Corrosion Science, Vol. 37, No. 9, pp. 1399-1410, 1995
Copyright 0 1995 Elsevier Science Ltd
Pergamon
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OOll&938X/95 $9.50 + 0.00
0010-938X(95)00042-9
CORROSION AND INHIBITION STUDIES OF COPPER IN
AQUEOUS SOLUTIONS OF FORMIC ACID AND ACETIC
ACID
V.B. SINGH
Department
of Chemistry,
Banaras
and
Hindu
R.N.
SINGH
University,
Varanasi
- 221005, India
Abstract-Corrosion
behaviour of copper has been investigated in different compositions
of formic acid and
acetic acid at 30°C by a potentiostatic
method. The maximum corrosion rate was found in 2&40mol/o
formic acid and in 20 mol/o acetic acid in aqueous solution mixtures. The corrosion rate depended on the
concentration
of either acid. Formic acid is observed to be more corrosive than acetic acid. The metal
exhibited active-passive
behaviour
in the concentration
range of 30_70mol/o
of HCOOH acid in the
solution mixture. A short passivity range of potential with a high passivity current density was observed for
the metal in the solution mixtures of HCOOH acid while in solution mixtures of acetic acid the metal
exhibited only active dissolution.
Some organometallic
compounds,
viz. BuzSnCIz, PhSnC13, Ph2SnC12,
Ph3SnCI have been subjected to inhibition studies in the aqueous solution mixture (20 mol/o) of either acid.
Among the inhibitors
used Ph,SnCI functions as a better inhibitor in both acids. A strong interaction
between the inhibitor and corroding surface of copper is speculated due to adsorption
of the inhibitor.
INTRODUCTION
Organic acids constitute a group of the most important
chemicals used in industry.
The acids are produced more as precursors for other chemicals than for end use as
organic acids. Acetic acid is the best known member of the group and is produced in
the largest volume, but other organic acids are also important
for the preparation
of
compounds
used in routine compounds
from aspirin to plastics and fibers. Corrosion
by organic acids is complicated
not only because there are numerous
acids to be
considered but also because the acids typically are not handled alone but as a process
mixture. They are even sometimes used as solvents for other chemical reactions.
Though organic acids are weakly acidic they provide sufficient protons to act as true
acids towards most metals, because most organic acids are neither oxidizing nor
reducing to metals, such as copper, which does not displace hydrogen from acids.
A high corrosion rate will be encountered
if acid is free of air and other oxidants. In
the absence of oxygen or other oxidants, copper is probably the most widely used
material for handling HCOOH and CH,COOH
acid. The electrochemical
study of
metals in organic solvent containing
different amounts of water indicates that water
plays a significant
role’ on the corrosion
behaviour
in formic acid solution.
Substantial
corrosion studies for different metals and alloys in these acids have been
and for handling
reported in the literature.2’3 Despite the wide use in industry
purposes of these acids the corrosion studies of copper are scarcely known on the
entire composition
range of formic and acetic acid. In view of the above, the corrosion
Manuscript
received
14 June 1993; in amended
forms 14 July 1993 and 14 February
1399
1995.
V.B. Singh and R.N.
1400
Singh
and inhibition behaviour of Cu in formic and acetic acid of different compositions
was
studied. The effect of de-aeration
and electrolyte addition in the acid solution on the
corrosion behaviour of the metal has been investigated.
A new class of inhibitor, i.e.
organometallic
compounds
of tin, has been tested for this system.
EXPERIMENTAL
METHOD
Aqueous organic acid mixtures of different compositions
(20-70 moljo formic and acetic acid) were
prepared using double-distilled
water. Before experiments the solution mixture was kept at rest for about
24 h so that structuralization
of the mixture may reach completion. For electrochemical
polarization
studies
the working electrode (copper) of area 2 cm* was employed. First the electrode was properly polished with
I/o to 4/o emery paper. The electrode was then dipped in soap solution which emulsified the particulate
material sticking to the electrode surface, and subsequently
washed in flowing water. The electrode was
then degreased in acetone. The working electrode was pickled in 5% H2S04 solution for a few seconds.
Finally it was washed several times with double-distilled
water, acetone and dried by softly pressing
between warm filter papers.
The solution was de-aerated with purified nitrogen for 3 h and the corrosion studies were carried out
potentiostatically
(WENKING
POS 73). The experimental
arrangement
and working procedures
are the
same as described elsewhere.4 The polarization
studies were carried out when the open circuit potential was
stabilized. The potential was carried in step of 40mV and steady state current was noted. A saturated
calomel electrode was used as a reference electrode. The experiments were carried out in unstirred solution
mixtures at 30* 1 “C.
Additions of 0.5 M HCOONa and 0.5 M CH$OONa
were made to solution mixtures of formic and
acetic acid solutions, respectively, to examine the influence on corrosion behaviour
of the metal. Some
organometallic
compounds,
viz. Bu?SnCl,, PhSnCla, Ph2SnClz, PhaSnCl, were added in different quantities
(20,40, 100 ppm) separately to the only selected composition of solution mixture (20 mol/o formic and acetic
acid) to see the inhibition effect. The inhibition efficiency for each concentration
of inhibitors was calculated
according
to the equation,
tit, = (I -i) x 100. where II, is the percentage
of inhibition
for each
concentration
of inhibitor and i and i. are the corrosion current densities (mA/cm2) with and without
inhibitor, respectively.
EXPERIMENTAL
RESULTS
AND
DISCUSSION
The illustrations
and discussion in text are related to de-aerated solutions in the
presence of respective electrolyte unless specifically mentioned.
Open circuit potential
(OCP) vs composition
of either acid was plotted and is shown in Fig. 1. It was found
that the OCP tended towards active potential (less noble direction) up to 40 mol/o of
formic acid and above 40 mol/o it shifted towards the noble direction. A decrease in
OCP indicates a greater corrosion tendency in 40 mol/o of HCOOH acid. In the case
of acetic acid, the OCP shifted to the most noble potential values with increasing acid
concentration,
which shows the decreasing corrosion tendency of the metal.
Polarization
curves of Cu in HCOOH acid are shown in Fig. 2. It is observed that
the cathodic current decreases as the concentration
of HCOOH acid increases from
20 to 70 mol/o at all potentials,
except in 40 mol/o of HCOOH acid. The cathodic
curves are of a similar nature, which shows that the cathodic reactions are the
same. The nature of the curve obtained in 40 mol/o formic acid indicates a different
type of cathodic reaction at higher cathodic potentials. Similarly the current density
decreases
as the concentration
of acetic acid increases
(Fig. 3), however, the
current density is comparatively
lower in this acid than that in HCOOH acid for the
respective compositions.
The cathodic Tafel slope was found to lie between 100 and
140 mV/decade I for the solution mixtures of either acid. These values suggest that the
Corrosion
and inhibition
Concentration
1401
studies of copper
(molio)
CIIJ COOH
IIO-
9n -
g
7050 -
%
30 -
InI
20
in
I
30
Concentration
Open circuit potential
Fig. 1.
Deaerated
2
12lln
Aerated
I
50
I
40
I
6n
(molio)
vs composition
I
40
I
70
HCOOH
of either acid (HCOOH,
CH$OOH).
(mol1o HCOOH)
(molto
HCOOH)
cA
c
>
s
;;j
.,_
9
‘3
a
8nn
-1no
0
I
I
I
I
In-’
Io”
II)’
I n?
Current
Fig. 2.
Polarization
dewily
curves of Cu in different
(mA cm’)
compositions
of HCOOH
at 30°C.
1402
V.B. Singh and R.N. Singh
10-l
I0"
Current
Fig. 3.
Polarization
density
curves of Cu in different
(mA:cm’)
compositions
of CH$OOH
at 30°C.
cathodic reaction is hydrogen evolution. Sekine’ also considered hydrogen evolution
as a cathodic reaction on iron in formic acid. With the addition of electrolyte to either
acid solution, the cathodic current is increased. The cathodic curves remained almost
unchanged when the solution was de-aerated.
Anodic polarization
curves of Cu in different compositions
of formic acid at 30°C
reveal active-passive
behaviour in all compositions
of the acid except in 20 mol/o of
formic acid where it remained only active (Fig. 2).
Electrochemical
corrosion parameters,
derived from the polarization
curves, are
given in Table 1. The corrosion
potential
of copper in different compositions
of
the HCOOH
acid differed significantly.
The metal possesses a negative value of
corrosion potential
in 2&40mol/o
of HCOOH acid and shows positive potential
in other compositions
of the acid. Corrosion current (iorr ) and critical current density
for passivity (icr) decrease with increasing concentration
of formic acid except for
40 mol/o. The critical potential for the onset of passivity and passivity current density
also vary with formic acid concentration.
The curves showed that the dissolution
tendency is more in the anodic region up to 400 mV, because current increases rapidly
with small change in the potential.
A transpassive
region is not observed in any
solution mixture. The passivity current density is generally high (40-150 mA) which
shows considerable
dissolution
of metal in the passive region.
The anodic polarization
curves of copper in different compositions
of acetic acid
are shown in Fig. 3, copper exhibits active behaviour in all the compositions
of acetic
acid. The corrosion potential (I?,,,,) of copper progressively
attained nobler values
with increasing acetic acid concentration
in the solution (20-70 mol/o) while corrosion
current and critical current density decreased (Table 2). The values of i,,,,, i,, are
found to be lower for copper in acetic acid than those obtained in formic acid in all the
solution mixtures, though copper is active in all the compositions
of acetic acid
solution. In (2040 mol/o) acetic acid the curves show a high dissolution
tendency in
comparison
to higher concentrations
of acetic acid as the current increases with an
-100
+ 100
+ 100
+ 100
+120
+ 160
70
E cDrr
(mV)
x
x
x
x
x
lop2
10-3
10-3
10-I
10-3
1.2 x 10-3
1.8
1.5
1.2
1.0
1.0
i,,,,
(mA/cm2)
mixtures
60
50
solution
40
60
40
40
60
60
80
80
90
100
100
0.01
ba
(mV/decade
0.32
0.018
0.045
0.025
0.06
‘cr
(mA/cm’)
I)
I)
-300
+80
+80
100
200
180
140
(?q)
100
110
110
120
136
bc
(mV/decade
I)
+60
120
(24
80
30
0.08
0.01
0.80
0.02
x
x
x
x
1.8
1.6
1.5
1.1
1O-3
lop3
10-j
10-3
1.0x 10-3
1.2 x 10-3
(mkfLm2)
In the presence
(m.$m2)
10-2
40
60
80
80
90
100
b.
(mV/deLade
80
100
100
120
120
130
(mV/dkade
80
80
40
40
b,
(mV/decade
60
110
40
120
I)
I)
40
40
20
40
b,
(mV/decade
of 0.5 M HCOONa
25
40
2.6x
85
90 10’
150
50
65
2.7x IO2
2.1 x 102
2.8 x 10’
10-2
1O-2
10-2
lO-2
10-2
1.5 x
1.6x
2.0 x
I.8 xx
1.2
1.5 x
‘P
of 0.5 M HCOONa
(m,$~m2)
In the presence
of formic acid at 30°C
(m,$m2)
mixtures
-20
-25
-40
+80
+40
I)
solution
100
140
100
140
120
(mV/d:ade
of Cu in different
of acetic acid at 30°C
(mV/dkade
150
48
42
45
lP
In the absence of electrolyte
of Cu in different
1.2 x 10-2
parameters
20
30
40
50
60
(mol/o)
ofCH,COOH
Concentration
Corrosion
+80
70
Table 2.
1.1x102
1.8 x 10’
1.9x IO2
90
1.6x lo*
1.2x
1.3 x
1.4x
1.3 x
1.2 x
-20
-25
-40
+60
+40
20
30
40
50
60
75
lW
(mA/cm’)
i,,,,
(mA/cm2)
E,,,,
(mV)
(moI/o)
10-l
10-2
10-2
10-2
10-z
parameters
In the absence of electrolyte
Corrosion
ofHCOOH
Concentration
Table I.
I)
I)
L
8
3-I
0,
s
0
E1
;:
8.
S
S
e
5’
V.B. Singh and R.N. Singh
1404
increase of potential in these compositions.
However, at higher concentrations
little
increase in current is observed with successive increases of the potential.
Beyond a
certain potential the current remained almost constant and in few cases increased only
a little. It can be considered that either the metal is tending to attain passivity, the
corrosion product is not taken away promptly from the double layer, or the product is
not further soluble. A salt-like film may be considered to be formed on the surface of
the electrode through which the metal dissolution
occurs sluggishly. This film would
show a poor protective character. Despite of the fact that the passivity was obtained in
formic acid in most of the solution mixtures the current density is high in comparison
to acetic acid in the active region and the corrosion rate of copper in formic acid is
found to be higher than that in acetic acid. Similar results were reported’-’ for stainless
steel which corroded more easily in formic acid than acetic acid. A lower corrosion
rate in the higher concentrations
of organic acids (HCOOH,
CHsCOOH)
was
obtained by these investigators.
The present results can be explained on the basis of the
conductivity
of the solution mixture. The maximum conductivity
of the solution was
reported73’0”i for 2&40 mol/o of either acid composition
which may be considered
responsible for a higher corrosion rate of metal in these compositions.
Comparing the
values of the anodic Tafel slope in different compositions
of acid solution (Table 2),
the lowest value of the Tafel slope was obtained in the case of 40 mol/o HCOOH and
20 mol/o of CHsCOOH
acid solution. This also indicates a higher metal dissolution
rate in the said acidic solution mixture.
It is seen that the corrosion current and critical current density (&,.) (Tables I and 2;
Figs 4 and 5) increased in each composition
of the solution due to the addition of
respective electrolyte
(HCOONa,
CHsCOONa)
in formic acid or acetic acid, for
example the corrosion current and critical current density increased from 1.4 x 1OV2
to 2 x 1O-2 mA/cm2 and from 190 to 280 mA/cm2, respectively,
in 40 mol/o of
HCOOH acid solution when the electrolyte was added to the solution. Similarly the
Aerated
2000
-
A
Deaerated
1600 -
%
_
1200
-
(ml/o
HCOOH
+O..sM HCOONa)
50
(ml/o
l
20
x
40
0
50
0
70
HCOOH
+O.SM
HCOOSa)
cj
x00 -
Current
Fig. 4.
Polarization
density
(mAicm’)
curves of Cu in HCOOH
+ 0.5 M sodium forrnate
Corrosion
and inhibition
studies of copper
1405
Aerated
(molto
CH$WOH
+ O.SMCH$XXIN~)
A
.
;
i
SO
Deacrated
:
x00
10.’
I
I
1 I)”
10-I
Current
Fig. 5.
Polarization
I
I
I
density
0”
10’
101
(mAicm2)
curves of Cu in CH,COOH
+ 0.5 M sodium acetate
corrosion
current and the critical current density increased
from 5.0 x 10K3 to
2.8 x lop2 mA/cm* and from 0.32 to 80 mA/cm2, respectively, in the case of 20 mol/
o of CH$OOH
in the presence of CHsCOONa.
After the addition of the electrolyte
(CH&OONa),
feeble passivity was observed in 40 and 70 mol/o of acetic acid and in
remaining compositions
of acetic acid solution the nature of the curves was found to
be almost similar to those obtained in the absence of the electrolyte, but the curves
shifted to some extent towards higher current region (Figs 4 and 5). The passivity
current density in each solution
mixture of the HCOOH
acid with or without
electrolyte is found to be high for the metal, and the passivity range of potential is
large.
The passivity current density was found to increase when electrolyte was added to
the solution.
The corrosion
current is observed
to increase in the presence of
electrolyte probably due to the increase in conductivity
of the solution mixture in the
presence of added electrolyte. The critical potential for the onset of passivity becomes
more noble in the presence of electrolyte in either acid. Polarization
studies were
performed in non-de-aerated
solution of only one selected composition
of formic and
acetic acid (50 mol/o). The corrosion potential was found to shift in the more active
direction in each case (Figs 4 and 5). The polarization
curves for de-aerated solutions
and non-de-aerated
solutions are almost similar in nature. The corrosion current did
not vary significantly
upon de-aeration
of the solutions. The passivity current density
was found to be higher in the aerated solution mixture in comparison to the de-aerated
one. In the case of acetic acid the value of the dissolution
current was found to be
higher in aerated solution mixture in comparison
to the de-aerated one, showing a
higher rate of dissolution/reaction
in the former case. The lower corrosion rate in deaerated solution can be ascribed to the virtual absence of oxygen in de-aerated
observed that the corrosion rate of copper is
solutions. Syrett and MacDonald’2,13
reduced as the content of oxygen is reduced in solution.
V.B. Singh and R.N. Singh
1406
Li
2000
-
I600
-
I200
-
x Without
A IOOppm
q IOOppm
l
IOOppm
o IOOppm
inhibitor
Bu2 SKI:
Ph SnCI,
Ph, SnCl
Ph3 SnCl
‘d
m
‘2
>
E
x00 -
Ann-
-z
‘Z
o-
B
=,
P
-4on -
-xnn
I
I
10-l
Id’
I
Current
Fig. 6.
Polarization
curves
I
dcnslty
I
I n2
In’
IO
(mA;cm’)
of Cu in 20 mol/o HCOOH
+ 0.5 M sodium
presence of different inhibitors.
formate
in the
Corrosion data based on the polarization
studies (Figs 6 and 7) of Cu in solution
mixtures of 20 mol/o formic acid and 20 mol/o acetic acid, respectively, at 30°C in the
PhSnCls,
PhZSnClz, PhsSnCl),
are
presence
of different
inhibitors
(BuzSnClz,
summarized
in Table 3. In both the acid solutions it is observed that the corrosion
potential shifted in a noble direction. The magnitude
of the shift depends upon the
x Without
I OOppm
o IOOppm
l
IOOppm
o IOOppm
A
inhlbitor
Bu: SnCI?
Ph SnCll
Ph: SnCl
Phj SnCl
i
i
i
I 100 ‘4
x
!lnn
z
J
-
J
x’
JO0
v=z---~
-xnn
I
Io-2
in-l
IO0
Current
Fig. 7.
Polarization
J
I
I
10’
10’
density
IO’
(mA/cm’)
curves of Cu m 20 mol/o CH$ZOOH
presence of different inhibitors.
+ 0.5 M sodium
acetate
in the
Corrosion
Table 3.
(a) The effect of different
Concentration
Inhibitor
Nil
Bu$SnCI~
PhSnCI,
Ph,SnCl;?
Ph$nCl
(wm)
100
100
100
100
(b) The effect of different
Concentration
and inhibition
studies of copper
inhibitors on corrosion behaviour
M HCOONa solution at 30°C
of Cu in 20 mol/o formic acid + 0.5
$6
(mA/cm’)
ba
(mV/decade I)
-20
-15
-10
+30
+40
1.5x 10-l
0.6 x lop2
0.5 x 10-2
0.4 x 10-2
0.3 X 10-2
40
40
60
80
90
inhibitiors
I?,,,,
‘corr
1407
bc
(mV/decade I)
60
90
100
120
130
Percentage
inhibition
efficiency
60.0
66.6
73.3
80.0
on corrosion behaviour of Cu in 20 mol/o acetic acid + 0.5 M
CH$OONa
solution at 30°C
Inhibitor
@pm)
(mV)
i,,,,
(mA/cm’)
Nil
Bu,SnCIZ
PhSnC&
Ph2SnClz
Ph$nCl
100
100
100
100
-100
-80
-70
-50
-50
1.8
0.6
0.5
0.4
0.3
x
x
x
x
x
1O-2
1O-2
10-2
10-2
lo-’
b,
(mV/decade
40
60
70
75
80
I)
b,
(mV/decade
80
120
130
140
140
I)
Percentage
inhibition
efficiency
66.67
72.2
77.7
80.5
type and concentration
of inhibitor used. The corrosion current and current density at
a particular potential was lower in the presence of these inhibitors; a high value of the
cathodic Tafel slope is obtained in the presence of the inhibitors which verifies the
formation
of a film with a physical barrier effect. This view seems to support an
inhibition
mechanism
based on surface film formation
by initial de-adsorption
followed by reduction
polymerization
reactions14 of inhibitor.
Such a mechanism
was emphasized by Growcock et a1.‘4’7 for 1-octyn-3-01 and trans-cinnamaldehyde
when used as inhibitors in acidic solutions. The anodic Tafel slopes also increased in
the presence of these inhibitors. According to Donahue et al. I8such increases in Tafel
slope suggest a mode of inhibition
involving an interposition
of organic into the
charge transfer process for the anodic reaction. It is observed that the corrosion
current and current densities in the cathodic and anodic region decreased when
inhibitors
were present in the solution. This suggests that the inhibitors
BuzSnCIZ,
PhSnC13, PhZSnClz, PhSnC13 suppress the anodic and cathodic reactions involved in
the corrosion process by being adsorbed on the metal surface where they act as a mixed
inhibitor.
The results show (Tables 3(a) and 3(b)) that among the inhibitors
used
Ph$nCl
exhibits
an inhibition
efficiency
superior
to those of the aromatic
organometallic
compounds
used in present studies. Percentage inhibition
efficiencies
of the organometallic
compounds
increases in the following order in both the acid
solutions: BuzSnClz < PhSnC13 < PhZSnClz < PhSnC13.
Such a trend in the variation of inhibition
efficiency can be explained in terms of
the molecular size of the inhibitors. In aqueous solutions the inhibition efficiency of a
series of related organic compounds increased with an increase in the molecular size of
organic compounds.
A positive shift of the corrosion potential due to addition of
BuZSnClz, PhSnC13, PhzSnC12, Ph$nCl,
individually,
is seen (Tables 3 and 4) which
1408
V.B. Singh and R.N. Singh
Table 4. (a) The effect of concentration
of Ph,SnCl on inhibition efficiency in 20 mol/o HCOOH + 0.5 M HCOONa at 30°C
Concentration
Lx,
(mA/cm’)
@pm)
0
1.5
6.0
4.5
3.0
20
40
100
(b) The effect of concentration
in 20 mol/o CH$ZOOH
Concentration
(wm)
0
20
40
100
x
x
x
x
10-2
10-j
lo-’
lo-’
Percentage
inhibition
efficiency
60.0
70.0
80.0
of Ph,SnCl on inhibition efficiency
+ 0.5 M CH&OONa
at 30°C
k”,,
(mAjcm2)
1.8
0.7
0.5
0.35
x
x
x
x
10~ z
10-2
lop2
10-z
Percentage
inhibition
efficiency
67.8
7 1.4
80.6
indicated that these compounds
are effective suppressors
of the anodic dissolution
reaction.
The functional
group and structure
of the inhibitor
molecules
play
significant
roles in the adsorption
process. Adsorption
of the organometallic
compounds
at the metal surfaces takes place by electron transfer through the loosely
bound electrons of the 71bond or the aromatic rings. The results can be visualized on
the basis that in Ph$nCl
the de-activating
effect of the phenyl group is predominant
over the aggressive effect of chloride and Ph$nCl acts as best inhibitor. It appears that
Ph$nCl
is adsorbed on the copper surface through the de-activated
phenyl group.
Different concentrations
of Ph$nCl
(20, 40, 100 ppm) were added to 20mol/o
HCOOH and also to 20 mol/o CHsCOOH. The lowest values of the corrosion current
and current density in the entire potential range were observed when the experimental
solution contained
100 ppm of the above inhibitor (Figs 8 and 9). The cathodic and
anodic Tafel slopes are also found to be higher in such cases. The inhibition efficiency
is found to be at a maximum at a concentration
of 100 ppm of Ph$nCl in the aqueous
acidic solution of either acid (Tables 4(a) and 4(b)). It appears that the efficiency of
inhibition
is in general directly proportional
to the amount of inhibitor adsorbed or
the surface coverage. This may be the reason for variation of efficiency with content of
Ph$nCl.
CONCLUSIONS
The corrosion of Cu in formic acid is more than in acetic acid in different solution
mixtures, which can be attributed
to their relative acid strengths.
The corrosion
behaviour of the metal in concentrated
solutions of acid is different from that in lower
concentrations
of acidic solution. The corrosion rate exhibits a non-linear dependence
upon HCOOH and CH,COOH
concentration.
Maximum corrosion is observed in
Corrosion
and inhibition
1409
studies of copper
c
x Without inhibitor
o 20ppm Ph$nCI
l
40ppm Ph$nCl
. IOOppm PhJSnCI
l-
I-
I-
I-
I-
I
I
I
?
Current
Fig. 8.
Polarization
2000
1bO0
I
IO-
density (mAi’cm’)
curves of Cu in 20 mol/o HCOOH
+ 0.5 M sodium
presence of different concentrations
of Ph3SnC1.
formate
in the
x Without inhibitor
0 20ppm PhGnCl
l
4Oppm PhsSnCl
l
10.’
I
IO’
n
10”
IO“
1 O‘-
1OOppm Ph$nCl
IO-':
IO“
IO”
IO’
If9
Current density (mAicm’)
Fig. 9.
Polarization
curves of Cu in 20 mol/o CH,COOH
+ 0.5 M sodium
presence of different concentrations
of Ph3SnC1.
acetate
in the
V.B. Singh and R.N. Singh
1410
40 mol/o HCOOH acid and 20 mol/o CHsCOOH acid. Addition of sodium formate or
sodium acetate increases the rate of copper corrosion in respective acids. Among the
inhibitors used 100 ppm of Ph$nCl
was found to be the most suitable for inhibition of
copper corrosion, although other inhibitors used are also suitable.
Acknovledgemenrs-The
Chemistry, for providing
authors
necessary
wish to thank
facilities.
Prof.
P.K.
Srivastava,
head
of the
Department
of
REFERENCES
1. E. Heitz, Advances in Corrosion Science and Technology (ed. M.G. Fontana and R.W. Staehle), Vol. 4,
Ch. 3. Plenum Press, New York (1974).
2. 1. Sekine, Corros. Sci. 27, 275 (1978).
3. I. Sekine and K. Momi, Corrosion 44, 136 (1988).
4. N.N. Rao and V.B. Singh, Corros. Sci. 44, 136 (1985).
5. I. Sekine, Corros. Sci. 22, 1113 (1982).
6. I. Sekine and A. Chinda, Boshoku Gijutsu 31, 313 (1982).
7. I. Sekine and K. Senoo, Corros. Sci. 24, 439 (1984).
8. I. Sekine and A. Chinda, Corrosion 40, 95 (1984).
9. I. Sekine and M. Koeda, Boshoku Gijustu 33, 500 (1984).
10. I. Sekine Shvichi, Nrctrochim.
Actu 32, 915 (1987).
11. J.J. Demo, Corrosion 24, 139 (1968).
12. B.C. Syrett, Corrosion 32, 242 (1976).
13. D.D. MacDonald,
B.C. Syrett and S.S. Wing, Corrosion 349, 1289 (1978).
14. F.B. Growcock,
W.W. Frenier and V.R. Lopp, Proc. 6th Europ. Symp. on Corrosion Inhibitors, Ann.
Univ. Ferrara, N.S. Sez. V. Suppl. No. 8, 167 (1985).
15. W.W. Frenier, F.B. Growcock and V.R. Lopp, Proc. 6th Europ. Symp. on Corrosion Inhibitors. Ann.
Univ., Ferrara, N.S. Sez, V. Suppl. No. 8, 183 (1985).
16. F.B. Growcock
and V.R. Lopp, Corrosion 44, 248 (1988).
17. W.W. Frenier and F.B. Growcock.
Proc. 7th Europ. Symp. on Corrosion
Inhibitors.
Ann. Univ.
Ferrara, N.S. Sez, V. Suppl. 661 (1990).
18. F.M. Donahue, A. Akiyama and K. Nobe. J. Elecrrochem. Sot. 114, 1006 (1967).