Titanium standard reduction potentials

For solutions with unit activities of ions, the standard reduction potentials for these reactions are 0.337 Vsh and -1.630 Vsh. respectively The reduction potentials in our case are shifted in the active direction however because the activities of the metal ions in solution are less than unity. Because the reduction potential of titanium is more active (more negative) than that of copper, the reduction of copper ions by the titanium metal and the concurrent oxidation of titanium metal by the copper ions will be thermodynamically favored. 

If it is shown that titanium can be used as a sacrificial anode to protect iron, what conclusion can be drawn about the standard reduction potential of its half-reaction ... 

Platinum—The high standard reduction potential for platinum makes it an ideal anode material (although Pt corrosion does occur during some oxidations reactions, such as the Kolbe oxidative coupling reaction [29, 58, 59]). For anode potentials greater than about 0.50 V (on the hydrogen scale), an oxide film covers the Pt surface, so the electrode material is often platinum oxide. Large anodes are often titanium coated with platinum in order to reduce costs. 

As a result of the high ionic charge to radius ratio of titanium(IV), normal salts of titanium(IV) are difficult to prepare from aqueous solutions these often yield basic, hydrolyzed species. A tris-catechol species, [Ti(cat)3], prepared by Raymond etal. is one exception it is stable in aqueous solution up to pH 12. The catechol ligand is so stabilizing to Ti that the Ti ATi reduction potential is shifted from the value of -1-0.1V cited as the standard potential in acid in Scheme 1 to a value for [Ti(cat)3] of -1.14 V vs. NHE, affording a powerful example of ligand tuning of metal redox potential. 

Flow controllers set the rates of both streams, one being under flow-ratio control. In principle, either caustic soda or dilution water can be the master stream, with the other following it to maintain the ratio. Blending is controlled by a feedforward system, ultimately reset by the product concentration or density. Feedback from caustic concentration measurement (usually by density) could be used for final adjustment, but the concentration of the hypochlorite solution is the more important variable. The simple flow-ratio controller mentioned here can be replaced by a multi-stream version that allows use of other streams in addition to the principal 50% NaOH and dilution water. A cooler downstream of the mixing point removes the heat of dilution. The standard design is a titanium plate exchanger, which can also provide turbulence to complete the mixing process. Chlorine joins the diluted caustic in the reactor. Its rate of addition is controlled by an oxidation-reduction potential (ORP) instrument. The reaction mass recirculates from a collection tank around the system to reduce the increase of temperature across the reactor and to promote turbulence. The net production is removed from the tank, normally under level control. 

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. 

The shape of the curve for an oxidation-reduction titration depends on the nature of the system under consideration. The titration curve in Fig. 7 is symmetric about the equivalence point because the molar ratio of oxidant to reductant is equal to unity. An asymmetrical curve results if the ratio differs from this value. Solutions containing two oxidizing or reducing agents yield titration curves containing two inflection points if the standard potentials for the two species are different by more than approximately 0.2 V. Fig. 8 shows the titration curve for a mixture of iron(II) and titanium(III) with cerium(rV). The first additions of cerium are used by more readily oxidized titanium(III) ion, thus, the first step in the titration curve corresponds to titanium and the second to iron. 

It has been demonstrated that the half-wave potential for the reduction of Ti(IV) to Ti(III) is -0.81 V (against the standard calomel electrode) in 0.1 M HCl [27]. The further reduction of Ti(III) to Ti(ll) can be observed in alkaline media, but this reaction has no useful analytical significance. In these methods, oxalate, tartrate, or citrate buffer systems are used as supporting electrolytes to prevent the hydrolytic precipitation of hydrated titanium oxides. In the presence of tartrate buffer, well defined waves are obtained only at pH values less than 2, or between 6 and 7. The Ti(lV)-Ti(III) couple is reversible only in tartrate buffer at pH values less than 1. 

Abstract - The standard potentials of the reaction steps for the reduction of TiCLi in alkali chlorides were calculated from transient electrochemical techniques. It is shown that the stability ranges of the various oxidation states of titanium depend on the composition and temperature of the solvent. The presence of strong chloride ion donors, such as cesium chloride, enhances the stability of the high oxidation states. The results are interpreted in terms of formation of chlorocomplexes. The thermodynamic properties of solutes were calculated and the Gibbs energy of dissolution of the titanium salts determined. 

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