Effects of annealing on phase evolution, microstructure and magnetic properties of mechanically synthesized nickel-ferrite
Abstract The influence of milling and subsequent annealing on nickel-ferrite phase formation was investigated by X-ray diffraction (XRD). Microstructure and magnetic properties of NiFe 2 O 4 were determined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibration sample magnetometry (VSM). Single phase nanosized nickel-ferrite was obtained by 30 h mechanical alloying (MA) and subsequent annealing at 600 °C for 1 h. Magnetic properties of the milled powder were extensively affected by the annealing temperature. Considerable growth of the particles and necking by sintering resulted from annealing at 1000 °C.
Formation of NiFe2O4 nanoparticles by mechanochemical reaction
Preparation of nanosized NiFe{sub 2}O{sub 4} particles by mechanochemical reaction(NiO+{alpha}-Fe{sub 2}O{sub 3}) and subsequent thermal treatment was investigated using X-ray diffraction (XRD). Thermal treatment of the as-milled powder at 700 deg. C for 1 h led to the formation of NiFe{sub 2}O{sub 4} nanoparticles with an average crystal size of about 23 nm. Effect of thermal treatment temperature on the crystal size of the nanoparticles was studied. The mechanism of nanoparticles growth was primarily discussed. The activation energy of NiFe{sub 2}O{sub 4} nanoparticle formation during calcination was calculated to be 16.6 kJ/mol.
Ozonation of polycyclic aromatic hydrocarbons in oil/water-emulsions: mass transfer and reaction kinetics.
The ozonation of highly condensed polycyclic aromatic hydrocarbons (PAH) was studied in oil/water-emulsions, which are comparable to poorly water-soluble PAH in industrial wastewaters and at contaminated sites. As there was a lack of knowledge about the ozonation in oil/water-emulsions, first the ozone mass transfer was studied and optimized from the gas to the water phase and from the water to the oil phase. The ratio of mass transfer and oxidation reaction was determined by the Hatta-number and revealed a slow, quasi homogeneous reaction of ozone with PAH inside the oil droplets. Because the ozone gas concentration had no influence under the optimized conditions, the selective PAH-ozonation could be described microkinetically by a direct ozone reaction of pseudo-first order regarding PAH-concentrations. The determined PAH mean reaction rate constants of 1.02 min(-1) in oil/water-emulsions are in the upper range as found for PAH dissolved in water. These results give a new insight into the ozonation in the three-phase systems and into the treatment of highly condensed, hardly biodegradable PAH.