This process makes use of the fact that carbon monoxide complexes with nickel readily and reversibly to give nickel carbonyl. No other element forms a carbonyl compound under the mild conditions used in the process.
This process has three steps:
3. The mixture of excess carbon monoxide and nickel carbonyl is heated to 220 - 250 °C. On heating, tetracarbonyl nickel decomposes to give nickel:
The decomposition may be engineered to produce powder, but more commonly an existing substrate is coated with nickel. For example, nickel pellets are made by dropping small, hot pellets through the carbonyl gas; this deposits a layer of nickel onto the pellets.
This process has also been used for plating nickel onto other metals, where a complex shape or sharp corners made good results difficult by electroplating. Although the results are good, the toxicity makes it impractical as an industrial process. Such parts are now plated by electroless nickel plating instead.
|Nickel carbonyl||0.001 ppm (Ni)||0.007 mg m-3 (8 hour)|
|Nickel (II) oxide||1 mg m-3 (8 hour)|
|Carbon monoxide||50 ppm (100 min)||2000 ppm|