Finely dispersed iron particles are widely used for magnetic fluids, particulate composites, magnetic microcarriers of biologically active substances etc. The environmental stability of the particles is determined by the peculiarities of the physicochemical structure of self-assembling surfactant layers along with the formation of the surfactant-metal particle interface.
Hence, the surface phase structure and physicochemical structure of the stabilizing layers on the surface of iron particles obtained at different stages of high-temperature reduction in H₂ flow have become the focus of the present investigation performed by means of the XPS, AFM and Mössbauer spectroscopy. Oleic acid was used as a stabilizing agent. For comparison, hexamethylenediamine and acrylamide were also taken as stabilizerz. Particles for Mössbauer spectroscopy study were prepared using an original procedure with the particle "nuclei" from ⁵⁶Fe and with the particle surface layer, enriched in ⁵⁷Fe. It follows from Mössbauer spectroscopy data that after partial reduction in H₂ flow disordered or highly distorted ⁵⁷Fe₃O₄ phase is seen to be present on the surface of particle "nuclei". The particles are essentially ⁵⁶Fe with the ⁵⁷Fe surface layer at the end of reduction. According to the XPS data, all stages of reduction are characterized by the presence of an oxide layer, with its nature dependent on the reduction stage. The peculiarities of the physicochemical structure of the stabilizing layer on the base of oleic acid for the particles obtained on different stages of reduction were clarified using XPS. Also, the structure of the protective layers based on nitrogen-containing organic compounds was studied for the final particles. The corrosion study have shown that it is the structure of stabilizing layers that will determine the iron particle stability in the environment.
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