R. Fedyk, T. Chudoba, , E. Grzanka, S. Gierlotka, K. Dabrowski, E. Reszke, W. Lojkowski
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Hydrothermal reactions are a well known and convenient method for producing nanocrystalline powders of various ceramics. Recently it was shown that microwaves can be used produce submicron Goethite-Magnetite particles [1]. The particles had the form of elongated needles several nanometers in diameter. This hyrothermal synthesis was carried out at atmospheric pressure at 80 C. Reaction times of several hours were necessary to perform the reaction.

We studied the same reaction in a high pressure microwave reactor. The synthesis was carried out in a closed teflon bomb at pressures up to 10 MPa and temperatures up to 160 C. For reaction times up to 10 minutes we obtained suspensions of Fe3O4 and Fe3O2 powders of grain size in the range 20 - 200 nm. The grains were equiaxial and had a regular crystallographic structure. The ratio of Fe3O4 to Fe3O2 was a function of reaction parameters and reaction time. The fluid with a high magnetite content was dark brown in colour and displayed strong magnetic properties. For comparison, the same reaction was carried out at atmospheric pressure, with similar long reaction times and elongated particles as quoted in ref. [1].

Experiments are being carried out to find out whether the reaction enhancement is solely caused by a relatively high reaction temperature comparing to the reaction at room temperature, or specific microwave effects on the reaction mechanism were involved.

1. G. Wang, G. Whittaker, A. Harrison, L. Song, Mat. Res. Bull. 33, 1571 (1998)

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