PREPARATION AND CONTROL OF MAGNETIC-PROPE RTIES OF ULTRAFINE IRON PARTICLES BY CHEMICAL-VAPOR-DEPOSITION OF FE(CO)5

A technique for controlling secondary particle length and magnetic pro perties of ultrafine iron particles prepared by pyrolysis of Fe(CO)5 w ere studied. The distributions of length of the secondary particles ar e almost log-normal and their geometric standard deviations are 1.3 ap proximately 1.9. The length of secondary particles is closely related to the primary particle diameter; the larger the diameter, the longer the length. It is affected by the feed concentration, residence time a nd pre-decomposition ratio of Fe(CO)5. The strength of magnetic flux i n the axial direction of the reactor also affects the length of second ary particles; the length increases with increasing strength and becom es constant above a strength of 0.15T. The coercive force of the iron particle powder reaches its maximum value of 120 kAm-1 at a primary di ameter of 20 approximately 25 nm. The squareness of video tapes is imp roved by using longer secondary particles. The static magnetic propert ies of video tapes and floppy disks prepared by the present iron parti cles compete with those of commercial ones.