Cluster mediated self-hydrolysis of γ-Al(OH)₃ to γ-AlOOH

We report a mechanism by which γ-Al(OH)₃ is converted to γ-AlOOH through hydrothermal reaction at 473 K. X-ray pair distribution function measurements indicate that γ-Al(OH)₃ decomposes to amorphous clusters upon contact with water, while nanocrystalline γ-AlOOH precipitates within 1 h of hydrothermal exposure. Solid state nuclear magnetic resonance measurements show that resonant features associated with four- and five-member Al clusters persist through 20~min of hydrothermal treatment, while ultraviolet (UV) spectra mark the onset of UV-induced photoluminescent features characteristic to γ-AlOOH with 10 min of exposure, indicating a coexistence region of γ-Al(OH)₃-like and γ-AlOOH-like amorphous species. Powder x-ray diffraction measurements of desiccated powders reveal that the conversion process takes place in three distinct, power law-defined stages with initial γ-AlOOH nucleation occurring within the first 20 min, followed by a ~1 h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.