Innovation in Ceramic Science and Engineering

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Authors: Kenji Suzuki, Kazuhiko Kusunoki, Nobuyoshi Yashiro, Nobuhiro Okada, Kazuhito Kamei, Akihiro Yauchi
Abstract: Solution growth of 6H-SiC single crystal from Si-Ti-C ternary solution using the accelerated crucible rotation technique (ACRT) was performed. The SiC growth rate exceeding 200 μm/hr was achieved in several ACRT conditions. Such a high growth rate can be ascribed to the enhancement of the carbon transport from the graphite crucible to the growth interface due to the use of the ACRT. The incorporation of inclusions of Si-Ti solvent in the grown SiC crystal was also significantly suppressed by using the ACRT. The intensive convection near the growth interface induced by the ACRT resulted in not only the marked increase of SiC growth rate but also the superior homogeneity in the surface morphology. It was concluded that faster stable growth could be accomplished in the SiC solution growth using the ACRT. The obtained SiC self-standing crystal exhibited homogeneous green colour without cracks and inclusions. We investigated the crystalline quality of the grown SiC crystal by means of X-ray diffraction. The, ω-scan rocking curves of (0006) reflection measured by X-ray diffraction provided the FWHM of 15-20 arc-second showing the excellent crystallinity of the solution grown 6H-SiC single crystal.
Authors: Manabu Fukushima, You Zhou, Yuichi Yoshizawa, Hiroyuki Miyazaki, Kiyoshi Hirao
Abstract: Mesoporous silicon carbide with and without SiC filler was prepared from the pyrolysis of polycarbosilane (PCS), and the relationship between pyrolysis and properties of micro/meso pores was investigated. The surface area of pyrolyzed PCS without filler significantly decreased from 268 to 0.5m2/g with increasing pyrolysis temperature, and disappearance of the micropores was observed. In contrast, the pyrolyzed PCS with filler showed the retention of micro/mesopores, regardless of pyrolysis temperature. In addition, high surface area ranging from 120 to 180m2/g and a bimodal pore distribution were observed in pyrolyzed PCS with filler. FT-IR showed the decomposition of Si-H, Si-CH3 and Si-CH2-Si in the PCS network during pyrolysis, which led to the evolution of hydrogen and methane gas. However, the obtained pores might be larger than the size of evolved gases. Thus, though micro/meso pores and large surface area were retained by the addition of filler, coalescence between pores could occur during pyrolysis.
Authors: Yoshio Sakka, Tohru Suzuki, Tetsuo Uchikoshi
Abstract: Recently to improve properties, highly microstructure controlled ceramics such as fine-grained, textured and laminated structures are required. We have demonstrated a new processing of textured ceramics with a feeble magnetic susceptibility by colloidal processing in a high magnetic field and subsequent heating. As colloidal processing, slip casting and electrophoretic deposition (EPD) have been conducted successfully. Colloidal processing is known to be a powerful method for consolidating fine particles with a high density and homogeneous microstructure. The degree of orientation strongly depends on the particle dispersion and some processing factors, such as particle size, applied magnetic field, concentration of the suspension, sintering temperature, etc. Crystalline-textured controlled laminated composites can be fabricated using EPD by varying the angle between the vectors of electric field and magnetic field. Also textured ceramics with complicated structure can be fabricated by reaction sintering. The colloidal processing in a high magnetic field confers several advantages and it is possible for this type of processing to be applied to non-cubic ceramics, such as alumina, titania, zinc oxide, tin oxide, hydroxy apatite, aluminium nitride, silicon carbide, silicon nitride, etc. The textured ceramics showed anisotropic properties depending on the crystal plane.
Authors: Snezana Dević, R. Carli
Abstract: The basic idea of the work was to analyze the effect of the wollastonite mineral CaO SiO2 content in the continuous casting powder related to the SEN erosion. In order to realize the research, experiments were conducted in the laboratory conditions. The research, experiment, was realized in the Magnohrom Kraljevo laboratory, and cryptonym furnace EV16 was used for refractory material behavior. Cut SEN pieces from the slag zone in the reduction atmosphere were treated in the furnace with three types of casting powder of different mixtures ratio of SRD1 (without wollastonite) and SRD2 (with wollastonite): Casting powder 1 - SRD1/SRD2 = 50/50 %, Casting powder 2 - SRD1/SRD2 = 25/75 % and Casting powder 3 - SRD1/SRD2 = 75/25 %. Temperature of the experiment was in the range of 15200C – 15400C, and treatment time was changed simulating the average casting time of the heat; one heat (45 min), two heats (90 min), and three heats (135 min). The experiment pointed out that the erosion of the SEN was reduced with the increased ratio of wollastonite in the casting powder. The erosion rate of the SEN exposed to the casting powder 2 in the laboratory conditions was 0.0055 mm/min, whilst the erosion rate of the SEN exposed to the casting powder 3 (with the least wollastonite content) was 0.0075 mm/min. Erosion rate of SEN exposed to the casting powder 2 was lower for the 26.27 % related to the casting powder 3, and 17.90% lower than the erosion rate of the casting powder 1 (the erosion rate of the casting powder 1 was 0.0067 mm/min). These laboratory experiments are very consistent with results obtained in the plant conditions [1,2,3]. At that time, results indicated that SRD1 casting powder without wollastonite has the erosion rate 46 % higher than SRD2 casting powder with wollastonite. On the basis of the laboratory researches and earlier plant conditions researches it could be concluded that wollastonite mineral content in the casting powders has significant effect on the SEN erosion, in the way that the SEN erosion rate was decreased with the increased wollastonite content in the casting powders.
Authors: Xiao Hu Chen, Xiao Min Chen, Huang Zhao, Ji Huai Wu
Abstract: The purpose of this paper is to investigate the possibility of rod-like Al2TiO5 / α-Al2O3 composites in situ formation via a mechanical activation process. A QM-ISP-4 Planetary Mill was employed to activate mechanically the mixtures of anatase and corundum in air at room temperature for different times. The milled powder mixtures were pressed into platelets and then sintered in air at 1300°C for 3 h. The XRD results showed that only Al2TiO5 and α-Al2O3 phases could be detected in the sintered samples when the activated time reached 30 hours. The SEM observations illustrated the unusual microstructure of Al2TiO5 / α-Al2O3 ceramic composite materials. Abnormal grains with longitudinal length ~10 μm23 transversal length ~1 μm and equiaxed matrix grains of ~3 μm on an average were observed. EDXA proved that the rod-like grains and the fine equiaxed matrix grains were composed of Al2TiO5 and α-Al2O3, separately. The roles of anisotropic grain growth caused by mechanical activation are discussed for the in situ formation of rod-like Al2TiO5 / α-Al2O3 ceramic composite materials.
Authors: Shan Zheng, Lian Gao, Hiroshi Watanabe, Junichi Tatami, Toru Wakihara, Katsutoshi Komeya, Takeshi Meguro
Abstract: Dense and homogenous Si3N4-TiN composites (5 vol% TiN) were prepared by using in situ synthesis method from Si3N4, AlN and TiO2 mixtures, containing Y2O3 and Al2O3 as sintering aids. In the prepared Si3N4-TiN composites, TiN grains were formed from TiO2 and AlN powders during the sintering process, in which ammonium citrate was used as a dispersant for raw TiO2 powders. The microstructures of the Si3N4-TiN composites with the increase of ammonium citrate were investigated by scanning electron microscopy (SEM). Citrate ions modified on the surface of TiO2 particles and protected the TiO2 particles in the mixed slurry to reduce the aggregations of TiO2 powders, and homogenous Si3N4-TiO2-AlN composite powder was prepared for sintering. The microstuctures of Si3N4-TiN were developed after sintering with the uniform distribution of TiN grains in the Si3N4 ceramics. It was found that the microstructure of Si3N4-TiN composite was improved significantly with 0.20 g ammonium citrate in the system, TiN grains with 0.2-0.3 μm in diameter distributed throughout Si3N4 matrix. It was a practical and useful way to improve the microstructure of Si3N4-TiN composite without the alteration of the preparation procedure.
Authors: Takamasa Ishigaki, Ji Guang Li, Masashi Ikeda, Rubin Ye, Yusuke Moriyoshi
Authors: Xi Hai Jin, Lian Gao, Jing Sun
Abstract: Co/ZnO and Ni/Al2O3 composites were prepared by in-situ decomposition of CoNx and NiNx during sintering, using CoNx/ZnO and NiNx/Al2O3 mixtures synthesized through an in-situ nitridation method as the starting powders. It was found that these composites showed a very uniform microstructure with metal particles homogeneously distributed among matrix grains. The microstructure and properties were tentatively studied.
Authors: Qing Hong Zhang, Lian Gao
Abstract: In this paper, we reported the preparation of nanocrystalline Ta3N5 particles by nitridation of Ta2O5 nanoparticles using NH3 as reactant gas. It was found that nanocrystalline Ta2O5 was converted into Ta3N5 completely at 700°C within 5.0 h, which was much lower than the temperature 850°C for the complete nitridation of micron-sized Ta2O5 powder. The resulting nitride was characterized by X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (FE-SEM). The nitrogen contents in the prepared Ta3N5 powders were quantitatively determined with CHN elemental analyzer and thermogravimetry and differential scanning calorimetry (TG-DSC). The color of nanocrystalline Ta3N5 is in fresh red while the one of micrometer-sized Ta3N5 is in dark red.
Authors: Katsumi Yoshida, Hideki Hyuga, Naoki Kondo, Hideki Kita
Abstract: Graphite powder was treated with lanthanum, aluminum and magnesium phosphate solution, and oxidation resistance of the obtained graphite powder was evaluated. Oxidation starting temperature and oxidation completion temperature of graphite powder treated with various phosphates were 50-100oC higher than those of as-received graphite powder. Graphite powder treated with small amount of lanthanum phosphate exhibited the higher oxidation starting temperature than graphite powder treated with aluminum and magnesium phosphates. LaP5O14 would partially exited on graphite powder, and protect the edge carbon atoms of graphite and reduce the reactivity of carbon atoms toward oxygen, resulting in improving the oxidation resistance.

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