Preparation and study of magnetic fluids

Abstract

A study of the preparation and characterization of hydrocarbon based metal particle magnetic fluids (ferrofluids) is reported. Bimetallic alloy particle magnetic fluids with the particle compositions: FeCo, Co(_3)Fe and Ni(_3)Fe have been prepared by the thermal decomposition of the organometallic complexes: [ ( π-C(_5)H(_5)) Fe (CO)(_2)Co(CO)(_4)], HFeCo(_3)(CO)(_12) and [(π-C(_5)H(_5))(_2)Ni(_2)Fe(CO)(_5)] respectively. In all cases the magnetic fluids were superparamagnetic at room temperature, containing particles with diameters in the 5-8nm range. In the FeCo and Ni(_3)Fe systems electron diffraction revealed alloy particles with ordered "superlattice" structures. In these iron alloy systems, the iron content of the particles is less than that of the organometallic starting material, due to chemical reaction. A cobalt magnetic fluid prepared in collaboration with Bristol University by the evaporation of cobalt metal has been examined and compared to cobalt fluids prepared from the decomposition of Co(_2)(CO)(_8). Characterization indicated no significant differences between fluids prepared using the two contrasting techniques. The surfactant Sarkosy l-0 is completely converted to a cobalt carboxylate derivative during the preparation of cobalt magnetic fluids from CO(_2)(CO)(_8). This result, determined by IR spectroscopy implies both surface active and "free" solution Sarkosy l-0 are in the form of a cobalt complex. The atmospheric oxidation of the metallic cobalt particles in these systems has been observed by EXAFS spectroscopy. Preparation of iron particle magnetic fluids has proven difficult. Particles believed to consist of iron-carbon alloy are produced during thermolysis of Fe(CO)(_5). Decomposition of organometallic compounds was concluded to be an unsatisfactory method of producing iron magnetic fluids. In general nickel magnetic fluids were also difficult to prepare. However, large {13-27nm) regularly shaped nickel particles were obtained on decomposition of [π-C(_5)H(_5)Ni(CO) ](_2). [brace not closed]