Cadmium ( ) is a chemical element with the symbol Cd and atomic number 48. A relatively abundant (price 3.55 USD/lb as of 2008-02-15), soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores. Cadmium is used largely in batteries and pigments, for example in plastic products.
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Cadmium ( ) is a chemical element with the symbol Cd and atomic number 48. A relatively abundant (price 3.55 USD/lb as of 2008-02-15), soft, bluish-white, transition metal, cadmium is known to cause cancer and occurs with zinc ores. Cadmium is used largely in batteries and pigments, for example in plastic products.
Extraction
Cadmium is a common impurity in zinc, and it is most often isolated during the production of zinc. Zinc sulfide ores are roasted in the presence of oxygen, converting the zinc sulfide to the oxide. Zinc metal is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc metal by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution.
Characteristics
Cadmium is a soft, malleable, ductile, toxic, bluish-white bivalent metal. It is similar in many respects to zinc but reacts to form more complex compounds.
The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.
One particular isotope of cadmium, 113Cd, absorbs neutrons with very high probability if they have an energy below the cadmium cutoff and transmits them readily otherwise. The cadmium cutoff is about 0.5 eV. Neutrons with energy below the cutoff are deemed slow neutrons, distinguishing them from intermediate and fast neutrons.
Applications
About three-quarters of cadmium is used in batteries (especially Ni-Cd batteries), and most of the remaining quarter is used mainly for pigments, coatings and plating, and as stabilizers for plastics. Other uses include:
- In some of the lowest-melting alloys
- In bearing alloys, due to a low coefficient of friction and very good fatigue resistance
- In electroplating (6% cadmium)
- In many kinds of solder
- As a barrier to control nuclear fission
- In black and white television phosphors and in the blue and green phosphors for color television picture tubes
- As a photoconductive surface coating for photocopier drums. (Cadmium Sulphide)
- In paint pigments: Cadmium forms various salts, with cadmium sulfide being the most common. This sulfide is used as a yellow pigment. Cadmium selenide can be used as red pigment, commonly called cadmium red. To painters that work with the pigment, cadmium yellows, oranges, and reds are the most potent colours to use. In fact, during production, these colours are significantly toned down before they are ground with oils and binders, or blended into watercolours, gouaches, acrylics, and other paint and pigment formulations. These pigments are toxic, and it is recommended to use a barrier cream on the hands to prevent absorption through the skin when working with them. Cadmium blue, green, and violet do not exist.
- In some semiconductors such as cadmium sulfide, cadmium selenide, and cadmium telluride, which can be used for light detection or solar cells. HgCdTe is sensitive to infrared.
- In PVC as stabilizers.
- In molecular biology, used to block voltage-dependent calcium channels from fluxing calcium ions.
