THE IRON REDOX COUPLE AND ITS INTERACTION WITH SULFUR IN GLASS

Ferrous-ferric equilibria in float glass were studied by equilibrating the glass melts with various oxygen partial pressures over the temper ature range 1250-1500 degrees C. Under oxidising conditions, a linear relationship between log[Fe2+]/[Fe3+], log P-O2, and 1/T was found. Th e enthalpy of the ferrous-ferric reaction in float glass was determine d to be 150 kJ/mol. At lower oxygen partial pressures (P-O2 < 10(-10) at 1250 degrees C), iron and sulphur form the amber chromophore. The c oncentration of amber chromophore increased with increasing temperatur e and glass sulphide content. The enthalpy for amber chromophore forma tion in float glass was 100 kJ/mol.