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Propriedades estruturais e eletroquímicas de espinélios de lítio e manganês dopados para uso em baterias de lítio
(Universidade Federal de São Carlos, 2005-09-02) Amaral, Fábio Augusto do; Bocchi, Nerilso; https://lattes.cnpq.br/5930614700886481; https://lattes.cnpq.br/7993900569181366
The spinels investigated in the present work were obtained by solid state reaction at 750 ºC for 72 h among the precursors ε-MnO2, LiOH and the respective oxides/salt of the doping ions. In order to control the particles size, all the spinels were milled in a ball milling for 30 min. The mechanical milling, associated or not to further calcination, was also used for obtaining the pure spinel LiMn2O4. The different obtained spinels were characterized by the average manganese valence (n), X ray diffractometry, electronic scanning microscopy, particles size distribution and specific superficial area. From the X ray diffractograms, spinels of single cubic phase belong to the Fd3m space group were identified. The calculated values for the unity cell parameter (a) were lower for the doped spinels (8,221 Å at 8,229 Å) than for the pure one (8,234 Å), decreasing in the following order: a(Li1,05Ga0,02Mn1,98O4) > a(Li1,05Co0,02Mn1,98O4) > a(Li1,05Al0,02Mn1,98O4) > a(Li1,05M0,02Mn1,98O3,98S0,02) > a(Li1,05M0,02Mn1,98O3,98F0,02). The values of n were higher for the doped spinels (3,56 3,50) than for the pure one (3,53 ± 0,01), decreasing in the following order: n(Li1,05Ga0,02Mn1,98O4) > n(Li1,05Co0,02Mn1,98O4) > n(Li1,05Al0,02Mn1,98O4) > n(Li1,05M0,02Mn1,98O3,98F0,02) > n(Li1,05M0,02Mn1,98O3,98S0,02). The mechanical milling after calcination changed the spinel particles in three aspects: formation of nanometer-scale particles, generation of lattice strain and partial oxidation of manganese ions. Before calcination, it allowed obtaining of pure spinel LiMn2O4 with highly disordered lattice structure, nanometer particles and high number of structural defects. A gel polymer electrolyte of the polyacrylonitrile (PAN)/polyvinylacrylate (PVA) was developed with different mixtures of organic solvents and lithium salts. From impedance measurements, the highest value of ionic conductivity (1,47 x 10-3 S cm-1) was obtained, at 25 oC, for the electrolyte prepared from the mixture (1:1) of ethyl (EC) and dimethyl (DMC) carbonates containing 1 mol L-1 of lithium tetrafluoroborate (LiBF4). Cyclic voltammetric measurements showed that this gel electrolyte only oxidizes at potentials close to 5 V vs. Li/Li+. In the charge and discharge tests, the cathodes of the doped spinels presented values of specific discharge capacity decreasing in the following order: C(Li1,05Al0,02Mn1,98S3,02O3,98) > C(Li1,05Al0,02Mn1,98F3,02O3,98) > C(Li1,05Ga0,02Mn1,98S3,02O3,98) > C(Li1,05Ga0,02Mn1,98F3,02O3,98) > C(Li1,05Co0,02Mn1,98S3,02O3,98) > C(Li1,05Co0,02Mn1,98F3,02O3,98). Although the Li1,05Al0,02Mn1,98S3,02O3,98 cathode presented the highest initial capacity value (126 mA h g-1), the Li1,05Ga0,02Mn1,98S3,02O3,98 cathode presented the lowest capacity fading (from 120 mA h g-1 to 115 mA h g-1, that is, only 4%) after three hundred cycles of charge and discharge.
Papel dos receptores 5-HT2 da amígdala e hipocampo na modulação da ansiedade em camundongos expostos ao labirinto em cruz elevado
(Universidade Federal de São Carlos, 2005-09-02) Cornélio, Alianda Maira; Souza, Ricardo Luiz Nunes de; https://lattes.cnpq.br/9404997187273622
It has been demonstrated that serotonin (5HT) plays a dual role on anxiety states. Depending on the type of 5HT receptor and cerebral sites serotonin increases or decreases anxiety. Several studies have emphasized a role of the 5HT2 receptors on anxiety modulation. In rats, intra-hippocampus or intra-amygdala infusions of 5HT2 receptor ligands result in inconsistent effects in many animal models of anxiety. This study investigated the effect of the 5HT2B/2C receptor agonist mCPP bilaterally microinjected into dorsal (DH: 0, 0.3, 1.0 or 3.0 nmol/0.2 µl) or ventral (VH: 0, 0.3, 1.0 or 3.0 nmol/0.2 µl) hippocampus and amygdaloid complex (0, 0.15, 0.5, 1.0 or 3.0 nmol/0.1 µl) in mice exposed to the elevated plus maze (EPM). Test sessions were videotaped and subsequently scored for conventional indices of anxiety (percentage of open arm entries and percentage of open arm time) and locomotor activity (closed arm entries). Results showed that mCPP microinfusions into DH or VH did not affect any behavioral measure in the EPM. However, when injected into the amygdaloid complex this 5HT2 receptor agonist selectively increased anxiety at 1 nmol dose. In addition, none dose of mCPP changed locomotor activity when injected into the amygdaloid complex. Our results suggest that the 5HT2B,2C receptors located within the amygdaloid complex (but not within the hippocampus) play a role on anxiety in mice exposed to the EPM.