High-Performance Ceramics V

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Authors: Zi Cheng Li, Zhi Hong Li, Ai Ju Zhang, Yu Mei Zhu
Abstract: Synthesis processes of nano alumina abrasive precursor using precipitation method and sol-gel method were investigated in this study. Using pressureless sintering, the nano alumina abrasive was prepared. Mechanical properties of the samples were measured by using single particle compressive strength tester. The microstructures of them were examined by using field emission scanning electron microscopy (FESEM). The results indicated that the performance and microstructure of the samples are greatly relative to the synthesis processes. Compared with samples prepared by precipitation method, the samples prepared by sol-gel method have higher compressive strength, smaller grain size and more uniform microstructure. The average grain size of the alumina abrasive was below 100nm.
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Authors: Feng Sun, Ting Yan Tian, Wei Ru Zhang, Bo Chen
Abstract: High-purity alumina ceramics were prepared by sintering at low temperature, using rare earth oxide Y2O3 and Tm2O3 as sintering aids. Adding the mixture of Y2O3 and Tm2O3 in the alumina powders can effectively improve the sintering ability and mechanical properties. The mixture, Y2O3+Tm2O3, can restrain the grains growth, fine the grain size, make the grain uniform and finally help to form compact structure. The transgranular fracture was the main fracture mode. It was found the relative density of alumina ceramics with 0.3wt% Y2O3 and Tm2O3, sintered at 1620°C for 3hrs, can be over 99.2% and the strength, toughness and microhardness reach 533.1MPa, 4.9MPa⋅m1/2 and 17.2GPa, respectively.
694
Authors: Ling Chen, Xu Peng, Yun Huang, Lin Li, Xiao Xi Li
Abstract: Porous ceramic materials usually require an optimal porosity and pore-size distribution to maximize the yield of the required function. In the starch consolidation forming for porous ceramic materials, the porosity and pore size distribution are corresponding closely to the particle size and swelling property of starch. In order to control the porosity and pore size distribution of the porous alumina ceramics, different modified starches with different amounts were added to the alumina slurry with a 58 vol% alumina solid volume loading. The effects of different modified starches and their content on the rheological behavior of the alumina slurry and the porosity, pore size distribution, compressive strength and microstructure of the sintered body were investigated. The results indicated that alumina/starch composite slurry still maintain stable and plastic in suitable condition of slurry preparation. After drying and sintering, materials with ultimate porosities between 22.7 and 68.7% were obtained. The pore of the resulting materials distributed uniformly and the average size was varied from 10 to 40μm. It concluded that the average size was controlled by the modified starch type, amount and the degree of modification. When the amount of the modified starches was reached to 60 vol% the porosities of the sintered samples were varied from 63.5 to 68.7% with different modified starch type and their bending strength varied within the range of 24-32 MPa.
697
Authors: Kaleem Ahmad, Wei Pan, Chun Lei Wan
Abstract: Multi-walled carbon nanotube (MWNT) reinforced alumina composites with different MWNT contents (5 and 10 vol %) were fabricated by spark plasma sintering. The room temperature dc electrical conductivity, thermal conductivity, and mechanical properties were investigated. Results showed that the electrical conductivity has improved around twelve orders of magnitude by addition of 5 vol% of MWNT. The fracture toughness changed from 3.2 to 4.4 MPa m1/2 with 39% improvement over monolithic Al2O3. The thermal conductivity decreased with increase of MWNT contents. The low values of thermal conductivity suggest that interfacial thermal barrier play an important role in determining these properties. MWNT can be used to improve concurrently electrical, mechanical properties of Al2O3 but with lower values of thermal properties.
701
Authors: Zhi Yong Yu, Han Xing Liu, Ming He Cao, Shi Xi Ouyang, Yong Huang
Abstract: Extrusion gelation freeform fabrication process is an extrusion-based freeforming technique capable of fabricating complex shaped monolithic ceramic prototypes by the sequential deposition and solidification of ceramic suspensions from a computer aided design model. In this process, ceramic parts are produced using an extrusion nozzle suitable for extruding ceramic suspensions. In this study, the processing parameters influencing on manufacturing Al2O3 parts were discussed. Air pressure on top of suspensions, rotating speed of screw, nozzle diameter and scan speed are the main factors to influence the dimensional precision of ceramic bodies. By optimizing these processing parameters, the green bodies were fabricated with high precision. The sintered samples with homogenous microstructure and ~97.6% relative density could be prepared by sintering of these green bodies at 1600oC for 2 hours.
704
Authors: Shi Gang Long, Feng Cao, Liu Heng Sun, Qing Min Meng
Abstract: Al2O3 ceramics samples were prepared by changing the ingredient and sintering conditions. The resistance experiment of the Al2O3 ceramics to hydrochloride corrosion and thermal shock were carried out, and then identified by means of scanning electron microscopy and energy dispersive spectral analysis. The results indicated the optimal Al2O3 and sintering condition for the dechlorinating reactor.
707
Authors: Zhi Wang, Guo Pu Shi, Xiang Sun, Xian Qin Hou
Abstract: Mullite fiber reinforced alumina ceramic matrix composites (MFACC) were prepared using CaO-MgO-SiO2 (CMS) and TiO2 as sintering aids. The effects of the contents of sintering aids and mullite fiber on the density and sintering temperature of MFACC are studied. The results showed that when the CMS content is 8.0% and the TiO2 content is 1.0%, the density of the as-sintered MFACC is 98.9%. When the mullite fiber content is 15.0% and the sintering temperature is 1450 °C, the flexural strength of the resultant composite increases to 504.5MPa, 70.7% higher than the original matrix, and the relative density of the composites reaches 98.4%. The reinforcement mechanisms are fibers pull-out and sticky point.
710
Authors: Jiang Tao Zhang, Li Sheng Liu, Peng Cheng Zhai, Qing Jie Zhang
Abstract: The dynamic compressive behavior of Al2O3 (10% vol.) / TiB2 ceramic composite had been tested by using a split Hopkinson pressure bar in this paper. The results show that the main failure modes of the ceramic composite include crushed failure and split fracture along the loading direction. The former is the typical compressive failure of brittle materials. The later is tensile failure along the flaws produced during the composite manufacturing. The numerical simulation was also used to study the effect of the diameter/length ratio of the samples on the experimental results. The effect of the deformation in the bars’ ends, which contacted with the samples, was also studied in the numerical models.
713
Authors: Yong Hui Zhou, Xing Ai, Jun Zhao, Xun Liang Yuan, Qiang Xue
Abstract: The Al2O3/(W, Ti)C nanocomposite was fabricated by hot pressing technique at 1650-1700°C under 30MPa for 10min. The fracture toughness remarkably increased by adding nano-scale Al2O3 (11vol %) particles into Al2O3 matrix. The flexural strength, fracture toughness and Vickers hardness are 840 MPa, 6.55 MPa•m1/ 2 and 20.1 GPa, respectively. The microstructure of the nanocomposite is homogenous skeleton structure. Nano particles could refine matrix grains and lead to the crack deflection as well as branching and bridging. The coexistence of nano-scale Al2O3, micro-scale Al2O3 and (W, Ti)C can reduce the sintering temperature and sintering time as well as the grain size, and improve the densification and mechanical properties of materials.
717
Authors: Jian Hua Nie, Ya Wei Li, Hao Yan, Yong He Liang, Yuan Bing Li
Abstract: TiN/Al2O3 composite material was prepared by aluminothermic reduction of TiO2 in coke bed from mixtures of TiO2 powder and metal Al powder. The phase composition, lattice parameter and microstructure of products after treatment in different temperatures were analyzed by XRD, SEM. The results show that TiN/Al2O3 composite material can be produced in coke bed via aluminothermic reduction reaction. Moreover, the treatment temperature affects the evolution of aluminothermic reaction and morphology of products obviously. The content, grain size and lattice parameter of TiN in products in coke bed increase with the increasing of treatment temperature. Thermodynamically it confirms that metal Al reacts with oxygen in coke bed while it is involved in aluminothermic reduction reaction, and then it causes the lack of Al, which takes part in the aluminothermic reaction leading to a surplus rutile in the products.
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