Antimicrobial and mechanical properties of silver ion-exchanged transparent lithium-mica glass-ceramics

This study investigates silver ion-exchange of the transparent lithium-mica glass-ceramic in a molten mixture of AgNO3 and Ag2SO4 to realize the glass-ceramic antibacterial activity and improved mechanical properties. The ion-exchanged glass-ceramic was heated at 700 °C. Li+ ions in the interlayers of mica near surface of the glass-ceramic were exchanged for Ag+ ions in the molten salt. Ag+ ions intruded deeper inside from surface as the soaking time of the ion-exchange increased, disturbing the layer structure of the mica. Heating also diffused Ag+ ions deeper inside the glass-ceramic, reducing the concentration of Ag+ ions near the surface and realizing a uniform distribution of Ag+ ions to create a regular layer structure of mica. Both the ion-exchanger and the heated ion-exchanger showed antibacterial activity against Escherichia coli. However, their activities decreased in repeated antimicrobial tests. Because ion-exchange generated compressive stress near the surface, the Vickers hardness and fracture toughness increased, whereas heating lowered the heightened hardness. Although ion-exchange and subsequent heat treatment improved the machinability of the glass-ceramic, ion-exchange alone did not.