544
O. Lavrynenko et al.
of Ag
+ , the primary magnetite particles appeared on the steel surface within 1 h.
Lepidocrocite was formed on the St3 surface as a second phase. Development of
the surface structures within 24 h led to an increase in the intensity of the reflexes
in the XRD-patterns. The following phase transformation process was directed on
the partial oxidation of magnetite and the appearance of the second oxyhydroxide
phase—goethite. In addition, among the surface structures, we can see the small
quantity of the primary hydroxycarbonate Green Rust. The average size of magnetite
particles was ~22 nm. At the initial pH value 11, the typical structures formed on the
steel surface were iron oxyhydroxides—lepidocrocite and goethite. The magnetite
reflexes appeared on the XRD-pattern only after 24 h of the phase formation process.
The average size of magnetite particles equaled 38 nm.
To determine the influence of the oxygen originate from air to the reaction area
on the phase distribution, we analyzed three separate layers of particles: he outer (I)
contacts with air and water solution, the inner (III) contacts with the steel surface
and, corresponding, the middle one (II) between (I) and (III). The distribution of the
surface phases includes decrease the lepidocrocite’s part and, corresponding; increase
the magnetite’s part from layer (I) to layer (III). The particles size of magnetite
gradually decreased from 24 nm in (I) layer to 21 nm in (II), and 19 nm in (III).
Probably, the particle size can influence the processes of oxidation of magnetite and
the formation of lepidocrocite shell on its surface [22].
XRD-analysis of the aurum-bearing samples obtained in the range of c(Au
3+ )
from 0.5 to 20 mg/dm
3 shows the formation of two-phase systems, where magnetite
is estimated as a dominant component of the surface structures, while lepidocrocite
is present as an admixture only. In all cases, the gold peaks (JCPDS file No 02-1095)
are small because the aurum content in the nanocomposites lies on the detection
limit of XRD method. Typical XRD-patterns of the surface structures are present in
Figs. 1c, d.
The crystallite size of magnetite is insignificantly growing from 21 nm at c(Au
3+ )
= 1 mg/dm
3 –24 nm at c(Au
3+ ) = 20 mg/dm
3 . The CSR of lepidocrocite is found in
the range 12.5–16 nm.
3.2 The Thermal Behavior and Chemical Composition
of the Nanoparticles Formed on the St3 Surface
in the Presence of Au(III) and Ag(I)
3.2.1 IR-FT Spectroscopy
The surface properties of magnetite nanoparticles doped with argentum cations were
studied for the samples formed at c(Ag
+ ) 0.5–5 mg/dm
3 (Fig. 3). Analysis of infrared
spectrum (1) corresponding to c(Ag
+ ) = 0.5 mg/dm
3 shows the band at 3509 cm
−1
lied in the interval of the moisture vibration. The band at 1473–1430 cm
−1 appears in
the area of the CO 3
2− vibration. The band at 1369, 570, and 424 cm
−1 can be related
O. Lavrynenko et al.
of Ag
+ , the primary magnetite particles appeared on the steel surface within 1 h.
Lepidocrocite was formed on the St3 surface as a second phase. Development of
the surface structures within 24 h led to an increase in the intensity of the reflexes
in the XRD-patterns. The following phase transformation process was directed on
the partial oxidation of magnetite and the appearance of the second oxyhydroxide
phase—goethite. In addition, among the surface structures, we can see the small
quantity of the primary hydroxycarbonate Green Rust. The average size of magnetite
particles was ~22 nm. At the initial pH value 11, the typical structures formed on the
steel surface were iron oxyhydroxides—lepidocrocite and goethite. The magnetite
reflexes appeared on the XRD-pattern only after 24 h of the phase formation process.
The average size of magnetite particles equaled 38 nm.
To determine the influence of the oxygen originate from air to the reaction area
on the phase distribution, we analyzed three separate layers of particles: he outer (I)
contacts with air and water solution, the inner (III) contacts with the steel surface
and, corresponding, the middle one (II) between (I) and (III). The distribution of the
surface phases includes decrease the lepidocrocite’s part and, corresponding; increase
the magnetite’s part from layer (I) to layer (III). The particles size of magnetite
gradually decreased from 24 nm in (I) layer to 21 nm in (II), and 19 nm in (III).
Probably, the particle size can influence the processes of oxidation of magnetite and
the formation of lepidocrocite shell on its surface [22].
XRD-analysis of the aurum-bearing samples obtained in the range of c(Au
3+ )
from 0.5 to 20 mg/dm
3 shows the formation of two-phase systems, where magnetite
is estimated as a dominant component of the surface structures, while lepidocrocite
is present as an admixture only. In all cases, the gold peaks (JCPDS file No 02-1095)
are small because the aurum content in the nanocomposites lies on the detection
limit of XRD method. Typical XRD-patterns of the surface structures are present in
Figs. 1c, d.
The crystallite size of magnetite is insignificantly growing from 21 nm at c(Au
3+ )
= 1 mg/dm
3 –24 nm at c(Au
3+ ) = 20 mg/dm
3 . The CSR of lepidocrocite is found in
the range 12.5–16 nm.
3.2 The Thermal Behavior and Chemical Composition
of the Nanoparticles Formed on the St3 Surface
in the Presence of Au(III) and Ag(I)
3.2.1 IR-FT Spectroscopy
The surface properties of magnetite nanoparticles doped with argentum cations were
studied for the samples formed at c(Ag
+ ) 0.5–5 mg/dm
3 (Fig. 3). Analysis of infrared
spectrum (1) corresponding to c(Ag
+ ) = 0.5 mg/dm
3 shows the band at 3509 cm
−1
lied in the interval of the moisture vibration. The band at 1473–1430 cm
−1 appears in
the area of the CO 3
2− vibration. The band at 1369, 570, and 424 cm
−1 can be related