Redox dynamics of cerium ions in soda-lime glass during cooling analyzed by in situ X-ray absorption fine structure

Ozawa, Saki*; Shiozawa, Yudai*; Saijo, Yoshitaka*; Miyajima, Tatsuya*; Matsumura, Daiju   ; Tsuji, Takuya  ; Nakase, Masahiko*; Maehara, Terutaka*

The optical properties of glass are strongly influenced by the redox states of trace multivalent elements. Ce ions are commonly added to soda-lime glass to remove Fe-induced coloration via the redox reaction Ce + Fe Ce + Fe during cooling. Herein, the redox dynamics of cerium ions in soda-lime glass melts during model industrial cooling processes (from 1523 K at 20 Kmin) were investigated using in situ time-resolved Ce K-edge dispersive X-ray absorption fine-structure (DXAFS) spectroscopy. To evaluate the effect of the iron concentration, three soda-lime glass samples containing 2 mass% CeO were examined: Fe-free, Fe-05 (0.5 mass% FeO), and Fe-20 (2.0 mass% FeO). Above 1383 K, the Ce/total Ce ratio remained stable for all samples, showing no significant change during cooling. Below 1383 K, the ratio decreased for the Fe-free glass, indicating the oxidation of Ce ions, and increased for the Fe-containing glass owing to the reduction of Ce ions. The temperature dependence of the redox change (Ce redox) showed Fe-dependent behavior: Fe-20 exhibited more pronounced Ce reduction above 1200 K, while Fe-05 showed accelerated changes mainly below approximately 1100 K. These results indicate that cerium oxidation in Fe-free glass is strongly influenced by oxygen transport limitations, while cerium reduction is closely associated with availability of Fe ions, providing quantitative insights into the control of Ce-based decolorization during industrial cooling.