Titanium, oxidation states

Titanium oxidation state Fluoride Chloride Bromide Iodide... 

The Ti02 (001) surface was cleaned and reduced by cycles of ion bombardment as previously described [3]. The distribution of titanium oxidation states was determined from cxirve fitting the Ti(2p3/2) envelope in x-ray photoelectron spectra [3]. After surface preparation, reaction experiments were conducted in either the TPD or steady state mode. TPD experiments have been described [1]. XPS spectra were also obtained following a saturation exposure of the sample using the same procedure as that for the TPD experiments. After pump down, the crystal was placed under the Mg X-ray source and the Ti(2p), 0(ls), and C(ls) regions were scanned. For steady-state experiments a dosing needle was aligned perpendicular to the axis of the mass spectrometer. It was used to direct a steady beam of methylacetylene (Linde, 95%) at the crystal surface when the sample was placed at the aperture of the mass spectrometer. Steady state reaction experiments were... 

Presence of Titanium Oxidation-State Species in a PtlTiO (lOO) System as Determined by Angular-Resolved XPS... 

Case Study 1 - Titanium Oxidation States ON Titanium Thin Films and Bulk Surfaces... 

Chloride melts generally lead to powdery or dendritic deposits due to the existence of three low-stability titanium oxidation states and disproportionation reactions. In fluoride melts, only two oxidation states exist and the high stability of the titanium fluoride complexes results in two reduction steps ... 

In this oxidation state the titanium atom has formally lost its 3d and 4s electrons as expected, therefore, it forms compounds which do not have the characteristics of transition metal compounds, and which indeed show strong resemblances to the corresponding compounds of the lower elements (Si, Ge, Sn, Pb) of Group IV—the group into which Mendeleef put titanium in his original form of the periodic table. 

With the outer electronic configuration 3d 4s vanadium can attain an oxidation state of -I- 5, but it shows all oxidation states between -I- 5 and -I- 2 in aqueous solution (cf titanium). 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

Impurities that form volatile chlorides leave as gases at the top of the furnace together with the TiCl. By cooling those gases, most impurities, with the exception of vanadium and siUcon chlorides can be separated from the titanium tetrachloride [7550-45-0]. Vanadium chlorides can be reduced to lower oxidation state chlorides that are soHds highly volatile SiCl can be removed from TiCl by fractional distillation. 

In iadustrial production of titanium carbide, pure (99.8%, with minor impurities of Si, Fe, S, P, and alkahes) titanium oxide [13463-67-7] Ti02, iu the dry or wet state is mixed iu 68.5 31.5 ratio with carbon black or finely milled low ash graphite. The dry mixture is pressed iato blocks that are heated iu a horizontal or vertical carbon-tube furnace at 1900—2300°C hydrogen that is free of oxygen and nitrogen serves as protective gas. In the vertical push-type furnaces, the Hberated CO itself provides protection. 

The chemistry of hafnium has not received the same attention as that of titanium or zirconium, but it is clear that its behaviour follows that of zirconium very closely indeed with only minor differences in such properties as solubility and volatility being apparent in most of their compounds. The most important oxidation state in the chemistry of these elements is the group oxidation state of +4. This is too high to be ionic, but zirconium and hafnium, being larger, have oxides which are more basic than that of titanium and give rise to a more extensive and less-hydrolysed aqueous chemistry. In this oxidation state, particularly in the case of the dioxide and tetrachloride, titanium shows many similarities with tin which is of much the same size. A large... 

Table 21.2 Oxidation states and stereochemistries of titanium, zirconium and hafnium...

Perhaps because of inadequate or non-existent back-bonding (p. 923), the only neutral, binary carbonyl so far reported is Ti(CO)g which has been produced by condensation of titanium metal vapour with CO in a matrix of inert gases at 10-15 K, and identified spectroscopically. By contrast, if MCI4 (M = Ti, Zr) in dimethoxy-ethane is reduced with potassium naphthalenide in the presence of a crown ether (to complex the K+) under an atmosphere of CO, [M(CO)g] salts are produced. These not only involve the metals in the exceptionally low formal oxidation state of —2 but are thermally stable up to 200 and 130°C respectively. However, the majority of their carbonyl compounds are stabilized by n-bonded ligands, usually cyclopentadienyl, as in [M(/j5-C5H5)2(CO)2] (Fig. 21.8). 

Platinised-titanium anodes may also be used in soils when surrounded by a carbonaceous backfill. Warne and Berkeley " have investigated the performance of platinised-titanium anodes in carbonaceous backfills and conclude that the anodes may be successfully operated in this environment at a current density of up to 200 AmThis also supplements the findings of Lewis, who states that platinised-titanium anodes may be used in carbonaceous backfill without breakdown of the titanium oxide film. Success with platinised-titanium anodes has been reported with anodes operating at a few tens of Am and failures of anodes have often been attributed to operation at high current densities . 

The maximum oxidation state observed for the elements first increases and then decreases as we go across the transition row. Thus we have 4-3 for scandium, 4-4 for titanium, 4-5 for vanadium, 4-6 for chromium, and 4-7 for manganese. The 4-7 represents the highest value observed for this transition row. After manganese, the maximum value diminishes as we continue toward the end of the transition row. 

It is possible to titrate two substances by the same titrant provided that the standard potentials of the substances being titrated, and their oxidation or reduction products, differ by about 0.2 V. Stepwise titration curves are obtained in the titration of mixtures or of substances having several oxidation states. Thus the titration of a solution containing Cr(VI), Fe(III) and V(V) by an acid titanium(III) chloride solution is an example of such a mixture in the first step Cr(VI) is reduced to Cr(III) and V(V) to V(IV) in the second step Fe(III) is reduced to Fe(II) in the third step V(IV) is reduced to V(III) chromium is evaluated by difference of the volumes of titrant used in the first and third steps. Another example is the titration of a mixture of Fe(II) and V(IV) sulphates with Ce(IV) sulphate in dilute sulphuric acid in the first step Fe(II) is oxidised to Fe(III) and in the second jump V(IV) is oxidised to V(V) the latter change is accelerated by heating the solution after oxidation of the Fe(II) ion is complete. The titration of a substance having several oxidation states is exemplified by the stepwise reduction by acid chromium(II) chloride of Cu(II) ion to the Cu(I) state and then to the metal. 

Other ions which are reduced in the reductor to a definite lower oxidation state are those of titanium to Ti3+, chromium to Cr2+, molybdenum to Mo3+, niobium to Nb3+, and vanadium to V2 +. Uranium is reduced to a mixture of U3 + and U4+, but by bubbling a stream of air through the solution in the filter flask for a few minutes, the dirty dark-green colour changes to the bright apple-green colour characteristic of pure uranium(I V) salts. Tungsten is reduced, but not to any definite lower oxidation state. 

Unsubstituted bisphthalocyanines 2 are formed in the presence of several elements which exist in a stable oxidation state of + III or +IV such as titanium, zirconium, hafnium, indium and most of the lanthanide and actinide elements. 

D.20 The formal rules of chemical nomenclature result in a certain compound used for electronic components being called barium titanate(IV), in which the oxidation state of titanium is +4. See if you can work out its likely chemical formula. When you have identified the rules for naming oxoanions, suggest a formal name for H,S04. 

A number of metal oxides are known to form nonstoicbiometric compounds, in which the ratios of atoms that make up the compound cannot be expressed in small whole numbers. In the crystal structure of a nonstoichiometric compound, some of the lattice points where one would have expected to find atoms are vacant. Transition metals most easily form nonstoichiometric compounds because of the number of oxidation states that they can have. For example, a titanium oxide with formula TiO, I( is known, (a) Calculate the average oxidation state of titanium in this compound. 

The most common oxidation state of titanium is +4, in which the atom has lost both its 4s-electrons and its two 3d-electrons. Its most important compound is tita-nium(IV) oxide, Ti02, which is almost universally known as titanium dioxide. This oxide is a brilliantly white (when finely powdered), nontoxic, stable solid used as the white pigment in paints and paper. It acts as a semiconductor in the presence of light, and so it is used to convert solar radiation into electrical energy in solar cells. 

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