REDOX CHEMISTRY OF IRON-MANGANESE AND IRON-CHROMIUM INTERACTIONS IN SODA LIME SILICATE GLASS MELTS

Redox interactions between the Fe2+-Fe3+ and Mn2+-Mn3+ redox couples a nd the Fe2+-Fe3+ and Cr6+-Cr3+ redox couples were spectrophotometrical ly determined in soda lime silicate compositions quenched from differe nt melting temperatures (1100 to 1400 degrees C) at air. Both Mn3+ and Cr6+ stoichiometrically oxidized Fe2+. Thus, for example in the iron- manganese system, the color of the glass was determined by Fe3+ and Mn 2+ along with either Fe2+ or Mn3+, whichever one being in excess at th at temperature. The electron exchange between the redox couples occurr ed during equilibration at melt temperature and not as an artifact of the quench. No evidence was obtained for a rapid internal re-equilibri um of redox states with decreasing temperature during the normal cooli ng of a melt to a glass. The degree of redox interaction of manganese or chromium with iron is independent of the manganese or chromium comp ound added, as long as the oxygen fugacity over the glass-forming melt is held constant externally.