Redox equilibria in glass

Data for redox equilibria in silicate glass melts, for the ion couples: Fe2+/Fe3+, Cr3+/Cr6+, Ce3+/Ce4+, Sn2+/Sn4+ and As3+/As5+, can be related to the glass composition and indicate that increasing basicity favours the upper oxidation state. The relationships are simplified by making the correlation with the optical basicity of the glass rather than with its composition. The optical basicity model is concerned with the electron density environment provided by oxygen atoms for the hosted metal ions and, in principle, allows comparison between any oxidic environment. Comparison between glass melts and aqueous solution establishes a relationship between the redox behaviour in the melt and standard electrode potentials in aqueous solution. The applications of this relationship are discussed.