Cristobalite formation from the thermal treatment of amorphous silica fume recovered from the metallurgical silicon industry

Abstract

Silica fume was thermally treated to 700–1100°C in air to transform it into crystals and cause it to reach the metastable cristobalite state. The phase transition behaviour of the silica fume crystallisation process and the main factors influencing the crystallisation behaviour were investigated via thermogravimetry differential thermal analysis, X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The results show that when the treatment temperature reaches 800°C, the silica fume undergoes a displacive phase transformation and begins to nucleate. At 1100°C, the silica fume fully converts to cristobalite. Alkali metal impurity compounds in the silica fume promote the phase transformation of silica fume.