Mechanisms of Al and titania hydrogel complex formation via a mechanical route

The process of complex formation has been studied during milling a powder mixture of metallic Al and titania hydrogel, TiO₂ · H₂O. Solid state ²⁷Al NMR and ESR are employed together with conventional x-ray diffractometry and thermal analyses. Al atoms partly changed from metallic to oxide state. ²⁷Al NMR analyses indicate that two metallic Al states are allotted to distorted and undistorted lattices, while the other to AlO_x units in the oxide state, where x is 4, 5, or 6. As detected by ESR, Ti⁴⁺ was partly reduced to Ti³⁺, suggesting a redox reaction during milling. A vigorous thermit reaction was detected during subsequent heating of the mixture after prolonged milling. These results indicate the formation of Al-O-Ti bonds during milling, leading to Al₂TiO₅ on subsequent heating.