A History of Metal

1. A History of Metal Metallurgy for the Non-Metallurgists

2. Learning Objectives • After completing this lesson, students will be able to: • Summarize the history of metallurgy from ancient to modern times. • Define such terms as metal, ore, alloy, refining, and smelting • Outline the relative availability of specific metals

3. What is a Metal? • Generally in Crystal Form as a Solid • Normally Solid at Room Temperature (Mercury is an exception) • Good conductors of Heat and Electricity • Opaque to Light • High Density • Ductile

4. Native Metals • Metals that are found in an unreacted state • These metals include: • Gold • Silver • Copper • Mostly used for ornamental purposes • Copper was used for tools although they were not strong enough for weapons

5. Bronze Age • Mixtures of metals could make them stronger • Copper + Tin made Bronze • Sterling Silver was made by adding a small amount of copper to silver • Alloying allowed humans to make tools and weapons • Alloyed casting and forging

6. A bronze Kuei handled vessel on a rectangular plinth (34.30  44.50 cm) cast in China in the 7th century B.C. (Courtesy of The Cleveland Museum of Art, Leonard C. Hanna, Jr. Fund, 1974).

7. Smelting • Most metals are found in ores • Ores are rocks that contain minerals and metals • Bornite is an ore that contains copper, iron and sulfur (Cu5FeS4) • Takes energy to extract metals from ore • Heating the ores can extract some metals such as copper

8. Pyrometallurgy • Pyrometallurgy is the extraction of metals from ores by chemical reaction at high temperatures • Lead comes from galena—a lead sulfide ore that also contains silver • Galena was heated over a fire which caused it to react with oxygen in the air and carbon from charcoal • Lead blast furnaces were made to produce lead (see next slide)

9. Lead blast furnace, open-top type.

10. Iron Age • Extracting Iron takes a lot more heat than copper • Improvements in blast furnace design enabled higher temperatures • Blast furnaces produced pig iron • Blast furnaces uses forced air

11. Early American chimney or blast furnace

13. Schematic of a blast furnace

14. The temperatures in a blast furnace range from 400–500 °C (750–930 °F) at the top, where the gasses have cooled by flowing through tons of unreactedcharge materials, to near 2000 °C (3630 °F) where the air is blown into the reaction zone through the tuyeres

15. Blast Furnaces • Rapidly produces pig iron • Pig Iron has a high carbon content • Pig Iron is hard and brittle • Difficult to shape by forging • Pig Iron can be casted • During the process free carbon produces soot • Caused skies above iron-producing cities to become dark (illustrated on the next slide)

16. Sketch from De Re Metallica showing soot emissions from a medieval blast furnace

17. Wrought Iron • First Iron Developed • Contains minute insoluble nonmetallic particles • The particles are relatively uniformly distributed • The particles are termed “inclusions” • Next slide shows these inclusions • Wrought Iron can be forged to shape • It is ductile and tough • Wrought Iron has little strength

18. Fig. 7 Micrograph showing typical slag inclusions in wrought iron. Original magnification: 500×

20. Steels • Wrought Iron contains little carbon—less than .05% • Pig Iron contains more than 3% carbon • Iron alloys with between .1 and 2% carbon are called steels • Made from heating iron with charcoal—carbon came from the charcoal • Steel can be strengthened by quenching (rapid cooling) • Steel gave ancient civilizations an advantage over other societies without steel

21. Refining • Metal is rarely found in a pure state • Gold was refined in a sluice operation • Gold was denser than other minerals • Since gold was denser, it was harder for the gold to be washed away in the sluice (next slide has an image of a sluicing operation) • Purifying metals is called refining • To further purify gold, it requires heating • Impurities are either turned to gasses or form a slag that floats on top of the molten gold

22. Sketch from De Re Metallica showing a medieval gold sluicing operation

23. Pure Metals • Metals can be refined to near purity • Pure metals are typically soft • Purification is typically expensive • Most engineering allows contain impurities • These are inclusions and can be seen in the micrograph on the next slide

24. Micrographs of nonmetallic inclusions in typical, commercially pure aluminum. Original magnification: 500×. (a) Annealed structure. (b) Cold worked structure

25. Limited Resources • Metals and minerals are limited to those contained in the earth’s crust • Crust is approximately 10 to 100 miles thick • About 50% of the crust is composed of oxygen • About 25% is silicon • Aluminum, iron, calcium sodium, potassium and magnesium each account for over 2% each of the crust • Other metals such as zinc, lead, silver, gold, etc… are much more rare

26. Cross-sectional representation of various zones through the earth

27. Composition of the earth’s crust

28. Material Needs • Engineers need many different materials • High-strength • Lightweight • Good conductors of electricity • Corrosion-resistant • Engineers often need to compromise since a single material cannot offer all needed characteristics • Three main properties of materials • Mechanical • Chemical • Physical