Physical–Chemical Properties of Magnetite Nanoparticles Doped …
553
3.4.3 The Role of the Primary Phases Formed on the Steel Surface
We compare magnetic properties of the surface structures obtained when the aurumbearing solutions were contacting with cleaned and activated St3 surface with the
same characteristics of the powders obtained when Green Rust or lepidocrocite
layers were formed preliminary on the steel surface, afterward the corroded steel
was placed into contact with aurum-bearing solutions. The initial c(Au
3+ ) was set 50
and 500 mg/dm
3 . So, at c(Au
3+ ) = 50 mg/dm
3 the parameter M s gradually increased
from 18 A · m
2 · kg
−1 for the sample obtained on the non-oxidized St3 surface to
25 A · m
2 · kg
−1 for nanopowders formed on the surface Green Rust layer and to
30 A · m
2 · kg
−1 when the particles were formed on the lepidocrocite layer. But at
c(Au
3+ ) = 500 mg/dm
3, the value of M s equaled 40 A · m
2 · kg
−1 for the flimsy
samples obtained on the cleaned steel surface and on the lepidocrocite layer. But the
nanostructures formed on the Green Rust layer were characterized by lower value,
where M s = 14 A · m
2 · kg
−1 . Hence, we expect that the role of the primary species
in the process of composite structure formation will be the most determinative, but
the obtained data are ambiguous.
3.4.4 The Role of Noble Metal’s Cations
The comparative study of magnetic properties of the samples formed on the steel
surface contacting with aurum- and argentum-containing solutions was performed
in the concentration range of the precious metals from 1 to 20 mg/dm
3 . So, all
samples, like a previous case, showed the absence of the coercivity and remanence
magnetization. The highest values of the saturation magnetization are typical for
the samples formed at the metal concentration 10 mg/gm
3 . It got 49 A · m
2 · kg
−1
for aurum-bearing system and 24 A · m
2 · kg
−1 for the argentum-bearing system,
respectively. The similar high M s = 40 A · m
2 · kg
−1 was found for the sample
obtained at c(Au
3+ ) = 1 mg/dm
3 . The range of concentration 3–5 mg/dm
3 was not
favorable for the formation of magnetic nanoparticles, the values of M s did not
exceed 5 (for Ag
+ )–13 (for Au
3+ ) A · m
2 · kg
−1 But increase in the initial c(Ag
+ ) up
to 20 mg/dm
3 led to sharply decreasing of M s to 1.3 A · m
2 · kg
−1 .
3.4.5 Core and Shell Type Nanocomposites
Whereas the most common structures formed on the steel surface in the open-air
system are magnetite and lepidocrocite, core and shell-type composite nanoparticles
are typical products formed in the dispersion medium under the RCD process. Determination of the shell thickness precious metallic shell on the magnetic properties of
the composite particles was studied for argentum-bearing structures. Precious metal
aquaforms may be reduced on the magnetite cores as clusters, porous or compact
layers depending on their initial concentration in the solution. We fixed a decrease
in the saturation magnetization for Fe 3 O 4 and Ag
0 nanocomposite particles from 40
553
3.4.3 The Role of the Primary Phases Formed on the Steel Surface
We compare magnetic properties of the surface structures obtained when the aurumbearing solutions were contacting with cleaned and activated St3 surface with the
same characteristics of the powders obtained when Green Rust or lepidocrocite
layers were formed preliminary on the steel surface, afterward the corroded steel
was placed into contact with aurum-bearing solutions. The initial c(Au
3+ ) was set 50
and 500 mg/dm
3 . So, at c(Au
3+ ) = 50 mg/dm
3 the parameter M s gradually increased
from 18 A · m
2 · kg
−1 for the sample obtained on the non-oxidized St3 surface to
25 A · m
2 · kg
−1 for nanopowders formed on the surface Green Rust layer and to
30 A · m
2 · kg
−1 when the particles were formed on the lepidocrocite layer. But at
c(Au
3+ ) = 500 mg/dm
3, the value of M s equaled 40 A · m
2 · kg
−1 for the flimsy
samples obtained on the cleaned steel surface and on the lepidocrocite layer. But the
nanostructures formed on the Green Rust layer were characterized by lower value,
where M s = 14 A · m
2 · kg
−1 . Hence, we expect that the role of the primary species
in the process of composite structure formation will be the most determinative, but
the obtained data are ambiguous.
3.4.4 The Role of Noble Metal’s Cations
The comparative study of magnetic properties of the samples formed on the steel
surface contacting with aurum- and argentum-containing solutions was performed
in the concentration range of the precious metals from 1 to 20 mg/dm
3 . So, all
samples, like a previous case, showed the absence of the coercivity and remanence
magnetization. The highest values of the saturation magnetization are typical for
the samples formed at the metal concentration 10 mg/gm
3 . It got 49 A · m
2 · kg
−1
for aurum-bearing system and 24 A · m
2 · kg
−1 for the argentum-bearing system,
respectively. The similar high M s = 40 A · m
2 · kg
−1 was found for the sample
obtained at c(Au
3+ ) = 1 mg/dm
3 . The range of concentration 3–5 mg/dm
3 was not
favorable for the formation of magnetic nanoparticles, the values of M s did not
exceed 5 (for Ag
+ )–13 (for Au
3+ ) A · m
2 · kg
−1 But increase in the initial c(Ag
+ ) up
to 20 mg/dm
3 led to sharply decreasing of M s to 1.3 A · m
2 · kg
−1 .
3.4.5 Core and Shell Type Nanocomposites
Whereas the most common structures formed on the steel surface in the open-air
system are magnetite and lepidocrocite, core and shell-type composite nanoparticles
are typical products formed in the dispersion medium under the RCD process. Determination of the shell thickness precious metallic shell on the magnetic properties of
the composite particles was studied for argentum-bearing structures. Precious metal
aquaforms may be reduced on the magnetite cores as clusters, porous or compact
layers depending on their initial concentration in the solution. We fixed a decrease
in the saturation magnetization for Fe 3 O 4 and Ag
0 nanocomposite particles from 40