海藻酸钠冷冻干燥制备环保型直通孔多孔氧化铝陶瓷(英文)

将海藻酸钠、氧化铝混合制成的浆料定向冷冻,使水定向结冰成孔,再对坯体进行冷冻干燥,使冰升华留下的孔隙结构得以保存,制备具有直通孔结构氧化铝多孔陶瓷。气孔率为66.7%的多孔氧化铝陶瓷具有比传统氧化铝泡沫陶瓷高10倍的渗透率。利用固相体积含量25%的浆料制备的多孔陶瓷抗压强度达到16.03 MPa。通过在原料中加入天然无毒的海藻酸钠作为黏结剂,不仅使整个工艺过程和原料都环境友好,而且使干燥后的坯体具有一定强度,可以满足搬运和机加工的要求。通过控制浆料的黏度和流动性以及分散剂加入量,获得均匀的孔隙结构。此外,还研究了固相含量、烧结温度对气孔率、压缩强度及渗透率等性能的影响。随着固相含量从30%降低到20%,样品的气孔率从61%提高了到72%,而压缩强度从16.03 MPa下降到3.42 MPa,渗透率从0.19×10–11 m2提高到4.51×10–11 m2。随着烧结温度从1 300℃提高到1 500℃,材料的气孔率从69.72%下降到67.02%,而压缩强度从4.45 MPa提高到18.66 MPa,渗透率从4.51×10–11 m2下降到4.09×10–11 m2。     

以冰为模板制备氧化铝多孔陶瓷及其结构特征

以水玻璃溶液为粘结剂,以冰为造孔模板制备氧化铝多孔陶瓷。采用扫描电镜观测多孔陶瓷的显微结构。结果表明,冰是一种理想的造孔模板,浆体特性对多孔陶瓷结构影响较大,当浆体中相对固相含量增大,多孔陶瓷的孔隙会减小;当浆体粘度降低,易得到片层状与微孔复合结构的多孔陶瓷。     

Microstructure and Mechanical Properties of Porous Alumina Ceramics Fabricated by the Decomposition of Aluminum Hydroxide

The mechanical properties of Al₂O₃-based porous ceramics fabricated from pure Al₂O₃ powder and the mixtures with Al(OH)₃ were investigated. The fracture strength of the porous Al₂O₃ specimens sintered from the mixture was substantially higher than that of the pure Al₂O₃ sintered specimens because of strong grain bonding that resulted from the fine Al₂O₃ grains produced by the decomposition of Al(OH)₃. However, the elastic modulus of the porous Al₂O₃ specimens did not increase with the incorporation of Al(OH)₃, so that the strain to failure of the porous Al₂O₃ ceramics increased considerably, especially in the specimens with high porosity, because of the unique pore structures related to the large original Al(OH)₃ particles. Fracture toughness also increased with the addition of Al(OH)₃ in the specimens with higher porosity. However, fracture toughness did not improve in the specimens with lower porosity because of the fracture-mode transition from intergranular, at higher porosity, to transgranular, at lower porosity.     

Fracture of Alumina with Controlled Pores

Fracture from artificial spherical pores, as well as natural defects, in alumina in a grain-size range of 0.8-9.2 µm has been studied experimentally and compared with a fracture-mechanics model. Results from fracture-strength measurements have been combined with detailed fractographic analysis to elucidate the ensuing crack instability. Two existing models of possible crack configurations have been extended and contrasted. The semicircular crack as well as the circumferential crack both are described as flaws in the stress-concentrating field of a spherical pore. Surface correction terms afforded by the presence of the pore have been incorporated. A comparative computation shows that fracture occurs more likely from the semicircular crack configuration than the circumferential crack configuration.     

挤出胎面气孔的形成机理及解决措施

分析挤出胎面气孔的形成机理并结合生产实践提出相应的解决措施。机头温度过高、挤出速度过快、原材料中水分和挥发分含量较大、热炼时混入空气、供胶不足及机头内部压力不足等是胎面气孔产生的主要原因,分析时既要考虑内在因素(如胶料配方),也要考虑外在因素(如挤出机温度、挤出速度等),选择内、外因素的最佳结合点才是提高胎面挤出质量的关键。添加加工助剂GE3082可以有效降低胶料的挤出温度,增大挤出速度,减小主机电流,降低能耗。     

Al2O3纳米线薄膜的制备及其生成机理研究

研究了一种简单新颖的制备Al2O3纳米线薄膜的电化学方法。以阳极氧化法在高纯铝片表面制备多孔阳极氧化铝的工艺为基础,在草酸电解液中通过一次阳极氧化过程,将阳极氧化铝孔壁溶解形成Al2O3纳米线,均匀覆盖在阳极氧化铝有序孔道的上方,得到一种特殊结构的纳米线薄膜。使用扫描电镜、高分辨透射电镜和X-射线能谱仪对纳米线的形貌、结构及成分进行了表征分析。并结合扫描电镜对不同反应时间长度的产物形貌来观察纳米线的生成过程。探讨了Al2O3纳米线薄膜的生成机理。     

微生物在毛细圆孔中运移的模拟研究

1 INTRODUCTION Microorganisms have been extensively used in industry including microbial enhanced oil recovery[1], groundwater contamination cleanup[2,3], bioremedia- tion of sewage and contaminated soil[4―6]. Since most of microorganism inhabits in porous media like soil and subsurface environments, it is important to under- stand the mechanism of the microbial transport in po- rous media. The transport of microorganism in porous media is involved in both physicochemical and biological p…     

模板组装纳米TiO2多孔膜及形成机理

以钛酸丁酯(TBTi)为原料，加入高分子表面活性剂聚乙二醇(PEG)作模板，采用溶胶-凝胶技术合成了孔径10～500nm可调的纳米TiO2多孔薄膜。扫描电镜(SEM)观察结果表明，合成过程中水含量增加形成的薄膜孔密度减小，而PEG加入量的增加，薄膜表面孔径和孔密度增大。通过红外光谱测试对溶胶-凝胶过程中发生的物理化学变化进行了系统的分析，初步探讨了薄膜多孔结构的形成机理。     

Instability of Cylindrical Voids in Alumina

It is shown from experimental observation that cylindrical voids in polycrystalline alumina are unstable. When isothermally annealed, they undergo various configurational changes, in accordance with the theoretical prediction, prior to an ultimate breakup into rows of spherical voids. The breakup occurs by ovulation, if the aspect ratio is appropriate. If the required aspect ratio is not met, cylindrical voids are directly transformed into spherical voids by spheroidization. The predominant mechanism for void breakup on thermal anneal confirms a model for surface-diffusion-control material transport. The estimated surface-diffusion coefficients at the experimental annealing temperatures agree, within an order of magnitude, with the values reported in the literature.     

氧化电压对多孔阳极氧化铝膜结构及形成的影响

以草酸为电解液研究了氧化电压对多孔阳极氧化铝膜的影响,采用场发射扫描电子显微镜(FE-SEM)对多孔阳极氧化铝膜的表面形貌进行表征.结果表明:氧化电压决定多孔阳极氧化铝膜纳米孔的大小;在一定电压范围内,氧化膜厚度随氧化电压的升高而增加.电流密度与氧化时间的关系曲线表明:在不同电压下多孔阳极氧化铝膜的形成历程基本相同,但形成多孔氧化铝膜时的电流密度随氧化电压的升高而增加.XRD分析结果证实:多孔氧化铝膜由非晶态的Al2O3组成,其组成不随阳极氧化电压而变化.     

Microstructural Characterization of Porous Silicon Carbide Membrane Support With and Without Alumina Additive

Porous silicon carbide (SiC) membrane supports sintered at 1500°–1800°C were prepared by cold isostatic pressing (CIP) under different pressures and using different amounts of alumina additive (0%–4%). The relationship between processing factors and pore size and microstructure was examined. Varying the sintering temperature, the CIP pressure and the amount of additive used were found to be effective for controlling pore size and microstructure. The pore size and particle size of the membrane support prepared without alumina were found to increase with increasing sintering temperature. This was attributed to surface diffusion. Densification of the undoped support did not occur, however, because of concurrent pore development. In the SiC membrane support containing 4% alumina, small particles and a pore size of around 100 nm were retained. This was because of the formation of a limited amount of SiO₂–Al₂O₃ liquid phase during sintering.     

On the Mechanism of Densification of Porous Alumina by Infiltration with an Aqueous Solution of Chromium Oxide

Densification of porous alumina by CrO₃ infiltration was investigated on model composites containing a sapphire interface. Gas–solid deposition of Cr₂O₃ from CrO₃ source on sapphire and glass at 600°C was also investigated. The deposited Cr₂O₃ layers were characterized using X-ray diffraction and transmission electron microscopy. It was found that similar to gas-phase deposition on sapphire, in CrO₃-infiltrated porous alumina Cr₂O₃ grows epitaxially on adjacent alumina surfaces, suggesting a gas–solid condensation mechanism. The deposition rate and morphology of the Cr₂O₃ film deposited on alumina depend strongly on the crystallographic orientation.     

Solidification Microstructures of Laser-Melted Alumina Powder Compacts

Dense, thin sheets of α-alumina formed after solidification of powder compact surfaces which were melted using CO₂ laser radiation. The microstructures and surface topographies varied with the depth of melt. Most significant was a zone of columnar grains oriented in the [661] direction which yielded smooth surfaces for intermediate depths.     

Dispersion and Setting of Powder Suspensions in Concentrated Aqueous Urea Solutions for the Preparation of Porous Alumina Ceramics with Aligned Pores

Highly concentrated alumina powder suspensions have been prepared in aqueous urea solutions of concentrations in the range 200–360 g/100 mL using an ammonium poly(acrylate) dispersant at 80°C. The dispersant concentration for the suspension viscosity minimum in the urea solutions is higher than that in water due to the higher processing temperature. The urea solutions having higher dielectric constant than that of water offer higher interparticle potential that resulted in better dispersion of the powder as evidenced from the lower viscosity and yield stress of the suspensions. The decrease in temperature increased the suspension viscosity and the suspension formed a strong gel when cooled to room temperature due to the crystallization of urea. The minimum urea solution concentration for a 55 vol% alumina suspension to form a dimensionally stable gel is 240 g/100 mL. The compressive strength and Young's modulus of the gels increased with the increase in urea solution concentration. The alumina ceramics prepared by the urea removal followed by sintering at 1500°C had porosity in the range 28–36 vol% with the rectangular rod‐shaped aligned pores.     

氧化铝粉体性能对流延法生产陶瓷基板的影响

流延法是一种生产电子陶瓷基板广泛使用的先进工艺方法.本文分析了氧化铝原料杂质含量、结晶形貌、α-相转化率、粒度分布等对流延工艺及陶瓷基板的质量影响,并提出了适用流延法陶瓷基板用氧化铝原料性能指标.     

多孔氧化铝陶瓷的研究进展

综合论述了国内外多孔氧化铝陶瓷的制备方法及性能的研究进展,并对目前存在的问题及将来的研究方向进行了展望。     

氧化铝泡沫多孔陶瓷的制备

采用有机泡沫浸渍工艺制备氧化铝泡沫多孔陶瓷。研究了聚丙烯酰胺添加剂对浆料粘度,挂浆成型性能及样品烧后强度的影响,还研究了二次挂浆对氧化铝泡沫多孔陶瓷强度的影响。实验结果表明:当配方组成为氧化铝77.3%、龙岩高岭18.2%、膨润土2.7%、滑石粉1.8%,外加聚丙烯酰胺0.5%,浆料的粘度η0为6.325pa.s,厚化度为1.27,于1600℃,保温2小时烧后样品的强度高。二次挂浆可以显著提高氧化铝泡沫多孔陶瓷强度的影响。对1100℃烧成的样品二次挂浆,在1500℃二次烧成,样品抗弯强度达到3.54MPa。     

Surface Activation of Conductive Porous Alumina by Depositing Nickel Particles

Electrically conductive porous ceramics have gained a recent surge of interests in development of high-performance electrocatalysts. This paper mainly describes the electrochemical activation of conductive porous alumina (CPA) by depositing nickel nanoparticles as an electrocatalyst. The surface of the porous alumina was initially pretreated with mixed acids, followed by depositing nickel particles using an electroless method. Field-emission scanning electron microscope observation and energy diffraction X-ray spectroscopy analysis verified that Ni nanoparticles were successfully deposited onto surface of the CPA. Cyclic voltammetry and chronoamperometry analyses showed that the CPA deposited with nickel nanoparticles behaved as an efficient electrocatalyst for electrooxidation of methanol, which implied its potential application for fuel cells.