The synthesis of nickel hydroxide occurs by many stages. When the precipitating reagent is NH4OH solution, the precipitation of nickel hydroxide occurs between pH 8.0 and 8.6. For pH between 8.6 and 10.0, a soluble complex such as [Ni(NH3)(6)](2+) is formed. The precipitation of nickel hydroxide happens again after the pH equals 10.0. Finally, there occurs the ageing of alpha-Ni(OH)(2). A mixture of alpha-Ni(OH)(2) and beta-Ni(OH)(2) phases is formed when the solid state reaction is not totally completed. One adsorbed layer becomes very hard with the exit of the water intercalated in the a-Ni(OH)2. In presence of KOH solution occurs the formation and the ageing of alpha-Ni(OH)(2). Synthesis was characterized by the following techniques: X-ray diffraction, Fourier transform infrared spectroscopy (Fr-IR), differential thermal analysis (DTA) and gravimetric thermal analysis (GTA), and specific surface area and UV-vis spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.