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Nevertheless, anatase is often the first titanium dioxide phase to form in many processes due to its lower surface energy, with a transformation to rutile taking place at elevated temperatures. [7] Although the degree of symmetry is the same for both anatase and rutile phases, there is no relation between the interfacial angles of the two ...
Rutile is the next most abundant and contains around 98% titanium dioxide in the ore. The metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range 600–800 °C (1,110–1,470 °F). [14]
Rutile is an oxide mineral composed of titanium dioxide (TiO 2), the most common natural form of TiO 2. Rarer polymorphs of TiO 2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visible wavelengths of any known crystal and also exhibits a particularly large birefringence and high ...
This is the case for anatase, a metastable polymorph of titanium dioxide, which despite commonly being the first phase to form in many synthesis processes due to its lower surface energy, is always metastable, with rutile being the most stable phase at all temperatures and pressures. [1]
In contrast to gas phase interactions with the solid surface, the vast number of variables associated with the liquid solid interface (i.e. solution pH, photocatalyst concentration, solvent effects, diffusion rate, etc.) calls for greater care to be taken to control these variables to produce consistent experimental results.
Brookite is rare compared to anatase and rutile and, like these forms, it exhibits photocatalytic activity. [5] Brookite also has a larger cell volume than either anatase or rutile, with 8 TiO 2 groups per unit cell, compared with 4 for anatase and 2 for rutile. [6] Iron (Fe), tantalum (Ta) and niobium (Nb) are common impurities in brookite. [3]
Ultrafine anatase form is precipitated from sulfate solution and ultrafine rutile from chloride solution. In the chloride process, natural or synthetic rutile is chlorinated at temperatures of 850–1000 °C, and the titanium tetrachloride is converted to the ultrafine anatase form by vapor-phase oxidation. [6]: 1–2
Efforts to develop functional photocatalysts often emphasize extending exciton lifetime, improving electron-hole separation using diverse approaches that may rely on structural features such as phase hetero-junctions (e.g. anatase-rutile interfaces), noble-metal nanoparticles, silicon nanowires and substitutional cation doping. [23]