The methods of chemical strengthening for improving the mechanical properties of oxide glasses are reviewed. Chemical strengthening in compared with thermal strengthening and different methods of measuring strength are discussed. Different ions, salts and other related methods for improving the ion exchange process and mechanical properties are described as well as applications of strengthening.

The Surface Ablation Cell (SAC), a laboratory equipment for determining surface concentration profiles, has been utilised to characterise float glass surface ion exchange processes. In this paper, single-side ion exchange is reported. Data on the ion concentration profiles were used to calculate diffusion coefficients as well as the activation energy for K⁺-Na⁺ ion exchange. The air-sides of float glass samples were treated with two different salt mixtures, I) KNO₃:KCl, 2:1 and II) KNO₃:KCl, 1:2, and heated to different temperatures under T_g, 460-520 °C. The diffusion coefficients calculated with Green’s function were in the range I) 1.4x10^-11 to 6.8x10^-11 and II) 1.8x10^-11 to 6.0x10^-11 cm²/s while calculated according to Boltzmann-Matano I) 5.7x10^-12 to 1.4x10^-11 and II) 3.4x10^-12 to 6.0x10^-12 cm²/s. Average values of the activation energies obtained through Green’s function were I) 111.0 kJ/mol and II) 99.8 kJ/mol for the different salt mixtures.

We report the change of surface composition on commercial soda-lime-silica (SLS) float glass which results from single-side exchange of Na⁺ by Cu⁺, Ag⁺, Rb⁺ and Cs⁺, respectively. Ion exchange is achieved by in line melting of a directly deposited salt paste in a prolonged annealing procedure. Concentration profiles obtained and computed effective diffusion coefficients, as well as apparent activation energies for diffusion, are reported. Depending on exchange species, treatment time and treatment temperature, the penetration depths are in the range of 10-20 μm for K⁺, Cu⁺, Rb⁺ and Cs⁺. A penetration depth of >100 μm can readily be obtained for Ag⁺.

In this paper, colouration of the tin side of commercial soda lime silicate float glass by copper ion exchange is described and characterised. Data on the resulting concentration vs. depth profiles, absorbance vs. depth profiles, UV-Vis spectra  and CIE-Lab colour coordinates are reported. Fundamental aspects of the process of colouration are described and discussed. Optimum saturation of colouration is achieved after ion exchange at 520 °C for 10 h, or at 500 °C for 20 h, respectively. The depth of the coloured layer increases with increasing treatment time. At the same time, a linear dependency is found between the value of a and b in the CIE-Lab colour space for variations of treatment time and temperature. The latter indicates broad tunability of colouration between different shades of ruby and varying colour saturation. It is shown that colour arises from a redox reaction between copper species and residual tin ions, and that the depth of the coloured layer is governed by the position of the tin hump. The critical concentration of tin and copper to achieve colour formation was found to be ~0.25 mol% and >1 mol%, respectively.

The effect of single-side ion exchange (using a KNO₃:KCl mixture) on the ring-on-ring flexural strength of float glass has been studied. Two ion exchanged series, treated at 450 and 515°C, were investigated. The ion exchanged samples showed approximately 160 respectively 100% increases in their arithmetic mean strength compared to as-received float glass. Furthermore, a series of samples containing drilled holes were studied in order to investigate the effect of single-side ion exchange on such common construction elements. The samples that contained drilled holes were ion exchanged at 450°C and showed around 140% increase of the fracture load compared to the untreated samples containing drilled holes. As a general observation, the ion exchange treatment induced ~110 MPa compressive stresses (515°C) and ~180 MPa compressive stresses (450°C). The ion exchanged samples showed no significant increase in stiffness.