Surface oxidation of iron nanoparticles

The electrochemical reaction between aqueous ferric chloride solution and Mg powder has been carried out in open atmosphere to prepare iron nanoparticles. Since iron particles get easily oxidised to α-Fe2O3, γ-Fe2O3 and Fe3O4, the final product contains the oxides in different proportions with different dimensions depending on the concentration of the FeCl3 solution in the electrochemical reaction. The final products were characterised using X-ray and Mössbauer spectroscopy. The results may be summarised as: (1) concentrated solution yields Fe particles of smallest size with a superparamagnetic doublet in the Mössbauer spectrum arising from oxide nanoparticles; (2) moderately diluted solution yields Fe particles of maximum size, and the Mössbauer spectrum was a superposition of a sextet line arising from Fe3O4, a superparamagnetic singlet, and doublet from Fe and its oxides; (3) fairly diluted solution yields Fe particles of intermediate size and the Mössbauer spectrum was a superposition of a sextet line corresponding to metallic α-Fe and superparamagnetic line similar to case (2). The experimental results are discussed in terms of consecutive processes in the electrochemical reaction.