Titanium hydrated oxide

Hydrolysis of solutions of Ti(IV) salts leads to precipitation of a hydrated titanium dioxide. The composition and properties of this product depend critically on the precipitation conditions, including the reactant concentration, temperature, pH, and choice of the salt (46—49). At room temperature, a voluminous and gelatinous precipitate forms. This has been referred to as orthotitanic acid [20338-08-3] and has been represented by the nominal formula Ti02 2H20 (Ti(OH). The gelatinous precipitate either redissolves or peptizes to a colloidal suspension ia dilute hydrochloric or nitric acids. If the suspension is boiled, or if precipitation is from hot solutions, a less-hydrated oxide forms. This has been referred to as metatitanic acid [12026-28-7] nominal formula Ti02 H2O (TiO(OH)2). The latter precipitate is more difficult to dissolve ia acid and is only soluble ia concentrated sulfuric acid or hydrofluoric acid. 

The structure of these products is uncertain and probably depends on pH and concentrations in solution. The hydroxyl or carboxyl or both are bonded to the titanium. It is likely that most, if not all, of these products are oligomeric in nature, containing Ti—O—Ti titanoxane bonds (81). Thek aqueous solutions are stable at acidic or neutral pH. However, at pH ranges above 9.0, the solutions readily hydroly2e to form insoluble hydrated oxides of titanium. The alkaline stabiUty of these complexes can be improved by the addition of a polyol such as glycerol or sorbitol (83). These solutions are useful in the textile, leather (qv), and cosmetics (qv) industries (see Textiles). 

The principal use for the tetrachloride is in pyrots as a smoke agent (called FM ), Ref 5 reports that the tetrachloride. . is extremely reactive resulting in the formation of hydrated oxides, or with atmospheric moisture and, when used for screening, is often disseminated from aircraft spray tanks. Its reaction with water vapor is relatively complex. First, the titanium tetrachloride is hydrated. This reaction is followed by further hydrolysis yielding, finally, titanium hydroxide and HC1. The smoke consists of a mixture of fine particles of solid titanium hydroxide, Ti(0H)4 the hydrated oxide, Ti02-H20 intermediate hydroxychlorides of titanium and dilute HC1 droplets. The sequence of reaction is ... 

One can see that decomposition temperatures of these compounds are within temperature range 40-600°C. Some compounds, such as monohydrate of lithium hydroxide (40°C), hydrated titanium dioxide (60°C), iron hydroxide (100°C), manganese (145°C) and cobalt (150°C) hydroxides, tungsten acid (180°C), etc., start to release water at relatively low temperatures. Other compounds decompose at a temperature above 200°C. No correlation between formation enthalpy and thermal stability of hydroxides and hydrated oxides is observed. 

When this aqueous mixture is allowed to stand under vacuum, solid FeS04 7H2O forms and is removed. The mixture remaining is then heated, and the insoluble titanium(lV) oxide hydrate (Ti02 H20) forms. The water of hydration is driven off by heating to form pure Ti02 ... 

The two most important sources of uranium are the minerals carnotite, where uranium occurs in the hexavalent oxide or hydrated oxide, and pitchblende, where uranium occurs mostly in the tetravalent state as a compound salt with other metals. It also occurs as a mixed oxide with titanium, thorium, and niobium in the tetravalent form. The tetravalent uranium minerals appear to have been geologically formed in the presence of reducing agents such as hydrocarbon minerals, graphite, native metals, and sulfide minerals, while such association is rarely observed with the hexavalent uranium minerals. 

There are two major processes for the manufacture of titanium dioxide pigments, namely (1) sulfate route and (2) chloride route. In the sulfate process, the ore limonite, Fe0Ti02, is dissolved in sulfuric acid and the resultant solution is hydrolyzed by boiling to produce a hydrated oxide, while the iron remains in solution. The precipitated titanium hydrate is washed and leached free of soluble impurities. Controlled calcinations at about 1000°C produce pigmentary titanium dioxide of the correct crystal size distribution this material is then subjected to a finishing coating treatment and milling. The process flow sheet is shown in Fig. 7.1 [4],... 

The hydrated oxides of titanium, zirconium and hafnium are soluble in acids, but heating produces oxides which resist solution, as it does with AlgOg and CrgOg. 

Titanium(iv) Complexes. Aqueous Chemistry Oxo Salts. There is no simple aquated Ti4+ ion because of the high charge-to-radius ratio, and in aqueous solutions hydrolyzed species occur and basic oxo salts or hydrated oxides may be precipitated. Although there have been claims for a titanyl ion, Ti02 +, this ion appears not to exist either in solutions or in crystalline salts such as Ti0S04-H20. The latter has been shown to have (TiO)2"+ chains Ti Ti... 

The barium bis-isopropoxide was prepared by the metal/alcohol reaction method. Appropriate amounts of these alkoxides were dissolved in a mutual solvent, such as isopropyl alcohol or benzene, for a barium and titanium molar ratio of 1 1. The solution was refluxed for 2 h with vigorous stirring before the hydrolysis reaction. Drops of deionized triply distilled water were slowly added to the solution, which was continuously stirred. The reaction was carried out in a C02-free atmosphere. The hydrated oxide was dried in vacuum or in a dry helium atmosphere at 50°C for 12 h. At this stage the oxide was a finely divided, stoichiometric titanate with 50-150 A (maximum agglomerate size <1 pm) particles and was more than 99.98% pure. TEM photomicrographs of the as-prepared and the calcined (700°C for 1 h) powders are shown in Fig. 8. The rectilinear symmetry of the particles is evident in the calcined powders. 

Finally, let us cite a number of new publications dealing with the preparation and testing of hydrated oxide gels hydrated aluminum oxides [30, 32] silica gels, unmodified [11, 13, 16, 21, 27] silica gels, modified [1-4, 9, 14, 19] hydrated titanium oxides [8, 15, 28, 33, 34] hydrated chromiiun oxides [5, 10, 18, 23-25] ... 

Titanium dioxide is not hygroscopic, and does not form true hydrate phases. It is possible to prepare hydrated titanium oxide materials through the addition of alkali-metal hydroxides to a solution of a Ti(II) or Ti(III) salt. The resulting titanium hydroxide precipitate is extremely unstable, is a powerful reducing agent, and rapidly converts to a hydrated oxide material [4]. 

If the precipitation is performed at room temperature, one obtains a compound known as orthotitanic acid, and which has the approximate formula of TiOj 2HjO Ti(OH)4. If the suspension is boiled, or if the precipitation is effected from a hot solution, a compound known as metatitanic acid is obtained. This less hydrated oxidic compound has the approximate formula of Ti02 H20 Ti0(0H)2. Metatitanic oxide is commonly obtained in the colloidal state, and is the preferred intermediate in the manufacture of titanium dioxide pigments. 

As one of the transition elements, titanium can be readily precipitated with ammonium, sodium, or potassium hydroxide. The hydrated oxide is ignited to constant weight at any temperature exceeding 350 C. The method is not useful for complicated samples containing other cations which could be precipitated by hydroxide, but is very applicable to the analysis of U.S.P. grade titanium dioxide. 

If it is necessary to extract the rare metal from an acid or alkaline leach liquor, or similar solution, a resin should be selected which is known to be stable in the leaching reagent. For extraction of the rare metal ion itself, the resin would normally be of the cation-exchange type, unless the rare metal ion could be converted to an anionic complex. However, the possibility of designing a process in which the impurities are absorbed by the resin and the rare metal remains unextracted, should not be neglected. An example of this type has been developed by Ayres,i > in which iron, titanium, lanthanum and beryllium impurities are extracted from a zirconium nitrate solution by operation at a pH where the zirconium is converted to a non-ionic hydrated oxide sol. 

A process has been developed by Ayres for the purification of zirconium, in which the various impurities are absorbed upon a cation-exchange resin. The zirconium itself is not absorbed as it is in the colloidal condition. This state is not difficult to achieve with, for example, zirconyl nitrate ZrO(NOs)2, since it is normally hydrolysed to the highly insoluble hydrated oxide in a neutral or near neutral solution. A zirconium ore is therefore broken in concentrated sulphuric acid and the soluble zirconium sulphate converted to the nitrate by suitable means and passed through a column of resin in the usual manner. Amberlite I.R.-100 has been used, in the hydrogen form. Impurities such as iron, beryllium and rare earth elements are absorbed completely, together with about 80 per cent of the titanium. The resin capacity for zirconium, however, is as low as 0-84 mmoles/100 cm of resin, and it is therefore recovered virtually completely in the pure column effluent. The very small amount of zirconium taken up by the resin is probably retained by a surface absorption process rather than true ion-exchange. The zirconium can be precipitated by alkah from the effluent as the hydrated oxide, in massive form, for conversion to other compounds and finally to metal. The resin is regenerated for further use by elution of the cation impurities with, for example, dilute sulphuric acid. 

Titanium dioxide is insoluble in H2O. The hydrated oxide, Ti02-aq, is slightly amphoteric, with both basic and acidic salts hydrolyzing readily to Ti02-aq. Boiling makes it less hydrated and less soluble. 

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