|About this Abstract
||Materials Science & Technology 2012
||In-situ Characterization of Phase Transformations in Materials
||Observation of the Beta-Alpha Transformation of Cristobalite in Partially De-Vitrified Fused Silica
||Ryan C Breneman, John Halloran
|On-Site Speaker (Planned)
||Ryan C Breneman
The beta-alpha transformation of cristobalite was examined by direct optical observation and by differential scanning calorimetry (DSC). Cristobalite was surface nucleated on 99.99% pure fused silica and was observed passing through the beta-alpha transformation at 250°C by optical microscopy. Strain accommodation by twinning and micro-cracking was observed as well as size and cooling rate effects on behavior. The evolution of stress in the glass matrix was observed with polarized light. Fully devitrified bulk and powder material was cycled through the phase transformation while the enthalpy of transformation was observed by DSC. Hysteresis upon repeated cycling was observed, and the enthalpy of transformation was reduced after multiple cycles. Comparison to optical observation suggests micro-cracking continues to occur on repeated cycles through the transformation temperature. This micro-cracking continues to reduce the confinement stress of the transformation up to an equilibrium limit.