Crystal structures rutile

Black to blue-black powder, insoluble in acids. Crystal structure rutile type. 

Dark-gray powder with a metallic luster, iridesces green and blue. Insoluble in acids. Readily reduced by H2 even at moderate heating, d 7.0. Crystal structure rutile type. 

Formula weight 222.2. d 11.4. Black powder. Insoluble in water and acids. Forms OSO4 on heating in air readily reduced to the metal by H3. Crystal structure rutile type. 

Luehen, H. Elsenhans, U. Stamm, U. (1987). Low-Symmetric Coordination Polyhedra -Pseudosymmetry and Idealization, Acta Cryst. A, Vol.43, pp. 187-194 Meogher, E.P. Lager, G.A (1979). Polyhedral Hermale Xpansion in that Ion, Polymorphs Refinement of the Crystal Structures Rutile and Brookite at High Temperature, Canadian Mineralogist, Vol.l7, pp. 77-85... 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

This theoretical result is completely substantiated by experiment. Goldschmidt,31 from a study of crystal structure data, observed that the radius ratio is large for fluorite type crystals, and small for those of the rutile type, and concluded as an empirical rule that this ratio is the determining factor in the choice between these structures. Using Wasastjerna s radii he decided on 0.67 as the transition ratio. He also stated that this can be explained as due to anion contact for a radius ratio smaller than about 0.74. With our radii we are able to show an even more satisfactory verification of the theoretical limit. In Table XVII are given values of the radius ratio for a large number of compounds. It is seen that the max-... 

Three forms of titanium dioxide, Ti02, are known. Of these the crystal structures of the two tetragonal forms, rutile and anatase, have been thoroughly investigated2) in each case only one parameter is involved, and the atomic arrangement has been accurately determined. The third form, brookite, is orthorhombic, with axial ratios... 

Titania photocatalyst is used for air and water purification, photo-splitting of water to produce hydrogen, odor control and disinfectant. Crystal structure and crystallite size of titania particles are one of the most important factors that affect on the photoactivity. Photoactivity of anatase is higher than that of rutile, and increases with crystallite size [1]. Therefore, to increase photoactivity, it is desirable to find a route for the synthrais of the pure anatase titania with large crystallite size. 

The similarity of the structures of rutile, CaCl2 and marcasite also comes to light by comparison of their crystal structure data (Table 17.2). The space groups of CaCl2 and marcasite (both Pnnm) are subgroups of the space group of rutile. The tetragonal sym-... 

There are three crystal structures of titanium dioxide rutile, anatase, and brookite. The most active phase is rutile, which has a tetragonal structure [133], as shown in Figure 8.5 [134],... 

The aggregation of vacancies or interstitials into dislocation loops will depend critically upon the nature of the crystal structure. Thus, ionic crystals such as sodium chloride, NaCl, or moderately ionic crystals such as corundum, AI2O3, or rutile, TiC>2, will show different propensities to form dislocation loops, and the most favorable planes will depend upon chemical bonding considerations. 

Table 2.1 shows the crystal structure data of the phases existing in the Mg-H system. Pnre Mg has a hexagonal crystal structure and its hydride has a tetragonal lattice nnit cell (rutile type). The low-pressure MgH is commonly designated as P-MgH in order to differentiate it from its high-pressure polymorph, which will be discussed later. Figure 2.2 shows the crystal structure of p-MgH where the positions of Mg and H atoms are clearly discerned. Precise measurements of the lattice parameters of p-MgH by synchrotron X-ray diffraction yielded a = 0.45180(6) mn and c = 0.30211(4) nm [2]. The powder diffraction file JCPDS 12-0697 lists a = 0.4517 nm and c = 0.30205 nm. The density of MgH is 1.45 g/cm [3]. 

Studies of the V20a-V204 system have confirmed that the phases V 02 i ( = 2—9) exist below 1400°C. ° The crystal structure of V4O7 has been shown to be based on the rutile lattice, the VOg octahedra being considerably distorted with V—O = 178—212 pm. The heat and entropy of formation of Vj Ojj at 1333 K have been determined as —373 kJmol and 146Jmol K respectively, by electrochemical measurements. ... 

Rutile and anatase are used in photocatalysis and as catalyst supports and we describe some important structural features later. The titanium-oxygen system plays a key role in understanding stoichiometric variations. The highest oxide, Ti02, is polymorphic and the four known crystal structures are rutile, anatase, brookite and a high-pressure form similar to a-Pb02. 

FIGURE 1.41 The crystal structure of rutile, T102. (a) Unit cell, (b) parts of two chains of linked [TiOe] octahedra, and (c) projection of structure on base... 

Hiickel calculations have been employed extensively in other approaches such as the angular overlap model and the method of moments developed by Burdett and coworkers. Stabilities of crystal structures, pressure- and temperature-induced transitions, dynamical pathways in reactions and other phenomena have been analysed using angular overlap models. Thus, the electronic control of rutile structures and the stability of the defect structure of NbO have been examined (Burdett, 1985 Burdett Mitchell, 1993). In the case of NbO, the structure is stable at involving the formation... 

In certain cases, distortion may be imposed by the crystal structure. Nickel and palladium(II) fluorides have the rutile structure (16, 18, 239) in the nickel salt the fluoride octahedron is slightly flattened, whereas in palladium(II) fluoride, it is elongated. The metal-fluorine distances are shown in Table VIII. The fluoride is, incidentally, the only paramagnetic... 

With the aid of the data of Appendix F, predict the crystal structure of magnesium fluoride. (The observed structure is of the rutile type.)... 

When the ratio of the radii increases, then a new type of crystal structure occurs, in which each divalent ion is surrounded by six univalent ions, and each univalent by three divalent ones. This arrangement, shown in Figure 14, is called the rutile type, named after the mineral Ti02. While CaF2 still has the structure with 8 4 coordination, the rutile structure is observed in MgF2 because of the smaller radius of the Mg2+ ion. After the rutile type there is a further reduction of the coordination to 4 2 this type of structure occurs in BeF2 and Si02 in the different modifications of silica, each silicon ion is surrounded by 4 O2" ions, and each O2 ion is between two Si4+ ions. The ionic ratio r+/r can also be decreased if,... 

It has recently been recognized that crystal structure and particle size can also influence photoelectrochemical activity. For example, titanium dioxide crystals exist in the anatase phase in samples which have been calcined at temperatures below 500 °C, as rutile at calcination temperatures above 600 °C, and as a mixture of the two phases at intermediate temperature ranges. When a range of such samples were examined for photocatalytic oxidation of 2-propanol and reduction of silver sulfate, anatase samples were found to be active for both systems, with increased efficiency observed with crystal growth. The activity for alcohol oxidation, but not silver ion reduction, was observed when the catalyst was partially covered with platinum black. On rutile, comparable activity was observed for Ag, but the activity towards alcohol oxidation was negligibly small . Photoinduced activity could also be correlated with particle size. 

As a result, they confirmed the existence of the homologous compounds expressed by V O2 i, Ti Oj -1 etc. (n = 2, 3, 4,...) and also predicted that the crystal structure of these compounds could be derived from a mother structure, rutile . 

Table 13-16.—Radios Ratio Values fob Crystals with Rutile and Fluobitb Structures...

The crystal structure of the pigments is determined by X-ray analysis which is sensitive enough to determine 0.3-0.5% anatase in the presence of 99.7-99.5% rutile. For standards, see Table 1 (Titanium dioxide pigments Methods of analysis and Specification ). 

Fig. 4.4 Crystal structures of two more 1 2 compounds oxygen is the larger circle in both (a) unit cell of rutile, Ti02l tetragonal, space group Pd1fmmr, (b) unit cell of 0-crKtobaiite, SiO, [From Ladd. M. F C. Structure and Bonding in Solid State Chemistry, Wiley ...

The concentrated mother liquor contains a laige amount of sulfuric acid in a free form, as titanium oxy-sulfate, and as some metal impurity sulfates. To yield the purest form of hydrated Ti02, the hydrolysis is carried out by adding crystallizing seeds to the filtrate and heating the mixture close to its boiling temperature, 109° C. The crystal structure of the seeds (anatase or rutile) and their physical properties affect the pigmentary characteristics of the final product. 

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