are fitted via a computer graphics procedure to a model employing five anodic reactions with activation, concentration and resistance polarization, and passivation. The resultant empirical parameters are interpreted in terms of absolute rate expressions describing possible anodic reactions. Three of the anodic reactions are found to be in accord with the findings at inert electrodes by previous investigators, i.e. oxidation of CO by two mechanisms and oxidation of carbonate, while the cathodic reaction is consistent with reduction of CO₂. The remaining two anodic reactions were associated with the oxidation of nickel to Ni²⁺ with formation of a NiO film above a passivation potential, and, at higher anodic overpotentials, oxidation of NiO to a higher oxide, e.g. Ni₂O₃. There is an indication of the formation of a third oxide at still higher anodic overpotentials.     

Flow stress and softening behavior of wrought magnesium alloy AZ31B at elevated temperature

1　INTRODUCTIONThewroughtmagnesiumalloyshaveexcellentspecificstrengthandstiffness ,machinability ,dampcapacity ,dimensionalstability ,lowmeltingcostsandare ,hence ,veryattractiveinsuchapplicationsasau tomobile ,aviation ,electronicandcommunicationin dustry[16 ] .Investigationsontheflowstressandsofteningbehaviorofmagnesiumalloysathigherformingtem peratureandstrainratehavebeenanimportantsub jectinwroughtmagnesiumalloysforming[710 ] .InthispapertheflowstressandsofteningbehaviorofAZ31Bdeform…     

Effects of can parameters on canned—forging process of TiAl base alloy（Ⅱ）——Mechanical behavior

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Microstructural evidence for short-circuit oxygen diffusion paths in the oxidation of a dilute Ni-Cr alloy

A comparative study of high-temperature oxidation of Ni containing 1 at.% Cr and pure Ni was carried out. Instead of the conventional kinetics study using thermogravimetry, a microlithographic marker experiment was designed. Observation of the markers using cross-sectional TEM and SEM has revealed striking differences in the scale morphology, microstructures, and oxidation mechanisms between pure Ni and the Cr-doped Ni substrates. In particular, the results suggest that a small addition of Cr promotes significant inward transport of oxygen. Marker experiments revealed that NiO grown on pure Ni is wholly attributable to outward-cation diffusion. In contrast, NiO grown on Ni–1 at.% Cr exhibited formation of a substantial inner layer having a submicron grain size, established by the markers to have formed from oxygen ingress. For pure Ni, voids were observed to be distributed only within oxide grains. In contrast, for Ni containing 1 at.% Cr, elongated pores formed extensively along oxide-grain boundaries. Formation of new fine-grain oxide in these pores was observed to have sometimes completely resealed the void. It is, therefore, proposed that the transport of oxygen in the case of oxide scale grown on Ni–1 at.% Cr occurs via voids (pores) formed by vacancy coalescence at the grain boundaries.     

Carbon-nanotube-based electrochemical double-layer capacitor technologies for spaceflight applications

Electrochemical double-layer capacitors, or supercapacitors, have tremendous potential as high-power energy sources for use in low-weight hybrid systems for space exploration. Electrodes based on single-wall carbon nanotubes (SWCNTs) offer exceptional power and energy performance due to the high surface area, high conductivity, and the ability to functionalize the SWCNTs to optimize capacitor properties. This paper will report on the preparation of electrochemical capacitors incorporating SWCNT electrodes and their performance compared with existing commercial technology. Preliminary results indicate that substantial increases in power and energy density are possible. The effects of nanotube growth and processing methods on electrochemical capacitor performance is also presented. The compatibility of different SWCNTs and electrolytes was studied by varying the type of electrolyte ions that accumulate on the high-surface-area electrodes. For more information, contact W.J. Ready, Georgia Tech Research Institute, 925 Dalney St., Atlanta, GA 30332; (404) 385-4497; fax (404) 894-0580; e-mail jud.ready@gtri.gatech.edu.     

带材的纠偏控制

本文对带钢生产线上常见的带材跑偏现象，进行了详细的分析。对带钢跑偏的原因，进行了研究。同时，对带钢跑偏应采取的措施，也给出了相应的方法。