Chapter 22: The Elements in Nature and Industry

Homework:

How Elements Occur in Nature

Sources Of Elements

Metallurgy

 Cycling Elements Through the Environment

Carbon

Nitrogen

Phosphorous

Metallurgy

Metallurgy is the scientific study of the production of metals from their ores and the making of alloys.  Three steps are important in obtaining metals from ore.

Preliminary treatment concentrates the ore.

Reduction reduces the metal to elemental form.

Refining purifies the metal.

Smelting Process

3CO +   Fe₂O₃  --->  2Fe  +  3CO₂

Roasting 

Hall-Heroult Process

7.66 kg of aluminum oxide is converted to aluminum by the Hall-Heroult process. How many kg of  CO₂ are produced?

The term metallurgy refers to the science and technology of METALS. Metallurgy concerns the extraction of metals from their ores and the subsequent refinement of these metals. Physical metallurgy concerns the physical and mechanical properties of metals, and how metals may be shaped into useful products by means of heat and mechanical processes. Iron and steel and their alloys are among the most important metals and are known as the ferrous metals; aluminum, copper, zinc, nickel, tin, silver, and gold are particularly important nonferrous metals.

Early History                                                  

Metals came into limited use 5,500 years ago when the Egyptians made and wore copper beads, and their rulers bathed in water conveyed by copper pipes from the river Nile to their private pools. Copper nuggets and meteoric iron, as well as gold and silver, were also used in that time. Gold, in the form of nuggets found exposed along riverbeds, was pounded into crude ornaments with a stone hammer. (Unlike copper, gold did not harden appreciably with this pounding, and therefore could not be used to make tools.) Silver nuggets were also used to make rings, bracelets, and other fine ornaments, but not so extensively as gold.

 Some of the most sophisticated early metallurgical techniques evolved around the use of copper, the first industrial metal. The earliest use of natural copper involved an extremely limited Stone Age technique by which small, specially selected pieces of metal were made into beads, awls, pins, or hoops by cold forging, a technique that consisted simply of hammering the cold metal. Early attempts to cold-hammer small pieces of natural copper were able to give only a limited improvement to such pieces. The stone-working techniques (such as simple shaping) found greater success when smiths learned to produce copper of a more malleable form by the process of ANNEALING: exposing the copper to a slow, softening heat. Annealing was a step toward the subsequent melting, or SMELTING, of copper. When smiths discovered that melted pieces of copper could form a single puddle that hardens upon cooling, they were able to use small scrap pieces of metal that would otherwise have been unusable.

 The first efforts to shape molten metal consisted of cutting forms in slabs of stone, or molding forms in clay. To fill these molds, the smith transferred the molten metal to a crucible. Through this process of open-mold CASTING it was possible to shape objects so that very little annealing and hammering were required to produce a finished piece.

 The art of smelting ores to produce metals, discovered near the end of the Stone Age, was applied not only to copper, but also to silver, lead, tin, and probably iron. The production of stronger and more easily shaped ALLOYS proceeded by trial and error. Only after long and undoubtedly unintentional trials with such impurities as antimony and arsenic did tin reveal itself as the ideal addition to copper to form the alloy bronze.

 By the late 4th millennium BC, smiths were remarkably sophisticated in a practical way regarding the individual phenomena of metallurgy. They knew the effects on metals of hammering, annealing, oxidation, melting, and alloying; they were aware of the phenomena of simple decomposition of ores, their reduction, double decomposition, and exchange of impurities; and they knew something of the miscibility and immiscibility of solutions. By 2000 BC, the use of metals had become widespread throughout an area stretching from western and central Anatolia (Turkey), across the flanks of the Taurus and Zagros mountains, and to the edge of the central desert of Iran.

 The Iron Age dates from about 1500 BC, when iron ore is first known to have been smelted. During this era, iron was used mainly for making coins, cooking utensils, and implements of war. The cementation process for making steel and the art of quenching steel for HARDENING and TEMPERING of weapons were discovered early in the Iron Age. The progress of metallurgy moved slowly until about AD 1300, when the Catalan forge was developed in Spain. The forerunner of the modern OPEN-HEARTH FURNACE, it made possible for the first time in history the production of a sizable tonnage of iron in one heat. The forerunner of the modern BLAST FURNACE was the continuous-shaft furnace, developed in Germany about AD 1323. The high-carbon product of this furnace became known as cast iron and broadened the use of iron castings considerably.

From Art to Science

The transition of metallurgy from an art to a science was slow compared to the technological progress in other fields. Its advance was hastened by the beginning of the power age and the coming of the Industrial Revolution in England in the 18th century.

 With the Industrial Revolution came a demand for larger quantities of metal and for greater production capacities. An iron works was erected at Glasport, Hampshire, where the processes for puddling and rolling iron were perfected in 1700. This marked the beginning of the rolling mill, in which iron and steel bars, shapes, and sheets are produced. Because the cementation process of making crucible steels was very costly for large-scale consumption, the predominant structural metal at that time was WROUGHT IRON; it remained so until the invention of the Bessemer converter in 1855 by another English scientist, Sir Henry BESSEMER.

 Not until the 18th century did, scientists begin to appreciate the complex chemistry of metallurgy. Metallography, the study of the structural and physical properties of metals, grew throughout the 19th century. Modern metallurgical techniques such as X-RAY DIFFRACTION, which elucidates the atomic structure of metals, have been discovered in the 20th century.

Modern Techniques

Modern extractive and physical metallurgy makes use of a combination of ancient and modern techniques. Each metal requires a unique process for separation from the ore. By far the most important is the production of pig iron from iron ore by smelting in a blast furnace. Steel is then produced from the pig iron by one of several processes, including the Bessemer process, the open-hearth process, the ELECTRIC-FURNACE process, and the OXYGEN-FURNACE process. Another important extraction process is the production of alumina from bauxite by the Bayer process, and the production of ALUMINUM from alumina by the Hall-Heroult process. Other metals may be separated from their ores by a mechanical FLOTATION PROCESS, such as the CYANIDE PROCESS used for gold, or by an electrolytic process such as the Hall-Heroult process.

 Once the metal is extracted, the methods of physical metallurgy are employed to fabricate the metals into useful products. These include mechanical treatments such as rolling, drawing, forming, or extrusion, which change the shape of the metal; joining processes such as BRAZING and WELDING AND SOLDERING; and finishing techniques such as ELECTROPLATING and galvanizing. The mechanical treatment usually includes a combination of heating and cooling operations such as annealing or hardening to achieve desired properties.

 The techniques of metallography may be used to examine metallic structures before or after fabrication. This is useful for determining what metals are suitable to a particular purpose, or for analyzing deficiencies in metal products. Macroscopic examination is accomplished at a low magnification of less than 10 diameters using a magnifying glass. A specimen may be etched with chemicals to dissolve boundaries and reveal crystal sizes. Subsequent examination of the etched specimens may be used, for example, to control the fabrication of both steel and nonferrous metals and alloys. Microscopic examinations may require a special metallurgical microscope or an ELECTRON MICROSCOPE. The purpose of such examination may be to determine the cause of a metal failure; to study foreign bodies and metal inclusions; or to study the grain structure of a metal to determine how the metal was rolled or forged at the time of fabrication. Tension and compression tests are two of the most important methods of determining the strength of metals, and are relied upon by the metallurgist for basic information. The test bars for these tests are prescribed by the American Society for Testing and Materials (ASTM) and must be accurately prepared in order to yield reliable results.

 As industry requires materials with greater strength and greater resistance to corrosion, ablation, and abrasion, new metallurgical techniques are continually being developed. Among the most important advances have been techniques for joining metals together so that the junctures will be at least as strong as the parent metals themselves. The standard techniques of electric-arc and gas welding have now been joined by electron-beam welding, in which heat is produced by bombarding the metal with a dense beam of high-velocity electrons, and laser welding, which allows excellent control of the heat input for delicate work in the aerospace and electronics industries.

Bibliography: Cottrell, Alan H., An Introduction to Metallurgy, 2d ed. (1975);

Guy, Albert G., and Hren, John J., Elements of Physical Metallurgy, 3d ed.

(1974); Healy, J. F., Mining and Metallurgy in the Greek and Roman World

(1978); Johnson, Carl G., and Weeks, William R., Metallurgy, 5th ed. (1977);

McGannon, Harold E., The Making, Shaping and Treatment of Steel (1974); Nutt,

Merle C., Principles of Modern Metallurgy, 2d ed. (1972); Parr, James G., Man,

Metals and Modern Magic, (1958; repr. 1978); Reed-Hill, Robert E., Physical

Metallurgy Principles, 2d ed. (1972); Tylecote, R. F., A History of Metallurgy

(1977); Van Vlack, Lawrence H., Elements of Materials Science, 3d ed. (1975).

You will be held responsible for the Hall-Héroult process, the Bayer process, iron smelting process, the Hoopes process, and iron smelting. Yes, look it up in the library.