**Meet the editor**

Nasr Bensalah, Ph.D., H.D.R., is Associate Professor of Electrochemistry at University of Gabes, Tunisia, and Research Scientist at Texas A&M University at Qatar, Qatar. He received his B.Sc. degree in Chemistry in 1995, M.Sc. degree in Physical Chemistry in 1997, Ph.D. degree in Electrochemistry in 2002 from Faculty of Sciences of Monastir, Tunisia, and H.D.R. degree in Environmen-

tal Electrochemistry in 2007 from Faculty of Sciences of Tunis, Tunisia. Dr. Bensalah held the positions as Senior Lecturer from 1999 to 2003, Assistant Professor from 2003 to 2007, and Associate Professor since 2007 at University of Gabes, Tunisia. He taught courses related to Analytical Chemistry, Environmental Chemistry, and electrochemistry for undergraduate and graduate students.His awards include a Fulbright Scholarship from U.S. Department of State in 2008, AUF Fulbright fellowship in 2006, AECI Spanish government scholarship in 2004. During his academic career, He had been involved in many administrative positions at departmental and university levels. His research interests cover the fields of Electrochemical and Environmental Engineering. His research activities are mainly focused on the electrochemical treatment of water and wastewater, and the monitoring and the control of corrosion, with emphasis on Al and Fe Alloys. Additionally, he conducted some investigations on water and wastewaters treatment by different processes including coagulation and adsorption techniques, disinfection, and advanced oxidation processes. He authored and coauthored about 50 papers in recognized international journals and he supervised more than 10 graduate students.

Contents

**Preface VII** 

J. S. Punni

Chapter 2 **Mechanism of Pit Growth** 

G. Knörnschild

A. Prateepasen

Chapter 1 **Electrochemical Characterisation to Study** 

Dimitra Sazou, Maria Pavlidou,

Chapter 5 **Systemic and Local Tissue Response to Titanium Corrosion 93** 

Chapter 6 **Importance of Etch Film Formation** 

Fong-Yuan Ma

Chapter 7 **Corrosive Effects of Chlorides on Metals 139** 

**the Pitting Corrosion Behaviour of Beryllium 1** 

Chapter 3 **Pitting Corrosion Monitoring Using Acoustic Emission 43** 

Chapter 4 **Oscillatory Phenomena as a Probe to Study Pitting Corrosion of Iron in Halide-Containing Sulfuric Acid Solutions 61** 

Aggeliki Diamantopoulou and Michael Pagitsas

Daniel Olmedo, Deborah Tasat, Gustavo Duffó, Rómulo Cabrini and María Guglielmotti

**During AC Controlled Pitting of Aluminium 119**  Maria Tzedaki, Iris De Graeve, Bernhard Kernig, Jochen Hasenclever and Herman Terryn

**in Homogeneous Aluminum Alloys 27** 

## Contents

### **Preface XI**



Preface

The Pitting corrosion book covers recent research challenges and various accomplishments in the field of corrosion. The book is a proven record of excellent

Pitting corrosion involves local dissolution followed by the formation of cavities on metals surfaces coated with a passive film, when exposed to an aqueous solution containing aggressive anions, such as chloride and sulfate. Pitting is one of the most destructive forms of corrosion, as it causes potential failure of metals and alloys due to perforation/penetration. Pitting corrosion can be quite small on the surface and very large on the subsurface. The process consists of various stages including passive film breakdown, metastable attack, stable growth and pit stifling or death. The breakdown of the passive film is required for pits to initiate. The metastable pitting phase can be considered as a key stage of pitting corrosion, since only pits that continue to grow become stable growing pits. Pitting is influenced by metal composition, electrode potential, temperature, surface condition, and environmental parameters such as

Accurate and efficient detection and monitoring of pitting corrosion is very challenging. Pitting failures can occur unexpectedly, and with minimal overall metal loss. The monitoring of pitting corrosion can be further complicated by a distinction between the initiation and propagation phases of pitting processes. Developing and understanding the mechanisms by which pits form and propagate may allow engineers to build more accurate corrosion models in order to predict the lifetime of

The first chapter addresses the electrochemical characterization of pitting corrosion with an emphasis on the behavior of beryllium using single and poly crystalline scales under different conditions, such as the presence of chloride, using SEM examination techniques. The second chapter discusses the general mechanisms of pit growth during pitting corrosion in general, using Al and Al alloys as examples while focusing

Pitting corrosion monitoring and detection using acoustic emission is covered in chapter three using detailed discussions of the theoretical and experimental design of

components and, thus plan when inspection and replacement are needed.

on pitting morphology, pit propagation, and hydrogen evolution results.

scientific achievements in the field of pitting corrosion.

aggressive ion concentration, pH, and inhibitor concentration.

## Preface

Pitting corrosion involves local dissolution followed by the formation of cavities on metals surfaces coated with a passive film, when exposed to an aqueous solution containing aggressive anions, such as chloride and sulfate. Pitting is one of the most destructive forms of corrosion, as it causes potential failure of metals and alloys due to perforation/penetration. Pitting corrosion can be quite small on the surface and very large on the subsurface. The process consists of various stages including passive film breakdown, metastable attack, stable growth and pit stifling or death. The breakdown of the passive film is required for pits to initiate. The metastable pitting phase can be considered as a key stage of pitting corrosion, since only pits that continue to grow become stable growing pits. Pitting is influenced by metal composition, electrode potential, temperature, surface condition, and environmental parameters such as aggressive ion concentration, pH, and inhibitor concentration.

Accurate and efficient detection and monitoring of pitting corrosion is very challenging. Pitting failures can occur unexpectedly, and with minimal overall metal loss. The monitoring of pitting corrosion can be further complicated by a distinction between the initiation and propagation phases of pitting processes. Developing and understanding the mechanisms by which pits form and propagate may allow engineers to build more accurate corrosion models in order to predict the lifetime of components and, thus plan when inspection and replacement are needed.

The first chapter addresses the electrochemical characterization of pitting corrosion with an emphasis on the behavior of beryllium using single and poly crystalline scales under different conditions, such as the presence of chloride, using SEM examination techniques. The second chapter discusses the general mechanisms of pit growth during pitting corrosion in general, using Al and Al alloys as examples while focusing on pitting morphology, pit propagation, and hydrogen evolution results.

Pitting corrosion monitoring and detection using acoustic emission is covered in chapter three using detailed discussions of the theoretical and experimental design of

The Pitting corrosion book covers recent research challenges and various accomplishments in the field of corrosion. The book is a proven record of excellent scientific achievements in the field of pitting corrosion.

### VIII Preface

such testing techniques with application to stainless steel. Chapter four discusses the use of oscillatory phenomena and non-linear dynamic behavior as a probe to study pitting corrosion of iron in halide-containing sulfuric acid solutions. Chapter five deals with the effect of micro-structural heterogeneity on pitting susceptibility, with an application to induction-quenched steel pipeline using different metallographic examination techniques.

Chapter six discusses a very interesting topic related to associated toxicity and biological risks of pitting corrosion of metallic biomaterials, used as dental and orthopedic implants, with emphasis on biological, sanitary, metallurgical, economical, and social point of view.

In chapter seven, positive application to the pitting phenomena, such as the importance of etch film formed during an alternating current electrograining mechanism, as well as the morphology for pitting of aluminum surfaces to obtain high surface area. The chapter discuses in details the different conditions and parameters that affect the AC electrograining process in relation to the final pitting morphology.

Chapter eight discusses the corrosive effect of chloride ions on metals, with emphasis on pitting corrosion and fatigue of stainless steel in relation to changes in microstructure and the durability of the metal.

Taking into account that corrosion is costly and dangerous phenomenon, it becomes obvious that people engaged in the design and the maintenance of structures and equipment, should have a basic understanding of localized corrosion processes. The Editor hopes that this book will be helpful for researchers in conducting investigations in the field of localized corrosion, as well as for engineers encountering pitting and crevice corrosion, by providing some basic information concerning the causes, prevention, and control of pitting corrosion.

> **Dr. Nasr Bensalah**  Associate Professor, Faculty of Sciences of Gabes, Tunisia

VIII Preface

examination techniques.

and social point of view.

microstructure and the durability of the metal.

prevention, and control of pitting corrosion.

such testing techniques with application to stainless steel. Chapter four discusses the use of oscillatory phenomena and non-linear dynamic behavior as a probe to study pitting corrosion of iron in halide-containing sulfuric acid solutions. Chapter five deals with the effect of micro-structural heterogeneity on pitting susceptibility, with an application to induction-quenched steel pipeline using different metallographic

Chapter six discusses a very interesting topic related to associated toxicity and biological risks of pitting corrosion of metallic biomaterials, used as dental and orthopedic implants, with emphasis on biological, sanitary, metallurgical, economical,

In chapter seven, positive application to the pitting phenomena, such as the importance of etch film formed during an alternating current electrograining mechanism, as well as the morphology for pitting of aluminum surfaces to obtain high surface area. The chapter discuses in details the different conditions and parameters that affect the AC electrograining process in relation to the final pitting morphology.

Chapter eight discusses the corrosive effect of chloride ions on metals, with emphasis on pitting corrosion and fatigue of stainless steel in relation to changes in

Taking into account that corrosion is costly and dangerous phenomenon, it becomes obvious that people engaged in the design and the maintenance of structures and equipment, should have a basic understanding of localized corrosion processes. The Editor hopes that this book will be helpful for researchers in conducting investigations in the field of localized corrosion, as well as for engineers encountering pitting and crevice corrosion, by providing some basic information concerning the causes,

> **Dr. Nasr Bensalah**  Associate Professor,

> > Tunisia

Faculty of Sciences of Gabes,

**1** 

J. S. Punni\* *AWE, Reading* 

*UK* 

**Electrochemical Characterisation to Study the** 

Beryllium has widespread uses in aerospace industry as it has attractive mechanical properties, a high melting point (1289 °C), a low density (1.85 g/cc), high specific heat capacity and thermal conductivity. It has a hexagonal close packed (hcp) structure and due to its low neutron cross section it is widely used for nuclear applications. To achieve the required mechanical properties beryllium is produced by vacuum hot pressing in the temperature range 1000 to 1100°C, using a high purity and fine grained beryllium powder. To get stress relief, the material is subsequently heat treated at 800°C; this also serves to remove elemental aluminium at grain boundaries in material structure, by converting it to the intermetallic form AlFeBe4. A proper balance between Fe and Al is required to avoid

'hot shortness' due to the presence of elemental aluminium at the grain boundaries.

Other elements are also present but generally at very low levels.

leads to accelerated attack in this location.

© British Crown Owned Copyright 2011/MOD

 \*

The principle contaminants within commercial beryllium are oxygen (as beryllium oxide), carbon, silicon, iron, aluminium and magnesium. Silicon, iron and aluminium principally come from the ore, although additional iron may be contributed from billet machining operations. Magnesium arises primarily from reduction of beryllium fluoride using magnesium to produce beryllium metal. Carbon arises principally from casting operations, which use graphite moulds. Oxygen is always present as an oxide film on powder particles.

Past studies have shown that beryllium is susceptible to pitting corrosion in the presence of chloride, fluoride and sulphate ions (Hill, et al., 1996, 1998; Stonehouse & Weaver, 1965). This is due to the breakdown of passive film at localised sites resulting in sporadic pits. The pitting is an insidious form of corrosion since it can proceed unnoticed and can lead to a catastrophic component failure. During the pitting process most of the metal surface remains passive and acts as the cathodic site for a small anodic area inside the pit which

Pitting corrosion is a localised form of corrosion by which cavities and holes are produced in the material, which are generally plugged with corrosion products. Corrosion, in general, is an electrochemical process in which electrons are generated and consumed at the corroding metal surface. This process consists of (i) an anodic site at the metal surface where metal is

**1. Introduction** 

**Pitting Corrosion Behaviour of Beryllium** 
