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 AlOx 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.
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