Navegando por Assunto "Nanoestruturas"

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Acesso aberto (Open Access)
Formação de heteroestruturas compostas por microtubos de Cu/Cu2O/CuO decorados com nanocristais de CoO
(Universidade Federal do Pará, 2024-08-21) SANTOS, Suzilene Vasconcelos dos; PASCA, Gabriel Adolfo Cabrera; http://lattes.cnpq.br/5642784995274060; https://orcid.org/0000-0002-9411-0889
A particularly important class of micro/nanostructured materials is that of transition metal oxides. In this work, copper and cobalt oxides are used to obtain micro/nanostructures. Copper (II) oxide (CuO) and copper (I) oxide (Cu2O) are p-type semiconductors, widely studied due to their peculiar characteristics and potential technological applications. Specifically, copper (Cu) microwires with approximately 50 μm in diameter and 4 cm in length, extracted from discarded cellphone earphones, were subjected to thermal treatments at 600°C with different synthesis parameters to obtain CuO microtubes. On the other hand, cobalt acetate was used in the synthesis of nanoparticles through the chemical method called thermal decomposition, which uses organometallic salts in organic solvents, being a suitable method for the synthesis of CoO nanostructures. Metallic cobalt and its oxides have been intensively studied due to numerous applications enhanced by their properties. CoO nanoparticles exhibit instability in the hexagonal close-packed Wurtzite structure (hcp - space group P63mc). This implies that, depending on the synthesis parameters, phase transition can occur, that is, from CoO-hcp to CoO-fcc (face-centered cubic phase - space group Fm3m), which is considered the most stable phase for CoO. However, in order to obtain a hierarchical structure of CuO microtubes decorated with CoO nanoparticles, this work uses different synthesis methodologies to produce a micro-nano-hierarchical structure. In this study, X-ray diffraction was used to identify the crystalline structures present in the microwires and nanoparticles, highlighting the influence of the time parameter on the phase transition of both structures. The morphological characterization of the samples was performed using scanning electron microscopy (for the microwires) and transmission electron microscopy (for the nanoparticles). Raman spectroscopy was also employed to obtain information about the sample surfaces. With these characterization techniques, it was possible to determine the elemental and structural composition of the microtubes and nanoparticles composed of copper and cobalt oxides, as well as to evaluate the influence of the laser on the nanoparticle samples. Thus, a Cu/Cu2O/CuO heterostructure with CoO monocrystals on the surface was developed, presenting potential sensory properties.
Acesso aberto (Open Access)
Influência dos parâmetros de preenchimento, forma e reforço nanoestruturado em matriz polimérica de PLA impressos em 3D
(Universidade Federal do Pará, 2024-04-08) FARIAS, Dorivane Cohen; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637; https://orcid.org/0000-0003-2226-2653
With the advancement of Additive Manufacturing and its applications in various industrial sectors, it becomes increasingly important to investigate the processability parameters associated with this technology. Thus, the present study aimed to investigate the influence of shape (solid and honeycomb), infill patterns (concentric, hexagons, and triangles), and concentrations of Carbon Nanotubes - CNTs (1 and 2 wt%) in a polymeric matrix of Poly (Lactic Acid) - PLA. The material was fabricated using the Fusion Deposition Modeling - FDM technique. The CNTs, PLA, and nanocomposites were characterized by Scanning Electron Microscopy - SEM, X - Ray Diffraction (XRD), and Raman Spectroscopy. Mechanical properties were analyzed through tensile, compression, and Charpy impact tests. The results of the SEM analysis before and after mechanical testing show: voids, CNTs, cracks, pores, and fractures. XRD analysis reveals two diffraction peaks for CNTs at 2θ: 30.01° and 2θ: 50.03°, while PLA and nanocomposites exhibit predominantly amorphous phases. In Raman characterization, the vibrational bands of CNTs, PLA, and nanocomposites were deconvoluted into subbands. CNTs showed the following subbands: DL, DR, DLO, Dmiddle, Gout, Ginn, D', 2DL, 2DR, DL + Gout, and DR + Ginn, in PLA the most prominent subbands are associated with symmetric and asymmetric vibrations of CH3. In nanocomposites, the subbands manifest as overlap of the vibrational modes of their respective constituents (PLA and CNTs). The mechanical analyses of tensile, compression, and Charpy impact tests indicate that infill patterns, shapes, and nanoreinforcement influence the mechanical properties. In tensile testing, the concentric infill pattern exhibited better performance for both shapes, with 40.75 MPa for the solid shape and 9.76 MPa for the honeycomb shape. The nanocomposites in tensile testing showed lower performance compared to the matrix. In compression testing, the triangular infill pattern showed better performance, with 52.8 MPa for the solid shape and 20.8 MPa for the honeycomb shape. In compression testing, the nanocomposites exhibited higher strengths than the matrix, with the PLA/2%CNTs nanocomposite showing the best performance in the solid shape at 73.5 MPa, and in the honeycomb shape, the PLA/1%CNTs nanocomposite performed the best at 33.2 MPa. In Charpy impact testing for the solid shape, the infill patterns did not differ in performance. However, in the honeycomb shape, the hexagon pattern stood out, with 2.88 J/m. For the nanocomposites, in both shapes, the PLA/2%CNTs fraction showed better performance, with 3.8 J/m for the solid shape and 2.98 J/m for the honeycomb shape.
Acesso aberto (Open Access)
Propriedades magnéticas de nanoestruturas de metais de transição 3d em superfícies de Pd
(Universidade Federal do Pará, 2012) RODRIGUES, Débora Carvalho de Melo; KLAUTAU, Ângela Burlamaqui; http://lattes.cnpq.br/4323567432559309
Motivated by experimental studies of 3d transitional metal monolayers on Pd surfaces, we studied the complex magnetism of nanostructures, intermixed or adsorbed, on metallic surfaces, via ab initio calculations. We used the RS-LMTO-ASA method (Real Space - Linear Muffin-Tin Orbitals - Atomic Sphere Approximation), which is based on the Density Functional Theory and has been implemented to calculate non-collinear magnetic structures. With this purpose, we investigated intermixed metallic (Cr, Mn, Fe, Co and Ni) nanostructures and alloys (2 x 2) in Pd (110) surface and also adsorbed nanostructures on Pd (111). For intermixed nanostructures in Pd (110), we analyzed the behavior of the spin and orbital magnetic moments as function of the number of first neighbors and the valence number of the 3d metals. We verified a collinear magnetism for most of the cases, except for the Cr and Mn geometrically frustrated structures, which present noncollinear magnetic configurations. For Cr nanowires adsorbed on Pd (111), we obtained a collinear antiferromagnetic configuration for chains with up to 9 atoms. For the nanowire with 10 atoms of Cr, the magnetic ordering is antiferromagnetic canted. For two dimensional Cr nanostructures adsorbed on Pd (111), we obtained complex noncollinear magnetic structures, with different chiralities.