IndianJournalofChemicalTechnology
Vol.3,January1996,pp..32-36
Corrosion characteristics of some aluminium alloys in oxalic acid
MM Singh& ArchanaGupta
DepartmentofAppliedChenustry,InstituteofTechnology,BanarasHinduUniversity,Varanasi221005, India
Received19 May 1995; accepted29 August1995
The corrosion behaviour of 1060 and 1100 aluminium alloys in different concentrations (0.1,
0.25, 0.5, 0.75, 1.0, 2.0 and 5.0%) of oxalic acid solutions has been investigated by weight loss and
potentiostatic polarisation techniques, at 25°C. The data indicate that 1100 aluminium is lesscorrosion resistant than 1060 aluminium. The corrosion rates of these alloys are a function of the concentration of electrolyte in a narrow range of concentration, only. The anodic polarisatlon curves of
bQth the alloys exhibit active behaviour at each concentration of oxalic acid and in the whole range
of the applied potential. The ~athodic polarisation curves are almost linear in both the cases, resembling that for hydrogen evolution reaction.The corrosion behaviour of aluminium alloys in oxalic
acid has been explained in terms of the acidity of the solution and self inhibition due to the adsorption of oxalate ions.
Aluminium is highly resistant to most of the acidic and neutral solutions due to the formation ofa
protective oxide film on its surface. Aluminium
equipments, commonly used in textile industries,
frequently come in contact with oxalic acid solutions which are used as a neutralizer during the
processing of fibresI•2• Failure of such apparatus
due to corrosion in oxalic acid is widely reported
in textile and metallurgical industries. Hence, the
understanding of corrosion behaviour of aluminium alloys in oxalic acid solutions is very much
desirable.
In the present investigation, an attempt has
been made to elucidate the corrosion behaviour
of 1060 and 1100 aluminium alloys in different
concentrations of oxalic acid, at 25°C.
Experimental Procedure
For the present investigation, 1060 and 1100 aluminium alloys were used. The composition of aluminium alloys are as follows:
Aluminium (1060): Si - 0.12%, Fe- 0.02%,
Mn - 0.04% ahd rest AI.
Results and Discussion
Aluminium (1100): Si - 0.13%, Fe- 0.32%,
Mn - 0.07%, Mg - 0.02%
Cu - 0.01 % and rest AI.
Oxalic acid and sodium oxalate (BDH, Analar
grade) were used for the preparation of the solutions. These. were recrystallized from their aqueous solutions.
I
r
I
I 'I
""
'1'"'ll'II'
Specimens used for weight loss experiments
were of 5 x 5 cm in size. These were polished
successively with 1/0 to 4/0 grades of emery paper, followed by cleaning with soap and finally
with acetone. The weight loss experiments were
performed in 500 mL corping glass beakers, containing 300 mL of the electrolyte. Triplicate experiments were performed in an air thermostat
maintained at 25 ~ O.2°C, to ascertain the reproducibility of the data.
Potentiostatic
polarisation
experiments
were
carried out using a potentiostat (Wenking model
POS73). A three-necked glass assembly containing
a working electrode of size 1 x 1 cm, platinum foil
of size 2 x 2 cm as counter electrode and a Luggin type saturated calomel electrode were used
for polarisation measurements. Experiments were
performed in unstirred solution, without deaeration. Starting from the open circuit potential, different values of potential were applied on the
electrode surlace in steps and the resulting steady
state currents were measured.
'II
"I'
"',"
In the present investigation, corrosion rate of
1060 and 1100 aluminium alloys has been determined by weight loss and electrochemical techniques, at 25°C. Corrosion rates of 1060 and
1100 aluminium alloys in different concentrations
of oxalic acid (0.10, 0.25, 0.50, 0.75, 1.0, 2.0 and
5.0%) have been determined for 24 h immersion
period from weight loss, using the formula;
'\
II II 'II~ ;~l. ill :~
III;d. ,III ,. '"~"'.
"
,,,
SINGH & GUPTA: CORROSION
534 W
Corro~onrare(mpy)=----
DAT
where W=weight loss (mg), D=density of specimen (glcm3), A=area of specimen (square inches)
and T= exposure time. (h)
The evaluation of corrosion rate by electrochemical technique has been done with the help
of the.equation
. rate (mpy) = ----12.4 x Ex
CorrosIon
D
33
BEHAVIOUR OF SOME ALUMINIUM ALLOYS
icorr
where E, icorr and D are electrochemical equivalent, corrosion current density and density of
specimen, respectively. The corrosion current in
the above equation has been determined by extrapolation method3•
Fig. 1 illustrates the variation in corrosion rate
with acid concentration evaluated by weight loss
and electrochemical techniques. There exists ('
good agreement between the corrosion rates mea·
sured by the two techniques. It is noted from the
nature of the curves that initially with increase in
the acid concentration, corrosion rate increases
rapidly up to 1% of oxalic acid. On further in~
crease in its concentration, corrosion rate becomes almost constant for 1060 aluminium, however, rapid increase in corrosion rate of 1100 aluminium continues up to 2% of oxalic add. Corrosion rate exhibited by 1100 aluminium at each
20.0
concentration of the electrolyte is higher than that
for 1060 aluminium.
As the concentration. of oxalic add is- succes~
sively increased from 0.1 to 5.0%, the 'pH of the
solu'ion decreases. gradually. With increase in the
acidity of the. electrolytic solution the corrosion
rate of aluminium alloys is expected to increase as
reported earlierA for most of the acidic solutions
including those of oxidizing acids. Thus, the initial
increase in corrosion rate of different aluminium
alloys with concentration up to 2% or less may be
very well explained in terms of the decrease in
pH of the electrolyte. However, at higher concentration, the increase in the corrosion rate is relatively sluggish although the decrease in pH continues up to 5% oxalic acid. This shows that there
are some factors other than the decrease in pH .of
the electrolyte which affect the corrosion rate of
aluminium alloys. It is known that oxalate ions act
as a good inhibitor for the corrosion of aluminium in acidic solutionS, the inhibition of corrosion
in the present case, as well, cannot be over ruled.
To confirm the inhibitive action of oxalate ions,
additional experiments were performed by adding
sodium oxalate to a solution of oxalic acid of
known concentration. The inhibitive action of oxalate ions is quite evident from the nature of the
curves in Fig. 2. It was observed that on increasing the oxalate ion concentration in the electrolyte
the corrosion rate of aluminium alloys decreases
appreciably. An inhibition efficiency of nearly 7779% was observed at the concentration of 1.00 M
sodium oxalate (88 x 103 ppm of oxalate ion).
Thus, it is apparent that even such a large concentration of oxalate ions is not sufficient to ar-
-------------16.0
Corrosion I"QWof 1060 Al
••• 15.0
f
-'-'-
III
Corrosion
zo
-----By w.lllht ID_
--•• ~tro ch.mlcol
-
~
a:
iiI
o
a:
a:
r---.-.-.
1 ....-.
----
10
ou
/'
I
-.I
Byw.lllht
-.
IDss
--
-wetro ",,-",Icol
of 1100 Al
I"QW
-.-.-.-.-
--
·1
_n
12.0
/
•••
Fig. 1-Corrosion Pate of 1060 and 1100 aluminium alloys in
different concentrations of oxalic acid, at 25°{:
-i
eo
Q.
E
ft
~~::;:.:::
~.:.:.:-:.::.:::..:.::-..:.:.:=
10 ~
:0:
:A
eo
e
2
c:
oS
o
50
---- --------1.01
o
CONCENTRATION OF OXALIC ACID,
•..
l!
u
/
2.0
to
•..
1
5,01-/1
-'-
Corrosion r-oft 01 1010 Al
••
1100 Al
•••IE of
1010 Al
••
1100 Al
I
0.%5
. I
0.50
I
0.75
I
Conc:•••tl'1ltlon 01 sodium _loW.~.
I
I
1.0
130
Fig. 2-Variation of corrosion. rate and %IE with different
concentrations of sodium oxalate in 1% oxalic acid, at 25°C
34
INDIAN J, CHEM. TECHNOL..
rest the corrosion rate completely. Perhaps this is
the reason why no decrease in corrosion rate has
been observed at any concentration of oxalic acid
used during the presentinvesti~ation.
Once, the
corrosion rate becomes constant.
Thus, the variation in corrosion rate of aluminium alloys with increasing concentration of oxalic
acid may be explained in terms of both, the increase in acidity of the solution with concentration as well as the self-inhibition of corrosion process due to adsorption of oxalate ions. It appears
from the data of the present investigation that in
lower acid concentration range the rate of corrosion is probably higher than the inhibition
achieved due to adsorption. Hence, the corrosion
rate steadily increases with the increasing acid
concentration. At higher concentrations,. the increase in corrosion rate may be almost completely
compensated by the inhibition of corrosion due
to adsorption of oxalic acid and the corrosion
rate becomes almost constant.
The variation of open circuit potential (OCP) of
1060 and 1100 aluminium alloys with acid concentration has been shown in Fig. 3. it is' to be
noted from the figure that on increasing the acid
concentration from 0.1 to 1%, the OCP of the alloys rapidly shifts towards more active direction.
On further increase in acid concentration from '1
to 5% it becomes almost constant for 1060 aluminium and shifts very slightly towards more active
direction for 1100 aluminium.
The continuous shift in OCP in active direction
in both the cases, with the increase in the concentration of oxalic-acid indicates that the corrosivity
of oxalic acid increases with its concentration up
to 1%. Almost constant values of OCP from 1 to
5% of the solution further' indicates that the cor-
JANUARY
1<}<}6
rosion rate should be more or less independent of
concentration. It may also be noted that the values of OCP at each concentration of oxalic acid
are more negative for 1100 aluminium as compared
to that for 1060 aluminium. Thus, 1060 aluminium appears to be more resistmt to corrosion in
oxalic acid at each concentration. Similar results
were obtained by other investigators with respect
to the relative corrosion resistance of aluminium
alloys in nitric acid6•
Figs 4 and 5 illustrate the anodic polarisation
behaviour of 1060 and 1100 aluminium alloys respectively, in different concentration of oxalic acid, at 25°C. An analysis of the plots reveals that
active corrosion behaviour is exhibited by both
the alloys in the whole range of potential and at
each concentration of oxalic acid. Well defined tafel regions followed by distinct limiting current
densities were observed at all concentrations of
the acid. It is to be noted from the figures that on
increasing the acid concentration, the anodic polarisation curves shift towards higher current
density region without any change in their nature.
The shift of curves towards higher current density
is gradual till 1% of oxalic acid for 1060 aluminium (Fig. 4) and after.wards the curves for 1 to 5%
solution almost overlap ~ach other. However, the
anodic polarisation curves for 1100 aluminium
gradually and continuously shift towards higher
800
----0000.'0"10
--0.25"10/
600
--0·7S"Io
I
,,,
,
,I,
,,
-'-'-0.50'"
-"---
'"10
-"'-'-Z"lo
-· ..·--5*10
>
E,
--'1060AI
---1100
a
••
Al
I
,,,
,
,,
,
0
,,
I
I
I
c
:o -zoo
,Q.
---------. --'--'--'--' --.-
I
I
-'00
'----------------------------
-'200
4.0
5.0
CONCENTRATION OF OXALIC ACID, •••
Fig. 3-Variation of OCP of 1060 and 1100 aluminium alloys
with concentration of oxalic acid
I' ,
1
"I
"I
"
o
1.0
z.O
IOQ CD,
3.0
J'A/crnZ
Fig. 4-Anodic polarisation curves-of 1060 aluminium in oxalic acid solutions
SINGH
& GUPTA:
CORROSION
35
BEHAVIOUR OF SOME ALUMINIUM ALLOYS
800,
600~ ----
0.1 01.
--
0.25°1.
-.-
0.50"10
-'j;j
()
200
!!
0.15%
-
.. -
1°1.
-
-
2°1.
-
-
5°1.
>
E
0
-'
c
;:
ffi
-200
1.0
~
-"00
2.0
3·0
100 CD, IJA/ern2
Fig. 6-Cathodic
-600
polarisation curves of 1060 aluminium
oxalic acid solutions
fu
-800
-1000
U
~
W
~
U.
100 CD,pA/e"?-
Fig. 5-Anodic
Concen-
polarisation curves of 1100 aluminium in oxalic acid solutions
3.64
AI
1.26
0.30
1.21
A
I IumNcm2
13.21
4.80
24.05
1060
-840
4.18
-850
-890
18.24
-860
-875
-880
-870
39.91
-865
2.76
1100
1.74
33.19
2L93
0.79
0.55
0.91
23.50
22.44
1.29
13.21
17.83
4.58
27.61
38.11
2.09
1.26
10.50
1060
icom
flNcm2
Table I-Corrosion
EcommV
parameters from polarisation .curves of
of1060
oxalicand 1100 aluminium
of oxalic alloys
acid, atin 25°C
different concentrations
current density region up to 5%, nevertheless, the
magnitude of shift is not proportional to the concentration change.
The values of corrosion current (icorr)' corrosion
potential (Ecorr) and limiting current density (iL)
calculated from the· polarisation curves at different concentr.atigns of oxalic acid for 1060 and
1100 aluminium alloys have been recorded in
Table 1. The data in the table indicate that the values of icorr and iL gradually increase with increase
in the acid concentration. Whereas, Ecorr values
become more negative in solutions of higher conconcentration. The values of i,orr and iL are larger for
1100 aluminium alloy than the corresponding values for 1060· aluminium, at each concentration of
oxalic acid solution. From the comparison of
these data it is apparent that 1060 aluminium is
more resistant to corrosion in oxalic acid than
1100 aluminium, irrespective of the concentration
of the electrolyte.
The shift of Ecorr values towards more active direction give the indication for the increased probability of corrosion process in lower concentration range. At higher concentrations, ~most constant Ecorr is attained due to the adsorption of oxalate ions. A critical analysis of icorr and iL values mentioned in the Table 1, reveals that initially the increase in icorr value with concentration is
quite appreciable, indicating the dependence of
corrosion rate on oxalic acid concentration. Small
increment in icorr and iL from 1 to 5% solution for
1100 aluminium: alloy again confirms the slowing
down the corrosion process at higher concentrations. The conclusions arrived at from the polarisation experiments are in good agreement with
those obtained from weight loss d~ta.
The cathodic pol~risation curves for 1060 and
1100 aluminium alloys in solutions containing different concentrations of oxalic acid are depicted
in Figs 6 and 7 respectiyely,. at 25°C. if is to be
noted from the figures that the cathodic polarisation curves are iimost linear and parallel to each
other at each concentration of oxalic acid. The
shift in cathodic p'olarisation curves towards higher current density region with increase in the concentration of oxalic acid has been observed for
both the alloys. However, the magnitudes of the
shift are different for different alloys., A large shift
in cathodic polarisation curves occurs as concentration of the acid is raised from 0.1 to 1.0% and
36
INDIAN 1. CHEM. TECHNOL.,
-800
------
0.10 '4
0.25'4
-100'
-'-- ..-
0.50'4
0·75'4
1'4
-"'- ....-
2'4
5'4
III
...
en
1.0
2·0
lot CO,
Fig. 7-Cathodic
3.0
1996
cathodic polarisation curve is not that marked.
On the other hand, at higher concentrations of
oxalic acid, the inhibition resulted from the adsorption being almost the same for both the alloys, the shift in cathodic polarisation curves at
higher concentrations of oxalic aCid is almost
identical. Although, this interpretation could very
well explain the results of the present investigation" it is difficult to correlate the relative adsorbability of oxalate ions with the composition of the
alloys chosen.
3.'
""/e'/
polarisation curves of 1100 aluminium
oxalic acid solutions
JANUARY
in
closely spaced curves are obtained in the range
1-5% oxalic acid, in the case of 1060 aluminium.
For 1100 aluminium, the curves are almost equidistant in the whole range of experimental concentrations.
The discharge of hydrogen being the only possible cathodic reaction in the acidic solutions and
the cathodic polarisation curves being more or
less linear it may be assumed that activation controlled hydrogen evolution reaction 7 occurs in the
present case, also. The continuous shift in the polarisation curves towards higher current density
region may, therefore, be attributed to the increase in the rate of hydrogen ion discharge due
to the availability of H+ in large extent at higher
concentrations of oxalic acid.
However, the relative magnitude of the shift in
cathodic polarisation curves from 0.1 to 1% of
oxalic acid is much more significant in the case of
1060 aluminium. This seems probably due to the
competition between oxalate and H+ ions for adsorption at the same sight, oxalate ions seem to
be Qlore easily adsorbed on 1100 aluminium at
their lower concentrations, and thus the shift in
Conclusion
From the present investigation, following conclusions can be drawn:
1 1060 Aluminium is more resistant towards
corrosion in oxalic acid solutions than 1100 aluminium.
2 The rate of corrosion of the aluminium alloys
is function of the concentration of oxalic acid in a
narrow range of concentration (up to or below
2%) and at higher concentration the corrosion
rate becomes almost independent of concentration.
3 Oxalate ions present in the electrolyte solutions seems to act as a self inhibitor.
4 The corrosion of both the alloys follow the
same mechanism.
References
1
2
3
4
Sekine I & Okano C, Corrosion, 45 (1989) 924.
Sekinel, Okano C & YuasaM, Corros Sc~ 30 (1990) 351.
WagnerC& Traud W,ZPhys Chern, 441 (1938) ..
Evans U R & Hoar T P, J Electrochem Soc, 99 (1952)
212.
5 Chakraborty C, Singh M M & Agarwal C Y, Indian J
Techno~ 20 (1982) 371.
6 Chakraborty C, Ph D Thesis, Banaras Hindu University,
India, 1983.
7 Antropov L I, Theoretical Electrochemistry (Mir Publisher,
Moscow), 1977,440 .
..•
I
I' I