Zinc electrochemical reduction on a steel cathode in a weak electromagnetic field

Article abstract of DOI:10.1134/S0036024407100330

The influence of weak periodic electromagnetic pulses with a repetition rate of 215 kHz on the process of zinc electrochemical reduction at a structural-steel cathode under the conditions of working galvanic production was studied experimentally. The results of studying zinc coatings using scanning electron microscope and X-ray microanalyzer are presented. The effects are discussed in the context of external synchronization of the self-organized dissipative structures in the reaction zone.

Full text of DOI:10.1134/S0036024407100330

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2007, Vol. 81, No. 10, pp. 1715–1717. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © A.A. Kolesnikov, Ya.V. Zarembo, L.P. Puchkov, V.I. Zarembo, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 10, pp. 1914–1916.
SHORT
COMMUNICATIONS
Zinc Electrochemical Reduction on a Steel Cathode
in a Weak Electromagnetic Field
A. A. Kolesnikov, Ya. V. Zarembo, L. V. Puchkov, and V. I. Zarembo
St. Petersburg State Technological Institute (Technical University), ul. Politekhnicheskaya 29, St. Petersburg, 195251 Russia
e-mail: wisekaa@bk.ru
Received November 24, 2006
Abstract—The influence of weak periodic electromagnetic pulses with a repetition rate of 215 kHz on the pro-
cess of zinc electrochemical reduction at a structural-steel cathode under the conditions of working galvanic
production was studied experimentally. The results of studying zinc coatings using scanning electron micro-
scope and X-ray microanalyzer are presented. The effects are discussed in the context of external synchroniza-
tion of the self-organized dissipative structures in the reaction zone.
DOI: 10.1134/S0036024407100330
For the practical problems of electroplating, the for- ZnSO4 · 7H2O (100), NH4Cl (100), H3BO3 (25); dextrin
mation of a defectless electrode coating is of prime as brightener) at pH 5.0–5.5, room temperature, cath-
interest. This is particularly important for the applica- ode current density j = 1 A/dm2, and after preparing
tion of cathode-type decorative metallic films to corro- electrodes and electrolyte according to the technologi-
sion-nonresistant metals (steel plating with tin, nickel, cal requirements. Electrolysis time was 20 min without
chrome, and gold). The anode “zinc-steel” coatings, forced convection. In the experiments, a short-circuit
despite the good film adhesion and corrosive insensitiv-
ity to film porosity (especially in alkaline cyanide
baths), suffer from hydrogen embrittlement because of
the attendant hydrogen reduction. The decorative prop-
erties of zinc layers are highly sensitive to the compo-
sitions of electrolyte and zinc anodes. The possibilities
of heterogeneous control in electroplating are well
known. These are the general-action methods with lim-
ited possibilities of local and selective effects, such as
the preparation of electrodes and an electrolyte, varia-
tion of temperature and current density, and convection
in a solution.
magnetic-dipole loop isolated from electrolyte by gal-
vanization was used as a load of a pulsed electrical-cur-
rent oscillator with a total power of 10 V A. The elec-
tromagnetic-field power (milliwatts) delivered by the
oscillator to the surrounding medium is vanishingly
small compared to the heat flows. The pulse repetition
rate in a dipole wire was 215 kHz at an amplitude of 1 A.
The plates were plated with zinc in the standard and
background regimes (with electromagnetic pulse feed-
ing) and subjected to a comparative analysis. The com-
parable parameters were as follows: the visual overall
coating thickness (H); “atomic” thickness of zinc layer
(h) reduced to crystal close packing and characterizing
the current output and surface molar density of coating;
estimated coating density (ρ) with allowance for its
porosity; and diameter (D) of distinct pores. In addi-
tion, microscopic visual control of the character of the
resulting zinc layers was performed. Visual investiga-
tions, including measurement of the overall thickness
(H), were carried out by scanning electron microscopy
(SEM JSM-35CF (JEOL)) with an accelerating field of
25 kV and a probe current of 0.6 nA. The reduced coat-
ing thickness (h) was measured on a Link 860 (Link)
X-ray microanalyzer (XMA) of the energy-dispersion
type by the Jacovitz-Newbery method [6] in a field of
25 kV with a probe current of 10 nA during 100 s fol-
The spatiotemporal ordering effects in the regime of
feeding weak (background) electromagnetic pulses into
the galvanic system can remove the disadvantages of
the existing methods without radical modification of
technology [1–5]. It should be emphasized that the
choice of the galvanochemical processes as the object
of background control was not accidental but predict-
able on the basis of the effect of background acoustic
resonance self-organization control (BARSC) theory
that was put forward and cited in the literature for non-
equilibrium nonlinear systems. Among the systems
with perpetually arising dissipative structures is an
electroplating reactor under real technological condi-
tions for performing electrode processes.
We checked these presumptions in actual galvanic lowed by the TFOS-program computation [6]. The ele-
production by direct experiments on zinc electrocrys- mental composition of coating was determined also
tallization on the surfaces of steel (St. 8) cathode plates using microanalyzer. The experimental SEM results
(4-dm2 group) in a standard acid sulfate bath with a vol- obtained in different regimes for the planar and profile
ume of 3 × 2 × 1 m3 (electrolyte composition (g/l): views of zinc coatings are presented in the figure.
1715

1716
KOLESNIKOV et al.
10 µm
10 µm
(‡)
(b)
10 µm
10 µm
(c)
(d)
Planar (a, b) and profile (c, d) SEM photographs of the zinc coatings at steel cathodes, as obtained in the standard (a, c) and back-
ground with 215-kHz CPs and (b, d) zinc-coating regimes. Photography in reflected electrons, 3000×. Zinc coating: porous, pore
size 5–15 µm (a, c); (b, d) dense homogeneous, pore size 1–4 µm.
The visual estimate of the results of background conducting media (electrodes, electrolytes) reactive
regime of steel zinc-plating indicates, in both planar toward electromagnetic fields and dispersive toward
and profile photographs, that, at a CP frequency of mechanical vibrations, acoustic waves can propagate in
215 kHz, the coating is considerably more homoge-
neous and dense with a smaller size of zinc grains,
smaller number and size gas lacunas, which, besides,
become isolated contrary to the through channels
appearing in the standard regime.
such media under given conditions to synchronize the
periodic motion (vibration and rotation) of the distrib-
uted self-excited generators representing dissipative
structures (DSs) that form and govern the final proper-
ties of the reaction product.
The quantitative computational results for the SEM
and XMA data are presented in the table.
The regulation acoustic wave forms as a result of the
well-known electromagnetic-acoustic transformation
effect in a wire of a magnetic-dipole current loop. For
the CP shape and rate characteristic of such a con-
densed energy-saturated medium, a weak regulation
signal is not damped but, rather, strengthens due to the
The analysis of these results suggests that the action
of weak electromagnetic pulses in the electrochemical
zinc plating of steel products modifies substantially the
coating parameters, although the approved standard
technology does not suffer noticeable changes. In addi- energy of physicochemical processes to become a plec-
tion, the data obtained above are in complete agreement trum—a peculiar kind of “guide” that provides ampli-
with the BARSC theory [1–5], according to which, in tude-phase coherence in the motion of the normally sto-
Comparison of the parameters of zinc coatings obtained for steel cathodes in the standard regime and under the action of weak
electromagnetic pulses
CP frequency
Zn, %
Fe, %
h(XMA), µm H(SEM), µm
ρ, kg/m3
D1, µm
D2, µm
f, kHz
0
90.1
94.8
4.7
2.6
1.6
2.1
4.5
5.0
2500
3000
0.20
0.10
0.15
0.10
215
3
Note: h(XMA) is the thickness determined by the TFOS method for ρ(Zn) = 7100 kg/m ; H(SEM) is the thickness determined from the
SEM data for the profile sections of the samples; ρ = 7100h/H is the estimated coating density with allowance for its porosity; D
1
and D are the mean sizes of zinc grains in the profile and planar view of coating, respectively.
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 81 No. 10 2007

ZINC ELECTROCHEMICAL REDUCTION ON A STEEL CATHODE
1717
chastic DSs, thereby increasing cardinally the correla- structural entropy of the DS system and decreasing the
tion length of their parameters.
global entropy production at all hierarchy levels in the
system and thermostat, which enhances the energetic
efficiency of the technological process, its velocity, and
the degree of spatial inhomogeneity of the end product
[1–4]. These theoretically substantiated model notions,
at least, are contradictory to none of the observed
effects occurring in the process of electrochemical steel
zinc-coating, which allows the BARSC in electroplat-
ing to be considered as a predictable, reproducible, and
stable way of control and opens up prospects for apply-
ing this method in other electrochemical technologies.
As a result, a nonequilibrium system stabilizes (the
external regulation signal can be switched off), and the
distribution over the DS parameters for the nonequilib-
rium system narrows drastically to smooth out both
intensive and extensive properties of the reaction zone.
For high currents in the voltaic circuit, chaotic diffu-
sion (described by the equation of the parabolic type)
can no longer provide adequately fast charge transfer.
An essentially nonequilibrium drift of current carriers
in near-electrode areas of electrolyte organizes convec-
tive Rayleigh-Benard cells, which afford high velocity
of the convective (perpendicular to the electrode) and
advective (tangential) ion transfer and equalization of
the concentrations, temperatures, and chemical poten-
tials, favoring the dominant role of the target reaction
and suppression of the side processes, in particular, the
hydrogen reduction reaction. Parametrically, such sce-
nario inevitably manifests itself in the buildup of the
load voltage, current, and efficiency.
REFERENCES
1. O. L. Kiseleva, A. A. Kolesnikov, V. I. Zarembo, et al.,
Khim. Prom-st. 80 (5), 12 (2003).
2. V. I. Zarembo, O. L. Kiseleva, A. A. Kolesnikov, et al.,
Neorg. Mater. 40 (1), 96 (2004).
3. V. I. Zarembo and A. A. Kolesnikov, Teor. Osn. Khim.
Tekhnol. 40 (5), 520 (2006) [Theor. Found. Chem. Eng.
40 (5), 483 (2006)].
In the context of the percolation theory, DS synchro-
nization amounts to the elimination of dislocations and
disclinations in the convective cells to form the so-
called infinite percolation cluster that affords the
“short-circuit” regime in the chain of charge-density,
mass, and temperature transfer in the zone of forming
synchronous DSs. In the context of the nonequilibrium
nonlinear thermodynamics, DS synchronization
amounts to lowering the stationary nonequilibrium
4. V. I. Zarembo, A. A. Kolesnikov, and E. V. Ivanov, Izv.
Akad. Nauk, Ser. Fiz. 70 (8), 1088 (2006).
5. A. A. Kolesnikov and V. I. Zarembo, Vestn. Voronezhsk.
Gos. Tekhn. Univ., Ser. Fiz. Mat. Model. 2 (8), 73
(2006).
6. Practical Scanning Electron Microscopy: Electron and
Ion Microprobe Analysis, Ed. by J. I. Goldstein and
H. Yakowitz (Plenum, New York, 1975; Mir, Moscow,
1978).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 81 No. 10 2007