engleski

Effects of Cr3+ ions and hexamethylenetetramine on the forced hydrolysis of FeCl3 solutions

Abstract: The structural analysis and nano/microstructural properties of the precipitates formed by forcedhydrolysis at 160°C of FeCl3 solutions in the presence of Cr ions and HMTA (hexamethylenetetramine) were investigated. Phase compositions were determined by combining X- ray diffraction, Fe Mössbauer and FT-IR spectroscopy, whereas nano/microstructural properties were analyzed with scanning electron microscopy (FE SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The phase analyses of the precipitates showed the presence of 2-XRD lines ferrihydrite (amorphous- like), α-FeOOH, β- FeOOH, and α-Fe2O3, and the exact phase composition was strongly dependent on the starting chemical composition in the solution and the precipitation time. 2-XRD lines ferrihydrite, α- FeOOH and β-FeOOH were the precursors of the α- Fe2O3 as end-product. Upon 2 h of autoclaving at 160°C, the precipitates consisted of nanoparticles in size ~35 to ~50nm and after 24 h their size increased to ~100 nm. New shapes of these nanoparticles were found. The formation of solid solutions between Cr ions and iron oxides cannot be excluded taking into account the decreased values of hyperfine magnetic field (HMF) relative to reference samples as well as EDS. Uponautoclaving of the precipitation system 0.01 M FeCl3+0.01 M CrCl3 + 0.25 M HMTA up to 6 h the 2- XRD lines ferrihydrite was obtained, whereas after 24 h the cracking of amorphous-like matrix (2-XRD lines ferrihydrite)occurred and in the cracking area the formation of dendritic nano/microstructures appeared.

hematite ; forced hydrolysis

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