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

Pure gamma -Fe2O3 particles were continuously prepared by a continuous wave CO2 laser-induced pyrolysis of iron pentacarbonyl vapour in an oxidizing a tmosphere. Two different oxidation procedures were investigated: (1) air-ar gon mixtures were employed to fill the apparatus; (2) air-ethylene mixtures were employed as carrier gas. The powders were identified by X-ray diffrac tion. The grain size was measured using transmission electron microscopy an d the degree of order was estimated by IR spectroscopy. The products obtain ed have grain sizes in the range 4 to 17 nm and different degrees of struct ural order depending on the synthesis conditions. The productivities attain ed are typically 0.05 gh(-1). Finally, the magnetic properties of the maghe mite powders are discussed. It seems that, for very small magnetic particle s, 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 (C) 2001 John Wiley & Sons, Ltd.