THERMAL-BEHAVIOR OF ALPHA-TYPE NICKEL HYDROXIDES

Thermal behavior of alpha-type nickel hydroxides has been studied by T G and DSC analyses. Additionnally, XRD and IR time-resolved investigat ions have been performed as a function of temperature. alpha-type nick el hydroxides present a very imperfect crystalline organization involv ing turbostratic stacking of Ni(OH)(2-x) layers with anionic species w hich compensate for hydroxide vacancies and with water molecules locat ed in the interlamellar space. Such phases, which exhibit the Ni(OH)(2 -x)(NO3)(y)(CO3)(z).nH(2)O (x=y+2z) composition decompose through heat ing following a three step transformation. The first step, which occur s around 100 degrees C corresponds to the departure of intercalated wa ter with modification of the NO3 and CO3 - Ni(OH)(2-x) interactions bu t with conservation of the turbostratic structure. The second step lea ds to finely divided NiO at about 250 degrees C with destruction of th e nickel hydroxide layers. In the last step, a growth of the NiO parti cles is observed with gradual elimination of adsorbed species at the s urface of NiO crystallites.