Síntese e Caracterização de nanopartículas de maghemita revestidas com ácido oléico para obtenção de fluidos magnéticos a base de óleos isolantes
Carregando...
Data
2009-03-18
Autores
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Federal de Goiás
Resumo
In this work maghemite nanoparticles were synthesized by co-precipitating
Fe2+ and Fe3+ in alkaline medium. The freshly prepared magnetite was
oxidized by two different routes: by bubbling O2 through an acid suspension
of magnetite nanoparticles or by hydrothermal treatment of magnetite with
ferric nitrate/nitric acid solution. After oxidation, the nanoparticles were
covered with oleic acid and the grafting coefficient was evaluated according
to the oxidation method and pH employed in the adsorption experiments. The
covered particles were dispersed in mineral and vegetable insulating oils,
resulting in magnetic fluids whose colloidal stability was investigated in
regard to the following parameters: dilution, heating, water content, chemical
composition of insulating oils and addition of oleic acid. The nanoparticles
were characterized by X-ray diffratometry, thermogravimetric and differential
thermal analyses and infrared spectroscopy. The Fe3+/Fe2+ molar ratio in the
solids was determined by UV-Vis spectrometry. The magnetic fluids were
characterized regarding the volume fraction of nanoparticles, the water
content, and their colloidal stability was monitored by dynamic light scattering
measurements and visual observations. The results obtained from the
analyses indicated that the oxidized magnetite nanoparticles (5 to 10 nm)
have inverse spinel structure and Fe3+/Fe2+ molar ratio varied from 20 to 70,
depending on the oxidation method and employed conditions. The grafting
coefficient varied from 2,1 to 4,8, reflecting the oleic acid adsorption
conditions, and the further treatments. It was also observed that by
controlling the experimental conditions, a grafting coefficient very close to a
Langmuir s monolayer can be achieved, together with a decrease in the
amount of physisorbed species which contribute negatively to the colloidal
stability. The study of colloidal stability showed that dilution, heating and
XVII
water content have a great influence in the sedimentation of diluted magnetic
fluids, when they are diluted with minerals insulating oils. It was verified that
the magnetic fluids diluted with vegetable insulating oil showed very high
colloidal stability in the accelerated thermal aging experiment
Descrição
Citação
VIALI, Wesley Renato. Synthesis and characterization of oleic acid coated maghemite nanoparticles
to obtain insulating oil based magnetic fluids. 2009. 100 f. Dissertação (Mestrado em Educação em Química) - Universidade Federal de Goiás, Goiânia, 2009.