Journal of Materials Science and Chemical Engineering, 2013, 1, 39-42 Published Online October 2013 (
Copyright © 2013 SciRes. MSCE
Study of Gallium Plating of Metal Electrodes
S. V. Gladyshev, R. A. Abdulvaliev, K. O. Beisembekova, G. Sarsenbay
Center of the Earth Sciences, Metallurgy and Enrichment, JSC, Science and Education Ministry of the Republic
of Kazakhstan, Almaty, Kazakhstan
Received August 2013
Conditions of gallium plating of metal electrodes were studied in the paper. It was found that stability of gallium cover
depends on the material and is increasing in the raw: stainless steel 08Х18Н12Т < Steel 1, Steel 2, Steel 3, Steel 45 < Ni
< Cd < Cu. Phase composition of the electrode surface layer obtained after gallium plating was studied. It was found
that gallium with nickel form Ga36Ni64(Ga Ni2) compound and gallium with copper form CuGa2 compound. Different
acids were used for electrode leaching: H2SO4; HNO3; H3PO4; HCI. It was shown that only hydrochloric acid is suit-
able for gallium plating of the electrodes.
Keywords: Gallium Plating; Metal Electrodes; Hydrochloric Acid; Gallium Coverin g; Stainless Steel 08х18н12т; Steel
1; Steel 2; Steel 3; Steel 45; Nickel; Cadmium; Copper
1. Introduction
Gallium is widely used in opto-electronics, telecommu-
nications, and airspace industry. Great share of gallium is
used for production of GaAs, integrated circuits for elec-
tronic industry. Importance of gallium for electronic in-
dustry of the world is great, whereas annual production
in tons is pretty small [1-4].
The analysis of the world market tendencies of non-
ferrous and rare metals indicates a rapid growth in de-
mand for gallium, up until 2020. For this reason there is a
need for substantial increase of its output. Currently, the
main source of gallium is aluminium raw materials proc-
essed by the aluminium oxide plants, which simultane-
ously extract gallium [5-9].
Use of gallium plated cathodes in electrolysis of alu-
minate-gallate solutions showed high efficiency of them
[10-12]. Therefore, determination of the conditions to get
stable and uniform gallium covering on metal electrodes
is an important practical task.
In electrolytic cells with solid revolving gallium plated
cathode the surface of the cathode is damping with liquid
gallium thus restoring the surface. The sites of the cath-
ode where gallium covering is poor could not be mois-
tening with liquid gallium.
When steel surface of the cathode in such sites in
alkaline solution becomes uncovered galvanic pair Me-
Ga is formed, where gallium is anode component. At
these sites gallium covering could be destroyed mechanic-
cally by evolved hydrogen gas. Vigorous bubble-forma-
tion at such sites during gallium electrolysis promotes
strong sludge formation. The sludge on the electrode
surface inhibits renovation of the sites during contact
with liquid gallium and promotes expansion of the sites
thus decreasing efficiency of gallium electrolysis on the
When uniformity of gallium covering on cathode sur-
face is broken activity of the electrolysis cell is stopped,
electrolyte is removed and the cathode is covered with
gallium again. The process requires additional work time,
additional amount of gallium and the acid.
Stable and uniform covering of the electrodes with
gallium lets to increase efficiency of gallium electrolysis
and facilitate maintenance of the electrolysis cell during
Covering of electrode surfaces with liquid gallium or
its compounds i s des cribed i n pa pers [13-15].
2. Experimental Method
We studied dependency of gallium cover stability in al-
kaline solution from material of the electrode and com-
position of leaching solution using different inorganic
The time from the beginning of exposure to the time
when uniformity of gallium cover is broken and potential
of the gallium plated electrode in alkaline solution drops
sharply is consider ed as stability of gallium co ver. Metal
electrodes in the kind of 8 mm rods were used for the
Before gallium covering surface of the electrode was
grinded, polished and degreased in the solution, g/dm3:
Copyright © 2013 SciRes. MSCE
NaOH 20.0; Na2CO3 25.0; Na2SiO3 10.0. The treatment
was made for 10 ÷ 30 min at 70˚C ÷ 90˚C until complete
watering. The degreasing solution was washed out with
hot water. To exclude oxidizing of the electrode it was
put in 5% sol ution of hy drochl oric acid.
Metal electrodes were cover ed with gallium via multi-
ple submerging in liquid gallium with 20% hydrochloric
acid solution over it at 70˚C - 80˚C [13]. The duration of
gallium covering was 1 ÷ 2 min. Surplus of liquid gal-
lium was removed from the electrode surface with a filter
moistened with 5% hydrochloric acid solution.
Phase composition of solid-liquid interface was stud-
ied with X-ray diffractometer D8ADVANCE “Bruker”
using filtered Со-Кα radiation.
Stationary potential was recorded with PGSTAT12
potentiostate. All potential values were measured refer-
ring to standard hydrogen electrode. Concentration of
gallium in the solution was determined using chemical
To determine stability of the gallium cover electrodes
were put in the 100 ml Pyrex glass cell filled with alka-
line solution at 50˚C. Composition of the solution was
similar to that for commercial electrolytic cells, i.e.
Na2Ototal = 160 g/dm3. Each result was reproduced five
3. Results and Discussion
Pretreatment of the electrode surface is very important to
get stable and uniform gallium cover.
Different inorganic acids, HCI, HNO3, H2SO4 and
H3PO4, with concentrations from 0.1% to 20%, were
used for the pretreatment but gallium covering is possible
only when hydrochl oric acid soluti o n wa s u s e d.
Leaching of metal electrodes (Steel 3) with HNO3,
H2SO4 and H3PO4, solutions cause vigorous hydrogen
bubble-formation on steel surface. The bubble-formation
is increased greatly when gallium is put in contact with
the surface.
Intensive gas formation on the surface of the electrode
excludes the possibility of damping the surface with gal-
lium. Besides, flow characteristics of gallium in solutions
of the acids are reduced.
The value of gallium potential in the acid solution (Ta-
ble 1) showed that in hydrochloric acid solution gallium
surface is activated. Potential of liqu id gallium is moving
to electronegative direction when concentration of hy-
drochloric acid in the solution is higher.
In the other acids potential of liquid gallium is be-
coming electropositive, i.e . the surface is passivated. The
passivation is most valuable in nitric acid solutions.
Stability of gallium covering was studied on the fol-
lowing electrodes: stainless steel 08Х18Н12Т, Steel 1,
Steel 2, Steel 3, Steel 45, nickel, cadmium and copper.
Thickness of gallium covering depends on gallium dif-
fusion into the metal, temperature of electrode and gal-
lium and the contact time. Chemical composition and
structure depend on the equilibrium diagram of gallium
and electrode material.
Initial compromise potentials of uncovered electrodes
in alkaline solution (160 g/dm3 Na2Ototal) at 50˚C are
shown in Table 2.
After submerging of steel gallium plated electrodes in
alkaline solution their stationary potential was 1,365 V
(Figu re 1). At the initial part А1В1 of the curve 1 one can
see small positive shift of the potential because of disso-
lution of gallium chloride and gallium oxide. Gallium
chloride is formed because of interaction of gallium with
hydrochloric acid solution whereas gallium oxide is
formed when gallium plated electrode is submerged in
alkaline solution [16].
Change of gallium diss olution rate dC/dt from the sur-
face of the metal electrode at this moment is reflected by
А3В3 part of the curve (Figure 2, curve 3). Sharp de-
crease of the rate of the process is related to decreasing
of gallium oxide amount on the surface of the gallium
plated electrode. The increase of gallium dissolution rate
at В3С3 part of the curve is related to de-passivation of
the gallium plated electrode surface due to disso lution of
the oxide film and the beginning of gallium layer uni-
formity breakage at point В3. After this potential of the
Table 1. Potential of gallium electrode in different acid so-
lutions at 80˚C.
Acid concentration, % Potential, V
0.1 0,520 0,56 0,55 0,530
0.5 0,520 0,56 0,46 0,525
1 0,560 0,54 0,44 0,522
3 0,562 0,52 0,40 0,520
5 0,565 0,51 0,38 0,500
10 0,570 0,50 0,25 0,485
20 0,585 0,49 0,20 0,450
Table 2. Initial compromise potentials in alkaline solution (160 g/dm3 Na2Ototal) at 50˚C.
Electrode material Stainless steel 08Х18Н12Т Steel 1 Steel 2 Steel 3 Steel 45 Ni Cu Cd Ga
φ, V 0,7 0,8 0,8 0.8 0.8 0,55 0,36 0,85 1,38
Copyright © 2013 SciRes. MSCE
electrode is declining slightly, and curves 1 and 2 have
almost horizontal parts (part С1Д1 and С2Д2).
Reduction of gallium dissolution rate at С2Д2 part of
the curve can be explained by sharp increase of gallium
ion concentration at the electrode-solution interface. This
is confirmed by minor decrease of electrode potential
during the said time.
At electrode potential equal to 1,295 V (point Д1)
surface of the electrode is covered with gallium mono-
layer, which is being dissolved in alkaline solution until
metal core is fully uncovered.
Galvanic pairs promote active dissolution of the gal-
lium. Potential of the electrode is moving fast to positive
direction beginning from 1.15 ÷ - 1.17 V and is reach-
ing eventually compromise potential of passive steel
electrode in alkaline solution 0,126 V.
Study of phase composition of gallium plated steel
electrode surface layer showed that gallium and steel do
not interact and the layer is formed only because of
damping. This could be confirmed by the fact that poten-
tial curves of steel electrode and steel electrode with re-
moved gallium cover via dissolution in alkaline media
are coincide in time. The thickness of the gallium cover
is (1.5 ÷ 2) *10 2 mm.
Stability of the gallium cover and potential curves of
gallium plated electrodes in time depending on the mate-
rial of the electrodes are shown in Table 3 and on Figure
3. It is seen from Figure 3 that stability of g allium cover
on the electrodes made of different steel (Steel 1, Steel 2,
Steel 3, Steel 45) is the same and is equal to 1.2 min after
2 minute gallium plating. The worst stability was found
for the stainless steel (curve 5), because of insufficient
activation of its surface in leaching solution before gal-
lium plating.
Stability of gallium cover on nickel core is 4 min
(curve 3), after gallium plating for 0.5 ÷ 1.0 min. Nickel
interacts with liquid gallium forming Ga36Ni64(Ga Ni2)
compound on the interface.
The best stability of gallium cover (14 - 15 min) was
found for copper core (Figure 3, curve 1), because of
good damping of copper with gallium. The surface layer
of the electrode is represented by Θ phase of CuGa2
compound. The layer is thin because X-ray diffracto-
gram has intensive lines of pure copper.
Potential of gallium plated copper electrod e in alkaline
solution is decreased from 1.43 V to 1.05 V (potential
of copper covered with CuGa2) and not to 0.36 V (po-
tential of copper).
Therefore, stability of gallium cover is mainly depends
on the core material in the following sequence: stainless
steel 08Х18Н12Т < Steel 1, Steel 2, Steel 3, Steel 45 <
Ni < Cd < Cu.
4. Conclusions
Conditions of gallium plating of metal electrodes were
studied. It is shown that stability of gallium cover de-
pends on the metal core and is increasing in the following
Figure 1. Dependency of gallium plated electrode potential
from time of exposition in alkaline solution.
Figure 2. Dependency of gallium concentration in the solu-
tion (2) and rate of gallium dissolution (3) from time of gal-
lium plated electrode exposition in alkaline solution.
Table 3. Stability of gallium cover depending on the electrode material.
Electrode Material of electrode
Stainless steel 08Х18Н12Т Steel 1 Steel 2 Steel 3 Steel 45 Ni Cd Cu
Stability of the cover, min 0,3 1,2 1,2 1,2 1,2 4 11 ÷ 12 14 ÷ 15
Time of gallium plating, min. 4 - 5 2 2 2 2 1 ÷ 0,5 0,5 0,2 ÷ 0,5
Copyright © 2013 SciRes. MSCE
Figure 3. Dependencies of gallium plated electrode poten-
tials from time for different electrode cores. Materials of the
core: 1—copper; 2—Steel 1, Steel 2, Steel 3, Steel 45; 3
nickel; 4 —cadmium; 5—stainl ess steel 08Х18Н12Т.
raw: stainless steel 08Х18Н12Т < Steel 1, Steel 2, Steel
3, Steel 45 < Ni < Cd < Cu. The best material for elec-
trode is copper.
Phase composition of electrode surface layer obtained
after gallium plating was studied. It was found that gal-
lium with nickel form Ga36Ni64(Ga Ni2) compound and
gallium with copper form CuGa2 compound.
Different inorganic acids were used for leaching of
electrode core surface before gallium plating. It was
shown that only hydrochloric acid activates damping of
the core with gallium
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