Magnetite/maghemite nanoparticles

Raman chemical imaging can be employed to access the homogeneity and the structural stability in terms of oxidation rates, onset of hematite, and organic contamination of as-precipitate and oxidized iron oxide samples. Oxidation-related Raman features have been established by comparative study of bulk oxides and nanoparticles attained in two different oxidation states, suggesting that the solid nanophase synthesized had a mixed magnetite-maghemite composition [52]. 

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. 

Figure 3.30 HRTEM of a wear particle, (a) Maghemite nanoparticle observed under a [1, —1, 0] azimuth. Distances measured on the calculated diffractogram d = 4.85 nm ) are in good agreement with the theoretical magnetite structure observed under a [1, -1, 0] azimuth, (b) Intact carbon onions are observed...

The magnetite (Fe304) nanoparticles obtained are not very stable under ambient conditions, and they are oxidized to maghemite (y-Fe203) or hematite with different magnetic properties. 

Table 14.2 summarizes typical phonons available in the literature for CoFe204 nanoparticles, compared with that obtained for CoFe204 crystal. As in the case of magnetite, more Raman modes are detected in nanosized samples [44] than in correspondent crystals. Furthermore, some observed phonons possess the characteristics of maghemite vibrational modes, which implies that a possible oxidation process occurs. 

A detailed investigation about the chemical and structural composition of maghemite (diameters in the range of 10-20 nm) based MF samples, prepared through the oxidation of magnetite nanoparticle, the latter synthesized by the coprecipitation route, was reported [53]. The precipitate containing the... 

PMAA- or citrate-coated magnetite [160] or citrate-coated maghemite [162] nanoparticles could successftiUy be encapsulated in a crosslinked polyacrylamide matrix using an inverse miniemulsion process. Here an inert hydrocarbon (cyclohexane or dodecane) was used as continuous phase and SpanSO as stabilizer. 

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