The chemical durability of tektites—A laboratory study and correlation with long-term corrosion behavior

Abstract

Leach tests carried out on tektite specimens (indochinites and australites) under high-dilution conditions show a common behavior characterized by low leach rates (1.8 × 10 −5 g · m −2 · d −1 or 7.2 × 10 −12 m · d −1 at 23°C) and an activation energy of (79.6 ± 0.7) × 10 3 J · mol −1. The extent of selective leaching is very small, of the order of 10 −8 m. Extrapolation of test results over the lifetime of the tektites gives an excellent agreement with field observations on the extent of corrosion, and this is an important step in establishing the validity of laboratory tests as a basis for the development of models and predictions concerning long-term durabilities at least in the limiting case of high dilution or rapid flow. The results are also shown to be in agreement with various previous observations on the corrosion resistance of tektites. The chemical durability of tektites is observed to be consistent with their composition, highlighting requirements for high corrosion resistance in glasses; these requirements include a silica content in excess of 67 mol%, an extremely low water content and an alkali content which is low both absolutely and relative to the di- and poly-valent metal oxide levels. It is shown that artificial glasses which fulfil these criteria are no less corrosion-resistant than the corresponding natural glasses. These conclusions have bearing on the development as well as on the evaluation of glasses intended for very long service, such as radioactive waste vitrification media.