We continue to review some of the most important materials in heat treatment and metallurgy.
Copper (Chemical symbol: Cu)
Copper is a soft, malleable and ductile metal with very high thermal and electrical conductivity. Pure copper has a reddish-orange color (Fig. 1) and becomes bright green-blue when oxidized (Fig. 2).
Copper is one of the most important elements in the history of metallurgy. It was the first metal to be used by humans. Copper was smelted from ore circa 5000 BC, cast into shapes around 4000 BC and was the first metal to be alloyed with tin to create bronze in 3500 BC, marking the beginning of the Bronze Age.
Egyptians used it to make agricultural tools such as hoes and sickles, as well as cookware, dishes and artisans' tools such as saws, chisels and knives. The Egyptians also made mirrors and razors out of copper and produced green and blue makeup from malachite and azurite, two copper compounds with brilliant green and blue colors.
The Romans used it extensively for coinage and architectural adornment. At one point, the Romans produced nearly 17,000 tons of copper annually, more than would be produced again until the Industrial Revolution in Europe.
In modern metallurgy, copper as an alloying agent enhances corrosion resistance to certain acids and promotes an austenitic microstructure. It can also be added to decrease work hardening in stainless steel for improved machinability and to improve formability. The high electrical and thermal conductivity of copper results from its atomic structure. Within the copper atom lattice, a cloud of free electrons is available for the transfer of electrical current. This same cloud of electrons also enhances the efficient transfer of thermal energy. The copper atom is quite similar to an atom of gold or silver, which together with copper make up a group in the periodic table of the elements.
Copper is essential to all living organisms as a trace element. In humans, copper is found mainly in the liver, muscle and bone, and the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. A healthy human weighing 60 kg contains approximately 0.1 g of copper. In mollusks and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the iron-complexed hemoglobin in fish and other vertebrates. However, this small amount is essential to the overall human well-being.
The average home contains 400 pounds of copper that is used for electrical wiring, pipes and appliances. The average car has 50 pounds of copper, and the Statue of Liberty (Fig. 3) contains over 89 tons of copper. The U.S. Geological Survey (USGS) estimates that every American born in 2008 will use 1,309 pounds of copper during their lifetime for necessities, lifestyles and health.
Here are a few important facts about copper.
- Atomic number: 29
- Melting point: 1084.62°C
- Boiling point: 2562°C
- Density near RT: 8.96 g/cm3
- Heat of fusion: 13.26 kJ/mole
- Heat of vaporization: 300.4 kJ/mole
- Molar heat capacity: 24.440 J/mole·K
- Thermal expansion at RT: 16.5 µm/(m·K)
- Thermal conductivity: 401 W/(m·K)
- Electrical resistivity at RT: 16.78 nΩ·m
- Young's modulus: 110-128 GPa
- Shear modulus: 48 GPa
2. DFS Inc.
3. Statue of Liberty Ellis Island Foundation