Maghemite y-Fe

Maghemite y-Fe O, 38.8 to >40.4 Same conditions as lepidocrocite, but formed in tropical and subtropical climates, especially in highly weathered soils. 

Morris, R.V., Fauer, H.V. Jr., Fawson, C.A., Gibson, E.K. Jr., Nace, G.A. and Stewart C., 1985. Spectral and other physicochemical properties of submicron powders of hematite (a-Fe Oj), maghemite (y-Fe Oj), magnetite (FCjO, ), goethite (a-FeOOH), and lepidocrocite (y-FeOOH). Journal of Geophysical Research, 90 3126-3144. 

The Derrick Peak iron meteorite was more extensively altered by chemical weathering than most other Antarctic meteorites which remained frozen until they were exposed by ablation of the ice in which they were embedded. The weathering products of DRP78009 (138.1 kg) include Cl-bearing akaganeite (f)-FeOOH) and goethite (a-FeOOH) with smaller amonnts of lepido-crocite (y-FeOOH) and maghemite (y-Fe Oj) (Buchwald and Clarke 1989). 

Maghemite y-Fe Oj Isometric Dark brown, brick red 4.9 Highly weathered sods, trebles and subtropics, from magnetite... 

Oxide mineralogy may influence rates of reductive dissolution in several ways. Hematite (ct-Fe203) and maghemite (y-Fe203), for example, have the same stoichiometry but contain Fe(III) in quite different coordinative environments. Fe(III) in hematite occupies trigonally-distorted octahedral sites, while Fe(III) in maghemite is found in both octahedral and tetrahedral sites (42). Differences... 

Recently, Thimmaiah et al. [74] have extended the thermolytic route to oxide nanoparticles devised by Rockenberger, Sdier and Alivisatos [57] to solvothermal conditions. Using solvothermal toluene (typically at 220 °C for 1 h), cupferron precursors of Fe, and Co and Fe are decomposed to obtain sub-12 nm maghemite y-Fe203 nanoparticles and spinel CoFe204 nanoparticles. The reactions do not... 

Lotgering, 1956) but their magnetic ordering, which is the important factor for applications, is observed only at low temperatures and therefore they are unsuitable for applications at room temperature. A particular case is maghemite, y-Fe203, which possesses a defect spinel structure. The Fe cations are in the trivalent state, and a fraction of the cation sites is vacant (Verwey, 1935). 

A. (2003) Thermodynamics of Fe oxides part II. Enthalpies of formation and relative stabilities of goethite (a-FeOOH), lepidocrocite (y-FeOOH) and maghemite y- e20 ). Am. Mineral, 88, 855-859,... 

Litter et al. (1991) found that the dissolution of maghemite was also considerably speeded up, once a dissolved Fe "-oxalate or Fe" -EDTA complex was reduced to an Fe" complex by UV irradiation 1 = 254 nm). This system also showed an induction period which could be eliminated by addition of Fe " (see Fig. 12.28). In a study concerned with dissolution of corrosion oxide, electrons from viologen radicals produced by y-radiation ( Co) were used to dissolve hematite and goethite (Mulvaney et al., 1988) it was observed that the Fe " appearing in solution could only account for a fraction of the electrons consumed. The remainder was involved in conversion of the Fe " oxide into magnetite. 

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