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Effect of Ar or N2 sintering atmosphere on the high-temperature oxidation behaviour of pressureless liquid-phase-sintered α-SiC in air

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Title: Effect of Ar or N2 sintering atmosphere on the high-temperature oxidation behaviour of pressureless liquid-phase-sintered α-SiC in air
Authors: Rodríguez-Rojas, F.1, Ortiz, A.L. alortiz@unex.es, Borrero-López, O.1, Guiberteau, F.1
Source: Journal of the European Ceramic Society. Jan2010, Vol. 30 Issue 1, p119-128. 10p.
Subjects: Argon, Nitrogen, Sintering, Oxidation, High temperatures, Silicon carbide, Air analysis, Chemical kinetics
Abstract: Abstract: The effect of the Ar or N2 sintering atmosphere on the oxidation behaviour of pressureless liquid-phase-sintered (PLPS) α-SiC was studied. PLPS α-SiC specimens processed under Ar or N2 atmospheres were isothermally oxidized at 1100–1450°C in air for up to 500h, and their oxidation kinetics, activation energy, and rate-controlling mechanisms were compared. It was found that, regardless of the sintering atmosphere, the oxidation is passive due to the formation of oxide scales. In addition, below 1350°C the oxidation is protective, with a kinetics that follows initially the arctan-rate law and then the parabolic-rate law. However, from 1350°C onwards the oxidation becomes only semi-protective, with a kinetics that obeys the arctan-rate law briefly and then the paralinear-rate law. Furthermore, the activation energies and rate-controlling mechanisms are similar for the arctan and paralinear oxidations, but different for the parabolic oxidation. It was also observed that the N2-processed material oxidizes more slowly than the Ar-processed material below 1200°C due to a greater crystallization of its oxide scale, whereas above 1200°C the Ar-processed material is more oxidation-resistant due to greater viscosity of its oxide liquid. Implications concerning the optimization of the processing route of PLPS SiC for high-temperature applications in air are discussed. [Copyright &y& Elsevier]
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Abstract:Abstract: The effect of the Ar or N2 sintering atmosphere on the oxidation behaviour of pressureless liquid-phase-sintered (PLPS) α-SiC was studied. PLPS α-SiC specimens processed under Ar or N2 atmospheres were isothermally oxidized at 1100–1450°C in air for up to 500h, and their oxidation kinetics, activation energy, and rate-controlling mechanisms were compared. It was found that, regardless of the sintering atmosphere, the oxidation is passive due to the formation of oxide scales. In addition, below 1350°C the oxidation is protective, with a kinetics that follows initially the arctan-rate law and then the parabolic-rate law. However, from 1350°C onwards the oxidation becomes only semi-protective, with a kinetics that obeys the arctan-rate law briefly and then the paralinear-rate law. Furthermore, the activation energies and rate-controlling mechanisms are similar for the arctan and paralinear oxidations, but different for the parabolic oxidation. It was also observed that the N2-processed material oxidizes more slowly than the Ar-processed material below 1200°C due to a greater crystallization of its oxide scale, whereas above 1200°C the Ar-processed material is more oxidation-resistant due to greater viscosity of its oxide liquid. Implications concerning the optimization of the processing route of PLPS SiC for high-temperature applications in air are discussed. [Copyright &y& Elsevier]
ISSN:09552219
DOI:10.1016/j.jeurceramsoc.2009.08.004