Corrosion of a 3D-C/SiC composite in salt vapor environments

Corrosion behavior of the three-dimensional C/SiC composite was investigated in a Na2SO4 vapor environment at temperatures from 1000 to 1500degreesC. The degradation mechanisms for the C/SiC composite could be determined by dividing a complicated function describing the weight change of the composite with temperature into several monotone functions describing the mechanisms, and then identified by the strength change of the composite with temperature. There were three reactions between the C/SiC composite and the Na2SO4 vapor. The First one was the passive oxidation of the CND SiC, leading a small weight gain. The second one was the oxidation of the carbon phases, leading a small weight loss. The third one was the active oxidation of the CVD SiC, leading a large weight loss. The threshold temperature for these reactions was, respectively, 1080, 1100 and 1300degreesC. The transition temperature from passive to active was 1200degreesC. The activation energy for these reactions was, respectively, calculated by the weight chance with temperature to be 114, 105 and 112 kcal/mol. The flexural strength loss of the composite reached its minimum value when the weight gain of the composite reached its maximum value at 1200degreesC. Below 1200degreesC, the C/SiC composite had a higher corrosion resistance to the Na2SO4 vapor. Above 1300degreesC, the poor corrosion resistance of the CVD SiC made the composite having a poor corrosion resistance to the Na2SO4 vapor. (C) 2002 Elsevier Science Ltd. All rights reserved.