Applications
Due to the physical similarities which they share, the group 12 elements can be found in many common situations. Zinc and cadmium are commonly used as anti-corrosion (galvanization) agents as they will attract all local oxidation until they completely corrode. These protective coatings can be applied to other metals through by hot-dip galvanizing a substance into the molten form of the metal, or through the process of electroplating which may be passivated by the use of chromate salts. Group 12 elements are also used in electrochemistry as they may act as an alternative to the standard hydrogen electrode in addition to being a secondary reference electrode.
In the US, zinc is used predominantly for galvanizing (55%) and for brass, bronze and other alloys (37%). The relative reactivity of zinc and its ability to attract oxidation to itself makes it an efficient sacrificial anode in cathodic protection (CP). For example, cathodic protection of a buried pipeline can be achieved by connecting anodes made from zinc to the pipe. Zinc acts as the anode (negative terminus) by slowly corroding away as it passes electric current to the steel pipeline. Zinc is also used to cathodically protect metals that are exposed to sea water from corrosion. Zinc is also used as an anode material for batteries such as in zinc–carbon batteries or zinc-air battery/fuel cells. A widely used alloy which contains zinc is brass, in which copper is alloyed with anywhere from 3% to 45% zinc, depending upon the type of brass. Brass is generally more ductile and stronger than copper and has superior corrosion resistance. These properties make it useful in communication equipment, hardware, musical instruments, and water valves. Other widely used alloys that contain zinc include nickel silver, typewriter metal, soft and aluminium solder, and commercial bronze. Alloys of primarily zinc with small amounts of copper, aluminium, and magnesium are useful in die casting as well as spin casting, especially in the automotive, electrical, and hardware industries. These alloys are marketed under the name Zamak. Roughly one quarter of all zinc output, in the United States (2009), is consumed in the form of zinc compounds, a variety of which are used industrially.
Cadmium has many common industrial uses as it is a key component in battery production, is present in cadmium pigments, coatings, and is commonly used in electroplating. In 2009, 86% of cadmium was used in batteries, predominantly in rechargeable nickel-cadmium batteries. The European Union banned the use of cadmium in electronics in 2004 with several exceptions but reduced the allowed content of cadmium in electronics to 0.002%. Cadmium electroplating, consuming 6% of the global production, can be found in the aircraft industry due to the ability to resist corrosion when applied to steel components.
Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. It is used in some thermometers, especially ones which are used to measure high temperatures. A still increasing amount is used as gaseous mercury in fluorescent lamps, while most of the other applications are slowly phased out due to health and safety regulations, and is in some applications replaced with less toxic but considerably more expensive Galinstan alloy. Mercury and its compounds have been used in medicine, although they are much less common today than they once were, now that the toxic effects of mercury and its compounds are more widely understood. It is still used as an ingredient in dental amalgams. In the late 20th century the largest use of mercury was in the mercury cell process (also called the Castner-Kellner process) in the production of chlorine and caustic soda.
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