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<p>This study examines whether different strategies for increasing crystal number density in CaO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> glasses influence the crystallization mechanism of cristobalite and the stabilization of <i>β</i>-cristobalite during cooling to room temperature. Four bulk glasses were investigated: two compositions in the mullite primary phase field and two compositions containing the classical nucleating agents ZrO<sub>2</sub> or TiO<sub>2</sub>. Phase formation after heat treatment was analyzed by X-ray diffraction and dilatometry, while the resulting microstructures and local chemical distributions were studied by electron microscopy including energy-dispersive X-ray spectroscopic analyses. The mullite-containing glasses crystallize predominantly in the volume and, together with mullite, form <i>β</i>-cristobalite, whereas the ZrO<sub>2</sub>- and TiO<sub>2</sub>-containing glasses show surface crystallization under the conditions studied. For all compositions, heat treatment at 1,250&#xa0;°C leads to the precipitation of <i>β</i>-cristobalite which does not transform into <i>α</i>-phase during cooling, while higher crystallization temperatures promote partial transformation to <i>α</i>-cristobalite. Among the investigated compositions, the ZrO<sub>2</sub>-containing glass shows the smallest increase in the cristobalite-related dilatometric volume jump after high-temperature treatment. The results show that mullite can promote volume crystallization, whereas ZrO<sub>2</sub> and TiO<sub>2</sub> do not act as nucleating agents in these glasses. The thermal stability of <i>β</i>-cristobalite is controlled by both composition and microstructure.</p>

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Volume crystallization of β-cristobalite from CaO–Al2O3–SiO2 glasses—Influence of different nucleation strategies

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月16日

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  • Christian Thieme,
  • Katrin Thieme,
  • Susanne Selle,
  • Lars Ortmann,
  • Thomas Höche

摘要

This study examines whether different strategies for increasing crystal number density in CaO–Al2O3–SiO2 glasses influence the crystallization mechanism of cristobalite and the stabilization of β-cristobalite during cooling to room temperature. Four bulk glasses were investigated: two compositions in the mullite primary phase field and two compositions containing the classical nucleating agents ZrO2 or TiO2. Phase formation after heat treatment was analyzed by X-ray diffraction and dilatometry, while the resulting microstructures and local chemical distributions were studied by electron microscopy including energy-dispersive X-ray spectroscopic analyses. The mullite-containing glasses crystallize predominantly in the volume and, together with mullite, form β-cristobalite, whereas the ZrO2- and TiO2-containing glasses show surface crystallization under the conditions studied. For all compositions, heat treatment at 1,250 °C leads to the precipitation of β-cristobalite which does not transform into α-phase during cooling, while higher crystallization temperatures promote partial transformation to α-cristobalite. Among the investigated compositions, the ZrO2-containing glass shows the smallest increase in the cristobalite-related dilatometric volume jump after high-temperature treatment. The results show that mullite can promote volume crystallization, whereas ZrO2 and TiO2 do not act as nucleating agents in these glasses. The thermal stability of β-cristobalite is controlled by both composition and microstructure.