A new condensation product for zinc plating from non-cyanide alkaline bath

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Bull. Mater. Sci., Vol. 28, No. 5, August 2005, pp. 495–501. © Indian Academy of Sciences.
A new condensation product for zinc plating from non-cyanide
alkaline bath

Department of Studies in Chemistry, Kuvempu University, Shankaraghatta 577 451, India

Abstract. Zinc electroplating from non-cyanide alkaline solution is carried out in the presence of condensation
product formed between DL-alanine (DLA) and glutaraldehyde. The bath constituents and bath variables are
optimized through standard Hull cell experiments. The current efficiency and the throwing power are mea-
sured. High shift of potential towards more cathodic direction was observed in presence of addition agents.
Corrosion resistance test reveals good protection of base metal by zinc coating obtained from the developed
electrolyte. SEM photomicrographs show fine-grained deposit in the presence of condensation product. IR
spectrum of the scraped deposit shows the inclusion of the condensation product in the deposit during plating.
The consumption of brightener in the lab-scale is 6 mLL–1 for 1000 amp-hour.

Keywords. Alkaline bath; electroplating; Hull cell studies; non-cyanide bath; zinc plating.

1. Introduction
2. Experimental
Electrodeposition of zinc on steel is carried out to protect
The chemicals used were of AR grade and the solutions
steel from corrosion. The sacrificial protection afforded
were prepared with distilled water. Zinc plate of 99?99%
by zinc is due to its position in the electrochemical series
purity was used as anode. Mild steel plates (AISI-1079)
with respect to iron. The reason for the pre-eminence of
of standard Hull cell size were polished mechanically and
zinc in the world of electrodeposition can be attributed to
degreased by dipping in boiling trichloroethylene. Finally
its relative ease of deposition and better corrosion resis-
these were dipped in 10% HCl followed by electrocleaning.
tance. To get good bright zinc deposition certain organic
The standard Hull cell of 267 ml capacity was used to
compounds are being used in the bath solution (Rosenberg
optimize the bath constituents and bath parameters (Par-
and Holland 1991; Tang 1993; Bapu et al 1998). Deve-
thasaradhy 1989). The zinc electroplated steel plates
lopment of these brighteners for non-cyanide alkaline
were subjected to water wash and given bright dip in 1%
solution is continuously taking place even though few
nitric acid for 2–3 s. The nature and appearance of zinc
efficient commercial brighteners are available (Blount
plating was carefully studied and recorded through the
1970; Arthoba Naik et al 2000a,b). It is evident from the
Hull cell codes (figure 1a).
available literature that single addition agent generally
The optimized solution was taken in a rectangular
does not produce good deposit over a wide current density
methacrylate cell of 2?5 l capacity. Polished, degreased
range. In order to get good deposit, two or more addition
and electrocleaned cathodes of 3 × 4 cm2 were used for
agents are required (Hayashida 1972; Hoyer 1973;
plating. These plated steel cathodes were used to test dif-
Rushmore 1977; Suzuki and Susa 1996). The presence of
ferent metallurgical properties. Experiments were done in
many addition agents poses problem in determining their
triplicate. Standard experimental procedures (Partha-
consumption during plating. Also some of the addition
saradhy 1989) were adopted for the measurement of meta-
agents cause pollution problem and health hazard.
llurgical properties of the deposit such as ductility,
In the present work, efforts have been made to develop
hardness, adherence etc. In all the above studies the ave-
non-cyanide alkaline bath solution containing single bright-
rage thickness of the deposit was 25 µm. The coating
ener. In the present work, various amines and aldehydes
thickness was measured by using ?-ray back scattering
are subjected to condensation reaction by adopting stan-
gauge (Permascope ESD9, West Gut-ESD9 KB4, 220 ×
dard procedures (Moris and Boyd 1973). The obtained
50–60 Hz, Germany) and BNF jet methods.
products are subjected to Hull cell experiment. Among
For polarization studies, a three-compartment cell was
these, condensation product formed between DL-alanine
used. The zinc metal plate was used as anode and steel
(DLA) and glutaraldehyde (GTD) acts as a very good
plate as cathode. The cathode potential was measured
brightener and it is easily soluble in water.
galvanostatically, with respect to saturated calomel elec-
trode at different current densities. Current efficiency and
throwing power measurements were carried out by using

*Author for correspondence ([email protected])
Haring and Blum cell. The current distribution ratio be-

Y Arthoba Naik and T V Venkatesha
tween anode and cathode was 1 : 5 for throwing power
improve the nature of the deposit, condensation product
formed between DL-alanine (AR grade, s.d. Fine Chemi-
IR spectrum of the scratched deposit was taken to
cals, Mumbai, India) and glutaraldehyde (AR grade, s.d.
study the inclusion of addition agents. SEM photomicro-
Fine Chemicals, Mumbai, India), was added to the bath
graphs were taken to ascertain the nature of the deposit in
solution. Condensation product was prepared by mixing
presence of addition agents. For determining consumption
5 g of DL-alanine and 20 mL of glutaraldehyde (25%
of brightener a rectangular 2?5 l methacrylate cell was
aqueous solution) in distilled water and refluxing the re-
sulting aqueous solution for 3 h at 343 K (Moris and Boyd
1973). The resulting dark red product was diluted to
3. Results and discussion
100 mL with distilled water and a known amount of this
solution was added to the bath. At low concentration of
3.1 Hull cell studies
the condensation product the deposit was semibright bet-
ween the current density range of 1?0 and 3?0 Adm–2. At
3.1a Effect of condensation product: Bath solution con-
low current density, dull and at high current density, burnt
taining zinc sulphate, sodium hydroxide, CTAB and
deposits were obtained. With increase in the concentra-
EDTA gave coarse dull deposit between the current den-
tion of condensation product, nature of the deposit im-
sity range of 0?5 and 3?5 Adm–2 at 1A cell current. To
proved and at a concentration of 4 mLL–1 the Hull cell

Figure 1. Hull cell figures: (a) key, (b) effect of condensation product, (c) effect of
CTAB, (d) effect of EDTA, (e) effect of ZnSO4, (f) effect of NaOH, (g) effect of
temperature and (h) effect of cell current.

A new condensation product for zinc plating from non-cyanide alkaline bath
panels were bright between the current density range of
a concentration of 100 gL–1 the bath solution was clear.
0?1 and 3?5 Adm–2. Further increase in the concentration
At a concentration of 110 gL–1 the nature of deposit was
of the condensation product gave dull deposit in the high
full bright in the current density range 0?1– 4?0 Adm–2.
current density region. Based on the above observation
Further increase in the concentration of sodium hydroxide
the concentration of the condensation product was kept at
resulted in the black deposit in the high current density
40 mLL–1 as optimum. The Hull cell patterns are shown
region. Therefore, the concentration of sodium hydroxide
in figure 1b.
was fixed at 110 gL–1 as optimum in the bath solution.

The Hull cell patterns showing the effect of sodium hy-
3.1b Effect of CTAB: The concentration of CTAB was
droxide are shown in figure 1f.
varied from 1–12 gL–1, keeping the concentration of so-

dium hydroxide at 100 gL–1, zinc sulphate at 30 gL–1 and
3.1f Effect of temperature: The effect of temperature
condensation product at 20 mLL–1. At low concentration
on electrodeposition was investigated by conducting Hull
of CTAB the nature of deposit was semibright in the cur-
cell experiments at controlled temperature. The tempera-
rent density range 0?5–3?5 Adm–2. Above 3?5 Adm–2,
ture of the bath solution was varied from 293–323 K. At
burnt deposit was observed. With increase in the concen-
lower temperatures (< 303 K), the deposit was bright in
tration of CTAB from 1 to 6 gL–1, burnt deposit area was
the current density range between 0?1 and 4 Adm–2 at 1A
reduced and at a concentration of 6 gL–1, bright deposit
cell current. Above 308 K the entire Hull cell cathode
was obtained in the current density range 0?2–3?8 Adm–2
was covered with dull deposit. So the optimum tempera-
at 1A cell current. With increase in the concentration, no
ture range was 298–303 K. Hull cell panels showing the
change in the nature of deposit was observed. Therefore,
effect of temperature are given in figure 1g.
the concentration of CTAB was fixed at 6 gL–1 as opti-

mum in the bath solution (figure 1c).
3.1g Effect of cell current: The Hull cell experiments

were carried out at different cell currents (1– 3A) for 5
3.1c Effect of EDTA: Further, the concentration of
min using optimized bath solution. It was found that at a
EDTA was varied from 5–50 gL–1. At low concentration
cell current of 1A, the deposit was bright in the current
of EDTA (< 20 gL–1), the deposit was bright in the current
density range 0?1–4?0 Adm–2. At a cell current of 2A, the
density range 0?2–3?8 Adm–2. At a concentration of
deposit was bright in the current density range 0?1–
20 gL–1 in the bath solution, bright deposit was obtained
5?5 Adm–2. At a cell current of 3 A the deposit was bright
over the entire current density region (0?1– 4?0 Adm–2 at
over the current density range 0?1–5?6 Adm–2. These
1A cell current). Above 20 gL–1 of EDTA, no improve-
observations revealed that the bath produced the bright
ment in the nature of deposit was observed. Therefore,
deposit in the current density range 0?1–5?6 Adm–2. The
the concentration of EDTA was fixed at 20 gL–1 as opti-
Hull cell patterns are as shown in figure 1h.
mum. The effect of EDTA on Hull cell cathodes at 1A
cell current is as shown in figure 1d.
3.2 Current efficiency and throwing power

3.1d Effect of zinc sulphate: To know the effect of zinc
The current efficiency and throwing power were measured
metal ion concentration, the zinc sulphate concentration
under different plating conditions. The effect of tempera-
was varied from 10–40 gL–1. At low concentration, the
ture, EDTA, CTAB, zinc and condensation product on
bright deposit was observed in the current density range
current efficiency and throwing power were investigated
between 0?5 and 3?0 Adm–2. In the low current density
at a current density of 3 Adm–2 and the values are given
region, dull and at high current density region, burnt de-
in table 2a. The current efficiency was found to vary
posits were obtained. With increase in the concentration
from 58–65% and the throwing power from 40–49%.
of zinc sulphate, the brightness range was extended to
The current efficiency and throwing power were mea-
high and low current density regions. At a concentration
sured at different current densities using optimum bath
of 35 gL–1, satisfactory bright deposit was obtained in the
composition. The current efficiency varied from 47–65%
current density range of 0?1–4 Adm–2 at 1A cell current.
and throwing power from 44–49%. The variation of cur-
With increase in the concentration of zinc sulphate no
improvement in the nature of deposit was observed. The
concentration of zinc sulphate was fixed at 35 gL–1 as
optimum and Hull cell patterns are as shown in figure 1e.
Table 1. Basic bath composition and operating conditions.

Bath composition
Operating conditions
3.1e Effect of NaOH: The concentration of sodium hy-

droxide was varied from 80–120 gL–1. At low concentra-
ZnSO ?
4 7H2O (gL–1)
25 Anode : Zinc metal (99?99%)
tion (< 100 gL–1), the bath solution was turbid and the
NaOH (gL–1)
Cathode : Mild steel
nature of deposit was patchy and dull. With increase in
CTAB (gL–1)
Temperature : 293–303 K
EDTA (gL–1)
Cell current : 1A
the concentration, the turbidity found to disappear and at

Y Arthoba Naik and T V Venkatesha
rent efficiency and throwing power with current density
different current densities. Cathodic polarization was
is given in table 2b.
measured using the bath solution with and without addi-
tion agents. The variation of cathode potential with cur-
3.3 Polarization study
rent density is shown in figure 2. At any given current
density, the cathode potential became more negative in
The potential of steel cathode was measured galvano-
presence of CTAB and EDTA. This shift was still higher
statically with respect to saturated calomel electrode, at
in presence of all the addition agents.
Table 2a. Current efficiency and throwing power at 3 Adm–2 current density.

Current efficiency Throwing power
Bath constituents/parameters

ZnSO ?
4 7H2O (gL–1)
NaOH (gL–1)
CTAB (gL–1)
EDTA (gL–1)
Condensation product
(DLA–GTD) (mLL–1)
Temperature (K)

Table 2b. Current efficiency and throwing power at different
current densities.

Current density
Current efficiency
Throwing power


Figure 2.
Effect of addition agents on cathodic potential (—, ZnSO4 + NaOH (BB); ?,
BB + EDTA; ?, BB + CTAB; O, BB + EDTA + CTAB; ×, BB + DL-alanine; £,
BB + glutaraldehyde; ¿, BB + EDTA + CTAB + DL-alanine–glutaraldehyde).

A new condensation product for zinc plating from non-cyanide alkaline bath
In IR spectrum of the scraped deposit the absorption
posits of 15 µm thickness were obtained under optimum
peak near 1600 cm–1 (stretching frequency of –C=N–
conditions of plating bath on mild steel plates (1 ×
bond) indicates and confirms the inclusion of the conden-
10 cm2). These plated specimens were subjected to bend
sation product in the deposit (figure 3).
test through 90° and finally through 180°. Even after
180° bending no crack or peel off was observed in the
deposit. This reveals good adhesion of zinc deposit to the
3.4 Corrosion resistance
substrate. The more useful method for measuring micro-
hardness involves making an indentation with an indenter
Mild steel panels of 2 × 2 cm2 area were polished, de-
of specified geometry under a specified load. The length
greased and treated with 10% hydrochloric acid followed
of indentation is expressed in vickers hardness number
by water wash. These plates were plated with zinc in op-
(VHN). Zinc was electroplated on mild steel panels up to
timum plating bath at different current densities. In pre-
a thickness of 25 µm and a load of 50 g was employed.
sence of addition agents, it was found that the deposits
The microhardness of zinc was found to be 130.
were pore-free above a thickness of 5 µm as indicated by
SEM photomicrographs of zinc deposit obtained from
ferroxyl test. In absence of addition agents, the coating
the basic bath solution with and without addition agents
was highly porous even at a thickness of 8 µm.
are shown in figure 4. These indicate that the basic bath
The corrosion resistance of zinc plated steel plates was
produced only coarse-grained deposits. The grain size
tested by salt spray method (ASTM B–117). Mild steel
was refined further in presence of addition agents. Fine-
plates (5 × 5 cm2) were coated with zinc from an opti-
grained smooth deposit was obtained from the bath solution
mum bath solution. These plates were given bright dip in
containing an optimum concentration of all the addition
1% nitric acid followed by chromate passivation. Before
subjecting to the salt spray test, the plates were kept in a
clean and dry atmosphere for 24 h. Even after 120 h of
salt spray test no white rust was observed on the speci-
3.6 Consumption of brightener
mens. This indicated good corrosion resistance of the
To know the amount of addition agents consumed in the
bath, 2?5 l of bath solution was taken and plating was
3.5 Metallurgical properties
carried out at different current densities. The total num-
ber of coulombs passed to the bath solution was recorded
An important property of an electrodeposit is its adhesion
at the time when the bath just started to give semibright
to the base metal. Usually, zinc deposits on mild steel
deposit. The bath solution after use was subjected to Hull
have good adhesion. To measure adherence the zinc de-
cell test by adding different amounts of condensation

Figure 3.
IR spectrum of the scraped zinc deposit.

Y Arthoba Naik and T V Venkatesha
product. The concentration of condensation product, at
explored by performing the plating experiments in a vat
which once again bright deposit was obtained, was de-
bath of 25 l capacity. The bath solution with optimum
termined. The amount of condensation product consumed
concentration of bath constituents was prepared. Steel
for 1000 amps-h was 2 mLL–1.
components of different sizes and shapes (plates, rods, nuts,
bolts, small pipes, clamps, etc) were degreased, electro-
cleaned and given acid dip followed by water wash.
3.7 Pilot plant study
These treated components were rigged by copper wire
and connected to the negative terminal of d.c. source.
The commercial applicability of the developed bath was
Electroplating was carried out at different current densi-

Figure 4.
SEM photomicrographs of the deposits obtained at 3 Adm–2 in the presence
and absence of addition agents at 298 K: (A) basic bath (BB), (B) BB + CTAB, (C)
BB + EDTA, (D) BB + CTAB + EDTA, (E) optimized bath and (F) passivated deposit.

Table 3. Optimum bath composition and operating conditions.

Bath composition
Operating conditions

ZnSO ?
4 7H2O (gL–1)
Anode : Zinc metal (99?99%)
NaOH (gL–1)
Cathode : Mild steel
CTAB (gL–1)
Temperature : 293–303 K
EDTA (gL–1)
Bright current
Condensation product
density range : 0?1–5?6 Adm–2
(DLA-GTD) (mLL–1)
Agitation : Air

A new condensation product for zinc plating from non-cyanide alkaline bath
ties with and without agitation of the bath solution. The
deposit is pore-free and corrosion resistant. The bath
components after deposition were removed from the plat-
could be easily commercialized.
ing vat and subjected to bright dip and passivation. The
passivated articles were subjected to corrosion resistance
test in salt spray chamber. Adhesion of the deposit to the
substrate was good as it was confirmed by bend test and
heat test methods. The components of irregular shapes
Arthoba Naik Y, Venkatesha T V and Vasudeva Nayak P 2000a
plated under stirred and unstirred condition showed no
B. Electrochem. 16 481
rust at the recesses even after 96 h of salt spray test. This
Arthoba Naik Y, Venkatesha T V and Vasudeva Nayak P
indicated the ability of the bath to produce uniform de-
2000b J. Electrochem. Soc. India 49 170
Arthoba Naik Y, Venkatesha T V and Vasudeva Nayak P 2001
posit on the components of irregular shape. The decrease
Indian J. Chem. Technol. 8 390
in metal ion concentration for 1000 amps-h was deter-
Bapu G N K, Rames G Devaraj and Ayyapparaj J 1998 J. Solid
mined and it was 1?5 g L–1. This was replenished by add-
State Electrochem. 3 48
ing an equivalent amount of zinc sulphate to the bath
Blount E A 1970 Electroplat. Metal Finish. 23 27
Hayashida 1972 Japan Patent 7,216,521
Hoyer 1973 German Patent 2,247,875
4. Conclusions
Moris R T and Boyd R N 1973 Organic chemistry (New Delhi:
Prentice-Hall of India Pvt Ltd) 2nd ed., p. 633
Parthasaradhy N V 1989 Practical electroplating handbook
The developed bath produces good deposit over the cur-
(New Jersey: Prentice Hall Inc) 1st ed., p. 283
rent density range of 0?1–5?6 Adm–2. The optimized bath
Rosenberg W E and Holland F H 1991 Plat. Surf. Finish 78 51
composition is shown in table 3. The throwing power is
Rushmore 1977 German Patent 2,643,898
reasonably good. The brightener can be easily synthe-
Suzuki Isamu and Susa Hideo 1996 Jpn Kokai Tokkyo Koho JP
sized. The addition agents are non-toxic, easily soluble in
08209393 A2
water and hence require no treatment of the effluent. The
Tang Chun-hua 1993 Diandu Yu Tushi 12 33