Evidence of anatase intergrowths formed during slow cooling of reduced ilmenite

Abstract

Controlling the parameters during synthetic rutile production is essential to minimize production costs and ensure final product quality. Powder X-ray diffraction (PXRD) is typically used within the industry to guide process control. This work investigated the source of unusual features observed in the PXRD pattern of a slow-cooled reduced ilmenite (RI), which were not observed for a rapid-cooled RI. For the slow-cooled RI, the 002 peak of M3O5 (anosovite) had disappeared and the intensity of the \bar 203, 203, 204 and 402 peaks had decreased significantly compared to the pattern for the rapid-cooled RI. Using transmission electron microscopy, selected area electron diffraction (SAED) and pair distribution function (PDF) analysis, the authors attribute these features to M3O5–anatase intergrowth formation, which causes a loss in long-range order along the M3O5 c axis. Strong diffuse streaking in the SAED patterns was also evident and supported the presence of disordered intergrowths from the oxidation of M3O5. PDF analysis showed a significant improvement in the fit to the data for the slow-cooled RI, primarily in the <17 A region, when anatase was added to the PDF model. The results presented here highlight the importance of the reduction and cooling stages during the formation of these industrially relevant RI minerals, which may be used to direct the production process and final TiO2 product quality.