Abstract:

Nano-sized cobalt particles with the diameter of 2 nm were prepared via an organic colloidal process, with sodium formate, ethylene glycol and sodium citrate respectively as the reducing agent, the solvent and the complexing agent. The effects of sodium citrate addition on the yield, crystal structure, particle size and size distribution of the prepared nano-sized cobalt particles were then investigated. The results show that the average particle diameter decreases from 200 nm to 2 nm when the molar ratio of sodium citrate to cobalt chloride changes from 0 to 6, that the sodium citrate plays a crucial role in the controlling of size distribution of the nano-sized particles, and that the size distribution of the particles without sodium citrate addition ranges from tens of nanometers to 300 or 400 nm, while that with sodium citrate addition is limited in the range of （2±0.25） nm. Moreover, it is found that the addition of sodium citrate as a complexing agent may decrease the yield of the nano-sized cobalt particles.

Key words: sodium citrate, cobalt, organic colloidal process, nano-sized material, complexation