Reducing the sulphate content of soda-lime-silica glasses with the aid of physical refining

Abstract

Soda-lime-silica glasses from the float glass production sector have sulphate contents of ≈ 0.27 wt% SO3. These sulphate contents contaminate the tin bath for the float process with sulphur. The thus-formed tin sulphides cause production faults by forming top-specks on the atmospheric surface of the glass ribbon. The aim of the described experiments is a reduction of the sulphate content of such glass melts. For this purpose, within the scope of a physical refining process, the glass melts are rinsed with nitrogen in order to drive SO3 (i.e. SO2 + 1/2 O2) from the melt and thus support the decomposition of sulphate. The sulphate content can thus be reduced to values of 0.11 to 0.13 wt% SO3. Parallel to this, a shifting of the Fe3+/Fe2+ ratio in favour of the bivalent iron is observed. It is thus possible to supervise the success of the physical refining process directly in the melt with the help of oxygen ion sensitive probes.