Effect of the oxidation conditions on the maghemites produced by laser pyrolysis

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Abstract
Pure γ − Fe2O3 particles were continuously prepared by a continuous wave CO2 laser‐induced pyrolysis of iron pentacarbonyl vapour in an oxidizing atmosphere. Two different oxidation procedures were investigated: (1) air–argon mixtures were employed to fill the apparatus; (2) air–ethylene mixtures were employed as carrier gas. The powders were identified by X‐ray diffraction. The grain size was measured using transmission electron microscopy and the degree of order was estimated by IR spectroscopy. The products obtained have grain sizes in the range 4 to 17 nm and different degrees of structural order depending on the synthesis conditions. The productivities attained are typically 0.05 gh−1. Finally, the magnetic properties of the maghemite powders are discussed. It seems that, for very small magnetic particles, the actual differences in the sizes of the particles are less important than differences in crystallinity with regard to the magnetic properties of the samples. Copyright © 2001 John Wiley & Sons, Ltd.