Crystallization mechanism and properties of a blast furnace slag glass

The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between T-g (742 degrees C) and the DSC crystallization peak (T = 1000 degrees C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition, Particles of Pt,Fe, detected by EDS and SAD-TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites, Only melilite and larnite precipitated in a glass sample heat-treated at 1000 degrees C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite. (C) 2000 Published by Elsevier Science B.V. All rights reserved.