Microstructural effects in relation to the leaching of glasses
A study of the acid leaching of a series of glasses has been made. This was undertaken to provide information concerning the production of microporous glass membranes with reverse osmosis desalination potential. The chemical compositions of the glasses investigated were developed from a commercial glass composition known as 'E-glass'. This glass~phase separates into mutually interconnecting acid soluble and acid insoluble phases, during cooling from the molten state. Treating the glass with mineral acid solutions removes the soluble phase, yielding a porous glass skeleton. The amount of Si02 in the original composition was varied, and it was found possible to produce microporous glass skeletons from glasses having a range of Si02 contents. These glasses also phase separated into mutually interconnecting phases during cooling. The parent glasses were studied by viscosity and electrical conductivity measurements. The results of those investigations were consistent with the rapid phase separation of the glasses. The leaching rates of the glasses were studied by weight loss measurements and those measurements indicated that the leaching rate was controlled by the durability of the acid soluble phase. The leached glasses were characterised by some electron microscopy, but primarily by inert gas adsorption measurements. The porous glasses contained pores of about 2 nm radius although there was also evidence of the presence of even finer pores. The reverse osmosis performance of several of the glasses was investigated using single hollow fibre membranes and salt rejections of up to 50% were recorded.