Papers by Keyword: Corundum

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Authors: Tatiana V. Vakalova, Larisa P. Govorova, Antonina A. Reshetova, Anna Y. Tokareva, Ekaterina V. Shvagrukova
Abstract: It is found out that activation of the sintering process for refractory clay-containing raw materials (rusk kaolin and wocheinite) is provided using additives of 3d-transition elements oxides (Fe2O3 and MnO2) in the amount of 2 - 5 wt. % due to formation of defective solid solutions of mullite by isovalent substitution mechanism as well as fluxing additives of alkaline and alkaline-earth oxides (Na2O, MgO) in the amount of 2 wt. % by regulating rheological properties of silicate melts.
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Authors: Taufik Aboud
Abstract: Reagent grade chemicals were used to explore glass formation ability and allocate the glass forming area for the glass system SiO2-P2O5-Al2O3-MgO-Na2O. FT-IR, DTA, DSC and TMA techniques were employed to characterize the obtained glasses. The multicomponent, mixed network glasses, in which AlPO4 tetrahedral units are being incorporated into the network structure through substitution for pairs of SiO4 tetrahedra, exhibit high durability, low thermal expansivity (at Al2O3/P2O5 ˃1), relatively high softening temperatures (at low P2O5 contents) and an increased thermal stability (poor tendency for crystallization). When heated at high temperatures and / or for long periods of time, and depending on their AlPO4 content, together with the Al2O3/P2O5 ratio, the glasses crystallize through a multistage process involving reconstruction and depolymerization of the glasses network structure. The crystallization behavior of many different glasses was investigated, phases identified and characterized, through XRD, and SEM coupled with EDX and X-ray mapping together with optical microscopy. The powder ceramization route had to be used to achieve the devitrification of the glasses with high thermal stability. Berlinite, corundum, spinel, indialite and cordierite among others were the crystallizing phases when different glasses were heated for various times. Microporous materials made of some of these technically favorable minerals, and characterized by an interesting morphologies were obtained, through acid leaching of some of the glass-ceramics produced. It is believed that the glass system under investigation is a fertile one, the crystallization of some glasses within it, represents another fabrication route for obtaining glass-ceramics with specific crystalline phases, as well as microporous materials made of such phase. In both cases, packages of the most suitable properties are obtainable.
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Authors: Lin Chun Zhang
Abstract: In this paper, we choose heat resistant material wollastonite and corundum to get the concrete which has heat resistance up to 600 centigrade. SEM reveals that at the temperature of 400 centigrade and 600 centigrade, the material is very dense. But when the temperature gets 800 centigrade and 1000 centigrade, the SEM reveals cracks. The refractory concrete made by magnesium potassium phosphate as the binder and wollastonite and corundum as aggregate has short setting time, early strength and rapid hardening. And it is suitable for emergency repair materials for the kiln.
341
Authors: P. Jantaratana, Pisutti Dararutana, Wiwat Wongkokua, Sorapong Pongkrapan, P. Wathanakul
Abstract: The dielectric constant values of a set of synthetic alpha alumina samples doped with Cr and Be were determined using parallel plate method. The voltage frequency was selected at 1 MHz. When Cr was doped to the sample, the dielectric constant was increased due to the increase in polarizations of the sample, whereas the Be-doped one showed the decrease in dielectric constant cf. the undoped synthetic alpha alumina (reference sample). Experiments on doping alpha alumina with both elements showed increasing in dielectric constant compared to the undoped reference sample, i.e., Cr has more influence to the dielectric constant value. Dielectric constants of a set of natural sapphires were also measured and compared to those obtained from the synthetic ones. The results of both natural and synthetic samples varied in the same direction. It suggests, however, that the geological origins of the samples are needed to be considered. This is due to the differences in physico-chemical conditions of their formations that would have influenced partitioning of trace elements as well as evolving of defects in natural samples. Increasing of the R1 and R2 photoluminescence wavelengths and decreasing of refractive indices of the doped samples cf. those of the reference sample were obtained from the experiments.
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Authors: Leonid G. Znamenskij, O.V. Ivochkina, Aleksey S. Varlamov
Abstract: Ceramic corundum molds on hydrolysed ethyl silicate solution which have insufficient inertness to poured alloys are widely used in the production of castings from reactive metals alloys. This is due to the presence of free silica, which is a strong oxidant of such alloy components as aluminium and titanium in vacuum conditions, in the form of a high content. To solve the indicated problem using aluminium-borophosphate concentrate, chemically cured with periclase, as a silica free binder of ceramic corundum molds was suggested. The use of the combination of the indicated mold materials allows not only enabling chemical inertness of the molds, but also operating the process of mold forming. The developed technology provides the acceleration of the mold manufacturing cycle in 4...6 times, the increase the strength of the mold covers, the reduction in the heat-resistant alloy casting cost. It enables significant improvement of the quality and increase of the economic efficiency of manufacturing of precision casting from reactive metals and alloys.
208
Authors: Xing Yong Gu, Shao Ling Wu, Ai Hua Zhang, Ting Luo, Yun Xia Chen
Abstract: To improve the thermal conductivity of alumina ceramics, different inorganic materials such as AlN, BN, Si3N4 and SiC which own high thermal conductivity were integrated with 96% alumina ceramic. The effect of addition of AlN, BN, Si3N4 and SiC on water absorption, flexural strength and thermal conductivity of the as-prepared alumina-based composite ceramics were investigated. Field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) were employed to characterize the microstructure and phase compositions of the composites. The results showed that sintering temperature of 96% alumina ceramic matrixes were improved in varying degree due to adding AlN, BN, SiC and Si3N4. A small quantity of Al6Si2O13 crystals were formed in the case of adding Si3N4 and SiC, which is due to the oxidation of Si3N4 and SiC into SiO2 in the air and the subsequent reaction with alumina. At appropriate firing temperature, the flexural strength of the composites with the addition of AlN is the best and higher than corundum matrixes. Meanwhile, the thermal conductivity of the composites with AlN has 110% improvement. It is obvious that AlN with high thermal conductivity is suitable for improving the thermal conductivity of corundum ceramics.
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Authors: K.H.W. Seah, R.S. Kulkarni, S.C. Sharma, A. Ramachandra
809
Authors: Bin Xiang Fang, Bo Quan Zhu, Wen Jie Zhang, Xue Dong Li, Zheng Yun Fan
Abstract: The Al/AlN bonded corundum based multiphase material was prepared by raw materials of fused alumina and metallic aluminum powder by in situ reaction at 1100°C for 3h in N2 . The XRD analysis showed that the mineral phases of prepared material are corundum, metallic aluminum and AlN respectively. The SEM investigation revealed that both tetragonal whiskers and hexagon powders of AlN were formed. The results of hydration tests indicated that the rate of weight gain and pulverization of the material were negligible and the ratio of residual crushing strength was kept at a high level. The XRD patterns of samples after hydration tests identified that the AlN phase still remained although a small amount of AlOOH and Al(OH)3 was formed due to the hydration of AlN. It is believed that the limited hydration of AlN should be contributed to the dissolution of O element to AlN. The hydration mechanism of AlN was discussed.
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Authors: Miroslav Müller, Petr Valášek
Abstract: Polymers rank among a significant group of technical materials. One of requirements for this constructional material is to have enough resistance to a dynamic loading. Especially in the area of connecting the materials reactoplastics are used, which are distinguished for a low resistance to the dynamic loading. One solution for increasing an impact strength is filling the reactoplastics, i.e. a formation of polymer composites. The aim of the research was to evaluate an impact strength of various polymer materials (composites filled with different types of a filler, structural two-component epoxies, mixed recycled plastics, PPO – polyphenyle oxide and PS – polystyrene). The Dynstat method CSN 64 0611 was chosen for the evaluation of the impact strength. Reactoplastics matrix on the basis of two-component epoxy adhesive with high liquidity and an increased speed of a hardening GER reaches low values of the impact strength (2.54 ± 0.30 kJ·m-2). It is evident from the experimental results the positive effect of aluminium microparticles GER MFAI (3.26 ± 0.35 kJ·m-2), glass beads GR B134 (2.83 ± 0.29 kJ·m-2) and microfibres of polyamide from the process of tyre recovery GER MPA (3.92 ± 0.25 kJ·m-2) on the impact strength. The results of this experiments show the possibility of the modification of the relative fragile epoxy resin with the filler, which increases the impact strength.
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Authors: Yue Chao Tian, Xi Liu, Hui Tang, Jing Long Bu, Dong Mei Zhao, Yue Jun Chen, Li Xue Yu
Abstract: Mullite-corundum multiphase ceramic materials were prepared at 1400°C for 2h with bauxite chamotte and clay clinker as raw material (size<74 μm), molded at pressure of 50 MPa. Effect of raw materials composition on sintering and themal shock resistance of composite were researched by measurements of apparent porosity, bending strength,thermal shock resistance and thermal expansion rates, and analysed by XRD and SEM. The results showed that the best weigh percentage of raw materials with better sintering and themal shock resistance are bauxite chamotte 50 wt%, clay clinker 50wt% for mullite-corundum multiphase ceramic materials. The test results for high temperature gas cleaning dust removal technology development and the application of the composite ceramic material has important application value.
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