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Micro-Structural Characterization of Si-SiC Ceramic Derived from C/C-SiC Composite
American Journal of Materials Science , 2012, DOI: 10.5923/j.materials.20120201.01
Abstract: The main objective of the present work is to processing the porous Si-SiC ceramic by the oxidation of C/C-SiC composite. Phase studies are performed on the oxidized porous composite to examine the changes due to the high temperature oxidation. Further, various characterization techniques are performed on Si-SiC ceramic in order to study the material’s microstructure.
Microstructure Evolution and Reaction Mechanism of Microporous Carbon Derived SiC Ceramic
XU Shun-Jian,QIAO Guan-Jun,WANG Hong-Jie,LI Di-Chen,LU Tian-Jian
无机材料学报 , 2009, DOI: 10.3724/sp.j.1077.2009.00291
Abstract: The process of reaction of silicon carbide ceramics derived from microporous carbon was investigated. The reaction mechanism was also analyzed. The ultimate microstructure of SiC ceramics are affected by the mass ratio of C to Si and infiltration time. Composite materials, which consist of SiC, Si and a small fraction of unreacted C, are obtained when the mass ratio of C to Si is higher whereas partial infiltration occurs when the mass ratio of C to Si is lower. Composite materials demonstrates many uniformly distributed stripa2shaped SiC grains in certain region at transitional stage of reaction, and shows irregular SiC grains and an obvious bimodal distribution of grain size at terminal stage of reaction. The process of silicona2carbon reaction can be described as follows, melted Si ascends via capillary of micropore carbon and reacts with contacted carbon forming SiC. Size difference of pore and carbon wall induces difference of the infiltration deep of melted Si within micropore carbon and thicknesses of the dissolved carbon layer, respectively. As a result, some carbon particles are embedded in SiC grain and pore channel system is restructured. New pore channel with bigger pore size are formed, which accelerates infiltration rate of melted Si. Then the unreacted carbons embedded in SiC grain are firstly diffuse through the SiC layer and dissolved in the Si melt, and then deposits on the first SiC formed. Finally, liquid epitaxial growth of SiC causes coalescence of SiC grains and envelopment of some Si in SiC grains, resulting in change of microstructure of SiC ceramics.
Preparation of biomorphic SiC ceramics  [PDF]
Egelja A.,Gulicovski J.,Deve?erski A.,Nini? M.
Science of Sintering , 2008, DOI: 10.2298/sos0802141e
Abstract: This paper deals with a new method for producing non-oxide ceramic using wood as a template. SiC with a woodlike microstructure has been prepared by carbothermal reduction reactions of Tilia wood/TEOS composite at 1873K. The porous carbon preform was infiltrated with TEOS (Si(OC2H5)4), as a source of silica, without pressure at 298K. The morphology of resulting porous SiC ceramics, as well as the conversion mechanism of wood to SiC ceramics, have been investigated by scanning electron microscopy (SEM/EDS) and X-ray diffraction analysis (XRD). Obtained SiC ceramics consists of β-SiC with traces of α-SiC.
Research Progress of Optical Fabrication and Surface-Microstructure Modification of SiC  [PDF]
Fang Jiang,Yan Liu,Yong Yang,Zheng-Ren Huang,Dan Li,Gui-ling Liu,Xue-Jian Liu
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/984048
Abstract: SiC has become the best candidate material for space mirror and optical devices due to a series of favorable physical and chemical properties. Fine surface optical quality with the surface roughness (RMS) less than 1?nm is necessary for fine optical application. However, various defects are present in SiC ceramics, and it is very difficult to polish SiC ceramic matrix with the 1?nm RMS. Surface modification of SiC ceramics must be done on the SiC substrate. Four kinds of surface-modification routes including the hot pressed glass, the C/SiC clapping, SiC clapping, and Si clapping on SiC surface have been reported and reviewed here. The methods of surface modification, the mechanism of preparation, and the disadvantages and advantages are focused on in this paper. In our view, PVD Si is the best choice for surface modification of SiC mirror. 1. Introduction At present, mirror systems as the most important device are applied commonly in the optical system with high precision. Until now, three generations of reflector materials have been developed. The first generation is glass-ceramic; the second one is mainly made of metal, such as Beryllium metal and its alloys; the third generation of the reflector material is based on silicon carbide. SiC may be the best material available for mirror optics because of its outstanding combination of thermal and mechanical properties. It has remarkable dimensional stability even under the disturbances of temperature, humidity, and chemicals. Its specific stiffness and elastic modulus are higher than that of beryllium, which has toxicity. The density of SiC is slightly higher than aluminum and its fracture toughness is higher than glass. The remarkable properties of SiC in terms of hardness, stiffness, and thermal stability combined with a reasonable density are indeed of primary importance for all space applications. This combination of material advantages makes SiC an excellent material candidate for space optical instruments [1, 2]. Based on microstructure and processing routes, four kinds of SiC ceramics including hot-pressed SiC (HP-SiC), reaction-bonded SiC (RB-SiC), sintered SiC (S-SiC), and chemical vapor deposition SiC (CVD-SiC) were developed. The properties of different SiC materials and the brief description of various SiC component manufacturing techniques are summarized in Table 1 [2, 17]. Whatever the preparation process, it is difficult to obtain high-quality optical surface due to polishing the bare SiC very difficultly. Moreover, microstructure defects, like pores, steps at different phases, and grain
Reaction Mechanism of Silicon Carbide Ceramics Derived from Woods

CAI Ning,MA Rong,QIAO Guan-Jun,JIN Zhi-Hao,

无机材料学报 , 2001,
Abstract: The process of reaction of silicon carbide ceramics derived from wood was investigated. The reaction mechanism was also analyzed. The results show that the temperature of silicon infiltration determines the ultimate microstructure of SiC ceramics. Porous SiC materials are formed at lower temperature, while at higher temperature, compact Si/SiC composite materials formed. The process of silicon-carbon reaction can be described as three steps: (1) Melted Si ascends via capillary of charcoal and reacts with contacted carbon forming silicon carbide. (2) The thickness of SiC layer increases toward carbon layer till the end. (3) Reaction-formed SiC will re-crystallize in the later stage of the reaction, and the ultimate microstructure is composed of large size of polygonal SiC and free Si.
Microstructure and Mechanical Properties of Mg-5Nb Metal-Metal Composite Reinforced with Nano SiC Ceramic Particles  [PDF]
Jayalakshmi Subramanian,Zhenhua Loh,Sankaranarayanan Seetharaman,Abdelmagid S. Hamouda,Manoj Gupta
Metals , 2012, DOI: 10.3390/met2020178
Abstract: In this work, a Mg-5Nb metal–metal composite was reinforced with nano SiC (SiC n) ceramic reinforcement of varying volume fractions, using the disintegrated melt deposition technique. The extruded Mg-5Nb-SiC n composites were characterized for their microstructure and mechanical properties. Based on the results obtained, it was observed that the volume fraction of nano-SiC reinforcement played an important role in determining the grain size and improving the mechanical properties. A comparison of properties with those of pure Mg and Mg-5Nb composite showed that while the improvement in hardness occurred at all volume fractions, a minimum volume fraction of ~0.27% SiC n was required to increase the tensile and compressive strengths. The observed mechanical response of the composites were investigated in terms of the effect of SiC n volume fraction, processing, distribution of metallic and ceramic reinforcements and the inherent properties of the matrix and reinforcements. The influences of these factors on the mechanical behavior of the composites are understood based on the structure–property relationship.

JMYang,JCLei,JPLi,PCheng Dept MaterSciand Eng Xi''an Institute of Technology,Xi''an,China,
,J.C.Lei,J.P.Li and P.Cheng Dept. Mater.Sci.and Eng. Xi'an Institute of Technology,Xi'an,China

金属学报(英文版) , 1999,
Abstract: BAS (BaAl 2Si 2O 8) glass ceramic was prepared by a sol gel process and the SiC W/BAS composites were fabricated by hot pressing. The transformation from hexacelsian to celsian, the microstructure and mechanical properties of the composites was investigated. The results show that the transformation promoted by adding celsian seeds is retarded in the composite by the presence of SiC whisker. SiC whisker has a good effect of improving the mechanical properties of BAS glass ceramic matrix. The toughening mechanisms are crack deflection and whisker fracture. The strengthening mechanism is loading transition. The amorphous phase at SiC W/BAS matrix interface damages the fracture toughness and high temperature strength of the composites.
Removal Behaviors of Different SiC Ceramics during Polishing

Guiling Liu,Zhengren Huang,Xuejian Liu,Dongliang Jiang Structural Ceramics Center,

材料科学技术学报 , 2010,
Abstract: Comparative experiments were conducted to reveal the removal behaviors of three kinds of silicon carbide (SiC) ceramics during polishing and the effects of ceramic microstructure on the surface quality were also reported. Experimental results show that the second phase in SiC ceramics plays an important role in the surface quality when its size is large enough. The surface quality is enslaved to the formation of steps at interfaces between second phase and SiC matrix that results from different elastic modulus and hardness between two phases. Under 3 μm abrasive grains polishing condition, different SiC ceramics show different removal mechanisms. With decreasing abrasive grain size, all of different SiC ceramics exhibit a ductile removal mode, which decreases surface roughness effiently.
Preparation of Ti-Si Eutectic Brazes and its Weldability to SiC  [PDF]
LI Jia-Keaa,LIU Lei,LIU Yi-Chun,ZHANG Wen-Long,HU Wen-Bin
无机材料学报 , 2009, DOI: 10.3724/sp.j.1077.2009.00204
Abstract: 91.5Ti-8.5Si (wt%) and 22Ti-78Si(wt%) eutectic brazes with fine structure were prepared by means of the non-consumable arc-melting technology. Wetting behavior and interfacial reactions of two kinds of brazes on silicon carbide (SiC) were investigated by using the sessile drop method in vacuum at 1400 or 10min. The results indicate that two kinds of the brazes exhibit good wettability to SiC ceramic, and their contact angles are about 10 d 25 respectively. After wetting, separation occurs between a 91.5Ti-a 8.5Si (wt%) and SiC, but adhesion is good between 22Ti-78Si (wt%) and SiC. At wetting temperature system, bending strength of the joint of SiC/22Ti-78Si (wt%) /SiC with the braze thickness of a 0.2aamm, may reach 72MPa by tentative joining. Microstructure, phase composition and melting temperature of two kinds of the brazes and the interface of the brazes / SiC are examined by SEM, EDS, XRD and DSC, a etca . Relationship between wettability of the brazes on SiC ceramic and interfacial reactions are investigated.
Influence Factors on the Porosity and Strength of SiC Porous Ceramic  [PDF]
LI Jun-Feng, LIN Hong, LI Jian-Bao
无机材料学报 , 2011, DOI: 10.3724/sp.j.1077.2011.00944
Abstract: The influence of ceramic binder contents, SiC particle sizes, and sintering temperatures on the porosity and flexural strength of SiC porous ceramics for high―temperature gas filtration were investigated. The composition of SiC porous ceramics was measured by X―ray diffraction. The porosity of SiC porous ceramics decreased with increasing the ceramic binder contents, and the SiC porous ceramic with a relatively high porosity of 37.5% and flexural strength of 27.63MPa was obtained with ceramic binder content of 15wt%. Both the porosity and flexural strength of SiC porous ceramics increased with SiC particle sizes decreasing from 300um to 87um, and the porosity increased from 35.5% to 42.4%, while the flexural strength increased from 19.92MPa to 25.18MPa. In addition, the porosity of SiC porous ceramics quickly decreased from 38.7% to 35.4% with sintering temperatures increasing from 1300 to 1400 , but the flexural strength of SiC porous ceramics had only a slight change, mainly standing at about 27MPa. Thus, the sintering temperature of SiC porous ceramics should be selected around the melting point of ceramic binder (1300 ).
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