ИСТИНА

Knowledge about the conditions that control aluminosilicate glass solubility in aqueous solution is essential for predicting durability of a wide range of natural and manmade materials. For example, rapid biosolubility is desirable in the case of inhaled glass particles or mineral wool fibres. Whereas for glass used in products exposed to water, the aim is to control dissolution and the formation of secondary phases. The mole fraction of Al in the original glass is clearly a factor but the fundamental mechanisms of glass corrosion are still debated. The purpose of this work was to relate the macroscopic dissolution data for calcium aluminosilicate glass (CAS, CaAl0.6SiO3.9) to submicrometre scale observations, to derive a more robust conceptual model for how dissolution takes place and to provide background for constructing a microkinetic model for predicting glass durability. CAS glass samples were leached in ultradeionised water for 7 and 123 days, and for pH controlled experiments (150 days), in acetate buffer (pH 4.4), pure water (initially pH 5.6) and 0.1 M NaOH (pH 13), with and without the presence of organic complexing agents, such as citric acid. The leaching vessels were covered to avoid dust but the lids were not intended to exclude atmospheric CO2. The pH controlled experiments were carried out in closed vessels, to prevent equilibration with CO2. Angleresolved X-ray photoelectron spectroscopy (AR-XPS) of untreated and leached glass samples showed Al enrichment at the surface. Scanning electron microscopy (SEM) showed secondary precipitates. Expected secondary phases are calcium carbonate, probably calcite, and aluminosilicates, such as protoclay, amorphous silica or Al hydroxides. Thus, after reaction, the elements of the glass can be present on the surface in three forms: 1) as secondary phases precipitated on the surface; 2) as ions adsorbed from the solution and 3) in a residual, aluminosilicate leached network.