Theoretische und experimentelle Untersuchungen der Frühstadien bei der wässrigen Korrosion von Silicatgläsern

The first steps of the glass corrosion by aqueous species are always of a big relevance for the application of the important oxide glass material group. The basics of the initiating aqueous attack are until today unfortunately not enough ascertained. In the current research work the initial stages during the corrosion process in deionized water at 90°C for four ternary praxis-oriented glasses of the following molar composition 14 Na2O, 14 MxOy, 72 SiO2 with MxOy = CaO, ZnO, B2O3, Al2O3 are investigated. Monolithic glass samples prepared via precise cutting, polishing and chemical nano-etching are immersed in H2O for selected exposure times between 1 and 96 h under static conditions at a constant remaining glass surface area to solution volume ratio s = 0.10 cm-1. After each corrosion test the mass loss of the treated specimen is measured with an analytical 6-digit balance. The equivalent components extracted from the examined glasses are detected by subsequent chemical analysis of the leachants via F-AAS and ICP-OES. The transformations in the corroded surface of the treated samples are further investigated through an optimized sequential etching technique using strongly diluted HF/HNO3. Thereby very small removal depths within the range between 5 and 20 nm per step for the four different glass types are obtained. The method allows the quantification of the stripped very thin surface layers in absolute concentrations. In addition the composition of the characteristic subsurface zone is analyzed with the help of SNMS. The obtained results are explained in view of the possible glass corrosion initiation and the competition between leaching, hydration, recondensation during the formation of the modified subsurface zone