Oscillatory circulation of copper particles during silver-displacement plating in a high magnetic field

Article abstract of DOI:10.1246/cl.2000.388

Motion of copper particles during silver-displacement plating in a high magnetic field was investigated. Immediately after injecting a silver nitrate solution to a vessel filled with copper powder and suspending the powder in the solution, the particles start to circulate along a vessel under a vertical magnetic field with suddenly changing their directions. The velocity of the motion increased with the magnetic field strength though the deposition rate remained constant.

Full text of DOI:10.1246/cl.2000.388

388
Chemistry Letters 2000
Oscillatory Circulation of Copper Particles during Silver-Displacement Plating
in a High Magnetic Field
Shin-ichi Yonemochi and Ryoichi Aogaki*†,††
Saitama Prefectural Industrial Technology Center, 1-1-56 Shibashimo, Kawaguchi, Saitama 333-0848
†National Research Laboratory for Magnetic Science, JST, 1-1-56 Shibashimo, Kawaguchi, Saitama 333-0848
††Department of Product Design, Polytechnic University, 4-1-1 Hashimoto-dai, Sagamihara, Kanagawa 229-1196
(Received January 11, 2000; CL-000030)
Motion of copper particles during silver-displacement plat-
a bore space of 10 cm in diameter and the maximum magnetic
flux density of 10 tesla (T). For a horizontally homogeneous
magnetic field, the interface of the plating solution was placed
at the distance of 11 cm from the top of the magnet, where the
magnetic flux density was kept constant within the error of
0.01 T. Copper powder with the average diameter of 0.1 mm
(99.9% pure) was used, and 0.3 mol dm-3 silver nitrate solution
was prepared as the plating solution.
ing in a high magnetic field was investigated. Immediately
after injecting a silver nitrate solution to a vessel filled with
copper powder and suspending the powder in the solution, the
particles start to circulate along a vessel under a vertical mag-
netic field with suddenly changing their directions. The veloci-
ty of the motion increased with the magnetic field strength
though the deposition rate remained constant.
After settling in the bore a test vessel (1.7 cm in diameter)
filled with 30 mg copper powder, the plating solution was
injected into the vessel. The temperature of the solution was
kept at 50 ºC. The motion of the particles was monitored with a
CCD camera through a microscope. The circulation velocity of
the solution was measured by using a tetrafluoroethylene
(Teflon ®) strip (0.2 cm × 1 cm) floating and rotating at the liq-
uid interface during the reactions as shown in Figure 2. The
circulation velocity of the particles was determined by measur-
ing the angle θ of the strip from a standard lines. After the
experiment, the plated powder was filtrated and supplied for
determining the amount of the deposited silver with the induc-
tive coupled plasma mass spectrometry (ICP-MS).
In recent years, following the development of the super-
conducting magnet, the magnetic field effects in various reac-
tion processes have attracted many researchers’ attention.1 As a
result, various phenomena have been reported in many fields.2-6
In electrochemistry, the MHD effect that a solution flow
(the MHD flow) induced by the Lorentz force greatly affects
reaction rates has been clarified.7 For chemical dissolution of
metals in magnetic fields, a new concept, i.e., the micro-MHD
effect has been proposed.8 In these reactions, without any
external electrolytic current, a kind of MHD flow takes place
on the metal surfaces.
If the metal is a particle suspending in a solution, there is a
possibility that the Lorentz force makes it move. Actually,
Shinohara et al. have found the gigantic circular motion of zinc
particles under high magnetic fields.9
The micro-MHD effect can be also considered for other
phenomena such as electroless plating and displacement plat-
ing.10-13 From the viewpoint of materials processing, the func-
tional electroless plating onto metal particles is an important
method for the surface finishing of metal powder. Therefore,
the aim of this paper is to examine a new possibility of the elec-
troless plating by observing the behavior of copper powder dur-
ing the displacement plating from a silver nitrate solution in a
high magnetic field.
Figure 2 exhibits the photos of the surface of the plating
solution and the inside of the solution; the solution together
with the mass of the copper powder rotated along the inner wall
of the test vessel, and the silver dendrites quickly developed.
Needle-like dendrites repeatedly grew up and fell off.
Simultaneously, as shown in Figure 3, the direction of the rota-
tion was changed suddenly. Such abrupt change of the rotating
direction seemed accidental and non-periodic, just like a chaot-
ic oscillation. In spite of the chaotic motion, the velocity
increased linearly with the magnetic field strength, and the dep-
osition rate was kept constant (1.34 × 10-5 mol s-1) independent
of the magnetic field strength.
Figure 1 shows the schematic configuration of the appara-
tus. The magnet was a liquid-helium-free superconducting
magnet (Sumitomo Heavy Industries Ltd., HF10-100VHF) with
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
389
On the anodic side, however, the silver ions can be sufficiently
supplied, so that the reduction of silver ions starts at the former
anodic site (c). On the former cathodic side, among the roots of
the dendrites, the copper substrate dissolves because of the
anodic dissolution of copper (d).
Namely, the cathodic and anodic sites are exchanged, so
that the current in (a) and (d) flow in the opposite directions,
and the Lorentz forces operate reversely. This is the reason why
the rotation changes the direction. As the reactions proceed, at
the new cathodic site, silver dendrites grow, whereas the silver
dendrites at the new anodic site are removed by the dissolution of
the copper substrate. Because the dendrites tend to fall off, the
period of each state of the plating becomes uncertain.
In this plating, it is thought that an electrochemical local cell
is formed between the following anodic and cathodic reactions,
In an actual system, all the particles behave cooperatively
just like one gigantic particle. This is because the particle den-
sity is so high that the neighboring particles have the great
probability to contact each other. Figure 6 schematically repre-
sents such effect; an electrolytic current penetrates all the
ordered particles in one direction. The anodic and cathodic
sites of each particle go hand in hand with those of the neighbor
particle. Therefore, according to the mechanism mentioned
above, if one particle changes the current direction, all other
particles also change the directions. This situation in Figure 6
is similar to the phase transition represented by the Ising model
for ferromagnetism materials.14
As mentioned above, the dendrites are rough and eager to
fall off from the copper substrate. From these experimental
results, as shown in Figures 4 and 5, we can suppose the mech-
anism of this phenomenon as follows: Assuming that this
motion comes from a cooperative effect of a lot of particles, we
can pick up one particle as the representative of all other parti-
cles. Figure 4 indicates how the particle moves, i.e., inside the
particle, from the cathodic site to the anodic site, an electrolytic
current flows, so that in the magnetic field, a localized Lorentz
force is produced, and the particle moves to the right side. As
explained in Figure 5, after a certain time elapses, the cathodic
portion is roughly covered with silver dendrites, and the silver
ions are depleted in the solution near the dendrites. Therefore, the
whole reaction rate decreases and finally the motion ceases (b).
This is only a qualitative elucidation, so that we are now
attempting to quantitatively examine the oscillatory behavior of
this rotation.
References
1
2
3
K. Kitazawa, Kagaku Kogyo, 48,769 (1997).
S. Ueno and M. Iwasaka, J. Appl. Phys., 75, 7177 (1994).
N. Hirota, T. Homma, H. Sugawara, K. Kitazawa, M. Iwasaka, S.
Ueno, H. Yokoi, Y. Kakudate, S. Fujiwara, and K. Kawamura, Jpn.
J. Appl. Phys., 34, 991 (1995).
4
5
Y. Ikezoe, N. Hirota, J. Nakagawa, and K. Kitazawa, Nature, 393,
749 (1998).
M. Hamai, M. Tagami, I. Mogi, K. Watanabe, and M. Motokawa, in
“The proceeding of 2nd Symposium on New Magneto-Science ’98,”
JST, Kawaguchi (1998), p. 150.
6
7
M. Motokawa, in “The abstract of the International Workshop on
Chemical, Physical and Biological Processes under High Magnetic
Fields,” JST, Kawaguchi (1999), p. 24.
R. Aogaki, A. Tadano, and K. Shinohara, in “Fluid Mechanics and
Its Applications, Transfer Phenomena in Magnetohydrodynamic and
Electroconducting Flows,” ed by A. Alemany, Ph. Marty, and J. P.
Thibault, Kluwer Academic Publishers, Dordrecht (1999), Vol. 51,
p. 169.
8
9
K. Shinohara and R. Aogaki, Electrochemistry, 67, 126 (1999).
K. Shinohara and R. Aogaki, Chem. Lett., 1998, 1239.
10 A. Katsuki, S. Watanabe, R. Tokunaga, and Y. Tanimoto, Chem.
Lett. 1996, 219.
11 I. Mogi, S. Okubo, and M. Kamiko, Curr. Top. Cryst. Growth Res.,
3, 105 (1997).
12 I. Mogi, Electrochemistry, 67, 187 (1999).
13 S. Yonemochi, T. Iwasaka, and R. Aogaki, The Journal of the
Surface Finishing Society of Japan, 50, 1015 (1999).
14 T. Yabe, S. Kawata, and M. Fukuda, in “Introduction of Physical
Simulation,” Asakura-shoten, Tokyo (1989), p.11.