The dissolution behavior in alkaline solutions of a borosilicate glass with and without P 2 O 5

Abstract There are a variety of applications for glasses in alkaline environments, including glass fibers and glass‐coated steel to reinforce concrete structures. To understand how a simple glass reacts in such environments, the dissolution behavior of a 25Na 2 O–25B 2 O 3 –50SiO 2 (mol%) glass, doped with and without 3 mol% P 2 O 5 , in pH 12 KOH and pH 12 KOH saturated with Ca 2+ ions was studied. Ca 2+ ions in the solution significantly reduce the glass dissolution rate by forming a passivating calcium silicate hydrate (C–S–H) gel layer on the glass surface. When these corroded glasses were then exposed to Ca‐free KOH , the C–S–H layer redissolves into the undersaturated solution and the glass dissolution rate increases. For phosphate‐doped borosilicate glass, PO 4 3− units released from the dissolving glass react with Ca 2+ ions in saturated solutions to form crystalline hydroxylapatite on the glass surface, but this layer does not protect the glass from corrosion as well as the C–S–H does. The nature of the C–S–H layer was characterized by Raman spectroscopy, which reveals a gel layer constituted mainly of silicate anions.