Accademia La Maison de la Danse Srld Italy

The flat glass produced by the float glass process has a tin-rich surface due to the contact with molten tin. The penetration of tin into the glass surface is assumed to involve coupled diffusion of stannous (Sn2+) and stannic (Sn4+) ions. The diffusion coefficients of these ions were calculated using the modified Stocks–Einstein relation with the oxidation velocity of stannous ions depending on the oxygen activity in the glass. The ion diffusion was analyzed using a coupled diffusion simulation with a modified diffusion coefficient to compensate for the negative effect of the glass ribbon’s stretching or compressing in the glass forming process. Tin penetration simulations for both green glass and clear glass show an internal local tin concentration maximum in green glass which is quite different from that in clear glass. The local maximum in the profile is associated with the accumulation of stannic ions where the greatest oxygen activity gradient occurs. Since more float time is needed in the manufacture of thicker glass plate, the tin penetrates to a greater depth with the maximum deeper in the glass and the size of the maximum larger for thicker glass.