The oxides of titanium

The elements Ti and V illustrate very well the extraordinary complexity of some metal-oxygen systems. 

Successive layers in the structure of TiO (defect NaCl superstructure). The small black dots indicate vacant cation or anion sites (one-sixth of the total of each kind). 

Interpolation gives 85 per cent of each type of site occupied at the composition TiO. 

The highest oxide is the familiar Ti02. The three forms stable at atmospheric pressure, rutile, anatase, and brookite, all occur as minerals. These three polymorphs, together with the high-pressure form with the a-PbOj structure, are all 

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The aforementioned inconsistencies between the paralinear model and actual observations point to the possibility that there is a different mechanism altogether. The common feature of these metals, and their distinction from cerium, is their facility for dissolving oxygen. The relationship between this process and an oxidation rate which changes from parabolic to a linear value was first established by Wallwork and Jenkins from work on the oxidation of titanium. These authors were able to determine the oxygen distribution in the metal phase by microhardness traverses across metallographic sections comparison of the results with the oxidation kinetics showed that the rate became linear when the metal surface reached oxygen... 

In the chloride process, developed in about 1960, the titanium in the ore is converted to titanium(IV) chloride by heating it to 800 °C with chlorine in the presence of carbon, which combines with the released oxygen. The purified chloride is then oxidised to titanium dioxide at 1000 °C and the chlorine formed is recycled. Technical problems arise because the oxidation of titanium(IV) chloride is not sufficiently exothermic to make the reaction self-sustaining but these can be overcome by pre-heating the reactants and by burning carbon monoxide in the reactor to raise the temperature. By careful control of the conditions, it is possible to produce pure rutile particles of a mean size of 200 nm. 

In related studies of metal ions, Krasnovski learned that the oxides of titanium, zinc, or tungsten possess high photosensitizing activity in redox reactions comparable to the activity of porphyrins and chlorophylls 15). 

As described previously, flame s3mthesis reactions include the oxidation of silicon chloride to produce silica the oxidation of titanium chloride to produce titania and the oxidation of other metal chlorides (see Table 7.2 also). 

For the sake of completeness, it should be mentioned that at variance with the corresponding silyl enolates, the oxidation of titanium bis(enolates) with a variety of oxidants does not show any diastereoselectivity in the formation of the enolate coupling product . On the basis of crossover experiments, it has been shown that the C—C bond formation occurs via an intramolecular route in the case of the silyl derivatives and intermolecularly in the case of the titanium derivatives. 

The interaction of titanium and copper ions during polishing may be illustrated schematically by the polarization diagrams shown in Figure 4,44. In creating Figure 4,44, we have assumed that the reduction of Oj (Equation 4.4) drives the oxidation of titanium in the absence of Cu ions. The data used to construct Figure 4.44 are ... 

The oxidation of titanium enolato complexes, derived from a transmetallation reaction of the corresponding lithium enolates with Cp2TiCl2, by dimethyldioxirane has been investigated as a general, convenient, effective, and chemo- and diastereoselective synthesis of cr-hydroxy carbonyl compounds. The Cp derivative shown in Scheme 601 results in much higher diastereoselectivities than other enolato complexes studied.1556... 

Processing of bauxite to produce alumina produces volumes of red muds, which contain principally water, iron oxide, silica, and the oxides of titanium, chromium, vanadium, and aluminum. The solids in this mixture eventually settle to a relatively high solids content sludge, so that a moderately sized holding pond may be used for many years. 

Reaction 10.11 involves the oxides of titanium and carbon, and the chloride of titanium thus we shall make use of both the chloride and the oxide diagrams (Figs. 10.3 and 10.1). The reaction takes place between 1000 and 1250 K. At 1100, AG° for equation 10.11 is ... 

Effect of Complex Environments on the Oxidation of Titanium Aluminides... 

In industrial applications the environments usually contain more than one reactant. For example high temperature oxidation occurs in air by the combined attack of oxygen, nitrogen and quite frequently water vapour. However, most of the studies concerning the oxidation resistance are performed in dry oxygen or dry air. The oxidation behaviour of the intermetallic phases of theTi-Al system has recently received considerable attention. The influence of water vapour on the oxidation of titanium aluminides has not been studied intensively. There are only a few studies of the high temperature corrosion of titanium and its alloys. 

A variety of other nanoparticles have been formed by such in situ sol-gel reactions. Examples are the oxides of titanium, aluminum, - tanta-lum, zirconium, niobium, and vanadium. Some nanocomposites of this type have also included barium titanate, calcium oxide, calcium salts, borates, HTiNbOg, and Eu dopants. ... 

Redox reactions in thionyl chloride include the oxidation of titanium(III) salts58. 

Electrochemical techniques have often been used to study the thermodynamics of solutions. The present study shows that the oxidation of titanium ions in fused alkali chlorides depends dramatically on the composition of the melt. Large cations weakly bonded to chloride ions, such as cesium ions, promote the formation of titanium hexachlorocomplexes, TiCl or TiCl , and results in a large stability range for the high oxidation states. Ti " reduces directly to metallic titanium. This behaviour is similar to that obtained with stronger ligands such as fluoride ions [9, 22]. 

Even more pronounced changes in chemisorption properties are observed using the oxides of titanium, vanadium, tantalum, and niobium as supports. The Strong Metal Support Interaction (SMSI) " occurs when the catalyst is reduced at high temperatures (about 773 K) and is believed to be due to a combination of effects ... 

In the case of the oxidation of titanium, the very regular repetition of the void bands between the rutile (oxide Ti02) layers is observed. The layer thickness decreases when the temperature is increased from 700 C to 950 C, whereas the void bands evolve inversely. It does not seem to depend on the initial sample thickness however the layers are not formed when the sample is too thin. Finally, if the oxide is kept under the reaction conditions, the bands may disappear through recrystallization the layers bind together and the scale becomes homogeneous and compact. 

The oxides of 48 metals were screened by the Ttacor Co. in a project conducted for the U.S. National Air Pollution Control Administration to determine which were best suited for the removal of sulfur oxides from flue gases by chemical reaction (Thomas et al.. 1969). The screening was accomplished by consideration of the thermodynamic requirements for efficient sulfur oxide removal and product regeneration. Sixteen potential sorbents were selected as a result of this screening process. These were the oxides of titanium, zirconium, hafnium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, aluminum, tin, bismuth, cerium, thorium, and uranium. 

In general, metal oxides, with the exception of those mentioned below, do not react with aluminium. This is the case of the oxides of titanium, zirconium (zircon), chromium, molybdenum, tungsten, iron, nickel, zinc, cadmium, aluminium (alumina, corindon), and silicon (silica). 

Harkins and Dahlstrom [31] have shown that the oxides of titanium, tin and zinc act like water in attracting polar rather than nonpolar groups. Thus in oils any -COOH, -OH, -CN and other similar groups orient towards the oxide powder and the hydrocarbon groups orient themselves towards the oil. 

Studies on the photochemical activity of pigments in polymers have, in fact, been mainly concerned with white pigments. Of all the white pigments used in commercial polymers, in particular polyalkenes and nylons, the oxides of titanium and zinc provide the most useful basis for discussion. 

The oxidation of titanium(m) chloride by chlorinated alkyl cyanides has been shown to result in the formation of Ti -chloroalkyl cyanide species, the mechanism suggested involving the transfer of a chlorine atom from the co-ordinated alkyl cyanide to the metal followed by loss of a CCI2CN group. A comparative spectro-electrochemical, stopped-flow kinetic, and polaro-graphic study has been made on the Ti i-hydroxylamine reaction. rate has been shown to be dependent on pH, and in the presence of 0.2M-oxalic acid (H2OX) the proposed reaction scheme may be expressed as... 

Sb, SI, Te, Se, etc. do. The oxides of titanium, tungsten, and molybdenum reaot slowly with HF. 2 5 also react... 

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