High-Performance Ceramics V

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Authors: In Sub Han, Jong Chul Park, Se Young Kim, Ki Seog Hong
Abstract: Silica wet gels were prepared from water glass (29 wt.% SiO2) by using Amberlite as a ion exchange resin. After washing in distilled water, the wet gels were further aged in a solution of TEOS/EtOH to strengthen the 3-dimensional network structure. With the increasing TEOS content in aging solution, BET surface area and porosity of the ambient dried silica aerogel were decreased, and the average pore diameter was decreased from 30nm to 10nm. Also, higher density and compressive strength were obtained in case of higher TEOS content. This is due to the precipitation of SiO2 nano particle by TEOS. Hence, TEOS addition plays an important role in both strengthening and increasing stiffness of silica wet gel network. By adding 30 vol.% TEOS, a crack-free monolithic silica aerogel tiles were obtained and its density, compressive strength, and thermal conductivity were shown 0.232 g/cm3, 7.3 MPa, and 0.029 W/mK, respectively.
Authors: Xiao Hui Wang, Xiao Ping Liang, Shao Bo Xin
Abstract: Silicon dioxide gel fibers were prepared by hydrolysis reaction of tetraethyl orthosilicate (TEOS). TEOS was used as basic materials, anhydrous ethanol (EtOH) as solvent and hydrochloric acid (HCl) as the catalyst. The best proportion of the chosen materials (TEOS, EtOH, H2O and HCl) was 1:1:1.5:0.03(molar ratio).Gel fibers were investigated by thermogravimetry (TG). Silicon dioxide fibers were obtained by treating the gel fibers at different temperatures. The calcined fibers were characterized by scanning electron microscopy (SEM). The optimal sintering schedule was obtained. Silicon dioxide fiber dried at 200°C for 1 hour then calcined at 800°C for 3 hours was the best.
Authors: Chien Jung Huang, Pin Hsiang Chiu, Yeong Her Wang
Abstract: This paper describes a sol-gel (SG) method for the coating of gold nanoparticles with uniform shells of amorphous silica. The thickness of silica could be conveniently controlled in the range of 10 to 120 nm by increasing the amount of water. Although spherical gold nanoparticles generally have a surface plasmon resonance (SPR) at a wavelength of about 520 nm, a spherical gold core with a silica shell offers a very highly tunable SPR wavelength depending on the thickness of the silica shell.
Authors: Shi Ying Zhang, Fan Ping Xiao, Luo Yi Wu, Cheng Yong Li, Zhen Hua Chen
Abstract: Using tetrabutyltitanate as titanium source, amorphous TiO2 powder was firstly prepared by a sol–miniemulsion–gel method. Prepared powder was refluxed in basic solution and then calcined at different temperatures to synthesize titania nanofibers. The prepared samples were characterized by XRD, TG–DSC, FT–IR and TEM. The results show that when the heat–treatment temperature increases, crystallization of the titania nanofibers occurs with two Ti–OH bonds dehydrate, meanwhile morphology of the fibers is gradually obvious and ratio of length to diameter decreases. When the temperature was raised above 550 °C, titania nanofibers were sintered.
Authors: Nan Chun Chen, Han Mei Ao, Dong Chen
Abstract: A new method of synthesizing mullite nanocomposite from raw natural kaolin is presented in the paper. Raw kaolin is processed by oxidation-reduction fining method and then baked to produce fine kaolin powder. The fine kaolin powder is further synthesized into mullite nanocomposite by open-system hydrothermal crystallization method under normal pressure. With proper controls of NaOH mole ratio in the hydrothermal solution, crystallization time, and constant temperature, the average grain size of synthesized nanocomposite changed from 80nm to 100nm. The morphology of the nanocomposite could gradually change from platy to short prismatic, lamellar, and needle-like with increasing nucleation rate.
Authors: Xiao Lin Jia, Su Ping Li, Hai Jun Zhang, Jiang Tao Zhu, He Long Hu
Abstract: Nanosized mullite powders were prepared by hydrothermal method with bauxite as precursor. The effects of mineralizer, hydrothermal temperature, hydrothermal time, dispersant on the phase, crystal size and secondary granularity of the powders were discussed. The properties of the prepared powders were characterized by XRD, SEM, and ZETASIZER. The results show that the spherical nanosized mullite powders with crystal size of 28nm are prepared under the conditions of 0.92 mol·L-1 concentration of NaOH, less than 85% filling ratio, 110°C for 6 h with bauxite calcined at 1040°C as starting material.
Authors: Hui Wang, Ling Ke Zeng
Abstract: Mullite fiber porous ceramic was prepared by forced liquid displacement forming and using Mullite precursor sols as binders. SEM studies have shown that the uniformity of integral ceramic is good although the binder and fiber congregate slightly. Mullite precursor sols spread to films or congregate together in miniature. The mullite sol binders between fibers limit to the contact points and the redundant binders form flat film even if they are superfluous, and the pores were not built up even where the binders congregate badly. The results from mercury porosimetry testing of the mullite fiber porous ceramic showed the relationship of cumulative intrusion and diameter for mullite fiber porous ceramic using colloidal mullite binder, and the mean pore size is 45.6μm. The pore size distribution is very broad, from about 0.2 to 174.9μm.
Authors: Fu Jun Zhao, Lin Hai Han, Long Liang
Abstract: The nonstoichiometric Al-rich single crystal mullite nanosticks were prepared by sol-gel method without any catalysts. The nanosticks are straight and uniform with a width of 300-350nm and length of 3-5m. The nanosticks’ growth direction is along[210] . Detailed structural characterizations suggested that the growth of this novel nonstoichiometric structure was induced by the self-catalyzed process.
Authors: Shun Li, Jia Chen Liu, Zhong Qiu Li, Wei Fan, Peng Yu Zhang
Abstract: A novel technique to synthesize mullite by the oxidation of Al-Si alloy powder was used for the manufacture of mullite via pressure molding. The mixed powder was consisted of powders of Al-Si alloy, Al2O3 and SiO2 and additives or powders of Al-Si alloy, Al2O3, SiO2 and ZrO2 and additives. Those mixed powders were milled in nonaqueous slurry in order to prevent the oxidation of Al-Si alloy. Then the green bodies were pressureless sintered in air at ≥1380 °C. The Oxidation caused an internal volume expansion, resulting in reducing shrinkage stresses during reaction- bonding of composites, which minimized the sensitivity to crack formation. Comparing with non zirconia reinforced mullite composites, the effect of the microstructure and mechanical properties of mullite composites were studied.
Authors: Lin Liu, Xin Xing, Xiao Dong Li
Abstract: A novel SiC precursor antimony-substituted polymethylsilane (APS) is present in this paper. First, pre-APS was synthesized from polymethylsilane (PMS) and SbCl3 at room temperature. Pre-APS was a liquid mixture and could be used in PIP process without solvent. After the elemination of HCl and the crosslinking of pre-APS, the novel precursor APS with the ceramic yield 91% was prepared.

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