PREPARATION OF ULTRAFINE FE-SI-C POWDERS IN A RADIOFREQUENCY THERMAL PLASMA AND THEIR CATALYTIC PROPERTIES

Ultrafine Fe-Si-C powders were prepared from mixed gases of SiH4-CH4-Fe(CO)5 using a newly developed thermal-plasma apparatus with a dual-radio-frequency-coupled-plasma-torch system. The phases of the powders prepared were classified into two groups; one composed of beta-FeSi2 which was prepared by rapid quenching, while the other was composed of alpha-Fe, Fe3Si, Fe5Si3, FeSi, beta-SiC and amorphous Si, which were prepared by slow quenching. The diameters of these powders were in the range 5-50 nm. The catalytic activities of these powders for Fischer-Tropsch synthesis were examined. The ultrafine beta-FeSi2 powder was very active for the selective formation of olefin. On the other hand, powders of alpha-Fe, Fe3Si and Fe5Si3 were low in their selectivity but gave high CO conversion. Relations between the plasma conditions for the preparation of ultrafine Fe-Si-C powders and their catalytic properties are discussed.