Oxides and Oxide-hydroxides

The most important synthetic routes to iron oxide pigments involve either thermal decomposition or aqueous precipitation processes. A method of major importance for the manufacture of a-Fe203, for example, involves the thermal decomposition in air of FeS04-7H20 (copperas) at temperatures between 500 °C and 750 °C. The principal method of manufacture of the yellow a-FeO(OH) involves the oxidative hydrolysis of Fe(n) solutions, for example in the process represented by reaction (1). 

The reaction is sustained by addition of iron metal which reacts with the sulfuric acid formed, regenerating Fe(n) in solution. To ensure that the desired crystal form precipitates, a seed of a-FeO(OH) is added. However, with appropriate choice of conditions, for example of pH and temperature and by ensuring the presence of appropriate nucleating particles, the precipitation process may be adapted to prepare either the orange-brown y-FeO(OH), the red a-Fe203 or the black Fe304. 

Mixed-phase oxide pigments are manufactured by high temperature (800-1000 °C) solid state reactions of the individual oxide components in the appropriate quantities. The preparation of nickel antimony titanium yellow, for example, involves reaction of Ti02, NiO and Sb203 carried out in the presence of oxygen or other suitable oxidising agent to effect the necessary oxidation of Sb(m) to Sb(v) in the lattice. 

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Primarily, Fe is released from the lithosphere into surface environments including soils by veathering of primary silicate and sulphide minerals (Tab. 16.1). In the presence of O2 and H2O and in the common pH range (>2) of surface environments, the released Fe" is oxidized to Fe " which in turn, is immediately hydrolysed to form Fe " oxides and oxide hydroxides. For Fe" silicates these reactions involve breakage of an Fe"-0-Si bond and the formation of Fe "OH and SiOH groups. For example, goethite may be formed from the oxidation and hydrolysis of olivine (fayalite) through the reaction ... 

Shergold, H.L. Mellgren, O. (1971) Concentration of hematite at the iso-octane/water interface with dodecylamine as a collector. Inst. Min. Met. Trans. C 60-68 Sherman, D.M. Waite, T.D. (1985) Electronic spectra of Ee " oxides and oxide hydroxides in the near IR to near UV. Am. Min. 70 1262-1269... 

Oxides and oxide -hydroxides Iron oxide pigments Chromium oxide pigments Mixed metal oxide pigments chromium oxide cob chromium oxide hydrate green alt green and b lue iron oxide red iron oxide orange chromium rutile orange iron oxide yellow nickel rutile yellow, chromium rutile yellow iron oxide brown zinc iron spinell, Mn-Fe-brown... 

In many inorganic pigments, lanthanides and transition elements are responsible for color. Metal oxides and oxide hydroxides are, however, also important as colored pigments because of their optical properties, low price, and ready availability. Colored pigments based on oxides and oxide hydroxides are either composed of a single component or mixed phases. In the latter, color is obtained by incorporation of appropriate cations. 

Oxides and oxide hydroxides of Tc and Re are typically formed in an O2/H2O containing gas phase. They were extensively studied, mostly using the method of thermochromatography [56-67]. The technique has also been applied to develop Tc and Re generator systems for nuclear medical applications [68,69]. In their works, M. Schadel et al. [70] and R. Eichler et al. [53] studied the oxide and the oxide hydroxide chemistry of trace amounts of Re in an 02/H20-containing system with respect to its suitability for a first gas chemical identification of Bh. They investigated the behavior... 

Thermochromatography of oxides and oxide hydroxides. In thermochromatography experiments three different processes can be distinguished, reflected in the deposition peaks B, C, and D in Figure 17, depending on the pretreatment of the column surface and the oxidation potential of the carrier gas. These are ... 

All active solids are metastable and the loss of area may occur at temperatures well below the Tamman temperature, at which the classical form of sintering normally begins to become important. As we have seen in Chapter 10, water plays a key role in the ageing of the metastable oxides and oxide-hydroxides (Sing, 1972). This can be a serious problem when oxide adsorbents and catalysts are exposed to water vapour. 

Oxides and oxide-hydroxides Iron oxide pigments iron oxide red iron oxide orange iron oxide yellow iron oxide brown... 

Table 1-1. The Major Iron Oxides and Oxide Hydroxides...

Sherman DM, Waite TD (1985) Electronic spectra of Fe oxides and oxide hydroxides in the near IR to nearUV. Am Min 70 1262-1269... 

There is a large group of naturally occurring and synthetically produced pigments based on iron oxides and hydroxides. All of these contain one or more of a relatively small group of compounds oxides and oxide hydroxides of iron - which are found widely in the geological environment or can be manufactured via different routes, or formed by modification of another by a treatment such as calcination. 

By analogy to Mo and W, the oxides and oxide hydroxides of Sg are expected to be moderately volatile, whereas the heavy actinides and the groups 4 and 5 transactinides Rf and Db do not form volatile oxides and oxide hydroxides. For... 

Oxides and oxide hydroxides of Tc and Re are typically formed in an O2/H2O containing gas phase. They were extensively studied, mostly using the method of thermochromatography [65-76]. The technique has also been applied to develop... 

Isothermal chromatography of chlorides and oxychlorides As in smdies of group-7 oxides and oxide hydroxides short-lived " Re was used. Short-lived and were obtained from a Cf fission... 

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