Unveiling the Atomic Mechanism of Hydroxide Catalysis Bonding: Ab Initio Molecular Dynamics Study and Experimental Validation

Hydroxide catalysis bonding (HCB), also known as silicate bonding, is widely employed to join oxide materials in precision optical instruments due to its ability to form strong, thin bonds under mild conditions. The chemical reactions underlying HCB, including hydration, polymerization, and dehydration, have been relatively well understood, yet the atomic-scale chemical structure of the bonded interface after water removal remains unexplored, limiting a complete mechanistic understanding of HCB. In this study, sodium silicate (mSiO2:Na2O) was employed as the HCB layer, with sapphire chosen as a model substrate to resolve the interfacial bonding mechanism. We combined ab initio molecular dynamics (AIMD) simulations and experimental validation to elucidate the interfacial chemistry. AIMD simulations revealed atomic-level processes including interfacial Al–O partial amorphization, Na migration, and formation of Al–O–Si and Al–O–Na linkages. The simulations predicted that the optimal bonding strength appears at a SiO2/Na2O molar ratio (m) of approximately 2, a result validated by bonding tests and corroborated by ATR-IR spectroscopy showing Al–O–Si bond formation at the interface. These results establish a direct relationship between SiO2/Na2O molar ratio, interfacial atomic structure, and mechanical strength, providing valuable guidance for designing robust HCB technologies.