EFFECT OF COMPOSITION ON THE PHYSICOCHEMICAL PROPERTIES OF NICKEL-ALUMINUM HYDROTALCITES

Ni-Al hydrotalcite compounds with the structural formula [Ni1-xAlx(OH) (2)](x+) [(CO3)(x/2) . mH(2)O](x-) were synthesized in the composition range Al/Ni + Al (x) = 0.20-0.50 by sequential precipitation. The sam ples were characterized by X-ray diffraction, infrared absorption, the rmogravimetry-differential scanning calorimetry-evolved gas analysis, transmission electron microscopy and BET surface-area measurements. Th e crystallinity and the lattice parameters of the samples are signific antly affected with respect to composition. Hydrothermal treatments pe rformed on the aged samples enhanced the crystallinity. The nitrate io n is also present along with carbonate ion as the charge-balancing ani on in the interlayer space. The thermal stability of these materials i ncreased with decrease in Ni/Al atomic ratio. Thermal calcination of t hese compounds yielded non-stoichiometric NiO whose crystallinity and thermal stability depends on the composition as well as on calcination temperature.