Water-assisted sintering of silica : Densification mechanisms and their possible implications in biomineralization

Taking silica as an exemplary material system, we studied water-assisted densification behaviors of different crystallinities (quartz, glass, and vitreous silica). To avoid the complexity in data interpretation, we adopted a simple procedure similar to those used for pressing salt pellets for IR: compressing silica powders in a mold with pure water under ambient conditions. It is discovered that crystalline silica is compacted through liquid lubrication, while amorphous silica's densification behaviors contradict the widely regarded dissolution-reprecipitation mechanism. Another mechanism is thus proposed: stress-driven water incorporation into the solid structures produces hydrated silica of considerable plasticity for deformation and fusion. Inspired by this water-assisted mechanism, a more effective sintering method is developed via repetitive stressing/destressing treatments at room temperature, enabling dramatically boosted densities (e.g., over 90% with transparent appearance for silica glass) and enhanced mechanical performance. This generic strategy may apply to a wide range of materials. Furthermore, the hydration-enabled deformation/sintering mechanism proposed in this work offers fresh insights into the biomineralization puzzles, particularly those on how life accomplishes some of the most challenging tasks faced by humans in modern ceramic technology, for example, to fuse, mend or reshape the rigid brittle ceramic objects in aqueous environments under ambient conditions. This purely inorganic biomineralization mechanism may be particularly important for life at its early stage of evolution on earth.