Honours Project 40069944

THE DESIGN AND
MANUFACTURE OF AN
EXPERIMENTAL RIG FOR
CORROSION RATE
MEASUREMENTS USING
IMPEDANCE ANALYSIS
BEng (Hons) Mechanical Engineering
Joyce, Steve
40069944
Supervisor – Dr Mike Barker

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ABSTRACT
The following report highlights the methods used within the Bio-Logic software and hardware
in order to measure corrosion rates using Electrochemical Impedance Spectroscopy. The
main objectives are to research the methods to an appropriate level and design an
experimental rig around the appropriate set up based upon research. With the successful
design of the rig, manufacturing will take place in order to conduct corrosion rate testing upon
coated and uncoated samples. The uniform corrosion rates recorded were of a satisfactory
level and highlighted the effectiveness of the methods for use in industrial applications.
Further investigation was taken into Electrochemical Noise Analysis and localized corrosion
procedures where the results offered no effective conclusion. The limitations and problems
were then discussed and the full report concluded with reference to the original objectives of
the project.
Word Count 10506

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CONTENTS
Abstract...................................................................................................................................................1
Table of Figures.......................................................................................................................................5
Table of Graphs.......................................................................................................................................5
Table of Tables........................................................................................................................................5
Table of Equations ..................................................................................................................................6
Symbols/Abbreviations...........................................................................................................................6
Acknowledgements.................................................................................................................................7
1. Introduction ....................................................................................................................................8
2. Literature Review............................................................................................................................9
2.1. Basic Corrosion Mechanics .....................................................................................................9
2.2. The Use of Coatings With Respect To Corrosion ..................................................................10
2.2.1. Ceramic Coatings...........................................................................................................10
2.2.2 Polymer Coatings ..........................................................................................................10
2.2.3. Metallic Coatings...........................................................................................................11
2.2.4. Composite Coatings ......................................................................................................11
2.3. Coatings Tested.....................................................................................................................12
2.3.1. Nickel.............................................................................................................................12
2.3.2. Titanium Nitride............................................................................................................12
2.3.3. Silicon Carbide...............................................................................................................12
2.4. Processes of Selected Coatings.............................................................................................13
2.4.1. Ni...................................................................................................................................13
2.4.2. TiN.................................................................................................................................13
2.4.3. SiC..................................................................................................................................13
2.5. Corrosion Due To Salt Water ................................................................................................14
2.6. Corrosion Testing Settings ....................................................................................................15
2.7. Corrosion Testing Methods...................................................................................................15
2.7.1 Physical methods ..........................................................................................................15
2.7.2. Electrochemical Methods .............................................................................................16
2.8. Electrochemical Impedance Spectroscopy History...............................................................16
2.9. Electrochemical Impedance Spectroscopy In Industry.........................................................17
2.10. Recent Advancements In The Industry .............................................................................17
3. Design of experimental rig............................................................................................................18
3.1. Problem Analysis...................................................................................................................18
3.2. Design Brief...........................................................................................................................18

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3.3. Product Design Specification ................................................................................................18
3.4. Concept development...........................................................................................................21
3.4.1. Initial concepts..............................................................................................................21
3.4.2. Selection Table..............................................................................................................23
3.4.3. Design evolution ...........................................................................................................24
3.5. Detailed design .....................................................................................................................27
3.6. Modularity.............................................................................................................................29
3.7. Manufacturing ......................................................................................................................29
3.8. Product specification ............................................................................................................29
4. Methodology.................................................................................................................................30
4.1. Electrochemical Impedance Spectroscopy Basics.................................................................30
4.2. Hardware and Software Used...............................................................................................30
4.3. Test Set Up and Parameters .................................................................................................31
4.3.1. Test Parameters............................................................................................................31
4.3.2. Electrodes......................................................................................................................31
4.3.3. Testing Solution.............................................................................................................32
4.3.4. Sample preparation ......................................................................................................32
4.4. EC-Lab Software Practical Applications and Procedures ......................................................32
4.4.1. Linear Polarization ........................................................................................................32
4.4.2. Generalized Corrosion ..................................................................................................35
4.4.3. Constant Amplitude Sinusoidal microPolarization .......................................................36
4.4.4. Zero Resistance Ammeter.............................................................................................37
4.4.5. Cyclic Potentiodynamic Polarization.............................................................................39
4.4.6. Multielectrode Potentiodynamic Pitting ......................................................................40
4.4.7. Multielectrode Potentiostatic Pitting ...........................................................................41
5. Results...........................................................................................................................................42
5.1. Corrosion Rates.....................................................................................................................42
5.1.1. Linear Polarization Corrosion Rates..............................................................................42
5.1.2. Further Corrosion Rate Results.....................................................................................43
5.2. Polarization Resistance through Generalized Corrosion ......................................................44
5.3. Electrochemical Noise...........................................................................................................45
5.4. Pitting Potential ....................................................................................................................46
6. Discussions....................................................................................................................................47
6.1. Design evaluation..................................................................................................................47
6.1.1. Final Evaluation.............................................................................................................47
6.1.2. Design for Manufacture................................................................................................47

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6.1.3. Design for Assembly......................................................................................................47
6.1.4. Other Uses.....................................................................................................................48
6.2. Results........................................................................................................................................48
6.2.1. Corrosion Rates.............................................................................................................48
6.2.2. Polarization Resistance .................................................................................................48
6.2.3. Electrochemical Noise...................................................................................................48
6.2.4. Pitting Potential ..................................................................................................................49
6.3. EC-Lab Software use evaluation............................................................................................49
6.4. Project limitations.................................................................................................................50
7. Conclusions ...................................................................................................................................52
8. Recommendations........................................................................................................................53
8.1. Industry Applications ............................................................................................................53
8.2. Future work...........................................................................................................................53
9. Appendix .......................................................................................................................................55
9.1. Appendix - Design Portfolio .......................................................................................................55
10. References ................................................................................................................................58

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TABLE OF FIGURES
Figure 1 - Concept 1..............................................................................................................................21
Figure 2 - Concept 2..............................................................................................................................22
Figure 3 - Concept 3..............................................................................................................................23
Figure 4 - Week 7 Design ......................................................................................................................24
Figure 7 - Exploded View of Final Design..............................................................................................27
Figure 8 - Final Design Assembled ........................................................................................................28
Figure 9 - Experimental Rig Set Up .......................................................................................................28
Figure 10 - VMP3 Hardware (Low Impedance Setting Far Left) ...........................................................30
Figure 11 - TiN Samples, Worn Sample on Right ..................................................................................31
Figure 12 - EC-Lab General Procedure Window....................................................................................49
Figure 13 - EC-Lab Characteristics Tab Window ...................................................................................50
Figure 14-19 Complete Design Portfolio...............................................................................................55
TABLE OF GRAPHS
Graph 1 – LINEAR POLARIZATION (E V T)..............................................................................................33
Graph 2– LP (log(I) v E)..........................................................................................................................33
Graph 3 - LP (I V E) ................................................................................................................................34
Graph 4 – GENERALIZED CORROSION (E V T) .......................................................................................35
Graph 5 – CONSTANT AMPLITUDE SINUSOIDAL MICROPOLARIZATION ..............................................36
Graph 6 - CASP (I v t,f)...........................................................................................................................37
Graph 7 – Zero Resistance Ammeter (E v t)..........................................................................................38
Graph 8 - ZRA (E,I v t)............................................................................................................................38
Graph 9 - Cyclic Potentiodynamic Polarization (E v t)...........................................................................39
Graph 10 - CPP (E v log(I)) (Anderson Materials Evaluation, 2015)......................................................40
Graph 11 - MPSP (E v t).........................................................................................................................41
Graph 12 - AVERAGE CORROSION RATES OF SAMPLES........................................................................44
Graph 13- Polarization Resistance of Samples .....................................................................................44
Graph 14– NOISE RESISTANCE OF SAMPLES.........................................................................................45
TABLE OF TABLES
Table 1 - Selection Table.......................................................................................................................23
Table 2 - LP Corrosion Rates .................................................................................................................42
Table 3 - Further Corrosion Rates.........................................................................................................43
Table 4 - Polarization Resistance ..........................................................................................................44
Table 5 - Electrochemical Noise............................................................................................................45
Table 6 - Pitting Potentials....................................................................................................................46

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TABLE OF EQUATIONS
Equation 1 - Stern-Geary (Icorr, nA) .....................................................................................................34
Equation 2 - Stern- Geary (Rp, Ω)..........................................................................................................34
Equation 3 - Corrosion Rate (mmpy) ....................................................................................................35
Equation 4 - Noise Resistance (Rn, Ω)...................................................................................................38
Equation 5 - Standard Deviation for Rn ................................................................................................38
SYMBOLS/ABBREVIATIONS
EIS – Electrochemical Impedance Spectroscopy
I – Current
E – Potential
A – Amps
V – Volts
mm,cm – millimetre, centimetre
cm2 – area by cm
cm3 – volume by cm
OCV – Open Current Voltage (Eocv, Eoc)
Icorr – Corrosion Current
Ecorr – Corrosion Potential
Ewe – Working Electrode Potential
Ece – Counter Electrode Potential
Ba – Anodic Tafel Coefficient
Bc – Cathodic Tafel Coefficient
Rp – Polarization Resistance
Rn – Noise Resistance
Epit – Pitting Potential
Ni – Nickel
TiN – Titanium Nitride
SiC – Silicone Carbide
mA,nA – milliAmps, nanoAmps
CAD – Computer Aided Design
LP – Linear Polarization
GC – Generalized Corrosion
CASP – Constant Amplitude Sinusoidal micro-Polarization
VASP – Variable Amplitude Sinusoidal micro-Polarization
ZRA – Zero Resistance Ammeter

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EN – Electrochemical Noise
CPP – Cyclic Potentiodynamic Polarization
MPP – Multielectrode Potentiodynamic Pitting
MPSP – Multielectrode Potentiostatic Pitting
CPT – Critical Pitting Temperature
CM – Corrosimetry
HV – Victor’s Hardness
ACKNOWLEDGEMENTS
Module Leader - Martin Askey
Supervisor – Dr Mike Barker
Alan Davidson
2nd
Supervisor – John Sharp
Laboratory - Callum Wilson
Workshop - Brian Black
Dave Baxter
Sample Source - Mark Docherty

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1. INTRODUCTION
The materials science laboratory within the university requires the investigation of impedance
analysis in order to measure corrosion rates of materials. The report will focus on the use of
such an application with regards to the marine industry where material selection is key to
factors such as; safety, performance, economy and durability. Establishing such parameters
is key material selection with respect to design of components, maintenance of materials, and
establishing failure causes. This report will outline the use of the VMP3 potentiostat hardware
and EC-Lab electrochemical software, produced by Bio-Logic, in terms of corrosion testing for
the marine industry. This will be done through the Electrochemical Impedance Spectroscopy
process and its procedures. By first understanding all corrosion mechanisms including the
relevant electrochemical reactions, and the use of coatings as an aid to reduce the effect of
corrosion, an outline of EIS procedures will be determined and explored within the practical
section of the report. An in depth look into seawater corrosion will highlight the types of
environments that the marine industry is required to protect its corroding components from.
The determination of the coating types to be examined will allow the research of their specific
uses and particular corrosion effects within the marine environment, as well as their application
techniques, highlighting the theoretical procedure of each application and performance of
each coating. Research will explore the industry behaviour for corrosion testing based on the
type, either physical or electrochemical, as well as common practise for testing environments
based upon the specific industrial requirement of the investigation and test. A short section
will also highlight the advancements of EIS uses with corrosion within industry. A methodology
based around researched procedures, as well as those available with the testing software, will
be defined. The relevant process, results format and analysis, of each procedure will be
outlined for the laboratory to reference in future work. Based on the procedures outlined by
the methodology, a suitable rig will be designed. This will take into account important aspects
including safety, functionality and the ease of manufacture in order to produce an appropriate
rig within the time frame constraints of the project. Experimental work will be undertaken in
order to highlight the approachability of each procedure, and results recorded. With reference
to the researched behaviour of the relevant coatings within the marine industry, the procedures
will be critically discussed according to their performance in offering suitable results. The full
project will be further critically discussed based on the overall performance with reference to
the project proposal and outline created at the start of the project offering a conclusion to the
effectiveness of the project.

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2. LITERATURE REVIEW
2.1. BASIC CORROSION MECHANICS
Corrosion plays a very important role in engineering design and comes in many forms varying
substantially in different environments. The effects of corrosion are also substantially varied.
In some cases, only cosmetic degradation is seen for example in the tarnishing of silver. In
other cases, however, corrosion causes damage to the material's properties such as with the
corrosion in metals within electrical circuits. This corrosion will soon lead to the degradation
of the electrical conductivity of the material or could simply allow the connections within the
circuit to break making the entire circuit redundant. There are nine types of corrosion -
 General Attack Corrosion caused by a chemical or electrochemical reaction resulting
in uniform corrosion over the entire exposed surface.
 Localized Corrosion – i) Pitting occurs when a small hole or cavity is formed on the
surface of a material, this then creates a localized galvanic reaction with the
surrounding material.
ii) Crevice corrosion occurs with a stagnant micro-environment where the material in
the crevice is depleted of oxygen or subjected to acidic conditions.
iii) Filiform corrosion occurs under painted or plated surfaces where water breaches
the coating.
 Galvanic Corrosion occurs when two different metals are located together in a
corrosive electrolyte. One material will become the anode and the other the cathode.
The higher corrosion of the anode (or sacrificial material) will allow slower corrosion of
the cathode material.
 Environmental Cracking is the combination of environmental conditions such as
chemicals, temperature and stress which in turn can create stress corrosion cracking,
corrosion fatigue, hydrogen-induced cracking and liquid metal embrittlement.
 Intergranular Corrosion is the chemical or electrochemical attack on grain boundaries
within a material. This is often due to impurities in the metal which are more
concentrated around the grain boundaries.
 De-alloying occurs when a single material within an alloy is corroded independently.
This can result in a porous material such as copper when brass is de-zinctified.
 Fretting Corrosion is present in materials that are subjected to repeated wearing,
weight or vibrations. Commonly found in transportation and rotational/impact
machinery.
 High Temperature Corrosion can be caused by high temperature oxidization,
sulfidation and carbonization as well as in the low melting point compounds formed
during combustion.

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2.2. THE USE OF COATINGS WITH RESPECT TO CORROSION
Many widely used materials are unstable in the atmosphere and return to their original ores or
to a similar metallic compound. The use of coatings is highly beneficial to engineers as it
protects materials with superior properties, such as steel and its strength, from degradation
due to this environment. This in turn can significantly increase the lifespan of a component
and the materials it consists of. Coatings protect the base material by establishing a boundary
between itself and its environment (Suzuki, 1989). As long as the coating itself is resistant to
the environment, this boundary will work. Thus ceramic, polymer, metallic and some
composite materials are used, each with unique benefits.
2.2.1. CERAMIC COATINGS
Ceramic coatings are applied to metals to protect them from oxidation and corrosion at room
temperature, as well as at elevated temperature (Davis J. R., 2001). They can vary from use
in typical everyday products such as those in kitchen where porcelain enamels protect from
the heat and chemicals typically seen in those surroundings, to high performance applications
such as silicate glasses and oxides. Hot-Corrosion coupled with increasing levels of erosion
are the problems anticipated in industrial and marine gas turbines (Narnedra B. Dahotre,
1999). For example, Silicate glasses are prepared from glass powders and through their
resistance to extreme heats, have been found to be extremely beneficial in such applications,
as well as in aircraft, turbine and heat exchanger applications. These glasses are usually
applied through a spray-sinter process. Various oxides such as alumina, zirconia and
chromium oxides provide similar thermal protection while chromium also offers great wear
resistance aspects and alumina can offer great abrasion and corrosion protection. These
oxide coatings are commonly applied by flame spraying or plasma spraying.
2.2.2 POLYMER COATINGS
Polymer coatings have been an important part of corrosion protection for decades, most
notably in the painting of steel and iron for both aesthetic and corrosion resistance reasons.
Through the years however polymer coatings have become a keen part of research and
development programmes for many electronic companies, offering both safety in some cases
as well as corrosion protection where it has been recognized that conductive polymer coatings
on a steel surface stabilizes the potential of the substrate in the passivation region and thus
protecting it from corrosion (Marijana Kraljic, 2003). Current research is tending towards the
development of multi layered polymer coatings that could drastically decrease the corrosion
rates of both the components as well as the deterioration of the coating.

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2.2.3. METALLIC COATINGS
Polymer coatings have a downside where the surface connection (especially in simple painting
terms) is bad and blistering occurs. This requires the use and development of longer lasting
coatings for use in many building environments where life span of building components is key.
Galvanisation is now widely used to protect many weathered components such as street light
poles. This zinc metal coating is the primary example for a metal coating protecting steel or
iron from oxidisation and rusting. Metals are commonly used in specialist engineering
applications where high temperatures or chemicals are present and alloys are constantly being
developed to deal with the ever increasing demands on materials in this time of substantial
engineering development.
2.2.4. COMPOSITE COATINGS
Composite coatings are used to enhance the material properties of a coating by mixing two or
more different materials. Processes such as electrodeposition with a co-deposit allow
materials such as Nickel and Alumina to cover the surface of a substrate. The low hardness
and high ductility of nickel can then be manipulated by the volume of co-deposited alumina to
create a harder and tougher coating material. Composite coatings offer the opportunity to
achieve fantastic mechanical properties with simpler processes than that of plasma spraying
and other high cost procedures. The deposition matrix (usually metallic) can also potentially
offer electrical conductivity that can be useful within the electronics industry (Saha, Mohamed,
& Khan, 2011).

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2.3. COATINGS TESTED
2.3.1. NICKEL
One such metal is nickel which, in relation to steel, offers better toughness, better strength at
high and low temperatures, and a range of special magnetic and electronic properties. Nickel
is resistant to many corrosives and is a natural for alkaline solutions therefore it is used in
most tough corrosion problems. Another important aspect of a nickel coating is it's resistance
to stress-corrosion resistance due to the nickel content within a stainless alloy exceeds 10%.
With the exception of use with sulphur-bearing gases, nickel offers a good base for alloys
required to operate at high temperatures. Many of these benefits can of course also be seen
in nickel coatings too. A correlation has been found in research work that supports the
conclusion that nickel coatings deposited with a lower Ph level have a lower corrosion rate.
2.3.2. TITANIUM NITRIDE
Titanium is a reactive metal and relies on its natural protective film to protect it from corrosion.
It is extremely good with chemical resistance and thus can be used very well in resistance to
chloride-salt, hypochlorite’s, wet chloride and nitric acid solutions. It's resistance to crevice
and pitting due to salts is extremely good. Special care must be taken when using titanium in
industry however because contamination through preparation or contact with a corroding
metal has catastrophic effects on the titanium's structure.
2.3.3. SILICON CARBIDE
Silicon Carbide coatings are used most commonly for their superior resistance to wear and
great hardness ratings. For example an electroless nickel material has a hardness of 1000HV,
while an electroless nickel and silicon carbide composite has a value of around 1300HV.
Corrosion resistance of silicon carbide compounds are however significantly lower than that
of electroless nickel coatings. The electroless nickel matrix contains a large amount of co-
deposited inhibitor which in turn reduces the passivity and therefore corrosion resistance of
the compound. Due to the particulate form of the coating thus exposing steel that corrodes in
galvanic form with the Nickel. This galvanic reaction around the phosphides, nickel and
particles means silicon carbide compounds are also subject to cracking over the coating.
(Davis J. R., 2000)

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2.4. PROCESSES OF SELECTED COATINGS
2.4.1. NI
Electroless nickel plating is used with two of the coated samples examined in this report
including the co-deposition of SiC. Electroless Nickel plating is a chemical reduction process
in which a reducing agent is oxidised and Nickel ions are deposited onto the substrate (steel
sample) surface (Taheri, 2003). Typical coating processes for a steel substrate involve the
following steps, cleaning, de-oxidizing and autocatalyzing. Surface cleaning is critical to
ensuring effective coatings and usually involves the pre-treatment using a series of alkaline
cleaners that must be rinsed off with water multiple times to ensure no chemicals are adhered
to the surface, as well as de-greasing to remove oils. Surface oxidization and unwanted metal
is then removed through chemical attack using acid pickling solutions (Hajdu, 1990). The
most commonly used reducing agents are that of sodium hypophosphite and formaldehyde
which reduce metallic ions to the metal state. The first layer of nickel which is deposited acts
as a catalyst for the process. Since the reaction is therefore autocatalytic (Schlesinger, 2010),
a linear relationship between coating thickness and time is present. The deposition process
starts on the catalytic surface and works through diffusion of chemicals to the deposited
surface and the by-products, such as hydrogen, away from the surface. Electroless Nickel
coatings have many applications due to excellent mechanical, electrical and corrosion
resistance properties. Typical coatings can be applied to many substrate materials and onto
intricate components where such coatings offer uniform plating over edges and projections.
2.4.2. TIN
The electroless nickel procedure was manipulated for the use of titanium nitride, where the
same basic principle is used except by depositing the titanium instead of the nickel on the
surface of the substrate.
2.4.3. SIC
Co deposition of Silicon Carbide particles can be easily incorporated into the electroless nickel
solution where the deposition of nickel carries with it the ceramic particles, creating a
consistent concentration of particulate material coating on the steel substrate. The deposition
of finely dispersed particles in a metal matrix by electroless co-deposition processes led to a
new generation of composites. These composite deposits present particular chemical and
physical properties that each component, taken separately, does not possess (A Grosjean,
2000).

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2.5. CORROSION DUE TO SALT WATER
For the purposes of this report we will look at the effect of seawater on uncoated and coated
materials. Sea water is slightly alkaline with a salt content of around 3.4%, this can cause
galvanic and crevice corrosion and breaks down the oxide film that all metals (except gold)
have when in air (Thomas, 1996). The degree of corrosion is determined by oxygen content,
temperature, depth and the velocity of flow a component may be moving through the water.
Other factors include specific conductivity, the content of calcium, magnesium and pollution
as well as biological activity and the possible treatment of the water. These can all be partially
defined by geographical location.
 Natural Sea Water – where outside influences such as pollution are neglected and the
natural composition of sea water is used.
 Brackish Coastal Sea Water – differences in oxygen, chloride and pollution will be seen
as well as changes in specific conductivity and levels of organic compounds.
 Polluted Sea Waters – the combination of lower oxygen levels and the presence of
sulphide ions and ammonia can result in decreased Ph levels.
 Stored or Recirculated Sea Water – changes in Ph and oxygen levels will occur over
time as well as change in biological activity due to storage and manipulation.
 Synthetic Solutions – characterised by the absence of all organic, biological and
bacteriological species and thus will not reflect real life reactions with samples.
Corrosion in sea water will be seen in different ways with a mixture of both uniform and
localized corrosion. The first and most evident corrosion method is that of general uniform
corrosion due to the reaction of the surface with the environment. There are however many
other forms of corrosion found with seawater. These include bimetallic, crevice and erosion
corrosion as well as pitting, intergranar and selective attacks, stress corrosion cracking and
corrosion fatigue (IJsseling, 1989). The chemical reaction present with rust which includes all
ferrous based materials including the steel sample examined in this report is as follows,
Fe(OH)2+ H2O + O2→ 4Fe(OH)3 (Fontana, 1986).
Measuring corrosion rates within these conditions is especially difficult with the classic
methods of density and weight comparisons not giving much insight into the actual corrosion
reaction mechanics. With the development of Electrochemical Impedance Spectroscopy, we
can now look at the characteristics of the reactions as well as denote meaningful information,
most notably, a samples corrosion rate.

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2.6. CORROSION TESTING SETTINGS
Since corrosion plays such a major role in industry where safety, sustainability and economic
factors are all greatly affected, the measurement of corrosion is key to determining the
appropriateness of a design and selection of material. Testing can be found in three separate
environments, in laboratory testing, a semiworks setting, and in field tests. Laboratory tests
can be defined as small specimens with defined conditions tested to the best convenience
possible. These tests serve as screening tests to determine the appropriability of a material
for an application. Semiwork testing is the most desired setting where testing takes place in
a small scale set up, mirroring the environment of the intended large scale application. This
allows a great insight into how materials and components will act in reality and will in most
cases finalize the simulation of a plant and prove either its failure, or success. Plant testing is
commonly used to evaluate better materials or components based on its actual application.
These three settings can be sequenced in order to offer a logical evaluation from the material
selection, to testing and system monitoring (Fontana, 1986).
2.7. CORROSION TESTING METHODS
2.7.1 PHYSICAL METHODS
Visual inspection is a fundamental and key corrosion observation. Usually quantifying this
observation comes from measuring the weight loss after a period of time, problems arise
however when accuracy is key and localized corrosion must be quantified. This localized
problem raises the question of whether material appearance or strength is most important to
the application. If appearance is of importance, the frequency of pits or crevices can be
measured using microscopes, the higher the frequency, the more irregular the surface.
Strength applications require the measurement of depth and diameter of the crevices, or
arguably, the crevice with the greatest of these attributes. Feeler gauges and ultrasonic
methods can easily measure shallow depths, and with small, isolated pits, the limited depth of
focus on visible-light microscopes can be exploited to measure the distance between the
surface and the pit bottom. Problems arise when long, narrow and deep crevices must be
examined. These can only be measured by metallographic section which in turn will destroy
the component.

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2.7.2. ELECTROCHEMICAL METHODS
Electrochemical corrosion testing methods offer the opportunity to derive values for both
uniform and localized corrosion rates as well as chemical reaction behaviour without the need
to destroy the sample. The determination of potential slopes and measurement of current let
us find corrosion rates as a penetration rate (mm/yr) value. Other methods are used again
through the determinations of potentials and resistances to find reaction behaviour as well as
localized corrosion causes and values. This report will go further into these measurements
based upon the procedures outlined by the VMP3 device upon which these experiments will
take place.
2.8. ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY HISTORY
Over the past few decades, Electrochemical Impedance Spectroscopy has become the most
powerful electrochemical technique for determining reactions such as corrosion. The basis of
EIS can be seen in the work on operational calculus by Heaviside, and the diffusion process
work by Warburg (MacDonald, Reflectrions on the History of Electrochemical Impedance
Spectroscopy, 2005). However, the results of Epelboin in Paris through the 1960’s forced EIS
to the forefront of corrosion analysis. Through a partnership between Epelboin and
SOLARTRON Instruments Ltd, the frequency response analyser (FRA) was developed and
allowed impedance to be analysed at frequencies as low as 0.1 mHz, much like the first
potentiostat developed two decades earlier. Since then, EIS has progressed to contribute
more to our understanding of corrosion reaction mechanisms than any other process. This
theoretical investigative work was used to develop techniques for deriving the impedance
functions used to represent complex reaction mechanisms. These included coupling between
charge transfer, chemical, and mass transfer processes. Theoretical work has since
developed practical algorithms for performing Kramers-Kronig transforms, where the
amplitude of a response can be broken down to represent both the real resistance, and
imaginary impedance functions (Harbecke, 1986), for assessing the viability of impedance
data by testing for compliance with the constraints of the linear systems theory, the definition
of alternate perturbation/response transfer functions, and the development of harmonic
analysis. Fundamental outstanding issues are still present however, such as the
determination of the extent to which transfer function analysis need to conform to the linear
systems theory constraints (MacDonald, A Brief History of Electrochemical Impedance
Spectroscopy, 2002).

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2.9. ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY IN INDUSTRY
Electrochemical Impedance Spectroscopy is primarily used within the research areas of
material science and industry. With such a fragile test procedure where parameters must be
met with low levels of error in order to measure accurate readings, performing a test in the
middle of a stormy north sea is not ideal. The procedure is therefore commonly used in
laboratory, research based environments where parameters can be closely met. A high
investment is also required for companies wishing to use the procedure with purchases
including expensive hardware, software, rigs, electrodes (both reference and noble), solutions
and samples as well as the expertise to analyse results. EIS offers a great number of highly
accurate results including both uniform corrosion values, and localized corrosion types and
values. These results are invaluable to companies looking into material selection for
component design in harsh environments. Advanced procedures involve the control of
temperature and flow rate within the test solution which offer amazing detail into types of
corrosion and values present in components such as high temperature fluid pipes. One major
downfall of the procedure is the inability to examine samples without a testing solution contact
between the potential readings. Therefore, for instance salt spray corrosion cannot be tested
other than through surface examinations and physical changes such as weight loss. Based
on the limitations experienced, EIS is commonly used in semiwork and laboratory
environments for the evaluation of a material in a particular environment, or for research
applications evaluating the performance of new developments.
2.10. RECENT ADVANCEMENTS IN THE INDUSTRY
Although Electrochemical Impedance Spectroscopy has limitations on where the procedures
can be conducted, recent developments are trying to incorporate the highly detailed and
accurate test into the field and real time scenarios. One such step can be seen with the design
of the ACM Instruments Field Machine. This brings the potentiostat hardware and software
required for EIS into the field in a portable format. This system is however still subject to the
same limitations found in the laboratory where samples will need to be cut and the testing
parameters monitored closely. This does however open opportunities for on-site consultancy
offering quick and accurate results to field problems (Instruments, 2015). Significant
developments have however been made in the procedural aspects of EIS. These include the
validation of electrochemical impedance spectra (Ehm), a new approach to investigating the
origin of the faradaic time constants of solid electrodes (Antono-Lopez, 2001), and detailed
analysis of EIS data for mass transfer controlled electrochemical systems (Pauwels, 2010).
Significant developments are also seen in polymer based investigations, to address specific
corrosion phenomena, and the application of Electrochemical Noise Analysis for the
evaluation of a number of different corrosion phenomena (Mansfield, Huet, & Mattos, 2001).

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3. DESIGN OF EXPERIMENTAL RIG
3.1. PROBLEM ANALYSIS
This project requires the design and manufacture of a laboratory rig in order to conduct
experimental work into Electrochemical Impedance Spectroscopy procedures. The rig
should primarily offer a stable environment in order to conduct accurate and reliable
experiments which can in turn highlight the methodology of a series of EIS procedures.
3.2. DESIGN BRIEF
A single three electrode rig must be designed comprising of a working, counter and reference
electrode. Differing testing solutions must be considered in order to increase the adaptability
of the rig. The design project should be completed before the interim break in order to ensure
the experimental work can be completed within the full project time frame. Materials and
technologies are based upon the universities workshop limited scope including basic materials
and manned machinery.
3.3. PRODUCT DESIGN SPECIFICATION
Environment
The rig embodiment should be designed around a dry, room temperature environment. The
experimental solution components should be designed around the safe containment of a
series of harsh, aggravating chemicals such as sodium chloride and Hydrochloric acid.
Life span
Due to the low expected use, the life span of the rig should be excessive, around ten years.
Maintenance
The university workshop should be able to conduct maintenance work if required, thus a
simplistic design is desired. Components should also be independent, allowing the
replacement of a single component rather than the whole rig.
Cost
Due to the high cost of the reference electrode (£85), and the budget of around £100, the rig
should cost around £15.
Production Quality
A rigid and stable rig is required, therefore appropriate tolerances must be used. The materials
used must also be of an appropriate standard to deal with the harsh experimental solution.
Manufacturing constraints

19
The university workshop determines the manufacturing constraints. Thus most in house
components must be manufactured using manual machines such as lathes, milling machines
and pillar drills. There is scope for some outsourced components such as standard nuts, bolts
and washers.
Size
The size of the rig should be approximately 100x100x100mm based on sample sizes
(30x40x3mm), while also leaving scope for unconventional samples to be tested. The rig
should also have an appropriate centre of gravity for stability due to the use of potentially
harmful solutions.
Weight
The weight of the rig should be somewhat high for the size of rig to offer stability due to, again,
the containment of potentially harmful solutions.
Appearance
The only notable aesthetic property of the rig is that of a clear containment tube. This should
allow a sight of all the electrodes and allow future users a clear view of the experimental set
up.
Materials
A clear material such as Perspex which also offers the chemical resistance to the experimental
solutions should be used for the rig containing tube. All embodiment materials should be
efficiently cost effective, strong, and offer a suitable life span for the rig.
Standards
BS308 (BS8888) and ISO TC/213 standards should be used for engineering drawings with
appropriate tolerance methods.
ISO TC 10 should be consulted to complete the design documentation.
Ergonomics
The rig should be designed around a suitable level of safety for the user due to the use of
harmful substances. The rig should also be designed to be set up and broken down very
easily and quickly offering experiments to be completed quickly. A simplistic design should be
established for the quick and efficient manufacturing of the rig within the time frame with
respect to the manufacturing constraints.
Quality and Reliability
The rig should be extremely reliable due to the use of potentially harmful solutions. Reliability
must also take into account offering a reliable testing environment throughout the rig's life,
through its cleanliness and geometrical aspects such as the area of sample examined.
Time scales
The design aspect of the project has a deadline of around 4-5 weeks, then manufacturing
must take place either before, or during the interim break in order to provide a suitable rig for

20
experimental use after the interim break. Testing of the rig will occur throughout the
experimental procedures.
Testing
Testing will comprise of using the rig in experimental procedures and monitoring its suitability
based on its effectiveness in providing a reliable environment, as well as safety parameters
such as any experimental solution leakage.
Safety
Primary safety concerns should revolve around the use of the experimental solution and it's
containment as well as filling and emptying. Further safety considerations should also be
taken around the embodiment design and any sharp edges involved in this. Any clamping
mechanism must also be evaluated for safety when in use.
Project constraints
The main constraint on the project is the time frame. The university workshop also inflicts
some constraints, however it will be more than adequate for the size of rig and the mechanisms
it will involve.
Documentation
Further documentation will include a product specification, outlining the scope of the rig and
its full intended application use. A design evaluation will also be included to determine the
success of the design project.
Disposal
The rig should focus on using recyclable materials in order to recycle the rig once it becomes
redundant. The use of standardized components will also allow certain components to be
used elsewhere without being recycled.
Competitors
Companies such as Bio-Logic offer corrosion testing rigs based solely on their hardware's
requirements. With the design of an independent rig, the scope for experimental procedures
is increased and the project should aim to offer this at a much lower cost than that of
commercial rigs.

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3.4. CONCEPT DEVELOPMENT
3.4.1. INITIAL CONCEPTS
Concept 1
The first concept is that of the commonly found corrosion test rig found in industry, featuring a
U-shaped containing tube, a clamping mechanism on the bottom, and holes at the top of the
rig for electrodes.
FIGURE 1 - CONCEPT 1

22
Concept 2
The second concept is derived from the first commercial inspired concept, however
incorporating simpler components and geometries.

23
Concept 3
The third concept portrays the very basic three electrode set up principle by offering the
solution, and three electrode connections in a very simplistic manner.
3.4.2. SELECTION TABLE
TABLE 1 - SELECTION TABLE
Concept 1 Concept 2 Concept 3
Functionality 5 5 5
Safety 4 5 1
Manufacturability 2 4 2
Production Time 2 3 3
Cost 1 3 5
Ease of assembly 4 4 4
18 24 20
Based on the selection process, Concept 2 shall be developed further.

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3.4.3. DESIGN EVOLUTION
Week 7 – This first CAD visualization builds on the primary concept design and its set up
procedure. It also highlights questions around the control electrode and its seal to the
containing tube. The testing solution would also be difficult to implement due to a very
accurate volume having to be poured in to ensure both electrodes were touching. A possible
solution was to use the rig on its side, however this also gave the problem of pouring in the
testing solution in the first place. The reference electrode has not been taken into account and
with further research, it was clear that this design would not work with the two electrodes
creating seals on either end.
FIGURE 4 - WEEK 7 DESIGN

25
Week 8 – The control electrode was chosen to be in rod in form to allow an open ended
containing in order to pour the solution in. The number of clamps could then be significantly
decreased due to them not being required for the control electrode. With the overall clamping
nature of the rig, the working electrode clamps were decreased to one in order to simplify the
design, while maintaining an electrical connection. A cap was designed in order to hold the
control and reference electrodes.

26
Week 9 – The engineering drawing for all components were completed highlighting the
components required to be manufactured, and the ones to be outsourced. This full
manufacturing drawing portfolio (Appendices 1) was used to liaise with the workshop and
dictate the manufacturing process, while simplifying and optimising component geometries.

27
3.5. DETAILED DESIGN
Week 11 – Rig was completed by workshop and the full completed design is as follows.
FIGURE 7 - EXPLODED VIEW OF FINAL DESIGN

28
FIGURE 8 - FINAL DESIGN ASSEMBLED
FIGURE 9 - EXPERIMENTAL RIG SET UP

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3.6. MODULARITY
The modularity of the final design can be split into three separate applications. That of the
end bases, used to contain the electrodes and provide relevant electrical connections. The
containing assembly comprising of the sample and the containing tube, used between the two
bases to safely hold the testing solution. Finally the clamping mechanism, used to complete
the rig and hold all the components together.
3.7. MANUFACTURING
Outsourced materials comprised of the containing tube, threaded rod, screws, the nut and the
bolt. All other components where produced in house. The two bases were manufactured
using a milling machine and pillar drill to produce the square edges and holes respectively.
The containing tube material had to be manipulated with the use of a lathe to create a v-groove
on one end where the O-seal could be glued in. The O-seal was manipulated to size with the
use of an O-seal cutter. The clamp threaded rod was cut to size and tapered on the end, then
glued into the base hole. The actual clamp piece was produced with the use of a milling
machine throughout. The clamping rods where produced cut to size and with the use of a
lathe, the end holes were drilled. A thread tap was then used to produce the threaded ends.
The final electrode holding cap component was produced mainly with a lathe, with the holes
being drilled with a pillar drill.
3.8. PRODUCT SPECIFICATION
The final rig can be used for three electrode electrochemical corrosion testing procedures. It
offers the safety required to hold dangerous testing solutions, therefore it offers great scope
for manipulating the testing parameters. The rig can be used with varying sizes of testing
samples with the use of an adaptable sample clamping mechanism.

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4. METHODOLOGY
4.1. ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY BASICS
Electrochemical Impedance Spectroscopy is conducted by manipulating potentials and
currents through electrodes in an electrochemical reaction and measuring the appropriate
responses using a potentiostat. This can offer values on applications such as battery capacity
and performance, super capacitor performance, photovoltaic and fuel cell characteristics and
corrosion.
4.2. HARDWARE AND SOFTWARE USED
The hardware used in this project was the Bio-Logic VMP3. The VMP3 is a research grade
multi-channel, multi-user potentiostat which includes 16 independent channels with a unique
counter electrode – ground connection offering the possibility of multielectrode experiments.
Each channel offers two analogue inputs and one analogue output for the control of external
devices such as rotating electrodes. With the corrosion application, the low impedance setting
is used which allows reading to be taken at 1 nA. The device is controlled by a PC USB
connection and the EC-Lab Software. The EC-Lab software includes all techniques used
across all of Bio-Logic's devices and offers the simulation, analysis and fitting of techniques
and their results.
FIGURE 10 - VMP3 HARDWARE (LOW IMPEDANCE SETTING FAR LEFT)

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4.3. TEST SET UP AND PARAMETERS
Electrochemical cells can be analysed using a variety of different set up's including two, three,
four or even more electrode set ups. These each provide their own benefits from the two
electrode set up requiring only a little investment, to the four electrode set up providing the
opportunity for the use of two measuring electrodes, and two stimulating electrodes. This
offers more accurate results compared to the two electrode system when monitoring multi-
electrode systems. With the corrosion experiment, the three electrode set up is suitable as it
determines the working electrode, the material in which the electrochemical reaction is
occurring. The counter electrode is used to close the current circuit within the cell, while also
measuring potential and current difference readings. The reference electrode is independent
of the electrochemical reaction due to its noble form and offers a known and unchanging
potential that can be used as a reference in the cell to dictate potential sweeps and control.
4.3.1. TEST PARAMETERS
In order to conduct a primarily investigative experiment in order to assess the procedures used
within the EC-Lab hardware and software, the following parameters have been determined.
4.3.2. ELECTRODES
Working Electrode – Samples – 2 x uncoated samples
2 x Nickel coated samples
2 x Titanium Nitride coated samples
2 x Silicon Carbide samples
2 x Nickel coated samples after wear resistance test
2 x Titanium Nitride coated samples after wear resistance test
2 x Silicon Carbide coated samples after wear resistance test
FIGURE 11 - TIN SAMPLES, WORN SAMPLE ON RIGHT
Counter Electrode – 1mm Pure 99.999% Silver Wire
Reference Electrode – Ag/AgCl Silver Chloride Electrode +0.210 V at 25C reference potential

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4.3.3. TESTING SOLUTION
An artificial seawater testing solution was selected in order to mirror the marine environment
this project covers. Around 3.5% by volume of sodium chloride was mixed with tap water in
order to simulate this substance.
The test was conducted under room temperature with negligible wind effect and solution
velocity.
4.3.4. SAMPLE PREPARATION
Samples were prepared for analysis by surface inspection and cleaning if required using water.
Degreasing agent was used on an uncoated steel sample to remove oil. Samples were then
clamped into the rig ensuring the O seal stopped solution leakage. The mild steel clamp was
then applied with the electrical connection between itself and the washer. The solution was
then poured in to an appropriate level (around 15.7cm3, or around 50mm in height inside the
containing tube) and the two further electrodes placed and electrical connections made.
4.4. EC-LAB SOFTWARE PRACTICAL APPLICATIONS AND PROCEDURES
This project uses various procedures offered by the hardware and software in order to
formulate accurate recommendations around the operation and effectiveness of the EC-Lab
system. These procedures measure both uniform and localized corrosion (Bio-Logic, EC-Lab
Software User's Manual, 2014) (Bio-Logic, Software Applications and Tecniques, 2014).
4.4.1. LINEAR POLARIZATION
Background
This technique is particularly designed for determining the polarization resistance in corrosion
cells and the corrosion current. It takes potential steps around the corrosion potential in order
to plot current density vs potential, and the Log (current) vs potential curves.

33
The corrosion potential (Ecorr) is determined through an open circuit analysis of the cell. From
this the software induces a potential scan around the Eoc and current readings are then taken.
Visualization of results and Corresponding fits
Current reading can be plotted on a log (I) vs Ewe graph as follows.
The software assumes that the all electrochemical systems are tafelien, meaning the current
flowing in the electrode is only limited by the electron transfer and not by mass transfer. The
anodic and cathodic Tafel coefficients which represents the corresponding current values
within the system can be found from this visualization based upon the two linear regressions.
With the manipulation of the limitations of the two linear fits, the Tafel curve can be best fit in
order to mirror that of the results. The middle part of the graph where log (I) is at its lowest, is
also the position of the corrosion potential and the corrosion current.
GRAPH 1 – LINEAR POLARIZATION (E V T)
GRAPH 2– LP (LOG(I) V E)

34
The anodic region of the cell is determined as when a ferrous atom at the metal surface
dissolves into moisture film leaving a negative charge in the metal. The cathodic region is
determined as a depolarizer removes electrons from the metal. The larger the difference
between the anodic and cathodic potentials, the larger the corrosion current. From this
manipulation the software determines the two Tafel constants Ba and Bc, the corrosion
potential Ecorr, and finally the corrosion current Icorr based upon the manipulation of the
Stern-Geary equation,
EQUATION 1 - STERN-GEARY (ICORR, NA)
𝐼 = 𝐼𝑐𝑜𝑟𝑟 exp (
𝑙𝑛10(𝐸 − 𝐸𝑐𝑜𝑟𝑟)
𝐵𝑐
) − 𝐼𝑐𝑜𝑟𝑟exp⁡(
−𝑙𝑛10(𝐸 − 𝐸𝑐𝑜𝑟𝑟)
𝐵𝑎
)
The current readings are also displayed on a Current vs Potential graph. From this the
software uses an Rp fit in order to determine the polarization resistance of the material.
By determining the Tafel coefficients found previously, and the manipulation of the range, the
software calculates the inverse of the linear fir slope as the Polarization Resistance as the
user matches the Corrosion Potential with the one found in the Tafel fit previously. An Rp fit
is again calculated through the Stern-Geary relationship seen here,
EQUATION 2 - STERN- GEARY (RP, Ω)
𝑅 𝑝 =
𝐵 𝑎 𝐵 𝑐
𝐼 𝑐𝑜𝑟𝑟(𝐵 𝑎−𝐵 𝑐)𝑙𝑛10
+ 𝐸𝑐𝑜𝑟𝑟
Analysis of results
From the corrosion current found through the software, the corrosion rate of a material can
then be calculated where
GRAPH 3 - LP (I V E)

35
EQUATION 3 - CORROSION RATE (MMPY)
𝐶𝑅 =
𝐼𝑐𝑜𝑟𝑟⁡𝐾⁡𝐸𝑊
𝐷⁡𝐴
CR is in millimetre per year (mmpy) or mill inches per year (mpy)
Icorr corrosion current (in A).
K constant that defines the units of the corrosion rate.
EW equivalent weight (in g/equivalent). Defined as the molar mass of the oxidized metal
divided by the number of electrons involved in the dissolution reaction. For instance, for the
corrosion of iron Fe → Fe2+ + 2e- EW = 55.85/2 = 27.925 g/equivalent.
D density (in g/cm3).
A sample area (in cm2).
Where K = 3272mm/ (A cm year), CR = mm/year (mmpy)
The Polarization Resistance is key to the corrosion characteristics of a material because it
measures the resistance to the flow of current in a cell caused by chemical reactions. Hence,
the higher the Polarization Resistance, the greater the resistance to corrosion reactions.
4.4.2. GENERALIZED CORROSION
Background
The generalized corrosion technique is used for the measurement of uniform corrosion based
on the assumption that the anodic dissolution is uniformly distributed over the entire sample
surface. This technique uses a half potential sweep around the Eoc and again, the current is
measured as the potential changes.
GRAPH 4 – GENERALIZED CORROSION (E V T)

36
Visualization of results, Corresponding fits and Analysis
Similar to Linear Polarization, the Generalized Corrosion technique relies on the log (I) vs Ewe
graph to determine the Tafel parameters and corrosion current through a Tafel fit, as well as
the Current vs Ewe graph to determine the Polarization Resistance through a linear fit.
These results can then be analysed to determine the corrosion properties of materials through
the corrosion rate and the polarization resistance.
4.4.3. CONSTANT AMPLITUDE SINUSOIDAL MICROPOLARIZATION
Background
Constant Amplitude Sinusoidal microPolarization is used to determine the corrosion
characteristics of a Tafelian system. A sinusoidal voltage is applied around the open circuit
potential at a low amplitude and frequency. Based upon the Fourier transform, which
decomposes the signal into the frequencies that make it up, the amplitude of the harmonics
can be examined to calculate the corrosion parameters. This technique is faster than the
Polarization techniques highlighted earlier, however accuracy can suffer due to the greater
voltage window examined. CASP does however offer a less damaging approach to the
sample than that of polarization techniques.
Visualization of results
From the Fourier transform graph, the harmonics of the signal can be seen. This is done
through the CASP fit option within the software and from this the software can calculate the
corrosion parameters.
GRAPH 5 – CONSTANT AMPLITUDE SINUSOIDAL
MICROPOLARIZATION

37
Analysis of results
As before the corrosion current found through the Fourier transform can be used to calculate
the corrosion rate of the material. All corrosion coefficient values are however not calculated.
4.4.4. ZERO RESISTANCE AMMETER
Background
The Zero Resistance Ammeter procedure is made to perform electrochemical noise
measurements. Electrochemical Current Noise is the spontaneous current fluctuations that
occur between two electrodes held at the same potential due to chemical reaction behaviours.
The process consists of applying zero volts between the working and counter electrodes and
measuring the current and potentials against that of the steady state reference electrode. An
initial open circuit voltage procedure takes place first, followed by the ZRA, this is repeated for
a set amount of times.
GRAPH 6 - CASP (I V T,F)

38
Visualization of results and Analysis of results
Results can be visualized through the (E, I) vs time graph.
The software then uses the standard deviation technique in its ENA tool to determine the Noise
resistance. Where
EQUATION 4 - NOISE RESISTANCE (RN, Ω)
𝑅 𝑛 =
𝜎 𝐸𝑊𝐸
𝜎𝐼
and 𝜎𝐼⁡and 𝜎 𝐸𝑊𝐸 is obtained from
EQUATION 5 - STANDARD DEVIATION FOR RN
𝜎𝑥 = √
1
𝑁−1
⁡⁡ ∑ (𝑥 − ẍ)2𝑁−1
𝑖=0 where 𝑥 = ẍ is the average of the parameter.
GRAPH 7 – ZERO RESISTANCE AMMETER (E V T)
GRAPH 8 - ZRA (E,I V T)

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Electrochemical Noise constitutes events such as film rupture and discrete events such as
metal dissolution and hydrogen discharge with gas bubble formation and discharge.
Measuring this therefore gives a great insight into the level of corrosion behaviour that a
material is subject to.
4.4.5. CYCLIC POTENTIODYNAMIC POLARIZATION
Background
Cyclic Potentiodynamic Polarization moves into the measurement of localized corrosion
mechanisms and is used to evaluate the pitting characteristics of a material. The potential is
swept around one cycle above the open circuit potential. A hysteresis loop is formed within
the log (I) vs Ewe graph which would be indicative of pitting. The size of the loop is then
related to the amount of pitting.
GRAPH 9 - CYCLIC POTENTIODYNAMIC POLARIZATION (E V T)

40
Visualization of results and analysis of results
The hysteresis loop can be seen in the Log (I) graph shown here.
GRAPH 10 - CPP (E V LOG(I)) (ANDERSON MATERIALS EVALUATION, 2015)
From this the pitting potential can be calculated using the Multi Pitting Statistics tool within the
software. This dictates the lowest positive potential in which the material will start to undergo
pitting. With this information, engineers can determine the appropriability of a materials use
based on the environment in which the material will be used.
4.4.6. MULTIELECTRODE POTENTIODYNAMIC PITTING
The Multielectrode Potentiodynamic Pitting technique is very similar to CPP however it
incorporates more than one electrode. Using multiple channels within the VMP3, the software
can conduct an identical potential sweep across various identical electrodes to comprise a
range of results for one material. From this an accurate reading can be found with an
appropriate tolerance value.

41
4.4.7. MULTIELECTRODE POTENTIOSTATIC PITTING
The Multielectrode Potentiostatic Pitting technique is very similar to that of the MPP technique
in regards to offering a range of results. In this technique however the potential is applied at
a constant value rather than being swept.
GRAPH 11 - MPSP (E V T)

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5. RESULTS
5.1. CORROSION RATES
5.1.1. LINEAR POLARIZATION CORROSION RATES
TABLE 2 - LP CORROSION RATES
From the above table highlighting corrosion performance through Linear Polarization, an initial
assumption can be made that the Titanium Nitride coatings performed the best, with Nickel
offering a similar level of corrosion protection. All coatings offered corrosion resistance,
however, Silicone Carbide coatings performed to a lesser extent than the Titanium and Nickel
coatings.
Sample10 Sample12 Sample1 – 4.9Ph Sample2 – 4.0Ph Sample8 Sample9 Sample5 Sample6
Icorr (nA) 253.6 237.39 30.6 26.12 11.37 16.05 171.59 118.07
Icorr (A) 2.5360E-04 2.3739E-04 3.0600E-05 2.6120E-05 1.1370E-05 1.6050E-05 1.7159E-04 1.1807E-04
(K EW)/(DA) 3389 3389 3389 3389 3389 3389 3389 3389
Corrosion Rate (mm/yr) 0.859 0.805 0.104 0.089 0.039 0.054 0.582 0.400
Sample1 – 4.9Ph Sample2 – 4.0Ph Sample8 Sample9 Sample5 Sample6
29.43 28.67 17.55 18.18 130.54 124.61
2.9430E-05 2.8670E-05 1.7550E-05 1.8180E-05 1.3054E-04 1.2461E-04
3389 3389 3389 3389 3389 3389
0.100 0.097 0.059 0.062 0.442 0.422
Icorr (nA)
Icorr (A)
(K EW)/(DA)
Corrosion Rate (mm/yr)
Coated
Coated – Worn
Nickel TiN SiC
Nickel TiN SiC
Uncoated

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5.1.2. FURTHER CORROSION RATE RESULTS
TABLE 3 - FURTHER CORROSION RATES
With further inspection into the Generalized Corrosion and Constant Amplitude Sinusoidal
microPolarization techniques offered by the software, the above corrosion rates were
recorded. With comparison to that of the LP results, a close tolerance can be seen between
all methods offering accurate results with the software.
The above also highlights secondary experimental procedures used on worn coatings with
exposed steel. Across the board, higher corrosion rate results can be seen again reiterating
the accuracy of the software techniques.
Sample10 Sample12 Sample1 – 4.9PhSample2 – 4.0PhSample8 Sample9 Sample5 Sample6
Icorr (nA) 247.89 221.5 26.48 27.94 12.8 14.56 187.1 120.86
Icorr (A) 0.00024789 0.0002215 2.65E-05 2.79E-05 1.28E-05 1.46E-05 0.000187 0.000121
(K EW)/(DA) 3389 3389 3389 3389 3389 3389 3389 3389
Icorr (nA) 276.23 243.67 27.08 31.97 15.1 12.31 140.12 104.01
Icorr (A) 0.00027623 0.00024367 2.71E-05 3.2E-05 1.51E-05 1.23E-05 0.00014 0.000104
(K EW)/(DA) 3389 3389 3389 3389 3389 3389 3389 3389
Sample1 – 4.9PhSample2 – 4.0PhSample8 Sample9 Sample5 Sample6
Icorr (nA) 30.53 30.41 19.1 19.411 145.9 133.62
Icorr (A) 3.05E-05 3.04E-05 1.91E-05 1.94E-05 0.000146 0.000134
(K EW)/(DA) 3389 3389 3389 3389 3389 3389
Corrosion Rate (mm/yr) 0.103466 0.103059 0.06473 0.065784 0.494455 0.452838
Icorr (nA) 31.04 27.86 18.11 18.29 102.43 176.88
Icorr (A) 3.1E-05 2.79E-05 1.81E-05 1.83E-05 0.000102 0.000177
(K EW)/(DA) 3389 3389 3389 3389 3389 3389
Corrosion Rate (mm/yr) 0.105195 0.094418 0.061375 0.061985 0.347135 0.599446
CASPGC
GCCASP
Uncoated Coated
Coated – Worn
Nickel TiN SiC
Nickel TiN SiC

44
GRAPH 12 - AVERAGE CORROSION RATES OF SAMPLES
5.2. POLARIZATION RESISTANCE THROUGH GENERALIZED CORROSION
TABLE 4 - POLARIZATION RESISTANCE
The corrosion characteristics and resistance of each coating can be reiterated with the
examination of the Generalized Corrosion. This again shows similar results where the TiN
and Ni coatings offer superior protection to that of SiC and uncoated samples.
GRAPH 13- POLARIZATION RESISTANCE OF SAMPLES
Sample10 Sample12 Sample1 – 4.9PhSample2 – 4.0PhSample8 Sample9 Sample5 Sample6
Rp (Ohms) 143 183 1348 1287 1573 1395 213 267
Uncoated Coated
Nickel TiN SiC

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5.3. ELECTROCHEMICAL NOISE
TABLE 5 - ELECTROCHEMICAL NOISE
With EN giving us an insight into the reaction characteristics of materials such as film ruptures
and discrete events such as metal dissolution and hydrogen discharge with gas bubble
formation and discharge, the EN results recorded above show a considerable difference
between all samples, even that of TiN and Ni, which show similar corrosion rate behaviour as
noted previously, except from the TiN and uncoated samples. EN values can be analysed
further through the root mean square of the recorded amplitudes in order to determine the
“fingerprint”, or type, of localized corrosion (Gaona-Tiburcio, Aguilar, & Zambrano, 2013).
GRAPH 14– NOISE RESISTANCE OF SAMPLES
Sample10 Sample12 Sample1 Sample2 Sample8 Sample9 Sample5 Sample6
Rn (Ohms) 24.06 26.75 84.89 118.9 30 23.68 56.76 72.73
Uncoated Coated
Nickel TiN SiC

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5.4. PITTING POTENTIAL
TABLE 6 - PITTING POTENTIALS
The Pitting Potential values recorded above offer no insight into the localized corrosion
characteristics of materials due to the obvious inaccuracies in the results. Even with the use
of multiple software techniques, the results show no similarity or correlation, therefore further
work is required to deduce the reason for such inaccuracies after the software previously
offered reliable results.
Sample10 Sample12 Sample1 Sample2 Sample8 Sample9 Sample5 Sample6
Epitting (V) 1.16 0.423 0.346 -1.1 0.283 0.108 -0.316 -0.108
Epitting (V) 0.677 -0.53 1.381 1 0.137 0.5 0.608 0.475
Epitting (V) 0.076 0.387 -0.355 -0.9 -0.16 0.238 -0.296 1.7
Uncoated Coated
Nickel TiN SiC

47
6. DISCUSSIONS
6.1. DESIGN EVALUATION
6.1.1. FINAL EVALUATION
Based upon the Design Brief and Product Design Specification, the design has met all
requirements, parameters and constraints. The design offers a safe and stable environment
in order to undertake EIS procedures and although the solution used was not harmful, the
design offers scope into highly corrosive solutions.
6.1.2. DESIGN FOR MANUFACTURE
Due to the simple geometry used within the liaising portfolio, there were no problems when
consulting the viability of manufacturing with the workshop. The clamp was simplified after
finding the easiest manufacturing option for the workshop, and the threaded rods were
changed to offer a more aesthetically appealing assembly. All materials were readily available
except the containing tube which took an extra few days to arrive and this minimally set back
the production time. Manufacturing was complete around three weeks before the interim
break and took only five days to complete which meant the rig was just waiting on the
electrodes to be sourced in order to be complete.
6.1.3. DESIGN FOR ASSEMBLY
The rig is extremely easy to set up and use, with the only tool required as an Allen key. The
hardest aspect is the positioning of the seal with the sample, however, with the transparent
containing tube a top filling hole, this can be fairly easily done. Although this can be fiddly, the
balance between the restriction of the tube size based on usable sample areas, and that of
the space within the containing tube for electrodes, has been well established. Filling the
containing tube with the solution is also easy provided an adequate pouring vessel is used.
The overall design could be simplified with the use of only three clamping rods around the
containing tube. This would offer the same adequate clamping performance with a little less
assembly time. The other major improvement that could be made to the design is that of the
electrode cap on the top. This is inadequate for the reference electrode purchased with has
a 6mm diameter while the cap was cut at 5mm. A piece of card was then used to hold the
electrodes, however, this caused some fiddliness in the movement of the electrodes to VMP3
connection. With a more appropriate electrode cap, the electrodes could be effectively kept
in position and more easily off the walls of the containing tube.

48
6.1.4. OTHER USES
The design has the scope to be used in the cathodic disbondment testing procedure where a
similar set up is required. A sample can be clamped into the rig and the electrolyte solution
added. The calomel electrode and anode can then be inserted into the solution from the
electrode cap, connections made, and the procedure carried out. This makes the working
electrode clamp redundant, however this can just be fixed away from the procedure and will
not affect results (Guo, 2006).
6.2. RESULTS
6.2.1. CORROSION RATES
The results seen in the corrosion rate techniques show strong correlations between the
coatings highlighting the best and worst, as well as the effect of a worn coating. Based on
previous research, the results can be seen as accurate where TiN and its passive oxide film
performs the best followed by Ni. The poor corrosion resistance of SiC can be explained from
research, where the particulate form due to the co-deposition process, exposes steel and thus
creates a galvanic coupling reaction between that of the steel and the nickel. The effect of a
worn coating can also be highlighted as having a negative effect on the corrosion resistance
of coated materials.
6.2.2. POLARIZATION RESISTANCE
Following from the results seen in the corrosion rates results, the results are expected to be
incredibly similar where a high corrosion rate has a low polarization resistance. This can be
clearly seen in the results and reiterates the effectiveness of EIS methods for measuring
corrosion rates.
6.2.3. ELECTROCHEMICAL NOISE
The electrochemical noise analysis of each coating highlights a great variance in the reaction
activity of each coating. This is highlighted in the likes of the passive oxide film present in TiN
coatings that protect against harsh corrosion reactions, and thus shows a very low noise value.
The results do not highlight the reasons or mechanisms for current fluctuation due to chemical
reactions within the cell however. This would be key information to engineers in the field and
therefore this project fails to offer usable results in the electrochemical noise area of EIS
corrosion testing.

49
6.2.4. PITTING POTENTIAL
The project also does not show any correlation into the pitting potential, and therefore localized
corrosion behaviour of the coated samples. This is due to the limitation of the low impedance
setting used within the experiments. The technique requires a high level of potential range in
order to reach the Pitting Potential. Due to the restrictions of the low impedance setting only
offering potentials to around 1.5V through the working electrode, the setting will simply not
work. A normal channel could be used with the VMP3 potentiostat in order to reach the
relevant potentials. Further research should also be undertaken in this case to effectively
analyse the results in order to not only the pitting potential, but also the types of localized
corrosion that these values can give an insight into.
6.3. EC-LAB SOFTWARE USE EVALUATION
The EC-Lab is incredibly simple to use with great documentation highlighting the steps of each
technique that it offers. Upon first use of the software, it takes a little time to understand the
jargon such as OCV periods, which refer to the open circuit voltage procedure used to find
Eoc at the start of each procedure.
The above set up procedure is used for the generalized corrosion technique and as can be
seen, the main steps within the technique are split into their own boxes or sections. The only
hurdle for new users is the understanding of each acronym such as the different potentials
and the understanding of the scope parameters such as the I and E ranges. These scopes
become apparent when the software warns of current or potential overload within the
procedure. This can be easily overcome with the manipulation of the ranges, and the
procedure retried.
FIGURE 12 - EC-LAB GENERAL
PROCEDURE WINDOW

50
Within the cell characteristics tab of the procedure set up, the attributes of the sample and
testing apparatus can be determined in order to provide personalised results for each sample
such as the specific corrosion rate. The software also offers options for all suitable reference
electrodes with their corresponding potential values, which in turn are used within the
procedure as a known reference. Within the Advanced Settings tab, the electrode connections
are defined and the option for Counter Electrode to Ground is available for the suitable
procedures.
6.4. PROJECT LIMITATIONS
Looking at the original project proposal and the corresponding aims, the project has been a
success. There were however some limitations to the work. The design of the rig was defined
around the workshops limitations including materials and machinery. Although not critical to
the success of the design, lower limitations would allow the scope of the experimental
procedures to be expanded into incredibly harsh environments as well as the use of
temperature control apparatus in order to perform Critical Pitting Temperature experiments to
find the temperature at which localized corrosion begins to occur. A key problem that occurred
during the use of the rig was the degradation of the counter electrode when used over an
extensive period of time. Coating material from the sample would separate from the coating
and become deposited onto the silver electrode. Due to the nature of a counter electrode
where it performs as measuring apparatus due to its noble form, the electrochemical reaction
occurring on its surface from this deposited material would disrupt the results and nullify the
procedure. This was fixed with the use of a three micron diamond lapping paste that would
be applied and subsequently break the deposited material from the electrode. A final polishing
would then be used to remove the paste and any debris from the surface of the electrode and
it would once again be ready for use. The average time for this polishing was 2 minutes and
FIGURE 13 - EC-LAB CHARACTERISTICS TAB
WINDOW

51
was performed after every change of sample, or every 45 minutes of operation.
Limitations within the software revolved around the time constraints of the project. The
Corrosimetry procedure could have technically been performed as it uses the same principle
as that of the Linear Polarization technique. Corrosimetry however measures the change in
polarization resistance over time and the test usually lasts for days or even months. This
would give a great insight into the changing characteristics of corrosion through a coating,
however, the time frame would not allow the individual inspection of each coating. The
procedures within this report also limit the insight into Variable Amplitude Sinusoidal
microPolarization. Similar to CASP, VASP uses a variable amplitude to find the corrosion rates
and polarization resistance of materials. With the use of three already defined experiments to
determine these material characteristics, it was decided that due to the time consuming and
complex nature of result gathering, VASP did not offer anything new to the overall results of
the project. The Depassivation Potential procedure was also neglected from the project. This
offers results on material pitting potential based upon a procedure incorporating both MPP and
MPSP. This was neglected due to the inability to compare the results with any other results
due to the inconclusive CPP, MPP and MPSP procedures as highlighted previously.
The only hardware limitation that occurred during the project was that of the low impedance
setting potential range when measuring the pitting potential. This could be easily rectified by
using a standard channel connection. The rig design was however based around the
significantly smaller low impedance connections and thus a middle connection between the
electrodes and VMP3 must be designed. This could however raise safety concerns where
high voltages are used with exposed metals and the grade of wire for the working electrode
would need to be examined for safety.

52
7. CONCLUSIONS
The overall project has been a success. By first establishing the use of the impedance
methods within industry, scope for the project was defined and the measurement of coatings
in artificial sea water was chosen in order to relate to that of the marine industry. Due to the
highly aggressive environments experienced, corrosion measurement plays a major role in
design and material selection of components to be used in such environments. Through initial
research into the modes of corrosion and the effects, the scope of the project was further
defined by the selection of coating materials. These were Nickel, Titanium Nitride and Silicon
Carbide, all of which offer great wear resistance and superior hardness values than that of
steel which was defined as the substrate material. Worn coating samples were also analysed
to give an insight into corrosion behaviours of incomplete coatings. An uncoated steel
substrate was also to be examined in order to compare coatings results to a standard
performance mark. With the scope of the project well defined, research was conducted into
the process of impedance analysis. This highlighted the methods and results available with
current technology, as well as the particular methods that could be used within the hardware
and software provided by the materials science lab. Relating to the known methods of
analysis, a rig was then designed around a generic three electrode set up where the samples
were defined as the working electrode, and a reference and counter electrode were also
required. A testing solution was required to initiate the electrochemical reaction and thus the
design would need to incorporate the three electrodes with relevant electrical connections to
the VMP3, submerged within the solution. Through liaising with the university workshop, the
design was optimised and produced within time to start testing after the interim break. Testing
then took place for all samples through the seven procedures; Linear Polarization, Generalized
Corrosion, Constant Amplitude Sinusoidal microPolarization, Zero Resistance Ammeter,
Cyclic Potentiodynamic Polarization, Multiple Potentiodynamic Pitting and Multielectrode
Poentiodynamic Pitting. These offered results in corrosion rates and polarization resistance,
electrochemical noise measurements, and pitting potentials. With the corrosion rate and Rp
procedure aims offering good results, the project can be seen as a success. The aims of the
project were however expanded in order to incorporate further results in Noise measurement
and localized corrosion characteristics. Due to lack of research into the deduction of Noise
results, only the process could be highlighted and the project offers no conclusions about the
type’s corrosion mechanisms apparent in the experiment. The localized corrosion procedures
also failed to offer any conclusive results on material behaviour based predominantly on the
limitation of the low impedance setting used with the VMP3. With correlating results and more
advanced research, the procedures demonstrated in this project could be used in accordance
with a suitably safe and operational rig, to perform these localized corrosion experiments and

53
deduct meaningful results from them. Overall, the project has been a success highlighting the
use of impedance analysis in order to measure corrosion rates in coated samples by designing
and using a suitable rig for the experiments.
8. RECOMMENDATIONS
8.1. INDUSTRY APPLICATIONS
The general corrosion rate experiments highlighted in this report offer a great deal of industrial
application. Experiments are done in a stable laboratory environment and offer great accuracy
in results. Through this investigative setting, the processes are ideal for research into new
material classifications, and testing materials for their suitability within industrial applications
such as from a guard rail on an oil rig in the North Sea, to the metal materials found on deep
sea divers uniforms. The accuracy of the results offers a great deal of safety and reliability in
material selection when designing new components and the speed in which these procedures
can be conducted offers the option to examine many different materials offering a greater
scope on possible material choices. As seen in the Silicon Carbide coating results, the
procedures can pick up important features of a compound such as a particulate form coating
exposing the substrate. This could be an invaluable piece of information in industry where
simple physical methods of testing, such as the mass change, would not pick up such features.
8.2. FUTURE WORK
Future work within this area would be the re-examination of the Pitting Potential techniques

54
and an appropriate design around the electrode connections. Research into the relationship
between the pitting potential value and the size of the hysteresis loop could prove valuable in
determining the actual corrosion mechanisms occurring on a materials surface.
Corrosimetry procedures could be conducted in order to re-iterate the Polarization Resistance
values recorded in the uniform corrosion measuring methods highlighted within this project.
This would also offer an insight into how coatings operate in terms of corrosion protection over
an extended period of time, and maybe even to the time where a coating is completely
removed due to corrosion.
Future work on the design of the rig could be done to incorporate temperature management
within the experiment. This would then offer the opportunity for the measurement of the critical
pitting temperature discussed previously. This work could prove extremely useful in other
industries outside of marine applications, where heat is more predominant and effective. The
materials used with the rig would however need to be examined for suitability as they were
chosen based on room temperature operation.
The rig has the scope to be used within a cathodic disbondment experiment and although this
would offer no insight into the use of the VMP3 and its software, it could offer results on the
effects of corrosion between materials which is highly beneficial to those in industry.

55
9. APPENDIX
9.1. APPENDIX - DESIGN PORTFOLIO
FIGURE 14-19 COMPLETE DESIGN PORTFOLIO

58
10. REFERENCES
A Grosjean, M. R. (2000). Surface and Coatings Technology. Some morphological characteristics of
the incorporation of silicon carbide (SiC) particles into electroless nickel deposits, 252 - 256.
Anderson Materials Evaluation, I. (2015, February 26). Electrochemical Qualification of Biomedical
Implantable Devices: Corrosion Case Study #2. Retrieved from Anderson Materials
Evaluation, Inc.: http://www.andersonmaterials.com/electro/electrochemical-qualification-
of-biomedical-implantable-devices-corrosion-case-study-2.html
Antono-Lopez, R. (2001). A New Experimental Approach to the Time-Constants of Electrochemical
Impedance. Electrichima Acta, 3611 - 3617.
Bio-Logic. (2014). EC-Lab Software User's Manual. Bio-Logic.
Bio-Logic. (2014). Software Applications and Tecniques. Bio-Logic.
Davis, J. R. (2000). Nickel, Cobalt, and Their Alloys. ASM International.
Davis, J. R. (2001). Surface Engineering for Corrosion and Wear Resistance. ASM International.
Ehm, W. (n.d.). ZHIT - A simple Relation Between Impedance Modulus and Phase Angle. 1.
Fontana, M. G. (1986). Corrosion Engineering. McGraw-Hill.
Gaona-Tiburcio, C., Aguilar, M. L., & Zambrano, P. R. (2013). Electrochemical Noise Analysis of Nickel
Based Superalloys in Acid Solutions. 523 - 533.
Guo, G. (2006). Laboratory and Field Tests of Multiple Corrosion Protection Systems for Reinforced
Concrete Bridge Components and 2205 Pickled Stainless Steel. ProQuest.
Hajdu, J. (1990). Surface Preperation for Electroless Nickel Plating. 193 - 206.
Harbecke, B. (1986). Application of Fourier's Allied Integrals to the Kramers-Kronig Transformation of
Reflectance Data. 151-152.
IJsseling, F. P. (1989). General Guidlines for Corrosion Testing of Materials for Marine Applications.
Literature Review on Sea Water as a Test Environment, 26.
Instruments, A. (2015, February 3). Field Machine Data Sheet. Retrieved from ACM Instruments:
http://www.acminstruments.com/datasheets/field-datasheet.pdf
Laque, F. L. (1975). Marine Corrosion Causes and Prevention. New York: Wiley.
MacDonald, D. D. (2002). A Brief History of Electrochemical Impedance Spectroscopy. 1.
MacDonald, D. D. (2005). Reflectrions on the History of Electrochemical Impedance Spectroscopy.
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Mansfield, F., Huet, F., & Mattos, O. R. (2001). New Trends in Electrochemical Impedance
Spectroscopy and Electrochemical Noise Analysis. The Electrochemical Society.
Marijana Kraljic, M. Z. (2003). The Effect of Polyaniline and Modified Polyaniline Coatings on
Stainless Steel Corrosion Protection. 1.

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Narnedra B. Dahotre, T. S. (1999). Intermetallic and Ceramic Coatings. Marcel Dekker.
Pauwels, L. (2010). Contribution to the Impedance Data Analysis of Mass Transfer Controlled
Electrochemical Systems. 1.
Saha, R., Mohamed, S., & Khan, T. (2011). Effect of Coating Parameters on the Electrodeposition of
Nickel Containing Nano-sized Alumina Particles. In N. Bansal, Processing and Properties of
Advanced Ceramics and Composites III (pp. 41- 43). John Wiley & Sons.
Schlesinger, M. (2010). Electroless Deposition of Nickel. 447- 458.
Suzuki, I. (1989). Corrosion-Resistant Coatings Technology. Merkel Dekker.
Taheri, R. (2003). Evaluation of Electroless Nickel-Phosphorous (EN) Coatings. 259.
Thomas, J. (1996). The Electrochemistry of Corrosion. 25.
*Some references are bibliographic and uncited within the text.

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