Doutorado em Física
URI Permanente para esta coleção
Nível: Doutorado
Ano de início: 2003
Conceito atual na CAPES: 4
Ato normativo: Parecer CES/CNE nº 487/2018, homologado pela Port. MEC 609, publicado no DOU em 18/03/2019.
Periodicidade de seleção: Semestral
Área(s) de concentração: Física
Url do curso: https://fisica.ufes.br/pt-br/pos-graduacao/PPGFis/detalhes-do-curso?id=1509
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Navegando Doutorado em Física por Autor "Ardisson, José Domingos"
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- ItemIdentificação, evolução e transformação de compostos de silício em uma biomassa tratada termicamente até altas temperaturas(Universidade Federal do Espírito Santo, 2019-02-04) Yapuchura Ocaris, Enrique Ronald.; Emmerich, Francisco Guilherme; Schettino Junior, Miguel Ângelo; Bueno, Thiago Eduardo Pedreira; Scopel, Wanderlã Luis; Dalmaschio, Cleocir José; Ardisson, José DomingosScanning electron microscopy (SEM) coupled with X-ray dispersive energy (EDS) spectroscopy, Raman spectroscopy and X-ray diffraction (XRD) were successfully used to observe the location and morphology of silica (SiO2) phytoliths in carbonaceous materials derived from biomass and its transformation into silicon carbide (SiC) and SiO2 particles at high heat treatment temperatures (HTT). The analyzes were conducted on carbonaceous materials (chars) derived from the endocarp of babassu coconut (ECB), which naturally contains 1.6 wt.% of silica in its mineral matter. It was observed that ECB chars with HTT between 500 and 1200 °C have globular echinate morphotype SiO2 phytoliths with sizes between 12 and 16 µm; these phytoliths are mainly concentrated around the surface of the char submillimetric fibers present in the endocarp of babassu coconut and also in the general carbonaceous matrix of the material. Phytoliths are not found within the submillimetric char fibers. At the HTT of 1200 °C the phytoliths begin to rounded, and above 1300 °C HTT, most of the phytoliths decompose, part of the silicon reacts with carbon forming nanocrystalline ß-SiC (crystallite size ~ 35 nm). Another part generates numerous (tens to hundreds) amorphous or nanostructured SiO2 microand sub-microparticles (with sizes predominantly below 2 µm) are observed at sites previously occupied by phytoliths. Few rounded phytoliths survive at 1400 °C HTT, but disappear in higher HTTs (1600-2000 °C). It is likely that the ensembles of SiO2 micro- and submicroparticles observed at many sites correspond to the remaining inner remaining part of the original phytoliths whose most external SiO2 structures (at and near the surface) decompose and participate in the carbothermic reaction for the formation of SiC. In addition, this study is complemented with the Raman spectroscopy characterization of the carbonaceous structure of the ECB heat treated samples, reporting characteristic parameters of the Raman D and G bands of carbonaceous materials.
- ItemMagnetismo de ferritas nanoestruturadas preparadas por mecanossíntese e Sol-Gel Protéico(Universidade Federal do Espírito Santo, 2011-01-21) Segatto, Breno Rodrigues; Caetano, Edson Passamani; Larica, Carlos; Proveti, José Rafael Cápua; Paniago, Roberto Magalhães; Ardisson, José DomingosMagnetic properties of nanocrystalline AFe2O4 (A = Ni, Zn and Co) spinel-like mechanically processed and also of the nanocrystalline NiFe2O4 ferrite prepared by sol-gel technique have systematically been studied using temperature dependent from zero-field 57Fe Mössbauer spectrometry and magnetization measurements, while the crystal structures were investigated by X-ray difraction. Specifically, for the NiFe2O4mechanically processed in-field 57Fe Mössbauer spectrometry has also been performed. For the nanocrystalline ferrite mechanically processed with spinel-like, the hyperfine structure studied by Mössbauer spectroscopy allows us to distinguish two main magnetic contributions: one attributed to the crystalline grain core (n-G), which has magnetic properties similar to the bulk AFe2O4 (A = Ni, Zn and Co) spinel-like structure (n-AFe2O4) and the other one due to the disordered grain boundary region (GB), which presents topological and chemical disorder features (d-AFe2O4). Mössbauer spectrometry determines a large fraction for the d-AFe2O4 region of the nanocrystalline AFe2O4 ferrite milled for long times (longer than 80 hours). Under applied magnetic field, from Mössbauer it is determined that the n-NiFe2O4 spins are canted with angle dependent on the applied field magnitude, whereas a speromagnet-like structure is suggested for the d-NiFe2O4 with 63% of the Mossbauer spectra area. Mossbauer data for the nanocrystalline NiFe2O4 also show that even under 12 T no magnetic saturation is observed for the two magnetic phases (n-NiFe2O4 and d-NiFe2O4). In general, hysteresis loops for the AFe2O4 (A = Ni, Zn and Co), obtained in field cooling protocol and recorded for scan field (maximum field of 7 T), are shifted in both field and magnetization axes, for temperatures below about 50 K. It has also been shown that the spin configuration of the spin-glass-like phase of the NiFe2O4 ferrite is strongly modified by the consecutive field cycles, consequently the n-NiFe2O4/d- XIII NiFe2O4 magnetic interaction is also affected in this process. One has to emphasize that the mechanically processed ZnFe2O4 ferrite has an inverse spinel-like structure with a magnetic ordering temperature (above 40 K) higher than that of the equivalent bulk ferrite (11 K). On the other hand, it is shown in this work that the NiFe2O4nanocrysalline ferrite, prepared by sol-gel method, has no hysteresis loop shift effects, after field cooling protocol, and, at the same time, the hysteresis loops do not saturate. The apparent absence of horizontal loop shift effect (exchange bias) is explained by the fact that in the sol-gel method the crystalline grains are big (~19 nm) and consequently the exchange bias field goes to zero due to the fact that the HEBa 1/tFI, where the tFIparameter is the ferrimagnetic thickness assumed to be the grain size. Comparing the magnetic results obtained for the nanocrystalline NiFe2O4 ferrites prepared by high energy milling and sol-gel methods, it can be concluded that the hysteresis loop shifts are extremely dependent on the high magnetic anisotropy of the d-AFe2O4 (A = Ni and Zn) phase. Therefore, the loop shift effects are due the exchange bias field at the d-AFe2O4/n-AFe2O4 interfaces and also from the spin freezing effect caused by cooling the spin-glass-like phase under applied magnetic field.
- ItemProdução e cinética de formação de nanoestruturas de α-Fe em ligas do tipo Nanoperm ativadas mecanicamente(Universidade Federal do Espírito Santo, 2008-03-28) Pereira, Rodrigo Dias; Caetano, Edson Passamani; Nascimento, Valberto Pedruzzi; Fernandes, Antonio Alberto Ribeiro; Biondo Filho, Armando; Caetano, Edson Passamani; Ardisson, José Domingos; Biasi, Ronaldo Sergio deNanostructured Fe84M9Cu1B6 alloys were produced by mechanosynthesis, using two different procedures (Serie I – sequential mixture of elemental powder or Serie II – mixture of all elemental powder). The amorphous phase type FeMCuB was dominantly obtained for the first procedure (Serie I), in the contrary, a-Fe(M) nanograins dispersed in an FeMCuB amorphous matrix were spontaneously produced by mechanosynthesis in samples of the serie II. The nanocrystalline material also was activated in the serie I using a temperature controlled annealing.The a-Fe (M) nanograins in both series I and II have sizes of grains, obtained by the Scherrer expression, of about 8 to 10 nm. Using the technique of exploratory differential calorimetry different aspects were studied: the kinetics of the processes of (I) the structural relaxation of the amorphous matrix produced by milling and of (ii) the amorphous to crystalline transformation of the amorphous phase and, (iii) the full crystallization of the materials produced by mechanosynthesis. The structural relaxation of the as-produced materials occurs around 500 K, independently of the refractory element (M), but its activation energy is in a range between 30 and 100 kJ /mol, which depends on the procedure (Series I or Series II) and also on the element refractory M (Zr, V, Nb). Considering, for example, the Fe84Zr9Cu1B6 alloy produced in the procedures of the series I and II, a reduction in the value of the peak temperature of the relaxation of approximately 3% was verified, but the energies of activation of the materials prepared in Series I and II are substantially different, respectively 96 and 31 kJ / mole for the Series I and II. The process of crystallization occurs in the range of temperature of 730 to 750 K for the first stage and with activation energy between 55 and 160 kJ /mol, while the second stage of IXcrystallization occurs between 636 and 939 K and with an activation energy between 105 and 330 kJ /mol, depending on the refractory element and the type of procedure for preparing the sample (Series I and Series II). The crystallization temperatures and activation energies, associated with the first and second crystallization stages, were found to be much lower for the milled alloys compared to corresponding melt-spun alloys, an effect associated with a larger number of defects induced by the mechanosynthesis process. Mössbauer spectroscopy was the technique used for a description of the microstructure of materials produced in series I and II. Three different regions were observed. The amorphous phases of the FeMCuB were characterized by containing distributions of magnetic fields with hyperfine peak around 20 T. Within the amorphous phases of the different matrixes, it was possible in some cases to determine regions rich and poor in Fe. Moreover the grain core of the a-Fe(M) nanograins have hyperfine magnetic fields around 33 T , While the atoms of Fe on the surfaces of the a-Fe (M) nanograins have a contribution in the distribution of hyperfine magnetic fields around 31 T. The hyperfine and magnetic properties of the amorphous Fe84M9Cu1B6 alloys produced in this thesis were comparable to those found in melt-spun alloys with similar composition.