Papers by Keyword: Silicon Carbide (SiC)

Abstract: Based on the theory of thermodynamics, the chemical compatibility of the possible composition system of ceramic material Al2O3/Cr3C2/SiC (for short ACS) was analyzed. The results show that no chemical reaction could take place under 1800°C through Cr3C2, SiC and Al2O3. And it was tested by the fabrication of the Al2O3/Cr3C2/SiC composite with the hot pressing sintering technique. The flexural strength and fracture toughness of ACS are super than the Al2O3 ceramic.

Abstract: In the field of high temperature sensing applications, Silicon carbide (SiC) is a superior material due to its excellent mechanical, thermal and chemical properties. Laser triangulation is a technology of non-contact, rapidity, and high accuracy. Its characteristic of non-contact can realize the high temperature non-resistance components’ isolation from the high temperature components of the sensor effectively, so as to achieve measurement under high temperature. Meanwhile, its measurement accuracy can be further improved effectively by using the principle of lens imaging of magnification and constant focus, combining with the high-resolution photodetector. This paper first applied it to the measurement of pressure under high temperature, and proposed a laser-type high temperature pressure sensor using SiC diaphragm as the pressure-sensitive diaphragm. The sensor measured the center deflection of the circular SiC diaphragm caused by pressure and temperature using the laser triangulation, then created the corresponding relationship between the pressure, temperature and deflection according to the thermoelasticity theory. The paper first established the mathematical model of the high accuracy laser triangulation. Afterward did the thermomechanical finite element analysis of the SiC diaphragm using ANSYS. The research and analysis demonstrate that this technical scheme of measurement of pressure under high temperature is effective and feasible, and provide a forceful and important basis for the design and realization of the sensor.

Abstract: With use of electron-assisted chemical vapor deposition technology, nanocrystalline diamond films were deposited on SiC ceramics substrates at various gas pressure ( 0.5 ~ 2 kPa ). Effect of the gas pressure on optical properties of the nanocrystalline diamond films was studied. Raman scattering spectra were measured. Photoluminescence spectra were investigated in the range of 420 ~ 680 nm. Spectroscopic ellipsometry were analyzed from the near IR to the UV region ( 1.5 ~ 5.0 eV ). Results show that, when the gas pressure increased from 0.5 to 2 kPa, Raman scattering intensity of diamond increase and D/G ratio decrease; when the gas pressure was 0.5kPa and 2kPa, there is not any PL peak, however, there is a stronger PL peak at 485 nm when the gas pressure was 1kPa; extinctive coefficient k for the nanocrystalline diamond films deposited at 1kPa increase obviously with increase of photo energy.

Abstract: Nanoparticles of silicon carbide were produced through direct pyrolysis of stoichiometerically balanced rice husk. Rice husk used in this study was treated with different type and amount of silica source in order to enhance the silica/carbon ratio and thereby increase the yield. The synthesis was carried out in argon atmosphere. To increase the yield, different process parameters were identified and experiments were conducted at various levels using Taguchi design. The process parameters optimized using this design include silica source, pyrolysis temperature, silica content and heating rate. Silicon carbide produced from rice husk was analyzed using X - ray diffraction to identify the phase. From taguchi factor effect diagram it has been found that pyrolysis temperature and silica source plays major role in improving the yield.

Abstract: Sintered Silicon Carbide material with fine grain structure shows excellent wear resistance, highly chemically resistance, excellent performance in a wide range of applications. This material can improve upon the exceptional corrosion and erosion resisting properties through the addition of unique micro pores. A designed spherical-pore Silicon Carbide material was obtained after pressureless sintering. The photomicrograph shows a typical appearance of unique micro pore. SEM was also employed to investigate the micro-structure of as-prepared SiC material. The properties of micro-pore Silicon Carbide, such as density, hardness, strength, etc. were determined in detail. The relationship between the spherical-pore structure and properties of Silicon Carbide were discussed.

Abstract: The oxidation kinetics of SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) and the constituent fibers was characterized by thermogravimetric analysis and microstructural characterization at temperatures (816-1538°C) and oxygen partial pressures (0.1% to 5% O₂) relevant to the hypersonic flight and re-entry environments. TGA of the SiC fibers showed that oxidation of the thin BN surface layer led to initially rapid oxidation kinetics and formation of a relatively thick silica scale at very short times under most test conditions. At longer times the fiber oxidation kinetics were representative of silica formation on pure SiC. Oxidation of the composites was conducted on coupons with the SiC seal coat removed on one edge to simulate damage to the composite, allowing ingress of oxygen to the fiber tows. Microscopy was conducted to determine the distance of oxygen ingress into the coupon. At the lower temperatures and oxygen partial pressures the exposed edge did not seal off by silica formation, yet the BN interphase areas were only minimally oxidized. At the intermediate temperatures silica formed at the exposed surface limiting further oxidation of the exposed fibers and BN interphase areas. Finally at the highest temperature and lowest oxygen partial pressure, active oxidation of SiC occurred for both the fibers and coupons resulting in irregular material attack. Implications for use of SiC/BN/SiC materials for hypersonic vehicle thermal protection systems are summarized.

Abstract: The objective of this study is to improve the high-temperature erosion-corrosion resistance Incoloy 800 for the application used as thermowell at 900°C. In weld cladding procedure, silicon carbide (SiC) particles were pre-deposited on the Incoloy 800 substrate, followed by the cladding of Ni-base alloy filler (34Ni-25Cr-0.4C-Ti-W-Mo) by a gas tungsten arc welding. A theoretical amount of SiC particles mixed with filler was 2 - 30%wt. A particle size of SiC was in the range of 50-150 mm. The results showed that the addition of 15%wt SiC led to the maximum hardness of the cladding layer. Addition of particles more than 15wt% tended to provoke cracks in cladding layer. The larger particle size exhibited the higher hardness. An erosion rate of cladding surface was further tested by the perpendicular impingement of 1-mm SiC abrasion sands on the sample surface with air flow velocity of 220 m s^-1 at 900°C in air. For cladding layer with the same amount of SiC mixed, the one mixed with larger particle size exhibited the higher erosion-corrosion resistance. Likewise, for cladding layer mixed by the same size of SiC, the addition of particle with a smaller amount promoted the higher erosion-corrosion resistance. The addition of 2.6 wt% SiC particles with 150 mm size in cladding layer showed the surface with the best erosion-corrosion resistance in this study. No oxide scale was, however, observed on eroded surface due to the spallation by high impact erodent particles.

Abstract: The nucleation mechanism during the epitaxial graphene films on Si-terminated SiC (0001) surfaces was investigated by atomic force microscopy (AFM) and Raman scattering spectrum. By imaging the change of Si-terminated SiC substrate surfaces, we observed the process of the initial nucleation and the wrinkle formation of graphene. The nucleation of epitaxial graphene phase initiates at 1450°C and the wrinkle formation depends on the thermal decomposition time.

Abstract: This paper studies the polishing mechanism of SiC optic surface; it also introduces the grinding mechanism of ceramic material – indentation fracture model. In this paper, the model of SiC polishing in ideal condition is analyzed and the mechanism of SiC polishing in real state is studied.

Abstract: Reaction-bonding sintering silicon carbide (RB-SiC) toughened by 10vol% short carbon fibers were produced by Gel-casting method using water soluble epoxy as gel former and then reaction sintering at 1750°C under vacuum atmosphere for 2 h . SEM showed that short carbon fibers could disperse uniformly in the preforms and sintered carbon fiber reinforced silicon carbide composites (C_f/SiC). The mechanical test results showed that the strength decrease from 286 MPa for RB-SiC to 231 MPa for C_f/SiC, however, the fracture toughness of Cf/SiC increased from 3.65 MPa m^1/2 to 5.28 MPa m^1/2 compared with RB-SiC. The strength decrease of the C_f/SiC should be ascribed to the chemical reaction between the addition of short fibers and matrix, and the increase of the fracture toughness could be attributed to fiber debonding, fiber pull-out and crack deflection .