Production of Titanium Nitride by Carbothermic Reduction of the Anatase and Rutile Forms of Titanium Dioxide

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 Ti5O9 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.