Sodium/potassium ion exchange of a soda-lime-silica float glass: mechanical strength, hardness, stress profile and thickness of the ion exchanged layer

Industrially produced soda lime silica glass was dipped into a potassium nitrate salt melt and tempered over a wide temperature (380-500 degrees C) and time (1-48 h) range. This led to an interdiffusion of the sodium ions from the glass with potassium ions from the salt melt. All samples were characterized by their alkali concentrations perpendicular to the ion exchanged surface, their bending strength and their microhardness. The residual compressive stresses in the ion exchanged layer were quantified by polarization microscopy. To the best of our knowledge, in the present scientific literature, only strength values of individual temperature time combinations or time series at certain temperatures are given. Thus comprehensive statements on the temperature and time dependence of the chemical strengthening can be made for the first time. The increase in strength runs approximately parallel to an increase in the microhardness.