- Cadmium oxide (CdO) is an inorganic compound composed of cadmium and oxygen, belonging to the family of binary metal oxides. In its pure form, it typically appears as a brownish-red or red crystalline powder, but it can also be obtained as a colorless to pale brown crystalline mass depending on its preparation method.
- CdO crystallizes in a cubic rocksalt (NaCl-type) structure, where each cadmium ion (Cd²⁺) is octahedrally coordinated to six oxygen ions (O²⁻) and vice versa. This dense ionic lattice contributes to its high melting point of around 1,550 °C and its stability under normal atmospheric conditions.
- Cadmium oxide can be produced by burning cadmium metal in air or by thermal decomposition of cadmium salts such as cadmium carbonate, cadmium hydroxide, or cadmium nitrate. It is sparingly soluble in water but dissolves readily in acids, producing cadmium salts, and also dissolves in strong alkalis to form cadmates. The compound is amphoteric, meaning it can react with both acids and bases. In powder form, CdO is sometimes found as a fine particulate with high surface reactivity, while crystalline forms are more stable and less reactive.
- CdO has a range of industrial and technological applications. It is used in the production of cadmium-based pigments (such as cadmium yellow and cadmium red), cadmium plating baths, and as a precursor to other cadmium compounds. In electronics, CdO is valued for its semiconducting and transparent conductive properties, especially when doped with other elements like indium or tin, making it useful in thin-film coatings for solar cells, photodiodes, and optoelectronic devices. Its relatively high electrical conductivity combined with good optical transparency in the visible spectrum allows CdO films to serve as transparent conducting oxides (TCOs) in photovoltaic and display technologies.
- In catalysis, cadmium oxide has been explored for its role in organic synthesis, polymerization reactions, and as a component in ceramic glazes. It can also be used in the manufacture of specialized glasses, including infrared-transmitting and heat-absorbing glass, where CdO modifies the optical and thermal properties. Additionally, CdO’s role as an intermediate in the chemical industry makes it an important compound for synthesizing cadmium halides, cadmium sulfide, and other derivatives.
- Despite its usefulness, cadmium oxide is highly toxic. Inhalation of CdO dust or fumes—especially during high-temperature processes such as welding or soldering—can cause severe lung irritation, chemical pneumonitis, and long-term respiratory damage. Chronic exposure can lead to kidney dysfunction, bone demineralization, and cancer, as cadmium compounds are classified as human carcinogens. CdO is also dangerous to the environment, as cadmium is persistent and bioaccumulative, posing long-term risks to ecosystems. Handling cadmium oxide requires strict safety protocols, including protective clothing, respirators, and fume hoods, as well as proper hazardous waste disposal to prevent environmental contamination.
