High-Performance Ceramics V

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Authors: Gang Shao, Hai Long Wang, Fang Shao, Kai Li, Rui Zhang
Abstract: SiC particulate-reinforced Fe composites were prepared by a powder metallurgy (PM) and conventional atmospheric sintering method. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques were used to characterize the obtained composites. The coating layer of Cu on SiC particles can suppress the reaction between SiC and Fe until 1250oC. The maximum microhardness of 283 Hv appears at near 1250oC. Substantial reaction occurs at above 1250oC, which leads to the deterioration in the microstructure and related properties. The inter-metallic compounds of FeSi or Fe2Si were detected which contributed to the enhancement of the interface between SiC and Fe.
Authors: Jian Qing Dai, Yong Huang, Jing Tao Ma, Zhi Peng Xie
Abstract: Particular attention is paid in this paper to understanding the surface characteristics and aqueous dispersibility of as-received commercial powders. The different production methods and specific pulverization processes used for the four powders studied (FD1, FD2, M11, UBE) result in obvious differences in such powder properties as surface groups, aqueous dispersibility, and water-soluble ions.
Authors: Jing Zhao, Wen Bin Cao, Jiang Tao Li, Zhao Han, Yan Hong Li, Chang Chun Ge
Abstract: Selective laser sintering (SLS) of Si3N4 and Al2O3 powders were investigated in this work. Copolymer was synthesized through monomer MMA and BMA. Infrared spectrum was employed to characterize the as-synthesized copolymer. Results show that the main compositions of the copolymer are PMMA and PBMA. The binders were prepared by mixing the copolymer and the inorganic NH4H2PO4 with certain ratio. Binders were used to coat the Si3N4 and Al2O3 powders by spray drying. The coated powders were sintered successfully by SLS to make cubic part and rotor part.
Authors: Ke Gang Ren, Ke Xin Chen, He Ping Zhou, Hai Bo Jin, Ji Dong Zhong, Xiao Shan Ning
Abstract: Effect of iteration times on mechanically-activated combustion synthesis of high α-content Si3N4 powders was investigated. Properties of the as-synthesized powders such as α-content (Cα) as well as specific surface area (As) were examined. Results showed that both of Cα and As became higher after iteration reactions. The mechanical properties of the sintered bulk ceramics from as-synthesized powders were also tested to reveal the sinterability of the powders. Results showed that relative density of all the sintered bulk ceramics were higher than 97%. Furthermore, fracture toughness had a trend of becoming higher, which reached a value of 10.2 MPam0.5. Correspondingly, bending strenth became a bit lower.
Authors: G.H. Liu, Ke Xin Chen, He Ping Zhou, Jiang Tao Li, Ji Dong Zhong, José Maria F. Ferreira
Abstract: β-Si3N4 and β-SiAlON powders were prepared by combustion synthesis with SrCO3 and NH4F used as additives. The resultant β-Si3N4 and β-SiAlON powders consisted of elongated prismatic microcrystals. By adding SrCO3, the anisotropic growth of β-Si3N4 and β-SiAlON crystals is improved and their aspect ratios increase. The addition of NH4F enhanced nitridation reactions and reduced the residual Si in combustion products. It was proposed that the elongated prismatic β-Si3N4 and β-SiAlON crystals grew from liquid phase and the composition and property of this liquid was affected by the addition of SrCO3.
Authors: Guo Qiang Tan, Hong Yan Miao, Hui Jun Ren, Zhi Wei Yu, Jia Li, Hui Qin Li
Abstract: Xerogel was prepared by the sol-gel method using ethyl ester orthosilicate, alcohol, carbamide and glucose with various contents as raw materials. The precursor powders were obtained after xerogel was solvothermally treated at 220oC for 2.5 h. IR analyses showed that the Si-O-Si and Si-O-NH2 bond are obtained in the precursors. XRD analyses indicated that the powders prepared by the solvothermal method are amorphous. Si3N4 powders are produced by heat-treating the precursors at 1400 oC in N2. It was proved that the synthesized powders are α–Si3N4 whiskers. With the increase of the glucose contents and the heat-treating temperature, the crystallization of Si3N4 is obviously improved.
Authors: Xin Wen Zhu, Tohru Suzuki, Tetsuo Uchikoshi, Yoshio Sakka
Abstract: This paper reports the texture development in Si3N4 by strong magnetic field alignment (SMFA), using slip casting of α-Si3N4 raw powder (SN-E10) and pressureless sintering. The texture of β-Si3N4 in the green and sintered bodies was characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The a, b-axis and c-axis aligned β-Si3N4 has been obtained by the static and rotating magnetic field of 12 T, respectively. The β-seed addition and prolonged sintering both enhance the texture, but the former is more efficient. This work suggests an efficient SMFA strategy of producing highly textured β-Si3N4, particularly the unidirectionally c-axis aligned β-Si3N4 by seeding the α-raw powder using the less-agglomerated β-phase particles.
Authors: Si Hua Ma, Xiao Shan Ning, Teng Fu, He Ping Zhou, Ke Xin Chen
Abstract: High thermal conductive Si3N4 is a promising candidate for producing high quality ceramic substrates used in vehicles. Although a lot of researches have been carried out on the tape casting of Si3N4, they were mainly restricted in fabricating thin films with a thickness less than 200μm which are not sufficient for producing substrate. With larger thickness, tapes tend to crack during drying. In this work, slurry of α-Si3N4 with Y2O3-MgO as additives was prepared using an azeotropic mixture of methylisobutylketone/methyehtylketone/cyclohexanone as media. To obtain thick green tapes, the amount of dispersant, binder and plasticizer in the slurry were optimized, and the effects of drying temperature on the cracking behavior of the tape were studied. By controlling the composition of the slurry and the drying conditions, thick green tapes with thicknesses up to 1.8mm were successfully fabricated, and Si3N4 substrates were produced after subsequent gas-pressing sintering, which were flat and had a relative density as high as 98.2%.
Authors: Yuan Lu, Jian Feng Yang, Shao Yun Shan, Ji Qiang Gao, Zhi Hao Jin
Abstract: In this paper, porous Si3N4 ceramics were fabricated by carbothermal reduction between silicon dioxide and carbon. The influences of four types of sintering additives on the microstructure and mechanical properties of the porous Si3N4 ceramics were investigated. XRD analysis proved complete formation of a single-phase β-Si3N4. SEM analysis showed that the resultant porous Si3N4 ceramics occupied fine microstructure and a uniform pore structure. The sintered sample with Lu2O3 as sintering additive showed finer, a higher aspect ratio β-Si3N4 grains. The addition of Eu2O3 accelerated the densification of porous Si3N4 ceramics, decreased the porosity and increased the flexural strength.
Authors: Yu Hui Bi, Jun Li, Fei Chen, Dong Ming Zhang, Qiang Shen, Lian Meng Zhang
Abstract: In this paper, silicon nitride (Si3N4) ceramics by aligning α-Si3N4 whiskers were prepared via tape casting, hot-press sintering technique using Y2O3 and MgO as sintering additives. Aligned α-Si3N4 whiskers were realized by modifying the tape casting technique. After tape casting, Si3N4 tape with good flexibility and uniform pores can be obtained. Microstructures of the tape, green body and sintered sample were observed by SEM images. The results show α-Si3N4 whiskers in Si3N4 tape and green body were aligned preferentially along the tape casting direction. Si3N4 ceramics with aligned elongated grains are developed by hot-press sintering technique based on the reaction between Si3N4 and the sintering additives which lead to the liquid phase.

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