Comparison of the Reaction Behavior of Hexagonal Silicon Carbide Powder in Different Atmospheres
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UCTION
SILICON carbide (SiC) is extensively applied in the fields of diesel engines, aerospace, thermal conductor, gas filter, etc.[1–4] due to its high strength, excellent corrosion resistance, good refractory, low density, etc.[5–7] However, as a kind of high-temperature structure material, SiC is usually confronted with oxidation at high temperature. Especially in combustion environment, water vapor is always inevitable. Under these conditions, SiC materials tend to be corroded, which weakens their durability and service life. In order to clarify both its specific degradation mechanism and reaction kinetics, the reaction behavior of bulk SiC and SiC-based composites under different conditions at high temperature has been widely investigated.[8–11] The general consensus is that the kinetic onset of oxidation lies between 1273 K and 1373 K (1000 °C and 1100 °C) according to the following reactions:
ENHUI WANG and XINMEI HOU are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, China, and also with the State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, China. Contact e-mail: [email protected] JUNHONG CHEN is with the School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, China. KUO-CHIH CHOU is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing. Manuscript submitted March 22, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
3 SiC þ O2 ðgÞ ¼ SiO2 þ COðgÞ; 2
½1
SiC þ 3H2 OðgÞ ¼ SiO2 þ 3H2 ðgÞ þ COðgÞ:
½2
With water vapor being introduced, the volatilization reaction of water vapor with the oxidation product SiO2 can further occur to form silicon oxyhydroxide species as follows[12,13]: SiO2 þ 2H2 OðgÞ ¼ SiðOHÞ4 ðgÞ:
½3
Further investigation indicates that water vapor can enhance the reaction of bulk SiC.[9,11] With respect to the reaction kinetics, much of the work based on Tedmon’s kinetic research of Fe-Cr alloy oxidation[14] has been conducted. Generally, it is concluded that the reaction follows parabolic law in dry conditions while it is dominated by paralinear behavior in water-containing atmospheres.[11] In view of the reaction behavior of SiC powder under different atmospheres, Yoshimura et al.[15] investigated the oxidation of SiC powder at 673 K to 1073 K (400 °C to 800 °C) under 10 and 100 Mpa. The results showed that the oxidation rate increased with temperature and pressure with the apparent activation energies ranging from 167 to 194 kJ/mol. Dutta[16] adopted pressureless sintering to prepare the SiC ceramics using a-SiC powder as the raw material. The experimental results showed that the oxidation resistance of synthesized SiC ceramics was acceptable under 1643 K (1370 °C). Hou et al.[17] proposed a kinetic model to describe the
reaction behavior of SiC powder in dry air. They further discussed the influence of particle size distribution on the reaction behavior at 1673 K to 1773 K (1200 °C to
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