Handbook of Aluminum

Volume 2: Alloy Production and Materials Manufacturing

George E. Totten, D. Scott MacKenzie, George E. Totten, D. Scott MacKenzie

• Publisher: CRC Press
• Year: 2003
• eBook ISBN: 9781135542238
• Topic: Technology & Engineering
• Subtopic: Industrial Engineering
• Index: Technology & Engineering

This reference provides thorough and in-depth coverage of the latest production and processing technologies encountered in the aluminum alloy industry, discussing current analytical methods for aluminum alloy characterization as well as extractive metallurgy, smelting, master alloy formation, and recycling. The Handbook of Aluminum: Volume 2 examin

1

Extractive Metallurgy of Aluminum

FATHI HABASHI

Laval University, Quebec City, Canada

1 HISTORY

Since Humphry Davy announced in 1808 his belief that the plentiful compound alumina was the earth (oxide) of an undiscovered metal, scientists had been making efforts to obtain this new metal. Davy never made any aluminum himself; but in 1825, the Danish scientist Hans Christian Oersted (1777–1851) published his successful experiment in producing a tiny sample of the metal in the laboratory by reducing aluminum chloride with potassium amalgam. Potassium was isolated a few years earlier by Davy.

Two years later, Friedrich Wöhler (1800–1882) in Germany produced tiny globules of aluminum by the same method, and was able to demonstrate the metal’s lightweight and malleability. Henri Sainte–Claire Deville (Fig. 1) in France in 1854 showed that cheaper sodium could also be used, and the first commercial plant producing small quantities of aluminum was begun in 1855. Since potassium and sodium were produced electrolytically, the process was expensive.

In 1886, following the development of large-scale equipment for generating electrical power, Paul Héroult (Fig. 2a) in France, and Charles Hall (Fig. 2b) in the United States, independently developed a process for the direct electrolytic decomposition of Al₂O₃. They discovered that when an electric current is passed through molten cryolite containing dissolved Al₂O₃ at 980–1000°C, molten aluminum is deposited at the cathode and carbon dioxide is liberated at the carbon anode. This discovery, coupled with the process developed by Karl Josef Bayer (Fig. 3) in 1888 for the production of alumina, resulted in the modern process for the production of aluminum.

Figure 1 Henri Sainte–Claire Deville (1818–1881), the first to produce aluminum on commercial scale by reduction of AlCl3 with sodium.

2 GENERAL REMARKS

Aluminum comprises 8% of the earth’s crust and is, therefore, the most abundant structural metal. Its production since 1965 has surpassed that of copper and now comes next to iron (Fig. 4). Its unit price started very high and today is comparable to copper (Fig. 5). It is competing with copper in the electric industry and as a material of construction. Although the electrical conductivity of aluminum is slightly lower than that of copper, it is still economical to use in preference to copper in power cables because of its lighter weight. As a material of construction, aluminum can be anodized to get a protective oxide film, which can be dyed to give a colorful appearance. For the production of the metal, the following points should be taken into consideration:

• The electrowinning of aluminum from an aqueous solution is not possible because of the strongly negative deposition potential of this metal and the rapid hydrolysis of the aluminum ion.

• Oxides in general have high melting points. Therefore, for the electrowinning of aluminum from its oxide, a suitable low melting point electrolyte must be found in which the oxide is appreciably soluble.

• In the manufacture of aluminum, there are two main stages. The first embraces the production of pure Al₂O₃ from bauxite, and the second is the reduction of this Al₂O₃ to the metal in a bath of fused cryolite (Fig. 6).

• In the electrowinning of aluminum from oxide melts, the carbon anodes are quantitatively consumed.

• The production of alumina from bauxite is the largest pressure leaching operation in the world.

• Similarly, the production of aluminum by the molten salt electrolysis of alumina in cryolite is the most important industrial application of molten salt electrowinning and is the largest electrolytic industry in the world.

• The electrolytic step in aluminum production is the most energy intensive operation (Table 1).

Figure 2 (Top) Paul Héroult (1863–1914) and (bottom) Charles Martin Hall (1863–1914) invented simultaneously and independently the electrolytic process for reduction of Al₂O₃.

Figure 3 Karl Josef Bayer (1871–1908) invented the process for producing Al₂O₃ from bauxite.

• Material handling is a major cost factor in aluminum production. For each ton of aluminum produced, more than 3 tons of materials are transported to and from potlines.

• The electrolytic process produces aluminum with purity as great as 99.5–99.8%. Higher purity (99.99%) is obtained by an electrolytic refining process.

3 RAW MATERIALS

The produc...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Preface
• Table of Contents
• Contributors
• 1. Extractive Metallurgy of Aluminum
• 2. Smelting of Aluminum
• 3. Creation of Master Alloys for Aluminum
• 4. Recycling of Aluminum
• 5. Analytical Techniques for Aluminum
• 6. Work Hardening, Recovery, Recrystallization, and Grain Growth
• 7. Modeling of Microstructural Evolution During Processing of Alumium Alloys
• 8. Texture-Property Relationships in Aluminum Alloys: Simulations and Experiments
• 9. Property Prediction
• 10. Mechanical Properties
• 11. Corrosion of Aluminum and Its Alloys
• 12. Surface Chemistry of Adhesion to Aluminum
• 13. Surface Modification
• 14. Aluminum Nitriding
• 15. Friction Stir Welding of Aluminum Alloys
• 16. Aluminum Intermetallics
• 17. Aluminum-Based Metal Matrix Composites
• 18. Environmental and Toxicological Effects
• Appendixes
• Index