Effect of composition on the physicochemical properties of nickel aluminium 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 samples were characterized by X-ray diffraction, infrared absorption, thermogravimetry-differential scanning calorimetry-evolved gas analysis, transmission electron microscopy and BET surface-area measurements. The crystallinity and the lattice parameters of the samples are significantly affected with respect to composition. Hydrothermal treatments performed on the aged samples enhanced the crystallinity. The nitrate ion is also present along with carbonate ion as the charge-balancing anion in the interlayer space. The thermal stability of these materials increased with decrease in Ni/Al atomic ratio. Thermal calcination of these compounds yielded non-stoichiometric NiO whose crystallinity and thermal stability depends on the composition as well as on calcination temperature.