The Science of Engineering Ceramics III

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Authors: Zoltán Lenčéš, Kiyoshi Hirao, Pavol Šajgalík, Michael J. Hoffmann
Abstract: Reaction bonded MgSiN2 (RBMSN) was prepared by direct nitridation of a Si/Mg2Si/Mg/Si3N4 powder compact in a temperature range of 1350-1550°C. The oxygen content of MgSiN2 was in the range of 0.4 – 0.6 wt%. A thermal stability examination showed that MgSiN2 is stable up to 1400°C at 0.1 MPa N2 pressure. The activation energy of decomposition calculated from the temperature dependence of weight loss is H = 383 kJ⋅mol-1. The time dependence and nitrogen pressure dependence of MgSiN2 decomposition was also investigated at constant temperature. MgSiN2 is stable at 1560°C in 0.6 MPa nitrogen atmosphere. Using these experimental data together with the heat capacity published in a literature the Gibbs free energy of formation of MgSiN2 was calculated in a temperature range 300-2500 K. Dense MgSiN2 ceramics or MgSiN2/Si3N4 composites with fluorine-based additives were prepared by hot pressing. The composite materials had a 4-point bending strength of 427 MPa and Vickers hardness (HV1) of 20.8 GPa, respectively. The indentation fracture toughness was 5.3 MPa.m1/2, due to the presence of elongated β-Si3N4 grains. The dielectric constant of dense reaction bonded MgSiN2 at 100 kHz was 9.5-10, while that of MgSiN2/Si3N4 composite in a wide range 50 – 6000, depending on composition and heat treatment.
Authors: Jae Seok Koh, Jae Chun Lee, Soon Haing Cho, Seung Chul Choi
Abstract: A new type of ultrasonic spray nozzle was fabricated employing PZT and Pb-free piezoelectric device. The spray nozzle was designed to disperse chemicals in a water treatment mixing tank. The piezoelectrics were packaged in an aluminum case with silicone resin for the aqueous solution proof packaging. Chemicals were dispersed with high efficiency, and the ultrasonic fine particle spraying was able to reduce the chemicals consumption. The removal efficiencies of heterotrophic bacteria and Escherichia coli by chemicals injected using designed ultrasonic spray nozzle were higher than the conventional methods.
Authors: Noriko Bamba, N. Endo, T. Takagi, Tatsuo Fukami
Abstract: Piezoelectric ceramic pressure sensors have been attracted great interest due to their simple and miniature structure compared with conventional sensors such as strain gauge sensor. A new type of static pressure sensor by using a change of permittivity upon applied mechanical pressure has been studied in this work. BaTiO3 ceramics with/without a small amount of Mn were used as sensing materials and the effect of poling treatment on their sensor performance was investigated. An anti-ferroelectric material, NaNbO3, was also examined. All materials could detect the change of pressure through the frequency shift of CR oscillator. Change of permittivity of non-doped BaTiO3 and Mn doped BaTiO3 without poling treatment were larger than that of PZT used as a reference, that is, BaTiO3 ceramics had higher-pressure sensitivity. BaTiO3 and relative materials, however, needed transit time to reach the steady state, while NaNbO3 was independent to the time. Conclusively, it seems that BaTiO3 and relative materials without poling treatment and the anti-ferroelectric material, NaNbO3, become possible candidates as a pressure sensor using permittivity change.
Authors: Jae Kyo Yang, D.J. Park, J. Kim, Si Young Chang, Chung Hyo Lee, Tohru Sekino, Koichi Niihara, Yong Ho Choa
Abstract: Fe/MgO nanocomposites, which are applicable to high frequency electronic devices, were fabricated by ultrasonic spray pyrolysis and selective reduction processes. Transmission electron micrographs showed that nano ferromagnetic Fe particles were isolated by MgO insulating matrix. With the increase of the reduction temperature, the particle size and saturation magnetization of the nanocomposites increased, which resulted in the decrease of the coercive force and the increase of the permeability. Furthermore, the ferromagnetic resonance peak of the nanocomposites was not observed up to 9 GHz.
Authors: A. Feteira, Derek C. Sinclair, M. Lanagan
Abstract: LaxBa1-xTi1-xYxO3 (0≤x≤0.5) powders were synthesised in air at 1400°C by the conventional solid state method. According to the X-ray results, the tetragonal distortion in undoped (x=0) BaTiO3 (space group P4mm) decreases with x and samples with x ≥0.05 show cubic symmetry (space group Pm3m). For x≥0.05, the lattice parameter increases linearly with x, until orthorhombic LaYO3 appears as a secondary phase for x>0.45. Dielectric properties of dense (>95% of the theoretical X-ray density) ceramics were studied at both radio and microwave frequencies. The permittivity maximum is shifted towards lower temperatures with increasing x and a broad permittivity peak is observed for samples with 0.05
Authors: Shunkichi Ueno, Halina B. Misram, Naoki Kamegashira
Abstract: The solubility of manganese ion in layered perovskite La4Ni3O10 phase was examined and the detailed crystal structure of this phase was discussed. The solid solution of La4Ni3-xMnxO10 was prepared by solid state reaction. The crystal structure of La4Ni3-xMnxO10 was analyzed by powder X-ray diffraction and Rietveld methods. The solid solution for x=0.5 had a orthorhombic system with lattice parameter a=0.5485(0), b=0.5433(6) and c=2.8034(9). In detailed observation of the X-ray diffraction data, some superlattice reflections that were forbidden for a face centered orthorhombic cell were identified. A possible space group Pnnn (no.48) was derived from the reflection conditions.
Authors: Deok Soo Kim, Yong Chae Chung, Sang Won Seo, Sang Pil Kim, Chong Min Kim
Abstract: The structural configurations of atom constituting materials are one of the fundamental factors in the study of physical properties of materials. Presented in this paper is a mathematical and computational methodology to efficiently classify a given atomic structure of an arbitrary material into groups of atoms in BCC, FCC, and HCP crystal structures. The approach is based on the angle distributions among neighboring atoms efficiently identified by a computational geometry technique called Voronoi diagram. In this paper, the presented mathematical theory was applied to analyze a multi-layer atomic structure in a geometric perspective so that a best condition for thin film growth can be found.
Authors: Qing Xu, W.F. Guo, Wen Chen, Hao Wang, Duan Ping Huang, B.T. Wang
Abstract: The sintering and electronic conducting properties of La0.8Ca0.2CrO3 synthesized by a glycine-nitrate process (GNP) were investigated in comparison with that synthesized by the conventional solid state reaction (SSR) method. The results demonstrate the advantage of the GNP method in producing La0.8Ca0.2CrO3 ceramic. Compared with the powder synthesized by the SSR method, that synthesized by the GNP method shows a higher sinterability due to its fine morphology. The relative densities of the ceramics made by the GNP and SSR methods attain 96.5 % and 96.0 % when sintering at 1450°C and 1550°C, respectively. In the case of similar relative densities, the ceramic made by the GNP method (sintered at 1450°C) exhibits superior electronic conducting properties to that made by the SSR method (sintered at 1550°C). This is attributed to a desired microstructure of the ceramic made by the GNP method.
Authors: Yoon Suk Kim, Han Chul Kim, Yong Chae Chung
Abstract: We used ab initio pseudopotential plane wave methods to study the magnetic and electronic properties of transition-metal doped ¯-SiC. It is found that the SiC:Cr reveals stable ferromagnetism with permanent magnetic moments as large as 2 μB regardless of substitution site. In addition, the SiC:CrSi is predicted to have good electron mobility and wide spin band-gap of 1.58 eV with the Fermi level at the center of the gap, which is desirable for realizing spintronic devices.
Authors: Dong Ying Ju, Pei Bian
Abstract: Magnetite (Fe3O4) ferrite magnetic materials have attracted attention arising by the chip coil electronic material. However, its industrial applications have been limited by the need for high temperature sintering under reduced pressure or vacuum. In order to develop the process method of low-cost and energy saving with high-strength and high magnetism of the magnet, in this paper, a new low-temperature sintering method using CO2 gas and adding a small amount of boric acid (H3BO3) is proposed. Here, the super fine magnetite powder was fabricated by decomposition from ferrous oxalate at 500 in CO2 gas. The ferrous oxalate was synthesized using iron chloride and ammonium oxalate through liquid phase precipitation. The magnetite powder compact was produced by Newton press and CIP (cold isostatic press) after adding a small amount of boric acid. In this study, the effects of the additive on the mechanical and magnetic properties of the sintered magnet were also evaluated. By characteristic evaluation of the magnet, the validity of the proposed new low-temperature sintering process and the optimal process conditions were confirmed.

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