Redox chemistry of iron-manganese and iron-chromium interactions in soda lime Silicate glass melts

Abstract

Redox interacdons between the Fe²⁺-Fe³⁺ and Mn²⁺-Mn³⁺ redox couples and the Fe²⁺-Fe³⁺ and Cr⁶⁺-Cr³⁺ redox couples were spectrophotometrically determined in soda lime Silicate compositions quenched from different melting temperatures (1100 to 1400°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 Mn²⁺ along with either Fe²⁺ o r Μn²⁺, whichever one being in excess at that temperature. The electron exchange between the redox couples occurred during equilibration at melt temperature and not as an artifact of the quench. No evidence was obtained for a rapid internal re-equilibrium of redox states with decreasing temperature during the normal cooling of a melt to a glass. The degree of redox interaction of manganese or chromium with iron is independent of the manganese or chromium Compound added, as long as the oxygen fugacity over the glass-forming melt is held constant externally.