Voltammetric investigations of the redox behaviour of Fe, Ni, Co and Sn doped glass melts of AR® and BK7® type

The redox behaviour of iron, nickel, cobalt, and tin ions was studied in glass melts with compositions near AR® and BK7® type by means of square-wave voltammetry (SWV). From the linear dependence of the peak potentials on the temperature, the standard enthalpies, ΔH 0 , and the standard entropies, ΔS 0 of the transitions Fe 3+ /Fe 2+ , Co 2+ /Co 0 , Ni 2+ /Ni 0 , Sn 4+ /Sn 2+ and Sn 2+ /Sn 0 were calculated. The reduced states are formed in the AR glass melt already at less reducing conditions than in the BK7 melt. The dependence of the redox ratios upon temperature is larger in the AR melt. As colouring ion Co 2+ is more advantageous than Ni 2+ because of its higher stability against reduction. It is possible to reduce the Fe 3+ /Fe 2+ ratio without formation of Co 0 in a disturbing concentration.