High-Performance Ceramics III

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Authors: Yan Ling Guo, Shi Gang Long, Rainer Telle
Abstract: Zirconia based material is one of the most interesting materials for semi-solid processing of steel because of its good mechanical properties and high corrosion resistance at high temperatures. In many cases, degradation of zirconia refractories or advanced ceramics is due to unexpected tetragonal-tomonoclinic^transformation accompanied by volume expansion. But only little attention was paid to outdiffusion of stabilising additives. In present paper, zirconia based ceramics with different rare-earth oxides (Y2O3 and CeO2) are used in contact with HS6-5-2 steel at 1330°C in order to obtain a good understanding about the corrosion behaviour of high-strength zirconia tool material, especially the effect of yttria and ceria on the corrosion behaviour of zirconia. The results showed that both Y2O3 and CeO2 diffused out of the zirconia structure and formed new compounds with alloying elements of steel at the zirconia grain boundaries. Both lack of stabiliser and grain growth result in t-m transformation and cracks were formed in zirconia ceramic.
Authors: Le Fu Mei, Kai Ming Liang, Hai Bin Li
Abstract: The effect of zirconia coatings deposited by the sol-gel technique on the oxidation of mild steel was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and measuring weight gain. It was found that the thickness of zirconia coatings is a crucial factor affecting the oxidation kinetics and the multilayer dip–coating is much more effective than the single coatings. Auger electron spectroscope (AES) was used to evaluate the depth composition of scale. The results suggest that the growth mechanism of the oxide scale for coated mild steel change from outward cation to inward anion diffusion, during oxidation.
Authors: X.J. Ren, R.M. Hooper, J.L. Henshall
Abstract: Time dependent deformation at room and elevated temperature is a significant property of zirconia ceramics and has a direct influence on their use. An understanding of this time dependent behaviour is therefore important in predicting the service life of a component. In this work, the indentation creep behaviour of two typical zirconia ceramics ¾ ceria stabilised polycrystalline tetragonal (Ce-TZP) and yttria (6%) stabilized polycrystalline cubic zirconia, YCPZ, have been investigated from room temperature to 600 °C. Indentation creep tests with various loads yielded identical creep rate, which indicates that indentation size effect has no significant effect on the indentation creep of zirconia ceramics. Tests with variable loads, using a spring loaded apparatus, exhibited comparable indentation creep rates to that under constant loading.
Authors: Ben Jun Cheng, Xing Zhong Guo, Li Li, Jian Ming Zheng
Abstract: The mechanism of the effect that zircon additive had on the properties of 95-alumina ceramic was studied and compared with that of zirconia additive. The results show that zircon additive can decrease the sintering temperature of 95-alumina ceramic, the suitable content of zircon additive is 3% and the suitable sintering temperature is1630°C; under these conditions, the 95-alumina composite ceramic can obtain satisfactory sintering and mechanical properties. Compared with zirconia additive, besides the stress-induced-phase-transformation of ZrO2 and micro-cracks, the toughened mechanism of 95-alumina ceramic with zircon additive also includes zirconia secondary crystallization in the liquid phase.
Authors: Hui Liang, Hai Bo Yang, Zhi Yong Xie, Ting Xian Xu, Ming Xia Xu
Abstract: The high dense pure cordierite ceramics and liquid-phase-sintering cordierite ceramics were prepared with the starting powder made by sol-gel progress. The porosities of them are less than 6.21%, and some can be up to 1.0% especially. The flexural strength of the sample can get to 167 MPa, which is greater than that of 103 MPa of pure cordierite ceramics. The composition, fracture behavior and microstructure of the liquid-phase-sintering cordierite ceramics are investigated. The result shows that the increased flexural strength is mainly attributed to the change in cell parameters of cordierite and the small grain size.
Authors: Ling Zhen Zhang, Chun Chao Zhang
Abstract: In this paper, the SHS process was accomplished using titanium dioxide and aluminum powders as raw materials. It was found that the combustion process exhibited the self-spiral combustion mode and alumina whisker had formed. The morphology, microstructure and growth mechanism of alumina whisker were investigated.
Authors: Wei Zhao, De An Yang, Xiu Xin Yin, Ting Xian Xu
Abstract: Al2O3 ceramic fillers were incorporated into polyetheretherketone (PEEK) to improve the mechanical property in order to suit its aerospace application. To get the high performance composite, it is important to control the dispersion of the nano-Al2O3 among the PEEK matrix. As a pre-fabrication process, the dispersion behaviors of the nano-Al2O3 particles in the liquid medium were studied. Thestability of suspensions was characterized by zeta potential, sediment volume, viscosity and TEM analysis. The mechanism of dispersing nano-Al2O3 aqueous suspension has been investigated including single-electronic stabilization, steric stabilization, and electrostatic stabilization. The highly dispersed and stabilized nano-Al2O3 aqueous suspensions were obtained at acidic condition (pH=3) with PEG-400 and tri-ammonium citrate (TAC).
Authors: Ling Chen, Xian Liang Song, Jian Dong Ye, Bing Li
Abstract: The forming of Al2O3 ceramics was carried out by the colloidal in-situ consolidation using modified starch in this work. The effects of the modified starch content in the alumina suspensions on their rheological behavior, consolidation, microstructure and properties of the green bodies were investigated. The different shape and high relative density of ceramic green bodies were achieved by this method. The results indicated that the alumina suspensions with modified starch were easier to cast due to their low viscosity and high fluidity. After drying, the linear shrinkage of the green bodies was low, ranging between about 1.5% and 2.2% and their bulk density was higher than 57% of the theoretical density. The maximum bending strength of the dried green bodies reached to 8.2 MPa and the microstructure of the green bodies was uniform with a narrow unimodal distribution of pore size. It is concluded that the colloidal in-situ consolidation casting using modified starch can perform near-net shaping of ceramic components with high-performance and it is a potential forming technique for ceramics.
Authors: Shi Guo Du, Jun Yan, Tong Lai Zhang, Hai Ping Cui, J.Z. Liu
Abstract: In this paper the surfaces of Al2O3 fine powders with average size of 500nm were modified by heterogeneous azeotropic distillation process. IR spectrums of the powders show that the distillation can effectively dehydrate hydrous Al2O3 powders, and succeed in substituting the hydrate water with butanol molecular. The dispersion of Al2O3 powders in epoxy resin is improved remarkably, which is observed by means of SEM. Experimental results show that abrasion property of the resin filled with modified Al2O3 powders is improved.
Authors: Tae Young Yang, Young Min Park, Gun Dae Lee, Seog Young Yoon, Ron Stevens, Hong Chae Park
Abstract: The sedimentation density significantly decreased after addition of dispersant; the effect was more pronounced with pure alumina, as compared with SiC-containing slurry. With further addition of surfactant, the sedimentation density increased somewhat, but decreased with binderadditions. The suspension viscosity generally behaved in an opposite manner to the sedimentation density, i.e., low sedimentation density gave high low-shear viscosity, indicative of high structure formation in the suspended particles. Shear rate rheological measurements showed continuous shear thinning behavior.

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