Redox dynamics in the high-temperature float-processing of glasses. II. Reaction between undoped and iron-doped aluminoborosilicate glassmelts and a gold–germanium alloy

Rutherford backscattering (RBS) and wavelength-dispersive X-ray (WDS) spectroscopies were employed to study the redox dynamics in reaction couples of liquid Au–28at.%Ge alloy and lightly iron-doped sodium aluminoborosilicate glasses. Glassmelts were floated in a reducing atmosphere for 30 min at temperatures from 1300°C to 1450°C. The depth of diffusive penetration of Ge2+,4+ into the glassmelt was generally ∼20 μm, similar to Sn ions in conventionally processed float glass. Doping of the glassmelt with Fe3+ affected significantly the penetration: with additional Fe3+, the internal redox reaction that forces germanium into the distinctly immobile Ge4+ (network-former) state occurs closer to the metal–alloy/glassmelt interface. The observed chemical profiles in the glassmelt are consistent fully with a description of the float reaction as a cation-diffusion-controlled reduction of the glassmelt that involves multiple diffusion steps and internal structural reactions acting in series.