Surface Reactivity and Dissolution Properties of Alumina-Silica Glasses and Fibers

The ability of bulk glass and fibers to react in aqueous solution, with organic polymers and coupling agents, depends on the surface charge, reactivity, and adsorption properties of the glass surface, i.e. the character and density of surface -OH groups, whereas glass and fiber chemical stability and biosolubility depend on the resistance to dissolution. If glass dissolution products are accumulated in a media, they can change the surface properties by specific adsorption. We determined the -OH surface concentration, reactivity, adsorption, and dissolution properties of aluminosilicate glasses containing various modifiers and compared the results with the behavior of complex mineral wool fibers. Using proton consumption and element release from batch surface titration experiments, over the range 5 < pH < 10, surface -OH adsorption properties were modeled with the FITEQL program. During titration, network modifiers in the glass subsurface are preferentially replaced by protons, resulting in cation accumulation in the solution and formation of a leached layer enriched with Si on the solid. The behavior of Al was different. At 5 < pH < 9, only very small amounts of Al were found in the leachates, which can be explained by almost complete Al adsorption as stable surface complexes, i.e. >XOAl(OH)₂ (where X = Si or Al and > represents the surface). At pH > 9, divalent cations adsorbed specifically, as >XOMe⁺ complexes (Me = Ca or Mg). This deeper understanding of the surface behavior of glasses and fibers is important for the design of composite materials, for applications in biology and medicine and in materials production in general, as well as for understanding natural processes, such as global uptake estimates of CO₂ during rock weathering.