Luis Felipe de Paula SantosCarlos Eduardo MoraesTamires Repullio do Amaral
13页
查看更多>>摘要：Carbon nanotubes have boosted research in several areas, especially in nanostructured thermoplastic composites. This work comes as its most significant contribution, the processing, and evaluation of the influence of the multi-walled carbon nanotubes (MWCNT) content on the viscoelastic, thermal stability, and flammability behavior of poly (ether imide) (PEI)/carbon fiber laminates. MWCNT favored an increase in composites' thermal stability, however, the pyrolysis temperature was not influenced by MWCNTs, and a reduction in pHRR (peak of heat release rate) and THR (total heat release) were observed. From DMA, despite the reduction in glass transition temperature (T_g), there was an increase of the storage modulus, an increase in the interphase region, and a more outstanding contribution to the viscoelastic properties from the MWCNT addition. TTS analysis also showed an enhancement of long-term stability when carbon nanotubes were added.
查看更多>>摘要：? 2022 Elsevier B.V.MXene has become a promising absorbing material because of its advantages of light weight, large specific surface area and special lamellar structure. In this work, Ag wrapped MXene (Ag@MXene) composite powders were prepared by an electroless plating method to achieve excellent absorbing performance. The phase compositions, morphology and electromagnetic properties of the Ag@MXene composite with various contents of Ag were characterized. XRD results indicated the Ag simple substance was successfully reduced from the solution. SEM images showed the Ag particles were coated on the MXene surface, and the silver layer become denser as well as more homogeneous with the rising content of Ag. As the weight ratio of Ag increased from 0 to 30 wt%, the real part increased from 10 to 17.1 while the imaginary part rose from 1.6 to 4.7, which resulted from the gradually formation of conductive network. The sample containing Ag@MXene powders with 30 wt% Ag exhibited the optimal microwave absorption performance. The minimum reflection loss was ?29 dB at 9.8 GHz with a thickness of 2.0 mm, and the effective absorption bandwidth was about 2.0 GHz. After incorporating with frequency selective surface (FSS), the absorbing performance was further improved and the effective absorption bandwidth reached to 3.96 GHz (8.36–12.32 GHz). The results show that wrapping MXene with Ag nanoparticles and incorporating with FSS can develop a novel absorber.
查看更多>>摘要：? 2022In this present paper, the effects of Ti/graphite mass ratio (4:1, 6:1, 8:1 and 10:1) on the composite, grain size and mechanical properties of TiCN coatings were investigated. Based on the solid-solid reaction of Ti with graphite and solid-gas reaction of Ti with N2 in plasma jet, TiCN phase were in situ synthesized. Results show that all coatings consist of TiCxN1?x(0 ≤ x ≤ 1) main phase, small amount of Ti2O, amorphous graphite and CNx phases. The amount of TiCN phase firstly increases and then decreases along with mass ratio increases, and the content reachs the maximum when the Ti/graphite ratio is 6:1. Besides, the highest sp3C-N fraction (about 36.22%) is detected in the coating, which is benefical to improve hardness and elasticity modulus. Therefore, the value of H/E (0.095) and H3/E2 (0.23 GPa) are higher than other three coatings, which is conductive to improve mechanical and tribological properties. A joint wear mechanism of abrasive wear and adhesive wear is found for TiCN coatings.
查看更多>>摘要：? 2022 The AuthorsFullerene C60 powder was loaded by 1 N normal force and exposed to sliding under different frequencies for 15 min. It is shown that the velocity of the sliding movement determines the stability of the fullerene C60 powder. At slow velocity of movement with a frequency of 1 Hz under 1 N normal force, the fullerene C60 structure remains undamaged after 15 min sliding. On the contrary, high sliding velocities of 10 Hz and 50 Hz affected fragmentation of the fullerene C60, which resulted in a reduction of the coefficient of friction (COF). During sliding with 1 Hz, the friction reached the highest level with an average COF of 0.59 ± 0.03. The faster relative motion under 1 N normal force gave a lower average COF with 0.39 ± 0.03. The initial fullerene C60 powder formed a thick compressed layer in the tribomechanical loaded zone. As proven by Raman spectroscopy, operating the tribomechanical sliding test at 50 Hz stimulated the re-attraction of fresh C60 fullerene island onto the fragmented layer from outside of the loaded powder regions. The COF was increasing again up to 0.44 ± 0.04 for 1 N normal force and 50 Hz frequency. The fragmentation and decomposition of fullerene C60 with increasing sliding velocity is attributed to thermal heating up during fast relative movement. Raman spectra of the tribomechanical loaded fullerene C60 are compared with Raman spectra from slowly heated up C60 in air and with Raman spectra of laser irradiated fullerene C60.
查看更多>>摘要：? 2022 Elsevier B.V.Carbon-based composite microwave absorption (MA) materials have been regarded as promising light and high-efficient microwave absorbers, but the cumbersome synthesis procedures of carbon matrix have hindered its large-scale application. Thus, it is necessary to find another environmentally friendly, reproducible and low-cost carrier for replacing these carbon materials, further tackling these issues. Herein, with coal gangue (CG) as the relatively low-quality carbon-contained matrix, starch as the cheap supplementary carbon source, CoCG composite was constructed by a solution impregnation and then a carbothermal reduction process at different temperatures. It was found that the state of carbon and Co species in these composites were strongly determined by carbothermal temperature further determining the electromagnetic properties, especially the dielectric properties. The optimal sample CoCG-600 obtained the best MA properties, which possesses the minimum reflection loss of ?39.8 dB at 11.8 GHz, the effect absorption bandwidth of 4.7 GHz with the thickness of 2.5 mm. And the widest effective absorption bandwidth of 5.5 GHz can be achieved as decreasing the thickness to 2 mm. Compared with the Fe/C/CG composite in our previous work, Co/C/CG composite exhibited the dual-enhancement MA performance, due to the magnetic and conductive Co phase can be wholly preserved at the relatively high temperature. The dominant MA mechanism, dielectric loss, was mainly included the conductive loss caused by nono-crystalline graphite and Co particles. Finally, the superior selection principle of magnetic component for constructing another MA composite based other impure low- and high-quality carbon-contained matrix was reasonably conjectured.
查看更多>>摘要：? 2022 Elsevier B.V.We describe new nanocomposite electrodes and actuators using highly conductive single-walled carbon nanotubes (<1 mm in length) fabricated using the ‘super-growth’ method (SG-SWCNT) pasted with poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and combined with electrostatic double-layer capacitors (EDLCs) and faradaic capacitors (FCs). The electromechanical/chemical properties of the SG-SWCNT/PEDOT:PSS/ionic liquid (IL) electrode and actuator were compared with those of the SG-SWCNT/IL electrode and actuator. The SG-SWCNT/PEDOT:PSS/EMI[C(CN)3] electrode (volume resistivity; 4.26 Ω cm, surface resistivity; 0.55 Ω/sq. and conductivity; 235 S/cm) was a more conductive electrode than the equivalent SG-SWCNT/EMI[C(CN)3] electrodes (36.0 Ω cm, 2.37 Ω/sq. and 28.0 S/cm). This is thought to be a result of the synergy between SG-SWCNT and PEDOT:PSS. The maximum strain of the SG-SWCNT/PEDOT:PSS/EMI[B(CN)4] actuator ranged from 0.39% to 1.88%, which is approximately 1.6–7.5 times larger than that of the SG-SWCNT/EMI[B(CN)4] actuator. The actions of the hybrid actuators differed from those of the SG-SWCNT/IL actuators, which function only as EDLC units. A kinetic model featuring double-layer charging successfully simulated the frequency-dependent displacement responses of both types of actuators. The use of a PEDOT:PSS polymer promotes higher conductivity, specific capacitance, and strain, which is thought to originate in synergy between SG-SWCNT and PEDOT:PSS. Thus, flexible robust films that exploit this synergy are likely to be useful as actuator components in energy conversion and wearable devices.
查看更多>>摘要：? 2022 Elsevier B.V.Humidity sensors are emerging in diverse technological areas in industrial and agricultural applications in diverse technological areas. Thus, the incorporation of desirable materials for acquiring enhanced performance is demanded. In this work, we have synthesized the PANI-TNT-rGO nanocomposite and applied it as a humidity sensor within the wide span of humidity levels. Incorporating PANI onto the structure increases the number of pores promoting the sensing possibilities. The synthesized TNT-rGO and PANI-TNT-rGO were prepared through two consequential processes, including hydrothermal and in situ polymerization methods. The synthesized TNT-rGO and PANI-TNT-rGO were characterized by X-ray diffraction, FTIR, Raman, scanning electron microscope (SEM), and BET surface area. The sensor's morphological, structural, and BET surface area affirm its quality for the humidity sensing areas. The fabricated sensor could propose a decent contribution in the sensing area with a quick response and recovery times. The sensitivity and sensing mechanism have been evaluated for both composites. The sensitivity of the PANI-TNT-rGO sensor was estimated to be 3.28 MΩ/RH%. The experimental evidence confirmed that the PANI-TNT-rGO exhibited a fast response time of 13 s.
查看更多>>摘要：? 2022The inefficient light absorption and gapless features of two-dimensional graphene (2D-graphene) severely impact quantum yield and electron-hole recombination, limiting its suitability in optoelectronics. Herein, a bottom 2D-graphene directly on the Ge substrate by chemical vapor deposition (CVD), a middle 3D-graphene is synthesized in-situ using 2D-graphene as the buffer layer via plasma-enhanced chemical vapor deposition (PECVD). A top 2D-graphene is transferred to 2D/3D-graphene/Ge by thermal release tape (TRT) technology to form a vertical 2D/3D/2D graphene sandwich cavity on the Ge substrate. The bottom 2D-graphene layer can not only perform as an interfacial layer for the in-situ preparation of 3D-graphene but also increase the electrical conductivity of the interface and advance the character of the Schottky junction formed between 3D-graphene/Ge, thereby improving the photon detection. The fabricated photodetector exhibits outstanding characteristics at a 1550 nm wavelength, with a high responsivity of 1.4 A/W and detectivity of 1.1 × 1014 Jones. This is due to the enhanced light absorption of the sandwich cavity and a high-quality interface layer (bottom 2D-graphene). The results reveal that this vertical 2D/3D/2D graphene sandwich architecture will facilitate the development of graphene-based NIR detection.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, a strategy consisting of a two-step carbonization and high temperature activation is developed to derive N, S and O co-doped carbon with three-dimensional pores from soybean roots. An optimized porous carbon activated at 700 °C (HSRC-700) displays an ultra-high specific surface area of 3107 m2 g?1 with rational 3-dimensional pores, contributing to a high capacitance of 486.8 F g?1 at 0.5 A g?1, which maintains 230 F g?1 even at 100 A g?1. Also, a stable life over 18,400 cycles at 20 A g?1 with a retention of 92.5% is delivered. Meanwhile, the energy density of a coin-type symmetric supercapacitor with HSRC-700 in 1 M LiPF6 is as high as 59.4 W h kg?1 at 1500 W kg?1, and the value remains 33.3 W h kg?1 at 30,000 W kg?1. The findings above indicate that green and eco-friendly soybean root-derived porous carbon exhibits great potential in supercapacitors.
查看更多>>摘要：? 2022The well-established structure and ultra-fine nanoparticles are vital for high-performance microwave absorption materials. Herein, three-dimensional hydrophobic graphene aerogels decorated with ultra-fine Fe3O4 nanocrystals composites (HGAFX, X stands for pyrolysis temperature) were successfully constructed via chemically self-assembly and in situ pyrolysis. Remarkably, the hybrids with only 5% filling contents exhibited excellent microwave absorption performance (MAP) in terms of both minimum reflection loss (RLmin) and effective absorption bandwidth (EAB), outperforming the most reported microwave absorbers. Moreover, the magnetic graphene aerogels composites possess strong hydrophobicity, endowing them attractive functions of self-cleaning, waterproof, anti-icing, and corrosion resistance. Importantly, experimental results and theoretical calculations indicate that superior MAP can be carried out by reasonably regulating the electromagnetic parameters. Considering the excellent absorption capacities, our strategy opened a novel way for anchoring ultra-small nanoparticles on graphene sheets as highly effective synergistic microwave absorbers at low filling contents.
NSTL
Elsevier