Mineral fusion via dehydration-induced residual stress: from gels to ceramic monoliths

Man-made ceramics generally undergo harsh manufacturing conditions (e.g., high-temperature sintering). In contrast, mineral structures with superior mechanical strength (e.g., teeth) are generated in organisms under mild biocompatible conditions. Herein, we report that ceramic objects can be directly produced and strengthened by drying purely inorganic gels (PIGs), mimicking the biological tactic of fabricating continuous monoliths from hydrated amorphous precursors. The overall process is easy and biocompatible in that solutions of common iron and molybdate salts are mixed to generate a PIG, which, upon drying under mild temperature, turns into a strengthened ceramic block that displays a high mechanical performance. Analogous to the well-known Prince Rupert’s drop reinforced by residual stress upon quenching, the uneven volume shrinkage from the outside inwards during dehydration builds up residual stress that enables amorphous mineral fusion and strengthening. Furthermore, a dramatic bandgap reduction is achieved in the dried objects due to local structural changes of the Fe atoms under residual stress. This PIG-dehydration approach holds promise for green ceramic manufacturing and offers insights into biomineralization puzzles.