PREPARATION AND CHARACTERIZATION OF WELL-DEFINED COLLOIDAL NICKEL COMPOUNDS

Uniform colloidal particles of nickel compounds were obtained by aging at elevated temperatures solutions of different nickel salts in the p resence of NH4OH, NaOH or urea. The morphology of the resulting disper sed precipitates was dependent on the nature of the base and on the an ions present in the reacting systems. Thus, aging N-1(NO3)(2) solution s containing NH,OH yielded green platelet-type Ni(OH)(2) particles in the 80 nm size range, whereas in the presence of urea much larger (sev eral microns) particles of similar morphology were generated. In contr ast, NiSO4-urea solutions produced large spherical particles which wer e composed of clearly discernible subunits. On calcination at temperat ures of 300 degrees C or above, all original solids transformed into N iO in mixture with a small amount of Ni2O3. The optical properties of the final products were evaluated as a function of the wavelength.