Chromium(VI) oxide (CAS: 1333-82-0)

Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating.

Applications

Chromium trioxide is mainly used in chrome plating. It is typically employed with additives that affect the plating process but do not react with the trioxide. The trioxide reacts with cadmium, zinc, and other metals to generate passivating chromate films that resist corrosion. It is also used in the production of synthetic rubies. Chromic acid solution is also used in applying types of anodic coating to aluminium, which are primarily used in aerospace applications. A Chromic Acid/ Phosphoric Acid solution is also the preferred stripping agent of anodic coatings of all types.

Safety

Chromium trioxide igniting ethanol

Chromium trioxide is highly toxic, corrosive, and carcinogenic. It is the main example of hexavalent chromium, an environmental hazard. The related chromium(III) derivatives are not particularly dangerous; thus, reductants are used to destroy chromium(VI) samples.

Chromium trioxide, being a powerful oxidizer, will ignite some organic materials (such as ethanol) on contact.