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41.
The cooling rate effects on the βo → ωo phase transformation in Ti–45Al–8.5Nb–(W, B, Y) (at.%) alloy were investigated by annealing the alloy at 950 °C followed by different cooling methods. The morphology and the distribution of the ω-related phases were analyzed by TEM. The amount and morphology of the ω-related phases are very sensitive to the cooling rate. The ω-related phases could not be resolved in the water-quenched sample whereas it grew into nano-particles in the air-cooled sample. In the furnace-cooled sample, the ωo phase with B82 structure grew into micron-sized particles and occupied the whole βo area. The nucleation of the ordered ω embryos can be explained by the well accepted displacive mechanism because of the instability of the βo(B2) structure, accompanied by a short-range diffusion process between neighboring {111}βo planes. However, the growth of the ω-related phases is controlled by a long-range diffusion process. Due to ready nucleation and growth, the ordered ω formation is bound to occur in as-cast and heat-treated high Nb–TiAl alloys. 相似文献
42.
One of the major expenses for steel structures is the anti-corrosion maintenance tasks. The maintenance of a steel structure depends on regular inspections, and visual inspections are often adopted in Taiwan. Using the naked eye to determine the rusted area percentage greatly depends on the experience of the inspector, resulting in subjective results. As an alternative, an algorithm consisting of three different approaches is proposed to automatically process images. The Hue percentage and coefficient of variation (COV) of the gray levels are used to divide images into three groups in which each group is assessed using a specific recognition technique. The three proposed techniques are the following: the traditional K-means method in the H component, the double-center-double-radius (DCDR) algorithm in the Red-Green-Blue (RGB) color space and DCDR in the Hue-Saturation-Intensity (HSI) color space. Additionally, the Least Square Support Vector Machine (LS-SVM) was adopted to predict the radii in the DCDR approaches. One hundred images, mostly collected outdoors, were used to verify the proposed algorithm. Promising performance was observed, particularly for images with non-uniform illumination. 相似文献
43.
《International Journal of Hydrogen Energy》2019,44(36):19841-19854
Improving the absorption of visible light, accelerating the separation of carries and reducing the recombination of electron-hole pairs are critical to enhance photoelectrochemical (PEC) performance of ZnFe2O4. Herein, the ZnFe2O4/Ag/Ag2S films are firstly prepared with a photocurrent density of 0.91 mA/cm2 at 1.23 V vs. RHE, which is 9.10 times higher than that of pristine ZnFe2O4 (0.10 mA/cm2 at 1.23 V vs. RHE). On the basis, Co-Pi cocatalyst is deposited on ZnFe2O4/Ag/Ag2S to further optimize PEC performance of ZnFe2O4, the photocurrent density of ZnFe2O4/Ag/Ag2S/Co-Pi is 1.18 mA/cm2 at 1.23 V vs. RHE. The improved PEC performance of ZnFe2O4/Ag/Ag2S/Co-Pi films could be attributed to: (i) fast transmission of electron-hole pairs owing to 1D ZnFe2O4 NRs; (ii) surface plasmon resonance (SPR) effect of Ag nanoparticles; (ⅲ) visible light absorption is improved by sensitization of Ag2S nanoparticles; (ⅳ) Co-Pi cocatalyst decreases the recombination of electron-hole pairs by capturing holes. This work provides new insights for metal plasmas, sensitizers and cocatalysts synergistically modify photoanodes for efficient PEC water splitting. 相似文献
44.
《International Journal of Hydrogen Energy》2019,44(41):23066-23073
Hydrogen evolution reaction (HER) in alkaline conditions usually requires a higher overpotential compared with acidic conditions due to the extra energy barrier originating from the additional water dissociation step. In this work, the theoretical calculation has confirmed that this challenge can be solved by the bimetallic synergic effect on binary transition metal catalysts. We report a simple method to synthesize NiMoP2 nanowires with (100) plane which can precisely expose Ni and Mo atom. The synthesized NiMoP2 nanowires exhibit a small overpotential of 87 mV to reach 10 mA cm−2 with a low Tafel slope of 66 mV dec−1 and long-term stability in alkaline solutions. 相似文献
45.
《International Journal of Hydrogen Energy》2019,44(26):13195-13204
It has been being an interesting challenge to develop novel electrocatalysts with advantageous nanostructures and thereby-improved catalytic performance for hydrogen evolution reaction (HER) over the past years. Herein, we report on the flower-like clusters of CoNiP nanofoils thickly grown on the randomly-interconnected reduced graphene oxide (rGO) nanosheets (CoNiP-NF/rGO) of 3-dimensional framework architecture, which has been successfully achieved via an optimized solvothermal process with Ni-doped ZIF-67 (Ni-ZIF-67) dodecahedral particles as the precursor and graphene oxide (GO) nanosheets as the substrate for the in-situ growth of flower-like CoNi-hydroxides nanofoils, as well as a following topotactic transformation in a controlled phosphorization. Benefiting from its distinctly advantageous nanostructures featured with extremely high specific surface area, enriched catalytic active sites and enhanced electronic transportation, the as-prepared CoNiP-NF/rGO exhibits an excellent electrocatalytic performance of HER with an onset overpotential of 33 mV, an overpotential of 82 mV at 10 mA cm−2, a Tafel slope of 37 mV dec−1 and a high chemical stability in acidic solutions. Such an advantageous nanostructure and its positive influences on the electrocatalytic performance are useful for the preparation of other nonprecious metal electrocatalysts. 相似文献
46.
Solvent engineering technique for planar heterojunction perovskite solar cells is an efficient way to achieve uniformly controlled grain morphology for perovskite films. In this report, diethyl ether solvent engineering technique was used for Methyl ammonium lead triiodide (CH3NH3PbI3) perovskite thin films for planar heterojunction solar cells which exhibited a PCE of 9.20%. Morphological improvements and enhanced grain sizes leads to enhanced absorption of CH3NH3PbI3. Moreover solar cells have showed an excellent environmental stability of more than 100 days. This increase in efficiency is due to improved film morphology of perovskite layer after solvent treatment which has been revealed under UV–Vis spectroscopy, SEM images, X-ray diffraction and impedance spectroscopy. 相似文献
47.
《Calphad》2018
Rare earth (RE) elements especially Yb, La and Ce have been frequently doped to Bi-Te alloys to improve thermoelectric performance. Three isothermal sections: Bi-Te-Yb at 573 K, Bi-Te-La and Bi-Te-Ce at 673 K were partly established by means of electron probe micro-analysis (EPMA) and powder X-ray diffractometry (XRD). The determined maximum solubilities of RE elements in Bi-Te alloys are very small and that of Yb reached the maximum about 0.3 at% at 573 K. Both LaTe2 and CeTe2 can dissolve a large amount of Bi, about 10 and 13 at% at 673 K, respectively. No ternary compound has been confirmed. 相似文献
48.
《Calphad》2018
The aim of this work is a formulation of a thermodynamic model for the development of new aluminum machining alloys. The three additives Bi, Pb and Sn have proven to help machining. Hence, a review of the literature showed that the liquid phase equilibria and thermodynamic data for the three binary systems Al-Bi, Al-Pb and Al-Sn is very thorough but the limited information for the FCC solution required the use of Density Functional Theory (DFT) to predict thermodynamic data. The partial heat of mixing of these three machining additives in Al(FCC) are obtained and the results helped to improve the thermodynamic model using the CALPHAD method. It was shown that for all three binary systems, the thermodynamic data obtained at three fixed compositions and that obtained for a very dilute solution gave different enthalpy curves. The thermodynamic model was used to compute the ternary systems Al-Bi-Pb, Al-Bi-Sn and Al-Pb-Sn and small adjustable parameters were added to reproduce the literature data. 相似文献
49.
Two polymeric hosts PCzTPP and PCzTPPO with twisted geometrical configurations for blue phosphorescent polymer light-emitting diodes (PhPLEDs) were designed and synthesized by incorporating electron-accepting carbazole units with electron-donating TPP/TPPO groups. This molecular design endows PCzTPP and PCzTPPO with high glass transition temperatures of 204 °C and 215 °C, high triplet energies of 2.72 eV and bipolar features. In addition, the HOMO and LUMO of these polymers matched well with the HOMO of the hole-transport layer and the Fermi level of cathode compared with PVK, which facilitated the injection of holes and electrons. PCzTPP- and PCzTPPO-based single-emissive-layer blue PhPLEDs were fabricated with simplified device configuration by solution process using FIrpic as a dopant. These devices exhibited lower turn on voltages (<8 V) than PVK-based devices (12 V). The maximum luminances of PCzTPP- and PCzTPPO-based devices were twofold and threefold that of PVK-based devices, and the maximum current efficiencies were nearly threefold and ninefold, respectively. Moreover, PCzTPPO-based solution processed blue PhPLEDs with improved configuration showed maximum current efficiency and external quantum efficiency of 14.5 cd/A and 6.6%, respectively. 相似文献
50.
《International Journal of Hydrogen Energy》2019,44(57):30208-30217
The present study is focused on the development of a structural model for multi−element AB5−type alloy which can correlate the hydrogenation characteristics with structural parameters. At present no such model is available, which can predict the trend of hydrogenation properties like hydrogen storage capacity, heat of formation and plateau pressure of multi−element hydrogen storage material. It is done by trial and error method. In present investigation efforts are made to correlate atomic radius of substituted elements with heat of formation of hydride, plateau pressure and hydrogen storage capacity by calculating equivalent radius of B (rB*) in multi−element composition, contraction in A−B bond, radius of voids and ratio of rA with rB*. The heat of formation decreases and hydride stability increases with increasing value of rB* and contraction in A−B bond. While hydrogen storage capacity decreases with increasing value of rB* and contraction in A−B bond. Based on this, correlation between thermodynamic and structural properties has been established and structural model has been developed. 相似文献