Page 6 - Corrosion Engineering Principles and Practice

iv C o n t e n t s C o n t e n t s v

4.5 Reference Half-Cells (Electrodes) . . . . . . . . . . . 62
4.5.1 Conversion between References . . . . . 66
4.5.2 Silver/Silver Chloride
Reference Electrode . . . . . . . . . . . . . . . 66
4.5.3 Copper/Copper Sulfate
Reference Electrode . . . . . . . . . . . . . . . 68
4.6 Measuring the Corrosion Potential . . . . . . . . . . 71
4.7 Measuring pH . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.7.1 Glass Electrodes . . . . . . . . . . . . . . . . . . 73
4.7.2 Antimony Electrode . . . . . . . . . . . . . . 74
4.8 Potential-pH Diagram . . . . . . . . . . . . . . . . . . . . 74
4.8.1 E-pH Diagram of Water . . . . . . . . . . . . 75
4.8.2 E-pH Diagrams of Metals . . . . . . . . . . 76
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5 Corrosion Kinetics and Applications
of Electrochemistry to Corrosion . . . . . . . . . . . . . 85
5.1 What Is Overpotential? . . . . . . . . . . . . . . . . . . . . 85
5.2 Activation Polarization . . . . . . . . . . . . . . . . . . . . 86
5.3 Concentration Polarization . . . . . . . . . . . . . . . . 90
5.4 Ohmic Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.4.1 Water Resistivity Measurements . . . . 94
5.4.2 Soil Resistivity Measurements . . . . . . 97
5.5 Graphical Presentation of Kinetic Data
(Evans Diagrams) . . . . . . . . . . . . . . . . . . . . . . . . 103
5.5.1 Activation Controlled Processes . . . . . 103
5.5.2 Concentration Controlled
Processes . . . . . . . . . . . . . . . . . . . . . . . . 104
5.6 Examples of Applied Electrochemistry
to Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
5.6.1 Electrochemical Polarization
Corrosion Testing . . . . . . . . . . . . . . . . . 107
5.6.2 Corrosion Monitoring . . . . . . . . . . . . . 121
5.6.3 Cathodic Protection . . . . . . . . . . . . . . . 134
5.6.4 Anodic Protection . . . . . . . . . . . . . . . . . 135
5.6.5 Aluminum Anodizing . . . . . . . . . . . . . 137
5.6.6 Chloride Extraction . . . . . . . . . . . . . . . 142
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
6 Recognizing the Forms of Corrosion . . . . . . . . . . . . 147
6.1 Recognizing Corrosion . . . . . . . . . . . . . . . . . . . . 147
6.2 General or Uniform Attack . . . . . . . . . . . . . . . . 151
6.3 Localized Corrosion . . . . . . . . . . . . . . . . . . . . . . 155
6.3.1 Pitting Corrosion . . . . . . . . . . . . . . . . . 155
6.3.2 Crevice Corrosion . . . . . . . . . . . . . . . . . 164