Quantification of the Fe3+ concentration in lead silicate glasses using X-band CW-EPR

Abstract

The majority of the existing experimental techniques for determining the fractions of Fe3+ and Fe2+ in silicate glasses are based on X-ray or γ-ray absorption. Materials with a high lead content are not suitable for these techniques because they strongly absorb such high-energy radiation. This work investigates the feasibility and precision of X-band CW-EPR as an alternative technique for the quantification of the concentration of Fe3+ in iron containing lead silicate glasses. This could be a viable alternative since it is based on the absorption of microwaves, which are not heavily influenced by the presence of lead. A practical and robust method using standards is proposed, based on the empirical relation between the concentration of Fe3+ species and the occurrence of two distinct features in the collected EPR spectra. It was found that EPR can indeed be used for the quantification of Fe3+ concentration in lead silicate glasses up until about 8 wt.% Fe2O3, depending on the lead content of the glass. A precision of about ± 0.10 wt.% (2σ) was observed for two tested experimental set-ups. The quantification method proposed requires standards of known composition.