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Effect of the sintering additive content on the non-protective oxidation behaviour of pressureless liquid-phase-sintered α-SiC in air

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Title: Effect of the sintering additive content on the non-protective 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. Apr2010, Vol. 30 Issue 6, p1513-1518. 6p.
Subjects: Silicon carbide, Sintering, Oxidation, Garnet, Chemical kinetics, Ceramic materials, Eutectics, High temperatures
Abstract: Abstract: The long-term oxidation resistance of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the content of sintering additive (in particular, YAG) at 1500°C in air. It is shown that, regardless of the vol.% YAG, the oxidation is passive at that high temperature, with a kinetics given by the paralinear-rate law. This is because the oxide scales grow due to oxidation of the SiC grains, but recede due to the formation of a eutectic phase and to the carbothermal reduction of YAG. It is also shown that the oxidation resistance of PLPS SiC decreases markedly with increasing vol.% YAG, an effect that is especially marked above 7.3vol.% YAG where a change in oxidation behaviour occurs. Thus, while up to 7.3vol.% YAG the PLPS SiC ceramics gain mass during the entire oxidation process (500h) because the oxide scales are at least semi-protective, from 11.1vol.% YAG onwards the PLPS SiC ceramics first gain mass and then lose mass linearly over oxidizing time because the oxide scales are non-protective. Finally, implications for the design of PLPS SiC ceramics that can tolerate prolonged exposures at high temperatures in air are discussed. [Copyright &y& Elsevier]
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Database: Engineering Source
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Abstract:Abstract: The long-term oxidation resistance of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the content of sintering additive (in particular, YAG) at 1500°C in air. It is shown that, regardless of the vol.% YAG, the oxidation is passive at that high temperature, with a kinetics given by the paralinear-rate law. This is because the oxide scales grow due to oxidation of the SiC grains, but recede due to the formation of a eutectic phase and to the carbothermal reduction of YAG. It is also shown that the oxidation resistance of PLPS SiC decreases markedly with increasing vol.% YAG, an effect that is especially marked above 7.3vol.% YAG where a change in oxidation behaviour occurs. Thus, while up to 7.3vol.% YAG the PLPS SiC ceramics gain mass during the entire oxidation process (500h) because the oxide scales are at least semi-protective, from 11.1vol.% YAG onwards the PLPS SiC ceramics first gain mass and then lose mass linearly over oxidizing time because the oxide scales are non-protective. Finally, implications for the design of PLPS SiC ceramics that can tolerate prolonged exposures at high temperatures in air are discussed. [Copyright &y& Elsevier]
ISSN:09552219
DOI:10.1016/j.jeurceramsoc.2009.10.008