Corrosion of granulated glassy blast furnace slags in aqueous solutions

Abstract

Structure and reactivity of several commercial and laboratory granulated glassy blast furnace slags were investigated. From the compositions NBO/T was calculated, the number of nonbridging oxygens per tetrahedron. Electron spin resonance spectrometry answered questions regarding the coordination numbers of the ions Mn2+ (Mg2+) and Ti3+. Both the hydrolytic reactivity of the slag glasses in water and their corrosion mechanisms in 0.1 mol/1 KOH model pore solution were studied. Scanning electron and atomic force microscopy showed the development of gel-like phases on the slag grains. Although distinct features could be resolved already, only the nanoscale in-depth profiles obtained by secondary neutral mass spectrometry helped to enlighten the complex reaction sequences. Thus, for example, it could be shown that first Mg2+ -rich gel phases developed by the corrosion process, however, after some hours the leach solutions became supersaturated successively with the consequence of forming a secondary calciumsilicate hydrate phase by a redeposition process. This phase showed a tobermorite-like structure. AI2O3- and TiO2-rich blast furnace slags were more stable than the CaO-rich materials and they also displayed reaction mechanisms at least partly dissimilar to the just mentioned.