Effect of aggressive gases on the behavior of glass surfaces in contact with mold materials

Abstract

The behavior of an industrially melted soda-lime-silica glass was studied in contact with metallic mold materials at temperatures above the glass transformation point. An apparatus is presented which allows the determination of the sticking temperature between glass and mold material and particularly the investigation of the effect of different aggressive gases on the contact behavior. This influence on the modification of the glass surface is discussed as well as the possible effects of surface treatments on the forming processes of container glass. A treatment of the glass surface employing gaseous HCl (≤ 5 vol%) leads to a drastic increase of the sticking temperature by at least 100 K. This increase is attributed to a dealkalization of the glass surface and, thus, to the silica-rich composition of near-surface regions displaying a higher viscosity and a decreased reactivity. Furthermore, due to the HCl treatment a decreased crack susceptibility is observed even if the temperature of contact is below the original sticking temperature.