Preliminary Kinetic Study of Chemical Tempering of Float Glass

Reference Presenter Authors
11-016 Pedro Costa Braga Braga, P.C.(Polytechnic School of São Paulo University); Beneduce, F.(Polytechnic School of São Paulo University); Chemical tempering is one of the most important techniques to increase the resistance of the glasses, in which is mainly used in cell phone glasses that require high resistance to abrasion and mechanical shock. Consequently it has been intensely studied in the last decade. However, few studies address or even cite the kinetic variables of this process. This technique consists of the cation exchange, usually sodium, of the glass, with any other alkaline ion with higher ionic radius. The new ion of greater atomic radius enters the same cationic site that generates a zone of compression. This state of compression stresses on the glass surface significantly increases its strength in that region. The present work will present the results of chemical tempering tests on calcium-sodium and borosilicate floating glasses using KNO3/KCl mixtures for 10 hours at temperatures that are completely liquid. The results were treated kinetically by applying one of the Fick's 2nd law solutions with the aid of the Green function. With them, it was possible to determine the mean diffusion coefficient of K in these glasses as well as the activation energy of the chemical tempering process. The results showed a mean diffusion coefficient and activation energies very similar to those presented in the literature, around 10-11 cm2/s and 100 kJ/mol, respectively. The modeling allowed to estimate the metastable equilibrium K2O contents in the glass with the salts used.
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