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dc.contributor.authorKhajotia, Sharukh S.
dc.date.accessioned2020-03-30T18:25:25Z
dc.date.available2020-03-30T18:25:25Z
dc.date.issued1997-07
dc.identifier.urien
dc.identifier.urihttp://hdl.handle.net/10675.2/623208
dc.description.abstractObjectives. Measurement of thermal expansion in glassy· materials is complicated by thermal history effects. The purpose of this research was to determine whether the occurrence of structural relaxation in glassy materials, such as dental porcelains, and changes in porcelain leucite content could interfere with the accurate measurement of the coefficient of thermal expansion during the thermal expansion measurement itself Methods. In a randomized design, thermal expansion specimens were fabricated using six commercial body porcelains and the leucite-containing Component No. 1 frit (Weinstein et al. patent, 1962), and subjected to one of the following heat treatments: a single heating run at 3 °C/min in a .conventional dilatometer followed by air quenching; three successive low-rate heating and cooling thermal expansion runs at ' 3°C/min in a conventional dilatometer; or three successive high-rate heating and cooling th~rmal expansion runs at 600°C/min in a laser dil~tometer. The remaining specimens were left untreated and served as controls. Potential changes in porcelain leucite content were monitored via quantitative X-ray diffraction. Thermal expansion data for each run over a- temperature range of 25-500°C and the_ leucite content of all specimens were subjected to repeated measures analysis of variance. Results. The thermal expansion coefficient measured on first slow heating was significantly lower than the values for succeeding low-rate heating and cooling runs in au· materials (p < 0.001). The high-rate thermal expansion coefficient obtained on first heating was not significantly different from the values · of succeeding heat and cool runs in all materials (p > 0.05). No significant. effect of dilatometer thermal treatments on leucite content (p > 0.05) was shown for all materials studied using both dilatometers. Significance. The. crystallization of additional amounts of leucite during thermal expansion runs can be ruled out as a possible interference in the determination of the thermal expansion coefficient of dental porcelain. Conventional dilatometer measurements exhibited structural relaxat1oh during the first heating run, as evidenced by the significant difference between the first heating and subsequent runs, while the laser dilatometer measurements were not affected by this thermal history effect. Therefore, high-rate dilatometry provides a more accurate thermal expansion measurement that is free of interference from structural relaxation and additional leucite crystallization.en_US
dc.rightsCopyright protected. Unauthorized reproduction or use beyond the exceptions granted by the Fair Use clause of U.S. Copyright law may violate federal law.en_US
dc.subjectCeramicsen_US
dc.subjectLeuciteen_US
dc.subjectLasersen_US
dc.titleThe Effect of leucite crystallization and thermal history on thermal expansion measurement of dental porcelainsen_US
dc.typeDissertationen_US
dc.typeDissertationen
dc.contributor.departmentSchool of Graduate Studiesen_US
dc.description.advisorMackert, J. Rodway;en_US
dc.description.degreeDoctor of Philosophyen_US
dc.description.committeeO'Dell, Norris; Pashley, David; Schuster, George; Cogburn, John; Myers, Michael;en_US
refterms.dateFOA2020-03-30T18:25:26Z


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