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.-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 gamma-Al(OH)(3)-like structure, while nanocrystalline gamma-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 gamma-AlOOH with 10 min of exposure, indicating a coexistence region of gamma-Al(OH)(3)-like and gamma-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 gamma-AlOOH nucleation occurring within the first 20 min, followed by a similar to 1 h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.