一种制备Ni/Al2O3复合陶瓷的新方法

借助异相成核技术，在镍粒子表面包覆氢氧化铝，经烧结制备得到了Ni/Al2O3复合粒子，以所得复合粒子为原料，采用凝胶注模成型工艺在石墨保护下的无压烧结过程，得到了致密复合陶瓷（相对密度＞95％）。实验表明，可以将有机凝胶铸模成型用于陶瓷－金属复合材料的制备，更进一步地避免了成本较高的热压烧结技术。     

The influence of brazing conditions on joint strength in Al2O3/Al2O3 bonding

The brazing of alumina ceramic to itself was performed using Ag₅₇Cu₃₈Ti₅ filler alloy. The bonding was carried out in a vacuum of 7 × 10^?3 Pa, and the joining conditions were at 1073, 1123, 1173, 1223, 1273 and 1323 K for 1.8ks under a pressure of 0.01 MPa, at 1123 K with a pressure of 0.01 MPa for 0, 0.3, 0.9, 1.8, 2.7 and 3.6 ks, and at 1123 K for 1.8 ks with pressures of 0, 0.01, 0.05, 0.10, 0.15, 0.20 and 0.30 MPa, to determine the effects of joining temperature, pressure and holding time on the joint strength. The joint strength was measured by shear tests. The interface microstructures and fractured surfaces after testing were observed by scanning electron microscopy (SEM). It was shown that the shear strength of Al₂O₃/Al₂O₃ joints was largely affected by the joining conditions; it first increased and then decreased with increasing joining temperature, pressure and holding time and depended mainly on the strength of interfacial reaction layer itself and the interface bonding strength between the reaction layer and the ceramic. The maximum joint strength was obtained when the reaction occurred under a suitable temperature, pressure and time, and the reaction layer thickness was about 2 μm. SEM observations revealed that there were four types of fracture and each kind corresponded to a different strength.     

Effect of preparation method on the dispersion and activity of V2O5–Al2O3 catalysts

Al2O3-supported 12 wt% V2O5 catalysts were prepared by physically grinding both the oxides (solid–solid wetting) and by wet impregnation techniques. The physical mixtures (PM) were treated under two different conditions – calcination in the presence of dry oxygen and wet oxygen. The catalysts were characterized by x-ray diffraction, scanning electron microscopy, electron spin resonance and oxygen and carbon dioxide chemisorptions. Vanadia dispersion of the physical mixture calcined in the presence of wet oxygen was found to be very similar to that of the V2O5/Al2O3 catalyst prepared by the standard impregnation method. Methanol partial oxidation activities of these catalysts were also comparable. This revised version was published online in November 2006 with corrections to the Cover Date.     

InP/GaAs低温键合的新方法

通过对 InP/GaAs 异质键合实验方法的研究,提出了包括表面活化处理、真空预键合和退火热处理的三步法,在350℃低温下实现了InP/GaAs异质材料的键合。界面电流 电压(I V)特性的研究表明,350℃样品的界面过渡层极薄,电子主要以隧穿方式通过界面,而450℃的扩散使得过渡层增厚,界面电流 电压特性可视为双肖特基二极管的反向串联。同时,对键合样品也进行了拉力测试,实验结果表明 450℃样品的键合强度优于350℃样品。最后,对InP/GaAs异质材料的键合机理进行了探讨。     

氧化铝-水纳米流体的制备及其分散性研究

通过在水介质中添加纳米氧化铝粒子,研制了一种新型传热冷却工质Al2O3-H2O纳米流体,给出的纳米流体沉降照片和粒径分布显示了加入分散剂的悬浮液具有较高的分散性、稳定性.同时还测定了纳米Al2O3-H2O悬浮液的zeta电位和吸光度,探讨了不同pH值和SDBS分散剂加入量对纳米氧化铝粉体在水相体系分散稳定性的影响.结果表明:zeta电位的绝对值与吸光度有良好的对应关系,zeta电位绝对值越高,吸光度越大,粉体体系的分散性能越好;pH值约在8.0时,溶液的zeta电位绝对值较高,吸光度较大,说明此时有较好的分散效果;SDBS能显著提高水溶液中Al2O3表面zeta电位绝对值,增大了颗粒问静电排斥力,改善了悬浮液稳定性.在0.1%纳米Al2O3-H2O悬浮液中,SDBS分散剂最佳加入量(质量分数)为0.10%时,能得到分散稳定的悬浮液体系.     

Properties of magnetron-sputtered electrically insulating Al2O3 coatings on copper

Amorphous Al₂O₃ coatings were deposited on Cu substrates with metallic bond layers by different magnetron-sputtering processes. Such sputtering conditions as the type of discharge, target material, total pressure, sputtering gas composition and substrate temperature were varied to study the process effects on the structure and properties of the coatings deposited. The structure and general properties were found to be strongly dependent on the type of process and parameters. The breakdown voltages did not show any significant lowering as the temperature was increased from 20 to 400–500 C. The maximum temperature without formation of cracks in the Al₂O₃ coating on Cu was about 700 C. The d.c. electrical conductivities of the Al₂O₃ were similar to that of bulk Al₂O₃ at different temperatures. The results reveal the potential use of magnetron-sputtered Al₂O₃ coatings on Cu for electrical insulation and oxidation protection in different high-temperature applications, e.g. on metallic magnetohydrodynamic electrode and insulator modules.     

A simple chemical method for preparation of hydroxyapatite coatings on Ti6Al4V substrate

A novel, simple and economical chemical bath method for deposition of calcium hydroxyapatite coating has been developed. The coatings were prepared from EDTA solutions in alkaline media on Ti6Al4V substrates. The method is based on thermal dissociation of the Ca(EDTA)^2- complex at 65–95 °C. Two chemical baths with and without presence of Na⁺ and Cl^- were used for the deposition. The Rutherford back scattering study shows that the coating material from bath which contained sodium and chlorine ions have their presence in the coated material. The bath which has been prepared with potassium substituting sodium and nitrate substituting chlorine produced coatings with better stoichiometry, with Ca/P=1,67. The X-ray analysis revealed that the calcium hydroxyapatite coatings have preferred crystal orientation in the 002 direction. © 2001 Kluwer Academic Publishers     

Al2O3 and TiO2 atomic layer deposition on copper for water corrosion resistance

Al(2)O(3) and TiO(2) atomic layer deposition (ALD) were employed to develop an ultrathin barrier film on copper to prevent water corrosion. The strategy was to utilize Al(2)O(3) ALD as a pinhole-free barrier and to protect the Al(2)O(3) ALD using TiO(2) ALD. An initial set of experiments was performed at 177 °C to establish that Al(2)O(3) ALD could nucleate on copper and produce a high-quality Al(2)O(3) film. In situ quartz crystal microbalance (QCM) measurements verified that Al(2)O(3) ALD nucleated and grew efficiently on copper-plated quartz crystals at 177 °C using trimethylaluminum (TMA) and water as the reactants. An electroplating technique also established that the Al(2)O(3) ALD films had a low defect density. A second set of experiments was performed for ALD at 120 °C to study the ability of ALD films to prevent copper corrosion. These experiments revealed that an Al(2)O(3) ALD film alone was insufficient to prevent copper corrosion because of the dissolution of the Al(2)O(3) film in water. Subsequently, TiO(2) ALD was explored on copper at 120 °C using TiCl(4) and water as the reactants. The resulting TiO(2) films also did not prevent the water corrosion of copper. Fortunately, Al(2)O(3) films with a TiO(2) capping layer were much more resilient to dissolution in water and prevented the water corrosion of copper. Optical microscopy images revealed that TiO(2) capping layers as thin as 200 ? on Al(2)O(3) adhesion layers could prevent copper corrosion in water at 90 °C for ~80 days. In contrast, the copper corroded almost immediately in water at 90 °C for Al(2)O(3) and ZnO films by themselves on copper. Ellipsometer measurements revealed that Al(2)O(3) films with a thickness of ~200 ? and ZnO films with a thickness of ~250 ? dissolved in water at 90 °C in ~10 days. In contrast, the ellipsometer measurements confirmed that the TiO(2) capping layers with thicknesses of ~200 ? on the Al(2)O(3) adhesion layers protected the copper for ~80 days in water at 90 °C. The TiO(2) ALD coatings were also hydrophilic and facilitated H(2)O wetting to copper wire mesh substrates.     

Al2O3/Cu/Al扩散连接工艺参数的优化

通过一定范围内的强度实验数据建立了Al2O3/Cu/Al扩散连接工艺规范参数优化的数学模型，得到了评价接头综合性能的回归方程。利用该方程求得最佳接头性能的工艺参数为：T＝777K、t=1226s。对该工艺规范扩散连接的Al2O3/Cu/Al接头进行强度试验，接头抗拉强度为108MPa、剪切强度为45MPa。强度试验结果表明，接头获得最佳综合强度值的工艺规范介于获得最大抗拉强度值时的规范与获得最大剪切值时的规范之间。在最佳综合规范下，接头的抗拉强度和剪切强度值与最大抗拉强度、最大剪切强度值接近，这表明数学模型所计算出来的最佳规范与实际值吻合较好。     

A new sol-gel route using inorganic salt for synthesizing Al2O3 nanopowders

Boehmite (γ-AlOOH) powder was first prepared by sol-freeze drying method using inexpensive AlCl₃.6H₂O as raw material, and then γ-Al₂O₃ nanopowder with average diameter of 6 nm and α-Al₂O₃ nanopowder with mean diameter of 30 nm were obtained by the calcination of the above γ-AlOOH powder at 500 °C and 1100 °C, respectively. Potential-pH diagrams of Al-H₂0 system at 25 °C and 90 °C were obtained, separately. Thermodynamic analysis of the main reactions in the process of thermal decomposition of Al(OH)₃ was also made using Temkin-Schwarzman's method and by means of regression analysis. Investigations of the potential-pH diagrams of Al-HO system and the thermodynamic analysis of thermal decomposition of Al(OH)₃ provide a guide to the formation of boehmite sol and heat treatment of boehmite powder, respectively.     

Properties of Al2O3 nano-particle reinforced copper matrix composite coatings prepared by pulse and direct current electroplating

Cu–Al₂O₃ nano-composite coatings have high potential for use in applications in which high mechanical properties together with high corrosion resistance are required. In the present study it is intended to produce copper nano-alumina composite coatings with various nano-alumina contents in order to investigate the effect of alumina reinforcement particles on corrosion resistance and mechanical properties such as hardness and wear resistance. The composite coatings were deposited using direct current (DC) and pulse current (PC) plating. The microstructures of the coatings produced from both methods were examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The wear behaviors, micro hardness, coating thickness, corrosion rate and coating porosity were examined using appropriate methods. Compared to DC deposition, PC plating facilitated higher amounts of particle incorporation with more uniform distribution. The results indicated that the mechanical properties of the applied coatings with incorporated nano-alumina reinforcement were far more superior as compared to its own matrix as well as non-composite copper coatings. It was also found out that increasing the amount of nano-alumina content in the coating, led to enhanced general properties of the coatings.     

Plasma spraying of Al2O3 and Al2O3Y2O3

A microstructural study has been carried out of plasma-sprayed Al₂O₃ and mixed and sintered Al₂O₃Y₂O₃. In order to ascertain the degree of metastability achieved by plasma spraying, these results are compared with a similar experiment utilizing a CO₂ laser for melting and the hammer-and-anvil technique for quenching of the same materials. X-ray diffraction methods were used to determine the obtained phases and crystal structures. In addition, transmission electron microscopy was used to confirm the phases present and to study their morpology. The porosity was studied with both mercury intrusion porosimetry and small angle neutron scattering. The addition of Y₂O₃ is shown to decrease the porosity from 15% to 7.5%. Adhesion is likewise related to the addition of Y₂O₃ and it is seen that adhesion of the mixture is measurably improved over that of pure Al₂O₃. The implication of these results is discussed.     

Fabrication and characterization of Au-nanoparticle/W-nanodendrite structures on Al2O3 substrate

An Au-nanoparticle/W-nanodendrite compound structure was fabricated on an insulator Al₂O₃ substrate using an electron-beam-induced deposition (EBID) process combined with an ion sputtering method. The as-fabricated compound structures were characterized and analyzed using conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) and X-ray energy dispersive spectroscopy (EDS). W-nanodendrite structures with the tips of 3 nm were grown self-standing at the edge of the Al₂O₃ substrate at positions separated from each other in distance of several nanometers. Au-nanoparticles with a grain size of 2.1 nm were uniformly distributed on the W-nanodendrites. The Au-nanoparticles were determined to be the equilibrium phase of Au with the face-centered cubic (fcc) structure.     

Al2O3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

1.IntroductionTo improve the mechanical properties and relieve mis-matches between the filler metals and base materials,the particulates of superalloys,ceramic or carbon fiberswere added into the conventional brazing filler metal toform composite filler material.The method has beenused in aero-engine component repairing[1,2],fine castcomponent joining[3],wide clearance butt jointing[4],ce-ramic brazing[5,6]and electronic package[7].However,the method was used mostly in metal brazing.The mi-cro…     

Interface compounds formed during the diffusion bonding of Al2O3 to Ti

The interfacial reaction products of Ti/Al₂O₃ joints obtained in the context of real diffusion bonding technology were investigated by means of X-ray diffraction analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy. Some Ti reacted with Al₂O₃ giving titanium oxides, but the main mass transport occurred into the bulk Ti due to Al₂O₃ dissolution. The formation of a Ti[Al, O] solid solution followed by a order/disorder reaction yielded Ti₃Al. Further Al enrichment at the interface could lead to the formation of TiAl, which was not observed in the present work due to either the short residence time at the bonding temperatures or to its lower oxygen solubility. For joints obtained at 800°C and shear test fractured it was ascertained that the crack always propagated within the Ti₃Al layer.