Reduction of Ions in Glass by Hydrogen

The reduction by hydrogen of Fe 3+ , Ce 4+ , and Sn 4+ in soda‐lime‐silica glass was found to be diffusion‐limited in the glass transition temperature range (500°C). The reduction was studied in fibers by chemical analysis and in bulk samples by optical absorption. Reduction to Fe 2+ , Ce 3+ , and Sn 2+ proceeds by a reaction of the type H 2 +2(ɛSi‐O) ‐ +2Fe 3+ →2Fe 2+ +2(ɛSi–OH). Since the rate of reduction by hydrogen is quite similar for these systems and since reduction cannot be accomplished with CO, it is concluded that hydrogen is the diffusing species. A mechanism is developed in which hydrogen diffuses through the glass until it is trapped by a reducible ion.