It was found that inward diffusion of network-modifying cations can occur in an

iron-containing silicate glass when it was heat-treated in CO/CO2 (98/2v/v) or

H2/N2 (1/99v/v) gases at temperatures around the glass transition temperature. The

inward diffusion was caused by the reduction of ferric to ferrous ions and this

diffusion leads to formation of a silica-rich surface layer with a thickness of 200–

600nm. The diffusion coefficients of the network-modifying divalent cations were

calculated and they were different for the glasses treated in the CO and H2 gases.

At the applied partial pressures of CO and H2, the H2-bearing gas created a silicarich

layer more effectively than the CO-bearing gas. The layer increased the

hardness and chemical durability of the glass due to the silica network structure in

the surface layer.

Redox Reactions and Inward Cationic Diffusion in Glasses Caused by CO and H2

Gases . M.M.Smedskjaer, Y.Yue: Solid State Ionics, 2009, 180[7-8], 1121-4