Papers by Keyword: Alumina

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Authors: Frank Kern, Rainer Gadow
Abstract: Zirconia-alumina composites are structural ceramics which due to their high strength and toughness are interesting in biomedical and engineering applications. Reinforcement of such materials with in situ formed platelets can improve fracture toughness and reliability, the mechanisms are however not yet fully understood. In this study alumina and zirconia based composites (ZTA and ATZ) reinforced with various hexaaluminates were investigated. In ZTA materials the main effect of platelets is the improvement of toughness as the the grain size distribution of the microstructure is broadened and transformability of the zirconia dispersion is improved. Crack deflection by platelets is unimportant, toughening is commonly achieved at the expense of strength and hardness. In case of zirconia based composites results are strongly depending on the type of stabilizer (Y-TZP or Ce-TZP) used and the type of hexaaluminates formed in situ. Here platelets can cause crack deflection and crack bridging. By variation of the composite recipes a multitude of compositions can be produced which have mechanical properties tailored for individual applications.
Authors: T. James Marrow, David Gonzalez, Mohsin Aswad, Joao Quinta Da Fonseca, Philip J. Withers
Abstract: A 3D model for intergranular thermal stresses in coarse polycrystalline alumina has been derived using Diffraction Contrast Tomography. Larger tensile thermal strains develop when the (0001) pole of adjacent grains lies closer to the grain boundary normal. This agrees with observations of cracked boundaries, obtained through digital image correlation of in-situ observations in fine alumina.
Authors: M. Federica de Riccardis, Virginia Martina, Daniela Carbone, Paolo Rotolo, Annapaola Caricato, Gilberto Leggieri, Luciano Pilloni, Leander Tapfer, Rossella Giorgi, Elena Salernitano
Abstract: Poly(etherether-ketone)-alumina coating were deposited by EPD. In order to densify the coatings, conventional thermal treatments were performed at a temperature equal or higher than the melting point of the polymer. The samples treated at the lower temperature showed an increase in the quality of crystallinity of the polymer. As an alternative method, an excimer laser was used to treat the surface of the composite coatings. The laser beam irradiation did not induce any modification in the crystalline structure of the polymer and at the same time did not produce strong degradation of the polymer molecule, also when the laser beam fluence was higher than the ablation limit. The most relevant modification induced by both the treatments was a change in the morphology and the porosity.
Authors: Teng Fei Shen, Ying Juan Sun
Abstract: In this work, nanoAlumina particles (nanoAl2O3) have been synthesized via solid state reaction. Effect of quantity of surfactant on particle size has been investigated. nanoAl2O3 was modified using chloroform as solvent and fatty acid as modifier at room temperature. The advantage of this modification is that it can be proceed at room temperature and it can reduce energy consumption. The products were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Authors: Lin Qi, Li Xin Song, Xin Fei Zhao, Chang Jiang Fang, Xing Ran Lin, Jie Xiong
Abstract: Flexible alumina (Al2O3)/carbon (C) composite nanofibers film has been fabricated via electrospinning, followed by pre-oxidation and carbonization. Polyacrylonitrile (PAN)/Polyvinylpyrrolidone (PVP) and aluminum hydroxyacetate (Al(OH)C4H6O4) acted as carbon precursor and Al2O3 precursor, respectively. The obtained Al2O3/C nanofibers films were systematically characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and flexural tests. The results indicated that Al2O3/C composite nanofibers with rough surface consisted of graphitic phase and γ-Al2O3 phase. The Al2O3 covering on the surface of nanofibers improved the flexibility of carbon nanofibers (CNFs) film. Moreover, with the amount of Al2O3 increasing, both flexural rigidity and flexural modulus of Al2O3/C nanofibers film decreased drastically. In the other words, the flexibility of CNFs film improved greatly. The Al2O3/C nanofibers film with the mass ratio of Al(OH)C4H6O4: PAN being 4:1 exhibited flexural modulus that was about 11 times lower than that of CNFs film without Al2O3, suggesting that the highly flexible Al2O3/C nanofibers film was obtained.
Authors: Hao Tung Lin, Chien Cheng Liu, Kuang I Liu
Abstract: A novel method to prepare the copper bonding on alumina substrate was presented. The cuprous Cu2O on the surface of Cu foil was prepared by covering cupric oxide (CuO) powder on Cu foil and treating at 600°C in N2 atmosphere. Then eutectic process was executed at 1075°C in N2 atmosphere to bond the Cu and alumina substrate. The cuprous grew on copper foil and bonding between Cu foil-alumina substrate were identified by XRD spectrum and SEM micrographs.
Authors: Kritkaew Somton, Kannigar Dateraksa, Ryan C. McCuiston
Abstract: The relationship between granule property, pressed green density and shrinkage of 92% alumina spray dried granules were studied for both simple and complex shapes. Two types of granules, the in-house granule (A) and the commercial granule (B), was observed morphology using microscopy and liquid immersion techniques. Examination of the granules showed that granule A have several undesirable features; agglomeration, hollow granules and non-spherical granules where granule B showed them to be unagglomerated and spherical. The mixture A and B were conducted to study the particle size distribution (PSD) and compared with Dinger-Funks ideal PSD. The result showed that granule mixture A: B 100:0 had closest PSD curve fitted but had lowest tapping and pressed green density than 70:30 and 30:70 mixtures. This is because the agglomerated shape in granule mixture 100:0 caused air gap in between granule contact resulting in low tap density. The specific fracture strengths of the granules can affect to the densification of green ceramic during pressing. Low pressed green density affected to a high amount of shrinkage during sintering and leading to small grain growth after sintered. The simple and complex shape follows the same trend in shrinkage.
Authors: Supawan Vichaphund, Duangduen Atong
Abstract: This work aimed to investigate the effect of different sintering routes on properties of Ni-Al2O3 membrane. Alumina powder was mixed with 10 wt% nickel powder by dried ball-milling. Then, the mixture powder was uniaxially pressed to a bar shape and sintered via different sintering conditions. First route, the Ni-Al2O3 specimen was sintered at 1300°C for 2 h under air and then reduced at 900°C for 2 h under H2 atmosphere. Second route, the specimen was sintered at 1300°C for 2 h under argon. After sintering process, the physical and mechanical properties of membrane obtained from two routes were compared and discussed.
Authors: Shenq Yih Luo, Chia Lin Lee, Yi Xian Liu, William Chen
Abstract: The purpose of the paper was to investigate the rough grinding and finish grinding of alumina ceramic using small diameter of diamond tools under high spindle speed. The effect of the grinding conditions on grinding forces and surface roughness was discussed. The three types of experiments were carried out: (1) For rough grinding of alumina, when a metal sintered diamond tool of grit mesh #100 under a lower spindle speed of 10000 rpm was used, the relatively higher grinding ratio of 2452 and the higher material removal efficiency were obtained. Oppositely, for a higher spindle speed of 30000 rpm, the lower grinding ratio of 503 and the lower material removal efficiency were produced. (2) For finish grinding of alumina, when the metal sintered diamond tool of grit mesh #1000 under a higher spindle speed of 50000 rpm and a lower depth of cut of 1 μm was employed, the resulting better surface roughness obtained was Ra 0.33 μm. (3) The pressure grinding of alumina was used to obtain a better surface roughness of Ra 0.23 μm than the high speed fine grinding. Hence, it can be used as an ultra finishing after rough grinding.
Authors: Shenq Yih Luo, Ching Win Shih, M.H. Chen
Abstract: The purpose of this paper is to investigate the performance of grinding alumina for the specific designed tools containing a controlled diamond protrusion and arrangement. The grinding forces, workpiece roughness and diamond wear at changing the depth of cut and feed under a fixed spindle speed were studied in the experiments. The experiment results showed that the grinding forces with the increase of feed slowly increased. However, the grinding forces with the increase of depth of cut showed a relatively larger rise. When the depth of cut reached to 0.09 mm that is about one fourth of diamond size, the axial grinding force obtained above about 20 N to cause some weaker or higher protrusive diamonds to produce a relatively larger fracture or pull-out. Furthermore, under a larger depth of cut and a larger feed rate the workpiece roughness obtained was the poorer. When diamond tool was employed for a longer time test under the depth of cut less than about one fourth of grit diameter, diamonds mainly displayed an attritious wear and the alumina roughness was about Ra 1.2-2.2 μm. This designed diamond tools are feasible for grinding alumina.
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