ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Inhibition of the Anatase—Rutile Phase Transformation with Addition of K₂O, P₂O₅, and Li₂O

B. Grzmil, B. Kic, and M. Rabe

Technical University of Szczecin, Institute of Chemical and Environment Engineering, PL-70 322 Szczecin

E-mail: barbara.grzmil@ps.pl

Received: 31 March 2004

Abstract:

During the sulfate process of TiO₂ pigment production, hydrated titanium dioxide is calcined. As a result of the polymorphous conversion, rutile is obtained. Roasting additives are introduced into the calciner, in order to achieve required process temperature, crystallite size of individual phases, optical properties, and the pigment photostability.

Calcination process was investigated on the laboratory scale with the use of hydrated titanium dioxide containing rutile nuclei from the industrial installation. The influence of both temperature and calcination time on the anatase—rutile transformation ratio and the crystallites growth was determined. The obtained dependences were described using exponential equations. The ratio of anatase—rutile transformation was higher at elevated temperatures. It was noticed that the process temperature affects the conversion ratio considerably more than the calcination time.

During the experiments alkaline metals (potassium, lithium) and phosphate were introduced into the calcination suspension. It was noted that the increase of phosphates content in the calcinated TiO₂ · nH₂O (0.1—0.5 mass % P₂O₅ in relation to TiO₂) caused the anatase—rutile transformation ratio to drop 2 to 10 times. Moreover, the phosphates presence restricted an unfavourable anatase and rutile crystallites growth. In fact, their crystallites size was 2—3 times lower, compared to the crystallites size measured when the phosphates were not added. If the potassium content in hydrated TiO₂ was increased (0.05—1.0 mass % K₂O in relation to TiO₂), during calcination the rutile formation passed through a maximum. Similar behaviour was observed when lithium (0.025— 0.5 mass % in relation to TiO₂) was introduced instead of potassium. Neither anatase nor rutile average crystallites size was influenced by the potassium or lithium addition.

Full paper in Portable Document Format: 586a410.pdf

Chemical Papers 58 (6) 410–414 (2004)