Insight into the dual effect of Fe2O3 addition on the crystallization of CaO-MgO-Al2O3-SiO2 glass-ceramics

In this paper, an iron-rich CaO-MgO-Al2O3-SiO2 glass-ceramic was prepared basing high iron chromium slag. We employ DSC, XRD and SEM validated the thermal behavior and the microstructure of the glass/glass-ceramics, and reveal a mechanism of the dual effect of high Fe2O3 addition on the crystallization. Here we show that Fe2O3 facilitates the formation of spinel, but inhibits the precipitation of pyroxene. Infrared spectroscopy analysis shows that its promotion to the precipitation of spinel is attributed to the depolymerization of the glass network. Scanning electron microscope observation shows that the inhibition to the crystallization of pyroxene due to the region where nucleation dose not occurs. The increase of Fe2O3 addition enlarges the volume ratio of the non nucleated region in the microstructure, and increases the crystallization activation energy of the pyroxene. In addition, we find that the crystallinity of the glass-ceramics decreased with the increase of Fe2O3 addition, but the average size of the pyroxene grains reduced from 116 +/- 4 nm to 84 +/- 3 nm. We also show that the distribution of chromium in glass-ceramics was largely influenced by Fe2O3 addition. This study is particularly instructive for controlling the crystallization of the iron-rich CMAS glass-ceramics, and provides some insight for solidifying chromium in high iron waste slag.