Quantum chemical SINDO1 study of vanadium pentoxide

An improved set of parameters for vanadium in the semiempirical quantum chemical SCF MO method SINDO1 is presented. It is shown that both the geometries and heats of formation of a number of vanadium-containing compounds calculated by this method are in good agreement with available experimental data. Model clusters of increasing size are used for the study of geometric and energetic properties of vanadium pentoxide. Both hydrogen atom and proton adsorption on the (010) surface of vanadium pentoxide and a subsequent formation of different oxygen vacancies have been investigated. Based on these computational results the reactivities of V₂O₅-surface oxygen atoms for adsorption are discussed.     

Computational study of transport processes in a single-screw extruder for non-newtonian chemically reactive materials

A numerical study of the transport phenomena arising in a single-screw extruder channel is carried out. A non-Newtonian fluid is considered, using a power law model for the variable viscosity. Chemical reaction kinetics are also included. Finite difference computations are carried out to solve the governing set of partial differential equations for the velocity, temperature and species concentration fields, over a wide range of governing parameters for the case of a tapered screw channel. The numerical treatment for this combined heat and mass transfer problem is outlined. A marching procedure in the down-channel direction is adopted and the validity of the scheme for practical problems discussed. For large viscous dissipation, the material heats up considerably due to the prevailing shear field, affecting the viscosity significantly, and results in large changes in the pressure development at the end of the channel. The rate of reaction controls the mass diffusion rate which in turn affects viscosity and the flow significantly. The dimensionless throughput,q _v , is one of the most important parameters in the numerical solution. The dimensionless pressure variation is very sensitive toq _v , and orders of magnitude changes are possible for small variations inq _v . Schemes for dealing with other important effects such as back flow, heat transfer by conduction in the barrel, and the effect of the die are also outlined. A list of symbols is given at the end of the paper This is publication No. F-10544-4-91 of the New Jersey Agricultural Experiment Station supported by State Funds and the Center for Advanced Food Technology (CAFT). The Center for Advanced Food Technology is a New Jersey Commission on Science and Technology Center. This work was also supported in part by the US Army Research Office.     

认清形势 振奋精神全面完成化工“八五”计划的各项任务

总结回顾了１９９４年中国化学工业的改革及发展现状，提出了１９９５年化工生产建设的目标及在化工行业改革方面的四项试点工作，强调了编制“九五”计划的重要性。     

Adhesion Mechanisms of Polyurethanes to Glass Surfaces. III. Investigation of Possible Physico-Chemical Interactions at the Interphase

Surface free energies of polyurethanes made from toluene diisocyanate and 1, 4 butanediol-based hard segments and caprolactone polyol-based soft segments were calculated using additive functions. Good agreement was found between the calculated values based on additive functions and the calculated values based on contact angle measurements. The phase-separated polyurethanes were found to have a higher polar surface free energy component (γ^P). This was linked to the preferential segregation of butanediol/butanediol-derived moieties to the polyurethane surfaces due to phase separation. The adhesion values of these polyurethanes to soda-lime glass were correlated with their respective γ^P values and a linear relationship was found. It was also shown that the adhesion values of the low γ^P polyurethanes improved substantially when the glass surfaces were coated with a thin layer of butanediol prior to the bonding. The modulus of the interphase region rich in butanediol was evaluated. Although a modulus increase was found at the interface, this increase was found to play a secondary role in the adhesion. The chemical interactions at the polyurethane/glass interphase were investigated by pre-treating the glass surfaces with methyl-trimethoxysilane and trimethylchlorosilane prior to adhesion testing. The adhesion data showed no significant difference between the uncoated and the silane-treated glass substrates. Based on this experimental evidence, the possibility of any covalent or ionic bonding at the polyurethane/glass interphase was assumed negligible. It was determined that the mechanism of adhesion between the polyurethanes and the glass surface could be through the formation of an interphase region in which hydrogen bonding between the butanediol-rich interphase region and the hydroxylated glass surface plays a key role.     

Symmetry properties and bifurcation analysis of a class of periodically forced chemical reactors

In this work, we discuss how periodic forcing may induce symmetry properties into mathematical models of chemical reactors. We define a class of reactors subjected to discontinuous periodic forcing, and show that all the reactors belonging to this class have spatio-temporal symmetry. This symmetry and its influence on the possible bifurcation scenarios are discussed. The bifurcation analysis is carried out with suitable discrete systems that exploit a property of the Poincaré map. In fact, it is shown that the spatio-temporal symmetry induced by the forcing makes the Poincaré map of the continuous system an iterate of another map. On this basis, a technique to implement parameter continuation methods is proposed. With such a technique, it is also possible to characterize symmetric and nonsymmetric regimes and unstable limit sets otherwise undetected with “bruteforce” approaches. Examples for reverseflow reactors and networks of n-reactors with periodically switched feed and discharge positions are presented.     

Electrical and optical properties of oxygen doped GaN grown by MOCVD using N2O

Oxygen doped GaN has been grown by metalorganic chemical vapor deposition using N₂O as oxygen dopant source. The layers were deposited on 2″ sapphire substrates from trimethylgallium and especially dried ammonia using nitrogen (N₂) as carrier gas. Prior to the growth of the films, an AIN nucleation layer with a thickness of about 300? was grown using trimethylaluminum. The films were deposited at 1085°C at a growth rate of 1.0 μm/h and showed a specular, mirrorlike surface. Not intentionally doped layers have high resistivity (>20 kW/square). The gas phase concentration of the N₂O was varied between 25 and 400 ppm with respect to the total gas volume. The doped layers were n-type with carrier concentrations in the range of 4×10¹⁶ cm⁻³ to 4×10¹⁸ cm⁻³ as measured by Hall effect. The observed carrier concentration increased with increasing N₂O concentration. Low temperature photoluminescence experiments performed on the doped layers revealed besides free A and B exciton emission an exciton bound to a shallow donor. With increasing N₂O concentration in the gas phase, the intensity of the donor bound exciton increased relative to that of the free excitons. These observations indicate that oxygen behaves as a shallow donor in GaN. This interpretation is supported by covalent radius and electronegativity arguments.     

溶胶－凝胶二氧化硅驻极体薄膜的物理化学改性

实验研究了由溶胶－凝胶法制备二氧化硅驻极体薄膜的工艺。用红外透射谱、扫描电子显微镜以及驻极体等温表面电位测量和热刺激放电等实验考察了热处理和化学表面修正两个关键工艺对溶胶－凝胶二氧化硅样品驻极体性能的影响。结果表明经过高温条件下一定时间的热处理和化学表面修正，可以制备出性能优良的驻极体薄膜     

In Situ FTIR Study of the Formation of an Organosilane Layer at the Silica/Solution Interface

An FTIR experiment especially designed to study the growth of an organosilane layer at the interface between a solution and a flat silica surface is presented. High sensitivity is achieved by using the attenuated total reflection (ATR) technique in a liquid flow cell. The ATR crystal, either silicon or germanium, is covered with a very thin silica layer. Chemical reactions of a mono-and a di-hydrolyzable silane with the silica substrate have been investigated. The grafting of a submonolayer of the first reagent has been monitored by following the C-H and SiO-H vibrations. The density of grafted molecules has been estimated and information on the nature of the chemical bonding has been achieved. Evidence for the chain-polymerization of the dihydrolyzable silane at the substrate/solution interface has been inferred from the appearance of a Si-O-Si absorption band.     

矢量图形智能判断技术的研究与应用

研究矢量图形识别是建立工程制图自动阅卷与计算机辅助教学系统的基础。由于组成二维矢量图形图元类型的多样化及图形整体位置状态的不确定性，增加了矢量图形的识别与判断难度。结合开发的《三视图智能解答》系统，研究其智能识别与判断技术。系统中引入三视图导航技术，解决了图形整体定位与识别问题。实现了对矢量图形图元素信息的分类和提取，能够对所提取的的信息与标准答案进行智能判断与评定。该方法已在AutoCAD2000环境下使用AutoLISP语言编程实现。     

30CrMnsi联接环断裂失效分析

对断裂的联接环进行了化学成分、机械性能、显微组织核验，指出回火工艺不当、锻造缺陷以及原材料化学成分不合格，是造成断裂事故的主要原因．在此基础上．提出了改进措施．