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Ind. Eng. Chem. Res. 2007, 46, 1018-1024
Influence of Phosphate, Potassium, Lithium, and Aluminium on the Anatase-Rutile Phase Transformation Barbara Grzmil,* Magdalena Rabe, Bogumił Kic, and Krzysztof Lubkowski Szczecin UniVersity of Technology, Institute of Inorganic Chemical Technology and EnVironmental Engineering, 70-322 Szczecin, Pułaskiego 10, Poland
Calcination process was investigated on the laboratory scale with the use of hydrated titanium dioxide containing rutile nuclei from the industrial installation (sulfate process). The influence of temperature (750-900 °C) on the anatase-rutile phase transformation and on the crystallites’ growth variation was determined. Phosphate, potassium, lithium, and aluminum were introduced into calcination suspension. It was found that whereas an introduction of lithium, in phosphate presence, either increased or stabilized the anatase-rutile transformation degree, the introduction of potassium significantly decreased it. The intensity of these changes depended on both the temperature of the process and on phosphate content. The introduction of aluminum, in constant phosphate presence, had an intermediate influence on the rutilization of anatase between that of either potassium and phosphate on the one hand and lithium and phosphate on the other. Similarly to potassium, aluminum intensified the influence of phosphate but to a smaller degree and only a lower temperature. The introduction of lithium, regardless of whether or not phosphate and potassium were present, increased rutilization degree. This dependence was more clearly seen at lower temperatures of the process. Aluminum, either in constant phosphate and potassium or phosphate and lithium presence, increased the anatase-rutile transformation. The degree of these changes depended on both the presence of modifying agents in their mixture and on the temperature of the process. It was found that the introduction to hydrated titanium dioxide of additives causing an increase in the surface area of TiO2, as a result of limitations of crystallite growth in the calcination process, results in elevation of temperature of the anatase-rutile phase transformation (phosphates, potassium) whereas the introduction of additives that decrease the surface area (crystallite growth) enhances the degree of transformation of anatase to rutile (lithium). Introduction In 2003, the global production capacity of titanium dioxide reached 4.8 million tons and its consumption 4.05 million tons, out of which 57% was used for paint coatings, 22% for plastics production, 12% went to paper industry, and 9% was used for other purposes (i.e., for rubber, ceramic, pharmaceutical, food, and cosmetics industries as well as for solar energy use, environmental protection, and catalytic converters).1 It is owing to titanium dioxide’s properties that it has found such a wide range of applications. Titanium dioxide is chemically highly stable. It is nonvolatile and nonflammable. It is not toxic and it has both a high refractive index and a high dielectric constant. Titanium dioxide can be observed in three polymorphous modifications: anatase (tetragonal system), brookite (orthorhombic system), and rutile (tetragonal system).2-4 Rutile boasts the highest thermodynamic stability. Rutile is characterized by a higher density, a higher packing density of atoms in its structure, and a higher hardness and refractive index. Its pigment properties are better than those of anatase. In photodegradation reactions, anatase is more active than rutile.2,4 The energy of the forbidden gap for anatase is higher than that for rutile and these bands are 3.29 and 3.05 eV, respectively.2 Rutile absorbs radiation P > PAl > KAl > PKLi > K > PKAlLi > PLi > PAlLi
whereas with regard to the degree of influence on a decrease of values of analyzed parameters, they can be arranged in the following order:
AlLi > Li > Al > KAlLi > KLi Conclusions On the basis of the conducted investigations, the following conclusions can be drawn: (1) In the presence of phosphate, lithium either increased or stabilized anatase-rutile conversion degree, whereas potassium significantly decreased it. It depended on both the temperature of the process and the phosphate content. When phosphate was present, lithium influence was other than that of potassium, the former being antagonistic and the latter synergetic. (2) The influence of aluminum addition, at a constant phosphate content, on anatase rutilization was intermediate between the influence of potassium and phosphate on the one hand and lithium and phosphate on the other. Aluminum, just like potassium, increased phosphate influence, but to a lesser degree and only at lower temperature. At higher temperature, its influence was close to that of lithium. (3) The synergic influence of phosphate and potassium on anatase-rutile transformation resulted from the precipitation of phosphates on the surface of hydrated titanium dioxide. Lithium inhibited the influence of phosphate. It is most probable that besides the precipitation of lithium phosphates (higher lithium content) vacancies were generated as a result of substituting titanium ions with lithium ions. (4) It was found that an addition of lithium, irrespective of phosphate and potassium content in the calcined substances, increased rutilization degree. This relation was more clearly observed at a lower temperature of the process. (5) Aluminum, at a constant addition of either phosphate and potassium or phosphate and lithium, increased the temperature of anatase-rutile transformation. The range and degree of these changes depended both on the contribution of some selected modifying agents in their solution and on the temperature of the process. (6) The pH of the calcined substances depended both on the composition of introduced modifying agents and on the tem-
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perature of the process. When phosphate was present, the alkalinity of calcined substances was significantly increased by lithium presence. The alkalinity was only a little increased owing to either potassium or aluminum presence. (7) Lithium exerted the most decisive influence on the alkalinity of pigments. The pH of calcined substances, obtained at 900 °C which also contained lithium, was 9-10. (8) The synergetic influence of phosphates and potassium on an increase in the surface area of titanium dioxide was limited by the addition of aluminum in a smaller degree, whereas in the case of lithium in a larger degree. Hence, it can be concluded that the addition of compounds causing an increase of the surface area of TiO2 (in relation to nonmodified TiO2) influences on an elevation of temperature the anatase-rutile transformation (phosphates, potassium), whereas the addition of those of decreasing surface area (lithium) influences on an enhancement of the degree of transformation of anatase to rutile. This conclusion is in agreement with the studies performed by other authors.23 An increase in the surface area may result from limitation of crystallites’ growth in the calcination process, the formation of particles with a nonuniform shape in a comparison with the spherical, or from the precipitation on the particle surface of compounds with a larger surface area than that of TiO2. Literature Cited (1) Cianfichi, G. L. Chinese TiO2 Markets. Presented at the UBS Grass Roots Chemical Conference, New Orlean, February 10, 2004 (www. media.corporate-ir.net/media_files/NYS/MCH/UBS_0204.pdf). (2) Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; WileyVCH: Weinheim, Germany, 2002. (3) Dobrowolskij I. P. Khimia i Tehnologia Oksidnyh Sojedinenii Titana; AN SSSR: Sverdłovsk, 1988. (4) Mills, A.; Le Hunte, S. An overview of semiconductor photocatalysis. J. Photochem. Photobiol., A 1997, 108. (5) Nanping, X.; Zaifeng, S.; Yiqun, F.; Junhang, D.; Jun, S.; Michael, Z.-C. H. Effects of Particle Size of TiO2 on Photocatalytic Degradation of Methylene Blue in Aqueous Suspensions. Ind. Eng. Chem. Res. 1999, 38, 373. (6) Bacsa, R. R.; Kiwi, J. Effect of rutile phase on the photocatalytic properties of nanocrystalline titania during the degradation of p-coumaric acid. Appl. Catal., B 1998, 16, 19. (7) Chan Chak, K.; Porter, J. F.; Li, Y.-G.; Guo, W.; Chan, C.-M. Effects of Calcination on the Microstructures and Photocatalytic Properties of Nanosized Titanium Dioxide Powders Prepared by Vapor Hydrolysis. J. Am. Ceram Soc. 1999, 82, 566. (8) Deren´, J.; Haber, J.; Pampuch, R. Chemia ciała stałego; Akademia Go´rniczo-Hutnicza w Krakowie: Krako´w, Poland, 1973.
(9) Tolchev, A. V.; Pervushin, V. Y.; Kleshchev, D. G. Thermal Transformations of Hydrated Titanium Dioxide with a Globular Structure of Aggregates. Russ. J. Appl. Chem. 2002, 75, 696. (10) Zhang, Q.; Gao, L.; Guo, J. Effects of calcinations on the photocatalytic properties of nanosized TiO2 powders prepared by TiCl4 hydrolysis. Appl. Catal., B 2000, 26, 207. (11) Shannon, R. D.; Pask, J. A. Kinetics of the Anatase-Rutile Transformation. J. Am. Ceram. Soc. 1965, 48, 391. (12) MacKenzie, K. J. D. The Calcination of Titania. Kinetics and Mechanism of the Anatase-Rutil Transformation in the Presence of Additives. Trans. J. Br. Ceram. Soc. 1975, 74, 77. (13) Criado, J.; Real, C. Mechanism of the Inhibiting Effect of Phosphate on the Anatase-Rutil Transformation Inducted by Thermal and Mechanical Treatment of TiO2. J. Chem. Soc., Faraday Trans. 1983, 1, 79, 2765. (14) Ratajska, H. The effect of certain promoters on TiO2 crystal structure transformation. J. Therm. Anal. 1992, 38, 2109. (15) Kumar, K.-N. P. Growth of Crystallites During the Initial Stage of Anatase to Rutile Transformation in Pure Tytania and in Tytania Alumina Nanocomposites. Scr. Metall. Mater. 1995, 32, 873. (16) Gesenhues, U. Doping of TiO2 pigments by Al3+. Solid State Ionics 1997, 101-103, 1171. (17) Gesenhues, U. Calcination of Metatitanic Acid to Titanium Dioxide White Pigments. Chem. Eng. Technol. 2001, 24, 685. (18) Gesenhues, U.; Rentschler, T. Crystal Growth and Defect Structure of Al3+ - Doped Rutile. J. Solid State Chem. 1999, 143, 210. (19) Zhang, H.; Banfield, J. F. Phase transformation of nanocrystalline anatase-to-rutile via combined interface and surface nucleation. J. Mater. Res. 2000, 15, 437. (20) Francisco, M. S. P.; Mastelaro, V. R. Inhibitation of the AnataseRutil Phase Transformation with Addition of CeO2 to CuO-TiO2 System: Raman Spectroscopy, x-ray Diffraction, and Textural Studies. Chem. Mater. 2002, 14, 2514. (21) Ruiz, A. M.; Dezanneau, G.; Arbiol, J.; Cornet, A.; Morante, J. R. Insights into the Structural and Chemical Modifications of Nb Additive on TiO2 Nanoparticles. Chem. Mater. 2004, 16, 862. (22) Grzmil, B.; Kic, B.; Rabe, M. Inhibition of the Anatase-Rutile Phase Transformation with Addition of K2O, P2O5 and Li2O. Chem. Pap. 2004, 58, 410. (23) LeDuc, Ch. A.; Cambell, J. M.; Rossin, J. A. Effect of Lanthana as a Stabilizing Agent in Titanium Dioxide Support. Ind. Eng. Chem. Res. 1996, 35, 2473. (24) Schmalzried, H. Chemical Kinetics of Solids; VCH: Weinheim, Germany, 1995. (25) Chung, F. H.; Smith, D. K. Industrial Application of X-Ray Diffraction; Marcel Dekker: New York, 2000. (26) Grzybowska-SÄ wierkosz, B. Elementy katalizy heterogenicznej; Wydawnictwo Naukowe PWN: Warszawa, Poland, 1993.
ReceiVed for reView February 15, 2006 ReVised manuscript receiVed November 6, 2006 Accepted December 2, 2006 IE060188G
