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Metals -- Copper
Copper
Copper is one of the most
useful of the metals, and probably the one first used. It is found native and
in a large number of ores. Its apparent plentifulness is only because it is
easy to separate from its ores and is often a by-product from silver and other mining.
Copper has a face-centered cubic crystal structure. It is yellowish red in
color, tough, ductile, and malleable, gives a brilliant luster when polished,
has a disagreeable taste and a peculiar odor. It melts at 1083C and boils at
2310C. Its specific gravity is 8.91, and weight 0.321 lb/in3. It
is the best conductor of electricity next to silver, with a conductivity 97%
that of silver. The coefficient of expansion is 0.000017 per degree Celsius.
The tensile strength of cast copper ranges from 17,000 to 20,000 lb/in2
(117 to 137 MPa) with elongation 49 to 50%. Annealed wrought copper has strength
of 32,000 lb/in2
(220 MPa) with elongation 56%, while cold-drawn copper has a tensile strength
of 56,000 lb/in2 (386 MPa)
with elongation 6%.
Busbar copper used in electrical devices
has a tensile strength up to 40,000 lb/in2 (275 MPa). Copper does not have the ductility
of brass for metalworking, but does not work-harden as rapidly as brass. Pure
copper is difficult to cast, as the molten metal absorbs oxygen, forming
oxides. Copper is used for electric conductors; for making brasses and bronzes;
for sheathing, fittings, and, pipe; and for cast articles. Small amounts of
copper are added to some steels to give corrosion resistance. Much of the copper marketed for commercial use as copper
contains slight amounts of silicon or other hardener, but even as little as
0.40% arsenic or other impurity will reduce the electric conductivity
drastically.
Copper is sold in
three general grades: electrolytic, lake, and casting. “Secondary” copper is
copper recovered from smelting scrap and old copper alloys. Commercial wrought
copper is available in bars, wire, sheets, and rods.
·
Phosphorized copper (the phosphorus raises
the softening point, giving better workability, for producing high-strength
wrought metals) has high strength, higher hardness and resistance to corrosion
than other copper, but has lower conductivity.
·
Oxygen-free copper is 99.9%
pure, has high conductivity, is not subject to brittleness, and will withstand
much cold working.
·
Leaded copper is copper in commercial rods and shapes containing a small amount
of lead to make it free-machining.
·
Free-cutting copper is deoxidized copper containing up to 0.70%
tellurium, marketed in rods for making screw-machine products.
·
The copper-silver
alloy developed by the Army Signal Corps for high-strength electric
conductors contains 6.5% silver. Wire drawn to a tensile strength of 160,000 lb/in2 (1,103 MPa) has a conductivity 70% that of copper.
When drawn to a tensile strength of 116,000 lb/in2 (799
MPa), it has a conductivity 85% that of copper. Fine-gage copper-silver wire
contains 94% copper and 6 silver, and has a tensile strength of 150,000 lb/in2 (1,034 MPa) and a conductivity 70% that of copper.
·
Beryllium copper is copper to which beryllium has been added. There
are many alloys of BeCu; these are useful as springs and/or electrical contacts.
Berylco alloy 165 (1.7% Be) made by the Beryllium Corporation, No. 1 hard alloy
has a tensile strength of 100,000 PSI (689 MPa) and can be bent 180 degrees
without fracture; it has an electric conductivity 23% that of copper. A wrought
alloy called BeCu by the American Brass Co. has 2.0-2.5% Be and 0.25%-0.50% Ni;
the soft material has a tensile strength of 70,000 lb/in2 (482 MPa), elongation 45%, and hardness 110 Brinell,
while the heat-treated alloy has a tensile strength of 193,000 lb/in2 (1,330 MPa), elongation 2%, and hardness 365
Brinell. The BeCu alloys with high electric conductivity (no more than 0.50%
Be) have electric conductivity 50% that of copper. There is a high-conductivity
beryllium bronze with electric conductivity 60-65% that of copper; this
material has 0.50% Be and a small amount of silver.
·
Silver-bearing
copper is 99.9% pure, carrying 8 to
30 oz (0.2 to 0.9 kg) of silver per ton (907 kg). The silver raises the
annealing temperature, and the metal is used for high-speed motors,
commutators, and semiconductor cases. Amsil, of American Metal Climax,
Inc., with 15 oz (0.4 kg) of silver per ton (907 kg), has the electric
conductivity at room temperature of pure copper.
·
Tellerium copper is a free-machining copper containing about 1% Tellerium.
It machines 25% more easily than free-cutting brass (free-cutting brass is a
leaded brass which contains 3.25% lead). The annealed strength of TeCu is
30,000 PSI (206 MPa) and its electric conductivity is 98% that of copper.
·
Sulfur copper is copper that contains about 0.3% sulfur, marketing in rods
for the production of screw-machine products. It is free-cutting, but does not
machine as easily as tellurium copper, and has higher electrical conductivity,
about 96% that of standard copper.
·
Copper aluminum is an alloy of 50% copper and 50% aluminum melting at 1070F
(577C), used for making aluminum alloys.