Monocrystalline silicon surface passivation by Al2O3/porous silicon combined treatment

In this paper, we report on the effect of Al₂O₃/porous silicon combined treatment on the surface passivation of monocrystalline silicon (c-Si). Al₂O₃ films with a thickness of 5, 20 and 80 nm are deposited by pulsed laser deposition (PLD). It was demonstrated that Al₂O₃ coating is a very interesting low temperature solution for surface passivation. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 2 μs to 7 μs at a minority carrier density (Δn) of 1 × 10¹⁵ cm^?3 and the reflectivity reduce from 28% to about 7% after Al₂O₃/PS coating.     

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…     

Dynamic mechanical response of a 1060 Al/Al2O3 composite

The flow stress of a 1060 Al/Al₂O₃ composite increases rapidly with strain rate due to the higher dislocation accumulation rate and the increasing strength of dislocation barriers. The Al/Al₂O₃ interfaces were found to be well bonded even after high-rate deformation of the composite. MgAl₂O₄ particles observed at Al/Al₂O₃ interfaces in the composite of the present study are thought to improve the interface strength. Unlike in pure aluminium, a well-developed cell structure was not observed in the deformed 1060 Al/Al₂O₃ composite. The absence of a well-developed cell structure is thought to result from a more homogeneous slip distribution in the composite.     

Microstructure and Strength of Al2O3/Al2O3 Joints Bonded with ZnO-Al2O3-B2O3-SiO2 Glass-Ceramic

ZnO-Al2O3-B2O3-SiO2 （ZABS） glass powder was used as interlayer to join alumina ceramics. The effect of joining temperature on the microstructure and strength of joints was investigated. The results showed that the ZABS glass can react with alumina substrate to form a layer of ZnAl2O4 at Al2O3/glass interface. Bending test exhibited that low joining temperature （1150℃） led to low joint strength due to the formation of pores in the interlayer, originated by high viscosity of the glass. High joining temperature （1250 ℃） also resulted in low joint strength, because of large CTE （coefficient of thermal expansion） mismatch between amorphous interlayer and alumina substrate. Therefore, only when the joining temperature was appropriate （1200℃）, defect-free interface and high joint strength can be obtained. The optimum joint strength reached 285 MPa, which was the same as the base material strength.     

Microstructure of the Al2O3/Al2O3 Joint Brazed with Cu-Zn-Ti Filler Metal

Microstructure and interface reactions of Al2O3 joints brazed by Cu-Zn-Ti alloy were studied by using SEM, EDS and XRD. The effects of brazing temperature and Ti content on interfacial reactions and microstructure were investigated, and the action of adding Zn into brazing alloy was also studied. TiO, Ti3Al and CuTi were formed at the interface of ceramics and the filler metal, while CuTi, Cu3Ti and alpha -Cu were found in the brazing. The thickness of the reaction layer increased with increasing of brazing temperature, under the same brazing process, the thickness increased with the Ti content.     

Novel silicon surface passivation by porous silicon combined with an ultrathin Al2O3 film

We report on a dual passivation approach of monocrystalline-silicon (c-Si), which combines porous silicon (PS) treatment and pulsed laser deposition (PLD) of Al₂O₃ ultrathin layer. Al₂O₃ ultrathin films were deposited, under an oxygen background pressure of 10 mTorr. In this work we demonstrate that the dual treatment Al₂O₃/PS provide excellent passivation quality of c-Si surfaces. Surface passivation and reflectivity properties are investigated before and after heat treatment at 700 °C. The level of surface passivation is quantified using photoconductance and Fourier-transform infra-red absorption techniques. X-ray diffraction analysis suggested that the heat treatment leads to an average crystallite size decrease which help the diffusion of the Al₂O₃ NPs along the wafer surface. As a result, the effective minority carrier lifetime increases from 2 to 7 μs. Our results demonstrate that this dual treatment not only provides strong passivation of the c-Si substrate but decreases also the total surface reflectivity at 500 nm (from 28 % for untreated c-Si samples to ～7 % for Al₂O₃/PS treated ones).     

硅基HA/Al2O3复合生物涂层的制备与表征

通过磁控溅射沉积、阳极氧化与溶胶-凝胶结合的多步技术在Si(100)表面制备了HA/Al2O3复合生物涂层材料.采用TG-DSC测定了复合涂层中HA外层的烧成温度,采用XRD、FT-IR以及EDS分析了Si(100)基HA/Al2O3复合生物涂层的组成,并借助SEM研究了复合涂层的表面与截面的微观形貌.研究表明,凝胶完全转变为HA外层的最低温度约为550℃,凝胶经600℃处理30min后可在Si(100)-Al2O3基上形成具有一定数量纳米细孔且含有少量CO3的HA外层;A外层嵌入Si(100)基阳极氧化Al2O3多孔层的孔洞中构成HA/Al2O3复合生物涂层.     

Slip casting of Al2O3 and Al2O3/ZrO2 composites

Al₂O₃ and Al₂O₃/ZrO₂ composites have been fabricated by slip casting from aqueous suspensions. The physical and structural characteristics of the starting powders, composition of the suspensions, casting behaviour, microstructure of the green and fired bodies and the mechanical properties of the products were investigated. The addition of ZrO₂ to Al₂O₃ leads to a significant increase in fracture toughness when ZrO₂ particles are retained in the tetragonal form (transformation-toughening mechanism) but when microcracking (due to the spontaneous transformation of ZrO₂ from the tetragonal phase to the monoclinic one) is dominant, an excellent toughness value is accompanied by a drastic drop in strength and hardness.     

光悬浮区熔定向凝固Al2O3/Er3Al5O12和Al2O3/Yb3Al5O12共晶陶瓷的制备与性能研究

本研究探索了光悬浮区熔法制备Al₂O₃/Er₃Al₅O₁₂(ErAG)和Al₂O₃/Yb₃Al₅O₁₂(YbAG) 定向凝固共晶陶瓷。在10 mm/h的抽拉速率下成功获得了凝固组织均匀、内部无裂纹或孔洞的高质量共晶陶瓷。通过高分辨三维X射线衍射仪研究了Al₂O₃和RE₃Al₅O₁₂在三维空间的分布与组织结构; 利用电子背散射衍射技术分析了定向凝固末期Al₂O₃和RE₃Al₅O₁₂两相的晶体学择优取向和相界面关系。力学性能表征结果显示, Al₂O₃/ErAG和Al₂O₃/YbAG具有优异的力学性能, 二者的维氏硬度分别为(13.5±0.4)和(12.8±0.1) GPa;断裂韧性分别为(3.0±0.2)和(3.2±0.1) MPa·m^1/2。     

Influence of surface modification of alumina on bond strength in Al2O3/Al/Al2O3 joints

The subject of the work was to study the effect of Ti thin film on alumina ceramic on mechanical strength and fracture character of Al₂O₃/Al/Al₂O₃ joints. The joints were formed by liquid state bonding of alumina substrates covered with titanium thin film of 800 nm thickness using Al interlayer of 30μm thickness at temperature of 973 K in a vacuum of 0.2 mPa for 5 min. The bend strength was measured by four–point bending test at room temperature. Scanning and transmission electron microscopy were applied for detailed characterization of interface structure and failure character of fractured joint surfaces. Result analysis has shown that application of the Ti thin film on alumina leads to decrease of bond strength properties of Al₂O₃/Al/Al₂O₃ joints along with the change either of structure and chemistry of interface or of failure character.     

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

Investigations of bilayer and trilayer Al₂O₃/SiO₂ and Al₂O₃/HfO₂/SiO₂ antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10^?3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al₂O₃, 0.6 nm ? 0.8 nm/s for HfO₂ and 0.6 nm/s for SiO₂. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al₂O₃/SiO₂ and 78 nm/156 nm/78 nm for Al₂O₃/HfO₂/SiO₂. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.     

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.     

Al2O3含量对PVDF/PVC/Al2O3共混中空纤维膜的影响

以聚偏氯乙烯(PVDF)、聚氯乙烯(PVC)和纳米氧化铝(Al2O3)三元共混,制备中空纤维膜,探讨Al2O3含量对膜性能的影响。结果表明,由于适量Al2O3的加入,中空纤维膜膜孔结构明显改善,大孔减少,微孔增多;亲水性明显提高。Al2O3为最佳含量3%时,水通量和截留率分别达到了289L/(h·m2)和77.2%。     

Al2O3/Ti-Al复合材料中Al2O3晶须的原位合成

利用氧对金属Ti、Al粉的部分氧化,原位合成了含有氧化铝晶须的Al2O3/Ti-Al复合材料,通过XRD和SEM等测试手段,发现Al2O3晶须呈网状交叉分布于基体内部的孔隙中.分析了晶须的生成机理,认为氧化铝晶须是通过VLS机理生成,复合材料的原始组成和温度对晶须的显微型貌有直接的影响:随原始组成中铝含量的增加,产物中晶须的数量总体上是在递增的,且发达程度逐渐提高;热处理温度对晶须直径有直接影响,温度升高可以增加晶须直径.     

Effect of atmosphere on superplastic deformation behavior in nanocrystalline liquid-phase-sintered silicon carbide with Al2O3-Y2O3 additions

Nanocrystalline -SiC with additions of 5.135 wt% Al₂O₃ and 3.867 wt% Y₂O₃ was subjected to tensile deformation in order to study its microstructural behavior under the dynamic process. The liquid-phase-sintered body had a relative density of >95% and an average grain size of 190 nm. Tension tests were conducted at initial strain rates range from 3 × 10^–4 to 2 × 10^–5 s^–1, in the temperature range 1873–2048 K, in both argon and N₂ atmospheres. Although grain-boundary liquids formed by the additions vaporized concurrently with the decomposition of SiC and grain growth, the maximum tensile elongation of 60% was achieved in argon. The grain-boundary amorphous phase formed a crystalline phase during testing in an N₂ atmosphere and fracture occurred at <8% elongation. Grain-boundary sliding was still the dominant mechanism for deformation.