Exchange-spring behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2 nanocomposites. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposites: (i) first preparation of CoFe2O4 nanoparticles using the a simple hydrothermal method and (ii) second reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe2O4 nanoparticles have been investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter of CoFe2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe2O4. TEM measurements of nanocomposite show the formation of a thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles increase to about 100 nm. The magnetization of nanocomposite showed hysteresis loop that is characteristic of the exchange spring systems. A maximum energy product (BH)max of 1.22 MGOe was achieved at room temperature for CoFe2O4/CoFe2 nanocomposites, which is about 115% higher than the value obtained for CoFe2O4 precursor. The exchange-spring interaction and the enhancement of product (BH)max in nanocomposite CoFe2O4/CoFe2 have been discussed.Comment: 9 pages, 10 figure

TRATAMENTO ELETROQUÍMICO DE EFLUENTE DA PRODUÇÃO DE BIODIESEL USANDO UM ELETRODO DO TIPO ADE: Ti/IrO2-Nb2O5

This work presents the electrochemical treatment of wastewater of biodiesel production, using DSA based on IrO2 and Nb2O5. The anode was prepared by modified Pechini method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), in order to evaluate structural and morphological properties and by electrochemical impedance spectroscopy, cyclic voltammetry and accelerated stability test to investigate the electrochemical behavior. The SEM image shows the typical mud-cracked layer. By the XRD measurements, the oxides onto the support were crystallized as tetragonal IrO2 and hexagonal Nb2O5. The amount of glycerin and methanol in the wastewater were 1.60 and 0.31% (w/w), respectively. The electrochemical treatment of the wastewater was evaluated by electrolysis at different current densities and time. The total organic carbon (TOC) and UV-Vis spectra were performed during the electrolysis. The UV-Vis spectra obtained during the electrolysis at 100 and 150 mA cm-2, shows the disappearance of an absorption band at 264 nm and the appearance of one at 290 nm, which the absorption increases as current and the time of the electrolysis increases. The electrochemical treatment with the proposed DSA leads to 80% of removal of TOC by electrolysis at 150 mA cm-2 during the first 6 hours of the electrochemical treatment

ELECTROCHEMICAL TREATMENT OF WASTEWATER FROM BIODIESEL PRODUCTION USING A DSA KIND ELECTRODE: Ti/IrO2-Nb2O5

<p></p><p>This work presents the electrochemical treatment of wastewater of biodiesel production, using DSA based on IrO2 and Nb2O5. The anode was prepared by modified Pechini method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), in order to evaluate structural and morphological properties and by electrochemical impedance spectroscopy, cyclic voltammetry and accelerated stability test to investigate the electrochemical behavior. The SEM image shows the typical mud-cracked layer. By the XRD measurements, the oxides onto the support were crystallized as tetragonal IrO2 and hexagonal Nb2O5. The amount of glycerin and methanol in the wastewater were 1.60 and 0.31% (w/w), respectively. The electrochemical treatment of the wastewater was evaluated by electrolysis at different current densities and time. The total organic carbon (TOC) and UV-Vis spectra were performed during the electrolysis. The UV-Vis spectra obtained during the electrolysis at 100 and 150 mA cm-2, shows the disappearance of an absorption band at 264 nm and the appearance of one at 290 nm, which the absorption increases as current and the time of the electrolysis increases. The electrochemical treatment with the proposed DSA leads to 80% of removal of TOC by electrolysis at 150 mA cm-2 during the first 6 hours of the electrochemical treatment.</p><p></p