Titanium trivalent

Whereas zirconium was discovered in 1789 and titanium in 1790, it was not until 1923 that hafnium was positively identified. The Bohr atomic theory was the basis for postulating that element 72 should be tetravalent rather than a trivalent member of the rare-earth series. Moseley s technique of identification was used by means of the x-ray spectra of several 2ircon concentrates and lines at the positions and with the relative intensities postulated by Bohr were found (1). Hafnium was named after Hafma, the Latin name for Copenhagen where the discovery was made. 

Titanium Dibromide. Titanium dibromide [13873-04-5] a black crystalline soHd, density 4310 kg/m, mp 1025°C, has a cadmium iodide-type stmcture and is readily oxidized to trivalent titanium by water. Spontaneously flammable in air (142), it can be prepared by direct synthesis from the elements, by reaction of the tetrabromide with titanium, or by thermal decomposition of titanium tribromide. This last reaction must be carried out either at or below 400°C, because at higher temperatures the dibromide itself disproportionates. 

Titanium Sulfates. Solutions of titanous sulfate [10343-61-0] ate readily made by reduction of titanium(IV) sulfate ia sulfuric acid solutioa by electrolytic or chemical means, eg, by reduction with ziac, ziac amalgam, or chromium (IT) chloride. The reaction is the basis of the most used titrimetric procedure for the determination of titanium. Titanous sulfate solutions are violet and, unless protected, can slowly oxidize ia coatact with the atmosphere. If all the titanium has been reduced to the trivalent form and the solution is then evaporated, crystals of an acid sulfate 3 Ti2(S0 2 [10343-61-0] ate produced. This purple salt, stable ia air at aormal temperatures, dissolves ia water to give a stable violet solutioa. Whea heated ia air, it decomposes to Ti02, water, sulfuric acid, and sulfur dioxide. 

If a chemical reaction regenerates the initial substance completely or partially from the products of the electrode reaction, such case is termed a chemical reaction parallel to the electrode reaction (see Eq. 5.6.1, case c). An example of this process is the catalytic reduction of hydroxylamine in the presence of the oxalate complex of TiIV, found by A. Blazek and J. Koryta. At the electrode, the complex of tetravalent titanium is reduced to the complex of trivalent titanium, which is oxidized by the hydroxylamine during diffusion from the electrode, regenerating tetravalent titanium, which is again reduced. The electrode process obeys the equations... 

Physical properties of binary or ternary Ru/Ir based mixed oxides with valve metal additions is still a field which deserves further research. The complexity of this matter has been demonstrated by Triggs [49] on (Ru,Ti)Ox who has shown, using XPS and other techniques (UPS, Mossbauer, Absorption, Conductivity), that Ru in TiOz (Ti rich phase) adopts different valence states depending on the environment. Possible donors or acceptors are compensated by Ru in the respective valence state. Trivalent donors are compensated by Ru5+, pentavalent acceptors will be compensated by Ru3+ or even Ru2+. In pure TiOz ruthenium adopts the tetravalent state. The surface composition of the titanium rich phase (2% Ru) was found to be identical to the nominal composition. 

The most widely studied transition metal is titanium. At various times, all oxidation states of titanium (II, III, IV) have been proposed for the active site of titanium-based initiators. Most of the evidence points to titanium (HI) as the most stereoselective oxidation state, although not necessarily the most active nor the only one [Chien et al., 1982]. (Data for vanadium systems indicate that trivalent vanadium sites are the syndioselective sites [Lehr, 1968].) Initiators based on the a-, y-, and 8-titanium trihalides are much more stereoselective (iso-selective) than those based on the tetrahalide or dihalide. By itself, TiCl2 is inactive as an initiator but is activated by ball milling due to disproportionation to TiCl3 and Ti [Werber et al., 1968]. The overall stereoselectivity is usually a-, y-, 8-TiCl , > TiCL > TiCLj P-TiCl3 [Natta et al., 1957b,c],... 

Although titanium retards the transformation of ferrihydrite (pH 6-11), it enhances the formation of goethite over hematite (Fitzpatrick Le Roux, 1976 Fitzpatrick et al., 1978). The opposite was found for trivalent chromium (Schwertmann et al., 1989) and vanadium (Schwertmann Pfab, 1994) besides retarding the transformation, higher concentrations of both ions led to enhanced hematite formation. 

Alum, KAl(S0i)i-l2H20.—Ammonium, rubidium, cesium, univalent thallium, and in some cases sodium may replace potassium, while the aluminum may be replaced by trivalent iron, chromium, indium, gallium, titanium, vanadium but not by the rare-earth metals. 

The trivalent iron is hydrolyzed together with the titanium compounds, and adheres to the titanium oxide hydrate. Therefore all the Fe3+ is reduced to Fe2+ by scrap iron during dissolution of the ilmenite product, or immediately afterwards. Reoxidation of the iron during subsequent processing is prevented with Ti3 + which is obtained by reducing a small part of the Ti4+. Alternatively, reduction of Ti4+ to Ti3+ can be carried out in part of the solution under optimized conditions this... 

Hydrated Vanadium Tri-iodide, VT3.6H20, is prepared by reducing, electrolytically, a solution of vanadium pentoxide, V2Os, in hydriodic add, until the product becomes green more hydriodic add is then added and the whole allowed to stand over lime and concentrated sulphuric add at 0° C. Small green needles separate, which have the same crystalline form as the hydrated trivalent halides of titanium, iron, and chromium. These crystals are extremely hygroscopic and deliquesce in air to a brown liquid8 which is extremely unstable. 

The result of the early work led to development of second-generation Ziegler catalysts (23-29). These are discussed in the next section and include (i) nonsupported trivalent titanium compounds, (ii) products of treating magnesium compounds with titanium compounds, and (iii)... 

Trivalent titanium has been positively identified by optical spectral measurements of a green calcic pyroxene from the meteorite that fell near Pueblo de Allende, Mexico, in 1969. The chemical analysis of this titanian pyroxene (Dowty and Clark, 1973) revealed it to be an iron-free subsilicic diopside (fas-saite) containing coexisting Ti3+ and Ti4+ ions and having the chemical formula Ca1.0lM 0.38,n3+0.34,n4+0.14Alo.87Sil.2606-... 

Mao, H.-K. Bell, P. M. (1974a) Crystal field effects of trivalent titanium in fassaite from the Pueblo de Allende meteorite. Ann. Rept. Geophys. Lab., Yearb. 73, 488-92. 

Prewitt, C. T., Shannon, R. D. White, W. B. (1972) Synthesis of a pyroxene containing trivalent titanium. Contrib. Mineral. Petrol., 35, 77-82. 

Depending on concentration of a hydrochloric acid during lixiviation of powders the process of saturation by gas develops ambiguously it has a sine wave character. The established dependence of an output in a solution of ions trivalent titanium on the concentration of a solution according to data, obtained by the method of electronic paramagnetic resonance, has shown that at small time of exposure (50-100 hrs) the output of ions of titanium in a solution proceeds with the increasing speed. The pure powders react with environment less actively, polluted -more intensively. The speed of saturation of powders by gas at corrosion in solutions of a hydrochloric acid is increased with growth of concentration, and then is sharply reduced. 

The activity was transported to ARCA II with a He(KCl) gas-jet within about 3 s. After deposition on a titanium slider it was dissolved and washed through the 1.6x8 mm column (filled with the cation-exchange resin Aminex A6, 17.5 2 pm) a flow rate of 1 mL/min with 0.1 M HNOj/5-10 4 M HF. 85% of the W elute within 10 s. Neither divalent or trivalent metal ions nor group-4 ions are eluted within the first 15 s. Also the pseudo-homologue uranium, in the form of U022+, is completely retained on the column. 

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