Crystallization of iron-containing Si–Al–Mg–O glasses under laser floating zone conditions

• Crystallization behaviour of Fe-containing Mg–Al–Si–O glasses by LFZ method.
• Fibre growth rate affects iron oxidation state and local coordination.
• Low growth rates are favourable for formation of nanosized Fe-containing clusters.
• Formation of nanosized clusters affects crystallization process and conductivity.
• LFZ method is flexible for redox tuning and attaining frozen-in conditions in glasses.

The glass system MgO–Al2O3–SiO2–FeOy has been mentioned as possible electrolyte for pyroelectrolysis of iron. This work was focused on the study of crystallization behaviour of the iron-containing Al–Mg–Si–O glass system under laser floating zone (LFZ) to identify expected changes occurring under freeze lining or other high temperature gradients at large industrial scale. Lower iron content and faster fibre growth were found favourable for the formation of isolated iron cations in the glass after cooling. The crystallization process, accompanied with separation of mullite and cordierite-type phases, is strongly affected by the formation of nanosized iron-containing clusters, confirmed by Mössbauer and EPR spectroscopies. LFZ method shows good prospects for studying crystallization/vitrification mechanisms in silicate-based glasses with additions of redox-active cations, by providing flexibility in tuning their oxidation state and attaining frozen-in conditions.