Immunodiffusion and immunohistochemical investigations on the reactivity of oxide ceramic middle-ear implants

Oxide ceramic materials (partial and total ossicular replacement prostheses) have been implants of preference for the reconstruction of the ossicular chain because of their excellent biocompatibility. The reaction on the surface of the implants takes place at three biodynamic levels according to the model of Stern's bilayer. We investigated the adsorption of proteins, which is determined by the cellular reaction and degradation to the surface using radial immunodiffusion and immunohistochemical methods. First, ceramic implants of aluminum oxide, hydroxyapatite, glass ceramic and zirconium oxide have individual actual (i.e. biological) surfaces. With a perthometer and the contact-free laser Focodyn method we determined each actual (i.e. biological) surface of the various ceramic implants mentioned above. Using radial immunodiffusion, the adsorption of albumin, glycoprotein, plasminogen, fibronectin, IgA, IgG and IgM shows characteristic rates of adsorption to the respective ceramic surfaces in correlating to the actual surface. A cross-check with fluorescent antibodies confirmed the protein adsorption. The individual surface adsorption of the proteins remains characteristic and is the basis for the recording of cellular reactions after implantation.     

Catalytic decomposition of ethyl acetate over La-modified Cu-Mn oxide supported on honeycomb ceramic

The La-modified Cu-Mn spinel oxide was successfully coated onto honeycomb ceramic by a washcoating method for complete catalytic decomposition of ethyl acetate.The La-modified Cu-Mn oxides were characterized by X-ray diffraction,X-ray fluorescence,H_2-temperature programmed reduction,Brunauer-Emmett-Teller method,field-emission scanning electron microscopy and high-resolution transmission electron microscopy.The effects of different precipitants and rare earth doping on the structure and catalytic performance of the catalysts were investigated.The results show that the CuMn_2 O_4 spinel with(NH_4)_2 CO_3 as a precipitant can form a larger specific surface area and a suitable pore size,which is beneficial to the absorption of ethyl acetate.Although the rare earth doping does not significantly change the crystal phase structure of the catalyst,it improves its reducibility and lowers the temperature of the catalytic decomposition.With respect to the catalytic decomposition of ethyl acetate,the rare earth-modified Cu-Mn oxide supported on honeycomb ceramic shows excellent catalytic performance with 100% conversion under the conditions of 239℃,space velocity of 12500 h~(-1) and1000 ppm.And the ethyl acetate removal rate is still 100% after 1440 min of continuous reaction.     

钢/Al2O3陶瓷/钢轻型复合装甲板抗弹性能

为优化设计钢/Al₂O₃陶瓷/钢轻型复合装甲板,结合薄板冲塞的极限速度方程与Florence模型建立了钢/Al₂O₃陶瓷/钢轻型复合装甲板的抗弹极限速度预测模型.根据模型,分析了不同面板、背板及陶瓷厚度组合对钢/Al₂O₃陶瓷/钢轻型复合装甲板抗弹极限速度的影响,并通过7.62mm普通钢芯弹侵彻钢/Al₂O₃陶瓷/钢复合装甲板试样实验验证了该模型的正确性.结果表明,钢面板厚度小于1.0mm时,复合板抗弹极限速度计算值和实验值之间的相对误差在15%以下,陶瓷芯与钢背板的厚度比保持在1.5~4.5之间比较合理.     

Thermomechanical stresses in the ceramic and cerametallic layers of tube solid oxide fuel elements

A model is proposed to calculate the residual thermomechanical stresses in the layers of a tube solid oxide fuel cell (SOFC) that are caused by the difference between the linear thermal expansion coefficients of these layers. The distributions of the residual stresses in the cell layers that appear during the production of SOFC and under operating conditions are determined, and the regions of probable failure in the cell are revealed.     

Tin-based reactive solders for ceramic/metal joints

Contact angle measurements on silicon-nitride substrates were conducted on tin-based alloys, containing titanium and zirconium, to determine the suitability of these alloys as filler metals for low-temperature joining of ceramics. Titanium-containing alloys exhibited excellent wettability characterized by contact angles less than 20 deg, whereas the Zr-containing alloys exhibited contact angles around 50 deg. The superior wettability of the Sn−Ti alloys is attributed to the higher activity coefficient of Ti in Sn−Ti alloys. The liquidus temperature of the Sn−Ti alloys is in the 400°C to 600°C range. Hence, these alloys are expected to reduce the residual stress problem.     

Cyclic fatigue-crack propagation along ceramic/metal interfaces

The integrity of ceramic/metal joints is investigated under mechanically applied cyclic stresses using double-cantilever-beam, and compact-tension, sandwich test specimens. Specifically, fatigue-crack propagation rates for interfacial cracks are characterized over a range of velocities from 10⁻⁹ to 10⁻⁴m/s for glass/copper and alumina/aluminum-alloy interfaces tested in moist air. Compared to corresponding (stress-corrosion) results under sustained loading, it is found that true interfacial cracks in glass-copper joints are significantly accelerated under cyclic loads. In addition, crack extension force (G) thresholds for interfacial crack growth under cyclic loads are some 46% lower than under sustained loads and are typically over six times lower than the interface toughness (G_c). For the alumina/aluminum-alloy system, conversely, fracture never occurs in the interface; under monotonic loading cracking progresses near the interface in the ceramic layer whereas under cyclic loading failure may occur either in the ceramic or in the metal. Based on a comparison with fatigue-crack growth data in bulk alumina and bulk aluminum alloys, it is found that near interfacial crack-growth rates in the metal are much lower than those of the bulk ceramic and show a far higher dependency on the range of G than behavior in the bulk metal.     

氧化铝基氧化物/氧化物复合材料的合成与评价

Al2O3 matrix oxide/oxide composites containing rod-like Ba-β-Al2O3 and equiaxed ZrO2 particles have been successfully synthesized by an in-situ process from a mixture of Al2O3 and BaZrO3 powders.The long-axis direction of rod-like Ba-β-Al2O3 phase is parallel to ,while the longitudinal interface between Ba-β-Al2O3 phase and Al2O3 matrix is parallel to(0001) of the Ba-β-Al2O3 phase.The mechanical properties of the composites,such as Vickers hardness and fracture toughness,are enhanced with increasing the sintering temperature.Furthermore,the presence of rod-like Ba-β-Al2O3 particles results in enhancement of fracture toughness of the in-situ synthesized composites due to crack deflection and crack bridging.     

Cracking and damage mechanisms in ceramic/metal multilayers

Investigations of cracking in multilayered ceramic/metal composites are presented. Two aspects are considered: crack renucleation across intact single metal layers and subsequent crack extension. Crack renucleation criteria are determined and compared with predictions. High-resolution strain-mapping techniques are employed to determine the surface strain fields surrounding cracks. Good agreement is found between these experimental measurements and the predictions of a small-scale yielding model. Subsequent crack progression occurs either by the extension of a dominant, nearly planar crack or by the formation of a zone of periodically spaced cracks. Both patterns are analyzed. The dominant cracking behavior is found to depend on the volume fraction and yield strength of the metal.     

The strength and fracture of metal/ceramic bonds

The fracture strength of ceramics bonded with metals is limited by the presence of stress concentrations that arise around the bond, especially near edges. Yet, in some cases, fracture can be induced to occur in the ceramic away from the bond. Analysis of the combined effect of elastic mismatch, plasticity and thermal expansion misfit is presented in this paper, to provide understanding of the trends in bond strength. Important influences of plastic relaxation and thermal expansion misfit are identified and some general fracture characteristics are described.     

Tribological properties of ceramic materials based on nonmetallic nitrides. II. Effect of oxide films on the process of friction in the system ceramic material-steel

Translated from Poroshkovaya Metallurgiya, No. 2, pp. 65–68, February, 1991.     

Plastic relaxation of thermoelastic stress in aluminum/ceramic composites

The dislocation generation due to a thermoelastic stress in 2024 Al/ceramic (SiC or TiC) composites was studied using transmission electron microscopy Composites containing different ceramic particulates, ceramic volume fraction, and particle size were investigated. Dislocation density profiles were measured as a function of the distance from an Al/ceramic interface and compared with those calculated from an elastoplasticity model which accounts for the volume fraction of the ceramic particles. The intensity of dislocation generation showed a strong particle size dependence: as the ceramic particle size became of the order of a micron, the intensity of dislocation generation increased significantly. With an increase in the volume fraction of the ceramic particles, the dislocation density also increased, and the dislocation structure became a more tangled arrangement. If heat dissipation was taken into account as part of the plastic work, the predicted dislocation densities of the elastoplasticity model were found to be in reasonable agreement with the measured dislocation densities of 10⁹ to 10¹⁰ cm⁻².     

The fracture resistance of a model metal/ceramic interface

Crack propagation has been measured for the Al₂O₃/Au interface subject to conditions that exclude stress corrosion. Crack growth has been shown to occur with a rising resistance, governed by intact metal ligaments in the crack wake. The level of resistance also increases as the metal layer thickness increases. Crack extension occurs by a combination of plastic void growth and interface debonding. The fracture energies are much larger than the work of adhesion, but appreciably smaller than those expected for ductile interface fracture. The fracture energy is nevertheless dominated by plastic dissipation, which increases at larger metal layer thicknesses.     

不同烧结气氛下SiAlON/cBN陶瓷复合材料的性能研究

以Si3N4、Al N、Al2O3和c BN为原材料,采用放电等离子烧结,在氮气、氩气和真空三种不同烧结气氛下制备Si Al ON/c BN陶瓷复合材料.通过XRD、SEM及力学性能评估等手段研究了材料的物相组成、显微组织、体积密度、硬度以及断裂韧性等性能.结果表明:真空气氛下制备的Si Al ON/c BN陶瓷复合材料显微组织相对致密,具有较高的体积密度、硬度和断裂韧性.     

TiB2/SiC陶瓷复合材料制备工艺的研究

以TiO2、B4C和C为原料,基于原位合成法在SiC基体中生成TiB2颗粒,并采用无压烧结法制备出TiB2/SiC复合陶瓷.通过对复合材料制备工艺的研究,发现:高于1 300℃的预烧结能形成TiB2/SiC复合陶瓷坯体.C含量、烧结温度和保温时间对复合材料的相对密度均有影响.当C含量(质量分数)为4%时、在1 400℃...     

金属间化合物/陶瓷基复合材料发展现状与趋势

金属间化合物/陶瓷基复合材料是近年内发展起来的一种新型复合材料,其发展与金属间化合物和高技术陶瓷的发展密切相关.利用金属间化合物的性能介于金属和陶瓷之间的特点,制备金属间化合物/陶瓷基复合材料,能使金属和陶瓷各自的缺点通过彼此的优点所弥补.该文简要介绍了Ni-Al/Al2O3、Fe-Al/Al2O3、Ni-Al/TiC、FeAl/TiC、FeAl/WC和Ni3-Al/WC等复合材料的发展现状以及金属间化合物/陶瓷基复合材料未来的发展趋势.