This paper describes the results of attempts at preparing fine metallic cobalt particles through reducing reaction in liquid phase.
The materials used were : cobalt chloride (II) and tris (acetyl acetonate) cobalt (III) (abbreviated as [Co(acac)
3], hereafter) as cobalt compound ; water, anisole and diphenylether as solvent ; hydrazine, hydroquinone and sodium borohydride as reducing agent.
Although the reduction in water or anisole was impossible, the black and strongly magnetic cobalt particles were formed through the procedure : refluxing diphenylether containing [Co(acac)
3] at its boiling point with an addition of sodium borohydride, and filtration after cooling and decomposition of sodium borohydride with an addition of methanol. Since the obtained particles were observed to be remarkably flocculated, refluxing with N
2 gas flow was attempted to prevent this flocculation. The result was that the flocculation was considerably suppressed. Although the formation of cobalt particles covered with thin oxide layer required the amount of sodium borohydride 20 times as much as that of [Co(acac)
3] in the molar ratio, the former amount was reduced to 1/2 with N
2 gas flow. The cobalt particles obtained by this method were in flocculated state of primary particles of 5 to 10 nm. The purity of this product was about 93 percent.
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