Ion Exchange Strengthening of Sodium-Calcium-Magnesium Silicate Glass Using a Silicon-Phosphorus-Antimony Cation Exchanger in Potassium Nitrate Melt

Abstract

This article examines the influence of the potassium form of silicon-phosphorus-antimony cation exchangers (K:SPA-cation exchangers) added to a potassium nitrate melt on the compressive stresses on the surface of sodium-calcium-magnesium silicate glass. Compressive stresses are induced by low-temperature ion exchange between Na⁺ ions in the glass and K⁺ ions in the molten salt. We compared two types of potassium nitrate: technical grade B and chemically pure grade CP. The distribution of compressive stresses in the surface layer of the glass was analyzed using waveguide spectroscopy; we determined the birefringence profile to calculate the stress profile. Microhardness was measured using a PMT-3 microhardness tester. The addition of a K:SPA-cation exchanger into the potassium nitrate melt was shown to improve ion exchange conditions for both types of nitrate compared to the salt melt without a cation exchanger, leading to an increase in compressive stress, depth of the ion-exchanged layer, and microhardness. Following ion exchange with the addition of a cation exchanger, an increase in compressive stress relative to the initial glass was 155 MPa and 450 MPa for grade B and grade CP, respectively. Microhardness increased by 120% and 240% for grade B and grade CP, respectively. The cation exchanger significantly improves ion exchange conditions for technical-grade potassium nitrate (grade B). The introduction of cation exchangers into the salt bath melt holds promise for advancing ion exchange technology, which is used to enhance the mechanical and thermal strength of glass products. The potential of this method is particularly relevant in glass strengthening production, where cheaper technical-grade potassium nitrate is used.