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51.
52.
《Ceramics International》2019,45(8):9799-9806
(Nb1-xTax)4AlC3 (x = 0–0.5) ceramics were prepared by the hot press sintering method. The XRD results show that the second phase (Nb1-xTax)C is formed when the Ta content increases to 25 mol%. The SEM micrographs show that (Nb1-xTax)C has a core/rim structure, whose formation mechanism was also investigated. Substituting some Ta for Nb can significantly improve the mechanical properties of Nb4AlC3. (Nb0.75Ta0.25)4AlC3 exhibits an excellent fracture toughness of 8.3 ± 0.3 MPa m1/2 at room temperature (RT). The highest Young's modulus (349 ± 16 GPa) and Vickers hardness (4.5 ± 0.3 GPa) at RT are exhibited by the (Nb0.5Ta0.5)4AlC3 sample, which correlate to increases of 18% and 80%, respectively, compared with those of Nb4AlC3. The flexural strengths of (Nb0.5Ta0.5)4AlC3 are 439 ± 18 MPa at RT and 344 ± 22 MPa at 1100 °C, which correlate to increases of 27% and 45%, respectively, compared with those of Nb4AlC3. The solid solution of Ta and the formation of (Nb1-xTax)C are beneficial to the strengthening of Nb4AlC3. The coefficient of thermal expansion (CTE) increases slightly from 7.08 × 10−6 K−1 for Nb4AlC3 to 7.24 × 10−6 K−1 for (Nb0.75Ta0.25)4AlC3 at 25–1400 °C. The thermal conductivity of (Nb0.75Ta0.25)4AlC3 (28.4–29.8 W/m·K) is higher than that of Nb4AlC3 (18.1–21.2 W/m·K) over the whole test range (25–1000 °C). Owing to their excellent mechanical and thermal properties, Ta-doped Nb4AlC3 ceramics have good potential as structural materials. 相似文献
53.
This paper proposes an approach to predict the efficiency of forced-air cooling of fresh apples that combines the optimized differential evolution (DE) algorithm and the back-propagation (BP) neural network algorithm. First, to balance population diversity and fast convergence, the individual mutation operation of the basic DE algorithm was optimized by dividing the entire population into two equal parts according to the fitness value of individuals, and DE-best-1 and DE-current-to-rand-1 are used as individual mutation operations for the superior- and inferior-part individuals, respectively. Moreover, the selection operation of basic DE was also changed by using a crowding scheme, which helps maintain population diversity and discover more regions containing the global optima. Second, an optimized DE-BP neural network model was established by using the optimized DE to determine the initial weights and thresholds of the BP neural network to avoid being trapped in local minima, following which the effect of input parameters on the network output was subjected to a comprehensive sensitivity analysis based on the trained neural network. The results show that the optimized DE-BP model accurately predicts the efficiency with which apples are cooled. Furthermore, the airflow velocity and total opening area have a significant negative correlation with the average apple temperature and a positive correlation with the cooling rate of the apples. Finally, the most important factor influencing the cooling efficiency of the pre-cooling system is the total opening area of the ventilated packaging. 相似文献
54.
《International Journal of Hydrogen Energy》2021,46(74):36811-36823
Nitrogen-doped transition metal materials display promising potential as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Fe/N co-doped three-dimensional (3D) porous graphene (FeN-3D-PG) is prepared via a template method using sodium alginate as the carbon source and low polymerization degree melamine resin as the nitrogen source. The low polymerization degree melamine resin can form complexes with Fe3+ in the aqueous solution and further forms high density Fe-Nx active sites during pyrolysis. Meanwhile, the formed 3D porous structure efficiently promotes the uniform distribution of Fe-Nx active sites. The FeN-3D-PG catalyst exhibits pH-independent ORR activity. For OER, the catalyst possesses a low over potential (370 mV at 10 mA cm−2) in alkaline electrolyte. The Zn-air batteries (ZABs) using FeN-3D-PG as cathode exhibits a power density up to 212 mW cm−2, a high specific capacity of 651 mAh g−1, and the charge-discharge stability of 80 h. This work provides new sight to transition metal materials based ZABs with excellent performance. 相似文献
55.
《International Journal of Hydrogen Energy》2021,46(58):29896-29904
Water oxidation is a key reaction for water splitting. The decomposition of Fe-based-molecular structures toward Fe-based oxides is a promising method for oxygen-evolution reaction (OER) through water oxidation. The decomposition of Fe-based-molecular structures method results in a slow decomposition of precatalysts and forms Fe oxide-based catalysts. In this study, the Fe species formed through the decomposition of a dinuclear Fe(III) complex under OER is investigated by X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and the electrochemical method. In addition, using Ni(OH)2, a new approach is reported for detecting trace Fe species on the electrode surface. The resulting Fe oxide-based catalyst shows a catalytic current with an onset of 621 mV overpotential and the Tafel slope of 113.7 mV/decade at pH 11 in a buffer phosphate. 相似文献
56.
We introduce a new, bespoke data structure to analyze and visualize the evolution of a technology. The technology under analysis is defined by a set of patents corresponding to a technical field, owned by a company or invented by a team of research. Our data structure, the Dynamic Technology Footprint –DTFootprint–, facilitates the analysis and visualization of trends and dynamics of a given technology, and therefore the evolution of a technical field, a company, or a team of people. A graphical tool based on our data structure is defined, it is named Technology Spectrogram –TechSpectrogram–, because it is inspired by the acoustic frequency spectrograms: as the acoustic frequency spectrograms visualize the dynamics of an acoustic wave showing the evolution of its frequency components our tool shows the dynamics of a technology showing the evolution of its technological components, which are represented by the whole set of IPC-codes. Our graphical tool, the TechSpectrogram is shown for some study cases, and its application to the history of technology and technology management are disclosed. 相似文献
57.
Irshad Ahmad Shazia Shukrullah Muhammad Yasin Naz Muhammad Athar Rasheed Mukhtar Ahmad Ejaz Ahmed Muhammad Shoaib Akhtar N.R. Khalid Abid Hussain Sadia Khalid 《International Journal of Hydrogen Energy》2021,46(53):26711-26724
CNTs were decorated onto Sr doped ZnO nanoparticles to construct an efficient photocatalyst via a facile sol-gel method. The as-fabricated Sr doped ZnO/CNTs with recyclability exhibits Sr and CNTs content dependent hydrogen evolution activit under visible light illumination. The Sr doped ZnO/CNTs photocatalyst shows the highest hydrogen evolution rate of 2732.2 μmolh?1g?1, which is 33.7 and 2.83 times higher than pure ZnO and Sr doped ZnO photocatalysts, respectively. The improved hydrogen evolution activity of Sr doped ZnO/CNTs is primarily assigned to high surface area, Sr doping and construction of heterojunction, which can extend the light absorption, decrease the optical band gap and improve the charge separation. Moreover, the underlying photocatalytic mechanism is proposed on the basis of Mott-Schottky study and explains the interfacial charge transfer process from ZnO to CNTs and Sr. This work open new strategies to synthesize CNTs based nanocomposite for hydrogen evolution. 相似文献
58.
59.
《Ceramics International》2021,47(22):31268-31276
The relationship between the tensile strength of corroded domestic second-generation (2ed-gen) SiC fibers at various temperatures for 500 h in 46.5LiF-11.5NaF-42.0KF (mol. %) eutectic salt and the typical microstructure was studied. Weibull theory was used to analyze the critical defects that caused the tensile fracture, and the microstructure of fibers before and after corrosion was characterized. It is concluded that the decrease of tensile strength after corrosion at 800 °C is caused by the surface injury of fibers, which led to the shift of critical defects from the internal defects of virgin fibers to surface defects. Moreover, corrosion at higher temperature accelerates the corrosion process and dissolve the surface O-contained layer thoroughly. This shifts the critical defects back to the internal defects and will be helpful for the recovery of tensile strength of corroded fibers at the higher temperature. 相似文献
60.
Min Ye Feng Hu Deshuang Yu Silin Han Linlin Li Shengjie Peng 《Ceramics International》2021,47(13):18424-18432
In high demand is developing trifunctional electrocatalysts to simultaneously drive hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) for metal-air batteries and water splitting. Here we develop the carbon nanotubes (CNTs)-grafted FeC/MnO2 nanocomposite catalyst by carbonizing FeMn metal-organic frameworks. The synergistic effect between FeC and MnO2 dominantly contributes the ORR, OER, and HER. The transition metal-mediated growth of CNTs by an in-situ catalysis mechanism enables high electrical conductivity, abundant active sites, as well as efficient reaction pathways. The optimized chemical composite and unique hierarchical structure endow the FeC/MnO2 with low overpotentials for multiply electrochemical reactions. Consequently, the composite catalyst successfully serves as the bifunctional electrode for water splitting with a voltage of 1.66 V at 10 mA cm?2 as well as the cathode for all-solid-state metal-air battery with Pt/C-comparable performance. The advanced transition metal composite presented in this work provides the guidance for rationally developing trifunctional electrocatalysts for efficient integrated energy conversion systems. 相似文献