PROPERTIES OF CADMIUM:
Cadmium is a silver white metal and has an excellent corrosion resistance in marine conditions. Cadmium is harder that tin but may be cut with a knife. Cadmium is very ductile & can easily be rolled into a foil or be drawn into a wire. Cadmium is electropositive to iron & has a very low contact potential with aluminum. Cadmiums' melting point is at about 320deg Celsius (610deg F) at this temperature it releases highly toxic fumes of cadmium metal vapour & cadmium oxide. Cadmium salts are also poisonous when ingested. Cadmium is usually deposited in the matt condition, when intended purely for protection, but can be electroplated fully bright if attractiveness or corrosion resistance is required. The deposit can be polished or scratchbrushed if necessary precautions are taken not to overheat the metal.
Electroplated Cadmium gives excellent protection to iron and steel, because under corrosive conditions the coating is electrolytically sacrificed to protect the underlying ferrous metal, however Zinc has a much lower basic cost than cadmium. Where marine & tropical are encountered cadmium forms a basic chloride on the surface which prevents further attack whereas zinc will continue to corrode away. Cadmium is unaffected by alkalis and can be used in situations where zinc would be attacked, ex: machinery which comes into contact with soaps, lyes, washing powders and domestic and Industrial cleaners. Electroplated Cadmium is used in the electrical & aircraft industries because of its low contact potential difference in relation to aluminum. Cadmium can not be electroplated onto articles which come into contact with foodstuffs or drinking water because of its toxic nature. Cadmium should therefore also not be applied to articles which may be subjected to temperatures in excess of 250deg Celsius (482deg F).
Cadmium is part of "The Restriction of Hazardous Substances Directive 2002/95/EC " Rohs, which restricts the use of certain hazardous substances. Rohs basically Restricts the use of six hazardous substances. Note the wording Restrict does not mean a substance is banned. Some restricted substances still need to be used in certain applications and therefore can not be banned, but rather restricted.