Cadmium oxide
Encyclopedia
Cadmium oxide is an inorganic compound
with the formula
Cd
O. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride
, with octahedral cation and anion centers. It occurs naturally as the rare mineral monteponite. Cadmium oxide can be found as a colorless amorphous powder or as brown or red crystals. Cadmium oxide is an n-type semiconductor
with a band gap of 2.16 eV at room temperature.
ores, cadmium oxide is a common by-product of zinc refining
. It is produced by burning elemental cadmium in air. Pyrolysis of other cadmium compounds, such as the nitrate
or the carbonate
, also affords this oxide. When pure, it is red but CdO is unusual in being available in many differing colours due to its tendency to form defect structures
resulting from anion vacancies. Cadmium oxide is prepared commercially by oxidizing cadmium vapor in air.
back in 1907. Cadmium oxide in the form of thin films has been used in applications such as photodiodes, phototransistors, photovoltaic cells, transparent electrodes, liquid crystal displays, IR detectors, and anti reflection coatings. CdO microparticles undergo bandgap excitation when exposed to UV-A
light and is also selective in phenol photodegradation.
in water, which likely form cadmium cyanide
and sodium hydroxide. A typical formula is 32 g/L cadmium oxide and 75 g/L sodium cyanide. The cadmium concentration may vary by as much as 50%. Brighteners are usually added to the bath and the plating is done at room temperature with high purity cadmium anodes.
A thin coat of cadmium oxide forms on the surface of cadmium in moist air at room temperature. Cadmium will oxidize at room temperatures to form CdO. Cadmium vapor and steam will form CdO and hydrogen in a reversible reaction.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
Cd
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
O. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
, with octahedral cation and anion centers. It occurs naturally as the rare mineral monteponite. Cadmium oxide can be found as a colorless amorphous powder or as brown or red crystals. Cadmium oxide is an n-type semiconductor
N-type semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....
with a band gap of 2.16 eV at room temperature.
Production and structure
Since cadmium compounds are often found in association with zincZinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
ores, cadmium oxide is a common by-product of zinc refining
Refining (metallurgy)
Refining consists of purifying an impure material, in this case a metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining, the final material is usually identical chemically to the...
. It is produced by burning elemental cadmium in air. Pyrolysis of other cadmium compounds, such as the nitrate
Cadmium nitrate
Cadmium nitrate describes any of a related members of a family of inorganic compound with the general formula Cd2.xH2O. The anhydrous form is volatile but the others are salts. All are colourless crystalline solids that absorb moisture from air and becomes watery, that is deliquescent...
or the carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
, also affords this oxide. When pure, it is red but CdO is unusual in being available in many differing colours due to its tendency to form defect structures
Colour centre
The colour centre is a region in the brain responsible for processing the light signals received by the eye into what humans and animals perceive as colour vision. It consists of two subdivisions, an anterior one, called V4α and a posterior one, called V4...
resulting from anion vacancies. Cadmium oxide is prepared commercially by oxidizing cadmium vapor in air.
Uses
Cadmium oxide is used in cadmium plating baths, electrodes for storage batteries, cadmium salts, catalyst, ceramic glazes, phosphors, and nematocide. Major uses for cadmium oxide are as an ingredient for electroplating baths, and in pigments.Transparent conductor
CdO is used as a transparent conductive material, which was prepared as a transparent conducting filmTransparent conducting film
Transparent conducting films are optically transparent and electrically conductive in thin layers.TCFs for photovoltaic applications have been fabricated from both inorganic and organic materials...
back in 1907. Cadmium oxide in the form of thin films has been used in applications such as photodiodes, phototransistors, photovoltaic cells, transparent electrodes, liquid crystal displays, IR detectors, and anti reflection coatings. CdO microparticles undergo bandgap excitation when exposed to UV-A
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light and is also selective in phenol photodegradation.
Cadmium plating
Most commercial electroplating of cadmium is done by electrodeposition from cyanide baths. These cyanide baths consist of cadmium oxide and sodium cyanideSodium cyanide
Sodium cyanide is an inorganic compound with the formula NaCN. This highly toxic colorless salt is used mainly in gold mining but has other niche applications...
in water, which likely form cadmium cyanide
Cadmium cyanide
Cadmium cyanide is an inorganic compound with the formula Cd2. This white crystalline compound is used in electroplating. It is very toxic, along with other cadmium and cyanide compounds.-Usage:...
and sodium hydroxide. A typical formula is 32 g/L cadmium oxide and 75 g/L sodium cyanide. The cadmium concentration may vary by as much as 50%. Brighteners are usually added to the bath and the plating is done at room temperature with high purity cadmium anodes.
Reactivity
CdO is a basic oxide and is thus attacked by aqueous acids to give solutions of [Cd(H2O)6]2+. Upon treatment with strong alkaline solutions, forms.A thin coat of cadmium oxide forms on the surface of cadmium in moist air at room temperature. Cadmium will oxidize at room temperatures to form CdO. Cadmium vapor and steam will form CdO and hydrogen in a reversible reaction.