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Abstract
The contact of a steel electrode with water dispersion medium in an open-air system leads to the development of various polymorphic iron oxides and oxyhydroxides on the steel surface. Whereas the usage of distilled water causes the obtaining of Fe(II)-Fe(III) layered double hydroxides (green rust) as a primary mineral phase, but in the presence of inorganic 3d-metal water salt solutions, mixed layered double hydroxides (LDHs) together with non-stoichiometric spinel ferrite nanoparticles are formed on the steel surface. Mixed LDHs keep stability against further oxidation and complicate the obtaining of spinel ferrite nanoparticles. Thermal treatment of mixed LDHs among other mineral phases formed via the rotation-corrosion dispergation process at certain temperatures permits to obtain homogenous nanoparticles of spinel ferrites as well as maghemite or hematite doped by 3d-metal cations.
Highlights
Nowadays, iron–oxygen-containing nanoparticles due to their high catalytic and magnetic properties are widely used as precursor species for the creation of various materials for technical and bio-medical application [1, 2]
X-ray fluorescence spectroscopy (XRFS) data confirmed that 3d-metal cations (Co, Ni, Zn, and Cu) associate with spinel ferrite phases but with mixed layered double hydroxides as well as ferric oxyhydroxides
The spinel ferrites and mixed layered double hydroxides (LDHs), formed under the rotation-corrosion dispergation (the RCD) conditions, belong to the non-stoichiometric mineral phases, and the first can be distinguished as the magnetite doped by various cations
Summary
Iron–oxygen-containing nanoparticles due to their high catalytic and magnetic properties are widely used as precursor species for the creation of various materials for technical and bio-medical application [1, 2]. The kinetic study of the processes of the phase formation on the steel surface contacting with distilled water showed the appearance of Fe(II)-Fe(III) layered double hydroxides (LDHs) or green rust as the primary (first nucleus) phase within 1–3 h. The presence of 3d-metal inorganic salts in the dispersion medium contacting with the iron or steel surface provides the nucleation of mixed Fe–3d-metal layered double or triple hydroxides, whose physical– chemical properties significantly differ from the properties of the chemically pure Fe(II)-Fe(III) LDHs. It is known that the typical mixed LDHs are remarkable for Lavrynenko et al Nanoscale Research Letters (2016) 11:67 their full oxidation of ferrous iron in a crystal lattice and they lose reductive properties as well as capability for phase transformation under standard conditions. The appearance of the mixed LDH structures on the steel surface can substantively complicate the obtaining of spinel ferrite nanoparticles on the steel surface when the RCD method is applied
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