Copper enhances corrosion resistance

Copper has played a significant part in the history of mankind, which has used the easily accessible uncombined metal for nearly 10,000 years. Civilisations in places like Iraq, China, Egypt, Greece and the Sumerian cities all have early evidence of using copper. During the Roman Empire, copper was principally mined on Cyprus, hence the origin of the name of the metal as Cyprium, metal of Cyprus, later shortened to Cuprum. A number of countries, such as Chile and United States still have sizeable reserves of the metal, which are extracted through large open pit mines. Nevertheless, the price of copper rose rapidly, increasing 500% from a 60-year low in 1999, largely due to increased demand. This metal has come into the limelight on account of high volatility in prices. According to New Scientist, the earth has an estimated 61 years supply of copper left. Copper is one of the few metals to occur naturally as an un-compounded mineral. It has a reddish, orangish, or brownish colour because a thin layer of tarnish, including oxides, gradually forms on its surface when gases, especially oxygen in the air react with it. But pure copper, when fresh, is actually a pinkish or peachy metal. Copper, caesium and gold are the only three elemental metals with a natural colour other than grey or silver. The usual grey colour of metals depends on their electron sea that is capable of absorbing and re-emitting photons over a wide range of frequencies. Characteristics of copper Copper has its characteristic colour because of its unique band structure. According to Madelung's rule, the 4s subshell should be filled before electrons are placed in the 3d subshell but copper is an exception to the rule with only one electron in the 4s subshell instead of two. The energy of a photon of blue or violet light is sufficient for a d-band electron to absorb it and transition to the half-full s-band. Thus, the light reflected by copper is missing some blue/violet components and appears red. This phenomenon is shared with gold, which has a corresponding 5s/4d structure. In its liquefied state, a pure copper surface without ambient light appears somewhat greenish, a characteristic shared with gold. When liquid copper is in bright ambient light, it retains some of its pinkish luster. When copper is burnt in oxygen it gives off a black oxide. Copper should not be in direct mechanical contact with metals of different electropotential. For example, a copper pipe joined to an iron pipe, especially in the presence of moisture, as the completion of an electrical circuit, for instance through the common ground, will cause the juncture to act as an electrochemical cell, like a single cell of a battery. The weak electrical currents themselves are harmless but the electrochemical reaction will cause the conversion of the iron to other compounds, eventually destroying the functionality of the union. This problem is usually solved in plumbing by separating copper pipe from iron pipe with some non-conducting segment, usually plastic or rubber. From rail tank cars to bridges Most of the tank-car shells are fabricated from 50ksi-yield strength TC128B carbon-manganese steel that contains more than 0.25% carbon and 1% manganese. This steel has a relatively high carbon equivalent weldability parameter. In addition, the steel has marginal fracture toughness characteristics at low temperatures. A new more easily weldable, higher strength and higher fracture toughness steel is sought for tank-car application. A series of high strength steels that satisfies these requirements was developed at Northwestern University. These are excellent candidates for substitution of TC128B steel in tank car shell applications. These steels have much lower carbon content. The strengthening is derived from copper precipitation on air-cooling from hot rolling. NiNike Air Max