Research on the strength of sodium-calcium-silicate glass strengthened by ion-exchange method

This study examines the influence of ion-exchange strengthening parameters on the mechanical properties of soda–lime–silicate float glass. Chemical strengthening was performed in molten KNO3 at 350–475 °C for up to 6 hours. During ion exchange, larger K⁺ ions replace smaller Na⁺ ions in the surface layer, generating compressive stresses that reduce the impact of surface flaws and improve the mechanical performance of the glass. The mass gain of samples, measured as a function of temperature and treatment duration, confirmed the diffusion-controlled nature of the process and enabled estimation of the modified surface layer depth. The depth of the modified layer increases with increasing temperature and treatment time and can reach tens of microns when ion-exchanged at 450 °C for 6 hours. Mechanical properties were evaluated using microhardness and flexural strength tests, with statistical analysis based on the Gaussian distribution. The results show that treatment at 475 °C for 6 hours increases flexural strength by approximately 2.5 times and microhardness by 10–12 % relative to untreated glass. Additionally, under these conditions, a decrease in the rates of further flexural strength and microhardness improvement was observed, indicating the onset of compressive stress relaxation in the surface layer of the glass. Differences between the Air and Tin surfaces of float glass were also identified, with the Air side demonstrating higher initial microhardness and strength. Additional mechanical edge processing reduced variability and aligned the strength values of both surfaces. The findings confirm the effectiveness of ion-exchange strengthening and provide guidance for optimizing temperature and duration parameters to improve the durability and performance of float glass.