Cadmium sulfide

Cadmium sulfide is a chemical compound with the formula CdS. It exists in nature as two different minerals, greenockite and hawleyite.

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Greenockite forms hexagonal crystals with the wurtzite structure. It has a yellowish colour with specific gravity of 4.7 and Mohs hardness of 3.8. Hawleyite has the sphalerite (zinc blende) structure.

Synthetic cadmium pigments based on cadmium sulfide are valued for their good thermal stability in many polymers, for example in engineering plastics. By adding selenium in its formula its possible to obtain colors ranging from a greenish yellow to red violet pigment. The weather resistance for this pigment is 8 in full tone, which means that it is a good pigment for UV.

Cadmium sulfide is a direct bandgap semiconductor with a bandgap of 2.42 eV. It has useful properties for optoelectronics, being used in both photosensitive and photovoltaic devices. One simple use is as a photoresistor whose electrical resistance changes with incident light levels.

Mixed with zinc sulfide, cadmium sulfide acts as a phosphor with long afterglow.

Cadmium sulfide was used as a pigment in paints as far back as 1819, but in small quantities due to its scarcity. Most cadmium sulfide used in paints is manufactured in chemical laboratories.

Such a painter as Claude Monet used it extensively due to its appealing shade of yellow well suited to his paintings.

References

• International Chemical Safety Card 0404
• Cadmium(II) sulphide information at Webelements