552
O. Lavrynenko et al.
3.4 Magnetic Properties of the Magnetite Doped with Ag +
and Au 3+
The role of the oxidative state of the steel surface in the phase composition and
magnetic properties of the surface nanostructures formed under the rotation–corrosion dispergation conditions were studied in the presence of aurum-containing solutions. Hence, to prepare the steel surface we used the activator solution H 2 SO 4
and supply its following contact with distilled water within 1–3, and 3–5 h at the
temperature 50 °C. The homogeneous surface layers of hydroxycarbonate Green Rust
and, corresponding, lepidocrocite were formed as the result of such interaction. The
as-prepared steel surface was moved into corresponding HAuCl 4 water solutions.
The magnetic characteristics of the nanopowders were considered depending on
the synthesis temperature, the initial concentrations of aurum-bearing solutions, and
the phase composition of the primary iron–oxygen structures preliminary formed
on the steel surface. In general, all synthesized samples do not show remanence
magnetization M r and coercitivity H c . The shape of hysteresis loops is indicative of
superparamagnetic nanoparticles, in our case—magnetite.
3.4.1 The Role of the Synthesis Temperature
To compare the magnetic properties of the surface structures depending on the
temperature conditions, we chose the samples formed at T 20 and 50 °C in 3 h
when the c(Au
3+ ) was set 20 mg/dm
3 . Whereas the saturation magnetization M s of
the sample obtained at T = 50 °C equals 14 A · m
2 · kg
−1 , the reduction of the
synthesis temperature up to T = 20 °C leads to decrease of M s to 2 A · m
2 · kg
−1
and it results in the disappearance of a hysteresis loop. Hence, in the last case, the
magnetite part of the surface structures was relatively small and the iron-oxygen
particles were represented as ferric oxyhydroxides, probably, lepidocrocite.
3.4.2 The Influence of Aurum Concentration
The role of the aurum concentration on the saturation magnetization of the surface
structures was studied in the wide range of c(Au
3+ ) from 20 to 1000 mg/dm
3 .
According to obtained data, the values of M s gradually grown from 14 to 40 A · m
2
· kg
−1 when the initial c(Au
3+ ) concentration was, correspondingly, increased from
20 to 500 mg/dm
3 . But the parameter M s sharply fell to 4 A · m
2 · kg
−1 at c(Au
3+ ) =
1000 mg · dm
−3 . In the latter case, the hysteresis loop had disturbed mode. So, we
suppose the appearance among the surface structures of the second non-magnetic
aurum-bearing phase, not excepting gold nanoparticles.
O. Lavrynenko et al.
3.4 Magnetic Properties of the Magnetite Doped with Ag +
and Au 3+
The role of the oxidative state of the steel surface in the phase composition and
magnetic properties of the surface nanostructures formed under the rotation–corrosion dispergation conditions were studied in the presence of aurum-containing solutions. Hence, to prepare the steel surface we used the activator solution H 2 SO 4
and supply its following contact with distilled water within 1–3, and 3–5 h at the
temperature 50 °C. The homogeneous surface layers of hydroxycarbonate Green Rust
and, corresponding, lepidocrocite were formed as the result of such interaction. The
as-prepared steel surface was moved into corresponding HAuCl 4 water solutions.
The magnetic characteristics of the nanopowders were considered depending on
the synthesis temperature, the initial concentrations of aurum-bearing solutions, and
the phase composition of the primary iron–oxygen structures preliminary formed
on the steel surface. In general, all synthesized samples do not show remanence
magnetization M r and coercitivity H c . The shape of hysteresis loops is indicative of
superparamagnetic nanoparticles, in our case—magnetite.
3.4.1 The Role of the Synthesis Temperature
To compare the magnetic properties of the surface structures depending on the
temperature conditions, we chose the samples formed at T 20 and 50 °C in 3 h
when the c(Au
3+ ) was set 20 mg/dm
3 . Whereas the saturation magnetization M s of
the sample obtained at T = 50 °C equals 14 A · m
2 · kg
−1 , the reduction of the
synthesis temperature up to T = 20 °C leads to decrease of M s to 2 A · m
2 · kg
−1
and it results in the disappearance of a hysteresis loop. Hence, in the last case, the
magnetite part of the surface structures was relatively small and the iron-oxygen
particles were represented as ferric oxyhydroxides, probably, lepidocrocite.
3.4.2 The Influence of Aurum Concentration
The role of the aurum concentration on the saturation magnetization of the surface
structures was studied in the wide range of c(Au
3+ ) from 20 to 1000 mg/dm
3 .
According to obtained data, the values of M s gradually grown from 14 to 40 A · m
2
· kg
−1 when the initial c(Au
3+ ) concentration was, correspondingly, increased from
20 to 500 mg/dm
3 . But the parameter M s sharply fell to 4 A · m
2 · kg
−1 at c(Au
3+ ) =
1000 mg · dm
−3 . In the latter case, the hysteresis loop had disturbed mode. So, we
suppose the appearance among the surface structures of the second non-magnetic
aurum-bearing phase, not excepting gold nanoparticles.