查看更多>>摘要：? 2022 Elsevier B.V.Fabrication of smooth damage-free diamond surfaces has been a popular subject in the manufacturing research field. In this study, the polycrystalline diamond was ground by a vitrified bonded diamond wheel to obtain damage-free diamond surfaces with low surface roughness and high quality. Atomic force microscopy verified that surface roughness of Sa 4.20 nm, Sa 2.06 nm, and Sa 0.548 nm were achieved under grinding speeds of 750, 1050, and 1350 rpm, respectively. Electron energy loss spectroscopy spectra confirmed the existence of a graphitic layer (black layer) with a thickness of ~15 nm in the subsurface after grinding. The “black layer” showed an easy ability to be removed under scratch and high-temperature oxidation. Moreover, transmission electron microscopy demonstrated that no damaged layer was observed in the subsurfaces at 750 rpm and 1050 rpm grinding speed. For grinding speed of 1350 rpm, stacking faults and micro-crack appear in the subsurface, thus forming a damaged layer with several microns in thickness. Our work proposes a new strategy to efficiently fabricate nanoscale smooth and damage-free diamond surfaces by diamond wheel grinding. More innovatively, this work demonstrates a unique removal mechanism for abrasive processing of hard-and-brittle materials, as distinct from either mechanical grinding or chemical mechanical grinding.
查看更多>>摘要：? 2022 The AuthorsIn this study, a facile phase inversion method was used to design an expanded graphite (EG)/polyvinylidene fluoride (PVDF) porous composite, simultaneously achieving good flexibility, mechanical strength, and satisfying electrostatic dissipation (EDS) material criteria (105–1011 Ω). The composite materials exhibit a dramatic improvement in the electrical conductivity, the electrical surface and volume resistivity of composite reducing by about six orders of magnitude from 1.78 × 1012 Ω and 4.31 × 1012 Ωcm to 4.79 × 106 Ω and 5.55 × 106 Ωcm, respectively, with the concentration of EG increment from 0 wt% to 5 wt%. Mechanical measurement shows that the Young's modulus of 2 wt% EG doped composites increases by 13 MPa compared to the 0 wt% EG. The thermogravimetric analysis demonstrates that the Tmax (maximum degradation rate) of 5 wt% EG composites enhanced by 16 °C, compared to pure PVDF. At the same time, the prepared composites have improved thermal conductivity and hydrophilicity, which endow certain advantages for its possible application in the field of EDS in the future.
查看更多>>摘要：? 2022In this work, the overall structure of the proposed “belfry-typed” absorber sensor is composed of four layers, from bottom to top are Si substrate, Au layer, SiO2 dielectric layer and the top “belfry-typed” graphene layer, respectively. Among them, the design of the “bell tower” pattern is inspired by the common bell tower building in daily life. Compared with the previous absorber based on frequency superposition method, the patterned graphene structure greatly simplifies the actual processing steps. By using FDTD to simulation, it is found that the structure has two perfect resonance absorption modes with absorption rates of 99.92% and 99.88% at 7578 nm and 8635 nm. Considering that the special surface plasmon tunability of graphene, the two-mode regulation can be achieved by controlling Fermi energy, relaxation times and structural geometry parameters. Moreover, the refractive index sensitivity of the device was discussed. The three basic parameters evaluating the performance of sensor are 1477.5 nm/RIU of sensitivity, 25.47 of FOM and 123.4 of quality factor. Finally, the specific circumstance of the absorber applied in actual life such as in aqueous solution, 10%, 20%, 25%, 60% glucose solution and 30%, 50% sugar solution was simulated and discussed. These results suggest that the proposed absorber has high refractive index sensitivity and high response speed, with which the absorber has high application value in photoelectric detection, switching and imaging.
查看更多>>摘要：? 2022 Elsevier B.V.This paper reports a simple reaction for the synthesis of sulfonated reduced graphene oxide composite with sulfonated diamond nanoparticles, (rGO/ND)-SO3H. It is based on the reaction of a mixture of graphene oxide (GO) and hydroxylated nano-diamonds (ND-OH) with 1,3-propanesultone at 150 °C for 48 h. During this process, ND-OH were converted to sulfonated ND (ND-SO3H) and composite sulfonated rGO formed rGO-SO3H. The electrochemical performance of (rGO/ND)-SO3H in 1 M H2SO4 was compared with that of ND-SO3H, rGO-SO3H and rGO/ND. It could be shown that a maximum specific capacitance of 160.1 F g?1 can be achieved by (rGO/ND)-SO3H at 1 A g?1. 81.5% capacitance retention upon increasing the charge-discharge current density from 0.5 A g?1 to 15 A g?1 was observed, making the material a potent candidate for supercapacitor applications. The high electrochemical surface area and easy accessibility of electrolyte to the electrode material are believed to be the underlying reasons for the improved performance. Furthermore, as-fabricated (rGO/ND)-SO3H shows excellent cycling stability with more the 99.1% retention of the specific capacitance after 6000 galvanostatic charge-discharge cycles, making it a promising matrix for high performance electrochemical capacitors.
查看更多>>摘要：? 2022 Elsevier B.V.Thin films of microcrystalline diamond-silicon carbide composite have been deposited by microwave plasma chemical vapor deposition (CVD) in methane-silane-hydrogen gas mixtures on Si substrates with an insulating polycrystalline diamond buffer layer. The structure and phase composition of the films were characterized by scanning electron microscopy, Raman and photoluminescence spectroscopy. The silicon carbide grains are identified to be cubic polytype 3C-SiC with only a minor admixture of hexagonal 6H-SiC. The measured electrical resistivity of the films is found to decrease with the temperature from ~10?1 Ω·cm at 300 K to ~10?2 Ω·cm at 460 K, with activation energy Ea = 0.20 eV. The conductivity is assumed to be realized via pathways in the SiC network immersed in isolating diamond matrix. The obtained results show that such diamond/SiC composites may be considered as an alternative to electrically conductive nitrogenated ultrananocrystalline diamond films for a number of practical applications.
查看更多>>摘要：? 2022 Elsevier B.V.Carbon nanomaterials are of great interest for next generation nanofluids. Carbon nanotubes and graphene are, in particular, highly thermally conductive and their use as thermal fluid is gaining momentum among the research community. This work investigates the thermal performance of graphene nanoplatelet (GnP)-nanofluid and multi-walled carbon nanotube (MWCNT)-nanofluid by using a concentric pipe heat exchanger. The prepared nanofluid flowed in the inner pipe as hot fluid, which was in the opposite direction of a colder water flow in the annulus pipe. The investigation was conducted by varying the volumetric flow (from 1.5 to 2.5 L/min) and nanofluid concentration (from 0.01 to 0.35 vol%). The heat transfer coefficient (HTC) of GnP-nanofluid was observed to be superior to that of MWCNT-nanofluid. The maximum increase in HTC relative to the pure base fluid is approximately 16.8, 24.2 and 26.1% for GnP-nanofluid; and 8.8, 13.8 and 14.4% for MWCNT-nanofluid flowing at 1.5, 2.0 and 2.5 L/min, respectively. This positive impact on heat transfer performance enhancement reached the maximum when an optimum concentration is reached in both nanofluids. Compared to the maximum HTC ratio brought by MWCNT-nanofluid at 0.15 vol% and 2.5 L/min, GnP-nanofluid produced a greater HTC ratio, even at relatively low concentration (0.05 vol%) and volumetric flow (1.5 L/min) which is rather desirable for practical applications.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, we develop a dual-controlled graphene plasmon-based broadband metamaterial absorber (BMMA) integrating the photosensitive silicon. The designed device can implement active frequency, intensity, and bandwidth modulations of broadband absorption by electrically doping graphene and optically pumping silicon individually or simultaneously, featuring terahertz devices with multidimensional manipulation. To interpret the modulation mechanism of the broadband absorption, an equivalent circuit model based on the transmission line theory is constructed, and theorical results agree well with the simulated ones. In addition, the absorption characteristics depending on polarization angles, incident angles, and structural parameters are also systematically investigated. Therefore, the proposed broadband metamaterial absorber with multidimensional tunability endowed by dual-controlled mode could have potential applications on the design of active and multifunctional terahertz metadevices, such attenuators, modulators, selectors, and detectors.
查看更多>>摘要：? 2022 Elsevier B.V.Affected by the characteristics of laser Gaussian beam, the spot size and laser energy irradiated on the grinding wheel surface change at any time with the dressing path, which makes it difficult to realize the dressing of high-precision arc-shaped diamond grinding wheel. In order to achieve high-efficiency and precise dressing of arc-shaped diamond grinding wheels, a composite dressing method using laser rough dressing and electrical discharge precision dressing was first proposed. Laser rough dressing method is used to quickly remove the excess abrasive layer to obtain an arc-shaped profile. Electrical discharge precision dressing not only improved the accuracy of arc-shaped contour, but also realized the grinding wheel sharpening. The optimization of kinematic parameters on the dressing profile accuracy in laser dressing and electrical discharge dressing was explored. An arc-shaped profile with a radius of 13 mm was tested on a diamond grinding wheel with a grain size of 120#. The radius of the final dressed arc-shaped profile is 13,007 μm, and the PV value of the profile error is 10.67 μm. It was found that the abrasive grains on the surface of the grinding wheel were slightly graphitized. The damage degree of the abrasive particles in laser dressing was more serious than that of in electrical discharge dressing. Most of the graphite layer on the surface of abrasive particles could be removed by grinding alumina ceramics. The fitting radius of the arc profile of the workpiece is 13.013 mm, and the profile error PV value is 11.91 μm.
查看更多>>摘要：? 2022Graphene oxide quantum dots (GOQDs) have been used in electrodes to improve the electrochemical energy storage behavior, but suffer from high cost and low yield. Here, GOQDs are prepared by high-yield cutting conversion of porous graphene (PG) with nano-sized crystal domains. The defective edges between the nano-sized graphene domains are selectively etched by a diluted acid, thus contributing to a low-loss deconstruction of the PG. As the result, the as-obtained GOQDs yield can reach up to 60 wt%, much higher than the GQDs yield derived from the decomposition of graphite. As the supercapacitor electrode additive, the simple moderate addition of GOQDs with abundant heteroatom functional groups into PG electrode can effectively alleviate the agglomeration and stacking between PG sheets, which not only improves effective specific surface area and stability of interlamellar storage of PG, but also enhances the electrical conductivity and improves the electrode wettability. Benefitting from above excellent features, the GOQDs-added PG electrode exhibits superior rate performance (120 F g?1 at 0.5 A g?1 and 102 F g?1 at 30 A g?1) and long-term cycling stability in the aqueous electrolyte. Moreover, in the organic electrolyte, it can also deliver specific capacitances of 119 and 106 F g?1 at 1 and 30 A g?1. Besides, the capacitance retention is as high as 97.3% when the temperature decreases from 25 to ?40 °C, exhibiting an exceptional low temperature adaptability. The capacitive behaviors in aqueous and organic electrolyte systems of GQDs-added PG electrode are superior to the original PG electrode. This work not only provides a new high-yield and scalable synthesis method for GQDs, but also broadens its application value by employing as the electrode additive in a simple way to boosting the capacitive energy storage behavior.
查看更多>>摘要：? 2022 Elsevier B.V.The hydrothermal approach was used to make nitrogen-doped carbon dots (NCDs) employing ginger mango and triethylene tetraamine as precursors. The as-synthesized NCDs with a size of 7 nm exhibited good aqueous dispersibility, photostability and green fluorescence under UV light. Various optical, morphological and electrochemical properties of NCDs were examined. It was used as a dual-mode probe for tetracycline and mercuric ion detection. It detected tetracycline selectively and sensitively using an inner filter-based fluorescence quenching mechanism with a detection limit of 32 nM. The NCD modified glassy carbon electrode detected mercuric ions electrochemically with a detection limit of 0.2 nM. Moreover, NCDs were utilized to sense tetracyclines and mercuric ions in tap and river water samples.
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