Preparation of magnetic nanoparticles in the presence of tubular lecithin assemblies.

摘要

A novel approach to synthesizing Fe particles for applications in metal particle magnetic tape was investigated. The desired particle size was 50 nm in length, with a aspect ratio of at least 6:1. Combinations of acicular, spherical-chain, and spherical Fe particles were prepared by borohydride reduction of Fe{dollar}sp{lcub}2+{rcub}{dollar} in tubular lecithin reverse micellar assemblies. Solutions containing 0.1 and 0.5 M ferrous chloride were reduced without an applied magnetic field. Ferrous chloride solutions of 0.15, 0.05, and 0.025 M were reduced under a 1.2K Oe magnetic field. Ternary phase diagrams were generated to follow coercivity patterns with respect to the ferrous ion concentrations. X-ray diffraction was used to determine the phase of Fe present in the sample. Confirmation of tubular assemblies, the presence of Fe within the tubules, the phase and growth patterns of the Fe were determined using transmission electron microscopy. The effect of ferrous ion concentration, presence of a magnetic field, and reduction reaction time was studied.; The size of the Fe particles was correlated to the concentration of Fe{dollar}sp{lcub}2+{rcub}{dollar} present in the ternary system. At 0.5 M FeCl{dollar}sb2,{dollar} the diameters of the particles were on the order of hundreds of nanometers. After reducing the concentration to 0.05 M FeCl{dollar}sb2,{dollar} particles with diameters of a few to tens of nanometers formed.; Field studies were performed to compare Fe particle formation without a magnetic field, with a 1.2K Oe and a 5K Oe applied magnetic field. The presence of a magnetic field was shown to play a major role in the formation of acicular Fe particles. In conjunction with controlling the diameter with the Fe{dollar}sp{lcub}2+{rcub}{dollar} concentration, high aspect ratios could be attained with the employment of the 1.2K Oe magnetic field. It was also determined that magnetic fields above approximately 1.2K Oe did not significantly improve the properties of the Fe particles.; Finally, the Fe particle formation was followed as a function of reduction reaction time.; Experiments were conducted in 2-minute intervals from 2 to 30 minutes. It was shown that Fe particles formed after 2 minutes were the smallest, had high aspect ratios and had the best magnetic properties. As the reaction continued, spherical-chain and spherical particles formed as a result of the lecithin tubules breaking upon the formation of hydrogen.; The Fe particles formed at the optimum conditions were of the {dollar}alpha{dollar}-phase with lengths of tens of nanometers and aspect ratios in excess of 6:1. Unfortunately, the coercivity for the particles was on the order of a couple of hundred Oe. Explanations are given for low coercivity values and future work is suggested.