226
7 Composites
of the deposit [43]. This is entirely in accord with the regular codeposition mode.
Baths with sodium citrate [43, 44] resulted in nanogranular deposits with a very
low level of the intermixing of the components (Ni could dissolve in Ag to a little
extent but not vice versa [44]). When the sample preparation was carried out by using
various other complexing agents (thiourea and sodium gluconate) and with pulsed
current, the X-ray diffractograms indicated the formation of a metastable Ni–Ag
phase beside the nearly pure phases of the components [45]. The diffraction lines
of the metastable Ag–Ni phase did not disappear after a 1-h-long heat treatment at
a temperature as high as 300 °C. The atomic-level intermixing of the constituents
was confirmed by the magnetization value of the mixed deposit. In the 80–92 at.%
Ni content range, the saturation magnetization was only 1–5 emu/g, as compared to
the 47 emu/g obtained in the same study for a pure Ni deposit from the Ag-free bath
(while the room-temperature magnetization value of the metallurgically processed
pure Ni is around 56–57 emu/g).
Another frequently studied system is Cu–Fe, mostly because of the interest in
its magnetic properties. There is little overlap between the electrochemical data of
the baths used for Cu–Fe codeposition. A composition diagram was published only
for a citrate bath [46], which indicated that the dominant component of the deposit
suppresses the codeposition of the other component. This is an indirect evidence
for the tendency of phase separation. The current density dependence of the deposit
composition corresponds to the regular codeposition, i.e., the Fe content increases
with the increase in the current density for a particular bath composition [47, 48],
although complexation of the cations can weaken this trend [48]. Oxygen incorporation into the deposits is also mentioned [48]. Concerning the structure of Cu–
Fe deposits, the phase separation is obvious from the appearance of the XRD line
systems characteristic for either bcc Fe or fcc Cu [46–50], at least in the range of the
nearly equimolar deposit composition. Nevertheless, the accurate structural analysis
leads to some controversy. While some studies indicate that the XRD peak positions
are somewhat shifted relative to the pure form of the constituents [46, 49] which
can be related to a slight intermixing of the components in the as-deposited state,
other studies do not confirm this observation [48, 50] but some scattering of the lattice
parameters can be seen within the standard error of the measurements. Surprisingly, a
completely opposite conclusion was drawn from Mössbauer spectroscopic measurement of Fe–Cu alloy powders electroplated from an additive-free solution [51]. The
analysis of the Mössbauer spectra resulted in nearest-neighbour atomic distribution
characteristic of solid solutions up to 45 wt.% Fe content. Where the data for the
crystallite size is available [48], it can be established that the as-obtained deposits are
nanocrystalline with about 8–70 nm grain size. The magnetization data are also quite
diverse. When the saturation magnetization as normalized to the Fe content is lower
than that expected from a simple dilution law, an alloying can be concluded [46]. In
contrast, when the reduced magnetization as a function of the temperature is not a
function of the composition, a complete segregation is assumed to take place [50].
The number of the available studies is insufficient to find the correlation between the
behaviour of the samples and the electrodeposition parameters.
7 Composites
of the deposit [43]. This is entirely in accord with the regular codeposition mode.
Baths with sodium citrate [43, 44] resulted in nanogranular deposits with a very
low level of the intermixing of the components (Ni could dissolve in Ag to a little
extent but not vice versa [44]). When the sample preparation was carried out by using
various other complexing agents (thiourea and sodium gluconate) and with pulsed
current, the X-ray diffractograms indicated the formation of a metastable Ni–Ag
phase beside the nearly pure phases of the components [45]. The diffraction lines
of the metastable Ag–Ni phase did not disappear after a 1-h-long heat treatment at
a temperature as high as 300 °C. The atomic-level intermixing of the constituents
was confirmed by the magnetization value of the mixed deposit. In the 80–92 at.%
Ni content range, the saturation magnetization was only 1–5 emu/g, as compared to
the 47 emu/g obtained in the same study for a pure Ni deposit from the Ag-free bath
(while the room-temperature magnetization value of the metallurgically processed
pure Ni is around 56–57 emu/g).
Another frequently studied system is Cu–Fe, mostly because of the interest in
its magnetic properties. There is little overlap between the electrochemical data of
the baths used for Cu–Fe codeposition. A composition diagram was published only
for a citrate bath [46], which indicated that the dominant component of the deposit
suppresses the codeposition of the other component. This is an indirect evidence
for the tendency of phase separation. The current density dependence of the deposit
composition corresponds to the regular codeposition, i.e., the Fe content increases
with the increase in the current density for a particular bath composition [47, 48],
although complexation of the cations can weaken this trend [48]. Oxygen incorporation into the deposits is also mentioned [48]. Concerning the structure of Cu–
Fe deposits, the phase separation is obvious from the appearance of the XRD line
systems characteristic for either bcc Fe or fcc Cu [46–50], at least in the range of the
nearly equimolar deposit composition. Nevertheless, the accurate structural analysis
leads to some controversy. While some studies indicate that the XRD peak positions
are somewhat shifted relative to the pure form of the constituents [46, 49] which
can be related to a slight intermixing of the components in the as-deposited state,
other studies do not confirm this observation [48, 50] but some scattering of the lattice
parameters can be seen within the standard error of the measurements. Surprisingly, a
completely opposite conclusion was drawn from Mössbauer spectroscopic measurement of Fe–Cu alloy powders electroplated from an additive-free solution [51]. The
analysis of the Mössbauer spectra resulted in nearest-neighbour atomic distribution
characteristic of solid solutions up to 45 wt.% Fe content. Where the data for the
crystallite size is available [48], it can be established that the as-obtained deposits are
nanocrystalline with about 8–70 nm grain size. The magnetization data are also quite
diverse. When the saturation magnetization as normalized to the Fe content is lower
than that expected from a simple dilution law, an alloying can be concluded [46]. In
contrast, when the reduced magnetization as a function of the temperature is not a
function of the composition, a complete segregation is assumed to take place [50].
The number of the available studies is insufficient to find the correlation between the
behaviour of the samples and the electrodeposition parameters.