Valence-to-core X-ray emission spectroscopy identification of carbide compounds in nanocrystalline Cr coatings deposited from Cr(III) electrolytes containing organic substances

Article abstract of DOI:10.1021/jp064569j

Valence-to-core X-ray emission spectroscopy was applied to study a composition of chromium coatings electrodeposited from Cr(III) sulfate electrolytes with the addition of formic or oxalic acid. It was shown that the obtained crystallographically amorphous deposits contain chromium carbide compounds. These results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.

Full text of DOI:10.1021/jp064569j

23192
J. Phys. Chem. B 2006, 110, 23192-23196
Valence-to-Core X-ray Emission Spectroscopy Identification of Carbide Compounds in
Nanocrystalline Cr Coatings Deposited from Cr(III) Electrolytes Containing Organic
Substances
Viktor A. Safonov,*,† Ludmila N. Vykhodtseva,† Yurii M. Polukarov,‡ Olga V. Safonova,*,§
Grigory Smolentsev, Marcin Sikora,§ Sigrid G. Eeckhout,§ and Pieter Glatzel§
Department of Electrochemistry, Faculty of Chemistry, Moscow State UniVersity, Moscow, Russia, A.N.
Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia,
European Synchrotron Radiation Facility, 38043 Grenoble Cedex, France, and Faculty of Physics, RostoV State
UniVersity, RostoV-on-Don, Russia
ReceiVed: July 19, 2006; In Final Form: September 15, 2006
Valence-to-core X-ray emission spectroscopy was applied to study a composition of chromium coatings
electrodeposited from Cr(III) sulfate electrolytes with the addition of formic or oxalic acid. It was shown that
the obtained crystallographically amorphous deposits contain chromium carbide compounds. These results
indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized
by very high electrocatalytic activity.
Introduction
Apparently, this can substantially enhance the current efficiency
of the target product. To answer the question on the role the
organic substances play in this process, it is essential to obtain
more detailed information on the composition and properties
of the chromium coatings formed.
Chromium electroplates represent great practical interest and
find wide application in various technologies. They exhibit
substantial hardness, wear, and erosion resistance and are known
for their high corrosion-resistive and decorative characteristics.
At the same time, because of the toxicity and the difficulties
associated with waste utilization, the conventional process of
metal electrodeposition from Cr(VI) electrolytes presents a
severe environmental hazard. This is why keen attention has
been drawn to date to the development of the process of
chromium deposition from Cr(III) electrolytes. Its practical
realization is largely complicated because the aqua complexes
[Cr(H2O)6]3+ are very inactive and their discharge can proceed
at far negative potentials in the range of active hydrogen
evolution.1-6 Under these conditions, it is impossible to form
high-quality coatings at sufficiently high current efficiencies.
As was shown in previous works,7-16 the high-quality
coatings with regard to their physicochemical, mechanical,
decorative, corrosion resistance, and other characteristics can
be obtained from Cr(III) electrolytes containing additions of
certain organic substances, particularly formic or oxalic acid.
To date, there is no ultimate opinion on the role played by these
organic substances during the electrodeposition of Cr(III). One
of assumptions considers the fact that organic molecules can
replace the water molecules in the inner sphere of Cr(III)
complexes. In this case, the reduction rate of the resulting Cr-
(III) complexes with organic ligands can be substantially higher
as compared with original aqua complexes because of the
transition from the outerspheric discharge mechanism to the
innerspheric one.17-19 It was also assumed that, being adsorbed
on the growing chromium crystals, the organic additives severely
inhibited the evolution of hydrogen molecules on them.20-22
The research in this direction has demonstrated that the
deposits formed from the proposed Cr(III) electrolytes exhibit
certain features that distinguish them from the deposits formed
in conventional Cr(VI) electrolytes. Thus, the XRD studies have
shown that the former deposits have crystallographically
amorphous structures with a grain size of ∼2-3 nm.12,13,23
However, the reliable identification of the phase composition
of deposits was impossible because of the presence of wide
“halos” in the diffraction patterns. It should be mentioned that
the annealing of deposits was accompanied by the appearance
in diffraction patterns of the lines typical of crystalline chromium
and chromium carbides.12,13,24 Of special interest were the
polarization curves measured on the deposits in 0.5 M H2SO4
solutions.19,23 As follows from these curves, the open-circuit
(corrosion) potential of amorphous chromium was shifted in
the positive direction by 0.3-0.4 V as compared with electrodes,
which were made of crystalline chromium formed by metal-
lurgical methods or deposited from Cr(VI) electrolytes, and was
located in the passivity range of chromium. It is remarkable
that such dependences are also typical of chromium carbide
electrodes.25, 26
Some X-ray studies19,23,27 devoted to the analysis of C KR
lines estimated the total amount of carbon in the deposits formed
in Cr(III) electrolytes with the addition of oxalic or formic acids
and also certain other organic substances. According to ref 27,
the deposits formed in sulfate-oxalate Cr(III) electrolytes
contained ca. 6 mass % carbon. In the deposits formed in
solutions with the addition of formic acid, formaldehyde, or
certain other organic substances, the carbon content was 2-2.5
times lower. In refs 19, 23, and 27, these deposits were examined
by the XPS method. As follows from the analysis of the C1s
spectral line, the surface layers of such deposits involved
considerable amounts of carbon-containing species. Using the
* Corresponding author. E-mail: safon@elch.chem.msu.ru (V.A.S.);
safonova@esrf.fr (O.V.S.).
† Moscow State University
‡ A. N. Frumkin Institute of Physical Chemistry and Electrochemistry.
§ European Synchrotron Radiation Facility.
Rostov State University.
10.1021/jp064569j CCC: $33.50 © 2006 American Chemical Society
Published on Web 10/20/2006

X-ray Emission Spectroscopy of Electrodeposited Cr Coatings
J. Phys. Chem. B, Vol. 110, No. 46, 2006 23193
layer-by-layer stripping of the chromium surface with a beam
of xenon ions or by mechanical scraping in the vacuum of the
preparative chamber of the spectrometer, the researchers at-
tempted to gain information on the state of carbon in the deposit
bulk.19,23,27 On the basis of the results of these studies, it was
assumed that the surface and bulk of deposited layers prefer-
entially contain polymeric products of carbonization of original
organic substances as well as carbide compounds of chromium.
In ref 27, the carbide composition in the deposits formed in
sulfate-oxalate Cr(III) electrolytes was assumed to be Cr23C6.
To elucidate the nature of organic polymeric products, a
procedure was proposed for their isolation from the deposits
and subsequent analysis.20-22 The deposits were dissolved in 6
M HCl. Organic substances were then extracted with chloroform
from these solutions, which was followed by their identification
by means of chromatography-mass spectrometry. It was found
that the deposits indeed contained the polymerization products
of original organic substances (the compounds with chains of
up to 36 carbon atoms were identified). However, the total mass
of these extracted carbon-containing substances was less than
10% of the overall amount of carbon in the deposits, i.e.,
substantially lower than could be expected on the basis of the
XPS studies of deep layers.
In principle, several hypotheses can be put forward to explain
the observed disbalance in the carbon content. Thus, the
chromium deposition could have produced such carbon-contain-
ing organic substances that fail to be extracted with chloroform
from the solutions obtained by the dissolution of the deposit in
acid. Moreover, the presence of organic substances in the
deposits, the retention time of which in the chromatographic
column is very great, cannot be ruled out. Obviously, the
chromatography-mass spectrometry method will then fail to
both identify such substances and estimate their masses. An
assumption that the electrodeposition of the metal can result in
the deep reduction of original organic substances and produce
carbide compounds of chromium may also be put forward,
although at first sight, this appears highly unlikely.
Cr(III) and other solution components. These electrolytes
provided the necessary high buffer capacity of solutions and
allowed high-quality chromium deposits of the required thick-
ness to be obtained at high deposition rates (2-3 µm/min).
The electrodeposition was carried out under galvanostatic
conditions in a thermostat-controlled cell made of fluoroplastic-
4, which had nonseparate cathodic and anodic compartments.
Platinized titanium used as the anode material, like platinum,30
ensured that the oxidation of Cr(III) ions to Cr(VI) ions, which
hinders the effective target process, proceeded at very low rates
compared to those of the oxygen evolution. In the course of
deposition, the pH was maintained in the range of 0.8-2.2 and
the current density (deposition rate) could be varied from 0.1
to 0.5 A/cm2. The solution temperature was 40-45 °C.
2. Sample Preparation. Using the described procedure, the
chromium deposits ∼30 µm in thickness were obtained in Cr-
(III) electrolytes containing formic or oxalic acid as the organic
additive. The deposits were carefully separated from the copper
substrates using a tool of a hard alloy in a vacuum chamber (1
× 10-7 Torr) and crushed in an agathic mortar. From the
resulting powder, a fraction with a particle size no less than 10
µm was selected. This fraction was mixed with BN powder (1
wt % Cr) and pressed into 5 mm pellets. In parallel, the reference
samples: metal chromium foil (5 µm thick) and Cr2O3, CrN,
and Cr3C2 powders mixed with BN (1 wt % chromium) were
prepared.
3. Measurements of X-ray Emission Spectra. We per-
formed high-energy-resolution X-ray emission spectroscopy
experiments at undulator beamline ID26 (High Brilliance XAFS-
XES beamline) of the European Synchrotron Radiation Facility
(ESRF) in Grenoble. The electron energy was 6.0 GeV and the
ring current varied between 150 and 200 mA. The incident
energy (6020 eV), which is above Cr K-edge (5989 eV), was
selected by means of a pair of Si(220) single crystals. Higher
harmonics were suppressed by two Si mirrors at 3.5 mrad. The
beam on the sample was 0.3 mm horizontal and 1 mm vertical
with a total flux on the order of 1 × 1013 photons/s. According
to our estimates, the heating of the samples during this intensive
beaming did not exceed 50 °C. We used an analyzer that
employs the (333) Bragg plane of one spherically bent (R )
850 mm) Ge wafer 89 mm in diameter. The energy bandwidth
in the X-ray emission detection was 0.6 eV. An avalanche
photodiode (APD) was used as the detector. The Kâ main and
Kâ satellite lines were measured from 5925 to 5995 eV and
then normalized by the integral spectral intensity.
To test the hypotheses put forward, it was essential to obtain
additional information on the composition of chromium deposits
and the state of carbon in them using one of direct methods.
From this viewpoint, a new method, viz. the valence-to-core
X-ray emission spectroscopy (XES), which was surveyed in ref
28, was of great interest. In ref 28, by the example of a number
of model systems, this method was demonstrated to be capable
of providing valuable information, which allows identification
of covalent bonds typical of metal compounds with metalloids.
Using the potentials of this method, we made an attempt to study
the composition of chromium deposits formed in Cr(III)
electrolytes with the addition of formic or oxalic acids.
4. Theoretical Simulations of X-ray Emission Spectra.
Valence-to-core X-ray emission spectra were calculated on the
basis of the full multiple scattering theory using the FEFF8.2
code.31 Self-consistency of the potential was performed for a
5.2 Å cluster using the Hedin-Lunqvist exchange potential. The
additional imaginary part of the potential equal to 0.6 eV was
used to take into account the experimental resolution. The
geometry of the cluster was constructed on the basis of the X-ray
diffraction data.32 Full multiple scattering calculations were
performed for a 6.5 Å radius. The spectra corresponding to
nonequivalent crystallographic positions were averaged.
Experimental Section
1. Deposition Procedure. To form chromium deposits on
copper or brass substrates, we used the electrolytes of the
following composition: 100 g/L Cr2(SO4)3‚6H2O, 100 g/L Al2-
(SO4)3‚18H2O, 80 g/L Na2SO4, and 20 g/L NaF, which
contained the addition of organic substances (sodium formate
or oxalate) in a concentration of ∼0.2 mol/L. Solutions were
prepared with reagent-grade chemicals and thermostat-controlled
at 90 °C for 30 min. Such a pretreatment of the electrolyte was
necessary for the intensification of the process of the exchange
of water molecules in the inner sphere of Cr(III) aqua complexes
for organic ligands.17,29 For example, after such a pretreatment,
the pH and color of oxalate electrolytes remained unchanged
for a year, which confirmed the stability of the ionic state of
Results and Discussion
For 3d elements, Kâ main lines (Kâ1,3 and Kâ′) correspond
to the 3p-1s transition, whereas Kâ satellite lines correspond
to the valence-to-core transitions.28 The valence-to-core transi-
tions are chemically sensitive fluorescence lines, because the
character of the valence orbitals changes the most for different
chemical species. The Kâ satellite region is divided into the

23194 J. Phys. Chem. B, Vol. 110, No. 46, 2006
Safonov et al.
Figure 1. Kâ satellite lines of Cr, Cr2O3, CrN, and Cr3C2. O, N, and
C indicate the positions of the crossover (Kâ′′) peaks of oxygen,
nitrogen, and carbon ligands. The main Kâ lines of Cr are shown in
the inset.
Figure 3. Theoretical simulations (red curves) and experimental spectra
(black curves) of Kâ satellite lines of Cr (solid lines) and Cr3C2 (dashed
lines).
respect, the data obtained in this study are, in fact, the first
example of the practical application of the XES method for
studying real objects. To estimate the concentration of the
carbide-like phase, we fitted the spectra of Kâ satellite lines of
the S1 and S2 samples as a linear combination of Cr and Cr3C2
(CrC0.67) references. For the S1 sample, the fit is shown in the
Figure 2. The calculated concentrations of chromium atoms in
the Cr3C2 local environment in the S1 and S2 samples are equal
to 34 and 26 mol % (this corresponds to 5.0 and 3.9 wt %
carbon), respectively.
The theoretical simulations of Kâ satellite lines of chromium
in Cr and Cr3C2 are given in Figure 3. In agreement with
experimental results, the experimental spectrum of Cr3C2 has a
clear Kâ′′ peak. This feature is due to the mixing of C 2s orbitals
with the Cr orbital of p symmetry. Metal Cr does not have any
features in this region, because Cr 3p orbitals are significantly
lower in energy and produce the Kâ main line, whereas 3d
orbitals are higher in energy and give rise to the Kâ2,5 peak.
The major contribution of metallic Cr to Kâ2,5 comes from the
transitions to d orbitals of the nearest atoms. For carbide
compounds, 2p orbitals of C also form a valence band and affect
the shape of spectrum in this region. Insofar as 2p orbitals of C
are lower in energy in comparison with 3d levels of metal, there
is a clear shift in the Kâ2,5 main maxima. The relative position
of the Kâ′′ peak can be used as a fingerprint of carbide
compounds, because the binding energy of the C 2s orbitals
should not depend very much on the carbide structure. However,
we cannot conclude that it is impossible to distinguish different
chromium carbides by measuring the fine structure and intensity
of Kâ satellite lines. We plan to consider this issue in detail
(experimentally and theoretically) soon.
Figure 2. Spectrum of Kâ satellite lines of sample S1 (solid line) and
the fit (dotted line) of this spectrum by a linear combination of Cr and
Cr3C2 references (dashed lines).
Kâ′′ or crossover peak at lower fluorescence (or higher binding)
energies and the Kâ2,5 structure immediately below the Fermi
level. For different ligands of the second period (C, N, O, ...),
the relative shifts between the crossover fluorescence energies
correspond mainly to the shift in 2s binding energies of atomic
species.
Figure 1 shows the Kâ satellite lines of metallic Cr, Cr2O3,
CrN, and Cr3C2. The Kâ main lines of Cr are given in the inset.
One can see that the shape of spectra and especially the position
of the Kâ′′ peak depend on the local environment of Cr.
Furthermore, the position of the Kâ′′ can be used as a fingerprint
of the presence of Cr-O, C-N, or Cr-C bonds in the sample,
which is very difficult to distinguish by conventional X-ray
absorption spectroscopy (EXAFS and XANES).
Figure 2 shows the Kâ satellite lines of the S1 sample
synthesized electrochemically from Cr(III) solutions containing
formic acids. The spectrum of the S2 sample prepared electro-
chemically from a Cr(III) solution containing oxalic acid is very
similar. The positions of the Kâ2,5 and Kâ′′ peaks clearly indicate
the presence of the carbide-like phase (a carbide compound) in
both samples. It should be recalled that in early studies, the
possibility of directly identifying the compounds of 3d metals
with metalloids from the Kâ satellite lines by using the new
XES method was considered only for model systems.28 In this
The results of direct studies allowed us to substantially refine
our concepts on the processes that involve the organic substances
and occur immediately at the formation of chromium deposits
from Cr(III) electrolytes. This refinement was based on the
following arguments. In the electrolytes we used, the mole
content of organic substances is substantially lower than the
mole content of Cr(III). Under these conditions, on the basis of
the dissociation constants of formic (pK ) 3.75) and oxalic (pK
) 3.8) acids as well as on the stability constants of Cr(III)
complexes with the molecules of these acids (pK1 ≈ 2 and 5.5,

X-ray Emission Spectroscopy of Electrodeposited Cr Coatings
J. Phys. Chem. B, Vol. 110, No. 46, 2006 23195
respectively),33 it can be assumed that the major part of formic
acid molecules and virtually all oxalic acid molecules enter into
the nearest coordination sphere of chromium complexes (i.e.,
the concentrations of these organic acids in the free state are
very low). An important qualitative result, which was obtained
on the basis of the XES studied, is that the reduction of Cr(III)
to the metal simultaneously results in the deep reduction of the
organic ligands from the inner coordination sphere of the
chromium complex to give carbide compounds of chromium.
It is noteworthy that such a deep reduction of organic ligands
points to the high electrocatalytic activity of metal nanocrystals,
which are formed in the course of electrodeposition and
apparently provide the sites for this process.
deposits obtained in ref 24 already contained carbide compounds
of chromium. Such deposits, like the majority of nanocrystalline
structures, are thermodynamically nonequilibrium and, when
heated, are prone to recrystallization and an increase in the size
of deposit particles. These processes accompany the transition
to the more equilibrium state, which, from our viewpoint, is
reflected in the transformation of the halo in the diffraction
patterns into obvious peaks corresponding to crystalline chro-
mium and its carbides.
Conclusions
Using the valence-to-core XES technique, new results were
obtained that characterize the composition of amorphous
chromium deposits formed at the electrochemical deposition of
the metal from Cr(III) electrolytes in the presence of organic
substances (oxalic or formic acid). These are, first of all, the
data on the presence of considerable amounts of chromium
carbide compounds in the deposited nanoparticles as well as
on the absence of chromium oxides in them.
The direct results on the formation of chromium carbide
compounds during the chromium deposition from Cr(III)
electrolytes in the presence of oxalic or formic acids point to
the extremely high electrocatalytic activity of this metal in
cathodic processes.
The idea of the possible formation of carbide compounds of
chromium in the studied process was originally put forward in
our studies.19,23,27 However, our assumptions were on the basis
of indirect data, viz., on the peculiarities in the electrochemical
and corrosion behavior of the deposits as well as on the XPS
results on the analysis of the deposit surface. From this
viewpoint, the XES data on the bulk composition of deposits
deserve great attention, because the previous literature contained
no information on such a deep electrochemical reduction of
organic substances to the carbide state in the compounds with
metals.
The conclusion that the deposit bulk contains no oxygen-
containing chromium compounds also deserves attention. To
be more accurate, we can affirm from our data that chromium
deposits do not contain more than 5-7 mol % chromium oxide
in their bulk. This conclusion results from the analysis of the
noise level in experimental spectra of Kâ satellite lines of
samples S1 and S2. It should be noted that substantially higher
concentrations of chromium oxides in similar samples were
observed before by XPS.23,27 The XPS measurements were
performed on the surface of the samples, which were transferred
into the spectrometer immediately after deposition, and also on
the same samples that were subjected to ionic etching or
mechanical scraping. On the basis of our XES result, we can
conclude that the XPS technique is not suitable for proving the
presence or absence of oxide compounds in the bulk of
nanocrystalline chromium films.
It is shown that the valence-to-core XES technique allows
for additional valuable information on the composition of
nanoparticles to be retrieved. This method appears to have good
prospects in studying the peculiarities of the electrochemical
formation of crystallographically amorphous deposits of metals
and alloys.
Acknowledgment. We gratefully acknowledge ESRF for
provision of facilities at ID26. This work is partly supported
by the Russian Foundation for Basic Research (Project 05-03-
32681)
References and Notes
(1) Potapov, I. I.; Kudryavtsev, N. T. Itogi Nauki i Tekhniki (AdVances
of Science and Technology); Ser. Elektrokhimiya; VINITI: Moscow, 1966;
Vol. 1, p 109.
(2) Danilov, F. I.; Velichenko, A. B.; Loboda, S. M.; Azorina, S. M.
Elektrokhimiya 1988, 24, 442.
We can also state that the main amount of carbon in our
chromium deposits presents in the form of carbide compounds.
However, taking into account the sensitivity of the XES
technique (5-7 mol %), we consider our quantitative results
as being merely initial, rough estimates. It is interesting to
compare the results of this study with the results obtained by
the XRD methods on the characterization of chromium deposits.
In a recent study,24 the authors considered the deposits from a
very complex electrolyte, which contained CrCl3 (0.5 M), formic
acid (0.8 M), and the components that provided the buffer
capacity and conductivity. Under these conditions, according
to the detailed XRD studies, the obtained deposits were also
crystallographically amorphous, and the authors considered them
as being intermediate Cr-C compounds. They also studied the
effect of the annealing temperature in the range of 200-800
°C on the deposit structure. The analysis of recorded diffraction
patterns showed that the annealing resulted in the appearance
of clear lines corresponding to chromium carbides. On the basis
of these results, it was assumed that the formation of deposits
involved the co-deposition of carbon, whereas chromium
carbides were formed only at the deposit annealing stage.
However, the XES results shown above suggest that the results
of XRD studies can be interpreted in a different way. It seems
more likely that the original crystallographically amorphous
(3) Burdykina, R. I.; Falicheva A. I. Elektrokhimiya 1988, 24, 1682.
(4) Elinek, T. B. GalVanotechnik 1996, 87, 42.
(5) Elinek, T. B. GalVanotechnik 1997, 88, 44.
(6) Kudryavtsev, V. N.; Vinokurov, E. G.; Kuznetsov, V. V. GalVan-
otekhnika i Obrabotka PoVerkhnosti 1997, 6, 24.
(7) Hashino, S.; Laitinen, H. A.; Hoflund, G. B. J. Electrochem. Soc.
1986, 133, 681.
(8) Tsai, R.-Y.; Wu, S.-T. J. Electrochem. Soc. 1990, 137, 637, 3057.
(9) Awari, J.; Kulkarni, S. K. J. Mater. Sci. 1990, 25, 1357.
(10) Edigaryan, A. A.; Polukarov, Yu. M. Zashchita MetalloV 1996,
32, 504.
(11) Danilov, F. I.; Popov, E. R.; Burykina, V. S.; Protsenko, V. S.
Elektrokhimiya 1997, 33, 543.
(12) Edigaryan, A. A.; Polukarov, Yu. M. Zashchita MetalloV 1998,
34, 117.
(13) Edigaryan, A. A.; Polukarov, Yu. M. Zashchita MetalloV 1998,
34, 609.
(14) Danilov, F. I.; Protsenko, V. S. Elektrokhimiya 1998, 34, 641.
(15) Edigaryan, A. A.; Polukarov, Yu. M. Zashchita MetalloV 1999,
35, 5.
(16) Edigaryan, A. A.; Polukarov, Yu. M. Zashchita MetalloV 1999,
35, 355.
(17) Kravtsov, V. I. RaVnoVesie i Kinetika Elektrodnykh Reaktsii
KompleksoV MetalloV (Equilibrium and Kinetics of Electrode Reactions of
Metal Complexes); Khimiya: Leningrad, Russia, 1985.
(18) Kravtsov, V. I. Elektrokhimiya 1995, 31, 1165.
(19) Edigaryan, A. A.; Safonov, V. A.; Lubnin, E. N.; Vykhodtseva, L.
N.; Chusova, G. E.; Polukarov, Yu. M. Electrochim. Acta 2002, 47, 2775.

23196 J. Phys. Chem. B, Vol. 110, No. 46, 2006
Safonov et al.
(20) Safonov, V. A.; Vykhodtseva, L. N.; Lubnin, E. N.; Polyakov, N.
A.; Polukarov, Yu. M. Abstracts from the 8th International Frumkin
Symposium “Kinetics of Electrode Processes”, Moscow, Oct 18-22, 2005;
p 313.
(21) Safonov, V. A.; Vykhodtseva, L. N.; Lubnin, E. N.; Polyakov, N.
A.; Polukarov, Yu. M. Abstracts from the 56th Annual Meeting of the
International Society of Electrochemistry, Busan, Korea, Sept 25-30, 2005;
p 697.
(22) Safonov, V. A.; Vykhodtseva, L. N.; Lubnin, E. N.; Polukarov,
Yu. M. Elektrokhimiya 2007, 43, in press.
(23) Vykhodtseva, L. N.; Edigaryan, A. A.; Lubnin, E. N.; Polukarov,
Yu. M.; Safonov, V. A. Elektrokhimiya 2004, 40, 435.
(24) Kwon, S. C.; Kim, M.; Park, S. U.; Kim, D. Y.; Kim, D.; Nam, K.
S.; Choi, Y. Surf. Coat. Technol. 2004, 183, 151.
(26) Tsirlina, G. A.; Petrii, O. A.; Kandakova, N. S. Zashchita MetalloV
1986, 22, 933.
(27) Lubnin, E. N.; Edigaryan, AÅ . A.; Polukarov, Yu. M. Zashchita
MetalloV 2000, 36, 339.
(28) Glatzel, P.; Bergmann, U. Coord. Chem. ReV. 2005, 249 (1-2),
65.
(29) Vinokurov, E. G.; Kudryavtsev, V. N. Elektrokhimiya 1992, 28,
331.
(30) Falicheva, A. I. Elektrokhimiya 1968, 4, 854.
(31) Ankudinov, A. L.; Ravel, B.; Rehr, J. J.; Conradson S. D. Phys.
ReV. B 1998, 58, 7565.
(32) Rundqvist, S.; Runnsjoe, G. Acta Chem. Scand. 1969, 23, 1191.
Swanson, H. E.; Gilfrich, N. T.; Ugrinic, G. M. J. Res. Natl. Inst. Stand.
Technol. 1955, 539, 5.
(33) Perrin, D. D. Stability Constants of Metal-Ion Complexes, Part B,
Organic Ligands; Pergamon Press: NewYork, 1979.
(25) Kolotyrkin, Ya. M.; Knyazheva, V. M. Itogi Nauki i Tekhniki
(AdVances of Science and Technology), Ser. Korroziya i Zashchita ot
Korrozii; VINITI: Moscow, 1974; Vol. 3, p 5.