Strengthening of container glasses and related compositions
Several methods of strengthening, including surface precipitation of low solubility particles, vapour treatment, ion-exchange, chemical vapour deposition (CVD) and combination treatments, have been investigated to improve the pristine strength of commercially available container and related glass compositions; their relative applicability in container manufacture has also been evaluated and discussed. As a part of this, a wide range of soda lime silica compositions, that includes typical container glass specifications, have been investigated to study their crystallisation behaviour in terms of the effect of nucleating agent, viscosity, time and temperature. Significant flexural strength enhancement of 16 to 163 % has been achieved for the processes studied, with a maximum of ~ 500 MPa and ~ 400 MPa for glasses using lithium ion exchange and exposure to LiBr and/or AlBr3 vapour respectively. Treatment times are short, compared to those currently used in industry. The mechanism of strengthening relies on surface compression by production of a glass skin or surface crystallised phase(s) having a low thermal expansion coefficient than the bulk of the glass. The physical properties of the glasses have been characterised by differential thermal analysis (DTA) and X-ray diffraction (XRD) as well as other methods such as high temperature viscometry and dynamic secondary ion mass spectroscopy (SIMS).