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21.
《Journal of the European Ceramic Society》2017,37(12):3805-3812
Alumina – carbon nanofibers (CNF) and alumina – graphene oxide (GO) composites were prepared by spark plasma sintering using freeze-dried powders prepared from optimized suspensions of the mixtures. The tribological behavior was studied using the ball-on-disk technique in dry sliding at ambient conditions and compared to a monolithic alumina used as a reference. At low loads there was little difference between friction and wear behavior, whereas at moderate loads the composites showed a noticeable reduction in wear rate over monolithic alumina, five and 2.5 times for the GO and the CNF composite respectively; the friction coefficient slightly decreased for the alumina – GO material. This behavior is related to the presence of a carbon-rich protecting tribofilm. The film present in the alumina – GO showed better tribological performance due to the absence of coalescence of cracks that led to delamination events in the case of the alumina – CNF composite. 相似文献
22.
《Reactive and Functional Polymers》2012,72(12):939-946
In this paper the synthesis and characterization of microporous polymer microspheres with ultra-high specific surface areas (>1000 m2/g) and strong cation-exchange character is described. The microspheres were synthesized by the hypercrosslinking of swellable precursor particles which had been produced by precipitation polymerization. The strong cation-exchange character, arising from the presence of sulfonic acid groups, was introduced through post-hypercrosslinking chemical modification reactions. Two alkyl sulfate reagents of differing polarity were compared as reagents for the sulfonation reactions, and a synthetic methodology was devised that allowed the sulfonic acid content of the microspheres to be controlled. Following a series of small-scale optimization experiments, optimized conditions were applied on a larger scale to the synthesis of three distinct polymers (HXLPP-SCX) tailored for use as strong cation-exchange (SCX) sorbents in solid-phase extraction (SPE) studies. All three polymers were in the form of polymer microspheres (mean particle diameters 3–5 μm) with relatively narrow particle size distributions and specific surface areas up to 1370 m2/g, and had tuneable ion-exchange capacities (IECs) ranging from 1.7–2.8 mmol/g. 相似文献
23.
《Polymer》2014,55(10):2501-2504
Ionic liquids (ILs) were fixed into polyether-based polyurethane (PU) films for sustainable antistatic properties. Preliminarily, ILs were screened in terms of efficiency of antistatic effect. Surface resistivity (ρs) for IL-doped PU films changed depending the anion species, and the smallest ρs was found for the PU films containing bis(trifluoromethanesulfonyl)imide ([Tf2N])-type ILs. Then, [Tf2N]-type ILs composed of ammonium cations having hydroxyl groups were fixed into the PUs through urethane bonds. The fixation of 1000 ppm of the ILs reduced the ρs of the PU films from 2.1 × 1012 to 2.1 × 109 Ω sq−1. These IL-fixed PU films were revealed to possess high washing durability confirmed by negligible change of ρs before and after ultra-sonication treatment in methanol. 相似文献
24.
The porous polyimide/hollow mesoporous silica nanoparticles (PI/HMSNs) composite films were fabricated via blending polymerization by using polystyrene (PS) microspheres as the pore-forming template. The morphologies, microstructures, thermal stability, thermal expansion coefficient (TEC), and mechanical performances of the porous PI/HMSNs films were characterized in detail. Results showed that the uniform dispersion of HMSNs benefits from the strong hydrogen-bonding interaction between the hydroxyl groups of HMSNs and poly(amic acid) chains. Both weight loss and TEC of the porous PI/HMSNs films are lower than those of the pure porous PI film. When 0.8 wt % HMSNs and 7.0 wt % PS were added into the PI matrix, the Young's modulus and tensile strength of composite film increased by about 32.4% and 68.1% compared with those of the pure porous PI film. Conclusively, the introduction of HMSNs in the porous PI matrix is an important strategy to enrich the diversity of porous structure, improve the thermal and mechanical properties of the porous PI material simultaneously. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48792. 相似文献
25.
In order to accelerate the application of bio-oil in the internal combustion engines, homogeneous catalytic esterification technology under vacuum distillation conditions was used to upgrade the crude bio-oil. The lubricities of the crude bio-oil (BO) and refined bio-oil with homogeneous catalytic esterification (RBOhce) or refined bio-oil without catalyst but with distillation operation (RBOwc) were evaluated by a high frequency reciprocating test rig according to the ASTM D 6079 standard. The basic physiochemical properties and components of the bio-oils were analyzed. The surface morphology, contents and chemical valence of active elements on the worn surfaces were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy, respectively. The results show that RBOhce has better lubricities than those of BO, but RBOwc has worse lubricities than those of BO. The tribological mechanisms of the bio-oils are attributed to the combined actions of lubricating films and factors that will break the film. Compared with BO, plenty of phenols in RBOwc results in corrosion of the substrate and destroys the integrity of the lubricating films, which is responsible for its corrosive wear. However, more esters and alkanes in RBOhce contribute to forming a complete boundary lubricating film on the rubbed surfaces which result in its excellent antifriction and antiwear properties. 相似文献
26.
《Ceramics International》2022,48(15):21451-21458
During the deposition of a-C:H film, defects (pinholes or discontinuities) caused by excessive stress will inevitably appear, which will reduce the corrosion resistance of the a-C:H film. In this study, top a-C:H:Si:O layers (thickness of approximately 0.3 μm) on the surface of a-C:H films were deposited on a large scale by PACVD technology using acetylene (C2H2) and/or hexamethyldisiloxane (HMDSO) as reactants, to improve the corrosion resistance of a-C:H films while ensuring the appropriate overall hardness of the films. The corrosion behaviors of the films were studied by electrochemical impedance spectroscopy (EIS) and Tafel polarization. We found that the a-C:H/a-C:H:Si:O films possess a lower electrolyte penetration rate due to their stronger capacitance characteristics. In addition, the corrosion current density of the a-C:H/a-C:H:Si:O films (10?10 A cm?2) were reduced by 2 orders of magnitude compared to the a-C:H film (10?8 A cm?2), and by 3 orders of magnitude compared to 316 stainless steel (10?7 A cm?2). The impedance results obtained by EIS were simulated using appropriate equivalent circuits, and the corresponding electrical parameters were used to further verify the electrochemical protection behavior of the top a-C:H:Si:O layer. 相似文献
27.
《International Journal of Hydrogen Energy》2019,44(54):28685-28697
The heterojunction of ZnO was deposited on hydrogenated TiO2 nanotube arrays (H–TiO2) by atomic layer deposition (ALD) with various cycles. The ZnO was uniformly wrapped with the H–TiO2 samples and the thickness could be accurately controlled by the cycle numbers of ALD. The higher growth rate ~2.7 Å/cycle was obtained due to the surface amorphous layer, compared with the air-treated samples (A-TiO2), ~2.3 Å/cycle. When the cycle numbers increased to 200, nanowire arrays appeared. Interestingly, the absorption in the visible light region improved more significantly when ALD ZnO was employed for the H–TiO2 rather than the A-TiO2 samples. The H–TiO2 samples with 42 nm of ALD ZnO exhibited enhanced photoelectrochemical water splitting performances, compared with the A-TiO2 with 42 nm of ALD ZnO. This was related to the higher degree of the electronic band bending and improved photo-response in the UV and visible light region, resulting from the oxygen vacancies. 相似文献
28.
Shuai Wang Xianjuan Pang Zhiyuan Zhang Baolin Chang Jun Yang Chenfei Song Sanming Du Yongzhen Zhang 《Journal of the European Ceramic Society》2021,41(10):5109-5114
Single-phase polycrystalline Mo2BC ceramic bulks were synthesized successfully from molybdenum, boron, and graphite powders using the spark plasma sintering method. Herein, it was established that the synthesis temperature of the Mo2BC ceramic could be as low as 1300 °C. Transmission electron microscopy (TEM) characterization confirmed that the crystal structure of the Mo2BC ceramic was comparable to that of the MoAlB ceramic. The Vickers hardness of the Mo2BC ceramic was measured to be 18.1 GPa. Additionally, the compressive strength, flexural strength, and fracture toughness were determined to be 1.74 GPa, 457.72 MPa, and 3.26 MPa· m1/2, respectively. The Mo2BC bulk exhibited typical brittle features, in which intergranular and transgranular fractures were the main failure modes. 相似文献
29.
Impact diamonds from Popigai astrobleme were found to consist of different carbon phases: cubic and hexagonal diamond with sp3 bonding according to X-ray structural analysis as well as amorphous, crystalline and disordered graphite with sp2-bonding (Raman scattering). The sizes of graphite domains vary from 10 to 100 nm. Fundamental absorption edge for Popigai impact diamonds is shifted ~ 0.5 eV to lower energies in comparison with kimberlite diamonds (5.47 eV) as a result of the lonsdaleite input, in good agreement with ab initio calculations (Eg = 5.34 and 4.55 eV for 3C cubic and 2H hexagonal diamonds, respectively). Yellowish color of impact diamonds is due to Rayleigh light scattering on structural defects whereas graphite is responsible for gray to black coloring. In the mid-IR region there is a multi-phonon absorption of 3C diamond in the 1800 to 2800 cm− 1 range and some new bands at 969, 1102, 1225, and 1330 cm− 1 in the one-phonon region. Micro-Raman study shows inclusions of side noncarbon minerals (quartz, magnetite, and hematite) some of which contain Cr3 + impurity. The vibration modes of cubic diamond and lonsdaleite exhibited in the Raman spectra were elucidated by the first-principles studies. Popigai impact diamonds demonstrate a broad-band luminescence in 2.1, 2.38, and 2.84 eV components similar to that for nanocrystal polycrystalline 3C diamond. All emissions are excited at band-to-band transitions whereas the last two are observed also at excitation into 2.4 and 3.0 bands supposedly as a result of intracenter processes within the H3(NVN) and NV0 centers. 相似文献
30.
《Carbon》2014
A new strategy is reported for the fabrication of silver nanowire (AgNW) film heaters using reduced small/or large-size graphene oxide (rSGO or rLGO) sheets as an over-coating protective layer. The results show that ultrathin rLGO microsheets provide the best combination of protective effect and electrical properties on AgNW networks and thus could enable the design of high-performance transparent film heaters. As a consequence, good optical transparency and electrical conductivity, good oxidation resistance and thermal stability, and good heating performances are achieved with as-made rLGO/AgNW film heaters. Specifically, the rLGO/AgNW hybrid film annealed at 700 °C shows a low sheet resistance of 27 Ω sq−1 and a good optical transparency of 80%. Furthermore, it exhibits good heating characteristics and defrosting performance at low voltages. The results presented here may pave the way for a new promising application of rLGO/AgNW hybrid film in transparent film heaters and other electrical devices. 相似文献