Navegando por Assunto "Carbon nanotubes"

Agora exibindo 1 - 7 de 7

Acesso aberto (Open Access)
Análise do enxofre corrosivo em óleo mineral isolante e remoção do dibenzil dissulfeto com nanotubos de carbono baseados em matriz metálica
(Universidade Federal do Pará, 2012-05-07) SARAIVA, Augusto Cesar Fonseca; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
Unexpected failures in transformers led to the identification of copper sulphide formation, deposited on the conductors. The qualitative presence evaluation of corrosive sulfur in insulating mineral oil, led to a change in the Brazilian standards ABNT NBR 10505, which assesses the presence of corrosive sulfur in mineral oil, change in the time and test temperature to 150 °C / 48 hours. Performing the chemical speciation of organosulfur compounds (by gas chromatography coupled to mass spectrometry), were found 13 compounds in the Nynas oil and 9 compounds in the Petrobras oil. DBDS, which was found only in the Nynas oil, and it was the compound with the highest concentration. To perform the determination of the presence of DBDS in insulating mineral oil, a method by gas chromatography coupled to mass spectrometry was developed, and it was possible to quantify the amount of DBDS in insulating mineral oil samples derived from the power transformer. The passivation process by tolutriazol and benzotriazol, used as anticorrosive additives in the core of electrical equipament, was evaluated; after a while the effect of the addition of passivating agent becomes ineffective with time. The solution for the remotionl of DBDS from mineral oil was realized by using carbon nanotube reinforced by metallic matrix as agent to remove the DBDS. It was found that the adsorption agent was able to realize the complete DBDS remotion from insulating mineral oil up to a volume of 4000 mL (oil contaminated with DBD).
Acesso aberto (Open Access)
Desevolvimento de dispositivos eletrônicos orgânicos nano e micro-estruturados: memória volátil, sesores e fotocélulas
(Universidade Federal do Pará, 2011-02-14) REIS, Marcos Allan Leite dos; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
In this work, several nano and microstructured organic devices were developed based on molecules of 4-dimethyl amino azobenzene-2-carboxylic acid (Methyl Red – VM), C60 Fullerene, nanocomposite of Aluminum/Carbon Nanotubes (Al/NC) and polymers: Poly(3, 4- dioxithiophene ethylene)-poly(sulfonate stireno) – PEDOT-PSS and poly(3-hexiltiofeno) – P3HT. These devices are volatile memory, fuel sensors, thermal-piezoresisitive sensor and photocells, which were manufactured by spin-coating, drop casting and chemical vapor deposition, resulting in devices with planar or layer by layer geometry. Morphological, optical, electrical and thermal characterizations were performed on devices, resulting: (a) volatile memory with a bit retention time of 4.5 s, the characteristic curves of current vs. voltage with peak-valley ratios of 8: under a 10:1 voltage positive and negative electrical energized with electrical conductivity of 10-4 S / m (OFF state) to 3.10 S / m (ON) at room temperature, (b) fuel sensors like chemiresistor sensors characteristics with sensitivity to ethanol and gasohol in concentrations of 26.25 ppm, (c) thermal-piezoresistive sensor with polynomial relationship between temperature and electrical resistance, linear relationship between pressure and electrical resistance, more accurate than a K type thermocouple when compared to a mercury thermometer at room temperature, (d) photocells with better performance when doped by Methyl Red showed quantum efficiencies up to 0.04%, real power at 0.27 and power conversion efficiency of 2.0%. These results indicate that electronic devices developed showed a better performance in comparison to similar organics.
Acesso aberto (Open Access)
Eletrodeposição pulsada e caracterização de revestimentos de cobre/nanotubos de carbono em ligas de alumínio 3003 e 1350
(Universidade Federal do Pará, 2025-06-25) SILVA, Alberto Solary da; SOUSA, Mário Edson Santos de; http://lattes.cnpq.br/4761512397509247; HTTPS://ORCID.ORG/0000-0002-7605-2371; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637; https://orcid.org/0000-0003-2226-2653
The demand for more efficient and sustainable electrical systems has driven research toward innovative materials that enhance the properties of electrical conductors. Aluminum (Al) and its alloys are widely used in power transmission and distribution due to their low density and good electrical conductivity. The pursuit of improved electrical properties has led to the development of coatings that increase conductivity without compromising the lightweight nature of the material. This study presents an investigation into the anodization of Al substrates as a preparation step for nanostructured coatings, combined with pulsed current electrodeposition of a copper (Cu) and multi-walled carbon nanotube (MWCNT)-based nanocomposite, focusing on the correlation between electrical properties and microstructure. Experiments were conducted on Al 3003 alloy sheets, and on wires and cables made from Al 1350 alloy. Optimized anodization parameters were established using 100% H₂SO₄, direct current of 3 A, and 10 V applied for 2 hours. For the pulsed current electrodeposition, a concentration of 1 mg/mL of MWCNTs, an 80% duty cycle, 2 A, and 10 V were applied for 1 hour. Field Emission Gun Scanning Electron Microscopy (FEG-SEM) micrographs confirmed the formation of a uniform and porous aluminum oxide (Al₂O₃) layer, essential for coating adhesion, and revealed the homogeneous and effective distribution of the nanocomposite over the anodized surface. Energy Dispersive Spectroscopy (EDS) verified the presence of Cu and carbon (C) elements distributed throughout the coating layer. Raman spectroscopy identified characteristic vibrational modes of MWCNTs: D, G, and G′ bands, showing variations in intensity and bandwidth due to structural modifications induced by electrodeposition. X-ray Diffraction (XRD) analysis revealed the crystalline phases present in the coating and structural changes resulting from the surface treatment, confirming the integration of the nanocomposite into the metallic substrate. Electrical conductivity tests using the four-point Kelvin probe method, before and after coating, demonstrated a significant increase in electrical conductivity (σ), indicating improved charge transport efficiency due to the synergy between Cu and MWCNTs. Among the results, a ∼ 52.33% increase in surface electrical conductivity (σₛ) of the Al sheets and an increase in IACS from 67.76% to ∼ 73.5% in the coated wires stood out. Similarly, the average resistance of the coated cable decreased from 4.88×10⁻⁴ Ω to 1.934×10⁻⁴ Ω, a reduction of ∼ 60.37% compared to the uncoated cable. Statistical analyses supported these findings and confirmed their significance. Joule heat dissipation and ampacity calculations confirmed the superior performance of the coated material and its potential for application in power transmission and distribution systems. Therefore, the Cu-MWCNT nanocomposite coating obtained via pulsed current electrodeposition on anodized surfaces represents a promising approach for improving the electrical properties of Al-based conductors.
Acesso aberto (Open Access)
Um estudo sobre a influência de defeitos de diferente natureza nas propriedades eletrônicas de nanotubos usando o método das ondas cilindricas linearizadas aumentadas
(Universidade Federal do Pará, 2014-12-12) GOMES, Fernando Antonio Pinheiro; PELAES, Evaldo Gonçalves; DMITRIEV, Victor Alexandrovich; http://lattes.cnpq.br/0684541646225359
The carbon and boron nitride nanotubes are one-dimensional structures which exhibit behavior both as metallic and semiconductor, depending on their chirality, except for the nanotubes of boron nitride which always have semiconductor characteristics, for pristine nanotubes. Due to their electronic characteristics, the nanotubes have great potential for application in nanoelectronic devices, such as nanodiodes, nanotransistors, interconnection elements, etc. For this reason, it is important to understand how external factors influence on the properties of such materials. One such factor is the introduction of external defects in the nanotubes. Such defects are the absence of one or more carbon atoms belonging to carbon nanotube and nitrogen or boron for boron nitride nanotubes, or the substitution of carbon, nitrogen or boron atoms by different ones in the structure of the corresponding nanotubes. This work presents a theoretical study of the effects of the introduction of a substitutional defects in the electronic properties of carbon and boron nitride nanotubes, via ab-initio simulation. The energy band and density of states structures was evaluated for both semiconducting and metallic carbon nanotube armchair and zig-zag types respectively and for boron nitride nanotube only armchair type using the method LACW - linearized augmented cylindrical waves. Furthermore, due to the boron nitride nanotubes are growing in importance, we make an additional systematic study of the electronic structure for these nanotubes, for a super cell formed by three unit cells, using intrinsic doping as well as quantitative analysis about relative stability based on the total energy and band gap value of these structures.
Acesso aberto (Open Access)
Influência da adição de nanotubos de carbono nas propriedades mecânicas da liga AL-2%NI solidificadas direcionalmente
(Universidade Federal do Pará, 2015-11-27) NASCIMENTO, Luiz Gabriel da Silva; SÁ, Fernando Antônio de; http://lattes.cnpq.br/8275621144223544; SOUZA, José Antônio da Silva; http://lattes.cnpq.br/6157348947425968
In this work, we produced a hypoeutectic Al-2wt%Ni matrix, to which we added various concentrations of carbon nanotubes, in order to evaluate the evolution of the mechanical strength of the new material. The manufacturing process occurred by melting and ascending unidirectional abrupt cooling, with extraction of the heat transient and determination of the thermal variables involved in the solidification. Scanning Electron Microscopy images show how the nanotubes are settled in the matrix, and by means of Raman Spectroscopy, we were able to determine the “D” and “G” bands and analyze the action of the process over them. By means of metallographic and mechanical tests, we were able to characterize the macro and micro-structural behaviors and the mechanical properties. The addition of small quantities of nanotubes led to a significant raise in the mechanical strength of the matrix.
Acesso aberto (Open Access)
Interações com nanotubos de carbono e pontos quânticos de óxido de grafeno com estruturas externas do Sars-cov-2 via simulações de dinâmica e docagem molecular
(Universidade Federal do Pará, 2023-06-02) LOBATO, Júlio César Mendes; OLIVEIRA, Mozaniel Santana de; http://lattes.cnpq.br/0810227136654245; https://orcid.org/0000-0002-4076-2443; CHAVES NETO, Antonio Maia de Jesus; Lattes: 3507474637884699
The interaction between nanoparticles and SARS-CoV-2 virus proteins was evaluated using ligands such as single-walled carbon nanotubes (NTCPUs) and receptors including envelope protein (E-pro), major protease (M-pro) and Spike glycoprotein (Sgly). Molecular docking modeling and molecular dynamics techniques were applied. Molecular dynamics revealed root mean square shift of atomic positions ranging from 0.5Å to 3.0Å. The results indicated that the zigzag nanotube showed better affinity energy, with binding free energy values of -9.48, -9.98 and -10.08 kcal/mol for E-pro, M-pro and S-gly, respectively. Furthermore, the mean square deviation of the atomic positions remained more stable for this type of nanotube, indicating a high probability of binding to the active sites of the macromolecules. Molecular couplings and binding free energy showed strong interaction between NTCPUs and residues of the S-gly active site, with values of -112.73, -94.38 and -80.49 kcal/mol for zigzag, chiral and armchair ligands, respectively. In a second step, five graphene oxide (GO) quantum dots smaller than 20 nm were used as ligands, interacting only with the spike receptors of three different strains: S-GLY-OMICRON, S-GLY-KAPPA and S-GLY-DELTA. Comparing the two ligands, it was observed that the S-GLY-OMICRON/OG-E interaction showed better affinity with Gibbs free energy of 172.2510 KJ/mol, compared to the better affinity of carbon nanotubes, S-gly/zig-zag, with ΔG of -112.73 KJ/mol. The eight proposed ligands have a high probability of binding to the active sites of the macrostructures. In conclusion, both carbon nanotubes and OG showed promise for application in SARS-CoV-2 inhibitor products, such as the development of materials for the manufacture of personal protective equipment, sprays and waterproofing solutions in general.
Acesso aberto (Open Access)
Reforço superficial em alumínio fundido por nanotubos de carbono via tratamento de solubilização
(Universidade Federal do Pará, 2021-10-14) BRITO, Paulo Roberto de Oliveira; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637
Carbon nanotubes (CNTs) are noteworthy, as they reinforce the metallic matrix, due to mechanical properties, such as the ~ 1.0 TPa Young module. To improve the maintenance of the commercially pure aluminum surface, multi-walled carbon nanotubes (MWCNTs) were incorporated into the aluminum surface with heat treatment by solid solubilization, in order to improve the surface properties of aluminum. The aluminum samples were subjected to chemically attacked with the Keller reagent, for a period of 30, 60 and 120 seconds, and soon after the roughness assessment was carried out, and then they were placed in a container containing NTCs, being subjected to a 640°C for one hour. Afterwards, the morphology was evaluated in the scanning electron microscope, where an aggregate of NTCs was observed, the DRX was performed to evaluate the addition of the NTCs in the matrix, and the Raman Spectrum that evaluated the charge transfer to the matrix. Microhardness was performed to evaluate the result of the incorporation of the NTCs in the matrix. The results obtained show that the incorporation of CNTs in the aluminum matrix increases the hardness in approximately 20% of the surface, in comparison with the control sample. The process of incorporating CNTs into the aluminum matrix by solubilization is a promising, simple and inexpensive alternative to improve the durability of the aluminum surface.