Mechanomaking of Fe/Al2O3 and FeCr/Al2O3 nanocomposites powders fabrication

Nanocomposite powders (Fe or Fe-Cr alloy)/-Al₂O₃ (75 and 85 vol.%) were obtained by room-temperature high-energy milling powder mixtures of hematite (and chromium oxide) with aluminum and alumina in a high-capacity mill for 8-10 h. The composition of iron and iron alloys was followed by Mössbauer spectroscopy, while the appearance of other phases was revealed by X-ray diffraction. The powder particles produced are assemblies of grains (10–20 nm in size) with a wide size distribution (from well below 1 μm up to several hundreds) and low porosity (fully dense particles). Both the metallic and ceramic phases have crystallite sizes below 15 nm for all the compositions investigated. Nano-nano type ceramic nanocomposites were, therefore, obtained.     

多层陶瓷结构Al2O3-Fe2O3/3Y-TZP梯度复合陶瓷的制备及性能

为更好地实现口腔修复体的美学修复效果,采用掺杂不同含量Fe₂O₃（0.01wt%~0.09wt%）和Al₂O₃（0.1wt%）的3 mol% Y₂O₃稳定的ZrO₂（3Y-TZP）粉体为原料,经过铺粉、压制、烧结等工艺制得色度渐变的多层陶瓷结构Al₂O₃-Fe₂O₃/3Y-TZP梯度复合陶瓷。对该梯度复合陶瓷的色度分布、烧结性能和力学性能进行检测,同时研究了Fe₂O₃和Al₂O₃的掺杂对3Y-TZP陶瓷组织和性能的影响。结果表明,制得的Al₂O₃-Fe₂O₃/3Y-TZP梯度复合陶瓷色度由红黄向白色沿成分变化方向呈梯度变化,与天然牙齿色度分布规律一致;力学性能呈梯度变化并从无色端到有色端逐渐降低,但仍满足牙科使用需求（≥ 800 MPa）;在无色瓷层中掺杂微量Al₂O₃（0.1wt%）可以改善Al₂O₃-Fe₂O₃/3Y-TZP梯度复合陶瓷的烧结性能,避免在预烧结过程中发生开裂。微量Fe₂O₃和Al₂O₃的掺杂会促进其在烧结过程中的致密化及晶粒长大;微量Fe₂O₃（0.01wt%）和Al₂O₃（0.1wt%）的掺杂有助于提高3Y-TZP陶瓷的挠曲强度,然而随着Fe₂O₃掺杂量的继续增多（≤ 0.09wt%）挠曲强度降低。      

Al2O3 / 3Y-TZP 层状复合材料的制备及其超塑性能

采用流延制膜和热压烧结工艺制备了Al₂O₃ / 3 Y-TZP 层状复合材料。用SEM 观察显微组织, 并采用高温深拉实验对该材料进行了超塑性能研究。结果表明: 1550 ℃热压烧结制备的材料晶粒细小, 界面结合良好;当应变速率一定时, 变形温度对Al₂O₃ / 3Y-TZP 层状复合材料的超塑性能具有重要影响, 1500 ℃时得到深拉成形最大高度, 温度较高和较低时超塑性能均会降低。      

Effect of Al2O3 particle size on vacuum breakdown behavior of Al2O3/Cu composite

In order to clarify the effect of Al₂O₃ particle size on the arc erosion behavior of the ceramic-reinforced Al₂O₃/Cu composite, Al₂O₃/Cu composites with different sizes of Al₂O₃ particles were prepared by powder metallurgy, the effect of Al₂O₃ particle size on the characteristics of arc motion was studied, and the mechanism of arc erosion of Al₂O₃/Cu composites was discussed as well. The results show that with decrease in the size of Al₂O₃ particles, the erosion area increases significantly and the erosion pits become shallower. The vacuum breakdown is preferred to appear in the area between Al₂O₃ particle and the copper matrix. Based on the experimental results and theoretical analysis, a particle partition arc model is proposed.     

In situ processing and aging behaviour of an aluminium/Al2O3 composite

Reactive sintering involving a displacement reaction between aluminium and CuO powders was applied to fabricate an aluminium based composite. The two powders were mixed in a ball mill and uniaxially pressed before sintering in nitrogen atmosphere at 900 °C. During sintering a displacement reaction between CuO and aluminium occurred, which resulted in in situ synthesis of alumina particles. Differential thermal analysis (DTA), X-ray diffractometry (XRD), optical and scanning electron microscopies were used to investigate the phase and microstructural changes taking place during processing of the composite. Results revealed that no chemical reaction occurred during ball milling and Al₂O₃ phase developed in two stages during sintering of the compact. Below 700 °C, amorphous alumina formed which transformed to crystalline alumina at higher temperature. Aging response of the composite was examined as a function of time in temperature range of 180–220 °C. Composite attained a peak hardness value of 133 H_v after 4 h of aging at 200 °C.     

Al2O3-TiC/Al2O3-TiC-CaF2复合叠层陶瓷材料摩擦磨损性能

将Al₂O₃-TiC陶瓷材料与具有固体润滑特性的Al₂O₃-TiC-CaF₂陶瓷材料进行叠层, 通过真空热压烧结制备Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料。在环盘式摩擦磨损试验机上进行摩擦磨损实验, 研究该材料在不同载荷、 转速条件下的摩擦系数和磨损率, 分别用SEM及EDS观察材料磨损前后的微观形貌和分析其成分组成, 研究其磨损机制。结果表明: 在相同载荷条件下, Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料的摩擦系数和磨损率随着转速的升高而下降, 在相同转速条件下, 其摩擦系数和磨损率随着载荷的增加而下降; Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料的磨损机制主要是磨粒磨损和黏着磨损。     

Al2O3颗粒形貌对注凝成型ZrO2/Al2O3陶瓷性能的影响

采用3种不同形貌的Al₂O₃原料对注凝成型制备ZrO₂/Al₂O₃（ZTA）陶瓷工艺中悬浮体的流变性能进行了研究。以低毒的单体N,N-二甲基丙烯酰胺（DMAA）制备了ZrO₂/Al₂O₃坯体和陶瓷。讨论了3种不同形貌的Al₂O₃原浆料的分散剂用量、球磨时间和固含量对浆料流变性的影响。Al₂O₃粉体呈扁平状有利于降低浆料的黏度,Al₂O₃粉体呈棒状对生坯强度的提高有利。制得的3种ZrO₂/Al₂O₃坯体颗粒间结合紧密,抗弯强度分别达到21.45,19.87,25.90 MPa。Al₂O₃粉体呈颗粒状有利于最终陶瓷力学性能的提高,陶瓷的抗弯强度及断裂韧性分别为680 MPa和7.49 MPa·m^1/2,453.1 MPa和6.8 MPa·m^1/2,549.4 MPa和6.34 MPa·m^1/2。     

Nanocomposite Al2O3–ZrO2 thin films grown by reactive dual radio-frequency magnetron sputtering

Crystalline alumina–zirconia nanocomposites have been synthesized at 450 °C and 750 °C with reactive magnetron sputtering using radio-frequency power supplies. The composition of the films ranged from pure alumina to pure zirconia as measured by ion beam techniques. Microstructural characterization showed the presence of monoclinic zirconia in the pure zirconia films and γ-alumina in the pure alumina films while the nanocomposites contained either an amorphous compound, γ-alumina, cubic zirconia or a mixture of these. The grain size was  5 nm for the nanocomposite compared to larger grains in the pure oxide films. Electron energy loss spectroscopy showed a clear progression from the pure alumina to the pure zirconia.     

Al2O3基多孔隔热材料表面Al2O3/MoSi2涂层的制备及其性能

采用刷涂法在Al₂O₃基多孔隔热材料表面制备Al₂O₃/MoSi₂涂层,涂层以硅溶胶作为粘结剂,纳米Al₂O₃与Al₂O₃纤维作为耐高温组分,MoSi₂为高发射率组分。通过SEM、XRD对Al₂O₃/MoSi₂涂层微观表面结构、物相组成进行分析。研究纳米Al₂O₃与Al₂O₃纤维的质量比和MoSi₂含量对Al₂O₃/MoSi₂涂层耐温性能的影响,并对Al₂O₃/MoSi₂涂层的抗热震性能、发射率进行表征。结果表明,当纳米Al₂O₃与Al₂O₃纤维的质量比小于1∶1时,热考核后Al₂O₃/MoSi₂涂层表面无裂纹产生;当纳米Al₂O₃与Al₂O₃纤维的质量比在1∶2~1∶4之间时,Al₂O₃/MoSi₂涂层中的纤维网络较完整。MoSi₂的含量为20%时,Al₂O₃/MoSi₂涂层抗热震实验循环25次后表面保持完好,热考核后在2.5~25 μm波段的平均发射率在0.85左右,具有较高的发射率。      

Hump peak formation and the crystallization in amorphous Al87Co10Ce3 alloy

A distinct hump peak was observed at the scattering angle 2θ ≈ 44° in the X-ray diffraction (XRD) pattern of rapidly quenched amorphous Al₈₇Co₁₀Ce₃ alloy. From the XRD patterns of amorphous Al-Co-Ce alloys with different compositions, it is found that the intensity of the hump peak increases as the Co/Ce atomic ratio increases, while the prepeak which characterizes the medium-range order (MRO) becomes weak. The hump peak has a close relationship with the glass forming ability in the Al-Co-Ce system. Furthermore, the crystallization behavior of Al₈₇Co₁₀Ce₃ alloy was investigated by the DSC and XRD methods. Compared with Al₈₇Ni₁₀Ce₃ alloy, Al₈₇Co₁₀Ce₃ alloy did not show a single process of grain growth for fcc-Al particle. The formation of a hump peak is presumed to be associated with the presence of pre-existing nuclei of fcc-Al and Co₂Al₉ in as-quenched amorphous Al₈₇Co₁₀Ce₃ alloy.     

Raman spectroscopic study of structure of WO3La2O3B2O3 glasses with no color and crystallization of LaBWO6

Glasses with the nominal compositions of xWO₃25La₂O₃(75 − x)B₂O₃ (mol%) with x = 15, 25, and 50 were prepared using a conventional melt quenching method, and their structure and crystallization behavior were examined from Raman scattering spectra and X-ray diffraction analyses. The glasses are colorless in the visible light region and give the optical band gap energy of 3.49-3.61 eV. The glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing WO₃ content. The strong Raman bands at 840 and 940-960 cm⁻¹ suggest that the main coordination state of W⁶⁺ ions in the glasses is isolated (WO₄)²⁻ tetrahedral units. The formation of WO₆ octahedral units is also suggested in the glasses with high WO₃ contents. The main crystallization mechanism in the glasses is the surface crystallization, and the glass of 50WO₃25La₂O₃25B₂O₃ shows the crystallization of LaBWO₆ single phase. The present study proposes that WO₃La₂O₃B₂O₃ glasses and crystallized glasses are very interesting as optical functional materials.     

Influence of rare-earth oxides on structure and crystallization properties of Bi2O3–B2O3 glass

Bi₂O₃·B₂O₃ glasses doped with rare-earth oxides (RE₂O₃) (RE³⁺ = La³⁺, Pr³⁺, Sm³⁺, Gd³⁺, Er³⁺ and Yb³⁺) were prepared by the melting–quenching method. The relationships between composition and properties were demonstrated by IR, DSC, XRD and SEM analysis. The results show that the network structure resembles that of undoped Bi₂O₃·B₂O₃ glass, composing of [BO₃], [BO₄] and [BiO₆] units. RE₂O₃ stabilizes the glass structure as a modifier. Transition temperature (T_g) increases linearly with cationic field strength (CFS) of RE³⁺. La₂O₃, Pr₂O₃, Sm₂O₃ and Gd₂O₃ are benefit to promote the formation of BiBO₃ crystal. When Er₂O₃ and Yb₂O₃ are introduced, respectively, the main crystal phase changes to Bi₆B₁₀O₂₄. Transparent surface crystallized samples are obtained by reheating at 460–540 °C for 5 h. In this case, needle like BiBO₃ crystal or rare-earth-doped BiBO₃ crystal (Pr_xBi_1−xBO₃ and Gd_xBi_1−xBO₃) are observed, which is promising for non-linear optical application.     

Precipitation of ZnO in Al2O3-doped zinc borate glass ceramics

Crystallization behavior of the oxide semiconductor ZnO in zinc borate glass was investigated. The precipitated crystalline phase of glass ceramics containing a small amount of Al₂O₃ was α-Zn₃B₂O₆ whereas that of the glass ceramics containing a large amount of Al₂O₃ was ZnO. It was found that the c-oriented precipitation of ZnO in a glass ceramic was brought about by the in-plane crystal growth of needle-like ZnO crystallites along the a-axis. Amount of Al₂O₃ that can make glass network affected the coordination state of B₂O₃ in the glass, and a three-coordinated BO₃ unit was preferentially formed in the glass containing a higher amount of Al₂O₃. The present results suggest that crystallization of ZnO from multi-component glass is dominated by the local coordination state of the mother glass.     

Preparation and properties of nano-SiC strengthening Al2O3 composite ceramics

The processing and mechanical behaviors of Al₂O₃-xwt.%SiC (x = 1, 2, 5, ASx) nano-composites prepared by the in situ synthesis of SiC from polycarbosilane (PCS) were investigated. The composites were densified by hot pressing. The microstructure and mechanical properties of the sintered composites were analyzed. The results showed that a fully dense structure was obtained when a few nano-SiC were doped and that the fracture toughness and strength were highly improved compared with those of monolithic Al₂O₃. The fracture toughness reached 5.1 MPa m^1/2 in AS2 composite. The maximum flexural strength was 516 MPa obtained in AS1 composite.     

Al/Al2O3多层膜的表面和界面的分析研究

用热蒸发沉积和自然氧化及加热法制备纳米量级的Al/Al2O3薄膜和多层膜.用X射线光电子谱仪(XPS)和透射电镜(TEM)对样品进行检测.XPS实验说明自然氧化的Al2O3膜层厚在2～5 nm.Al/Al2O3薄膜及多层膜的O与Al的原子浓度比为1.43～1.85.Ar离子刻蚀的XPS实验结果(刻蚀速率为0.09 nm/s)说明2个对层的Al/Al2O3多层膜截面样品具有周期性结构.TEM观察到了5个对层的Al/Al2O3多层膜的层状态结构,其周期为4 nm.由此说明,热蒸发及自然氧化法是制备纳米量级的Al/Al2O3多层膜的有效方法.     

High-temperature shear strength of lead-free Sn-Sb-Ag/Al2O3 composite solder

The lead-free Sn-1.7Sb-1.5Ag solder alloy and the same material reinforced with 5 vol.% of 0.3-μm Al₂O₃ particles were synthesized using the powder-metallurgy route of blending, compaction, sintering, and extrusion. The mechanical properties of both monolithic and composite solders were studied by shear punch testing (SPT) at temperatures in the range of 25-130 °C. Depending on the test temperature, the shear yield stress (SYS) increased by 4.8-8.8 MPa, and ultimate shear strength (USS) increased by 6.2-8.8 MPa in the composite material. The strength improvement was mostly due to the CTE mismatch between the matrix and the particles, and to a lesser extent to the Orowan strengthening mechanism of the submicro-sized Al₂O₃ particles in the composite solder. The contribution of each of these mechanisms was used in a modified shear lag model to predict the total composite-strengthening achieved.     

氧化铝粉体表面纳米化修饰及其在耐磨涂层中的应用

在低温条件(80℃)下,以钛酸丁酯为原料,利用胶溶–回流法在氧化铝粉体表面制备了纳米TiO2颗粒.通过扫描电镜、X射线衍射、X光电子能谱仪、BET等检测手段对复合颗粒的表面形貌、包覆层相组成、比表面积等进行了表征.结果表明,纳米TiO2颗粒在微粉表面形成纳米薄膜修饰层,包覆层主要为锐钛矿型相,表面纳米化修饰后氧化铝粉体表面的粗糙度显著增加,比表面积较包覆前提高了30倍以上.将经表面纳米化修饰后的微粉应用于以有机硅改性环氧树脂为基体的耐磨涂层中,其磨损失重仅为包覆前复合耐磨涂层的55%,耐磨性显著提高,并初步讨论了复合耐磨涂层的摩擦磨损性能.     

Microstructural characterization and properties of ZrO2/Al2O3 thermal barrier coatings by gas tunnel-type plasma spraying

Spraying condition plays an important role in the plasma-sprayed coating process and affects the final properties of the coatings. Zirconia, alumina and zirconia/alumina composite coatings were prepared on a stainless-steel substrate (SUS304) by the gas tunnel-type plasma spraying. Effects of different alumina mixing ratios on the coating properties were investigated. The results indicated that the mixing ratio of powders and the traverse number of substrate had an influence on the hardness, porosity and wear weight loss of composite coatings. The hardness increased while the porosity decreased with the increase in alumina mixing ratio. The porosity that was less than 10% and a hardness about Hv=1400 was obtained for the alumina coating. The adhesive strength and wear weight loss of the composite coatings were also clarified at different alumina mixing ratios.     

Characterization of PdAg/Al2O3 composite membrane by electroless co-deposition

In this work, PdAg/Al₂O₃ composite membranes prepared by electroless co-deposition technique have been studied. Effects of plating time, Ag composition and total concentration of metal ions on surface morphologies, composition and microstructure of the resulting layers were investigated. Scanning electron microscope, energy dispersive spectrometer and nitrogen permeation technique were used to characterize the as-prepared composite membranes. From the experimental results, it shows that the surface morphology of the deposited PdAg layer is strongly affected by the Ag content of the plating bath. Since large differences of deposition rates and growth modes are observed between Pd and Ag grains, the PdAg layer exhibits the dendritic structure. As the Ag content is approximately 50%, the dendritic structured PdAg layer reveals the largest nitrogen permeability with the smallest size of residual pores. Furthermore, a comprehensive electrochemical analysis is proposed to interpret the composition and structure of the PdAg layer. Eventually, the experimental results are quite consistent with those predicted from the electrochemical analysis.     

A facile method for nickel catalyst immobilization on ultra fine Al2O3 powders

A pure nickel coating has been successfully plated on the surface of ultra fine Al₂O₃ particles via a facile electroless plating method. Coating morphology and crystallite size can be tailored by pH values. Dense coating with the maximum crystallite size of 24 nm was obtained at pH 11.0 and porous coating with the minimum crystallite size of 15 nm was obtained at pH value 12.5. The plated powders have been demonstrated to be an effective catalyst for growing boron nitride nanotubes.