Liquid Impact Based Material Micro-Forming Technology

The objective of this study was to investigate material deformation in the course of a high-speed (>1500 m/s) water impact and to use the acquired knowledge for improvement of the forming technology. An experimental setup for projectile fabrication was constructed and a series of experiments involving sub-millimeter and micron scale metal deformation was performed. The geometry and topography of the generated samples were investigated using advanced surface examination techniques and the feasibility of the liquid impact based micro-forming technology was demonstrated. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

CVD法合成SiC晶须的实验研究

利用简单的实验设备，特殊的金属丝作触媒，以ＳｉＯ２和Ｃ为原料，利用碳热还原反应生成的ＳｉＯ和ＣＯ，通过ＣＶＤ的方法快速合成α－ＳｉＣ晶须，用光学显微镜研究了晶须的生长速度，通过ＴＥＭ研究α－ＳｉＣ晶须的结构和生长方式。讨论了这种方法中α－ＳｉＣ晶须生长的热力学条件，机理及生长动力学模型。     

Role of Al2O3 layer in oxidation resistance of Cu-Al dilute alloys pre-annealed in H2 atmospheres

Copper was alloyed with small amounts of Al (0.2, 0.5, 1.0 and 2.0 mass%) to improve the oxidation resistance. Copper (6 N) and the Cu-Al alloys were oxidized at 773-1173 K in 0.1 MPa oxygen atmosphere after hydrogen annealing at 873 K. Continuous very thin Al₂O₃ layers were formed on the surface of all Cu-Al dilute alloys during the hydrogen annealing. Oxidation resistance of Cu-Al alloys was improved especially for Cu-2.0Al at 773-973 K, while it decreases on increasing the oxidation temperature. Cu-Al alloys followed the parabolic rate law at 1173 K, but most of other cases do not at and below 1073 K. Oxidation resistance for Cu-Al alloys was found relevant to the maintenance of the thin Al₂O₃ layer at the Cu₂O/Cu-Al alloy interface.     

异形坯连铸结晶器内三维流场的数值模拟

根据湍流理论及异形坯连铸的特点, 建立了异形坯结晶器三维流场数学模型, 对不同条件下的流场进行了数值模拟, 分析了水口结构和工艺参数变化时异形坯结晶器内涡心深度的变化规律及液面湍动能的分布状态. 结果表明 采用上倾式水口, 水口夹角为120°, 拉速为0.9m/s时, 结晶器内流场分布较为合理, 液面较稳定. 模拟结果与水模实验结果吻合较好. 该模型可对连铸过程进行离线分析, 确定最佳参数, 并可作为在线控制模型的基础.     

SiO(g) formation from SiC in mixed oxidizing-reducing gases

The formation of SiO(g) from SiC by either active oxidation or an oxidation-reduction process is discussed. The Wagner criterion for the transition from active to passive oxidation is generalized for any oxidant. Kinetic modeling of both active oxidation and oxidation-reduction is described.Symbols - - MW _SiC/MW _Si - _CO CO(g) boundary layer thickness - _ox gaseous-oxidant, boundary layer thickness - stoichiometric factor from Eqs. (2)–(4), # of CO produced/# of oxidant (on oxygen atom basis) - gas viscosity - concentration of diffusing gas species in boundary layer - concentration of major gas species in boundary layer - _oxide density of SiO₂ - D diffusion coefficient of diffusing species in gas-boundary layer - D _CO diffusion coefficient of CO(g) - D _ox gas diffusion coefficient of oxidant - J flux, rate of weight loss limited by diffusion in gas-boundary layer - J _CO flux of CO(g) - J _ox flux of gaseous oxidant - K _g linear oxide growth constant, weight/(length² time) - k _g linear oxide growth constant, length/time - k _l linear volatilization constant for SiO₂,k _lo+k _ls, weight/(length² time) - k _lo linear volatilization constant for oxygen from SiO₂, weight/(length² time) - k _ls linear volatilization constant for silicon from SiO₂, weight/(length² time) - k _l linear volatilization constant for SiO₂, length/time - k _p parabolic oxide growth constant, weight²/(length⁴ time) - k _p parabolic oxide growth constant, length²/time - L sample length parallel to gas flow direction - (M/A)₁ specific weight change due to oxygen gain and associated carbon loss in paralinear oxidation - (M/A)_1L limiting value of weight change due to oxygen gain and associated carbon loss in paralinear oxidation - (M/A)₂ specific weight change due to silicon loss and associated carbon loss in paralinear oxidation - MW _C molecular weight of carbon - molecular weight of O₂ - MW _Si molecular weight of silicon - MW _SiC molecular weight of silicon carbide - molecular weight of silica - n number of oxygen atoms per oxidant molecule - P _CO ^eq eqiilibrium CO(g) pressure - P _CO ^g CO(g) pressure outside of boundary layer - P _CO ⁱ CO(g) pressure at SiC-gas interface - P _ox ^g oxidant gas pressure outside of boundary layer - P _ox ⁱ oxidant gas pressure at SiC-gas interface - R gas constant - t time - T absolute temperature - v linear gas velocity - x oxide thickness - x _L limiting oxide thickness achieved in paralinear oxidation - x _t oxide thickness at which transition from linear to parabolic growth occurs     

正己烷裂解反应自由基模型的理论研究

采用量子化学法研究了模型化合物正己烷裂解过程,并计算其动力学参数。依据自由基理论,建立由216个基元反应组成的正己烷裂解反应自由基模型,用CBS-QB3法计算链引发和终止反应动力学参数,用MPW1B95/6-311+G(2d,2p)法计算链增长反应动力学参数。根据动力学参数计算结果,忽略相对不重要的反应,将模型简化为160个基元反应。模拟计算表明,在相同的裂解条件下,简化模型模拟结果与完整模型模拟结果一致,各组分相差不大于0.1%wt;建立的动力学模型对主要产物收率预测较好,与实验值相差小于0.7%wt,可正确地预测正己烷裂解产物的组成和各组分含量沿反应管长度的分布,为进一步研究复杂的烃裂解过程提供了基础。     

烯烃催化裂解反应动力学的研究

根据脉冲微反条件下C5～C8烯烃裂解产物分布,建立烯烃裂解反应网络,通过参数估计方法确定反应网络动力学常数、反应活化能和指前因子.结果表明,随着碳数的增加,C5～C8烯烃单分子裂解反应速率加快.反应温度600℃时C5～C8正构烯烃裂解生成丙烯,其反应速率常数的比值为1:8.18:38.48:27.98,最快生成丙烯的是1-庚烯.反应温度相同,1-烯烃的主要裂解反应速率是碳数相同的2-甲基-2-烯烃的1.1～1.6倍.C5烯烃裂解为单、双分子裂化并存的反应体系,但双分子裂解反应速率远大于单分子裂解,双分子反应占优势.     

计算机曲线拟合求解析氢反应的动力学参数

应用电化学稳态极化方法,研究1M NaOH电解液中镍硫合金电极表面析氢反应电催化活性与沉积层中含硫量之间的关系.根据析氢反应机理,用理论电化学极化方程拟合实验稳态极化曲线,得到不同含硫量的镍硫合金电极表面氢原子吸附和脱附反应的速率常数、反应对称系数等动力学参数.     

Influence of grain boundary weak links on the nonequilibrium response of YBaCuO thin films to short laser pulses

The transient voltage response in both epitaxial and granular YBaCuO thin films to 80 ps pulses of YAGNd laser radiation of wavelength 0.63 and 1.54 m was studied. In the normal and resistive states both types of films demonstrate two components: a nonequilibrium picosecond component and a bolometric nanosecond one. The normalized amplitudes are almost the same for all films. In the superconducting state we observed a kinetic inductive response and two-component shape after integration. The normalized amplitude of the response in granular films is up to five orders of magnitude larger than in epitaxial films. We interpret the nonequilibrium response in terms of a suppression of the order parameter by the excess of quasiparticles followed by the change of resistance in the normal and resistive states or kinetic inductance in the superconducting state. The sharp rise of inductive response in granular films is explained both by a diminishing of the cross section for current percolation through the disordered network of Josephson weak links and by a decrease of condensate density in neighboring regions.     

A kinetic model for gas adsorption at solid surfaces by surface transient formation

In this paper is presented a model for the kinetics of gas adsorption at solid surfaces, in which transient formation is involved. In the case of ideal adsorption where the rate constants are independent of the surface coverages, the kinetics can be solved exactly in the framework of the first order kinetic law. The expression of the sticking coefficient for the final chemisorbed state is obtained in terms of the rate constants introduced in the model and compared to the expression commonly adopted in the literature. By means of a fitting procedure the kinetics were used to describe experimental data on the dioxygen adsorption at the Zn(0001) surface. An appropriate analysis of the fitting parameters, derived from adsorption data collected at different temperature of the substrate, allows for the activation energy of the processsurface transient final adsorbed species to be estimated.