Effect of Fe content on structure and surface properties of hydrotalcite-like compounds

A series of Mg-Al-Fe, Hydrotalcite-like compounds (Fe-HTlcs), as precursors of mixed oxides, were synthesized by direct coprecipitation. In a first step there were used constant ratios of Al/Fe and Mg/Fe with variable pH values; the pH as 10 was found as the best value. In a second step, the Fe-HTlcs were prepared varying the Fe/Al atomic ratio from 0 to 1.32 at the pH established previously. Then, these Fe-HTlcs were mechanically milled. Both, Fe content and milling effect on the crystalline structure and surface properties were studied. Lattice parameters were calculated, treating the Fe-HTlcs structure as a rhombohedral unit cell with the group R-3m, using data obtained from calculations with Winplotr software. Moreover, the microstructural parameters (crystallite size and strain), using the Two Stage Approach were determined. This study revealed that the materials synthesized were nanocrystalline powders. The crystal perfection was analyzed as a function of Fe content and mechanical milling effect. Changes of the microstructural parameters were related to the BET surface area determined by nitrogen sorption. The products were also analyzed by AA, TEM, SEM, TG and DTA measurements.