Relating atmospheric physics to borosilicate glass alteration under high temperature and saturated water vapour conditions

For temperatures below 100 °C, the alteration of a borosilicate glass in contact with liquid water usually creates a thin altered layer, with thicknesses that do not exceed a few microns after a period of several weeks or months. In contrast, the present experiment conducted with a four-oxide glass in contact with water vapour at 220 °C under saturated conditions, resulted in the formation of a thick layer of the order of 40 μ m within less than 100 h, without any crystalline compound present on the glass surface. Two sub-layers with different structures were observed. Through combined experimental characterization and theoretical arguments, it was inferred that water molecules within the glass undergo phase transitions, establishing an equivalence between alteration whether the glass is in contact with water in vapour or liquid state. This paves the way to a thorough characterization of the altered layer topology evolution in the future, and to a better understanding of the underlying physico-chemical phenomena. Furthermore, the overall mechanisms involved during the glass hydration and alteration, enable building a relationship with cloud formation, where water droplets formed around ‘condensation nuclei’ can condense when they experience supersaturated conditions.