Investigation of Various Water Sources on the Corrosion of Carbon Steel and
Aluminum
Kathryn Morris
Department of Chemical Engineering
Honors Research Project
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Executive Summary
Corrosion affects many applications in today’s society, especially in structural aspects. The effects of
corrosion were analyzed using twelve different samples of both carbon steel and aluminum (six each).
Three different sources of water were also utilized to determine the effects of lake/fresh water, ocean
water, and de-ionized water on metal corrosion behaviors. After allowing the samples to sit in nondisturbed water for forty-nine days, the samples were removed. The weights of the samples before and
after immersing in the water were measured, along with photos taken periodically throughout the
experiment. Appendices A and B contain these photos.
After assessing the corrosion rates of all the samples, aluminum was found to have better corrosion
resistance in all three water sources. It was also found that Lake Erie is the least corrosive for both
carbon steel and aluminum samples, and de-ionized water corrodes the metals the most. Since Lake
Erie is fresh water, it theoretically would give the least amount of corrosion to the metals. However the
most corrosive was thought to be ocean water because of its ions and chloride contents, but this was
not the case. The reasoning for DI water to be more corrosive was thought to have something to do
with how the DI water was made. Ideally, no ions or very little ions would be in the solution to make the
metal coupons corrode outside of equilibrium. However, if the filter was full when DI water was made,
this would allow ions and minerals to come into solution. This would make the coupons corrode more.
Another aspect that was initially not in the scope of this project was the analysis of grooved samples.
Since during polishing, these samples should be rotated 90° after each grit sandpaper, this eliminates
the grooves. Some aluminum samples were found to have grooves, and those samples had more
corrosion. The corrosion actually seemed to follow the grooves as well, which is shown in sample 4 in
appendix A. The last aspect analyzed was that the appearance of air bubbles on two aluminum samples
seemed to accelerate corrosion. Samples 1 and 3 show that in Appendix A.
Overall, this was a very interesting project and I have learned how to approach a broad topic like this
one. There are many different ways to go about analyzing corrosion, especially since it is a newer
program at The University of Akron. Personally I have gained the ability to find credible sources,
organize my own lab schedule, and increase my independence overall since it was mainly an
independent project. The actual hands-on aspect of this project allowed me to utilize a new type of
microscope, handle various metal coupons, and prepare the samples/water for analysis.
In the future, it would be desirable to use PVD (physical vapor deposition) to help making the surface of
the samples more uniform. It may also be desirable to repeat this experiment to see if de-ionized water
still yields the most corrosion in both aluminum samples and carbon steel samples. This will be
beneficial to society in terms of saving money, increase our understanding, and decrease disasters that
may occur due to corrosion.
2
Introduction:
Carbon steel and aluminum have many uses in everyday life, especially as structural materials. Learning
the mechanism of how both metals physically corrode could help life tremendously. There is an
innumerable amount of structural failures due to improper maintenance, a lack of understanding of how
corrosion works, and improper safety. For example, in 1967 a bridge called the ‘Silver Bridge’ across the
Ohio River connecting West Virginia to Ohio collapsed. The bridge was made of carbon steel with
aluminum painting, thus the name the ‘Silver Bridge’. It was a very unique design and used a ‘eye-bar’
method to support the weight with carbon steel. It was essentially chain links with a rod passing
through each link. The down-side to this new design was in the way the ‘eye-bars’ were placed because
the load was not supported evenly. In 1967, the bridge was 39 years old and unfortunately due to stress
corrosion cracking and corrosion fatigue, the bridge collapsed. The reason for this involved a very small
crack in the making of the eye-bars, which was not noticeable through maintenance checks. This crack
was subjected to a constant load and a corrosive environment. Since the corrosion will break down the
carbon steel quickly as seen in this report, the constant load would eventually tear it apart. This report
is more of an analysis of the physical corrosion rather than tensile strength, however the two are very
closely related (Roberge, 1999).
Aluminum and carbon steel were corroded in Lake Erie water, ocean water, and de-ionized water to
determine the aqueous medium affects on metal corrosion. The ‘Silver Bridge’ accident would most
closely relate to the Lake Erie water since the Ohio River is fresh water. As more is learned about the
topic of corrosion, hopefully disasters like the ‘Silver Bridge’ will not happen again.
Previously corrosion of a thin film of metal deposited on the glass surface using physical vapor
deposition chamber at The University of Akron was intended to be followed. The professors Dr. Bi-min
Newby, Dr. Lu-Kwang Ju, Dr. Gang Cheng, and Dr. Joe Payer have developed a flow chamber system that
allows one to monitor bio-film development of various species on metal thin film deposited glass and
the associated corrosion behaviors of these metal films. Due to time constraints, this project used metal
coupons of aluminum and carbon steel to monitor the effects of corrosion without microbial species.
The goal of this project was to hopefully separate the corrosion types of microbial corrosion and physical
corrosion so that more could be understood in each case.
3
Experimental Methods - Preparation:
The first step of any corrosion project is to make sure the starting sample is adequately prepared. Since
in this experiment six samples of both carbon steel and aluminum were used, the metals required
polishing. The picture below shows the configuration of how the samples were polished. The sand
paper was rotated in a clockwise direction and the samples were held down physically for approximately
one minute.
Figure 1: Sample Polishing Configuration
As these samples were polished, the carbon steel coupons were nearly mirror-like and the aluminum
had a slight cloudy look. Water was used as the cooling agent while the circular sand paper was rotated.
Six samples of carbon steel and aluminum were polished for a total of twelve samples. Four different
types of silicon carbide sandpaper were used, 400, 600, 800, 1200 grit and each sample was polished for
one minute on each side. Ideally the sample would be rotated 90° after each grit sandpaper. This would
minimize the grooves caused if the same direction was used each time. Below is an example of the
direction of the grooves when the same is rotated as described on a carbon steel sample. Also below is
an example of very deep grooves when the sample was not rotated.
4
Image 1: Sample 9 – Carbon Steel at 4x magnification
Image 2: Sample 2 – Aluminum at 4x
magnification
Samples with additional grooves could be used as activation sites for the corrosion and may skew the
data somewhat. Aluminum samples polished with a rotation will be compared with the non-rotated
samples.
After the samples were polished, the water for each source was boiled for about thirty minutes to
remove any microbial species. After boiling the water was cooled to room temperature and separated
into separate dishes for all twelve samples.
Experimental Methods - Testing and Analyzing:
Twelve samples total were analyzed to determine the effect of various waters on the samples.
Additionally, the presence of grooves may or may not have an effect on the amount of corrosion and
was considered for only the aluminum samples. Below is a table summarizing the types of samples used
in this experiment. All samples were monitored at ambient conditions.
Table 1: Summary of Samples Tested
Samples
1
2
3
4
5
6
7
8
9
10
11
12
Water
Lake Erie
Lake Erie
Ocean
Ocean
Deionized Water
Deionized Water
Lake Erie
Lake Erie
Ocean
Ocean
Deionized Water
Deionized Water
Type
Aluminum
Aluminum
Aluminum
Aluminum
Aluminum
Aluminum
Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
Carbon Steel
Grooved
No
Yes
No
Yes
No
Yes
No
No
No
No
No
No
5
The corrosion weights were measured along with optical microscopy to visually observe the effect of
corrosion. Appendix A contains the pictures of the samples taken using AMScope MT digital camera
attached to the eye piece of the IX71 Olympus microscope using 60x and 4x magnification objectives.
Appendix B contains the pictures of samples taken on a regular digital camera. Along with optical
means, each sample was weighed before and after the experiment to measure the amount of corrosion.
After research, it was found that simply brushing the samples vigorously before weighing would take the
necessary amount of actual corrosion off of the sample. This way an accurate sample weight would be
measured without any corroded metal.
Experimental Methods - Measuring Weight Loss:
The procedure developed by Hua Wang was utilized, the detailed steps were:
1.
2.
3.
4.
5.
Weigh coupon
Brush surface with a toothbrush
Rinse coupon with Deionized water and wash away the corrosion products
Dry the washed coupon under a stream of nitrogen
Weigh the dry coupon
6
Data and Results
Pictures of the difference between the samples are shown above in the ‘Experimental Methods –
Preparation’ section. Other pictures taken over the course of the corrosion time frame can be found in
Appendix B. The raw data can be found in the Appendices as well.
The chart below shows the corrosion rate for each sample. This was calculated by using the following
equation:
Where SA is the surface area, 49 days is the total allowed time for the corrosion to take place, W f is the
final weight, and Wo is the initial weight. The density for aluminum is 2.7 g/cm3 and carbon steel is 7.87
g/cm3.
Chart 1: Corrosion Rate
After visual and numerical analysis, it was found that the aluminum overall had a much higher resistance
to corrosion than carbon steel. An interesting point discussed later is that de-ionized water had a much
higher corrosion rate than the other waters. Below is a snapshot taken of the samples after 49 days in
the various waters. The samples were also brushed before the pictures were taken.
7
Image 3: Metal coupons after 49 days after brushing and washing (details of samples 1-12 are described
below the images)
By looking at the samples visually, one can see that the carbon steel (Samples 7-12) was more heavily
affected than the aluminum samples. One can clearly see the differences in the carbon steel samples as
well. Samples 7 and 8 were in Lake Erie water, samples 9 and 10 were in Ocean water, and samples 11
and 12 were in de-ionized water. The aluminum samples were not as distinct and did not show as much
corrosion. Samples 1 and 2 were in Lake Erie water, samples 3 and 4 were in Ocean water, and samples
5 and 6 were in de-ionized water. The corrosion on the carbon steel in de-ionized water (11 and 12) was
easily brushed off whereas the corrosion in Lake Erie water (7 and 8) was not easy to brush off.
There are also two points on the aluminum samples #1 and 3 (non-grooved). Those are where air
bubbles appeared on the coupon and remained for several weeks. The air bubbles seemed to
accelerate the corrosion process. As shown below, the white corrosion developed under that bubble.
In the bottom right picture below, the white solid developed is most likely salt crystallizing out of
solution. Since this is ocean water, and the water slowly evaporated from the dish, the salt
concentration slowly increased over time. Image 5 is a picture of where the air bubble was during
corrosion under 4x magnification.
8
Image 4: Sample 3 – Aluminum
Image 5: Sample 3 – Aluminum Under 4x Magnification
9
The graph below shows the difference between the aluminum and the carbon steel corrosion resistance.
Final weight represents the weight of the samples after the full length (49 days) for the coupons and
after being brushed. The initial weight is the coupon weight before being subjected to the various
waters. A low final/initial weight means that there was more corrosion on the sample. The raw data
can be found in the appendix.
Chart 2: Final/Initial Weight of All Samples
Final Weight / Initial Weight
1.000
0.950
0.900
0.850
Ocean Water
Lake Erie Water
0.800
De-ionized Water
0.750
As is stated above, the aluminum samples had a much higher resistance to corrosion. The average
final/initial value for aluminum was 0.938 versus carbon steel at 0.864. The mechanisms for the
corrosion are presented in the discussion and analysis portion.
As shown in the graph, aluminum has a high resistance; however the interesting point is that de-ionized
water was more corrosive than ocean water or water from Lake Erie. Initially, one would think that the
ocean water would be the most corrosive since it has salt, or even Lake Erie water since it has some
known contaminants in the water as stated in the discussion section; however that is not the case here.
De-ionized water is made by taking tap water and running it through an ion-exchange filter, which is
similar to how a softener filter works – it removes the minerals/ions such as sodium or chlorine. One
down-side to de-ionized water is that it does not remove bacteria, which is why these samples were
boiled before hand to remove that. One possibility for the increased corrosion would be the pH of the
systems - these were measured. Lake Erie had a pH of 5.33, Ocean water was 7.83, and de-ionized
water had a pH of 6. This is only slightly basic, and if basic versus acidic had a large enough affect on the
corrosion then either ocean water or Lake Erie water should show more corrosion, but that is not the
case. The only remaining possibility for the increased corrosion of the coupons in de-ionized water
10
would be that the filter was not working properly or was too full when the de-ionized water was first
made. If the filter was too full, then other contaminants (minerals) would be introduced to the water;
however this is only speculation since it is not known exactly what happened.
Grooved Samples:
Since grooved samples were measured for only aluminum, it was found that a grooved sample corroded
more than the non-grooved. This is most likely due to the grooves giving the sample more surface area.
The picture below shows sample 4 (at 4x magnification).
Image 6: Sample 4 – Aluminum at 4x magnification
The grooves in the sample are apparent, and it seems that the corroded portions follow the grooves.
When compared to sample three, the corrosion seemed to attack any deep scratches present in the
coupon, however it did not attack smooth portions of the metal. This supports the suggestion that
grooves in the metal promote corrosion.
11
Discussion and Analysis
A sixteen year study initiated by the U.S. Army and the Panama Canal Company in the 1940’s looked at
the pitting depth of both fresh and sea water of many different structural metals. Over 13,000 test
pieces were exposed, with Aluminum and Carbon Steel being part of it. According to this study, samples
of 99% aluminum was very resistant to corrosion in sea/ocean water. This study did not take into
account the affect of microbial corrosion versus physical corrosion, so there may be some differences
between this study and the one in this report. After 16 years of exposure, it was found that the pitting
was less than 18mil deep for aluminum. In fresh/lake water, the samples were much more deeply pitted
with the depth at about 97 mil. The lake water was from Lake Gatun, which is part of the Panama Canal.
The carbon steel corrosion in lake water had a very high rate during the first year, however after 16
years, the corrosion rate decreased significantly. The report suggested it was nearly parabolic with
respect to time. In fresh/lake water, the corrosion rate was about 2.7mil/year, so after 16 years it was
approximately 43.2 mil. The sea/ocean water had about the same corrosion rate at 2.7 mil/year
(Southwell, 1969).
In conclusion of this sixteen year study, it seems that Aluminum has a higher overall resistance in
sea/ocean water, however in lake water carbon steel has a higher resistance in the long term. This does
not agree completely with this report, however there are differences between the studies. For example,
the microbes were not removed prior to testing, so Aluminum may have a lower resistance to physical
corrosion in ocean water if microbes were kept in solution. It also looks at long term effects, whereas
this report only takes into account 49 days.
A recent study done in 2007 is a short term test, and measures the affect of Lake water (pH=8.3) versus
other pH ‘bulk’ waters (pH of 4 and 9.2 on carbon steel.) Light intensity was used to measure the
growth rate of microbial bio-films on the surface of the coupons, however the sediment formation
deposited on the samples looks to be very similar to the ones observed in this report. The following is a
picture of the coupon where A-D represent time frames (A=4min, B=8min, C=12min, D=15min). (Gobi,
Balaji Ganesh, Radhakrishnan, & Sastikumar, 2007)
12
Image 7: Sediment Formation on Carbon Steel Surface in Lake Water (Gobi, Balaji Ganesh,
Radhakrishnan, & Sastikumar, 2007)
When comparing these photos with the microscopic photos of the carbon steel in Lake Erie water, they
are similar. For example, in the image below from sample 8 at 4x magnification, one can see the black
deposits in the lower section. There will be some difference between the samples in the journal article
and the ones in this report mostly because of the additional brushing and time frame difference.
13
Image 8: Sample 8 in Lake Erie Water at 4x magnification
The conclusion of the journal article from 2007 was that in acidic solutions, the corrosion was much
worse. The images above attribute the blackish spots to be sediment formation rather than a bio-film
being produced on the surface. It was concluded, however, that the film was already starting to grow in
the first four minutes of exposure (Gobi, Balaji Ganesh, Radhakrishnan, & Sastikumar, 2007). Since the
blackish deposits are similar between the two studies, it can be assumed that this occurs in all lake
waters and is most likely because of the minerals found in lake water. It also should be noted that the
blackish deposits were found on the ocean water coupons as well and can be seen in appendix B.
14
Carbon steel mechanism of corrosion:
There could be many reasons for the difference in the corrosion of both the carbon steel and aluminum.
According to previous research, the amount of CO2 dissolved plays a large role in determining the
amount of corrosion (Louafi, Ladjouzi, & Taibi, 2010). Usually CO2 corrosion results in pitting and also
increases general corrosion. This can be seen in some of the pictures in Appendix A and B. This study
also examined the CO2 corrosion of carbon steel at various temperatures. They found that the highest
chance for pitting occurs between 60 and 80°C. This is due to the formation of carbonic acid, which is
more corrosive than another acid at the same pH. The cathodic reaction of the iron is below where (3) is
more prominent in a system without CO2 and (1) is prominent in the presence of CO2 (Louafi, Ladjouzi, &
Taibi, 2010):
The anodic reaction takes place as follows (Louafi, Ladjouzi, & Taibi, 2010):
Since this reaction is taking place at room temperature with small amounts CO2, the reactions above
may not be taking place since HCO3- would not be made at low temperatures. The following reactions
are more likely where all of the reactions are reversible (Senese, 2010).
Reaction 12 may dry and form the iron oxide that is a red/orange powder that many are used to seeing.
In acidic conditions, the additional hydrogen ions will force reaction 11 to the right and produces more
iron (III). In general, it is known that acidic systems corrode more than basic systems. The reason for
this is due to the mechanism of how corrosion occurs which was listed above. The pH of each system
used in this experiment is listed below, which was measured using litmus paper:
15
Table 2: pH of the Water Tested
Water
Lake Erie
Ocean
Deionized Water
pH
5.33
7.83
6
Another journal article shows the mechanism for iron corrosion as well as the following where reactions
9 and 10 are the same as above, however reactions 11 and 12 were changed to 13, 14, and 15 (Jiang,
Mao, Yu, & Gan, 2008).
The main difference in the mechanisms seem to be how acidic or basic the solution is. For example, if
the solution is acidic, it would push reaction 11 forward and would favor those products. If the solution
was completely neutral, like the ocean water in this report, it may favor the products in reactions 13
through 15.
There also may be a chance that reactions 13 and 11 would not occur as readily in Lake Erie water
because the amount of oxygen in Lake Erie is also much lower than most lakes. This is due to
‘eutrophication.’ This is a natural process is where a boom in phosphates and nitrates cause algae to
grow. Unfortunately this means that less sunlight reaches the bottom of the lake. This results in much
less plant growth and eventually depletes oxygen levels (Adedipe, 2010). In addition to the depleted
oxygen, manufacturing in Cleveland has also produced acid rain in the lake and dropped the pH as well.
Normally this would not affect the pH by a large amount, however this process called ‘acidification’ has
an abnormally high level of acid (Adedipe, 2010). As measured in the experiment, the pH of Lake Erie
water was slightly acidic at 5.33. This means that with the depleted oxygen and acidic nature, there
could be many products formed according to the reactions above. The most common type of corroded
iron seems to be Fe2O3 and FeOOH (Jiang, Mao, Yu, & Gan, 2008). This would explain what the orange
solids are in the pictures taken in appendix B.
16
Aluminum mechanism of corrosion:
Generally, aluminum has a very good resistance to a neutral pH (between 7 and 9). This is due to the
ability of aluminum to use the corroded portion of aluminum oxide to protect itself. Aluminum seems
to have very good adhesion to itself which in turn protects itself. This is contrary to carbon steel where
the oxidized film lifts off of the metal. According to research done, the chlorine ions will be the most
aggressive on aluminum, which is usually present in large amounts in sea water (Noble Company).
Generally, aluminum will react with water to form Al 2O3 and chlorine ions will break apart this white
pasty solid. As seen in the pictures in appendix B, the samples in Lake Erie water have this white pasty
solid, which can be assumed to be Al2O3. However, it should be noted that Lake Erie water also has a
noticeable amount of chlorine in solution as well. According to Adedipe, a significant toxin present in
Lake Erie is PCB, or polychlorinated biphenyls (Adedipe, 2010). This toxin has many chlorine ions
attached to it, which may aid in the additional corrosion of aluminum. According to the data above Lake
Erie water actually had the lowest amount of corrosion, however de-ionized water had the most. This
may suggest that perhaps the filter was full when the de-ionized water was made and some ions were
not removed from solution.
Summary
After following six samples of aluminum metal coupons and six samples of carbon steel coupons for 49
days in Lake Erie water, Ocean water, and de-ionized water it was found that aluminum has the higher
corrosion resistance. When comparing the types of water, de-ionized water corroded the most and Lake
Erie water corroded the least. Theoretically, ocean water should corrode the most due to the amount of
ions in solution. Based on that theory, the de-ionized water should corrode the least. Another aspect
that was initially not in the scope of this project was the analysis of grooved samples. Since during
polishing, these samples should be rotated 90° after each grit sandpaper, this eliminates the grooves.
Some aluminum samples were found to have grooves, and those samples had more corrosion. The
corrosion actually seemed to follow the grooves as well, which is shown in sample 4 in appendix A. The
last aspect analyzed was that the appearance of air bubbles on two aluminum samples seemed to
accelerate corrosion.
17
Works Cited
Adedipe, A. (2010). Toxins in Lake Erie. Cleveland: Case Western Reserve University.
Gobi, G., Balaji Ganesh, A., Radhakrishnan, T., & Sastikumar, D. (2007). Laser Based Optical Sensor to
Observe Metal Surfaces Subjected to Early Microbic Corrosion. Lasers in Eng. Volume 17 , 397-404.
Jiang, L., Mao, X., Yu, J., & Gan, F. (2008). Effect of humic acid on the corrosion behavior of carbon steel
in natural fresh waters. Anti-corrosion methods and materials, volume 55 , 204-207.
Louafi, Y., Ladjouzi, M. A., & Taibi, K. (2010). Dissolved carbon dioxide effect on the behavior of carbon
steel in a simulated solution at different temperatures and immersion times. J Solid State Electrochem ,
1499-1508.
Noble Company. (n.d.). General Corrosion Resistance of Aluminum. Retrieved March 16, 2011, from
http://www.noblecompany.com/LinkClick.aspx?fileticket=zCM5yb8%2Bt%2Fo%3D&tabid=67&mid=443
Roberge, P. R. (1999, August). Silver Bridge Collapse. Retrieved April 12, 2011, from Corrosion Doctors:
www.corrosion-doctors.org/bridges/silver-bridge.htm
Senese, F. (2010, February 15). How does iron rust? Retrieved March 16, 2011, from General Chemistry
Online: http://antoine.frostburg.edu/chem/senese/101/redox/faq/how-iron-rusts.shtml
Southwell, C. R. (1969). The Corrosion Rates of Structural Metals in Sea-Water, Fresh Water, and
Tropical Atmospheres. Corrosion Science Volume 9 , 179-183.
18
Appendix A: AMScope MT Pictures
Sample 1: Aluminum – Lake Erie Water
19
Sample 2: Aluminum – Lake Erie Water
Sample 3: Aluminum – Ocean Water
20
Sample 4: Aluminum – Ocean Water
Sample 5: Aluminum – De-ionized Water
Sample 6: Aluminum – De-ionized Water
21
Sample 7: Carbon Steel – Lake Erie Water
Sample 8: Carbon Steel – Lake Erie Water
22
Sample 9: Carbon Steel – Ocean Water
Sample 10: Carbon Steel – Ocean Water
23
Sample 11: Carbon Steel – De-Ionized Water
24
Sample 12: Carbon Steel – De-Ionized Water
25
Appendix B: Camera Pictures
Below is the format in which all of the pictures are shown with the time progression as shown below.
After day 24, approximately 10mLof water was added to each sample dish.
Sample 1: Aluminum – Lake Erie Water
As the sample was put in, a bubble formed on the sample which can be seen as the corroded portion
above.
26
Sample 2: Aluminum – Lake Erie Water
The sample was photographed over a darker background to show the corroded material.
Sample 3: Aluminum – Ocean Water
The sample was photographed over a darker background to show the corroded material. The samples
were bumped which formed a bubble on the surface at one point. Like sample 1, additional corrosion
took place there.
27
Sample 4: Aluminum – Ocean Water
Sample 5: Aluminum – Deionized Water
28
Sample 6: Aluminum – Deionized Water
Sample 7: Carbon Steel – Lake Erie Water
29
Sample 8: Carbon Steel – Lake Erie Water
Sample 9: Carbon Steel – Ocean Water
30
Sample 10: Carbon Steel – Ocean Water
Sample 11: Carbon Steel – Deionized Water
31
Sample 12: Carbon Steel – Deionized Water
On day 24, the sample was disturbed and the water was spilled.
32
Appendix C: Raw Data
The table below details all of the weight measurements where initial weight is the weight of the coupon
on day 1. After the samples were left to corrode for 49 days, the samples were weighed after drying
(weight before brushing). The samples were then brushed using the procedure above in the ‘Measuring
Weight Loss’ section and weighed (weight after brushing). The ratio of the final weight over initial
weight shows the overall corrosion.
Table 3: Weight Measurements
Samples
1
2
3
4
6
Water
Lake Erie
Lake Erie
Ocean
Ocean
Deionized
Water
Deionized
Water
7
Lake Erie
8
Lake Erie
9
Ocean
10
Ocean
Deionized
Water
Deionized
Water
5
11
12
Type
Grooved
Aluminum
No
Aluminum
Yes
Aluminum
No
Aluminum
Yes
Initial
Weight (g)
0.14826
0.14135
0.13926
0.15136
Weight
Before
Brushing (g)
0.1567
0.1376
0.1332
0.1616
Weight
After
Brushing (g)
0.1464
0.1322
0.1297
0.1406
Difference
(g)
Final/Initial
0.0019
0.987
0.0091
0.935
0.0096
0.931
0.0108
0.929
Aluminum
No
0.14003
0.1328
0.1307
0.0093
0.933
Aluminum
Carbon
Steel
Carbon
Steel
Carbon
Steel
Carbon
Steel
Carbon
Steel
Carbon
Steel
Yes
0.16621
0.1533
0.1511
0.0151
0.909
No
0.39149
0.376
0.3495
0.0420
0.893
No
0.40073
0.3839
0.3693
0.0314
0.922
No
0.37741
0.3364
0.3295
0.0479
0.873
No
0.37796
0.3601
0.3392
0.0388
0.897
No
0.43241
0.3729
0.3461
0.0863
0.800
No
0.40722
0.3476
0.3253
0.0819
0.799
33
Table 4: Corrosion Rate Calculations
Length
Height (mm)
(mm)
1
12.83
10.04
2
9.16
8.85
3
12.16
9.98
4
8.89
9.22
5
9.73
11.72
6
9.10
10.07
7
9.61
10.53
8
9.65
10.64
9
9.49
10.67
10
9.69
10.56
11
9.61
11.36
12
9.49
11.44
Surface Area
(cm2)
1.288
0.810
1.213
0.820
1.141
0.917
1.012
1.026
1.013
1.023
1.091
1.086
Wf-Wo (g)
0.0019
0.0091
0.0096
0.0108
0.0093
0.0151
0.0420
0.0314
0.0479
0.0388
0.0863
0.0819
g/cm2 over
49 days
0.001
0.011
0.008
0.013
0.008
0.016
0.042
0.031
0.047
0.038
0.079
0.075
mil/year
1.61
12.27
8.56
14.26
8.88
17.90
45.09
33.26
51.39
41.14
85.94
81.96
34