Doctor of Philosophy (PhD)
Spinel is one of the best known and widely used ceramic materials. It has good thermal shock resistance, high chemical inertness in both acidic and basic environments, excellent optical and dielectric properties, high strength at both elevated and normal temperatures, and has no phase transition up to the melting temperature (2135°C). Spinel is used in the metallurgical, electrochemical, and chemical industrial fields. It has also found some applications in dentistry, catalyst supports, humidity sensors, reinforcing fibers, photoluminescent materials, etc. One of the limitations of spinel ceramic is its brittleness. Furthermore, at high temperature applications, a rapid heating or cooling can cause a high thermal gradient. Building up of such thermal stresses can lead to surface microcracking and crack growth, which finally can lead to a catastrophic failure of the component. In order to overcome this problem, it is highly desirable that the self-healing capability of spinel and spinel composites are investigated. In this research for the first time we studied the crack self-healing capability of nanostructure spinel. The results showed that grain growth and sintering phenomena are the two factors controlling the healing procedures. In the case of spinel ceramic, cracks can be completely healed after annealing the specimens at 1600°C for 100h with the strength recovery of 91%. On the other hand, it has been found that SiC can be used as a healing agent in many ceramics even in those ceramics without any crack healing ability. Therefore, first SiC/spinel nanocomposite was synthesized using talc, aluminum and graphite powders. The sintering behavior of the SiC/spinel nanocomposite was investigated and the best pellets from physical and mechanical properties point of views were selected to study the self-healing behavior of SiC/spinel nanocomposite. The results showed that SiC/spinel nanocomposite has an exceptional crack-healing ability as the surface cracks can be healed after sintering the specimens at 1550°C for 1 min in air with the strength recovery of 99%. Reaction of SiC with air and formation of SiO2 and subsequently formation of mullite and dissociation of enstatite are the possible mechanisms responsible for crack healing in SiC/spinel nanocomposite.
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Tavangarian, Fariborz, "Crack Self-Healing in SiC/Spinel Nanocomposite" (2014). LSU Doctoral Dissertations. 1980.