Surface Analysis Of Float Glass Using Surface Ablation Cell (Sac). Part 2. Determination Of The Diffusion Characteristics Of K+-Na+ Ion Exchange

The surface ablation cell (SAC), a laboratory equipment for determining surface concentration profiles, has been utilised to characterise surface ion exchange processes in float glass. 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) 2:1 KNO3:KCl, and (II) 1:2 KNO3;KCl, (both by weight), and heated to different temperatures below Tg, 460-520 deg C. The diffusion coefficients calculated using Green's function approach were in the ranges (1) 1.4x10-11 and (II) 1.8x10-11 to 6.0x10-11 cm2/s while those calculated using Boltzmann-Matano were in the ranges (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 the Green's function were (I) 111.0kJ/mol and (II) 99.8kJ/mol for the different salt mixtures.