Corrosion of Aluminium

Christian Vargel

• Publisher: Elsevier Science
• Year: 2004
• Topic: Technology & Engineering
• eBook ISBN:
  9780080472362
• Subtopic: Mining Engineering
• Index: Technology & Engineering

Corrosion of Aluminium highlights the practical and general aspects of the corrosion of aluminium alloys with many illustrations and references. In addition to that, the first chapter allows the reader who is not very familiar with aluminium to understand the metallurgical, chemical and physical features of the aluminium alloys. The author Christian Vargel, has adopted a practitioner approach, based on the expertise and experience gained from a 40 year career in aluminium corrosion This approach is most suitable for assessing the corrosion resistance of aluminium- an assessment which is one of the main conditions for the development of many uses of aluminium in transport, construction, power transmission etc. - 600 bibliographic references provide a comprehensive guide to over 100 years of related study - Providing practical applications to the reader across many industries - Accessible to both the beginner and the expert

Part B

The Corrosion of Aluminium

Chapter B.1

Introducton to The Corrosion of Aluminium

The verb “corrode” is derived from the Latin word rodere which means “gnaw”. This word entered the French language in 1314 to designate the action of gnawing, progressively wearing away by a chemical effect. The noun “corrosion” was derived at the beginning of the 19th century from the Lower Latin corrosio, which designates the act of gnawing. It was first introduced in medical vocabulary [1], and later came into use for the phenomenon that forms the subject matter of the present book.

Defining “corrosion” is, however, not an easy task. Corrosion is a slow, progressive or rapid deterioration of a metal’ s properties such as its appearance, its surface aspect, or its mechanical properties under the influence of the surrounding environment: atmosphere, water, seawater, various solutions, organic environments, etc.

In the past, the term “oxidation” was frequently used to designate what is nowadays commonly called “corrosion”. Nevertheless, the former was the right word because corrosion also is an electrochemical reaction during which the metal is oxidised, which usually implies its transformation into an oxide, i.e. into the state in which it existed in the mineral.

1.1 SHORT HISTORICAL INTRODUCTION

The phenomenon of corrosion has been known ever since the discovery of metals. Pliny the Younger was already complaining about the Roman soldiers’ weapons getting rusty. Scientific investigation started at the beginning of the 19th century with Nicholson and Carlyle’s discovery of the electrolytic decomposition of water by the electric current supplied by a galvanic battery [2].

Humphrey Davy established a relationship between the production of electricity and the oxidation of zinc, in which one of the two metals was copper and the other acted as the generator of electricity. In 1830, the Genevan chemist Auguste de la Rive developed the basis of the electrochemical theory of corrosion. At the beginning of the 20th century, this theory was taken up by Whitney, and completed by Hoar and Evans at the end of the 1920s [3].

During the first quarter of the 20th century, the full economic cost of the corrosion of metals was perceived. The first reported corrosion experiments on aluminium started around 1890, when the metal was available in a quantity sufficient to envision its use for construction and as kitchen utensils. Its resistance to rainwater and various types of drinks, such as beer, coffee, and tea, was first assessed at the beginning of the 1890s [4].

1.2 THE ELECTROCHEMICAL BASIS OF METAL CORROSION

Corrosion of metals is caused by the electrochemical reaction between a metal (or an alloy) and an aqueous phase. It proceeds according to a complex electrochemical process that is related to the atomic structure of matter. Matter is built up from elementary particles that carry electrical charges, namely ions and electrons, and from particles that are electrically neutral, namely atoms and molecules. In metals, the electrical environment of atoms is made up of free electrons capable of moving throughout the metal.

In the aqueous phase, which is a solution, the following species can be found:

– positive ions (cations) and negative ions (anions),

– neutral molecules such as water and various undissociated compounds.

At the interface between metal and water, the transfer of electrical charges leads to electrochemical reactions (Figure B.1.1):

Figure B.1.1 Electrochemical reactions at the metal–solution interface [5].

– The metal atom is oxidised and forms Mⁿ⁺ions that are released in the aqueous phase. This creates a flux of electrons within the metal in the direction solution →metal. The resulting anodic oxidation current ia flows from the metal to the solution.

– The ions or molecules of the aqueous phase are reduced, which means that they take up electrons from the metal and get transformed into another chemical species. This creates a flux of electrons within the metal in the direction metal→solution. The resulting cathodic current i_k flows from the solution to the metal.

Electrons that interact at the metal- solution interface do not penetrate the solution.

1.2.1 Elementary electrochemical reactions of corrosion

The corrosion of a metal is the result of two simultaneous reactions that are in electrical equilibrium:

– the oxidation of the metal, resulting in a loss of electrons, according to the fundamental reaction

It results in an anodic current i_a that flows in the direction

– the reduction of an ion present in the aqueous solution according to the fundamental reaction

It results in a cathodic current i_k that flows in the direction

– The reactions of oxidation and reduction proceed at distinct sites of the metal surface. The surface a...

Table of contents

• Cover image
• Title page
• Table of Contents
• Inside Front Cover
• Copyright
• Dedication
• Foreword
• Foreword to the Original French Edition
• Introductory Remark
• Preface to the Original French Edition
• Acknowledgements
• Part A: Aluminium and Its Alloys
• Part B: The Corrosion of Aluminium
• Part C: Atmospheric Corrosion of Aluminium
• Part D: Corrosion in Water
• Part E: The Action of Inorganic Products
• Part F: The Action of Organic Products
• Part G: The Effect of Other Environments
• Products that may be Dangerous in Contact with Aluminium
• General References
• Glossary
• Index