Effect of additives in molten salt on ion exchange and strengthening of glass

The effect of additives in molten salt on the ion exchange and strengthening of float glass was investigated in the commercial purity KNO₃ or the mixtures of KNO₃ with the addition of KOH, K₃PO₄, K₂CO₃, K₂SiO₃ and Al₂O₃, respectively. Potassium concentration profiles of glass were measured by electron probe micro-analysis. The surface stress, bending strength and micro-hardness of glass samples were tested. The results show that these additives can deepen the ion exchange layer and shorten the ion exchange time, hence significantly improving the mechanical properties of the glass. The strengthening effect of the mixtures is as good as, or even better than, that of analytically pure KNO₃. At the treatment temperature of 450°C, the thickness of the ion exchange layer on the glass surface is more than 29 μm, and the mechanical properties of the glass with the ion exchange layer are as follows: surface stress >485 MPa, bending strength >400 MPa and micro-hardness 6.49 GPa.