Investigation On Surface Crystallization Of CaO-Al₂O₃-SiO₂ System Glass-ceramic

Recently, there are many researches on decorated CaO-Al₂O₃-SiO₂ system glass-ceramics for building at home and abroad. As a new material, the researches on CaO-Al₂O₃-SiO₂ system glass-ceramics mainly focus on the crystalline process, heating treatment and properties of product. The knowledge of nucleation and crystallization parameters is important in the preparation of glass-ceramic with desired microstructure and properties.In this paper, the CaO-Al₂O₃-SiO₂ system glass-ceramics were prepared by sintering method. The heating treatment was optimized, the surface crystalline mechanism and the influent of temperature and time was studied.Nucleation temperature and crystallization temperature and time were determined by DTA and XRD data. The activation energy for the crystallization of the glass samples can be determined by using the modified Kissinger method. The crystallization velocity of the cuboids samples was calculated in the different holding time at 960℃. The whole sintering process was observed by high temperature microscope. The surface crystallization trend of CaO-Al₂O₃-SiO₂ system glass-ceramics was described. The size, distribution and content of crystal were analyzed by SEM and XRD data. As the changing of holding time, size of glass grain and the velocity of increasing temperature, the influent to surface crystallization was studied in CaO-Al₂O₃-SiO₂ system glass-ceramics.The result indicated that the most suitable heating treatment of CaO-Al₂O₃-SiO₂ system glass-ceramics is determined. Between 20 ℃ — 750℃, the velocity of increasing temperature is 5℃/min;the velocity of increasing temperature is 2℃/min between 750℃-918℃ and the holding time is 4 hours at 918℃;between 918℃-1120℃, the velocity of increasing temperature 4℃/min and the holding time is 2 hours at 1120℃ .The main crystalline phase is 8 - wollastonite;The activation energy for the crystallization of the glass samples is 311.773 kJ/mol;the crystallization velocity of the cuboids samples is 11.10 mm³/min at 960℃;the surface mechanism of CaO-Al₂O₃-SiO₂ system glass-ceramics was described, the growth orientation of crystalline phase is vertical on the surface of glass grain, the flaws of the surface, for example, the impurity, pore and crack, offer the nucleus of crystal;the interface between grains decreased the activation energy for the nucleus because of the sintering in the grains . The most suitable granularity is 0.315mm— 0.7mm. With creasing of the holding time at 960℃, the crystalline shape was changed from the grain to the needle.