SOL-GEL SYNTHESIS OF NANOMATERIALS AND COLOURED GELS IN THE SiO_2 ― Fe_2O_3 SYSTEM

摘要

Magnetic nanomaterials from the gels of the SiO_2 ―Fe_2O_3 system containing 20 mol.% iron oxide have been synthe-sised. As precursors TEOS, HCONH_2, C_2H_5OH and H_2O in ratio 1:1:4:4, HNO_3 and Fe(NO_3)_3.9H_2O have been used. The obtained gels have been thermal treated at 100°C (12 hours) and at the temperature range from 200 to 1000°C (2 hours). The structural evolution has been studied using X-ray diffraction analysis IR spectroscopy, TEM and Moessbauer spectroscopy. The type of the Moessbauer spectra shows a size evolution of the iron oxide particles after treatment at different temperatures. After decomposition of the iron salt at 200°C the so formed iron oxide consists only of superparamagnetic nanoparticles. The thermal treatment at higher temperatures leads to increasing of the particle size and to obtaining of a spectrum with a hyperfine magnetic structure. It is established by TEM that nanomaterials possessing uniformly distributed nanoparticles with dimension about 50 nm can be obtained in the samples containing 20 mol.% Fe_2O_3 during their thermal treating at 600°C. The processes of gel ― glass formation and gel crystallisation have been described and the results have been discussed.