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Optics
Optik
Optik
Optik 118 (2007) 296–301
Zero resistance ammeter of metallic alloys in aqueous solutions
Khaled Habib
Department of Advanced Systems, Materials Science Laboratory, KISR, P.O. Box 24885, Safat 13109, Kuwait
Received 4 October 2004; received in revised form 27 December 2004; accepted 25 March 2006
Abstract
In the present work, the corrosion current density of a low carbon steel, a pure aluminum, a stainless steel, a
copper–nickel alloy were obtained in 1 M NaOH, 1 M KCl, 1 M NaCl, 1 M H
2
SO
4
solutions, respectively. The
obtained corrosion data from the optical interferometry technique, as a zero resistance Ammeter were compared with
corrosion data obtained on the same alloys, in the specified solutions, from an electronic zero resistance-Ammeter as
well as from the linear polarization method. The comparison among the three techniques indicates that there is a
contrast in the results among the investigated alloys. In general, the results of the optical interferometry were found to
fall in between the corrosion values of the zero resistance ammeter and the linear polarization method, because the
technique works based on the electromagnetic principle, in the absence of electronic noise. As a result, the optical
interferometry can be considered as a useful zero resistance-Ammeter for measuring the corrosion current density of
metallic electrodes in aqueous solutions, at the open circuit potential of the electrodes in the aqueous solutions.
r2006 Elsevier GmbH. All rights reserved.
Keywords: Holographic interferometry; Corrosion current density; Zero resistance ammeter; Linear polarization; Metallic electrodes
1. Introduction
It is well known that electronic instrumentations, i.e.,
Ammeter, Potential-meter, have been used for years to
measure electrochemical properties of metallic electro-
des in aqueous solutions. One of the disadvantages of
using electronic instruments for the measurement of
electrochemical properties is the invasive nature of those
instruments to the electrochemical systems of the
metallic electrodes in aqueous solutions. In recent work
published elsewhere [1–5], it has been shown that laser
optical interferometry can be used as an optical
transducer to characterize the electromagnetic field,
i.e., phase and amplitude of the reflected light waves of a
surface of a metallic electrode moving further away
from the light source, which develops as a result of the
electron conduction in metallic electrodes in aqueous
solutions due to the anodic reaction, corrosion pro-
cesses, between the electrodes and the aqueous solu-
tions. The characterization of such electromagnetic field
(phase and amplitude of the reflected light waves of a
surface) and a mathematical correlation of the electro-
magnetic field to any electrochemical properties, i.e.,
corrosion current density [1,2], double layer capacitance
[3], alternating current impedance [4], and electrical
resistance [5], would lead to the measurement of the
electrochemical properties by optical interferometry, by
the non-invasive method.
The objective of the present work was to measure the
corrosion current density of a low carbon steel ( UNS
No. 1020, 0.2% C, 0.45% Mn, 0.25% Si, and balanced
ARTICLE IN PRESS
www.elsevier.de/ijleo
0030-4026/$ - see front matter r2006 Elsevier GmbH. All rights reserved.
doi:10.1016/j.ijleo.2006.03.023
Tel: +965 543 0238; fax: +965 543 239.
E-mail address: khaledhabib@usa.net (K. Habib).
Fe), a pure aluminum (99.7% Al), a stainless steel (UNS
No. 304 stainless steel, 19% Cr, 9% Ni, 0.45% Mn, and
balanced Fe), and a copper–nickel alloy (70% Cu and
30% NI) in 1 M NaOH, 1 M KCl, 1 M NaCl, 1 M
H
2
SO
4
solutions, respectively, by the holographic
interferometry technique. Furthermore, the work aimed
to compare the obtained data of the corrosion current
density of the optical interfermetry with other techni-
ques of the corrosion measurement such as the zero
resistance Ammeter and linear polarization method
[6,7]. It is well known that the zero resistance ammeter
and linear polarization method [6,7] are widely used to
measure the corrosion current density of metallic
electrodes, which corresponds to the open-circuit
potential of the electrodes in aqueous solutions. In the
zero resistance Ammeter, one can measure the corrosion
current.
Current density of two similar metallic electrodes at
the open-circuit potential of the electrodes in an aqueous
solution without imposing any external voltage on the
electrodes. This normally occurs due to the presence of
the electronic noise and the absence of the electrical
resistance across the interface between two similar
electrodes and the aqueous solution, in the mechanism
of the zero resistance Ammeter. Consequently, measure-
ments of corrosion current density of metallic electrodes
by the zero resistance Ammeter are much higher than
other techniques, because of the presence of electronic
noise and the absence of the electrical resistance across
the interface between the solid electrodes and the
aqueous solution. On the contrary, in the linear
polarization method, one can measure the corrosion
current density of a metallic electrode at the open-circuit
potential of the electrode in an aqueous solution by
imposing an external voltage on the electrode. As a
result, a polarization resistance normally develops
across the interface between the solid electrode and the
aqueous solution. This leads to extremely low measure-
ments of the corrosion current density of the electrodes
in aqueous solutions, because of the presence of the
polarization resistance in the mechanism of the linear
polarization method.
2. Theoretical analysis
An optical interferometry such as the real time-
holographic interferometry [8] can be used to generate
interferograms of a solid surface. The real time-
holographic interferograms can develop when at least
two images of the surface are nearly superimposed,
having slightly different positions because the micro-
alterations which have taken place at the object surface.
In the case of corrosion of a metal surface, i.e., in the
anodic reaction of metallic alloys in aqueous solutions,
consider a point P on an un-reacted surface which
subsequently corresponds to point P’ after the corrosion
process, i.e., anodic reaction (see Fig. 1).
From Fig. 1, it is apparent that the path of a coherent
light such as a laser light would be different due to the
changes in position of P. A path length difference of an
odd multiple of 1/2 of the wavelength will produce a
dark fringe superimposed on the image of the object.
To measure the thickness of the metal layer which is
lost from the metal surface as a result of the anodic
reaction, we assumed that the object beam, changes in
the surface of the object, and the viewer’s eye (or
camera) all lie in the same plane. Consider the ‘‘move-
ment’’ of point P is orthogonal to the surface of the
object (see Fig. 1) where
OP ¼O0M¼D1;
PQ0¼NQ0¼D2;
PP0¼U¼orthogonal displacement:
Therefore, the change in the light path length is
D¼ðD1þUsin aþUsin bþD2ÞðD1þD2Þ, (1)
D¼þUðsin aþsin bÞ, (2)
where the angles aand bcan be obtained from the
experimental set up. Every time the path length changes
by one wavelength, the image of P goes from light to
dark to light. Hence, the number of fringes passing
through P is
N¼D=l, (3)
where lis the wavelength of the laser light.
By substituting Eq. (2) into Eq. (3), the orthogonal
displacement of point P can be found as
U¼þNl
ðsin aþsin bÞ. (4)
In order to relate the mass loss of an electrode sample
to its anodic current density, the following theoretical
ARTICLE IN PRESS
Old path
New path
Q
Q1
D2
D1
P
O
O1
M
α
αNU
β
β
p1
Fig. 1. The orthogonal displacement of point P (from
unreacted surface) to point P0(after the corrosion process) at
the surface of the object.
K. Habib / Optik 118 (2007) 296–301 297
model is proposed. Consider a metallic plate of original
width w, length L, and thickness tis subject to anodic
dissolution reaction in which the thickness decreases to
(tU), where Uthe thickness of the metal layer lost
from the plate surface (see Fig. 2). Accordingly, the
surface area of the plate, after the reaction becomes
A¼wL ¼ðV=UÞ, (5)
where Vis the dissolved volume of the plate into the
solution.
Also, the anodic current of the plate can be described
from Farady’s Law as
I¼WF jZj
MT , (6)
where Wis the weight loss, Fis Farady’s constant, |Z|is
the absolute number of electron charge, Mis the atomic
weight of the electrode material, and Tis the time of the
anodic reaction. Hence, the anodic current density can
be obtained by dividing Eq. (6) with Eq. (5); this yields
J¼FjZjdU
MT , (7)
where dis the density of the electrode material.
Eq. (7) represents a relationship between the thickness
of the removed layer (U) and the anodic current density
(J) of the electrode. In other words, Eq. (7) represents
the governing relationship of the zero resistance
Ammeter for measuring the corrosion current density
(J) of metallic alloys in aqueous solutions by the optical
interferometry technique, at the open-circuit potential of
the metallic alloys in the solutions, without any physical
contact.
In this investigation, the optical interferometry was
utilized for the first time as a zero resistance Ammeter
for measuring the corrosion current density (J)of
metallic alloys in aqueous solution, at the open-circuit
potential of the metallic alloys in the solutions, in a non-
invasive way.
3. Experimental work
In the present investigation, metallic alloys of a low
carbon steel (UNS No. 1020, 0.2% C, 0.45% Mn,
0.25% Si, and balanced Fe), a pure aluminum (99.7%
Al), a stainless steel (UNS No. 304 stainless steel, 19%
Cr, 9% Ni, 0.45% Mn, and balanced Fe), and a
copper–nickel alloy (70% Cu and 30% Ni) were used in
1 M NaOH, 1 M KCl, 1 M NaCl, 1 M H
2
SO
4
solutions,
respectively. The samples were fabricated in a plate form
with dimensions of 10.0 cm 5.0 cm 0.15 cm. Then all
samples were polished and ground by silicon carbide
papers until the finest grade (1200) was reached. Then a
coal tar (black) Epoxy (polyamide cured) was used on
one side and all edges of the samples. The reason behind
covering one side and all edges of the samples by the
coal tar Epoxy is for protection from the solutions while
testing the other side of the sample (exposed side to
solution) to corrosion. The exposed surface area of the
sample is 45 cm
2
. At the beginning of each test, a sample
of the above materials was immersed in a specific
solution for 1 h. While the sample in the solution, the
corrosion potential was measured by a potential-meter
with respect to the saturated calomel electrode (SCE), a
reference electrode. After the first hour of the immer-
sion, a hologram of the sample was recorded using an
off axis holography (see Fig. 3 for the optical set up). In
this study, a camera with a thermoplastic film was used
to facilitate recordings of the holographic interferometry
of the samples. The camera is HC-300 Thermoplastic
Recorder made by Newport Corporation.
During each experiment, the holographic interfero-
grams were recorded as a function of time, in which
each test lasted for 60 min. Then, the interferograms
were interpreted to orthogonal displacement of the
surface of the metal. Thereafter, the displacement
measurements are used in Eq. (7) to determine the
corrosion current density of the samples. Finally the
obtained data of the corrosion current density of all
metallic samples are compared with other data produced
by an electronic zero-resistance Ammeter and by the
linear polarization method on the same samples in the
specified solutions. In this study, a potentialstat made by
EG&G Princeton Applied Research was used to
measure the corrosion current density, data, by the
linear polarization method, using EG&G model 352
corrosion analysis software. In contrast, a potentialstat/
Galvanostat made by ACM instrumentations, the ACM
Gill 860 system, was used in this investigation to
determine the average noise of the potential/time and
current/time of a Galvanic coupling between two similar
samples in the specified solutions.
It is worth noting that there was no delay time at the
beginning of each test during the measurements of the
average noise of the potential/time and current/time of
the Galvanic coupling between two similar samples.
Also, in order to plot the potential/time and current/
time of the Galvanic coupling, the duration of the
recorded data between each sequence reading was 0.7 s,
and lasted for 15 min. In this study, the zero resistance
of the ACM Gill 860 system was used to determine the
ARTICLE IN PRESS
before reaction
after reaction
t
L
W
U
Fig. 2. A plate electrode prior to and after the anodic reaction.
K. Habib / Optik 118 (2007) 296–301298
corrosion current density which corresponds to the
open-circuit potential of the samples in solutions.
Finally the obtained data of the corrosion current
density of all metallic samples by the optical inter-
ferometry are compared with other data produced by
the other methods.
4. Results and discussion
Fig. 4 shows an example of progressive interfero-
grams of a carbon steel sample in seawater as a function
of time. Fig. 4a represents a real-time interferogram of
the sample after 10 min of the elapsed time of the
corrosion test, where six fringes appeared on the
photograph. Fig. 4b is the same interferogram after
14 min of elapsed time of the corrosion test, where 10
fringes detected on the photograph. It is obvious from
these interferograms in Fig. 4a and b that there is a
uniform chemical oxidation, depicted by the interfero-
metric patterns. These observations of Fig. 4a and b are
in agreement with interferograms documented on
metallic electrodes in aqueous solutions, elsewhere [2].
It is worth mentioning that each fringe in Fig. 4 (dark
line) accounts to an orthogonal displacement equivalent
to 0.3 mm according to mathematical models reported
elsewhere [2]. Also, there are neither gas formation nor a
significant variation in the refractive index were
observed at the samples during the optical interferome-
try measurements. In other words, holographic inter-
ferometry can be used as a powerful tool,
interferometric microscope, in the field of electrochem-
istry. By using data from interferograms such as those in
Fig. 4, one can measure the corrosion current density of
metallic electrodes in aqueous solutions by holographic
interferometry, using Eqs. (4) and (7).
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He Laser Light Beam Splitter
Mirror 1
Thermoplastic
Holographic Film
Corrosion Cell
Mirror 3
(object beam)
objective
lens 1
Magnifying lens
Camera
Collimating lens 2
objctive
lens 2
sample
(Reference beam) Collimating lens 1
y
z
α
φ
Mirror
2
Fig. 3. Optical setup of an off-axis holographic interferometry.
Fig. 4. An example of progressive interferograms of a carbon
steel sample in seawater as a function of time: (a) after 10 min
and (b) after 14 min. Fig. 5. The average noise of the current/time (a) and potential/
time (b) of a Galvanic coupling between two samples of the
low carbon steel in 1 M NaOH.
Fig. 6. The average noise of the current/time (a) and potential/
time (b) of a Galvanic coupling between two samples of the
pure aluminum in 1 M KCl.
K. Habib / Optik 118 (2007) 296–301 299
The average noise of current and potential measure-
ments of a Galvanic coupling between two similar
samples of the low carbon steel, a pure aluminum, a
stainless steel, a copper–nickel alloy are shown in
Figs. 5a–8a and Figs. 5b–8b, respectively. The average
noise value is based on two readings of the current
density of the Galvanic coupling as a function of time.
The average noise of the current/time was found to be
0.037, 4.22 10
6
, 0.042, and 0.1004 mA/cm
2
for low
carbon steel, pure aluminum, stainless steel, and
copper–nickel alloy, respectively. It is obvious that the
average noise of the current/time of all samples tend to
yield a zero value as a function of time, due to the low
Galvanic coupling current between the two similar
metallic samples (see Figs. 5a–8a). In addition, the
values of the average noise of the potential/time of two
readings tend to converge to a steady-state value as a
function of time (see Figs. 5b–8b).
Comparison between the corrosion data of the
metallic samples with respect to the three methods of
the corrosion measurement are given in Table 1.In
general the tabulated data indicate that there is a
contrast between the corrosion data which is measured
by the three methods. For instance, the electronic zero
resistance Ammeter was found to give the highest
corrosion values for all the samples investigated in this
study compared to the linear polarization method. In
contrast, the linear polarization method was found to
give the lowest corrosion values for all the samples
investigated in this study at the open-circuit potential of
the samples in solutions. On the other hand, the optical
interferometry method was found to give corrosion
values fall in between the values of the corrosion data of
the zero resistance Ammeter and the linear polarization
method. The high values of the corrosion data by the
(electronic) zero resistance Ammeter can be readily
explained due to the functional nature of the low
electrical resistance in this technique as well as to the
electronic noise which is involved in the process of the
measurement of the corrosion current density. In
contrast, the extreme low values of the corrosion data
by the linear polarization method is due to the presence
of the polarization resistance in the mechanism of the
linear polarization method. It is possible that the
corrosion values of the optical interferometry fall in
between the corrosion values of the zero resistance
Ammeter and the linear polarization method because
the technique works based on the electromagnetic
principle in the absence of electronic noise. In other
words, the optical interferometry can be considered as a
non-electronic zero resistance-Ammeter which works by
an electromagnetic mean rather than an electronic
mean. This implies that the optical interferometry
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Fig. 7. The average noise of the current/time (a) and potential/
time (b) of a Galvanic coupling between two samples of the
stainless steel in 1 M NaCl.
Fig. 8. The average noise of the current/time (a) and potential/
time (b) of a Galvanic coupling between two samples of the
copper–nickel alloy in 1 M H
2
SO
4
solution.
Table 1. Comparison between the corrosion values of the four metallic samples by different methods of corrosion measurement
(corroion current density 10
6
A/cm
2
)
Materials Optical interferometry Zero resistance ammeter Linear polarization
Low carbon steel 23,024.5 19,617.8 10
3
6.2
Stainless steel 13,400 6,554,300 0.02
Aluminum 19,625.8 3600 3.2
Copper–nickel alloy 11,060.3 73,951 10
3
9.25
K. Habib / Optik 118 (2007) 296–301300
comprises neither electrical resistance nor electronic
noise, as compared to the other techniques used in this
investigation. It is worth noting that the corrosion
current density in Table 1 was determined based on an
average of two readings for the zero resistance
Ammeter, the optical interferometry, and the linear
polarization methods.
5. Conclusions
The following conclusions are drawn from the present
investigation:
1. Holographic interferometry is found very useful
technique as a zero resistance Ammeter for measur-
ing the corrosion current density of metallic alloys in
aqueous solutions.
2. The corrosion current density (J) was directly
measured without any physical contact for the low
carbon steel, the pure aluminum, the stainless steel,
and the copper–nickel alloy in 1 M NaOH, 1 M KCl,
1 M NaCl, 1 M H
2
SO
4
solutions, respectively.
3. The (electronic) zero resistance Ammeter was found
to give the highest corrosion values for all the samples
investigated in this study compared to the optical
interferometry and linear polarization method. The
high values of the corrosion data by the zero
resistance Ammeter can be readily explained due to
the functional nature of the low electrical resistance
in this technique as well as to the electronic noise
which is involved in the process of the measurement
of the corrosion current density.
4. In contrast, the linear polarization method was found
to give the lowest corrosion values for all the samples
investigated in this study at the open-circuit potential
of the samples in solutions. This is because of the
presence of the polarization resistance in the mechan-
ism of the linear polarization method.
5. It is possible that the corrosion values of the optical
interferometry fall in between the corrosion values of
the zero resistance Ammeter and the linear polariza-
tion method because the technique works based on
the electromagnetic principle, with the absence of
electronic noise.
6. The optical interferometry can be considered as (a
non-electronic) zero resistance Ammeter, which
works by an electromagnetic mean rather than an
electronic mean. This implies that the optical inter-
ferometry comprises neither electrical resistance nor
electronic noise, as compared to the other techniques
used in this investigation.
References
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[3] K. Habib, Measurement of the double layer capacitance of
aluminium samples by holographic interferometry, Opt.
Laser Technol. 28 (8) (1996) 579–584.
[4] K. Habib, Measurement of the a.c. impedance of
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[5] K. Habib, Measurement of the electrical resistance of
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[8] R. Jones, C. Wykes, Holographic and Speckle Interfero-
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