Preparation of ultrafine magnetite and its oxygen adsorption

Ultrafine magnetite was prepared in aqueous solution by reflux method with ethylenediamine as precipitant. On partial substitution of ethylenediamine for distilled water in the solution, the crystallite was reduced in size linearly. Ethylenediamine worked as not only a precipitant but also a inhibitor for crystal growth. Substituting ethyleneglycol for distilled water at the constant concentration of ethylenediamine, the crystallite was steeply reduced in size to around 2 nm. Specific surface area reached to around 340 m²/g. Such decrease of the crystallite size probably results from increase of viscosity of the solution. High viscosity of the solvent poses to decrease diffusion of iron cations to magnetite nuclei. The adsorption isotherms of O₂ and N₂ were measured at 298 K using each gas and mixed gas with ratio of 2:8. Under the existence of both the gases, the obtained magnetite adsorbed only O₂ with maximum amount of about 1.5 mass%.