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Untersuchungen zur Synthese von Eisenoxid-Nanopartikeln in der Gasphase
In the present work, the formation of iron oxide nanopatzicles from iron-pentacarbonyl in the gasphase was studied experimentally and was compared to computer simulations. Three gasphase reactors, which are different regarding energy tranfer into the reactive gases, were employed: a low-pressure flame reactor, a microwave reactor and a hot-wall reactor. The effects on the growth processes of the particles were studied with a particle-mass-spectrometer. The physical and chemical properties were measued by X-ray diffraction, transmission electron microscopy, and SQUID magnetometry.
Reasults from the flame reactor have shown that in all cases g-Fe2O3 particles were formed. The single phase particles exhibit superparamagnetic behaviour with a size-depending saturation magnetization and blocking temperature. The flow coordinate was shown to be the most influencing paramter in the flame reactor. A change from the burner exit to the probing nozzel in the ange from 65 to 120 mm revealed a mass growth of about 180%. Variation of the gas compsition, pressure, and precursor concentration have no distinct influence on the mean particle mass. A comparison with a computer model yield a good agreement to the experimental data.
Experiments with the microwave driven reacor showed similar results regarding the phase of the formed particles. The mean particle sizes were between 3 and 5 nm. Besides the precursor concentratrion, the microwave power is the main size determining factor while the reaction chamber pressure has no influence. Between concentrations of 520 ppm and 2060 ppm, the particle size increases by 20%, with increasing microwave power the particle size decreases.
The formation of iron oxide nanoparticles in the hot-wall reactor could be followed by transmission electron microscopy. Below T = 500°C the particles are a mixture of amorphous and crystallin iron oxide. An increasing precursor concentration leads to an increase in particle size as well as an increasing reaction chamber pressure. The tempereature has only a marginal effect on particle size.