微细浸染型金矿酸性热压氧化预处理动力学研究

以氧气消耗速率表征氧化速率,研究了微细浸染型硫化物金矿热压氧化预处理过程动力学的影响因素,考察了矿浆pH值、温度、矿样粒度、氧分压、气液界面面积和矿浆浓度对氧化速率的影响,以及氧化率和氧化速率的关系。结果表明,矿浆pH2.5时,保持较高的氧化速率;氧化速率随温度升高、氧分压增加和矿浆浓度降低而增大;增加气液接触面积可提高氧化速率,当矿浆浓度为33%、氧分压1.6 MPa,在优化条件下,气液接触比表面积达到25 m2/m3,40 min可完成氧化预处理。     

Molecular simulation of interfacial reaction between TiAl alloy melts and different coatings

The effect of coatings (Y2O3, ZrO2 and Al2O3) on the interfacial reaction of TiAl alloys was studied with molecular dynamics. The binding energy of coatings and the diffusion process of oxygen in the melt were simulated, and then the simulation results were compared with the experimental results. The simulation results indicate that for each of the three simulated coatings, inordinate interfacial reactions have occurred between the coating and the melt. The binding energy results show that Y2O3 has the best stability and is the most difficult to break down. ZrO2 has the greatest decomposition energy and is the easiest to break down in the melt. Besides,the molecular dynamics indicate that the diffusion coefficient of the oxygen atom in Al2O3 is larger than that in the other two coatings, indicating that oxygen diffusion in Al2O3 is the fastest at a given temperature. The experimental results show that the oxygen concentration of the melt with Al2O3 coating is the highest, and the oxygen diffusion is of similar magnitude to the simulation values, from which the conclusion can be obtained that the oxygen concentration is significantly influenced by the coating materials.     

Interfacial Reactions between Cu-Zr filler metal and alumina and kinetics of reaction layer growth

The interfacial reactions and kinetics of the reaction layer growth in Cu-Zr/A1₂O₃ system were investigated and compared with those in Cu-Ti/Al₂O₃ system. Therrnodynamic analysis showed that the interfacial reaction can proceed until the activity of aluminum in the Cu-5 at.% Zr filler metal reaches about 0.27 at 1373 K. Growth of reaction layer, ZrO₂, was controlled by the diffusion of oxygen through ZrO₂ layer. The activation energy for ZrO₂ growth was 126 kJ/mol. Instead of using a complex redox reaction, a simple oxidation model between reactive metal and oxygen was found to adequately describe the reaction layers growth in ceramic/metal systems. The parabolic rate constant could be expressed in terms of oxygen vacancy concentration at the reactive metal/reactive metal oxide interface. The slower growth of TiO, in comparison with ZrO₂, can be rationalized using the parabolic rate constant. The lower diffusion coefficient of oxygen vacancy and a less negative free energy change of TiO formation have a dominant effect over the higher oxygen vacancy concentration at the Ti/TiO interface which resulted in slower TiO growth.     

The analysis of Armos fibers reinforced poly(phthalazinone ether sulfone ketone) composite surfaces after oxygen plasma treatment

The effects of oxygen plasma treatment on both the fiber surface and interfacial adhesion of Armos fiber reinforced PPESK composites were investigated in this paper. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to analyze fiber surface chemical composition and surface roughness, respectively. The results indicated that oxygen plasma treatment had introduced a large amount of reactive functional groups onto the fiber surface and the fiber surface roughness was increased largely. The interlaminar shear strength (ILSS) of the untreated and oxygen plasma-treated composites was measured to evaluate the interfacial adhesion. The values of ILSS were enhanced dramatically; the water molecule diffusion into composite along interface was prevented effectively. The composite fracture mode was observed by scanning electron microscopy (SEM), which showed that the primary failure mode varied from interface failure to matrix failure after oxygen plasma treatment. Results indicated that oxygen plasma treatment was an effective method to improve the interfacial adhesion properties of Armos fiber reinforced PPESK composites by both chemical bonding and physical effects.     

Numerical simulation of interfacial reaction between titanium and zirconia

Based on the conservation laws of energy and mass,and taking into account the effect of chemical reaction between liquid titanium and zirconia ceramic mold on the concentration field and the temperature field,a comprehensive mathematical model for numerical simulation of heat and mass transfer has been established to study the interfacial reaction between liquid Ti and ZrO2 ceramic mold.With the proposed model,numerical simulations were preformed to investigate the effects of pouring temperature and holding time on the oxygen concentrations and reactive layer thickness in metal.The results showed that both the oxygen concentration and the thickness of reactive layer in metal increase with the increase of the holding time and the pouring temperature.The development of reactive layer thickness with time consists of three stages:inoculation (0-1 s),linear increase (1-5 s)and parabolic increase (after 5 s).     

Characterization of corrosion of X65 pipeline steel under disbonded coating by scanning Kelvin probe

Corrosion of X65 pipeline steel under a disbonded coating was studied by scanning Kelvin probe measurements. Three types of specimen were designed and prepared to investigate the effects of immersion time, oxygen concentration and wet-dry cycle on Kelvin potential profile and thus corrosion behavior of the steel. Kelvin potential measured on “intact” area is shifted negatively with time, indicating an increasing water uptake under the “intact” coating. With the increase of the amount of solution, it is expected that the electrolyte concentration and electrochemical reaction rate change, resulting in a significant decrease of interfacial potential. Moreover, there is a more negative Kelvin potential on disbonded area than that on “intact” area. The negative shift of Kelvin potential is attributed to corrosion reaction of steel occurring under the disbonded coating. Due to the narrow geometry of coating disbondment, an oxygen concentration difference exists along the depth of the disbondment. The corrosion behavior under disbonded coating strongly depends on the oxygen partial pressure and local geometry. With continuous purging of nitrogen and removing of oxygen, Kelvin potential tends to be identical throughout the disbonded area. During wet-dry cycle, the thickness of solution layer trapped under disbonded coating decreases due to evaporation of water. With the decrease of solution layer thickness, the measured Kelvin potential decreases, indicating that the effect associated with the reduction of oxygen solubility in the concentrated solution during drying of electrolyte is favored over that related to the enhanced oxygen diffusion and reduction. There exists a critical thickness of solution layer, below which the oxygen solubility is sufficiently low to support the electrochemical corrosion reaction of steel.     

Growth of gallium nitride on silicon by molecular beam epitaxy incorporating a chromium nitride interlayer

This study grew GaN epilayers on Si(1 1 1) substrate via molecular beam epitaxy, with a CrN interlayer fabricated through a nitridation process. The X-ray diffraction results showed two peaks corresponding to CrN(1 1 1) and GaN(0 0 0 2). The results of auger electron spectroscopy showed that the concentration of electrons was relatively low in the samples grown with a CrN interlayer, due to CrN preventing Si atoms from diffusing into the GaN epilayer, thereby reducing electron concentration. Photoluminescence spectra indicated that donor-accepter pair recombination (DAP) emission was not generated in the GaN with a CrN interlayer because of improved crystalline quality and a reduction in electron concentration.     

Effects of donor concentration and oxygen partial pressure on interface morphology and grain growth behavior in SrTiO3

Change in interface morphology with ionic vacancy concentration and the correlation between interface structure and grain growth behavior in strontium titanate (SrTiO₃) have been investigated using SrTiO₃ single crystals and powder compacts. Under experimental conditions where SrTiO₃ contains a negligible amount of ionic vacancies, the shape of the single crystal embedded in matrix grains was well faceted, showing a strong anisotropy in interfacial energy. However, as strontium or oxygen vacancies increased with the addition of an Nb₂O₅ donor dopant or reduction of oxygen partial pressure, the faceted shape changed to a smoothly curved rough one indicating that an interface roughening transition occurred and, as a result, the anisotropy in interfacial energy was considerably reduced. Grain growth behavior was also strongly dependent on the interface structures; while normal grain growth occurred when the interfaces were rough, abnormal grain growth behavior was observed in the samples with faceted interfaces. It appears, therefore, that the ionic vacancies in SrTiO₃ can cause the interface roughening transition and change the resultant grain growth behavior.     

Wetting anisotropy and oxygen activity dependency for oxides by liquid transition metals studied through shape changes of liquid Cu inclusions within MgO

The equilibrium shape of liquid metal inclusions in oxides is used to study anisotropy and oxygen partial pressure dependency of the metal–oxide specific interfacial free energy. Liquid copper inclusions are formed within single crystalline magnesia by internal reduction of mixed oxide (Mg,Cu)O. Their equilibrium shape is studied by TEM for various oxygen chemical potential. Precipitates always adopt cubo-octahedral morphology, but relative facet size strongly depends on the oxygen chemical potential. The shape evolution with oxygen chemical potential reveals important and anisotropic Gibbs' adsorption of excess oxygen to the interfaces at high oxygen activities. Gibbs' adsorption to crystallographically different MgO–liquid Cu interfaces is discussed in terms of a point defect model recently developed by the author (Backhaus-Ricoult, M., Phil. Mag., 2001, in press), where oxygen activity-dependent formation of interfacial charge transfer clusters between liquid metal and excess oxygen or magnesium is considered, while the relevant site and charge conservation laws in the two-phase system are respected and matter exchange with the surrounding gas atmosphere is allowed. Present experimental results are interpreted in terms of this interfacial defect model and compared with interpretation by other wetting models from the literature.     

EXTRACTION KINEIICS,MICELLIZATION AND INTERFACIAL CHARACTERISTICS OF A NEW EXTRACTANT SYSTEM

The interfacial kinetics,micellization and interfacial characteristics of the synergetic extrac-tion system,D_2EHPA-H_2RPA-Al~(3+),have been studied.H_2RPA is a single long chain alkylphosphate.We have found that H_2RPA in the mixed extractant system strongly exhibits thecharacteristics of micellization and interfacial activity.As the concentration of D_2EHPA in-creases,the micellization and interracial activity of H_2RPA decrease.The interfacialadsorption behaviour of H_2RPA is opposite to that of D_2EHPA.It was proved that the kine-tics of non-micella mixed extraction system was controlled by the chemical reaction at inter-face,and the reaction rate equation was obtained.This non-micella mixed extraction systemis expected to be used in the future.     

铜冰铜—炉渣间界面张力的研究

用X射线照相座滴法测量了Cu-Fe-S系冰铜与FeO-CaO-SiO_2-MgO系炉渣之间的界面张力。实验结果的相对误差为5-9％。讨论了1200℃下炉渣中FeO/SiO_2的重量比值、渣中CaO,Fe_3O_4,ZnO及CaF_2含量对渣-锍界面张力的影响,考察了冰铜品位、温度与渣-锍界面张力间的关系。计算了渣-锍系的浮游系数和膜系数,对O,Fe由渣相向冰铜相的传输机理作了探讨。     

Improving carbon fiber adhesion to polyimide with atmospheric pressure plasma treatment

Plasma treatment is frequently used to modify carbon fiber surfaces to improve adhesion of the fiber to matrices although it may also influence carbon fiber tensile strength. In order to determine the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength to polyimide, polyacrylonitrile (PAN) based carbon fibers are treated with atmospheric pressure oxygen/helium plasmas for different durations. Tensile strength change of the fiber is studied at different gage lengths before and after the plasma treatment. Interfacial bonding between the carbon fiber and a thermoplastic polyimide matrix is evaluated using a single fiber composite test system. Weibull analysis of the single fiber tensile test data shows no obvious changes in the tensile strength at short gage lengths after plasma treatment while the fiber strength tends to decrease at larger gage lengths. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the plasma treatments roughen the fiber surfaces. X-ray photoelectron spectroscopy (XPS) analysis of fiber surface shows a significant increase of oxygen concentration after plasma treatment and the oxygen containing functional groups reach their maximum levels after 32 s treatment time and further increasing treatment time does not achieve a higher level of oxidation. Plasma treatments decrease dynamic water contact angles and increase the surface energy of the carbon fibers as measured by the modified Wilhelmy method. The interfacial shear strength is improved 21% after the atmospheric pressure plasma treatment for 32 s. It is concluded that the increase of oxygen containing functional groups and changing of the surface topology may contribute collectively to the improvement of fiber/resin interfacial adhesion.     

Interfacial Segregation, Pore Formation, and Scale Adhesion on NiAl Alloys

Ni-40 and 50at various times in oxygen. Auger electron microscopy was used to study the interface chemistry after scale spallation in ultra high vacuum. The interfacial failure stresses were determined using a tensile pull tester and related to the interface chemistry, pore area and density. Results showed that sulfur started to segregate to areas of the Al²O³/Ni40Al interface, where the scale was in contact with the alloy after a complete layer of -Al²O³ developed there; the concentration then gradually increased to a steady level of ~0. 2 at %. However, sulphur did not segregate to similar areas of the Al²O³/Ni50Al interface even after extended oxidation when it was amply present on interfacial void faces. This behavior demonstrated a strong dependence of interface segregation on NiAl alloy composition. Interfacial failure stress was found to decrease with increasing sulfur content between voids and with higher interface porosity. The level of porosity was strongly related to the sulfur content in the alloy. When Ni40Al was doped with excess sulfur, the segregation behavior did not change, but the interfacial pore density increased significantly. The detrimental effect of sulfur on scale adhesion is 2-fold: to weaken the interface and to enhance interfacial pore formation.     

铝合金霉菌腐蚀研究进展

结合近年来铝合金霉菌腐蚀机制与防护领域研究成果,介绍了代表性霉菌的种类及影响霉菌活性的主要因素,重点总结和讨论了铝合金霉菌腐蚀机制,主要包括酸蚀机制、浓差电池机制、以及其他可能存在直接电子传递机制和霉菌铝合金直接界面作用机制.霉菌通过新陈代谢可以产生大量的有机酸,能够显著地降低介质和生物膜内的pH,从而导致酸蚀引发局部...     

Influence of turbulent flow on the corrosion of Al‐Zn‐Mg galvanic anode in artificial seawater media

The effect of hydrodynamics on the corrosion of Al(14 wt%)‐Zn(8 wt%)‐Mg alloy in artificial seawater media at room temperature was studied in a rotating cylinder electrode (RCE) system under turbulent flow conditions. Five different rotation rates were studied: 100, 1000, 3000, 5000, and 7000 rpm. The corrosion rates were measured by electrochemical impedance spectroscopy (EIS). For the system studied, the steady‐state corrosion potential increased with increase in rotation rate. The effect of increasing the rotation rate is to increase the availability of oxygen at the surface, which in turn will polarize the corrosion reaction in the more noble direction. The corrosion rate also increases with increase in RCE rotation rate. This reflects the fact that the rate of corrosion is controlled, at least in part, by the rate of mass transfer. In this case, the effect of increase in the rotation rate on the corrosion rate is to increase the interfacial concentration of the reactant (oxygen).     

用CA方法模拟过冷熔体中自由树枝晶的生长

基于溶质扩散和界面能的作用，建立了过冷熔体中自由树枝晶的生长模型，考虑了成分过冷、曲率过冷和界面能各向异性，用胞元自动机（CA）方法模拟了枝晶生长、界面扰动以及分枝的竞争演化，对枝晶尖端生长速度和过冷度的关系进行了模拟计算，并与L-G-K理论模型进行了定量的比较。     

Composition determination of Si/Si<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript>/Si by photoreflectance spectroscopy

UHVCVD-grown Si/Si_1−xGe_x/Si heterostructure is investigated by photoreflectance spectroscopy (PR). The principle of PR in determining Ge content of a Si_1−xGe_x epilayer is thoroughly described. The unambiguous E₁ transition energy in the Si_1−xGe_x epilayer is very useful to determine Ge content during PR analysis. R&R study with 10 repeats at the same point indicates that the measurements of PR are reproducible. These results demonstrate that PR is very promising for analysis of Si_1−xGe_x epilayer characterization with constant Ge content.     

An investigation of the reduction of oxygen at a rotating disc electrode with heat transfer facilities

The oxygen reduction reaction on a nickel rotating disc electrode has been examined under isothermal conditions and with heat transfer. The results show that although the limiting rate of oxygen mass transfer increases with an increase in the bulk temperature under isothermal conditions, the rate of charge transfer does not increase correspondingly. It is suggested that as the temperature is increased the oxygen reduction reaction on nickel moves from a predominantly 4 electron process to a predominantly 2 electron process. The effect of heat flux is to stimulate the limiting rate of mass transfer. This effect is attributed to the creation of thermal convection by the production of thermal eddies rather than to an increase in the interfacial temperature. It is shown that, notwithstanding the change from a4 to a2 electron process, as the temperature is raised, the effect of heat flux also gives rise to an increase in charge transfer in the oxygen reduction reaction on nickel since the thermal eddies increase mass transfer faster than the change in interfacial temperature decreases z. It is suggested that similar mass transfer effects produced by heat transfer will occur on other metals but that the charge transfer effect associated with oxygen reduction will depend on the mechanism of the reaction on the particular metal.     

Impact of diffusion on concentration profiles around near-critical nuclei and implications for theories of nucleation and growth

In order to better understand the interplay of diffusion and interfacial processes in nucleation phenomena we have performed kinetic Monte Carlo simulations of a lattice gas model with realistic but generic microscopic dynamics. These simulations are used to probe the complete dynamic range extending from diffusion-limited through interface-limited kinetics. Most phenomenological theories describing nucleation, growth and/or coarsening focus on either the diffusion-limited or interface-limited regime. Calculations are performed on initially monodisperse clusters placed into solutions of uniform concentration. In agreement with predictions, our simulations show the appearance of regions of enhanced solute concentration around clusters smaller than the critical size, and of solute depletion around clusters larger than the critical size. The range and magnitude of these effects are largely controlled by the ratios of the rate of free diffusion to those of interfacial attachment and detachment processes. Furthermore, these simulations show that the rate of cluster growth depends strongly on the diffusion rate and correlates well with the local solute concentration at the cluster surface, over the entire dynamic range studied. In “diffusion-limited” phenomenological models the solute concentration at the cluster surface is assumed to be determined by the radius of the cluster, through a local-equilibrium condition. Our results indicate that in the intermediate regime in which the rates of diffusion and interfacial processes are similar, such assumptions are qualitatively incorrect and so models that assume either fully diffusion-limited or fully interface-limited growth and coarsening should not be used. We show, in particular, that the recently proposed “coupled-flux model” correctly and naturally describes the underlying physics over the complete dynamic range and therefore is generally preferable.