Catalytic mechanism of iron oxide doping on the crystallization process of Cr2O3-containg glass ceramics

Abstract

The influence of Fe2O3 addition to the nucleation process of Cr2O3-containing CaO-MgO-Al2O3-SiO2 (CAMS) based glass ceramic was investigated by Raman spectroscopy, differential scanning calorimetry (DSC), X-Ray diffraction (XRD), electron back-scattered diffraction (SEM-EBSD) and transmission electron microscope (TEM). The experimental data illustrated that the single Cr2O3-doped specimens were insufficient in achieving the desired nucleation rate for high degree of polymerization. However, with the introduction of Fe2O3 to the Cr2O3-containing samples, the newly generated [FeO4] mended the glass network by inserting [Fe3+O4-SiO4] unit into the original Si-O network, which was helpful for the migration of the coordination polyhedron in the glass matrix. Additionally, [FeO4] unit and [MgO4] are equivalent when generating spinel crystal. Hence, the generated [FeO4] benefited the formation of spinel and diopside phases. This resulted in massive fine spinel crystal distribution in the glass matrix, which promoted the precipitation of diopside. Crystallographic examination confirmed the formation of partial diopsides on the spinel {111} lattice plane with epitaxial growth. The orientation relationships were 〈112〉spinel//〈001〉diopside and (111)spinel//(002)diopside. However, when higher Fe2O3 (that is, 2 wt% Cr2O3+15 wt% Fe2O3) was added to the glass system, abnormal grain growth of spinel occurred, which resultantly reduced the nucleation rate.