corrosion engineering_chapter 5_polarization methods danny a jones
DESCRIPTION
Chapter 5 of Danny A Jones BookTRANSCRIPT
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Corrosion Engineering ME 4953/ME 5013
Spring 2015
Chapter 5 Polarization Methods to Measure Corrosion Rate
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Introduction
3/25/2015 Corrosion Engineering, Spring 2015 2
Corrosion rate can be determined by weight loss measurements or electrochemical polarization methods. Weight loss measurements monitor the dissolution
rate as a function of area and time of exposure. These are time consuming.
Electrochemical polarization methods are based on the principle: Amount of metal dissolution Amount of current passing
through the solution
Corrosion rate Current density
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Electrochemical Polarization Methods
Polarization is defined as the deviation of potential from equilibrium potential because of net charge flow (current flow).
Polarization methods are nondestructive and may be repeated numerous times to measure consecutive corrosion rates on the same electrode.
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Electrochemical Polarization Methods
Tafel extrapolation
Polarization resistance
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Tafel Extrapolation
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Tafel Extrapolation
Method is applicable only to systems containing one reduction reaction.
Tafel region must extend over a current range of at least one order of magnitude.
Not achievable because of interference from concentration polarization and other extraneous effects.
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Applied-Current Linear Polarization method
The applied current density is a linear function of the electrode potential.
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Advantages of linear-polarization technique
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Polarization Resistance Method
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Galvanostatic Method
Polarization resistance curve Potential-time strip-chart trace during polarization resistance measurement on zinc coating on steel in 0.1N NaCl at room temperature.
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Electrochemical Impedance Spectroscopy Method
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Electrochemical Impedance Spectroscopy Method - Principles
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Electrochemical Impedance Spectroscopy Method - Equations
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Electrochemical Impedance Spectroscopy Method
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Electrochemical Impedance Spectroscopy Method
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Electrochemical Impedance Spectroscopy Method- Data
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Electrochemical Impedance Spectroscopy Method - Data
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Electrochemical Impedance Spectroscopy Method - Data
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Summary
EIS has the capability to give valid measurements of polarization resistance rate corrected for ohmic interferences from solution resistance.