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We report hierarchical CoSx/Ni(OH)2/NF heterostructure nanorod arrays, which manifest superior bifunctional catalytic activities for the HER and UOR due to amorphous Ni(OH)2, synergistic effect of multiple components and self-supported structure. The CoSx/Ni(OH)2/NF-based urea electrolyzer requires a low cell voltage of 1.485 V to deliver 10 mA cm−2, which is obviously lower than that needed in water electrolysis. [ABSTRACT FROM AUTHOR]

The 3%TiB2/2A14 (volume fraction) aluminum matrix composites were prepared by in-situ salts-metal reaction under ultrasonic field. The wear experiments with four different load (20, 30, 40, 50N) were carried out with a reciprocating tribometer. The abrasive resistance and friction behavior of composites with different ultrasonic vibration treatment (UVT) process were studied. The mircohardness of matrix and composites were measured by the microhardness tester. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied to identify the phase compositions and observe the microstructure and morphology of worn surfaces. And the wear mechanism was also studied. The results manifest that the ultrasonic can efficiently scatter the particle agglomerations, improve the state of particle distribution and reinforce the interfacial bonding strength between particles and matrix. Therefore, the abrasive resistance and microhardness of composites with UVT are obviously superior to alloy matrix. The wear rate and hardness of composites obtained by 120s UVT are about 57.43% and two times of that of the matrix alloy under 50N load. Under the dry friction condition, the main wear mechanism of alloy matrix is adhesion wear and composites is hybrid wear with adhesion wear and abrasive wear and the wear resistance is better.

Since the development of the aviation industry, improving the flight performance and reducing the weight of aircrafts has always been the goal pursued by aviation designers. Therefore, it becomes increasingly important to develop a new alloy material with high hardness, high strength, and light weight. To obtain excellent mechanical properties and good corrosion resistance, a new kind of alloy material, ZL205A alloy, was developed by the Beijing Institute of Aerial Materials (BAM) in the 1960s. Owing to its favorable mechanical properties and excellent corrosion resistance, ZL205A alloy has been well applied in the aviation industry. However, this kind of Al alloy still possesses some undesirable solidification defects: shrinkage, porosities, coarsening grains, and solute segregation. Ultrasonic melt treatment (UST) provides a means to eliminate or modify these defects. In the present work, the effects of UST on ZL205A alloy were investigated for two conditions, i.e., before casting and during solidification in ambient environment. Then, the effects of ultrasonication on the as-cast microstructures and the tensile properties were accordingly characterized and analyzed. For the case in which UST was only introduced before casting (holding temperature at 750℃), degassing and the distribution of secondary phases were modified. For the case in which UST was only introduced when cooling from 750℃ for 7 min 10 s to about 650℃, grain refinement and reduced porosities were generated. When UST was continuously employed for both conditions, the above properties were further improved compared with those of ingots without ultrasonic treatment. The mechanical tensile test results show that the improvement of the ingot internal structure can improve the ingot mechanical tensile properties, which proves the correctness of the above research results. Thus, UST carried out at two different conditions induced different regulatory functions and influencing mechanisms. This study shows that the UST of ZL205A aluminum alloy in different melt states has different emphases on improving the internal structure of the ingot.

With the development of the aerospace industry and the need for industrialized production, the casting processes of large diameter aluminum alloy ingot have come into focus in the industry. Among them, ultrasonic-assisted casting technology is widely used. Ultrasonic-assisted casting technology has the advantages of improving solute segregation of ingot and refining solidification organization. Other advantages have been widely reported. At present, most of the aluminum ingots used in the non-hot top ultrasonic casting process with very shallow liquid cavities, while the casting process does not involve the issue of ultrasonic vibration depth. With the use of a hot-top mold for ultrasound in the casting and casting process of large diameter ingot, the liquid level of aluminum melt is very high. The ultrasonic vibration depth will affect the cavitation range and finally affect the fine grain effect of the ingot. In the present study, a double source ultrasonic vibration system was applied in the process of semi-continuous casting of aluminum alloy with a diameter of 650 mm, and the influence of ultrasonic immersion depth on the macroscopic solidification structure of ingot was studied. Based on the test results of the solidified microstructure of aluminum alloy ingot and the simulation results of the sound field of the finite element software such as ANSYS, the mechanism of the microstructure refinement of the aluminum alloy ingot under different vibration depths was discussed at length. Study results show that, with increasing vibrational depth of the supersonic radiation rod, the whole cross section of the ingot is further refined, and grain shape changs from developed dendrites to equiaxed dendrites. Because of the end faces of the ultrasonic radiation rod, there is a vibrational peak at the fixed position, which leads to different ultrasonic cavities under different ultrasonic vibrational depths in the aluminum melt. This leads to different refinement mechanisms of the solidified structure.

The oxidation mass increasing method was adopted to explore the oxidation behavior of high-vanadium wear-resistant alloy at 950℃. The oxidation mechanism and cracks behavior were studied with different cooling types (furnace cooling and air cooling). The results indicated that the weight increment per unit area was obviously large at the beginning of the oxidation due to the matrix being in direct contact with the air. Additionally, the oxidation increase gains of furnace and air cooling were 82.7 mg·cm-2 and 39.1 mg·cm-2, respectively, after 8 h of oxidation. At the same time, the preferential formation of Cr2O3 was observed with 50-200 nm at the matrix and oxidation layer interface. Remarkable thermal stress was produced in the oxidation layer due to the larger cooling rate. The warped phenomenon appeared at the oxidation layer due to the production of growth stress. However, the shedding phenomenon rarely occurred in the oxide layer.

By applying ultrasonication during direct chill casting, a 2219 ingot with a diameter of 1250 mm was successfully produced. To study ultrasonic inner mechanism of ingot, the microstructure and macrosegregation of ingots cast after ultrasonication were analyzed by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and direct-reading spectrometry. The results show that the cavitation and acoustic streaming effects brought by ultrasonic vibration can obviously regulate the structure and refine the grain size of the resulting ingots. The central grain refinement rate observed is 39.6%. Ultrasonication promotes the formation of branched intergranular secondary phases with a discontinuous distribution, and transgranular precipitates present a dispersed distribution with dot. Ultrasonication also effectively decreases negative segregation near the surface of the ingots, reduces the difference solute concentration between their edge and center, and weakens fluctuations in concentration over the entire cross section of the samples, thereby improving the macrosegregation properties of the final products.

We developed an efficient MoS2 nanosheet electrode coupled with CeO2via a hydrothermal process to facilitate water adsorption and dissociation, which displayed good HER activity and stability at a large current density of 500 mA cm−2. In situ Raman spectroscopy confirmed the formation of hydroxide ions based on the strengthening of the Ce–O bond during the HER. [ABSTRACT FROM AUTHOR]

A multi-field coupling mathematical model was established to analyze the hot-top semi-continuous casting of a large-scale aluminum alloy of 630 mm in diameter with ultrasonic treatment (UST). The finite volume method combined with the self-com-piled function was used to get the distribution of the acoustic field, flow field and temperature field, and the industrial experimental re-search was also performed. The mechanism of ultrasonic treatment on the grain refinement of the large-scale aluminum alloy produced by hot-top semi-continuous casting was analyzed based on the simulation and experiment results. The simulation results show that ultra-sonic markedly influences the macroscopic physic field. With ultrasonic treatment, an upward recirculation zone forms beneath the end face of the radiation rod, the heat and mass transfer is promoted by the strong turbulence, the sump gets shallower and gentler, the ini-tial solidifying point on the ingot surface in the mold moves down, the transition zone becomes narrower, the width of it in the center drops from 342 mm to nearly 120 mm. The experimental results show that with ultrasonic treatment, the grain size becomes smaller and more homogeneous, the average grain size reduces by 103μm, the gap between the maximum and minimum grain size decreases from 135 to 64μm, and the grain boundary of the solidification structure becomes thinner.

The transformation behavior of secondary phases in conventional ingot and ultrasonic ingot during heat-treatment process were investigated by OM, SEM, EDS and DSC. Crystalline phase transition was observed by SEM with in situ heating station. The experiment results indicate that the ultrasonic melt treatment transforms from columnar crystals to equiaxed crystals, and obtains fine and uniform grains. The melting enthalpy of ultrasonic ingot is 4.60J/g, while the melting enthalpy of conventional ingot is 6.52J/g, combined with EDS analysis results, θ phase and T phase are found to be reduced by 29% after ultrasonic melt treatment. The secondary phases in the ingots include θ phase, T phase, Al3Fe phase and Mg2Si phase. θ phase is dissolved into matrix gradually, T phase transforms to S phase and is dissolved into matrix at high peak temperature, Al3Fe phase transforms to Al7Cu2Fe phase at low peak temperature and remains in the ingots, Mg2Si phase changes nothing during DSC analysis process.

Hierarchical Mn-Ni2P/NiFe LDH arrays were developed as a self-supported electrode. Because of the synergistic effect and self-supported structure, it presents brilliant bifunctional catalytic activities for the HER and UOR. Surprisingly, the voltage of a urea electrolytic cell coupling the HER with the UOR was as low as 1.494 V at 10 mA cm−2. [ABSTRACT FROM AUTHOR]

Rayleigh-Taylor instability of a fluid film, with the analysis of the effects of the cylindrical interfaces and finite film thickness provides a general dispersion equation, relating wave number, beta 1, to growth rate, c1. The setup is an axisymmetric cylinder between two inviscid fluids. The experimental and the theoretical analysis for the measurement is discussed.

Boiling is of three types, namely nucleate, transition and film boiling, by which bubbles are steadily formed and released at the liquid-over-vapor interface on top of a heating element. Mathematical models for film boiling on horizontal flat plates have been developed. A study used a cylindrical heater with radius Ro immersed in a liquid. The geometry of the liquid-vapor interface surrounding a wire during film boiling was taken to assume a sinusoidally undulating and asymmetric form. The vapor cover surrounding the heater was taken to be sufficiently thin, and the smallest radius of the interface larger than the radius of the heater.