Cadmium oxide is an inorganic compound with the formula CdO. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride, with

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

cation and

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

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.Lewis, Richard J. Sr., Hawley's condensed chemical dictionary, 13th ed., 1997, p. 189 Cadmium oxide is an n-type semiconductor with a band gap of 2.18 eV (2.31 eV) at room temperature (298 K).

Production and structure

Since cadmium compounds are often found in association with

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

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 A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing 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.

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, optoelectronic devices, and in pigments.

Transparent conductor

CdO is used as a transparent conductive material, which was prepared as a

transparent conducting film Transparent conducting films (TCFs) are thin films of optically transparent and electrically conductive material. They are an important component in a number of electronic devices including liquid-crystal displays, OLEDs, touchscreens and phot ...

as early as 1907 by

Karl Baedeker Karl Ludwig Johannes Baedeker ( , ; 3 November 1801 – 4 October 1859) was a German publisher whose company, Baedeker, set the standard for authoritative guidebooks for tourists. Karl Baedeker was descended from a long line of printers, boo ...

. 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 (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

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 cyanide Sodium cyanide is a poisonous compound with the formula Na C N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its hi ...

in water, which likely form

cadmium cyanide Cadmium cyanide is an inorganic compound with the formula Cd(CN)2. It is a white crystalline compound that is used in electroplating. It is very toxic, along with other cadmium and cyanide compounds. Preparation and structure Cadmium cyanide i ...

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.Clifford A. Hampel, Rare Metals Handbook, 1954, p. 87-103

Reactivity

CdO is a basic oxide and is thus attacked by aqueous acids to give solutions of d(H₂O)₆sup>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.

References

External links

Cadmium(II) oxide
information at Webelements. {{oxygen compounds Cadmium compounds Oxides II-VI semiconductors IARC Group 1 carcinogens Rock salt crystal structure