A history of metal
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A History of Metal. Metallurgy for the Non-Metallurgists. 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

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A History of Metal

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A history of metal

A History of Metal

Metallurgy for the Non-Metallurgists


Learning objectives

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


What is a metal

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


Native metals

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


Bronze age

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


A history of metal

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).


Smelting

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


Pyrometallurgy

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)


A history of metal

Lead blast furnace, open-top type.


Iron age

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


A history of metal

Early American chimney or blast furnace


A history of metal

Schematic of a blast furnace


A history of metal

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


Blast furnaces

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)


A history of metal

Sketch from De Re Metallica showing soot emissions from a medieval

blast furnace


Wrought iron

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


A history of metal

Fig. 7 Micrograph showing typical slag inclusions in wrought iron. Original

magnification: 500×


Steels

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


Refining

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


A history of metal

Sketch from De Re Metallica showing a medieval gold sluicing operation


Pure metals

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


A history of metal

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


Limited resources

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


A history of metal

Cross-sectional representation of various zones through the earth


A history of metal

Composition of the earth’s crust


Material needs

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


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