Influence of Nucleating Additions on the Crystallization in the CaO-MgO-Al2O3-SiO2 Glass-Ceramics

The crystallization behaviors and microstructural developments in the CaO-MgO- Al2O3-SiO2 glass with Fe2O3, ZrO2 and F as additives were investigated by using scanning electron microscopy, X-ray diffraction and differential scanning calorimetry techniques. In the glass sample with 1.0wt% Fe2O3, only surface crystallization were observed, in which a three-layer compound surface containing the fine dendrite, finer fibrous morphology and particle-shaped crystals was formed respectively from the near free surface to the inner region. The crystalline phases precipitated were anorthite and wollastonite at 1000°C, and diopside at 1040°C. The addition of ZrO2 suppressed the nucleation and growth of the crystalline phases. The addition of another 4.0wt% fluorine into the glass with a pair of 1.0wt% Fe2O3 and 2.0wt% ZrO2 induced the bulk crystallization, the surface and bulk crystallizations were both observed at 1040°C. At the surface, a three-layer morphology, which had similar morphology to the glass with 1.0wt% Fe2O3 was formed. In the bulk region, the block-shaped crystalline phases were precipitated homogeneously in the residual glass.