Anatase and rutile TiO2-δ powders are synthesized by the sol-gel method. The hysteresis loops and the zero field-cooled and the field-cooled magnetization curves indicate that reduced TiO2-δ powders exhibit the room-temperature ferromagnetism that becomes stronger with prolonging annealing time in H2/Ar mixture. Analysis of Ti 2p x-ray photoelectron spectroscopy spectra indicates that Ti ions are all in the Ti4+ state and that Ti3+ or Ti2+ ions do not exist in all samples. In addition, analysis of O 1s x-ray photoelectron spectroscopy spectra indicates that the concentration of oxygen vacancies increases with prolonging annealing time. Analysis of ultraviolet-visible absorption spectra also further confirms that the concentration of oxygen vacancies increases with prolonging annealing time. These results indicate that ferromagnetism in pure TiO2-δ powders stems from oxygen vacancies. The possible mechanism on ferromagnetism is discussed.

The Al-10Ti and Al-64Ti (wt-%) powders were synthesised by mechanical milling. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that aluminium and titanium powders are refined rapidly and mixed uniformly, and finer particles result from the increase in milling time. The average particle size reached 5 mm after 100 h of milling. The structure of a metastable Ti(Al) hexagonal close packed (hcp) supersaturated solid solution was obtained after 140 h of milling. With increasing milling time (t5300 h), an amorphous phase occurred in Al-64Ti powders. Thermodynamic results of various competitive phases in the process were calculated and compared according to the Miedema model, which revealed how these phases proceeded. The milled Al-10Ti and Al-64Ti powders were consolidated by cold pressing (15 MPa) and sintering. The longer the milling time, the more energy stored in the composite powders. Correspondingly, the activation energy of the reaction for Al-Ti intermetallics decreased. The 50 h milled powders produced Al 3 Ti after heat treatment at 450uC for 5 h. In the case of 110 h milled samples, the final equilibrium phase is AlTi.