Ductile behavior of glass-ceramics with precipitated CaF2, xonotlite, and cristobalite

Glass with a chemical composition of 69.7SiO(2)-7.9CaO-5.5Na(2)O-3.5K(2)O-1.4Al(2)O(3)-12CaF(2) (mol %) was crystallized via a simple heat treatment. CaF2 and xonotlite precipitated above the glass transition temperature, followed by the precipitation of a-cristobalite above 900 degrees C. Thermal expansion curve of the glass-ceramics containing a-cristobalite exhibited a steep increase around 270 degrees C due to a-fl phase transition of cristobalite. Ball indentation test on the glass-ceramics resulted in a clear circular dent in the glass-ceramics with precipitated cristobalite but only ring cracks in the glass-ceramics without cristobalite. X-ray computed tomography using synchrotron radiation revealed the formation of microcracks around cristobalite, with a greater number of microcracks observed after ball indentation. Therefore, it was concluded that the stress caused by a large volume change during the a-fl phase transition of cristobalite induced the generation of microcracks in the glass- ceramics during cooling, eventually leading to ductile behavior. The glass-ceramics also exhibited ductile behavior in the bending test that was used to measure fracture toughness. The obtained findings offer valuable insights into the fabrication of a new type of glass-ceramics with ductile behavior, which is expected to expand the application scope of glass-ceramics.