Enhancing Effect of Iron Chlorides on the Anatase‐Rutile Transition in Titanium Dioxide

The effect of solid Fe 2 O 3 and gaseous iron chlorides on the anatase‐rutile phase transition was investigated in the temperature range of 750°‐950°C via X‐ray diffractometry and scanning electron microscopy. In both cases, iron diffusion in the anatase lattice decreased the transition temperature and increased the anatase‐rutile transformation rate, in comparison with that in TiO 2 fired in air. The enhancement effect of iron on the anatase‐rutile transition is understood on the basis of oxygen‐vacancy formation, which favors rutile nucleation. Solid‐state iron diffusion between the contact points of TiO 2 and Fe 2 O 3 particles and vapor mass transport through gaseous chlorides were the primary mechanisms of iron mass transport to the TiO 2 surface in the presence of both Fe 2 O 3 and gaseous iron chlorides, respectively. The transformation rate at a given reaction temperature increased in the following order of reaction conditions: pure TiO 2 in air, TiO 2 in the presence of Fe 2 O 3 in air, TiO 2 in the presence of Fe 2 O 3 in chlorine, and TiO 2 in the presence of gaseous iron chlorides.