Critical Evaluation of Strength-Controlling Variables in Ceramics

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New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Porcelain bodies were created to test the hypothesis that critical flaws govern the strength of ceramics. By systematically evaluating controlled changes to the porcelain body on mechanical properties and critical flaw size, further insight was gained regarding their relationship to strength, as well as increased understanding of the complexities inherent to porcelain itself. Results of this study indicated the independence of critical flaw size to bulk density, firing temperature, and filler particle size; three parameters that, in literature, are continually cited as major factors that affect porcelain strength. Analysis also revealed the thermal expansion mismatch between filler particles and the porcelain glass phase does not favor glass matrix cracking in a quartz or alumina system shown to have a stronger, lower CTE glass phase. This idea challenges many central arguments that primary filler particles are critical flaws themselves or induce matrix cracks that become critical flaws. Statistical and microstructural evidence supports the hypothesis of a relatively large population of particle agglomerates residing within porcelain bodies, on the order of several times primary filler particle or pore size that control mechanical strength. Based on experimental data, it is proposed that critical flaws found in these bodies are particle agglomerates introduced to the microstructure, the result of inefficient mixing during the processing step. Efforts to increase mechanical strength must incorporate techniques to eliminate these particle clusters; several experimental suggestions are noted.
Advisory committee members: James Varner, Paul Johnson, Scott Misture. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University