An evaluation of a silicon carbide/alumina ceramic composite for use in high temperature air heaters

An evaluation of a ceramic composite tube for possible use in high temperature air heaters was conducted. A silicon-carbide/alumina composite ceramic tube which had been tested for 107 hours in a coal fired flow facility at a tube temperature of approximately 1149°C was evaluated by comparison of unexposed, exposed, and as-received samples of the material to determine changes in properties. The project included mechanical testing and microscopy. The mechanical testing consisted of compression and tension testing of circular rings of unexposed and exposed material. The microscopy included stereo, metallurgical, and scanning electron microscopy as well as microprobe analysis employing EDS and WDS analysis and x-ray mapping. Parameters such as Young's modulus, tensile and compressive strengths, porosity, and constituent distribution were determined to demonstrate any changes in the material due to exposure to high temperature. The strength of the material did not change significantly from the unexposed to the exposed, but the Weibull modulus was found to have decreased indicating a higher probability of failure. Porosity was found to have increased from as-received to unexposed and again from unexposed to exposed. Aluminum content was found to decrease in the same way from as-received to exposed.