Study on the model of corrosion resistance based on the semiconductive properties of the passive film formed on the surface of stainless steels

다국어 초록 (Multilingual Abstract)

The passive film is a key protective barrier that suppresses localized corrosion of metals, and its stability is governed by charge transport characteristics, structural composition, and point defect kinetics within the oxide. Early studies attempted to explain passivation based on oxide film theory and adsorption-based mechanisms; however, these approaches were insufficient to provide a comprehensive understanding of long-term film stability. To address these limitations, the Point Defect Model (PDM) and the Bipolar model have been proposed, but each has inherent constraints in either quantitative or structural interpretation. In particular, a unified understanding linking the effects of alloy composition and corrosion environments to the electrical and semiconductive properties of passive films and ultimately to corrosion resistance has not been fully established. In this study, the influence of alloying elements (Cr, Mo, and W), pitting resistance equivalent (PRE) number, and corrosion environment (pH) on the semiconductive characteristics and structural stability of passive films formed on stainless steels was systematically investigated, with the goal of proposing a new interpretive framework for passive film reinforcement. First, the passive films formed on ferritic stainless steels with varying Cr, Mo, and W contents were quantitatively analyzed, and a new parameter, the Bipolar index, was introduced based on the slopes of p-type and n-type semiconductor behavior. Second, the Bipolar index was expanded and applied to austenitic stainless steels with different PRE values, revealing that an increase in PRE enhances p-type characteristics attributable to Cr oxides in the inner layer, along with the development of n-type characteristics associated with Mo-containing oxides in the outer layer. This result demonstrates that the Bipolar index reflects the electrochemical driving force governing passive film formation and stabilization. Third, the electrochemical behavior of passive films formed on a representative super austenitic stainless steel, SR-50A, was examined under acidic and alkaline conditions. The results confirmed that corrosion resistance is maximized when the p-type and n-type semiconductive properties of the inner and outer layers, respectively, are balanced within a specific range, indicating the existence of an optimal electronic configuration for passive film stability. Lastly, dynamic environmental transition tests experimentally demonstrated that passive films are not static layers but dynamically reconstructed structures that adapt to external corrosion environments. This study clarifies the correlation between the structural and electronic characteristics of passive films and proposes a new evaluation basis for predicting corrosion resistance in stainless steels, providing both academic significance and practical implications for alloy design and passivation strategies. Keywords: Stainless steel, Passive film, Semiconductive properties, Point defect model, Bipolar model, Mott-Schottky, XPS, Difference in semiconductive tendencies, Bipolar index

목차 (Table of Contents)

• CHAPTER 1. INTRODUCTION 1
• 1.1 Literature survey 1
• 1.2 Objectives 3
• 1.3 References 4
• CHAPTER 2. THEORETICAL BACKGROUND 8
• 2.1.1 Concept Formation and Historical Development of Stainless Steel 8
• 2.1.2 Development of Stainless Steel by Alloy Series 9
• 2.1.1.1 Ferritic Stainless Steels 9
• 2.1.1.2 Martensitic Stainless Steels 10
• 2.1.1.3 Austenitic Stainless Steels 10
• 2.1.1.4 Duplex Stainless Steels 11
• 2.1.1.5 Precipitation Hardening Stainless Steels 11
• 2.1.3 Emergence of the PRE Concept and a Turning Point in Alloy Design 11
• 2.1.4 Development of High-Corrosion-Resistance (Super-Grade) Stainless Steels . 13
• 2.2 Passivity theory 14
• 2.2.1 Definition and concept of passivity 14
• 2.2.2 Major Theories on Passive Film Formation 15
• 2.2.2.1 Oxide Film Theory 15
• 2.2.2.2 Adsorption theory 16
• 2.2.2.3 Electron configuration induced adsorption passivity 16
• 2.2.2.4 Ion space charge induced passivity 16
• 2.2.3 Models for the Enhancement of Passive Film Characteristics 20
• 2.2.3.1 Point Defect Model (PDM) 21
• 2.2.3.2 Bipolar model 28
• 2.3 Reference 32
• CHAPTER 3. MECHANISM FOR STRENGTHENING THE PROPERTIES
• OF THE PASSIVE FILM BY THE ALLOYING ELEMENTS 36
• 3.1 Bipolar Index of the Passive Film Formed on Ferritic Stainless Steels by Cr,
• Mo, and W additions. 36
• 3.1.1 Introduction 36
• 3.1.2 Materials and Methods 39
• 3.1.2.1 Materials 39
• 3.1.2.2 Anodic Polarization Test 41
• 3.1.2.3 Potentiostatic EIS Test 41
• 3.1.2.4 XPS Analysis 42
• 3.1.2.5 Mott–Schottky Analysis 42
• 3.1.3 Results 43
• 3.1.3.1 Effect of Cr, Mo, and W Contents on the Electrochemical Properties 43
• 3.1.3.2 Effect of Cr, Mo, and W Contents on the XPS Analysis 48
• 3.1.4 Discussion 63
• 3.1.5 Conclusions 74
• 3.1.6 References 75
• 3.2 Bipolar Index of the Passive Film Formed on Austenitic Stainless steels by PRE
• number 82
• 3.2.1 Introduction 82
• 3.2.2 Experimental Methods 85
• 3.2.2.1 Materials 85
• 3.2.2.2 Polarization test 87
• 3.2.2.3 AC impedance test 87
• 3.2.2.4 XPS analysis 88
• 3.2.2.5 Mott-Schottky analysis 88
• 3.2.3 Results 89
• 3.2.3.1 Effect of PRE on the electrochemical properties of stainless steels 89
• 3.2.4 Discussion 99
• 3.2.5 Conclusions 125
• 3.2.6 References 126
• CHAPTER 4. MECHANISM FOR STRENGTHENING THE PROPERTIES
• OF THE PASSIVE FILM BY THE CORROSION ENVIRONMENT 132
• 4.1 Passive Film by the Corrosion Environment Semiconductive tendency of the
• passive film formed on super austenitic stainless steel SR-50A in acidic or alkaline
• chloride solutions 132
• 4.1.1 Introduction. 132
• 4.1.2 Materials and Methods 136
• 4.1.2.1 Experimental Alloy and Test Solution 136
• 4.1.2.2 Anodic Polarization Test 136
• 4.1.2.3 Potentiostatic EIS test 137
• 4.1.2.4 Mott-Schottky analysis 137
• 4.1.2.5 XPS 138
• 4.1.3 Result 140
• 4.1.3.1 Effect of pH on corrosion behavior and semiconductive properties 140
• 4.1.3.2 Surface analysis on the passive film formed in acidic or alkaline chloride
• solutions 152
• 4.1.4 Discussion 159
• 4.1.5 Conclusions 169
• 4.1.6 Reference 170
• 4.2 Dynamic Variation in the semiconductive Tendency of the Passive Film on
• Duplex Stainless Steel in Corrosion Environments 176
• 4.2.1 Introduction. 176
• 4.2.2 Materials and Methods 179
• 4.2.2.1 Experimental Alloy 179
• 4.2.2.2 Polarization Test 182
• 4.2.2.3 Potentiostatic EIS Test 182
• 4.2.2.4 Mott–Schottky Analysis 184
• 4.2.2.5 XPS 184
• 4.2.2.6 Dynamic Electrochemical Test 185
• 4.2.3 Results and Discussion 185
• 4.2.3.1 Electrochemical Properties and Semiconductive Tendencies in Chloride
• Solutions Under Static Conditions 185
• 4.2.3 Results and Discussion 200
• 4.2.3.1 Electrochemical Properties and Semiconductive Tendency in Acidic
• Chloride Solutions Under Dynamic Conditions 200
• 4.2.4 Conclusions 210
• 4.2.5 Reference 211
• CHAPTER 5 CONCLUSIONS 216