Corrosion Measurement Techniques Quiz

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Questions and Answers

What type of corrosion does the text primarily focus on?

Localized corrosion

Pitting corrosion

General corrosion (correct)

Stress corrosion cracking

What is the key assumption made when converting Icorr to corrosion current density?

The solution is perfectly homogeneous.

The current distribution is uniform across the exposed area. (correct)

The electrode surface is perfectly smooth.

The corrosion rate is constant over time.

How can localized corrosion affect polarization measurements?

It increases the exposed surface area, leading to lower current densities.

It prevents the formation of a passive layer, increasing the corrosion rate.

It decreases the exposed surface area, leading to higher current densities.

It alters the solution chemistry and electrode geometry, making interpretation difficult. (correct)

What is the formula used to convert Icorr to corrosion current density (icorr)?

icorr = Icorr / A (D) Signup and view all the answers

Which of these factors can influence the accuracy of polarization measurements for corrosion rate determination?

All of the above (D) Signup and view all the answers

Why are polarization methods generally limited to determining general corrosion rates?

They cannot detect the initiation and propagation of localized corrosion. (B) Signup and view all the answers

What is a potential drawback of using polarization methods to measure corrosion rates?

The results may not accurately represent the corrosion rate if localized corrosion is present. (B) Signup and view all the answers

What is the purpose of converting Icorr to corrosion current density?

To express the corrosion rate in terms of the metal's surface area. (C) Signup and view all the answers

What is the purpose of the 'water jacket' in the multiport corrosion cell?

To provide a constant temperature environment for the experiment. (A) Signup and view all the answers

What is the specific geometric area of a measurement in the context of polarization measurement?

The area of the sample that is in contact with the electrolyte. (B) Signup and view all the answers

What is the purpose of the 'O-ring' in the sample holder?

To ensure a tight seal between the holder and the cell. (B) Signup and view all the answers

What is the role of the 'sample window' in the sample holder?

To provide a visual observation point for monitoring the sample during the experiment. (C) Signup and view all the answers

What is the primary function of the 'electrical contact' in the sample holder?

To provide a pathway for electrical current to flow from the sample to the potentiostat. (A) Signup and view all the answers

What are the most common types of metal samples used in polarization measurements? (Select all that apply)

Plates (A), Coupons (C), Disks (D) Signup and view all the answers

Why is the 'multiport corrosion cell' called 'multiport'?

Because it has multiple ports for connecting different electrodes, such as the reference electrode, counter electrode, and working electrode. (B) Signup and view all the answers

What is the significance of maintaining a constant temperature in polarization measurements? (Select all that apply)

To minimize corrosion rates and ensure accurate and reproducible measurements. (B), To ensure the electrolyte remains stable and does not undergo changes in viscosity or conductivity. (D) Signup and view all the answers

What is the relationship between equivalent resistance and individual resistances when connected in series?

The equivalent resistance is the sum of the individual resistances. (C) Signup and view all the answers

What does Kirchhoff's first law state about currents at a junction in a circuit?

The sum of currents entering a junction is always equal to the sum of currents leaving the junction. (A) Signup and view all the answers

According to Kirchhoff's second law, what is the sum of voltage drops in a closed loop?

The sum of voltage drops in a closed loop is always zero. (C) Signup and view all the answers

What mathematical relationship describes the equivalent resistance of two parallel resistances?

The equivalent resistance is the harmonic mean of the two resistances. (D) Signup and view all the answers

What is the main principle behind Kirchhoff's first law?

Conservation of charge. (D) Signup and view all the answers

What is the relationship between Ohm's Law and the equivalent resistance in a series circuit?

Ohm's Law is used to calculate the current flowing through a series circuit, using the equivalent resistance. (E) Signup and view all the answers

What is the significance of the statement "there can be no accumulation of charges in conductors" in the context of Kirchhoff's first law?

It emphasizes that charges are not created or destroyed, only redistributed. (C) Signup and view all the answers

What is the main concept demonstrated by the discussion about the equivalent resistance of parallel connections?

The total resistance in a parallel circuit is always less than the smallest individual resistance. (A) Signup and view all the answers

What is the crucial property of a linear system in relation to its input and output signals?

The output is the sum of weighted responses to each input signal. (A) Signup and view all the answers

Why is it important to use a small AC signal in Electrochemical Impedance Spectroscopy (EIS) measurements?

To ensure that the system behaves pseudo-linearly. (A) Signup and view all the answers

What does 'pseudo-linear' mean in the context of electrochemical cells?

The cell's behavior appears linear within a small voltage range. (A) Signup and view all the answers

What is the impact of doubling the voltage applied to a non-linear electrochemical cell?

It will have no predictable effect on the current. (A) Signup and view all the answers

What is the primary reason why a steady state is required for accurate EIS measurements?

To allow the system to have a stable response to the applied signal. (D) Signup and view all the answers

How is the non-linear response of the electrochemical cell addressed in practical EIS measurements?

By applying a small AC signal, keeping the system within its pseudo-linear range. (D) Signup and view all the answers

What is the main reason why EIS spectrum measurement often takes a significant amount of time?

The system requires time to reach a stable equilibrium before and during the measurement. (D) Signup and view all the answers

What is the importance of the 'dc potential' in EIS measurements?

It determines the overall voltage applied to the cell. (B) Signup and view all the answers

What is the primary focus of the provided text?

The application of impedance spectroscopy to study corrosion processes (A) Signup and view all the answers

According to the provided text, what are the key types of plots utilized in impedance representation?

Complex admittance, complex capacitance, and tridimensional impedance plots (C) Signup and view all the answers

What is the significance of comparing electric equivalent circuits to physical models in EIS?

To understand the relationship between the observed electrochemical behavior and the underlying physical processes (C) Signup and view all the answers

What is the primary goal of analyzing impedance spectra?

To understand the overall electrochemical behavior of the system and its components (B) Signup and view all the answers

What is the key advantage of using the Zview software in EIS?

It allows for automated data analysis and the generation of impedance plots (A) Signup and view all the answers

What is a key application of Electrochemical Impedance Spectroscopy (EIS)?

Determining the kinetics of homogeneous reactions in solution combined with redox processes (B) Signup and view all the answers

What does EIS stand for?

Electrochemical Impedance Spectroscopy (D) Signup and view all the answers

What is one of the limitations that must be considered when using EIS?

It must be used with care due to its sensitivity. (A) Signup and view all the answers

Which of the following applications is NOT mentioned as a use case for EIS?

Optical Properties of Materials (D) Signup and view all the answers

What is the primary principle behind Ohm's Law in the context of EIS?

Describing the current flow through a resistor based on applied voltage and resistance (B) Signup and view all the answers

How does EIS differ from other electrochemical techniques?

It analyzes the system's response to a range of alternating frequencies (B) Signup and view all the answers

What is a significant advantage of using EIS?

It provides information about the surface area of the electrode in situ (A) Signup and view all the answers

What does EIS reveal about the relationship between current and potential?

That current can follow potential without any delay if resistance is present (A) Signup and view all the answers

Study Notes

Advanced Research Methods in the Engineering of Materials

Lecture 7 covered basic polarization techniques for testing corrosion resistance of materials.
Lecture 8 introduced electrochemical impedance spectroscopy (EIS) in material corrosion study.
Lecture 6 focused on coating and thin film thickness measurement methods.
Lecture 10a discussed the basics of scanning electron microscopy (SEM).
Lecture 11 explores energy-dispersive (EDS) and wavelength-dispersive (WDS) X-ray spectroscopy in material engineering.

Electrochemical Nature of Corrosion

Corrosion in aqueous or any other ionic conducting medium is electrochemical.
Corrosion reaction requires four elements: anode, cathode, metallic conductor, electrolytic conductor.
Oxidation reaction occurs at the anode, where the metal loses electrons.
The anodic reaction can be written as: M → Mn^+ + ne⁻.
Metallic ions are carried from the anode to the cathode by the electrolyte.
Electrolytes are mainly liquids but can also be solids.
Reduction reaction occurs at the cathode.
Two ion types exist: anions and cations. Anions are negatively charged and move towards the anode. Cations are positively charged and move towards the cathode.
Common reduction reactions at the cathode are hydrogen ion and oxygen reduction.
Electrons from the anode are carried to the cathode via a metallic conductor.
Electrochemical corrosion requires all four components to occur simultaneously for a reaction to take place.
The rate of anodic reaction (oxidation) is equal to the rate of cathodic reaction (reduction).
Electrochemical polarization measurements are used to determine the rate of anodic or cathodic reactions, either individually or collectively.
Gibb's free energy change (ΔG) is negative for a spontaneous process, making the product more stable. A positive value of ΔG indicates the reaction is not spontaneous.

Electrochemical Polarization Measurement

E (potential) is related to ΔG (Gibbs free energy change) using the equation E = −ΔG / nF, where n is the number of electrons transferred, and F is the Faraday constant.
A positive potential corresponds to a negative ΔG and vice-versa.
Arrangement of metals based on standard potentials is described by Standard Oxidation-Reduction (redox) potential, Standard Equilibrium Reduction Potential, Standard Potential, Electro-Motive Force (EMF), and Standard Reversible Potential.
Standard potential is the potential of a metal in contact with its own ions at a concentration equal to unit activity.
Several types of polarization techniques are employed, including potentiostatic, potentiodynamic, galvanostatic and galvanodynamic. Most electrochemical measurements control potential (potentiostatic or potentiodynamic) rather then controlling current (galvanostatic or galvanodynamic).
Linear Polarization Resistance (LPR) and Tafel extrapolation used for corrosion rate determination via electrochemical polarization techniques.

Nernst Equation

Nernst equation is used to calculate the potential of a metal when reactants are not at unit activity.
The equation is E = E⁰ + (RT/nF) ln(a oxid/a red), where E⁰ is the standard redox potential, R is the gas constant, T is absolute temperature, n is the number of electrons transferred, and a and a are activities (concentrations) of the oxidized and reduced species.
The more oxidized species present, the more positive the potential.

Mixed Potential

Corrosion needs all four components in contact with each other, simultaneously.
Corrosion potential (Ecorr) is the potential where the reaction rates match.
Methods to determine mixed potential and corrosion current are important tools in studying general corrosion rates.

Potential vs Reference Electrode

Corrosion potential is measured in relation to a reference electrode (like SCE, Ag|AgCl, or CCS electrodes).
All reference results need to be reported against a reference electrode.
Conversion can be done using relevant equations.
Modern potentiostats report potentials as referenced to a reference electrode, and sometimes to the open-circuit potential.

Corrosion current and potential.

A relation exists between the potential for activation-controlled processes and current, given by E − Ecorr = η = ±βlog(I/Icorr).
η stands for overpotential
Icorr depicts corrosion rate
β is a constant.

Tafel Equation

The rates of anodic and cathodic processes in corrosion are considered controlled by the kinetics of the electron-transfer reaction at the metal surface.
Electrochemical reactions under kinetic control are described by the Tafel equation, 1 = Io exp(±2.303(E − E⁰/β)), where i is the current, Io is the exchange current, and β is the Tafel constant.
The Tafel Equation reflects the behavior of one isolated reaction in a corrosion system, considering anodic and cathodic reactions that oppose each other.

Types of Polarization Control

Methods for controlling potential or current in polarization techniques are characterized by potentiostatic and potentiodynamic measurement.
Galvanostatic and galvanodynamic methods control current and the potential respectively.
Linear polarization resistance (LPR) and Tafel are common methods for determining general corrosion rates via polarization resistance techniques.
Cyclic potentiodynamic polarization can be used to examine localized corrosion.

Linear Polarization Resistance

Rp is defined mathematically as ΔV/ΔI at Ecorr.
It's associated with the corrosion current (Icorr) through Icorr = B/Rp.
The constant B is defined as (βaβc)/(2.303(βa + βc)).
Given the values of βa and βc, the corrosion rate can be calculated from Rp.
Only a small potential perturbation is applied for this technique, so it does not substantially affect the corrosion reaction.

Tafel extrapolation method

A linear relationship exists between the potential (E) and the logarithm of the current (log I) for electrode polarization, both anodic and cathodic. This relationship is known as the Tafel relation.
The Tafel equation is a mathematical description of the relationship between potential and current.
The equation often assumes kinetic control of the reaction at the metal surface.

Electrochemical impedance spectroscopy (EIS)

EIS is used for fine-tuning mechanisms, determining kinetics of processes, resistances, and capacitances, and for in-situ determination of real surface areas.
EIS is a very sensitive electrochemical technique, but needs careful use to avoid errors.

Electrochemical impedance spectroscopy (EIS) - Applications

EIS is applied in interfacial processes (redox reactions, adsorption, electrosorption, kinetics of homogeneous reactions).
It's used in geometric effects (like linear, spherical, cylindrical, and limited-volume electrodes) to determine solution resistance and porous electrodes,
Also in power sources (batteries, fuel cells, supercapacitors); corrosion for, coatings, paints, electrocatalytic reactions, and various other applications such as in membranes, water electrolysis, halogen evolution or for studying conductive polymers, self-assembled monolayers, biological or semiconductor materials and sensors.

Ohm's Law

Ohm's law describes the relationship between voltage (V), current (I), and resistance (R) in a simple electrical circuit.
The law states that the current (I) through a conductor between two points is directly proportional to the voltage (V) across the two points.
The constant of proportionality is the resistance (R). This relationship is expressed mathematically as V = IR.

Kirchhoff's laws

The algebraic sum of currents entering any node (junction) in a circuit is equal to zero.
The algebraic sum of voltage drops around any closed loop in a circuit is equal to zero.
These laws are fundamental principles in circuit analysis and understanding the flow of current and voltage within complex circuits.

Impedance Definition

Impedance is a measure of how much a circuit or material resists the flow of alternating current.
Unlike resistance, impedance considers the phase shift between current and voltage in AC circuits, and can be a complex number, containing both magnitude (resistance) and phase angle components.
Impedance may be used to measure more complex electro-chemical behavior.
Measurements are usually conducted by applying an AC potential.

Corrosion Current and Potential

Describes the relationship between corrosion potential and current during activation-controlled corrosion using an equation;
This method is related to the calculation of the corrosion rate.

Basics of polarization techniques

Potentiostatic method involves keeping the potential constant, while the corresponding current is monitored.
Potentiodynamic method varies the potential actively at a constant rate and continually monitors the current.
Galvanostatis and galvanodynamic methods actively control current.
Linear polarization resistance (LPR) and Tafel extrapolation can examine corrosion rate changes over time through polarization resistance techniques.

Coating and Film Thickness Measurement Methods

Various techniques for determining coating and film thickness can use optics, X-rays, or physical methods.
Reflectometry analyzes intensity of reflected light corresponding to the wavelength.
Ellipsometry uses polarized light to analyze reflectivity changes.
Step height measurement is a direct technique that measures the difference in height with a stylus.
Energy dispersive X-ray flourescence (XRF) analysis uses high energy X-rays that produce fluorescence in materials identifying chemical elements.
Magnetic induction (MI) based on measuring induced magnetic fields as a result of material property changes.

Electrochemical Impedance Spectroscopy Analysis

The electrochemical impedance spectroscopy (EIS) method is used for fine-tuning mechanisms, determining kinetics of processes, resistances and capacitances.
It is used for measuring the in-situ areas of real surfaces. Its high sensitivity requires care during use.

Control Questions

Includes questions to characterize various material testing methods: electrochemical corrosion, polarization measurements, Nernst equation, mixed potential, potential reference electrodes.

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Description

This quiz examines key concepts related to corrosion measurement techniques, including various types of corrosion, the conversion of Icorr to corrosion current density, and factors influencing polarization measurements. It also explores the design elements of a multiport corrosion cell and the implications of using polarization methods for measuring corrosion rates.