AN ABSTRACT OF THE THESIS OF
Jarinee Chattratichart
in
Chemical Engineering
Title:
for the degree of
Master of Science
presented on
May, 19, 1981
A.C. Corrosion of Various Metals in a Salt Solution
Abstract a:proved:
Redacted for privacy
Robert E. Meredith
In recent years, the effect of alternating current as a cause
of corrosion of substructures has received considerable attention.
The present study, firstly, represents an overview of previous research on ac corrosion--its cause and behavior.
Secondly, the ex-
periments are performed to investigate ac density effect on the
corrosion of aluminum, brass, copper, cupro4nickel alloy, lead,
304-stainless steel, cold-rolled steel, titanium, and zirconium,
all in a 3% sodium chloride solution.
The experiments are designed
to provide identical conditions so that comparison of the experimental results is feasible.
Finally, as a preliminary study for
further research, several recommendations are made for the study
of various aspects and possible causes of oC corrosion.
The experimental results along with tliCse reported in the lit-
erature are tabulated-
The graphical presentation of the corrosion
rate and the ac corrosion factor (actual corrosion by ac as percentage of the equivalent dc corrosion) are also included.
The re-
sults presented show that ac accelerates thecorrosion of all metals
tested.
Different metals and alloys are observed to possess differ-
ent resistance to ac corrosion.
Consequently, future study con-
cerning ac corrosion behavior of the individual metals is
indispensable.
A.C. Corrosion of Various Metals
in a Salt Solution
by
Jarinee Chattratichart
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Commencement June 1982
APPROVED:
Redacted for privacy
Professor of Chemical Engineering
in charge of major
Redacted for privacy
Head of Department of Chemical Engineering
Redacted for privacy
Dean of Graddate
5j
7:3 1
Date thesis is presented
Typed by Donna Lee Norvell-Race for
May 19, 1981
Jarinee Chattratichart
ACKNOWLEDGMENTS
I wish to express my appreciation and gratitude to many people
and friends to whom I am indebted during the course of this work.
Should I try to mention all, my acknowledgment will never be adequate.
In particular, my thanks go to Professor Charles Wicks 'for
taking a chance on me, and Professor Robert Meredith for proofreading this thesis, for his advice, and, most of all, for his great
patience as my major advisor.
I am especially thankful to Bill
Johnson for his assistance with the equipment and to Teledyne Wah
Chang Albany for the titanium and zirconium kindly supplied to me.
I can hardly omit mentioning some of my friends whose criticisms,
help, encouragement, and friendship are invaluable:
Wataru Nishimura,
Jambulingam Palaniappan, and Yawar Mahmood, I thank you all.
Last, and most of all, I am deeply grateful to my parents and
my family for their support by all means, which made my dream come
true.
TABLE OF CONTENTS
Chapter
I
II
Page
INTRODUCTION
1
THEORETICAL BACKGROUND
3
A.
A.C. as a Cause of Corrosion and Factors
Affecting its Corrosion
1.
2.
3.
A.C. Densities
Electrode Nature and Characteristics
Electrolyte
3.1
3.2
4.
5.
B.
2.
3.
4.
5.
6.
V
Oxidation Theory
Redeposition Theory
Galvanic Couples
Capacitor Theory
Rectification
Depolarization
EXPERIMENTAL PROCEDURES
A.
B.
C.
D.
IV
Temperature
Frequency
Mechanisms
1.
III
Chemical Composition
Degree of Mixing
Electrodes
Electrolyte
Apparatus and Electrical Circuit
Procedures
4
6
6
6
7
7
7
8
9
9
10
11
12
15
17
17
18
18
18
RESULTS
22
DISCUSSION
61
A.
B.
Aluminum
Copper and Copper Alloys
61
62
Chapter
page
C.
D.
E.
F.
VI
VII
Lead
304-Stainless Steel and Cold-Rolled Steel
Titanium
Zirconium
0008.0
63
65
66
67
CONCLUSIONS
69
RECOMMENDATIONS
71
BIBLIOGRAPHY
72
APPENDICES
Appendix
Appendix
Appendix
Appendix
A:
B:
C:
D:
Tabulated Final Data
Samples of Calculation
Cleaning Solutions
Molecular Weights of Tested Metals
76
85
87
88
LIST OF FIGURES
Figure
Page
1
Electrical Circuit for the Experiment
19
2
Corrosion Cell
20
3
Corrosion Rate of Aluminum versus A.C. Densities
43
4
Corrosion Rate of Brass versus A.C. Densities
44
5
Corrosion Rate of Copper versus A.C. Densities
45
6
Corrosion Rate of Cupro-Nickel Alloy versus
A.C. Densities
46
7
Corrosion Rate of Copper and Its Alloys versus
A.C. Densities
47
8
Corrosion Rate of Lead versus A.C. Densities
48
9
Corrosion Rate of Cold-Rolled Steel versus
A.C. Densities
49
10
Corrosion Rate of 304-Stainless Steel versus
A.C. Densities
50
11
Corrosion Rate of Steels versus A.C. Densities
51
12
Corrosion Rate of Titanium versus A.C. Densities
52
13
Corrosion Rate of Zirconium versus A.C. Densities
53
14
A.C. Corrosion Factor of Aluminum and Zirconium
as a Function of A.C. Densities
54
15
A.C. Corrosion Factor of Aluminum at Low Current
Densities as a Function of A.C. Densities
55
16
A.C. Corrosion Factor of Copper and Its Alloys
as a Function of A.C. Densities
56
17
A.C. Corrosion Factor of Brass as a Function of
A.C. Densities
57
Figure
Page
18
A.C. Corrosion Factor of Lead as a Function of
A.C. Densities
58
19
A.C. Corrosion Factor of Titanium as a Function
of A.C. Densities
59
20
A.C. Corrosion Factor of Steels as a Function
of A.C. Densities
60
LIST OF TABLES
Page
Table
II-1
III-1
Previous Work Reporting an Increase of A.C.
Corrosion with Current Densities
5
List of Metals Used as Electrodes
17
IV-1
A.C. Corrosion Rate of Aluminum in 3% NaC1
Solution
23
IV-2
A.C. Corrosion Rate of Brass in 3% NaC1 Solution
24
IV-3
A.C. Corrosion Rate of Cold-Rolled Steel in 3%
NaC1 Solution
25
IV-4
A.C. Corrosion Rate of Copper in 3% NaC1 Solution
26
IV-5
A.C. Corrosion Rate of Cupro-Nickel Alloy in
3% NaC1 Solution
27
IV-6
A.C. Corrosion Rate of Lead in 3% NaC1 Solution
28
IV-7
A.C. Corrosion Rate of 304-Stainless Steel in
3% NaC1 Solution
29
IV-8
A.C. Corrosion Rate of Titanium in 3% NaC1
Solution
30
IV-9
A.C. Corrosion Rate of Titanium at Different
Degrees of Pitting
31
IV-10
A.C. Corrosion Rate of Zirconium in 3% NaC1
Solution
32
IV-11
A.C. Corrosion Factor of Aluminum
33
IV -12
A.C. Corrosion Factor of Brass
34
IV -13
A.C. Corrosion Factor of Cold-Rolled Steel
35
IV -14
A.C. Corrosion Factor of Copper
36
IV-15
A.C. Corrosion Factor of Cupro-Nickel Alloy
37
Table
Page
TV-16
A.C. Corrosion Factor of Lead
38
IV-17
A.C. Corrosion Factor of 304-Stainless Steel
39
TV-18
A.C. Corrosion Factor of Titanium
40
1V-19
A.C. Corrosion Factor of 304-Stainless Steel
41
IV -20
Corrosion Products
42
Appendices
A-1
Tabulated Final Data for Aluminum
76
A-2
Tabulated Final Data for Brass
77
A-3
Tabulated Final Data for Cold-Rolled Steel
78
A-4
Tabulated Final Data for Copper
79
A-5
Tabulated Final Data for Cupro-Nickel Alloy
8Q
A-6
Tabulated Final Data for Lead
81
A-7
Tabulated Final Data for 304-Stainless Steel
82
A-8
Tabulated Final Data for Titanium
83
A -9
Tabulated Final Data for Zirconium
84
C-1
Cleaning Solutions
87
A.C. Corrosion of Various Metals
in a Salt Solution
I.
INTRODUCTION
In the last two decades, failures in underground cables and
piping systems in close proximity to ac power, lines or railroad
tracks have been observed.
Unexplainable corrosion in substruc-
tures such as water mains used for ac grounding has also been encountered.
It had been controversial whether the cause of the
failures is the leakage of ac into underground systems.
Recently,
it has been learned that ac indeed endangers the systems and
causes the failures.
Considering the extensive use of under-
ground piping systems, ac can cause fairly large magnitudes of
overall metallic losses of substructures, incurring unnecessary
cost to utilities companies each year.
To abate ac corrosion and,
hence, the additional cost, it is important to study ac corrosion
behavior of metals.
AC corrosion and its potential mechanisms have been studied
quite extensively.
According to the literatUre, there have been
great variations in the kinds of the electrolytes, the electrodes,
the ac frequencies, etc., used in the experiments performed by
different authors.
Therefore, it is prerequisite that one must
employ identical conditions in performing his experiments to make
feasible the comparison of different ac corrosion behavior of
different metals.
It is the intent of this thesis to, first, study
other authors' previous works, assemble their thoughts and explanations to the results they observed, and present here a brief summary
of factors affecting ac corrosion.
Secondly, by keeping other vari-
ables constant, the corrosion rates of different metals in 3% sodium
chloride solution are observed as a function of current densities,
all the experimental conditions being identical.
Finally, to cope
with the various trends observed on the metals, explanations are
attempted on the basis of the literature and recommendations for
future research are presented.
3
II. THEORETICAL BACKGROUND
A. A.C. As a Cause of Corrosion and Factors
Affecting Its Corrosion
Installation of gas, water, and sewer pipelines near ac power
lines has become a common practice.
Water piping systems have been
used for ac grounding by the electric profession.
Recently there
have been increasing reports of corrosion failures of underground cataes; of piping systems in the vicinity of ac. power iines and of bare
neutral wires in URD (underground residential development) systems.
Corrosion by alternating stray current has then become a subject of
concern to the utility industry.
Many reports confirming the exis-
tence of ac leakage support the controversy that ac is a cause of
Induced ac voltage of 5-30 v. and ac density as high
the failures.
2
as 2.79 ma/ft
for a holiday size of 1 cm radius are commonly en-
countered on pipelines parallel to high voltage ac power lines.
The San Diego Utilities Department reports that there is an average
of three ampere of ac flowing on 90% of water services connected to
the metallic mains in San Diego.
It is also estimated, based on
60,000 services affected by ac, that 36,000 lb/yr of iron is removed
by ac if 1% of the equivalent dc loss is caused by ac.
Besides the
ac grounding, another possible cause of ac flowing in the under
ground pipe system, is the shifting of railway loads which continually changes the polarity of the substructure nearby with respect to
the earth.
Alternating stray current affects different metals in
4
different ways depending upon the nature of the metals and their environments.
Alternating stray current could, initiate and accelerate
dezincification or buildup of deposits in faCilities such as meters
or valves.
Quantitatively, it would seem that ac corrosion rate should be
50% of the equivalent dc corrosion rate.
In other words, according
to the Faraday relationship, theoretical ac corrosion rate is half
of the corrosion rate that would have been ecperienced had the
current been dc.
For ac is anodic for one-half of each cycle and
cathodic for the other.
However, such is not generally the case.
Hayden (1907) reported ac corrosion of lead in soil being less than
0.5% of the equivalent dc loss.
Waters (1963) also reported ac
corrosion to be 1% and less than 4% (in 1962) of the equivalent dc
loss.
Galimberti (1966) stated that ac corrosion of lead in tap
water was 1.3% of that of the dc.
The considerable deviation from
its theoretical value of 50% is worth investigation.
Qualitatively,
there are several factors affecting ac corrosion as follows:
1.
A.C. Densities
It is widely accepted that ac corrosion increases with current
densities.
Bruckner (1965) and Williams (1966, 1967) tested ac
corrosion of copper, aluminum, lead, iron, and zinc in soil solution and in neutral soil, respectively.
They obtained the results
that agreed with others that current densities enhance ac corrosion.
Table II-1 is a list of the authors who reported an increase of ac
5
TABLE II-1. PREVIOUS WORK REPORTING AN INCREASE
OF A.C. CORROSION WITH CURRENT DENSITIES
Electrolytes
Year
Authors
1975
Amy and Mounois
Aluminum, coppet,
iron, lead
Chloride and sulfate solution
1958
Fuchs, et al.
Steel
Chloride and sulfate solution
1962
Juchniewicz
Platinum and
platinizedtitanium
NaC1
1962
1963
Waters
Copper, iron, and
galvanized steel
Soil solution
1963
Vijayavalli, et al.
Lead
H2SO4
1964
Bruckner
Aluminum, cast iron,
copper, lead and
zinc
Soil
1964
Galimberti
Lead
Tap water
1966
1967
Williams
Aluminum, copper,
iron, and lead
Soil solution
1967
Godard
Aluminum
0.5% salt solution
1967
Devay, et al.
Cadmium, copper,
and zinc
5% KC1
1973
French
Aluminum
3.5% NaC1
1973
Miura, et al.
Magnesium
1974
Kondrashin, et al.
Tantalum and
zirconium
0.1 N H SO
1978
Vasil'ev, et al.
Stainless steel
30% NaNO
Metals
2
3
4
6
corrosion with current densities.
Hayden (1907) and Juchniewicz
(1956), however, found ac corrosion to be independent of and to
decrease with current densities, respectively.
2. Electrode Nature and Characteristics
Different metals are affected differently by ac.
Surface
areas and conditions, electrode sizes and shapes, etc., contribute
somewhat to different behavior.
The effects are interrelated and,
hence, one could not predict precisely the effects of ac on the
corrosion rate by merely considering individual characteristics.
Bruckner (1964) mentioned that high corrosion rate may occur for
either large or small electrode areas and that many different tests
are necessary to define average behavior.
Larger surface areas are
less severely affected by ac corrosion because current densities
are inversely related to electrode areas.
3. Electrolyte
3.1
Chemical composition
AC corrosion is dependent upon the chemicals in the electrolyte.
Chloride, for example, is found to have the greatest effects on thecorrosion rate of copper, iron, and galvanized zinc and bicarbonate
to have the least effects (Waters, 1962, 1963).
Not only is the
corrosion rate affected by chemical composition but the films
formed on the electrodes are also affected.
Whether the film forms
depends in part on the chemical composition of the electrolyte
7
(Kulman, 1961).
This film plays an important role in the explana-
tion of ac corrosion behavior.
Hayden (1907) discovered that
chemical composition affected the extent of Corrosion rate increase
due to lowering frequencies.
He also did experiments using a mix-
.
ture of salts as the electrolyte.
The results showed higher ac
corrosion than those obtained when the electrolyte consisted of
individual components of the salt mixture.
3.2
Degree of Mixing
The reversibility of the ac corrosion process depends on the
freedom with which the electrolyte circulates.
Circulation of elec-
trolytes can retard the redeposition of metallic ions during
cathodic cycle.
Instead, the metallic ions form insoluble corrosion
products and thus rendering the corrosion process irreversible.
4. Temperature
AC corrosion increases with temperature as was reported by
Hayden (1907), Bruckner (1964), Kototyrkin and Strunkin (1970), etc.
The metals studied by these authors were copper, aluminum, cast
iron, lead, zinc, and titanium.
However, Pobkote and Chin (1978)
observed negligible effect of temperature om corrosion rate.
Galimberti (1964) also reported very small temperature effect upon
ac corrosion.
5. Frequency
In 1916, McCollum and Ahiborn tested ac corrosion of iron, lead,
8
platinum, and platinized-titanium in sodium Chloride solution and
found that corrosion decreased with ac frequencies.
The same re-
sult was also reported by Kondrashin, et al. (1974) who worked with
zirconium and tantalum electrodes in 0.1 N H SO
4'
et al. (1978), and by D-T Chin and T-W Fu (1979).
also by Timoshenko,
On the other
hand, Hayden (1907) not only obtained the same result as the above
authors, but also found the reverse to be true in carbonate electrolyte and reported the independence of frequency when the electrolyte
was alkali, nitrate, chloride, or their mixture.
Benley and
Prentice (1957) studied ac corrosion of stainless steel as functions
of frequencies.
They proposed that at low frequencies the transport
of ac through the electrolyte involved the discharge of ions at the
electrodes accompanied by dissolution of the metal.
At higher
frequencies than a few kilocycles, the transport process does not involve the discharge of ions at the electrodes and may be described
in terms of changes in the energy stored in and released from the
electric field between the ions during successive half-cycles.
At
low frequencies, the waveform was distorted from that at higher frequencies, indicating the possibility of correlating waveform difference with corrosion.
B. Mechanisms
Juchniewicz (1962) stated, "... the impedance measurements seem
to indicate that ac may affect the anodic behavior of different
9
metals by different mechanisms ...".
Up to the time of this thesis,
there have been apparently six ways to explain the mechanisms of ac
corrosion:
oxidation theory, redeposition theory, galvanic theory,
capacitor theory, rectification, and depolarization.
1. Oxidation Theory
Marsh (1920), with his work on ac electrolysis, explained the
decrease of gas evolution rate resulted from the electrolysis by
oxidation theory.
The anode is oxidized yielding a protective oxide
film which may be either soluble or insoluble in the electrolyte.
Hydrogen produced during cathodic half-cycle then reduces the oxide
film to a lower oxide in case of an insoluble film.
The quantity of
hydrogen liberated depends on the extent of the reduction of the
film by hydrogen.
As a consequence, corrosion is due to anodic
dissolution or oxidation of the electrodes and is less when the
dissolution is retarded by the reduction of oxide film by hydrogen.
2. Redeposition Theory
A theory was postulated by Hayden (1907), McCollum and Ahlborn
(1916), and Shepard (1921) to explain the fact that the coefficient
of corrosion decreased with time and that corrosion by ac was considerably less than 50% of that by equivalent dc.
(Coefficient of
corrosion was defined as ratio of ac corrosion observed to that determined by Faraday's law.)
According to this theory, the corrosion process is reversible.
10
For the metal that corrodes during anodic half-cycle is redeposited
in the cathodic half-cycle.
The redeposited metal serves as an
anode surface during the subsequent anodic half-cycle and hence protects the uncorroded metal beneath.
There exists also a large vari-
ation in the electrolytic action of ac compared with the constancy
of that of dc.
This is probably because electrolytic action of the
alternating current appears as a small difference between two large
and nearly equal quantities, the action of the anodic and cathodic
half-cycles.
A small variation in the action of either half wave
makes a very large difference in the result.
3. Galvanic Theory
The experimental results by Waters (1962) indicate that ac
corrosion is caused by galvanic couples and that ac increases the
galvanic corrosion rate.
Galvanic couples can definitely develop
on the basis of dissimilar electrodes, surface conditions, environments, and upon superimposing ac on a dc circuit.
Bruckner (1964)
found superimposed ac to have enhanced the dc in a galvanic cell
and thus the corrosion rate.
He suggested several forms of the
resulting galvanic modification as following:
a) The dc component of same polarity increases when no ac
exists.
b) The dc component of initial polarity decreases.
c) The polarity of dc component reverses.
11
d) The polarity of dc component reverses periodically.
e) The dc component reduces to zero with extended test duration.
f) The dc component increases with extended test duration.
Dissimilarity is not the only criterion for the modification
of galvanic cells, however.
Bruckner's L series test showed that
a galvanic cell could be established on similar steel electrodes
which developed a difference in dc potentialS under the influence
of ac.
The polarity of the dc frequently alternated with time from
one electrode to the other.
It has not yet been clear as to why
the two identical electrodes should perform differently.
4. Capacitor Theory
Godard (1967) explained the reason for the apparently low
efficiency of the ac corrosion process by the capacitive behavior
of the barrier oxide film formed on aluminum'
anodic half-cycle.
citor.
during
The film functions as a dielectric of a capa-
The capacitive current consists of the flow of electrons
onto and away from the conducting surfaces on each side of the
barrier layer to accumulate charges that form the "plates" of the
capacity due to the impressed ac voltage.
Therefore, there is no
passage of electrons or ions through the film to contribute to
corrosion.
At higher voltage, there is ionic current flowing,
thereby thickening the film.
However, since the capacitive current
remains constant, its percentage of the total current decreases,
12
yielding higher proportion of corrosion current and, hence, ac
corrosion efficiency.
5. Rectification
Rectification by oxides caused by ac corrosion was discussed
by Waters (1962) to explain the total effect.of ac corrosion and the
different performances of the two electrodes in a cell.
Woodward
(1956) described that dc flowing in the telephone cable sheath may
have been the result of rectification of ac leakage from railroad
tracks.
Bruckner (1964) explained the rapiciac corrosion of alumi-
num and magnesium electrodes as associated with corrosion films which
have rectifier characteristics and permit cathodic polarization of
the electrodes.
His reasoning agreed with that of Godard (1967)
who also believed in the rectifying effect of the oxide film formed
on aluminum electrodes.
The rectifying action results in what
Godard called "intermittent pulsed dc" or unidirectional current
flow.
Timoshenko, et al. (1978) studied corrosion cracking of steel
in 3% NaC1 and in 30% NaNO
solutions.
The results showed that ac
3
reduced the stability of the passive film, thereby intensifying
corrosion cracking.
He discussed that the rectifying effect might
have accompanied the passage of ac in the presence of a passive film
which would break down when the anodic activation potential was
reached.
In addition, pitting formation on the steel electrodes may
be due to the non-uniformity of the passive layer generating different microareas on the electrodes.
13
Haring (1952) discussed the mechanism of electrolytic rectification of aluminum and tantalum electrodes.
Tantalum oxide film
was formed and it blocked the flow of current whenever the electrode
was an anode because the step which the tantalum ion moved through
the film towards the electrolyte to combine with oxygen ion and to
become tantalum oxide was very slow.
when it was a cathode.
The electrode passed current
Electrons from the other electrode entered
the tantalum electrode via the external circuit, passed the oxide
film to react with hydrogen ions from the electrolysis of water
into hydrogen gas.
Therefore, during the cathodic half-cycle there
was hydrogen evolution at the tantalum electrode and oxygen evolution at the other electrode.
With alternating voltage applied, a
rectification process occurred in which the rectified current flowed
from the electrolyte to the aluminum- -the oxide film broke down when
the potential reached the oxygen evolution potential.
In general,
the mechanism could be written as follows:
During the anodic half-cycle of electrode "1",
M
x0
+x
M
2
+ xe
+ x02
+x
M
+ xe
x02
MO
2x
At the vicinity of electrode "2",
H20
H
+ OH
(oxide film)
14
4H2 0+0 + e
OH
cathodic reaction:
H
+
+ e
H2t
Current is blocked because the step which M
oxide film to combine with 0
2
is very slow.
+x
moves through the
Consequently, anodic
polarization occurs and corrosion current is decreased.
During the cathodic half-cycle of electrode "1",
Either or both of the following two reactions occur:
cathodic reaction:
or
+x
M
+ xe
M
H2O
H
+ OH
H+ +e÷Ht
2
At the vicinity of electrode "2",
anodic reaction:
OH
H2O +
t + ;
The process repeats in the subsequent cycles.
As more metal
ions accumulate on the oxide film, anodic potential increases until it reaches oxygen evolution potential where the film breaks
down and corrosion once again occurs at a more rapid rate.
It is apparent that the above mechanism could explain the
fact that ac corrosion is considerably lower than the theoretical
value and that the two electrodes are affected differently by ac.
However, this mechanism possesses one foible.
By rectification, it
seems that one electrode does not corrode and the other does, but
slowly unless the passive film breaks down.
This is contradictory
to the results of previous and present works which show the corrosion of both electrodes.
issue.
Yet there have been more arguments on this
Compton (1975) stated that rectification should protect the
metal at the site where it occurred.
For when metals are anodically
Current
polarized, they develop a blocking layer on the surface.
can only flow from the electrolyte to the metal.
In 1977, he
worked with copper and coated copper concentric neutrals on shielded
cable and reported no breaks in his polarization curves.
Conse-
quently, he discredited rectification as part of the cause of ac
corrosion.
Williams (1966) observed identical waveform of the test
current in comparison with that of the source current.
He concluded
that corrosion was not by rectification but by dc electrolysis with
attack occurring only on the anodic half-cycle instead.
6. Depolarization
Potentiostatic curves have been studied and have shown that ac
causes corrosion by its depolarizing action On electrodes.
Waters
(1962) proposed polarization of the metal oxide formed during the
anodic process as causing the two electrodes to be affected differently.
Juchniewicz (1962), Vijayavalli (1963), Compton (1977), and
Pookote and Chin (1978) all agreed experimentally that superimposed
ac reduced cathodic and anodic polarization.; In other words, ac
acted as a depolarizer.
The different behaviors of the two elec-
trodes found in many experiments could be due to the non-uniform
distribution of ac at the electrode surface Which could affect the
16
polarization and, in turn, the rate of corrosion.
Chin and Fu
(1979) studied the ac effect on corrosion potential of mild steel
and reported that superimposed ac shifted the potentials to more
active values, increased the passivitiy current densities, and that
the effect of ac was similar to that of chloride ions added into the
electrolyte.
The effect of ac on the polarization was found to be
directly proportional to current densities and inversely to frequencies.
Chin and Fu postulated the "mixed potential theory" which
made feasible the explanation of the accelerating effect of ac on
corrosion and of the different effects of ac on the two electrodes.
17
III. EXPERIMENTAL PROCEDURES
A. Electrodes
Both the anode and cathode in each experiment are made from
the same kind. and same size of. metals. (see Table
.
TABLE III 1. LIST OF METALS USED AS ELECTRODES
Major components
Metals
Aluminum 3003
99+% commercially pure aluminum
Cartridge brass w60
70% copper and 30% zinc
Cold-rolled steel
Drawing quality, 99% iron
C. P. titanium GR -2,
Ht870092
Supplied by Teledyne Wah Chang Albany
Albany
Electrolytic tough pitch
copper 110
99.9+% copper
Cupro-nickel alloy
30% nickel, 69.5% copper, and 0.5% tin
Sheath lead
99+% pure lead
304 stainless steel
70+% iron, 18-20% chromium, and
8-12% nickel
Zirconium 702, Ht840041
Supplied by Teledyne Wah Chang Albany
Average surface area exposed to electrolyte is approximately 12.75
square centrimetres.
some experiments.
However, the working surface area varies in
Prior to use, all coupons are cleaned with dis-
tilled water or pickled in their corresponding pickling acid solu
tion (see Appendix C), degreased in Trichlorobenzene, air-dried,
and stored in a desiccator.
The coupons are weighed, prior and after
experiments by a microbalance.
18
B. Electrolyte
Five litres of 3% by weight sodium chloride, reagent grade, in
distilled water is used throughout all experiments.
C. Apparatus and Electrical Circuit
The circuit is shown in Figure 1.
ternating current is employed.
Sixty cycle commercial al-
The cell is composed of a pyrex
glass container on a magnetic stirrer, a glasS cooling coil, two
steel rods, holding electrodes, a PVC cover sheet, a thermometer,
and an air-bubbling device.
Figure 2 shows the cell.
O. Procedures
The apparatus in Figure 2 is assembled.
At time equals zero,
current is passed into the cell as soon as the temperature of the
cell is 18°C.
The magnitude of current is determined by calculation
involving the working electrode surface area and the pre-determined
current density.
This current is kept constant throughout the ex-
periment by adjusting the variac.
The temperature is controlled to
be 18 ± 2°C by cooling water flow rate adjustment.
Close attention
is necessary, especially when high current density is employed, for
the temperature rises rapidly due to the high current passed.
Air
is constantly bubbled into the electrolyte to assure oxygen saturation.
The duration for most experiments is approximately one day.
Occasionally, the experimental periods vary depending upon corrosion
rates of electrodes.
Sufficient weight loss and relatively constant
19
110 V
VARIAG
Figure 1.
Electrical Circuit for the Experiment.
20
1
Connection wire
5
Rubber stopper
2
PVC cover sheet
6
Electrode
3
PVC tube
7
Air-bubbling device
4
Pyrex glass container
8
Thermometer
Distance between the electrodes is 6 in.
AIR
I
2
3
1
#
r
k
_.
9
A
r,
4
.
.0
..,
.4
.0
.0
.oi
/0/..
.,
..,
3% Nam
00
00
.601erlideore/..000"AorA01140149:0" Ageelied59:010,
Figure 2.
Corrosion Cell.
4
5
6
7
21
surface area are required for accuracy.
At the end of each experi-
ment, the electrodes are acid-pickled (see Appendix C), rinsed in
distilled water, air-dried, and weighed.
Corrosion rate, expressed
in mdd (milligrams per square decimeter per day), is determined by
a conventional method (see Appendix B).
The same procedure is re-
peated for the metals listed in Table III-1..
22
IV. RESULTS
The results are calculated from data in Appendix A by methods
described in Appendix B.
For each metal, the corrosion rate and ac
corrosion factor (samples of calculation and:definitions are shown
in Appendix B) are tabulated and plotted as a function of ac densities.
Statistical analyses are also included for linear plots.
Some data from the literature, though not obtained by similar experimental procedures and electrolytes, are included in Tables IV-11 to
IV-19 for comparison purposes.
In general, the results show, in tabulated and graphical form,
the following relationships:
1) A.C. corrosion rate as a function of current densities.
2) A.C. corrosion factor as a function of current densities.
23
TABLE IV-1. A.C. CORROSION OF ALUMINUM
IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
2
Current Density, A/cm
Corrosion Rate, mdd
0.00
0.00
0.08
0.15
0.18
0.25
0.30
0.35
0.35
0.38
0.45
0.50
0.75
1.00
6
8
25,169
35,942
57,305
81,613
109,971
127,511
129,868
128,785
144,522
187,783
294,016
399,588
Statistical Analysis:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
0.9958
112,356.4
-12,677.5
400,753.5
24
TABLE IV -2. A.C. CORROSION RATE OF BRASS
IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Current Density, A/cm
0.00
0.00
0.05
0.10
0.14
0.16
0.20
0.22
0.26
0.28
0.30
0.34
0.38
0.40
0.44
0.46
0.50
0.60
0.76
0.88
0.90
1.10
Corrosion Rate, mdd
30
34
260
235
264
311
444
423
544
842
725
908
1,073
1,698
2,290
1,730
2,002
2,731
3,461
7,328
6,363
8,531
25
TABLE IV-3. A.C. CORROSION RATE OF COLDROLLED STEEL IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Current Density, A/cm
Corrosion Rate, mdd
0.00
0.10
0.11
0.13
0.15
0.20
0.20
0.20
0.26
0.28
0.30
0.32
0.36
0.40
0.40
0.48
0.50
0.50
0.62
0.76
0.76
0.88
1.00
252
279
225
264
344
328
376
398
534
544
678
521
732
632
1,158
1,186
1,036
1,172
1,818
1,489
1,750
1,996
2,058
Statistical Analysis for Data No. 6-23:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
0.9574
585.7241
-5166290
2,296.3566
26
TABLE IV-4. A.C. CORROSION RATE OF COPPER
IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Current Density, A/cm2
0.00
0.00
0.03
0.08
0.16
0.22
0.30
0.36
0.38
0.38
0.44
0.50
0.50
0.60
0.66
0.74
0.80
0.92
Corrosion Rate, mdd
30
38
94
482
1,435
2,381
3,301
3,697
5,342
7,596
5,854
5,941
9,936
10,843
18,123
19,083
24,216
22,513
27
TABLE IV -5. A.C. CORROSION RATE OF CUPRO-NICKEL
ALLOY IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
2
Current Density, A/cm
0.00
0.00
0.05
0.10
0.15
0.19
0.26
0.30
0.33
0.36
0.39
0.42
0.50
Corrosion Rate, mdd
41
50
360
628
1,270
1160
1,474
1,823
2,535
2,981
6,881
7,518
9,158
28
TABLE IV -6. A.C. CORROSION RATE OF LEAD
IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
Current Density, A/cm
2
Corrosion Rate, mdd
52
56
642
672
809
0.00
0.00
0.05
0.10
0.15
0.18
0.24
0.26
0.29
0.36
0.39
0.43
0.50
951
861
942
1,222
1,876
1,937
1,710
1,941
Statistical Analysis:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
=
=
0.9551
654.0712
189.0166
3,802.6387
29
TABLE IV-7. A.C. CORROSION RATE OF 304-STAINLESS
STEEL IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
Current Density, A/cm
2
Corrosion Rate, mdd
1.57
1.96
542
930
3,838
6,164
8,532
11,238
16,650
17,318
19,222
0.00
0.00
0.05
0.10
0.16
0.20
0.26
0.30
0.38
0.40
0.44
Statistical Analysis for Data No. 4-11:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
=
=
0.9977
6,757
-4999
55,305
30
TABLE IV-8. A.C. CORROSION RATE OF TITANIUM
IN 3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Current Density, A/cm
Corrosion Rate; mdd
0.00
0.00
0.04
0.05
0.10
0.10
0.15
0.15
0.20
0.20
0.21
0.25
0.29
0.30
0.34
0.35
0.40
0.40
0.43
0.45
0.51
0.51
Coupons showed various degrees of pitting.
0.6
2.9
290
533
462
1,022
584
1,493
1,402
2,325
937
1,121
1,289
2,337
580
679
912
1,281
851
904
1,086
1,240
31
TABLE IV-9. A.C. CORROSION RATE OF TITANIUM
AT DIFFERENT DEGREES OF PITTING
Statistical
Analysis
No Pitting
A cm
0
0.04
0.10
0.15
0.34
0.35
0.40
0.43
0.45
Correlation
Coefficient
2
Moderate Pitting
mdd
A/cm
0
0.21
0.25
0.29
0.40
0.51
0.51
290
462
584
580
679
912
851
904
2
mdd
937
1,121
1,289
1,281
1,086
1,240
Severe Pitting
A/cm
2
mdd
0
0
0.05
0.10
0.15
0.20
0.20
0.30
533
1,022
1,493
1,402
2,325
2,337
0.9379
Standard
Deviation
868.83
Y-intercept
157.84
Slope
8,007.13
32
TABLE IV-10. CORROSION RATE OF ZIRCONIUM IN
3% NaC1 SOLUTION
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Current Density, A/cm
2
Corrosion Rate, mdd
0.00
0.05
0.10
0.15
0.20
0.25
0.26
0.26
0.28
0.32
0.33
0.35
0.36
0.41
0.45
0.46
2
523
2,834
11,697
40,943
115,871
104,453
112,115
202,928
145,305
180,970
257,329
296,529
377,058
366,557
402,464
.
Statistical Analysis for Data No. 5-16:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
0.9615
121,304
-246,864
1,416,001
33
TABLE IV-11. A.C. CORROSION FACTOR OF ALUMINUM
Current Density
(A/cm2)
AC Corrosion
Factor (%)
< 0.00008
< 0.0002
0.0015
0.0022
0.0035
0.005
Nil
Nil
5.0
13.5
15.0
20.0
0.01
0.016
0.02
31.0
40.2
39.0
0.04
0.08
40.0
40.1
0.15
0.18
0.20
29.7
39.5
48.5
0.25
40.6
0.30
0.35
0.35
0.38
0.45
0.50
0.75
1.00
45.5
45.2
46.2
42.1
41.2
46.6
49.1
49.1
Electrolyte
3.5% NaC1
0.5% NaC1
Reference
French, 1973
Godard, 1967
u
"
It
Artificial Soil
Solution
n
Soil
Artificial Soil
Solution
If
3% NaC1
u
H
11
Williams, 1966
u
Bruckner, 1964
Williams, 1966
If
Chattratichart,
1981
,,
.7
Artificial Soil
Solution
3% NaC1
Williams, 1966
Chattratichart,
1981
n
u
n
It
,,
u
If
u
u
It
n
H
n
u
34
TABLE IV-12. A.C. CORROSION FACTOR OF BRASS
Current Density
(A/cm2)
0.05
0.10
0.14
0.16
0.20
0.22
0.26
0.28
0.30
0.34
0.38
0.40
0.44
0.46
0.50
0.60
0.76
0.88
0.90
1.10
AC Corrosion
Factor (%)
Electrolyte
3% NaC1
0.18
0.08
0.07
0.07
0.08
0.07
0.07
0.10
0.08
0.09
0.10
0.15
0.18
0.13
0.14
0.16
0.16
0.29
0.25
0.27
=
=
=
=
Chattratichart, 1981
.,
i,
If
II
II
II
IV
II
It
II
,,
.,
II
II
il
II
n
,,
u
in
IV
II
II
II
/I
II
II
II
11
IT
n
n
i,
VI
11
It
II
11
Statistical Analysis:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
Reference
0.8360
0.0694
0.0514
0.1998
35
TABLE IV-13. A.C. CORROSION FACTOR OF
COLD-ROLLED STEEL
Current Density
(A/cm2)
AC Corrosion
Factor (%)
Control
(C.R.**55 mdd)
Control
0.005
0.008
0.01
0.016
0.02
0.04
0.047
0.078
0.10
0.11
0.13
0.15
0.20
0.20
0.20
0.26
0.28
0.30
0.32
0.36
0.40
0.40
0.48
0.50
0.50
0.62
0.76
0.76
0.88
1.00
Electrolyte
Soil
3% NaCl
(C.R.**252 mdd)
0.06
Artificial Soil
Solution
0.04
Soil
0.10
Artificial Soil
Solution
0.04
Soil
0.11
0.13
0.05
0.05
0.15
0.11
0.11
0.12
0.09
0.10
0.11
0.11
0.10
0.12
0.09
0.11
0.08
0.15
0.13
0.11
0.13
0.16
0.10
0.12
0.12
0.11
Reference
Artificial Soil
Solution
BrUckner, 1964
Chattratichart, 1984
Williams, 1966
BrUckner, 1964
Williams, 1966
Bruckner, 1964
Williams, 1966
"
Soil
3% NaC1
1,
Bruckner, 1966
Chattratichart, 1981
"
"
"
"
"
ff
"
.
1,
"
"
II
"
It
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
I,
.
"
"
"
"
"
"
*
Corrosion rate.
Statistical Analysis (data from the literature are excluded):
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
ffi
*
m
0.1731
0.0199
0.1095
0.0150
36
TABLE IV-14. A.C. CORROSION FACTOR OF COPPER
Current Density
(A/cm2)
Control
Control
AC Corrosion
Factor (%)
Electrolyte
Bruckner, 1964
*
(C . R. =3.4 mdd)
*
(C.R.=30,38
mdd)
0.002
0.5
0.005
0.27
0.005
0.33
0.01
0.18
0.016
0.02
0.08
0.11
0.03
0.04
0.11
0.09
0.08
0.16
0.22
0.30
0.36
0.38
0.38
0.44
0.50
0.50
0.60
0.66
0.74
0.80
0.92
0.21
0.32
0.38
0.39
0.36
0.49
0.70
0.47
0.42
0.70
0.64
0.97
0.91
1.06
0.86
Reference
3% NaC1
Chattratichart, 19814
Kingston Tap
Godard, 1967
Water
Artificial SOil Williams, 1966
Solution
Extrapolated from
3% NaC1
Chattratichart,1981i
results
Artificial Soil Williams, 1966
Solution
Bruckner, 1964
Soil
Artificial SoiliWilliams, 1966
Solution
Chattratichart,1981
3% NaCl
Artificial Soil Williams, 1966
Solution
Chattratichart, 1981
3% NaC1
n
n
II
It
If
II
n
n
It
II
n
.4
n
11
n
n
VI
11
II
It
n
n
II
II
II
II
in
u
*
Corrosion rate.
Statistical Analysis:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
=
=
0.8962
0.2788
0.1635
0.9244
37
TABLE IV -15. A.C. CORROSION FACTOR OF
CUPRO -NICKEL ALLOY
Current Density
AC Corrosion
Factor (%)
(A/cm2)
.
Control
0.05
0.10
0.15
0.19
0.26
0.30
0.33
0.36
0.39
0.42
0.50
Electrolyte
Reference
.
*
(C.R. =41,50 mdd)
0.26
0.23
0.30
0.22
0.20
0.22
0.28
0.30
0.63
0.64
0.66
Corrosion rate.
3% NaC1
Chattratichart, 1981
lI
if
II
*
*
*
If
if
*
*
*
*
*
*
*
*
*
.1
*
*
n
If
Statistical Analysis:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
=
=
0.7340
0.1862
0.0903
0.9661
38
TABLE IV-16. A.C. CORROSION FACTOR OF LEAD
Current Density
(A/cm2)
Control
0.005
0.04
0.05
0.10
0.15
0.18
0.24
0.26
0.29
0.36
0.39
0.43
0.50
AC Corrosion
Factor (%)
Electrolyte
Reference
3% NaC1
Chattratichart, 1981
(C.R.*=52,56mdd)
0.09
Artificial Soil Williams, 1966
Solution
0.05
0.28
Chattratichart, 1981
3% NaC1
II
II
0.15
II
0.12
It
0.11
u
u
0.08
u
0.08
II
II
0.09
It
0.11
/I
II
0.11
II
0.09
II
II
0.08
Corrosion rate.
11
11
11
11
11
11
II
39
TABLE IV-17. A.C. CORROSION FACTOR OF
304-STAINLESS STEEL
Current Density
(A/cra2)
Control
0.05
0.10
0.16
0.20
0.26
0.30
0.38
0.40
0.44
AC Corrosion
Factor (%)
*
(C.R. n., 2 mdd)
0.58
0.50
1.28
1.65
1.75
2.00
2.34
2.31
2.33
*
Corrosion rate.
Electrolyte
3% NaC1
Reference
Chattratichart, 1981
If
II
II
If
If
If
ur
u
u
u
fl
If
If
If
IP
If
.
u
40
TABLE IV-18. A.C. CORROSION FACTOR OF TITANIUM
Current Density
(A/cm2)
Control
0.04
0.05
0.10
0.10
0.15
0.15
0.20
0.20
0.21
0.25
0.29
0.30
0.34
0.35
0.40
0.40
0.43
0.45
0.51
0.51
*
AC Corrosion
Factor (%)
Electrolyte
(C.R!=0.6,2.9mdd)
0.68
0.99
0.43
0.95
0.36
0.93
0.65
1.08
0.42
0.42
0.41
0.73
0.16
0.18
0.21
0.30
0.18
0.19
0.20
0.23
Reference
Chattratichart, 1981
3% NaC1
n
n
It
It
n
n
v.
n
n
n
It
II
II
If
ft
II
n
n
n
n
It
It
n
n
n
ft
It
II
II
et
It
II
ft
II
ft
n
n
Corrosion rate.
Statistical Analysis:
For Severely-Pitted Data:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
=
=
-0.5478
0.1640
1.0593
1.0261
For Moderately-Pitted Data:
Correlation Coefficient
Standard Deviation
Y-intercept
Slope
=
=
=
-0.9823
0.1004
0.6018
-0.7516
41
TABLE IV-19. A.C. CORROSION FACTOR OF
ZIRCONIUM
Current Density
(A/cm2)
Control
0.05
0.10
0.15
0.20
0.25
0.26
0.26
0.28
0.32
0.33
0.35
0.36
0.41
0.45
0.46
*
AC Corrosion
Factor (%)
*
(C.R. = 2 mdd)
0.5
1.4
3.8
10.0
22.7
19.7
21.1
35.5
22.2
26.9
36.0
40.3
45.0
39.9
42.9
Corrosion rate.
Electrolyte
Reference
3% NaC1
Chattratichart, 1981
It
II
n
n
n
n
II
II
n
n
If
II
n
II
n
II
II
11
II
II
n
n
if
n
n
n
n
n
II
II
42
TABLE IV-20. CORROSION PRODUCTS
Metals
Aluminum
Brass
Colors Observed
White gelatineous
Al(OH)
Yellow
CuCl , CuCl
Green
3
+2
, CuC1
4
2Cu(OH)
or CuC12
Cu(OH)2
White
ZnC1
2
Cu(OH)2
Orange -red
CuOH
Cu(OH)2
Green
or
Ni (OH)
White precipitate
4H 0
3CuO
CuC12
Lead
.
2
Blue (most frequent)
Copper
Cupro-Nickel
Alloy
Possible Corrosion
Products
2
and/or
Pb0
2
Dark and smooth - textured
film on surface
Steels
Reddish brown
or
Pb(OH)
2
PbC1
Pb(OH)
2
2
or
Fe 0
3 4
Fe0
Titanium
Zirconium
White
TiO2
?
43
4-.'
a
Ler
'0
z
0
0
et
0
0.2
0.4
06
OS
CURRENT DENSITY (A/CM2)
Figure 3.
Corrosion Rate of Aluminum versus
A.C. Densities,
1.0
44
0
0
O
2
tr)
'0
4.1
I-
<
CC
0
04cc
cr
0
0
0.0
02
Figure 4.
04
0.6
CURRENT DENSITY ( A/ CM2)
Corrosion Rate of Brass versus A.C.
Densities.
45
240
200
a16-
ro
w
f-
CC
z0
0
0
..jCC
CC
C.)
8-
0
04
0.6
08
CURRENT DENSITY (A/CM23
Figure 5.
Corrosion Rate of Copper versus
A.C. Densities.
46
I00
011
Figure 6.
0:2
014
0:3
CURRENT DENSITY ( A/ C M2 )
Corrosion Rate of Cupro-Nickel
Alloy versus A.C. Densities.
d5
47
241,
Brass (70% Copper, 30% Zinc)
0
2,o Copper (99.90+% Copper)
20-4
3, p
Cupro-Nickel Alloy
(69.5% Cu, 30% Ni, 0.5% Sn)
0
4-
C12
Figure 7.
0.4
as
CURRENT DENSITY ( A/CM
Corrosion Rate of Copper and Its
Alloys versus A.C. Densities.
48
20
0
0
0
X
(NJ
10
0
0
O
0
0
0.0
0.1
0.2
0.3
0:4
CURRENT DENSITY (A/CM2)
Figure 8.
Corrosion Rate of Lead versus A.C,
Densities.
49
0
ES
a 16M
Nv
0
w
t--
cr
12
z
0
0
ca
0
cr
0
0
8-
4-
0.0
02
04
0.6
0.8
1.0
CURRENT DENSITY (A/CM;
Figure 9.
Corrosion Rate of Cold-Rolled Steel
versus A.C. Densities.
50
20
15
2
.0
x IC
H
0
5-1
0
0
0
0.0
Figure 10.
0.1
0.2
0.3
CURRENT DENSITY CA /CM2)
Corrosion Rate of 304-Stainless
Steel versus A.C. Densities.
0.5
51
200 304-Stainless Steel
A Cold-Rolled Steel
z
a 10
v0
0
cc
cc
0
0
5
A
0
0.0
0.1
02
Figure 11.
04
Q3
CURRENT DENS;TY
A
A/CM2)
Corrosion Rate of Steels versus
A.C. Densities.
52
0.1
02
03
04
CURRENT DENSITY (A/CM2)
Figure 12. Corrosion Rate of Titanium versus
A.C. Densities.
0.5
53
0
0
0.1
02
0.3
CURRENT DENSITY (A/CNI')
Figure 13.
04
Corrosion Rate of Zirconium versus
A.C. Densities.
0 Aluminum
M Aluminum (results from literature)
0 Zirconium
0
O
0
0
0.0
Figure 14.
0.1
0.1
0:2
CURRENT DENSITY ( A/CM )
A.C. Corrosion Factor of Aluminum and Zirconium as Functions of A.C. Densities.
From literature.
100-
0 Experimental datum.
Cr
0
:Z
u) 50~
O
CC
O
0
et
Q00
Figure 15.
0.62
0.04
0.66,1
CURRENT DENSITY
M (ae)
ad
A.C. Corrosion Factor of Aluminum at Low Current Densities as a Function
of A.C. Densities.
O Copper (experimental data)
Copper (from literature)
Cupro-Nickel Alloy
e-
lk
n Brass
CC
C3
I(3
0
0
OG
Ce
0
0 04
0
-4)-
0
O
0:2
O
0
a
a
O
cl
04
I
I
I
CURRENT DENSITY (A /CM2)
Figure 16.
A.C. Corrosion Factor of Copper and Its Alloys as a Function of A.C. Densities.
57
0.3
.11
0.20
0
0
0
cx
tx
g
0
o
OD
0.0
,
0
0
co
0:6
o4
ob
CURRENT DENSITY(A/CM
2)
Figure 17. A.C. Corrosion Factor of Brass as a
Function of A.C. Densities.
0 Experiment Results
CI
Results from Literature
m
0
H
o
0
0
ce
CC
0
0
0
0
OD
0
0.1
CURRENT
Figure 18.
CL3,
0.2
DENSITY
(Ad CIA 41
A.C. Corrosion Factor of Lead as a Function of A.C. Densities.
04
A Minute Pitting or Etching
1.0-
O Moderate Pitting and
Etching
0
Cr
N
Between Moderate and Sever(
Pitting and Etching
O
Severe Pitting and
Etching
0
O
OC
0U
0
0.05
0.15
015
035
CURRENT DENSITY (A/CM;
Figure 19.
A.C. Corrosion Factor of Titanium as a Function of A.C. Densities.
0.45
El
304-Stainless Steel
0 Cold-Rolled Steel (experimental results)
A Steels (from literature)
0
to
z
0
0
0
0.I
U
Q2
Q3
0
0
0.4
CURRENT DENSITY (A /CM c.)
Figure 20.
A.C. Corrosion Factor of Steels as a Function of Current Densities.
61
V. DISCUSSION
Experiments on all metals tested show that ac corrosion increases with current densities and that the ac corrosion factors are generally very low (not exceeding 3.0%) except that of aluminum and of
zirconium which approach 50% at high current densities.
observed on some metals but not on some others.
Pitting is
It is obvious from
Figures 3 to 20 that ac affects different metals differently as a
result of different characteristics and the nature possessed by each
metal.
To understand the ac effects on the corrosion of the metals
more clearly, the metals are discussed separately.
Since brass and
cupro-nickel alloy are alloys of copper, they and copper are discussed simultaneously, so are the two steels.
A. Aluminum
From Figures 3 and 14, one can see that the data obtained agree
very well with those obtained by Bruckner (1964), Williams (1966),
Godard (1967), and French (1973), who performed their experiments in different electrolytes.
It can be concluded that electro-
lyte has slight effect on corrosion rate of aluminum.
This agrees
with Tolstaya, et al. (1967), who reported that ac corrosion factor
ceased to depend on chemical composition at ac frequencies higher
than 0.5 cps.
The fact that the ac corrosion factor of aluminum,
as can be seen from the above-mentioned figures, approaches 50% or
100% of a half-wave rectified ac can be explained as ac depolarization
62
effect compensating the effect of time lag in dissolution reactions.
Tolstaya, et al. (1967) explained that as current densities increased, frequency exerted more influence on the variation in the
potential of the aluminum for both cycles.
At high frequency,
electrode reactions begin to lag behind the polarity change of the
current yielding the decrease of ac corrosion factor.
This is why
a lower corrosion rate was observed at higher frequencies.
However,
as current densities increase, the electrodes are depolarized causing higher corrosion rate and ac corrosion factor approaches 50%.
Williams (1963) reported identical weight loss on the two electrodes of similar metals, indicating identical reactions on each
electrode.
Nearly identical loss of the two electrodes is also ob-
served here by the author.
There is, however, a small discrepancy
of weight loss of the two electrodes.
This is probably due to ex-
perimental errors or due to the difference in the oxide film
characteristics.
The experimental errors could be incurred largely
during the cleaning process.
B. Copper and Copper Alloys
Copper, brass, and cupro-nickel alloy exhibit a dependence of
ac corrosion on current densities.
In spite of the scattering of
data obtained on copper and cupro-nickel alloy, both metals are not
affected by ac differently.
They yield the same blue or greenish
blue corrosion products which are suspected to be cupric hydroxide
and cupric oxychloride, respectively.
Moreover, from an ac corrosion
63
factor plot of copper and its alloys, one can see that results on
copper and cupro-nickel alloy fall within the same region, so do
the corrosion rate data.
Brass, on the other hand, though giving
a mixture of blue and white precipitates, shows much lower corrosion rate and an ac corrosion factor.
probably ZnC1
2'
The white precipitate is
Therefore, copper alloyed with zinc is more resis-
tant to ac corrosion in 3% NaC1 than that of nickel.
yet to be investigated further.
The reason has
Unlike other authors (Waters, 1962;
Williams, 1962), who found the ac corrosion factor of copper to
level off at high current densities, we observe a steady increase of
the ac corrosion factor at high current densities (above 0.1 A/cm
2
).
2
However, below 0.1 A/cm , ac corrosion factors of all three metals
are higher than expected.
The reason for this is that an oxide film
is formed during anodic dissolution.
At low current densities, ac
cannot depolarize the electrodes enough to retard the formation of a
passive film.
Chloride ions in the solution. locally penetrate the
film causing pitting corrosion.
At high current densities, the elec-
trodes are depolarized, passive films are not formed, and ac corrosion behavior is quite consistent.
It is reasonable to predict that
the ac corrosion factors of copper and copper-nickel alloy will
eventually approach or not exceed 50%, for half of the current is
anodic.
C. Lead
The ac corrosion of lead increases with current density.
The
64
corrosion rates obtained here are higher than those reported by
Williams (1966) as can be seen from Table IV 16.
No pitting on the
lead electrodes is observed, except probably at very low current
density.
This is why the corrosion rate, or more obviously ac cor-
rosion factor, is unexpectedly high.
After each run, a black and
smooth-textured film is noticed on the electrode surfaces.
Vijayavalli, et al. (1963)
observed large pits on lead electrodes
and reported that superimposed ac tended to increase dissolution
rate of lead by increasing the formation of Pb02 film on the surfaces.
This film was porous in structure and became more porous
as the ac densities increased.
pits on his tested lead coupons.
Williams (1966) also reported large
The above results disagree with
Costa and Hoar (1962), who reported decreasing weight loss of lead
with ac densities.
They explained that more Pb02 film formed upon
superimposition of ac acting as a barrier film attributed to the
decrease of corrosion rate with ac densities.
However, their ex-
planation is doubtful as the film is in fact porous and, hence, it
is more easily locally attacked by ac.
It cannot be clearly understood at the present time as to why
the ac corrosion factors observed here are much higher than those
by Williams (1966), even at high current densities where minimum
ac corrosion factor is observed.
One possible explanation is the
error caused by the cleaning process of the electrodes.
However,
even with this error existing, the results obtained, though not
65
accurate, can at least show the trend of ac corrosion behavior of
lead.
D. 304-Stainless Steel and Cold-Rolled Steel
Stainless steel is comparatively highly affected by ac.
Cold-
rolled steel, on the other hand, is relatively most resistant to
ac corrosion among the metals tested.
the same corrosion product.
Both metals gave apparently
Their corrosion behaviors conform to
those of other metals in that corrosion rate increases with current
densities.
The two ac corrosion factor curves establish the same
characteristics as that reported by Williams.
That is, ac corrosion
factor gradually increases at low current densities and approaches a
maximum value at high current densities.
However, Pookote and Chin
(1978) obtained a linear relationship for the ac corrosion factor
of steel rods and current densities.
They explained the difference
of their results from Williams' as being attributed to the difference
in the electrolytes (Williams did his experiments in soil solution
while Pookote and Chin did theirs in soil).
As a matter of fact,
the corrosion rate of cold-rolled steel reported by Bruckner (1964)
for the tests in soil differs greatly from those reported by Williams
in soil solution and from our experiments in 3% NaC1 solution.
On
the contrary, our results correspond very well with Williams' indicating that, in aqueous solution, ac corrosion depends minutely on
chemical composition of the electrolytes at ac frequency of 60 Hz.
Slight etching and pitting are observed on the stainless steel
66
electrodes but not on the cold-rolled steel.
The pits observed are
due to passive film breakdown or local attack by ac and chloride
ions on the defects of the film.
E. Titanium
Titanium possesses quite mysterious ac corrosion behavior,
for instance, the scattering of data with corrosion rate is found
to be characterized by the degree of pitting and etching during the
experiments.
Also, from Figure 19, it seems that the three lines
for different degrees of pitting approach one limiting value at a
current density out of the experimental range.
This limiting value
is suspected to be approximately 0.2% of the non-pitted data, because at high enough current densities
ac depolarizes the electrodes
so that no passive film could be established and that corrosion rate
is high, whereas the ac corrosion factor is approximately constant.
The difference in degrees of pitting is probably due to nonuniformity of the passive film on the surface and of the ac attack
on the film which is observed to be thin, transparent, and of tint
coloration.
Kolotyrkin and Strunkin (1970) observed pits on titanium
electrodes when tested with HC1 as the electrolyte, but not with
H SO
2
4.
This indicates that pitting of titanium is mainly due to
the attack of chloride ions in the solution.
During our experiments, a minor difficulty arose at low current
densities where current could hardly be controlled at the predetermined constant values for it kept drifting down.
The voltage had
67
to be increased in order to keep the constant current.
Practically,
the voltage had to be raised up to a critical value above
current could be easily kept constant.
This was due to the passive
film formed at the surface acting as a barrier layer.
al.
which
Tomashov, et
(1972) studied the passivation of titanium and its alloys.
They believed that the passive film was double- layered, one of
which being a barrier layer next to the metal surface, hence continuously protecting the metal.
protective porous oxide layer.
The second layer was an external nonIt is the barrier layer which inhi-
bits the anodic process of the alloys.
The protective properties of
the barrier layer are related to its character defectiveness and
semiconductor properties of which mechanisms are still unclear.
The main anodic process of dissolution in the passive state involves
2+
the direct electro-chemical transition of TiO
into the solution.
The oxide films formed on all titanium alloys tested in H2SO4 solution had a composition close to Ti02 with rutile and anatase mixed
structure (Tomashov, et al., 1972).
The change in defectiveness
and ionic conductivity of oxide films determines the change in anodic
dissolution of the titanium from the passive state.
F. Zirconium
Figure 13 shows an appreciable ac corrosion rate for zirconium.
At current densities above 0.2 A /cm2 a linear relationship between
current densities and corrosion rate is obtained.
Despite the fact
that the corrosion rate of zirconium is much higher than that of
68
aluminum, the ac corrosion factor of zirconium rises much more
slowly than that of aluminum.
This is because the theoretical
corrosion rate of zirconium, based on an equivalent amount of dc, is
high due to its high molecular weight.
The corrosion rate is nearly
negligible at very low current densities.
This is supported by the
results obtained by Kondrashin (1974) that below a current density
of approximately 4 mA/cm
2
oxidation of the electrodes is negligible.
He concluded that oxidation of zirconium requires a specific critical polarizing current density, <i >, and critical frequency,
cucr"
Above these critical values, ionic conductivity of the oxide, and
hence the corrosion rate, became appreciable.
The critical values
can be evaluated by:
UWE6
<1>
=
cr
71
7 <1>
Cr
CSC EE
cr
where
<1>
=
critical polarizing current density
critical frequency, Hz
cr
-4
C,
=
8.85 x 10
6
=
relative dielectric constant of the oxide film
=
critical electric field intensity, V/cm of the
oxide film
=
roughness factor
F
cr
6
F /cm of the oxide film
69
VI. CONCLUSIONS
It is the purpose of this thesis to study only the effect of
ac on the weight loss of metals.
Consequently, two parameters,
corrosion rate and ac corrosion factor, are discussed as related
to current density.
Conclusions can be drawn here as the following:
1. All tested metals are affected by ac differently.
Some alloys
are more resistant to ac attack than others.
2. Corrosion rate increases with ac densities, slowly at low
current densities and more rapidly
at high current densities.
3. The A.C. corrosion factor is a function of current density.
For
all metals except titanium and lead, the corrosion factor is
low, and gradually rises as current densities increase.
It
levels off at a maximum ac corrosion factor, which is below 3%
(or 50% in the case of aluminum and zirconium).
Titanium and
lead exhibit a reverse behavior, their minimum ac corrosion factor being approximately 0.2% and 0.1%, respectively.
4. The order of ac corrosion rate from the highest to the lowest is:
aluminum, zirconium, 304-stainless steel, copper and cupro-nickel
alloy, brass, titanium, lead, and cold-rolled steel.
5. Passive film are observed, visually on titanium and lead.
6. Pitting and etching play a significant role on ac corrosion, i.e.,
they cause higher corrosion than expected.
70
7. There is non-identical weight loss on the two electrodes tested
on every experiment except aluminum which yields virtually
identical weight loss.
Theoretically this loss should be the
same and the reason for this discrepancy is unknown.
71
VII. RECOMMENDATIONS
This thesis represents a preliminary study of ac corrosion rate
of various metals.
It is found that there are many aspects of ac
corrosion worth further investigations to make feasible the explanation of some behavior observed.
The followings are recommended for
subsequent researches on ac corrosion:
1. Potentiostatic curves studies,
2. Polarization studies,
3. Passive films studies,
4. Differentiation of ac effects on alloys of metals,
5. Investigation of instantaneous corrosion products during
experiments,
6. Varification of "mixed potential" theory postulated by Chin
and Fu (1979),
7. Varification of Kondrashin's formula on critical current density
and frequency for zirconium (see discussion, zirconium).
72
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"Function of A.C. Superimposed on D.C. in the Anodic Oxidation of Lead in H2S041" J. of the Electrochemical Society,
110(1), 1-4 (1963).
Waters, F. O., "A-C Corrosion:
Tests Show A-C Increase Corrosion
of Metals Underground," Materials Protection No. 3, 1, 26-32
(1962).
Waters, F. 0., "Alternating Current Corrosion Tests--Continued,"
Proceedings 2nd International Congress on Metallic Corrosion,
New York, 311-317 (1963).
Williams, J. F., "Corrosion of Metals Under the Influence of Alternating Current," Materials Protection No. 2, 5, 52 (1966).
Williams, J. F., "Alternating Current and Aluminum: Tests Determine
Effect of A-C on Aluminum Conductors," Materials Protection No.
2, 6, 50-52 (1967).
Woodward, W. S., "Two Cases of Corrosion in Suburban New York Disguised as Galvanic--Their Cause and Mitigation," Corrosion No.
9, 12, 17-22 (1956).
Zastrow, O. W., "Copper Corrosion in Moderate and High Resistivity
Soils," Materials Performance No. 8, 13, 31 (1974).
APPENDICES
76
APPENDIX A
Tabulated Final Data
TABLE A-1. TABULATED FINAL DATA FOR ALUMINUM
Z
Area of
One ElecCoupon
trode, =2
Original Wt.
of One Electrode, gm.
Final Wt. of
Electrode,
gm
Ampere
Duration,
hr
1
12.75
1.1666
1.1658
0.00
24.05
2
12.75
1.1559
1.1549
0.00
23.95
3
45.12
12.9460
11.5880
3.50
2.87
4
29.76
8.4395
6.6880
4.30
3.93
5
19.00
8.1785
6.8175
3.30
3.00
6
19.60
8.4905
6.4110
4.80
3.12
7
20.40
8.5800
6.7105
6.15
2.00
8
20.00
8.7005
7.1810
7.00
1.43
9
15.00
12.9020
11.5465
5.25
1.67
10
13.13
9.1790
7.1710
5.00
2.85
11
15.60
8.8065
7.2565
7.02
1.65
12
12.88
8.9400
6.9950
6.44
1.93
13
13.13
9.0880
8.3320
9.84
0.47
14
13.25
9.1165
8.3885
13.25
0.33
77
Appendix A, continued
TABLE A-2. TABULATED FINAL DATA FOR BRASS
Coupon
Area of
One Elec2
trode, cm
Original Wt.
of One Electrode, gm
Final Wt. of
Electrode,
gm
Ampere
Duration,
hr
----...
1
12.75
3.3460
3.3429
0.00
24.00
2
12.75
3.4219
3.4176
0.00
24.00
3
12.75
3.5246
3.4910
0.63
24.42
4
13.25
3.5572
3.5253
1.25
24.63
5
13.13
3.5872
3.5525
1.88
23.95
6
30.21
22.4805
22.1500
4.83
84.40
7
13.25
3.5227
3.4656
2.50
23.30
8
20.20
11.3545
11.0790
4.44
77.33
9
12.88
3.5340
3.4564
3.15
26.58
10
13.30
3.5184
3.3958
3.75
26.32
11
15.15
11.3230
11.0975
4.55
49.17
12
13.00
3.4562
3.3378
4.40
24.07
13
12.75
11.4505
11.2105
4.85
42.12
14
12.75
3.5447
3.3273
5.00
24.10
15
12.75
3.5738
3.2836
5.60
23.87
16
11.11
11.3005
11.0140
5.11
35.77
17
10.12
11.3450
11.1065
5.06
28.25
18
9.00
11.1925
10.9465
5.40
24.02
19
7.75
11.1850
10.9570
5.89
20.40
20
5.10
11.4060
11.1475
4.49
16.60
21
5.00
5.6290
5.3615
4.50
20.22
22
4.25
5.5805
5.4035
4.68
11.72
78
Appendix A, continued
Table A-3. TABULATED FINAL DATA FOR COLD-ROLLED STEEL
Coupon
Area of
One Electrode, cm2
Original Wt.
of One Electrode, gm
Final Wt. of
Electrode,
gm
Ampere
Duration,
hr
24.00
1
12.75
2.5033
2.4712
2
12.50
2.7504
2.7154
1.25
24.15
3
26.60
6.5640
6.4630
3.00
40.47
4
30.40
6.5835
6.3215
3.80
78.63
5
12.50
2.7393
2.6955
1.88
24.42
6
12.75
2.7642
2.7124
2.50
24.60
7
22.80
6.5160
6.3835
4.60
37.07
8
22.20
6.4165
6.1940
4.50
73.28
9
12.75
2.7548
2.6833
3.15
25.25
10
15.20
6.5430
6.3806
4.20
47.12
11
13.00
2.7259
2.6354
3.75
24.62
12
15.60
6.6230
6.4640
5.00
46.95
13
12.50
2.7268
2.6256
4.40
26.53
14
22.81
6.6245
6.4960
4.50
42.83
15
12.38
2.7312
2.5836
5.00
24.75
16
11.95
2.7149
2.5798
5.60
22.87
17
9.50
6.6615
6.5140
4.75
35.95
18
12.75
2.7331
2.5976
6.25
21.77
19
7.40
6.4690
6.2795
4.75
33.80
20
6.08
6.5805
6.4780
4.60
27.17
21
5.78
6.6345
6.5055
4.40
30.63
22
5.70
6.5930
6.4790
5.00
24.05
23
4.94
6.6230
6.5315
5.00
21.60
0
79
Appendix A, continued
TABLE A-4. TABULATED FINAL DATA FOR COPPER
Coupon
Area of
One Elec2
trode, am
Original Wt.
of One Electrode, gm
Final Wt. of
Electrode,
gm
Ampere
Duration,
hr
1
12,75
3.6247
3.6208
0.00
24.00
2
12.75
3.6263
3.6214
0.00
24.50
3
30.00
12.1130
12.0775
0.75
30.25
4
30.00
12.2600
12.1570
2.40
17.08
5
20.00
12.2450
12.0630
3.16
15.22
6
20.00
12.1980
12.0310
4.52
8.42
7
15.00
12.2120
12.0380
4.45
8.43
8
10.20
12.1900
12.0130
3.54
11.27
9
15.00
12.2265
11.8670
5.53
10.77
10
9.63
9.2840
8.9225
7.22
11.93
11
12.50
12.2880
11.9770
5.57
10.20
12
12.50
12.2835
11.9040
6.18
7.33
13
10.00
12.0260
11.7595
4.95
10.77
14
10.00
12.4675
12,1470
5.94
7.08
15
7.65
12.3340
11,8035
4.99
9.18
16
6.18
12.3205
11.8545
4.57
9.48
17
5.70
9.1890
8.7960
4.58
6.83
18
4.94
9.1165
8.7875
4.56
7.10
80
Appendix A, continued
TABLE A-5. TABULATED FINAL DATA FOR CUPRO-NICKEL ALLOY
.
Coupon
Area of
One Elec2
trode, cm
Original Wt.
of One Electrode, gm
Final Wt. of
Electrode,
gm
Ampere
Duration,
hr
1
12.75
19.4137
19.4070
0.00
31.08
2
12.75
19.3788
19.3726
0.00
23.50
3
13.00
17.6627
17.5676
0.63
48.72
4
12.88
17.4844
17.2532
1.25
68.60
5
12.88
17.0727
16.7468
1.88
47.85
6
13.00
17.4889
17.1811
2.50
48.98
7
12.25
17.6344
17.2716
3.15
48.20
8
12.50
17.3156
16.7140
3.75
63.37
9
13.25
17.4779
16.9274
4.40
39.33
10
13.39
19.2873
18.4911
4.80
47.88
11
12.75
17.3844
15.6640
5.00
47.07
12
13.50
19.4136
17.9824
5.70
33.83
13
12.50
17.1478
14.6994
6.25
51.33
81
Appendix A, continued
TABLE A-6. TABULATED FINAL DATA FOR LEAD
Coupon
Area of
One Elec2
trode, am
Original Wt.
of One Electrode, gm
Final Wt. of
Ampere
Duration,
hr
Electrode,
gm
1
12.75
14.7290
14.7220
0.00
25.43
2
12.75
12.8442
12.8370
0.00
24.00
3
13.25
11.2355
11.1505
0.63
24.00
4
13.00
10.3973
10.3095
1.25
24.00
5
13.00
12.8232
12.7144
1.88
24.82
6
14.28
10.7271
10.5787
2.50
26.22
7
13.38
10.6303
10.4974
3.15
27.70
8
12.25
12.6545
12.4530
3.15
41.90
9
12.76
11.2527
11.0968
3.75
24.00
10
12.26
12.4702
12.1950
4.40
28.72
11
13.00
12.6940
12.3930
5.00
28.68
12
13.00
12.5743
12.3083
5.60
28.72
13
12.62
12.4944
12.2355
6.25
25.37
82
Appendix A, continued
TABLE A-7. TABULATED FINAL DATA FOR 304-STAINLESS STEEL
Coupon
Area of
One Elec2
trode, am
Original Wt.
of One Electrode, gm
Final Wt. of
gm
Ampere
Electrode,
Duration,
hr
1
12.75
9.2065
9.2063
0.00
24.00
2
12.75
9.2020
9.1323
0.63
24.22
3
12.75
9.2127
9.0860
1.25
25.68
4
12.50
9.2034
8,7237
1.88
24.00
5
12.75
9.2090
8.6663
2.50
16.88
6
12.75
9.1374
8.4606
3.15
14.93
7
12.50
9.1781
8.7168
3.75
7.88
8
12.00
9.1413
8.5369
4.40
7.27
9
13.00
9.2799
8.4842
5.00
7.95
10
13.00
9.2100
8.1411
5.60
10.27
83
Appendix A, continued
TABLE A-8. TABULATED FINAL DATA FOR TITANIUM
Coupon
Area of
One Elec2
trode, cm
1
12.49
5.6159
5.6159
0.00
24.33
2
12.24
5.5898
5.5895
0.00
15.88
3
12.75
5.6245
5.5890
0.64
24.08
4
12.00
5.5887
5.5217
0.60
24.13
5
12.64
5.5870
5.5273
1.30
24.53
6
12.50
5.6502
5.5217
1.20
24.13
7
13.00
5.6949
5.6204
1.88
23.58
8
12.35
5.5737
5.3890
1.88
24.05
9
12.50
5.5858
5.4102
2.50
24.05
10
12.78
5.6734
5.3758
2.50
24.03
11
12.50
5.6535
5.5356
2.60
24.17
12
12.74
5.6429
5.5001
3.15
24.00
13
12.74
5.6433
5.4936
3.75
21.88
14
12.48
5.5348
5,2541
3.75
23.10
15
12.90
5.6377
5.5628
4.40
24.00
16
12.74
5.6996
5.6127
4.40
24.08
17
12.50
5.5887
5.4759
5.00
23.77
18
12.48
5.6428
5.4829
5.00
24.00
19
13.00
5.7472
5.6368
5.60
23.97
20
12.50
5.6387
5.5239
5.60
24.40
21
12.75
5.6057
5.4753
6.60
22.60
22
12.22
5.5414
5.3904
6.25
23.92
Original Wt.
of One Electrode, gm,
Final Wt. of
Electrode,
gm
Ampere
Duration,
hr
84
Appendix A, continued
TABLE A-9. TABULATED FINAL DATA FOR ZIRCONIUM
Coupon
Area of
One Elec2
trode, cm
Original Wt.
of One Electrode, gm
Final Wt. of
gm
Ampere
Duration,
hr
Electrode,
1
13.55
8.5355
8.5353
0.00
24.00
2
12.48
7.9921
7.9271
0.63
23.92
3
13.00
8.2700
7.9016
1.25
24.00
4
12.24
7.8467
6.4080
1.88
24.12
5
12.64
7.9102
5.3235
2.65
12.00
6
12.75
7.7365
4.5748
3.15
3.75
7
13.92
8.5649
6.2434
3.60
3.83
8
12.38
7.8629
5.6453
3.20
3.83
9
13.48
8.6169
6.0913
3.80
2.22
10
12.75
7.6890
5.1159
4.10
3.33
11
12.86
8.0826
5.8225
4.20
2.33
12
13.62
8.2731
5.3530
4.80
2.00
13
12.24
7.6311
5.5643
4.40
1.37
14
12.24
7.7397
5.8808
5.00
0.97
15
13.00
8.1151
6.0303
5.80
1.05
16
13.67
8.2750
5.9820
6.25
1.00
85
APPENDIX B
Samples of Calculation
1. Determination of Corrosion Rate
2
Corrosion rate is expressed in mg/dm 'day (mdd).
mdd
=
/weight loss in
day
cm2
/102 cm2
103mg
gm
t dm2
10 5 x (corrosion rate calculated in gm/day
Sample:
cm2)
Aluminum; Coupon No. 12
Original Weight
Final Weight
Electrode Area
Duration
=
=
=
=
8.9400 gm
6.9950 gm
12.88 cm2
1.93 hr
Corrosion rate in
(8.9400
6.9950)
(1,93/24)(12.88)
\day
2)
am
1.87784
Corrosion rate in mdd
=
187,783
day
gm
,
am'.
mdd
wisow---Nw
2. Determination of AC Corrosion Factor
AC Corrosion Factor (%)
Actual Weight Loss due to A.C.
Theoretical Weight Loss due to
an Equivalent D.C.
Theoretical Weight Loss due to Equivalent D.C.
(Equivalent Weight)(Current)
(Faraday's Constant)
x 100
86
(M
--mole
\
mole
equivalents)
,
/I
coulomb
S
\
/ equivalent
96500 coulomb,
)
MI
96500(n)
/
gm/s
AC Corrosion Factor (%) -
Actual Weight Loss due to A.C.
(MI/96500n)
x 100
Actual AC Corrosion Rate in mdd
x 100
(Mi/96500n)(3600)(24)(105) mdd
Actual AC Corrosion Rate in mdd
x 100
89533.679(Mi/n)
/Actual AC Corrosion\
= 1.1169x10-
Rate in mdd
Sample: Aluminum; Coupon No. 12
A/cm
Current Density,
= 0.5
Molecular Weight, M
= 26.9815
n
= 3
2
equivalent/mole
Actual AC Corrosion Rate
= 187,783
AC Corrosion Factor
= 1.1169%10
= 46.64%
====mg
mdd
-3
3 x 187,783
26.9815 x 0.51
87
APPENDIX C
TABLE C-1. CLEANING SOLUTIONS
-
.
Metal
Aluminum
2% H Cr0
2
Brass, Copper
Time, min
Cleaning Solution
10% H SO
2
4
+ 5% H PO
3
10
4
2-3
4
Cold-Rolled Steel
10% HC1
Lead
1% CH COOH
2-3
'1'10
3
Cupro-Nickel Alloy
10% H SO
2
304-Stainless Steel
Titanium
Zirconium
1,20
4
Distilled Water, Scrub
II
88
APPENDIX D
Molecular Weights of Tested Metals
Metal
Molecular Weight
Aluminum
26.9815
Brass (70% Cu, 30% Zn)
64.09
Cold-Rolled Steel
55.847 (Fe mol. wt.)
Copper
63.54
Lead
(Calculated value)
207.19
(Calculated value)
Cupro-Nickel Alloy (70% Cu, 30% Ni)
62.09
304-Stainless Steel
55.847 (Fe mol. wt.)
Titanium
47.90
Zirconium
91.22