Zinc ferrites

Hochepied et al. [313] reported synthesis of a compound Zno73Fe2.i8 0.0904 in nanocrystalline form from a direct micelle system . In this system, functionalized surfactants Fe(DS 2 andZn(DS)2, i.e. derivatives of Na(DS), sodium dodecyl sulfate were used for obtaining micelles in aqueous solutions. Methylamine was added to the mixed micellar solution and the system agitated for 2 h. The precipitate, gathered by centrifugation, was washed with water-ethanol solutions. The particles thus obtained were - 3-4 nm in size. 

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Reaction 3 also occurs on cooling since the concentration of SO is very low at roaster temperatures of 950°C and approaches zero at 1000°C. Another important reaction that occurs during roasting is the formation of zinc ferrite, Zn0-Fe2 03 above 650°C (see Ferrites). Zinc ores contain 5—12% iron. Zinc ferrite forms soHd solutions with other spinels, such as Fe0-Fe203, and therefore the zinc—iron compositions formed are of indefinite stoichiometry. Ferritic zinc is difficult to solubilize in hydrometaHurgical leaching but several recovery processes are discussed below. 

A limited number of laboratory results of varied nature will be cited for perspective. The mechanism of formation of zinc ferrite,... 

In this chapter synthesis of zinc ferrites, intermetallic compounds, and metal-oxides. 

Fig. 8.1. Shock-induced solid state chemical synthesis of a zinc ferrite has been studied over a wide range of temperature and pressure. The figure shows the location of conditions for which the reaction has been studied.

Fig. 8.2. The characteristics of shock-synthesized zinc ferrite are found to be sensitive to both shock pressure and temperature. The description of the product depends strongly on the materials probe used for analysis (after Graham et al. [86G01]).

In spite of careful analysis of the products with the various sophisticated probes, differences in the composition are reported. All measurements indicate a zinc-deficient zinc ferrite, but the indicated zinc concentration varies from 0.2 to 0.9. The EDS measurements are based on direct zinc concentration measurements. Determinations based on magnetization and Mdssbauer spectra are obtained on zinc ferrite synthesized in more conventional processes. 

One of the most interesting results of the zinc ferrite synthesis is the observation that the yield of the product is dependent on the early pressure history. This behavior is shown in Fig. 8.3, which plots the yield versus temperature for baratol explosive loading and for Composition B explosive loading. The difference between these loadings is that the initial pressure pulse amplitude is significantly greater with Composition B. Apparently, the early pressure history has an important conditioning effect for subsequent reactions. 

Fig. 8.3. The yield of shock-synthesized zinc ferrite is found to be strongly dependent on the early loading history. This characteristic is thought to be an indication of shock modification on subsequent chemical reaction.

This chapter presents detailed and thorough studies of chemical synthesis in three quite different chemical systems zinc ferrite, intermetallic, and metal oxide. In addition to different reaction types (oxide-oxide, metal-metal, and metal oxide), the systems have quite different heats of reaction. The oxide-oxide system has no heat of reaction, while the intermetallic has a significant, but modest, heat of reaction. The metal oxide system has a very large heat of reaction. The various observations appear to be consistent with the proposed conceptual models involving configuration, activation, mixing, and heating required to describe the mechanisms of shock-induced solid state chemistry. 

The conversion process (developed by Outokumpu) is a modification of the jarosite process and involves simultaneously zinc ferrite dissolution and jarosite precipitation in the same reaction vessel. The overall reaction may be represented in simplified form as ... 

The principal differences between the goethite and the jarosite processes take place following the hot acid leaching of the zinc ferrite residues. In the goethite process, the liquor from hot acid leaching, holding (in g l-1) 100 Zn, 25-30 Fe3+ and 50-60 H2S04, is initially subjected to a reduction step, where the ferric iron is reduced to the ferrous form by reaction with unroasted zinc sulfide concentrate at 90 °C ... 

Baranchikiv AE, Ivanov VK, Oleinikov NN, Tretyakov DYu (2004) Microstructural evaluation of Fe203 and ZnFe204 during sonochemical synthesis of zinc ferrite. Inorg Mater 40(10) 1091-1094... 

Baranchikiv AE, Ivanov VK, Muraveva GP, Oleinikov NN, Tretyakov Yu D (2004) Kinetics of the formation of zinc ferrite in an ultrasonic field. Dokl Chem 397(Part I) 146-148... 

Cheng, P., Li, W., Zhou, T., Jin, Y., and Gu, M. (2004) Physical and photocatalytic properties of zinc ferrite doped titania under visible light irradiation. Journal of Photochemistry and Photobiology A Chemistry, 168 (1-2), 97-101. 

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