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Magnetite/maghemite formation

Two different pathways of formation are possible (Stanjek, 2000). One route involves aerial oxidation of lithogenic magnetite as suggested for Brazilian Oxisols on basic igneous rocks. The mechanism of this topotactic reaction is described in Chapter 14. These maghemites are usually titaniferous as are the magnetites from which they are derived (see Chap. 15) and almost free from or very low in Al (Allan et al., 1989). Their unit cell size is a function of the residual Fe" and the Ti content. [Pg.451]

Burnishing is the formation of black-brown oxide films on iron and its alloys by controlled oxidation of cleaned metal surfaces. These films are extremely complex and contain, in addition to maghemite and magnetite (or a substituted magnetite for Ni, Mo or Co alloys), various nitride phases - Fe4N, FeaN and FeN. The nitride phases are adjacent to the metal and the iron oxides are in the outer layers of the film (Gebhardt, 1973). [Pg.506]

A single-pot reaction of maghemite nanoparticles, fluorescent pigment, polyester resin, TweenSO, SpanSO, AIBN, and styrene dispersed in an aqueous NaOH solution, led to the formation of ferromagnetic (hysteresis in vibrating sample magnetometry analysis) hybrid nanoparticles [164]. Magnetite compatibilization is ascribed to the application of polyester resin. [Pg.220]

Above 400 mV, reactions at the magnetite electrode are dominated by the oxidation to maghemite with the concurrent release of electrons (anodic current) and Fe(II) to solution (equation 5). Increasing positive potentials accelerate this reaction. Above 400 mV, the current density remains relatively constant up to the potential at which H2O begins to dissociate (Figure 2). Constant currents as functions of increasing positive potentials are commonly attributed in metal and metal oxide electrodes to passivation caused by the formation of unreactive oxidized surfaces. In magnetite, such passivation... [Pg.326]

The Fe(Il)-Fe(III) electron transfers, which allow the formation of iron oxide spinel, also play a role in the crystallization of the ferric gel adsorbed on the surface of colloidal particles of magnetite [114] (see Chapter 9). The electron mobility in the magnetite lattice is also responsible for the transformation to 7-Fc203 maghemite (see Chapter 9). [Pg.219]


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Maghemite

Maghemite formation

Maghemites

Magnetite

Magnetite formation

Magnetite/maghemite

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