Effect of Alloying Elements on the Corrosion Behavior of Low Alloy Steels

다국어 초록 (Multilingual Abstract)

Alloying effect of antimony (Sb) and chromium (Cr) on the corrosion behavior of low alloy steel for flue gas desulfurization (FGD) systems and for acid rain corrosion resistance, respectively, were studied based on the electrochemical measurements (potentiodynamic polarization test, potentiostatic test, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR)) and chemical measurement (weight loss test), together with surface analysis techniques (scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS)). The results of the measurements in modified green death solution
(pH -0.3, 60oC) revealed that Sb addition (0.05 or 0.10 wt.%) improved the corrosion rate of blank steel due to the formation of a highly protective Sb2O5 containing oxide film on the surface of the Sb-containing steels. Moreover, the addition of 0.10% Sb stimulated the development of high corrosion inhibiting, Cu-containing compounds which further inhibited the anodic and cathodic reactions. The results of the measurements in mild acid-chloride solution (200 ppm Cl-, pH 4) revealed that Cr addition (0.1or 0.3 wt.%) had a beneficial effect to blank steel since Cr promoted the formation of the Cu compounds on the rust layer surface of steels. However, the over-alloying circumstance of 0.5% Cr addition caused the negative effect of Cr addition by the mechanism of the hydrolysis of metal chlorides. That yielded to the localized pH decrease in the concentration cell, promoted the autocatalytic process and accelerated the propagation of the localized corrosion. The localized corrosion occurred on the steel surfaces was observed by means of SEM images.

목차 (Table of Contents)

• 1. INTRODUCTION 1
• 2. LITERATURE REVIEW 2
• 2.1. Corrosion of Steel Structures 2
• 2.1.1. Fundamental Theory 2
• 2.1.2. Thermodynamic Potential-pH Diagrams 8
• 2.1.3. Low-alloy Steels 9
• 2.1.4. Corrosion of Material in Flue Gas Desulfurization System 10
• 2.1.5. Corrosion of Material in Acid Rain Environment 13
• 2.2. Electrochemical Analysis Technique for the Study of Corrosion 15
• 2.2.1. Open-circuit Potential Test 16
• 2.2.2. Potentiodynamic Polarization Test 16
• 2.2.3. Potentiostatic Test 20
• 2.2.4. Linear Polarization Resistance (LPR) 22
• 2.2.5. Electrochemical Impedance Spectroscopy (EIS) 24
• 2.3. Weight Loss Measurement for the Study of Corrosion 38
• 2.4. Conducting an Electrochemical Experiment 38
• 2.5. Conversion of Experimental Data to Corrosion Rate 42
• 3. ALLOYING EFFECT OF ANTIMONY ON THE CORROSION
• BEHAVIOR OF LOW ALLOY STEEL FOR FLUE GAS ESULFURIZATION SYSTEMS 45
• 3.1. Experimental Procedures 45
• 3.1.1. Materials 45
• 3.1.2. Electrolyte 47
• 3.1.3. Electrochemical Measurements 47
• 3.1.4. Weight loss Measurements 48
• 3.1.5. Surface Analysis 49
• 3.2. Results and Discussion 50
• 3.2.1. Potentiodynamic Polarization Test 50
• 3.2.2. Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR) Measurements 52
• 3.2.3. Weight Loss Measurements 59
• 3.2.4. Surface Analysis 62
• 3.3. Conclusions 69
• 4. ALLOYING EFFECT OF CHROMIUM ON THE CORROSION BEHAVIOR OF LOW ALLOY STEEL IN A MILD ACID-CHLORIDE SOLUTION 70
• 4.1. Experimental Procedures 70
• 4.1.1. Materials 70
• 4.1.2. Electrolyte 71
• 4.1.3. Electrochemical Measurements 71
• 4.1.4. Surface Analysis 72
• 4.2. Results and Discussion 73
• 4.2.1. Potentiodynamic Polarization Test 73
• 4.2.2. Potentiostatic Test 75
• 4.2.3. Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR) Measurements 77
• 4.2.4. Surface Analysis 85
• 4.3. Conclusions 93
• 5. REFERENCES 94