How to prevent spontaneous breakage of thermally toughened alkaline earth silicate glass

摘要

Alkaline earth silicate (AES) glass is a glass recently developed by Saint-Gobain for application in demanding environmental conditions including fire protection. Comparison of its physical properties to that of standard soda-lime-silica glass at room temperature shows that there are no significant differences. The process for producing thermally toughened products out of both kinds of glass is similar, both bear the same stress profile, and both are sulfate refined. Consequently both are similarly sensitive to potential spontaneous breakage caused by nickel sulfide inclusions. The application of AES glass in fire protection glazing involves a particular risk because a fire acts on it like a heat soak test so that every critical nickel sulfide inclusion would cause spontaneous failure at the most awkward moment. It is therefore necessary to apply a heat soak test (HST) if AES glass is to be used in fire protection applications to guarantee long term security. The HST conditions must be the same as for standard soda-lime-silica glass because in fact, the HST does not act directly on the glass, but it provokes the premature transformation of the nickel sulfide inclusions. NiS transformation is exactly the same in both types of glass, and causes both glass types to break in the same way.