Pore surface fractal analysis of PEG and La(III)-doped mesoporous alumina obtained by the sol-gel method

Active porous alumina was prepared via a sol-gel method and sub- jected to thermal treatment in the temperature range 500-1200 °C. The addition of lanthanum effectively inhibited the surface area loss of the aluminas. Fractal analysis from nitrogen adsorption isotherm was used to study the pore surface roughness of alumina samples with different chemical compositions (PEG, PEG and lanthanum) and calcinations conditions in terms of the surface fractal di- mension, d. The Mahnke and Mogel (MM) model was used to determine the value of d of La(III)-doped alumina. Following the MM model, the d value of the activated aluminas increased as the calcination temperature increased from 500 to 700 °C but decreased after calcination at 1000, 1100 and 1200 °C. The addition of polyethylene glycol (PEG 5600) to the boehmite sol reduced the surface fractal of the activated alumina due to the heterogeneous distribution of the pores. With increasing La(III) concentration from 0.015 to 0.045 mol La(III)/ /mol Al(III), the d value of La-modified alumina samples decreased, indicating a smoother surface. The obtained PEG+La-doped boehmite sol can be used as a precursor dispersion for the deposition of mesoporous alumina coatings on stain- less steel foil, by the spray pyrolysis method.