Abstract
Two types of titanium oxide were used, rutile (>99.9% TiO2) and anatase (>99% TiO2). Both samples were mixed with graphite in accordance with the required stoichiometry, and then milled in a tumbling mill for 50 hours in an argon atmosphere to ensure thorough mixing. The mill vial was loaded with five 25.4 mm diameter stainless steel balls giving a powder to ball mass ratio of 1:43. After milling, samples were heated to 1400°C in an alumina crucible at 20°C min-1 under a flowing nitrogen (100 mL min-1) atmosphere in a thermogravimetric analyser (TGA). Srilankite was detected in the as-milled anatase sample but the anatase to rutile transformation was not completed during milling. After heating to 800°C most of the anatase had transformed to rutile. Reduction of anatase started just below 900°C whilst rutile underwent reduction below 800°C. TGA results showed that the anatase reduction was more complex than the rutile reduction with several stages evident between 880 and 1000°C in the anatase sample whilst only two steps were observed for rutile. The initial identified products were Ti5O 9 and Ti4O7 prior to TiN in anatase sample but in rutile sample only Ti4O7 was detected. Reduction was completed in rutile sample before 1180°C whilst in anatase completed at 1230°C. TiN was the final product in both systems after heating to 1400°C. These results are discussed in light of recent work demonstrating the different reductions paths of rutile and anatase.