Cluster mediated conversion of amorphous Al(OH)₃ to γ-AlOOH

We report a synthetic pathway by which amorphous Al(OH)₃ is converted to γ-AlOOH through hydrothermal reaction in the presence of water at temperature T ​= ​473 ​K. X-ray pair distribution function measurements reveal that the initially amorphous Al(OH)₃ possesses a locally γ-Al(OH)₃-like structure, while nanocrystalline γ-AlOOH precipitates within 1 ​h of continuous 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, and 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 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.