Navegando por Assunto "Nanotubos de Carbono"

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Acesso aberto (Open Access)
Desenvolvimento de sensor piezorresistivo nanoestruturado impresso em 3D
(Universidade Federal do Pará, 2023-07-05) QUARESMA, Luciano José Barbosa; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637; https://orcid.org/0000-0003-2226-2653; FEIO, Waldeci Paraguassu; http://lattes.cnpq.br/3512689932467320; https://orcid.org/0000-0003-4980-4694
The emergence of smart factories based on Industry 4.0 increases the automation and optimization of industrial processes in production chains. In this context, the integration between physical and digital systems depends on intelligent sensors, with greater sensitivity and integrated by the Internet of Things (IoT). The literature indicates that piezoresistive sensors can be produced by additive manufacturing (AM) and nanostructured with carbon nanotubes (NTCs), which generate a nanoelectromechanical system (NEMS) after its dispersion in the material. Thus, this work presents the development of a low-cost piezoresistive nanoelectromechanical sensor, produced by applying layers of NTCs on poly(acrylonitrile-butadiene-styrene) (ABS) parts printed by fused deposition modeling (FDM), integrable to the Industry 4.0 via IoT through ESP32 microcontrollers. For this, a diaphragm-type sensor device with dimensions 17.8, 17.8 and 5.5 𝑚𝑚 was developed, whose sensor element deformation occurs by pressing a button. After MA printing of the device parts, carboxylic acid functionalized multi-walled CNTs (MWCNT-COOH) were dispersed by ultrasonic bath in a solution with a concentration of 1 𝑚𝑔/𝑚𝑙 of acetone and dimethylformamide, in a ratio of 1 ∶ 1 in volume, for coating the sensor elements in successive layers with an aerograph. After the deposition of five layers of CNTs on the polymeric substrate, measurements of electrical resistance obtained with a picoammeter showed the percolation of the material in the second layer, with initial values above 10 𝑇 Ω and final values below 100 𝑘 𝑂𝑚𝑒𝑔𝑎 after the fifth layer, which occurs by the formation of conduction channels originating from the random arrangement of CNTs on the ABS surface, as observed by Field Emission Scanning Electron Microscopy (FEG-SEM). After that, the electrical resistance was measured during pressure cycles with progressive load and with maximum load, in which the sensor elements presented an operating range of 139.97 ± 0.46 to 363.25 ± 0.39 𝑘𝑃 𝑎. In the first test, the minimum sensitivity of 0.1 % and maximum sensitivity of 1.16 %. In the second, the highest average sensitivity was 0.63 ± 0.04 % and the lowest average response and recovery times were 0.55 ± 0.29 𝑠 and 12.29 ± 1.44 𝑠, respectively. Raman spectroscopy showed the overlapping of the signals of each material, in particular the ABS band at 1447 𝑐𝑚−1 which appears prominently between the NTCs 𝐷 and 𝐺 bands. Based on the piezoresistive response that the material presented from the NEMS generated by the deposition of NTCs on ABS, this concept of a load cell can be integrated into an ESP32 microcontroller board, making it an intelligent device with potential application in industrial systems. 4.0.
Acesso aberto (Open Access)
Desenvolvimento de termocélulas nanoestruturadas do tipo em camadas e coplanar
(Universidade Federal do Pará, 2021-08-10) PINHEIRO, Paula Fabíola Pantoja; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637; https://orcid.org/0000-0003-2226-2653
Environmental problems accentuated by fires and fossil fuels reflect the need to develop more accurate environmental monitoring systems, as well as the reuse of waste heat in thermoelectric conversion in industrial processes. Thus, in this research, thermocells based on Buckypaper (BP) were developed in two arrangements: layered and coplanar. BP was produced by vacuum filtration of functionalized Carbon Nanotubes (f-CNTs) through a filter paper with 14 μm pores. Scanning Electron Microscopy showed a BP consisting of cellulose fibers impregnated with agglomerated f-CNTs. By measuring two-point, a BP tape (1.0 cm2) showed an electrical resistance of 0.92 kΩ at 300 K. When heated in the range of 300-337 K, the BP reduced on average 22.39% of its electrical resistance, characterized as a thermoresistor. In the layered thermocell, keeping the copper electrode at room temperature while the BP electrode (active area: 5.5 cm2 ) was thermally excited generated a thermoelectric power (α) of 26.33 mV/K for ΔT = 3.0 K. This result is superior to that reported in nanostructured thermoelectrochemical cells and is close to that obtained by commercial silicon. In the coplanar thermocell, the BP was connected between two copper electrodes that acted as hot and cold sides (cooled by a heatsink) and reached α = -0.06 mV/K for ΔT = 19 K. This result was inferior to that obtained for Bi2Te3 and superior to that obtained by a free-standing BP based on nitrogen-doped CNTs.