Copper

Even in the age of information technology and increasingly complex technical and industrial processes, copper, one of the oldest metals known to man, plays an important role in our future.  Often referred to as the most important metal, copper can be found in almost all areas of human life at home.  Without copper there would be no electricity, no communication, no technical innovations.  Millions of meters of copper pipes or cables are essential for our daily needs such as drinking water or electricity.  Hundreds of thousands of square meters of copper cover our roofs and facades throughout the world.

Because of its many practical properties that can be often optimized through the creation of alloys, copper is one of the most useful materials.

Very rarely found in pure form, metals are often present in minerals such as compounds with oxygen (oxides) or sulfur (sulfides).  There are a few exceptions to this general rule.  Found in pure form are gold, silver, and - copper.  Copper's chemical symbol Cu (from Cuprum) is located on the periodic table of elements in a group together with silver and gold.  The metals have similarities:  copper and gold are, together, the only two coloured metal elements and copper and silver are the best thermal and electrical conductors.   

Properties of Copper

The excellent electrical and thermal conductivity of copper are the two mostt important features of the metal.  Thus, copper and copper alloys play a very important roll in technology.  Optimizing these properties through the creation of alloys has been performed for years and is, to this day, continuously developed.  The following table lists some of copper's most important numerical values (Cu-ETP, >99,9 % purity).

Chemical Symbol

Cu

Atomic Number

29

Standard Atomic Weight 

63,546

Density

8,93 g/cm3

Melting Point

1083 °C

Boiling Point 

2595 °C

Electrical Conductivity at 20 °C

57 m/(Ω*mm2)

Thermal Conductivity at 20 °C

394 W/m*K

Temperature coefficient of electrical Conductivity

0,0039/K

Thermal Expansion

17*10-6/K (von 25 bis 300 °C)

Specific Heat Density

0,39 J/g*K (20 bis 400 °C)

Heat of Fusion 

214 J/g

Crystal Structure 

face-centered cubic (fcc)

Physical Properties

Metal Electrical Conductivity (Copper: 100%) Thermal Conductivity
Silver 106 108
Copper 100 100
Gold 72 76
Aluminium 62 56
Magnesium 39 41
Zinc 29 29
Nickel 25 15
Cadmium 23 24
Cobalt 18 17
Iron 17 17
Platinum 16 18
Tin 15 17
Lead 8 9
Titanium 4 4

Copper is the only metal that has a salmon pink colour.  Copper and gold are the only two metals to have a natural colour outside of gray and silver.

With a density of 8,93 g/cm3 (small devations possible), copper, like gold, belongs to the group of heavy metals.  It has a melting point of 1083 °C and a boiling point of 2595 °C.

The most outstanding feature of the copper is the high conductivity of heat and electricity, which is surpassed only by that of silver.  Accordingly, a large portion of copper is utilized for electrical purposes.  The electrical conductivity of pure copper (» 99,998 % Cu) can reach approximately * 60 m / W mm2.

Setting the electrical conductivity and the thermal conductivity of copper respectively equal to 100, the values shown in the table on the left are shown for the main precious and utility metals (at 20 ° C).

Mechanical Properties

Soft copper has a tensile strength of about 200 MPa, a yield strength of 40-80 MPa, and a breaking elongation of over 40%.  With cold forming, the tensile strength can be increased to at least 350 MPa and the yield strength at least 320 MPa, however, then the breaking elongation is lowered to values below 5%.

Pure copper does not become brittle under warmer temperatures and thus can be shaped easily.  At the same time, copper does not turn brittle under colder temperatures.

Because copper has considerable fatigue-strength, it is also an ideal material for oscillating stresses without the danger of it becoming brittle and breaking. 

Even with slight variations in the purity of copper the physical properties will not vary much.  The creep tensile strength, however, can be enhanced through the creation of copper alloys such as copper-silver. 

With alloys, a greater strength of up to 700 MPa can be achieved and, in some cases, even up to 1500 MPa.  The disadvantage, however, is that the conductivity of such alloys decrease significantly.

Chemical Properties

Most copper compounds are either in monovalent or divalent (binary).  In some exceptional cases, such as in K3[CuF6] it occurs in trivalent and, in the exceptional case of Cs2(CuF6), in tetravalent.

Copper is the only metal in common use which has a standard potential higher than hydrogen.

Unlike acids, the corrosion resistance of copper depends not only on the type and concentration, but also on the amount of oxygen present and the oxidizing agent.  In non-oxidizing acids, which do not contain dissolved oxygen, copper is stable.

Alkaline aqueous solutions of the hydroxides and carbonates of alkali and alkaline earth metals - with the exception of NH3 - have only a small reaction with copper.

Copper is stable in the air, including salty sea air [24].  Its surface is first covered first with a dark brown, almost black protective layer, which, over time, changes to the familiar green patina such as that seen on an old copper roof.  Patina is a mixture of cuprous salts (sulfate, carbonate, and, near sea air, choloride), the composition of which is determined by the concentration of materials in the air.  Moist ammonia and hydrogen sulfide vapors do cause corrosion on copper surfaces.

Copper is resistant to water and drinking water, both warm and cold.  Therefore, it is the perfect material for water pipes.  Copper's excellence resistance to corrosion is made possible by its protective layer.

Physiological Properties

Copper is not only an element found in different forms and concentrations in nature such as the earth's crust, the ocean, lakes and rivers, but is also a trace element that is vital to life.  The life of all flora and fauna has evolved with the presence of copper.  Thus, most organisms use and need copper.  In this the human body is no exception.  Typically, the daily copper allowance for a person with a regularly balanced diet is approximately 2 milligrams.  Rich sources of copper include some wheats, meats, root vegetables, legumes, and even chocolate.  Because copper is particularily important for the metabolic process, a copper deficiency can cause serious health problems.

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