The Effect of Temperature and Fe3+ Concentration on the Formation of γ-Fe2O3 Nanoparticles Embedded in Silica Matrix.

The paper presents a study on the formation and thermal stability of γ-Fe2O3 nanoparticles within the silica matrix depending on the Fe(III) carboxylate-type precursors, their annealing temperature and the concentration of Fe3+. Obtaining of the precursors, within the pores of the gel, bases on the redox reaction between Fe(NO3)3 and diols: ethylene glycol (EG) and 1,4 buthane diol (1,4 BG), respectively. Thus, we have prepared gels with different Fe2O3/SiO2 ratios (20, 30, 50, 70 wt% Fe2O3) which were annealed in the temperature range 573-1273 K. The formation and stability of the single γ-Fe2O3 phase within the pores is strongly influenced by the reducing atmosphere generated upon thermal decomposition of the Fe(III) carboxylates. The XRD analysis evidenced a much stronger crystallization of γ-Fe2O3 in case of the nanocomposites synthesized with 1,4 BG than with EG. The magnetic measurements confirm the crystallinity of γ-Fe2O3 within the silica matrix.