Corrosion Rate and Galvanic Series in Material Engineering

This report discusses the measurement of corrosion rate for metallic materials and the development of a galvanic series for engineering metals in sea water. It also explores the use of the galvanic series in corrosion protection. The report provides procedures, techniques, and typical results for the experiments. The subject is material engineering and the document type is a report.

Running head: MATERIAL ENGINEERING
1
Material engineering
Name:
Institution:

MATERIAL ENGINEERING 2
Abstract
The report aims to measure corrosion rate for metallic materials and also to develop a galvanic
series for engineering metals in sea water. Also, the purpose of the paper is to understand how to
use the galvanic series in corrosion protection. Corrosion and its prevention is an important
aspect of materials studies. Procedures and techniques are presented in this paper describing how
to perform the experiments and equipment needed. Typical results are presented along with
explanations of the anticipated results. Potential pitfalls are also discussed.

MATERIAL ENGINEERING 3
Introduction
When metals are exposed in certain conditions such as presence of air or water, they experience
chemical transformation which reduces the metal reliability. Corrosion engineering is a
comparatively novel business devoted in reversing, decelerating and preventing the effects of
weathering on structure and materials (Marcus, 2011). They are accountable for advancing
treatment and coating that can be utilised to advance the metal resistance to deterioration
(Atkins, 2011).
Aim
To measure corrosion rate for metallic materials
To develop a galvanic series for engineering metals in sea water
To understand how to use the galvanic series in corrosion protection
Hypothesis
It is projected that when more reactive substance is coated around the nail, the nail will not be
corroded. It is also projected a metal having a higher positive potential becomes a more noble
metal.
Methodology
Corrosion rate determination
Materials
Laboratory equipment:

MATERIAL ENGINEERING 4
 Commercial bleach
 Beakers
 Digital balance
 Tweezers
 Gloves
 Safety glasses
 Apron (bring your own as bleach might discolour your clothing)
 Iron nails (without galvanising)
 Galvanised iron nails
Laboratory equipment:
 3.5% NaCl electrolyte about 250ml
 Multimeter
 Beakers
 Connectors with crocodile clips
 Stainless steel
 Aluminium
 Copper (or brass)
 Titanium
 Magnesium
 Galvanised steel nails
 Steel nails
 Ag/AgCl reference electrode

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Method
The weight of each nails were weighed and the three significant figures recorded. Beaker was
filled with sufficiency amount of commercial bleach and two nails were immersed in the beaker
and time of immersion recorded. The nails were left immersed for a week. After one week, the
nails were removed from the beaker using tweezers and rinsed thoroughly using water. Time of
removal was noted and then nails were dried immediately with air hose while wearing gloves.
The weight of the nails was recorded and changes on their surface noted.
Construction of galvanic series
250ml beaker was filled with sodium chloride solution. Reference electrode was immersed to the
solution. One metal was immersed in to the solution at time. Both reference and metal electrode
were kept apart and the solution was not allowed to touch the electrode contacts. Multimeter
was utilised to gauge the voltage between the metal and reference electrode.
Results

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specimen Surface
area
(cm3)
Initial
weight (g)
Final weight
(g)
Weight
loss (mg)
Exposed
time (hour)
Corrosion
rate (mm/yr.)
Iron nail 5.11 2.490 2.077 413 143 hours25
min
6.269
Galvanised
iron nail
484 2.661 2.629 32 143 hours25
min
0.0051
0.0254 mm/y= 25.4 microm/y=1 mpy
Rate of corrosion calculation
Formula for rate of corrosion in Mm /y = 87.6 x (W / DAT)

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A = surface area (cm2)
T = exposure time (hr)
W = weight loss (mg)
D = density (g /cm3)
Iron nail corrosion rate= 87.6 (413/7.874*5.11*143.42)
=6.269 mm/year
Galvanised iron nail corrosion rate=87.6 (32/7.874*484*143.42)
=0.0051mm/year
Silver-Silver chloride electrode
materials Potential difference (Volts)- salt solution at pH
value 7
Copper -195
Stainless steel -330
Titanium -185
Magnesium -1595
Galvanised piece -975
Aluminium -755

MATERIAL ENGINEERING 8
Discussion
Corrosion is the loss of substances due to electrochemical reactions. The corrosion rate of metals
is determined by their ability to “give up” electrons (Atkins, 2011). Mechanism of corrosion
protection by paint or inhibitors is based on this idea. This is well illustrated in the figure above
where the galvanised iron nail show minimal corrosion rate compared to the iron nail. In
corrosion cell, metals ions are generated from oxidation of metals passages from the anode to
cathode.
Metals when immersed in an electrolyte assume an electrical potential depending on its
propensity to corrode (Sastri, 2012). A metal that has a higher positive potential becomes noble
metallic. When a noble is connected to a less noble element, the less noble metal will likely
undergo more corrosion (Atkins, 2011). There are exceptions to this especially in this experiment
such as stainless steels, titanium and aluminium.
The most significant error in this experiment was failure to control the metal strips dimension.
This means that it is was more difficult to match various effectiveness of each material, given
that certain metals had a high mass which meant taking long time to react.
A further extension to the study would be to apply progressively huge substances to test whether
failure to protect iron from deterioration was due to its being completely used or other factors are
at play. Another approach of corrosion protection should be tested such as how painting iron
nails is at averting the redox reaction. It is also crucial to determine the effectiveness of
executing different protection approaches concurrently for improved protection and higher
efficiency level.

MATERIAL ENGINEERING 9
Conclusion
The paper has shown the corrosion rate for various substances, developed a galvanic series, and
demonstrated on how to apply the galvanised series in corrosion prevention. Understanding the
mechanisms in the electrochemical reaction is important to choosing the suitable and most active
preventative approaches for given situation. It is also crucial to note much protection can be
executed concurrently for improved protection and higher efficiency level.
Question 1
Corrosion rate causes the degradation of structures which can result to loss of production or
usefulness and in some scenarios, loss of life. Therefore, in the structure design, it is good to
incorporate physical barrier to avert direct contact with external surrounding. Anodizing is
important in structural design to offer wear protection and extra corrosion. Other methods to
boost corrosion resistance are substituting with inert material such as plastic.
Question 2
M=IZt
Where m= weight of metal (g)
I= current (A)
Z=electrochemical equivalent =a/nF (g/A-s)
A=atomic mass of rusting material (g)
F=faraday’s constant (96,500 A-s/mol/e)

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N= electrons transferred (mol/e)
T= reaction time (s)
Reaction in equation one
Fe Fe+2 + 2e (1)
Mass=0.413g
Time=143.42*60*60= 516,312 seconds
A=56 g
N=Electrons transferred (mol/e) =2
Therefore Z=56/ (2*96,500) = 0.00029
M=IZt
Hence, I=M/Zt
=0.413/ (0.00029*516,312)
Corrosion current (A) =0.00276A
Question 3
When two metals are linked electrically and are in contact with electrolyte, they create a galvanic
cell where the noble substance is cathodic and less noble material is anodic. The bigger the
surface area of anode matched to the cathode; the less the galvanic effects (Atkins, 2011).
Therefore, if the surface are of noble gas is increased, the galvanizing affects upsurges
Question 4

MATERIAL ENGINEERING 11
Electrolyte Isolation
One of the key aspects for galvanic deterioration to happen is an electrolyte, which has ions that
facilitate the reduction and oxidation reactions in the galvanic cell (Sastri, 2012). The above is
realised by utilising water-repellent substances that act as blockades between the electrolyte
solution and metal
Minimizing the Area Ratio
Many studies have demonstrated that the rate of galvanic corrosion is affected by the surface
area (S.A) of the cathode to the anode. The higher rate of reduction at the anode will be produced
as a result of the large S.A of the cathode in relation to the anode (Atkins, 2011).
Corrosion Inhibitors
Inhibitors are substances that are added to the electrolyte to suppress the chemical reaction that
result to galvanic reaction. The corrosion inhibitors that are more active are those that eradicate
the oxygen from the electrolyte, which minimises the reduction action occurring at the anode
(Atkins, 2011).

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Question 5
Figure 1: Pourbaix diagram for iron immersed in water
References

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Atkins, P. (2011). Reactions: The Private Life of Atoms. 1st ed. Oxford University Press, Oxford:
pp. 21-40.
Marcus, P. (Ed.). (2011). Corrosion mechanisms in theory and practice. 2nd ed. CRC press.
Retrieved from: https://books.google.com/books?
hl=en&lr=&id=8Kq7xVUpYuUC&oi=fnd&pg=PP1&dq=corrosion+theory&ots=Cap4Z
EDXUA&sig=EDYMGZUS1g_4bz3nTmzXC1XJnJQ
Sastri, V. S. (2012). Green corrosion inhibitors: theory and practice (Vol. 10). 1st ed. John Wiley
& Sons. Retrieved from: https://books.google.com/books?
hl=en&lr=&id=1xDur7RA9qgC&oi=fnd&pg=PR13&dq=corrosion+theory&ots=n_JAc
Zuew7&sig=1sQspukjSuKX1UOsfdF-kYlkxvM