Navegando por Data de Publicação, começando com "2008-08-07"

Filtrar resultados por ano ou mês

Agora exibindo 1 - 3 de 3

Síntese de nanocristais coloidais de TiO2 via método solvotermal
(Universidade Federal de São Carlos, 2008-08-07) Mambrini, Giovanni Pimenta; Leite, Edson Roberto; https://lattes.cnpq.br/1025598529469393; https://lattes.cnpq.br/7723027354150918
This work presents a systematic study about preparing titanium oxide nanoparticles by solvothermal method. TiO2 is a much studied material because its applications in areas like catalysis, sensors, energy conversion devices, and others. It is speculated that all this technologies can be promoted by using nanostructured oxide. In order to confirm this, it is necessary to develop synthetic routes that allow preparing the desired material with controlled size and shapes. The methodology utilized in this research work consists in dissolve titanium isopropoxide in a phenyl ether and oleic acid mixture. After the complete dissolution, a hydrogen peroxide aqueous solution is fast injected in the medium. Then, the resulting suspension is heated at 120oC and maintained by time intervals between 12 and 192 hours. It was analyzed the influence of Lewis bases addition at the reaction medium, using chloride, nitrate and sulfate in these experiments. The influence of different surfactants on the oxide properties was analized too. The powders were characterized by X-ray diffraction, Raman spectroscopy, infrared spectroscopy and scanning-transmission electron microscopy. It was verified that the addition of a Lewis bases is a key rule to obtain crystalline TiO2 by the proposed route. This could be observed by the addition of simple bases as well as by addition of basic surfactants. The synthesis methodology developed in this work allows the synthesis of nanostructured materials with narrow size distribution, with diameters between 7 and 4 nm and standard deviation of about 1 nm. It was observed that the materials have a hydrophobic character; this was attributed to the presence of surfactants bounded to the particles surface. Infrared spectroscopy allowed that confirmation. In summary, it was developed a synthetic methodology of TiO2 colloidal nanocrystals that allows a good control of the final material characteristics.
Conformação por spray da liga formadora de fase amorfa Fe66B30Nb4
(Universidade Federal de São Carlos, 2008-08-07) Bonavina, Luiz Fernando; Kiminami, Claudio Shyinti; https://lattes.cnpq.br/5443002033733395; https://lattes.cnpq.br/1415547884100471
The goal of this doctoral thesis was to contribute to the technology of amorphous metals production with dimensions of the order of millimeters or centimeters through the process of spray forming for the ternary Fe66B30Nb4 alloy. First the alloy has been rapidly solidified by "melt-spinning" to produce ribbons and by its comparison with those data from the literature, confirm the adequacy of the procedures used. Then the alloy has been processed by spray forming with the changing of processing parameters for increasing the fraction of solid particles in the deposition. The characterization of both the overspray powders and the deposits have been performed by combination of X-ray diffratometry XRD), scanning electron microscopy (SEM) and transmission (MET) with microanalyses by dispersion of X-ray energy (EDS) and also differential scanning calorimetry (DSC). Mechanical properties were evaluated by testing the hardness and compression resistance. The formation of only 35% of amorphous volume fraction of particles in the size range of 5-20 μ m in diameter indicates that the heterogeneous nucleation have been present in the overspray powder solidification and therefore leading to an increasing of the critical cooling rate necessary to suppress the crystallization process. The deposition under high volume fraction of already fully solidified particles fraction observed in the peripheral area of the atomization cone was not enough to guarantee the formation of bulk amorphous parts which has been confirmed in the peripheral area with 0.5 mm in thickness of the deposit, where the formation of amorphous phase reached only 10.6%. Considering that the literature reported 1,5 mm thick fully amorphous sample, here, as in the case of powders, the heterogeneous nucleation has been present. The production of deposit with high amount of amorphous structure needs a spray forming equipment capable of a high ratio G/M and that the whole process can be performed under controlled inert atmosphere.
Avaliação da eficácia de um programa suplementar para o ensino de leitura e escrita aplicado em ambiente escolar
(Universidade Federal de São Carlos, 2008-08-07) Reis, Thaíze de Souza; Souza, Deisy das Graças de; https://lattes.cnpq.br/4404800720856419; https://lattes.cnpq.br/3497049970396440
A computerized teaching program for the individualized teaching of reading and writing has been developed and periodically revised by a research team. Designed under the conceptual framework of stimulus equivalence, the program teaches conditional relations between printed words and dictated words. Additional teaching trials include matching printed syllables to dictated syllables. The assessment of the program in laboratory settings has systematically shown that it is very effective in promoting the emergence of reading (textual behavior) and dictation-taking (performances not directly taught). The present study is part of a broader research program on the feasibility and efficacy of the teaching program when implemented in school settings by the school s staff. The specific goal was to evaluate the efficacy of the teaching program under these new conditions. Sixty-four students participated. They were not learning to read and write in the classroom and a pre-test evaluation demonstrated that they did not read single words. The study used a group design. The Experimental Group (N=38) was exposed to the program (a sequence of 17 teaching units interspersed among 15 assessment units). The Control Group (N=26) was exposed to a similar program, except that the task required only matching pictures to dictated words and naming the pictures. Statistical analyses showed no significant differences between the groups on the pre-test, but on the post-test only the Experimental Group showed accurate reading and writing performances and also generalized those repertoires to new words. These results replicate and extend the findings of previous studies in laboratory settings, thus recommending the teaching program as a remedial tool that could be useful in supplementing the school efforts to teach students who fail with the conventional procedures.