A multi-step chemical ion-exchange process for alkali/alkaline-earth aluminosilicate glasses

Abstract The paper describes a multi-step chemical ion exchange method, also known as "Kailly Method", to increase the impact resistance of Na2O–Al2O3–SiO2 based glasses and derivatives. The chemical strengthening methodology comprises of three steps where the first step is a chemical ion-exchange process (labeled as IOX1) in KNO3 melt followed by a second step involving high temperature ion migration (HTIM), and the final step of another chemical ion-exchange (IOX2) step in KNO3 melt. The effect of the proposed strengthening mechanism on the compressive stress layer depth (DOL), diffusion coefficient (D) and surface compressive stress (CS) of a glass with composition 16.11 Na2O-1.47 K2O-2.73 MgO-20.02 Al2O3-59.08 SiO2-0.1 CaO-0.49 SnO2 (wt.%) has been evaluated. The results show that the "Kailly Method" can promote a DOL to 120–150 μm which is 50–80% higher than the conventional one-step ion exchange process. The distribution of compressive stress has been positively correlated with K+ concentration and modulus of elasticity. Further the impact strength of a 0.5 mm thick glass specimen has been demonstrated to be linearly related to the compressive stress and the square root of DOL thus, indicating that the increase of DOL on the glass surface contributes to the improvement of impact resistance.