The effect of additives on the crystallization of Na2O-CaO-MgO-Al2O3-SiO2-TiO2 system glasses

The differential thermal analysis (DTA) curve of Na2O-CaO - MgO-Al2O3-SiO2-TiOs system glasses has two exothermic peaks, which means that at least two kinds of main crystal are produced in the process of heat treatment. Some additives such as typical network modifier (Na2O, CaF2), and network intermediate (Al2O3) are added in the above glasses. After the glasses with additives are heat treated in the different processes, they are investigated by the method of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Some important results are obtained. The main crystal corresponding to the first exothermic peak temperature is fassaite (Ca(Ti,Mg,Al)(Si,Al)(2)O-6), and another main crystal corresponding to the second exothermic peak temperature is anorthite (CaAl2Si2O8). The additives of Na2O and CaF2 play a role in decreasing the nucleation and growth of fassaite. Na2O has no obvious effect on the nucleation and growth of anorthite, but CaF2 suppresses the nucleation and growth of anorthite and itself comes out of the base glasses. B2O3 hinders fluorite's coming out of the base glasses and improves the nucleation and growth of fassaite and anorthite. (C) 1999 Elsevier Science S.A. All rights reserved.