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 are generated in organisms under mild biocompatible conditions. Herein, it is reported 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, consisting of 80 wt% liquid water and amorphous mineral nanoparticles (hydrated iron molybdate: FeMo₂H₇O₁₁), which, upon drying under mild temperature, turns into a residual stress-strengthened ceramic block that displays a high mechanical performance (with a hardness/elastic modulus of 1.7/17.5 GPa). 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 (with the assistance of hydration water) 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. © 2024 The Author(s). Advanced Functional Materials published by Wiley-VCH GmbH.