Rutile crystallization

Zhang Q, Gao L, Sun J, Zheng S (2002) Preparation of long Ti02 nanotubes from ultrafine rutile crystals. Chem Lett 31 226-227... 

The shapes of rutile crystals give no hint of polar character, hence the holohedral space-group P42jmnm is the more likely to be correct. It will be considered first. 

Rutile pigments, prepared by dissolving chromophoric oxides in an oxidation state different from +4 in the rutile crystal lattice, have been described (25,26). To maintain the proper charge balance of the lattice, additional charge-compensating cations of different metal oxides also have to be dissolved in the rutile structure. Examples of such combinations are Ni2+ + Sb5+ in 1 2 ratio as NiO + Sb2Os, Cr3+ + Sb5+ in 1 1 ratio as Ci C + Sb2Os, and Cr3+ +... 

A disc of reduced semiconducting rutile crystal 2 cm in diameter and 2 mm thick is heated in air for 10 s at 300 °C. After cooling, circular electrodes, lcm in diameter, are applied symmetrically to the two major surfaces. The chemical diffusion coefficient D for the oxidation reaction in reduced single-crystal TiC is given by... 

To ensure the rutile crystal form, seed crystals are added, otherwise anatase is obtained. The precipitate is thoroughly washed using water and sulfuric acid to remove all traces of discoloring elements, eg, iron, chromium, vanadium, and manganese. The TiO(OH)2 is finally calcined at 1000°C to Ti02 (8). 

The external surface of a rutile crystal is almost entirely composed of the three crystal planes (1 10), (1 0 0) and (101). The relative area of each crystal face in a sample of finely divided rutile probably varies from one polycrystalline sample to another but it is generally assumed that 60-80% of the overall surface area of the powder is provided by the (1 10) plane, with the remainder divided equally between the two other planes (Jaycock and Waldsax, 1974 Boddenberg and Eltzner 1991). 

Dehydration of rutile crystals involves the removal of hydrogen-bonded water, coordinately bonded water and surface hydroxyls (dehydroxylation). The temperature ranges corresponding to these three stages overlap and depend on the rutile sample and the conditions of heat treatment. Generally the removal of molecular water occurs at temperatures of up to about 300°C and progressive dehydroxylation... 

LA-ICP-MS using a multi-collector instrument for Pb-Pb dating via ° Pb/ °" Pb and ° Pb/ ° Pb isotope ratio measurements of natural rutile crystals has been utilized to study geological temperature-time histories. The significance of Devonian-Carboniferous igneous activity in Tasmania on the basis of U-Pb dating has been measured by sensitive high resolution ion microprobe (SHRIMP). ... 

Experimental studies of single crystal TiOi surfaces have utilized almost exclusively the rutile crystal structure, which is more stable than the anatase or brookite structures. Most of the work reviewed here was carried out on the (110) or (001) crystal planes, so a short introduction to the structures and coordination environments of those planes is presented first. 

There is only one way to cut a rutile crystal in (001) direction (Fig. 16.) Although this creates a non-polar, autocompensated surface, it does not represent a low-energy configuration. This becomes clear immediately when reviewing the coordination of the surface atoms. All the Ti atoms are 4-fold coordinated, and all the O atoms 2-fold coordinated. Hence the number of broken bonds on this surface is higher than on the other low-index rutile surfaces discussed so far. Consequently, the (001) surface has a high surface... 

There are two crystalline forms widely used in papermaking applications, anatase and rutile. The major difference between the two is crystal uniformity and size, which yields a slightly higher index of refraction in the rutile crystal (Fig. 6.8). There are two chemical processing manufacturing routes commercially viable for titanium dioxide production, the sulphate and the chlorine process. The older sulphate method may be used to produce both anatase and rutile, while the more recent chlorine process is utilised only for rutile crystal production. 

FIGURE 6.11 Rutile crystal structure viewed nearly parallel to the z-axis. Each of the pairs of overlapping octahedra (e.g., P1/P2) shares an edge. The two octahedra in the lower right thus have point T in common. The central octahedron touches each of the eight at the corners. 

The synthesis of pure rutile is difficult, as the crystallization normally yields mixtures of two, or even all three, polymorphs. Rutile is usually prepared via a hydrothermal synthesis from chlorides and oxychlorides of titanium seeded with rutile nanocrystals at temperatures below 250 °C. The addition of hydrochloric acid and aqueous alcohol solutions facilitates the preparation of rutile at temperatures between 40 and 90 °C [148]. Despite the risk of contamination, mineralizers (e.g., Sn02, NH4CI or N aCl) are often used in order to reduce the size of rutile crystals. The reaction times of the hydrothermal synthesis of rutile can be significantly reduced by microwave irradiation [149]. A single-phase rutile with nanosized, well-dispersed particles prepared by a 2 h treatment of partially hydrolyzed 0.5 M TiCU solution at 160 °C is shown in Figure 1.9. 

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