Physical–Chemical Properties of Magnetite Nanoparticles Doped …
541
as the anodic dissolution of an iron-bearing component in the steel composition
and oxygen depolarization in a cathodic part of the steel surface). Contact of the
present system with the air influence the oxidation condition in the reaction area
and promote the phase transformation of the metastable Fe(II)–Fe(III) LDHs (Green
Rust) structures into ferric oxyhydroxides (lepidocrocite and goethite) in the outer
layer, and, correspondingly, ferric–ferrous oxide—magnetite in the inner layer of
the corrosion products. The presence of the 3d-metal cations transition goes to the
non-stoichiometric spinel ferrites or magnetite formation. These formed particles are
dopped with corresponding metals. But when we add some noble metal aqua forms
to the water solutions, it is clear that the core and shell-type nanoparticles appear
into the dispersion medium to form different ionic-stabilized sols. In our methodic
system, Green Rust has role of a strong reducing agent, and because of this, it may
transform to the metal state all the precious metal ions it has [16]. Lepidocrocite
or goethite can bond precious metal ions via adsorption mechanism without red–ox
reactions because of having a well-developed surface area [19], whereas magnetite
simultaneously takes part in the various aurum and argentum aquaforms reducing
and sorption [20, 21].
Our previous research showed the appearance of a continuous Green Rust layer on
the steel surface in contact with water medium 1–3 h and its full oxidation into ferric
oxyhydroxides within the following 3–5 h. Hence, analysis of the phase formation
processes in the presence of aurum aquaforms took place on the activated steel surface
or on the preliminary formed Green Rust or lepidocrocite surface layers. The present
work is directed to study the phase and chemical composition, thermal behavior,
surface, and magnetic properties of the nanostructures formed on the steel surface
in the presence of aurum- and argentum-bearing aqua forms under the rotation–
corrosion dispergation conditions.
2 Experimental
The rotating disk electrode is made of steel 3 (St3), it’s composition has, %: C—0.14–
0.22; Si—0.05–0.15; Mn—0.4–0.5; Cr—0.3; Ni—0.3; P—0.04; S—0.05; N—0.01.
It was used to perform the phase formation process. The carrying out the synthesis
procedure was performed in the open-air system under galvanostatic conditions
via the rotation–corrosion dispergation route. During the experiment, our electrode
surface was contacting alternately with dispersion medium and air. The steel surface
was exposed to mechanical treatment and activating procedure to remove an oxidized
layer and supply equal conditions for the phase formation process. We used as the
dispersion medium distilled water and aurum- and argentum-containing water solutions with the precious metal concentrations in the range from 0.05 to 25 mg/dm
3 .
The pH value of the initial solutions lies in the range from 2.5 to 6.5 depending on the
541
as the anodic dissolution of an iron-bearing component in the steel composition
and oxygen depolarization in a cathodic part of the steel surface). Contact of the
present system with the air influence the oxidation condition in the reaction area
and promote the phase transformation of the metastable Fe(II)–Fe(III) LDHs (Green
Rust) structures into ferric oxyhydroxides (lepidocrocite and goethite) in the outer
layer, and, correspondingly, ferric–ferrous oxide—magnetite in the inner layer of
the corrosion products. The presence of the 3d-metal cations transition goes to the
non-stoichiometric spinel ferrites or magnetite formation. These formed particles are
dopped with corresponding metals. But when we add some noble metal aqua forms
to the water solutions, it is clear that the core and shell-type nanoparticles appear
into the dispersion medium to form different ionic-stabilized sols. In our methodic
system, Green Rust has role of a strong reducing agent, and because of this, it may
transform to the metal state all the precious metal ions it has [16]. Lepidocrocite
or goethite can bond precious metal ions via adsorption mechanism without red–ox
reactions because of having a well-developed surface area [19], whereas magnetite
simultaneously takes part in the various aurum and argentum aquaforms reducing
and sorption [20, 21].
Our previous research showed the appearance of a continuous Green Rust layer on
the steel surface in contact with water medium 1–3 h and its full oxidation into ferric
oxyhydroxides within the following 3–5 h. Hence, analysis of the phase formation
processes in the presence of aurum aquaforms took place on the activated steel surface
or on the preliminary formed Green Rust or lepidocrocite surface layers. The present
work is directed to study the phase and chemical composition, thermal behavior,
surface, and magnetic properties of the nanostructures formed on the steel surface
in the presence of aurum- and argentum-bearing aqua forms under the rotation–
corrosion dispergation conditions.
2 Experimental
The rotating disk electrode is made of steel 3 (St3), it’s composition has, %: C—0.14–
0.22; Si—0.05–0.15; Mn—0.4–0.5; Cr—0.3; Ni—0.3; P—0.04; S—0.05; N—0.01.
It was used to perform the phase formation process. The carrying out the synthesis
procedure was performed in the open-air system under galvanostatic conditions
via the rotation–corrosion dispergation route. During the experiment, our electrode
surface was contacting alternately with dispersion medium and air. The steel surface
was exposed to mechanical treatment and activating procedure to remove an oxidized
layer and supply equal conditions for the phase formation process. We used as the
dispersion medium distilled water and aurum- and argentum-containing water solutions with the precious metal concentrations in the range from 0.05 to 25 mg/dm
3 .
The pH value of the initial solutions lies in the range from 2.5 to 6.5 depending on the