Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly-exposed surface has a pinkish or peachy color. It is used as a thermal conductor, anelectrical conductor, a building material, and a constituent of various metal alloys.
Copper metal and alloyshave been used for thousands of years. In the Roman era, copper was principally mined onCyprus, hence the origin of the name of the metal as Cyprium, "metal of Cyprus", later shortened to Cuprum. There may be insufficient reserves to sustain current high rates of copper consumption. Some countries, such as Chileand the United States, still have sizable reserves of the metal which are extracted through large open pit mines.
Copper compounds are known in several oxidation states, usually +2, where they often impart blue or green colors to natural minerals such as turquoise and have been used historically widely as pigments. Copper metal architectural structures and statuary eventually corrode to acquire a characteristic green patina. Copper as both metal and pigmented salt, has a significant presence in decorative art.
Copper(II) ions (Cu2+) are soluble in water, where they function at low concentration as bacteriostatic substances, fungicides, and wood preservatives. For this reason, copper metal can be used as an anti-germ surface that can add to the anti-bacterial and antimicrobial features of buildings such as hospitals. In sufficient amounts, copper salts can be poisonous to higher organisms as well. However, despite universal toxicity at high concentrations, the Cu2+ ion at lower concentrations is an essential trace nutrient to all higher plant and animal life. In animals, including humans, it is found widely in tissues, with concentration in liver, muscle, and bone. It functions as a co-factor in various enzymes and in copper-based pigments.
The purity of copper is expressed as 4N for 99.99% pure or 7N for 99.99999% pure. The numeral gives the number of nines after the decimal point when expressed as a decimal (e.g. 4N means 0.9999, or 99.99%). Copper is often too soft for its applications, so it is incorporated in numerous alloys. For example, brass is a copper-zinc alloy, and bronze is a copper-tin alloy.
It is used extensively, in products such as:
- including water supply.
- used extensively in refrigeration and air conditioningequipment because of its ease of fabrication and soldering, as well as high conductivity to heat.
- Copper wire
- Oxygen-free copper
- Printed circuit boards
- Lead free solder, alloyed with tin
- Electrical machines, especially electromagnetic motors, generators and transformers
- Electrical relays, electrical busbars and electrical switches
- Vacuum tubes, cathode ray tubes, and the magnetrons in microwave ovens
- Wave guides for microwave radiation
- Integrated circuits, increasingly replacing aluminium because of its superior electrical conductivity
- As a material in the manufacture of computer heat sinks, as a result of its superior heat dissipation capacity to aluminium
Architecture and industry
- While electrical applications use oxygen-free copper, unalloyed copper used in architectural applications is the lower-purty Phosphorus Deoxidized Copper (also called Cu-DHP).
- Copper has been used as water-proof roofing material since ancient times, giving many old buildings their greenish roofs and domes. Initially copper oxide forms, replaced by cuprous and cupric sulfide, and finally bycopper carbonate. The final carbonate patina (termedverdigris) is highly resistant to corrosion.
- Statuary: The Statue of Liberty, for example, contains 179,220 pounds (81.29 metric tons) of copper.
- Alloyed with nickel, e.g. cupronickel and Monel, used as corrosive resistant materials in shipbuilding.
- Watt's steam engine firebox due to superior heat dissipation.
- Copper compounds in liquid form are used as a wood preservative, particularly in treating original portion of structures during restoration of damage due to dry rot.
- Copper wires may be placed over non-conductive roofing materials to discourage the growth of moss. (Zinc may also be used for this purpose.)
- Copper is used to prevent a building being directly struck by lightning. High above the roof, copper spikes (lightning rods) are connected to a very thick copper cable which leads to a large metal plate underneath the ground. Thevoltage is dispersed throughout the ground harmlessly, instead of destroying the main structure.
- Copper plumbing fittings and compression tubes.
- Doorknobs and other fixtures in houses.
- Roofing, guttering, and rainspouts on buildings.
- In cookware, such as frying pans.
- Some older flatware: (knives, forks, spoons) contains some copper if made from electroplated nickel silver(EPNS).
- Sterling silver, if it is to be used in dinnerware, must contain a few percent copper.
- Copper water heating cylinders
- Copper range hoods
- Copper bath tubs
- Copper counters
- Copper sinks
- Copper slug tape
- As a component of coins, often as cupronickel alloy, or some form of brass or bronze.
- Coins in the following countries all contain copper: European Union (euro), United States,United Kingdom (sterling), Australia and New Zealand.
- U.S. nickels are 75.0% copper by weight and only 25.0% nickel.
- As a biostatic surface in hospitals, and to line parts of ships to protect against barnacles andmussels, originally used pure, but superseded by Muntz metal. Bacteria will not grow on a copper surface because it is biostatic. Copper doorknobs are used by hospitals to reduce the transfer of disease, and Legionnaires' disease is suppressed by copper tubing in air-conditioning systems.
- Copper(II) sulfate is used as a fungicide and as algae control in domestic lakes and ponds. It is used in gardening powders and sprays to kill mildew.
- Copper-62-PTSM, a complex containing radioactive copper-62, is used as a positron emission tomography radiotracer for heart blood flow measurements.
- Copper-64 can be used as a positron emission tomography radiotracer for medical imaging. When complexed with a chelate it can be used to treat cancer through radiation therapy.