Marcos A.L. Reis

Microstructural Characterization of Aluminum-Carbon Nanotube Nanocomposites Produced Using Different Dispersion Methods.

This research focuses on characterization of the impact of dispersion methods on aluminum-carbon nanotubes (Al-CNTs) nanocomposite structure. Nanocomposites were produced by a conventional powder metallurgy process after the dispersion of the CNTs on the Al powders, using two approaches: (1) the dispersion of CNTs and mixture with Al powders were performed in a single step by ultrasonication; and (2) the CNTs were previously untangled by ultrasonication and then mixed with Al powders by ball milling. Microstructural characterization of Al-CNT nanocomposites was performed by optical microscopy, scanning and transmission electron microscopy, electron backscatter diffraction, and high-resolution transmission electron microscopy (HRTEM). Microstructural characterization revealed that the use of ball milling for mixing CNTs with Al powders promoted the formation of CNT clusters of reduced size, more uniformly dispersed in the matrix, and a nanocomposite of smaller grain size. However, the results of HRTEM and Raman spectroscopy show that ball milling causes higher damage to the CNT structure. The strengthening effect of the CNT is attested by the increase in hardness and tensile strength of the nanocomposites.

Raman spectroscopy fingerprint of stainless steel-MWCNTs nanocomposite processed by ball-milling

Stainless steel 304L alloy powder and multiwalled carbon nanotubes were mixed by ball-milling under ambient atmosphere and in a broad range of milling times, which spans from 0 to 120 min. Here, we provided spectroscopic signatures for several distinct composites produced, to show that the Raman spectra present interesting splittings of the D-band feature into two main sub-bands, D-left and D-right, together with several other secondary features. The G-band feature also presents multiple splittings that are related to the outer and inner diameter distributions intrinsic to the multiwalled carbon nanotube samples. A discussion about the second order 2D-band (also known as G′-band) is also provided. The results reveal that the multiple spectral features observed in the D-band are related to an increased chemical functionalization. A lower content of amorphous carbon at 60 and 90 min of milling time is verified and the G-band frequencies associated to the tubes in the outer diameters distribution is upshifte...

TEM and HRTEM characterization of nanocomposites reinforced with carbon nanotubes

The extraordinary properties of carbon nanotubes (CNT), as high stiffness (970 GPa), high strength (63 GPa) and high thermal conductivity, combined with its low weight [1], have generated a great attention from the research community. The use of CNT as reinforcement material for metal matrix composites has been explored in recent years due to the potential hardening effect of these hard and stiff nanomaterials [2]. Metal matrix nanocomposites are excellent candidates for various applications due to high strength and stiffness, desirable coefficient of thermal expansion and good damping properties. This investigation focus on the production of aluminium matrix composites reinforced with CNT, by powder metallurgy techniques. CNT used in this work (from FIBERMAX composites) are mostly multi-walled CNT agglomerated in large clusters. The characterization of CNT was performed by scanning and transmission electron microscopy (SEM and TEM) and high resolution transmission electron microscopy (HRTEM). The dispersion of CNT was carried out using an ultrasonicator during 15 minutes in isopropanol. Figure 1 shows that this dispersion treatment was effective to untangle the CNT clusters. To produce the composites, Al powders (from Goodfellow), with a maximum particle size of 50 m and a purity of 99.5 %, were mixed with CNT in a Turbula during 1h. Mixtures of Al powders and CNT (0 to 2 wt.%) were hot pressed and sintered at 600 oC during 90 min under a pressure of 50 MPa, with a vacuum of 10 Pa. Microstructural characterization of CNT/Al composites was performed by SEM, TEM and HRTEM. SEM and TEM images of the nanocomposites revealed a uniform dispersion of carbon nanotubes throughout the aluminium matrix for 0.75 wt.% of CNT. The CNT are observed through the composite at grain boundary junctions, as expected, but also in the matrix. TEM images of the nanocomposites produced with 0.75 and 1.0 wt. % of CNT are present in Figure 2. In these images it is possible to observe CNT inside the aluminium grains, HRTEM observation (Fig. 3) revealed that these CNT are well bonded to the aluminium matrix. A strong interface between CNT and matrix is essential to an effective load transfer. The formation of Al4C3 phase, due to the reaction between the CNT and the Al, was also identified by HRTEM observations.

Effect of functionalization and size of CNTs in the production of nanocomposites

CEMMPRE, Department of Metallurgical and Materials Engineering, University of Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal Materials Science and Engineering Program, University of Texas at Austin, Austin, TX, 78712, USA International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, 4715-330 Braga, Portugal Faculdade de Ciências Exatas e Tecnologia, Universidade Federal do Pará, Abaetetuba, PA 68440-000 Brazil

Study of Oxidation States with Heating on Charge Transport of the Graphene Nanoribbon.

In this paper, we present a study based on extended Huckel (ETH) and the Green function of the electron transport in a graphenenanoribbon with a nanopore oxidized in the middle. We con- sider several types of oxidation:hydroxyl, carboxyl and ketone groups adsorbed in edges, pore and surface of the riddon. The results indicate that nanoribbons with medium and high oxidation are more thermally stable than the low oxidation nanoribon that shows greater sensitivity at 120 °C. Finally, Ohmic and Negative Differential Resistance (NDR) were obtained from I(V) curves, thus was possible determine the current peaks and threshold voltages (V(Th1) < V(Th2) < V(Th3) < V(Th4)), which correspond to quantum transport of the nanoribbon not oxidized, high-oxy, med-oxy and low-oxy, respectively, so creating two nanoconstrictions as well as two regions of quantum confinement.