Synthesis of nickel hydroxide by homogeneous alkalinization. Precipitationmechanism

Uniform microcrystalline nickel(II) hydroxide particles have been prepared via the homogeneous alkalinization of nickel(II) nitrate solutions by urea hydrolysis. The nature of the precipitated solids depends on the temperatur e of synthesis. At ca. 423 K, i.e., under the hydrothermal conditions attai ned by microwave heating, beta-Ni(OH)(2) forms upon the fast ripening of al pha-Ni(OH)(2). In the range 363-343 K, alpha-Ni(OH)(2) is always the final product. The evolution of the systems during the precipitation of alpha-Ni( OH)(2) is analyzed in terms of the kinetic factors that control nucleation and growth. A precipitation mechanism, based on the principle of minimal st ructural change, is proposed; it is suggested that the edge-on condensation of Ni-4(OH)(4)(4+) tetramers is a key step in the sequence of events that conduct from hexaaquo Ni2+ to alpha-Ni(OH)(2).