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It has been of interest in seeking electrocatalysts that could exercise equally high-efficient and durable hydrogen evolution upon nonselective electrolytes in both acidic and alkaline environments. Herein, we report a facile strategy to fabricate cobalt tungsten phosphides (CoxW2−xP2/C) hollow polyhedrons with tunable composition based on metal-organic frameworks (MOFs) template method. By the deliberate control of W doping, the synthesized catalyst with the composition of Co0.9W1.1P2/C is found to be able to achieve a current density of 10 mA·cm−2 at overpotentials of 35 and 54 mV in acidic and alkaline media, respectively. This combined electrochemical property stands atop the state-of-the-art electrocatalyst counterparts. To unveil the peculiar behavior of the structure, density functional theory (DFT) calculation was implemented and reveals that the surface W-doping facilitates the optimization of hydrogen absorption free energy (ΔGH*) as well as the thermodynamic and kinetics barriers for water dissociation, which is coupled with the hollow structure of Co-W phosphides, leading to the prominent HER catalytic performance. Ministry of Education (MOE) This work was supported by the National Science Foundation for Young Scientists of China (No. 51901018), China Postdoctoral Science Foundation (No. 2019M660456), the National Natural Science Foundation of China (Nos. 51771027 and 21676216), Young Elite Scientists Sponsorship Program by China Association for Science and Technology (YESS, 2019QNRC001), the Fundamental Research Funds for the Central Universities (No. FRF-MP-19-001), National Key Research and Development Program of China (No. 2017YFB0702100) and Singapore MOE AcRF Tier 1 grant M4011528.

This paper presents a novel electrical discharge machining method, alternating energy electrical discharge machining (AE-EDM), for the machining and surface modification of the workpiece. A tungsten carbide–polycrystalline diamond (WC-PCD) combined electrode was used in the EDM process to change discharge energy alternately, resulting in lower surface roughness and higher surface hardness. Based on the relationship between discharge current and plasma channel extension, principles and discharge models of AE-EDM were established. To validate the theory and assumptions and investigate the effectiveness of the new approach, the discharge performance of PCD was analyzed and a comparative study was conducted. Experimental results show that the sustaining voltage of the plasma in the machining of the PCD material is 19 V, and a fraction of the energy was consumed by the bulk resistance of the PCD, which reduces the energy for eroding material. The surface roughness of the workpiece machined with AE-EDM was found to be reduced by 40% compared to normal EDM using copper electrodes, while the average surface hardness was improved by 28.6% and the thickness of the recast layer was decreased.

The catalysis of Au thin film could be improved by fabrication of array structures in large area. In this work, nanoimprint lithography has been developed to fabricate flexible Au micro-array (MA) electrodes with ∼ 100% coverage. Advanced electron microscopy characterisations have directly visualised the atomic-scale three-dimensional (3D) nanostructures with a maximum depth of 6 atomic layers. In-situ observation unveils the crystal growth in the form of twinning. High double layer capacitance brings about large number of active sites on the Au thin film and has a logarithmic relationship with mesh grade. Electrochemistry testing shows that the Au MAs perform much better ethanol oxidation reaction than the planar sample; MAs with higher mesh grade have a greater active site utilisation ratio (ASUR), which is important to build electrochemical double layer for efficient charge transfer. Further improvement on ASUR is expected for greater electrocatalytic performance and potential application in direct ethanol fuel cell.[Figure not available: see fulltext.]. Ministry of Education (MOE) This research was supported by the MOE AcRF Tier 1 grant M4011528. The XRD and FEG-TEM characterisations were performed at Facility for Analysis, Characterisation, Testing and Simulation (FACTS) Lab; the FEG-SEM/FIB characterisations were carried out at Microelectronics Reliability and Characterisation (MRC) Lab.

The mechanical properties, physical properties and electrochemical behavior of metal components produced by selective laser melting can be influenced by the relative density and building direction. To this end, the optimization of the building process was conducted by identifying the influence of process parameters on the relative density and determining the ideal combination of parameters using the Box–Behnken design response surface methodology to achieve a relative density of 99.303 pct. With the ideal process parameters, material strength, thermal, and electrochemical performance were evaluated in a series of experiments. Anisotropic characteristics were displayed due to the differences in build-direction, microstructural features, and phase composition. The 0 deg possessed the highest tensile strength measured to be 1263.03 ± 8.71 MPa, while the 45 deg demonstrated the highest ductility with an elongation of 13.21 ± 0.34 pct. Thermal expansion was governed by the heat treatment process, such that anisotropic traits were eliminated after solution treatment. Strip melt tracks on the X–Y plane differed from the strip and arcuate melt tracks observed in the X–Z and Y–Z planes, leading to significant deficiencies in electrochemical reactance with an open circuit potential of − 645.8 mV in comparison to the latter measured at − 397.7 and − 396.7 mV, respectively.

Electrical discharge machining (EDM) is a non-conventional machining process which has been widely used to machine difficult-to-cut materials. However, the efficiency of EDM hole making processes is low, and the quality of drilled holes is a concern especially when machining deep blind holes due to the poor removal of debris in the discharging gap. In this study, a new strategy based on shape modification of the electrode was developed to address this issue by indirectly changing the flow of dielectric. The electrodes of five different shapes with identical machining area were applied to improve the debris removal during the machining process. The effects of various electrode profiles on the machining performance were investigated. Machine time, material removal rate (MRR) and electrode wear rate (EWR) were used to evaluate the machining performance. The computational fluid dynamic (CFD) software Fluent was used to simulate the flow of dielectric caused by different electrode profiles. The results show that, compared with the straight electrode, the maximum effective cutting depth of curved electrodes and long-curved electrodes increased 13.793% and 132.184%, respectively, and the MRR of stepped electrodes was significantly higher after the machining depth reached 2 mm and 4 mm for electrodes with the working length of 2 mm and 4 mm, respectively. The surface roughness was identical for holes machined by all types of electrode. However, obvious carbon adhesion can be observed at lower cutting depth for straight electrode, followed by curved and long-curved electrodes.

Understanding the physical requirements for a broad bandwidth is vital for the design of high-efficiency microwave absorber. Our recent works on silicon carbide (SiC) fiber mats-based absorbers imply that metal modification (e.g., Fe or Hf) could benefit their bandwidth effectively. For verification, we fabricated a Co/SiC fiber mat via a similar electrospinning process and subsequent pyrolysis at 1400 °C in Ar atmosphere. The results indicate that after Co modification, the SiC fiber mats show elevated permittivity and tangent loss. With a proper amount of Co adding, the mats could exhibit a wide bandwidth of around 8 GHz (ranging from 10 to 18 GHz) for effective absorption (reflection loss (RL) less than -10 dB) at 2.8 mm thickness. This is similar to our previous findings, confirming that metal modification could be an effective approach to extend the bandwidth of SiC mat absorbers. Explanations can be found through theoretical analysis with the quarter wavelength (λ/4) cancellation theory. It suggests that the declining permittivity (with the increase of frequency) is the key to keep the wavelength in material (λ

This paper presented a new electrical discharge machining (EDM) method using powder mixed effects formed by the graphene–water dielectric to improve the machining performance in processing titanium alloy. Theoretical and simulation models were developed to analyze the effects of graphene bubbles on discharge breakdown characteristics and the plasma channel. To validate the theoretical model, single-pulse experiments were conducted by analyzing the shape and dimension of single-discharge craters. Comparative and exploratory experiments were carried out to investigate the erosion characteristics of the new machining approach. Experimental results show that graphene bubbles could affect the erosion characteristics and improve the machinability of titanium alloy. The material removal rate was increased by 28% and surface roughness was reduced by 55%, whereas relative electrode wear was reduced by 43% compared to traditional EDM processes.

Au is an ideal noble metal for use as an electrocatalyst for the ethanol oxidation reaction owing to its high performance-to-cost ratio. The catalyst usually exists as nanoparticles (NPs) for high surface area-to-volume ratio. In the present work, a nontraditional physical approach has been developed to fabricate ultrasmall and homogeneous single-crystalline Au NPs by ion bombardment in a precision ion polishing system. Transmission electron microscopy characterizations show that the Au NPs produced with 5 keV Ar

Flexible joint is a typical low-rigidity micro part, which has four narrow neck structures evenly distributed around its central axis. In the ultra-precision machining process, It is crucial to control the dimensional accuracy of the narrow necks to improve stiffness consistency. However, the limited space of the neck structures and the high accuracy requirements bring extremely difficulties to the measuring process. In this paper, a novel on-machine measurement method for the semicircular narrow necks was presented and a measuring device was developed based on the combination of high linearity incremental measurement method and on-machine measurement technology. Moreover, the uncertainty of measurement error was analyzed in detail. In view of the measurement error caused by temperature drift, a compensation method based on non-uniform rational B-spline (NURBS) surface interpolation was used to enhance the measurement accuracy. The experimental results showed that the measurement accuracy enhanced over 30% after compensation, which met the measuring requirement of flexible joint.

Polycrystalline diamond (PCD) is a type of ultra-hard material that is widely used in the industry. However, the high manufacturing costs caused by low machining efficiency impede the affor...

Purpose Direct additive manufacturing of ceramics (DAMC) is a highly promising ceramics preparation technology because of its simple process and rapid response capability, but the cracking issue prevents its industrial application. The purpose of this paper is to propose aluminum titanate (Al2TiO5) with low coefficient of thermal expansion (CTE) to suppress cracks during the DAMC. Design/methodology/approach Al2O3/Al2TiO5 (A/AT) composite ceramic samples with different compositions were in-situ synthesized from Al2O3/TiO2 (A/T) powder in a directed laser deposition (DLD) process. The relationship between the content of TiO2 and cracking characteristics of fabricated sample was discussed. Phase composition, microstructure and properties of the fabricated samples were also investigated. Findings The results of this paper show that the doping of TiO2 can obtain Al2TiO5 synthesized in situ by reaction with Al2O3 and effectively suppress cracks during DAMC. When the content of TiO2 reaches 30 wt.per cent, cracks hardly occur even under conditions of slow deposition. Crack-free structures such as vane, cone and pyramid were successfully prepared, with a maximum cross-sectional dimension of 30 mm and maximum length of 150 mm. A continuous matrix phase formed of the low CTE of Al2TiO5 is the major cause of crack suppression. The dispersed distribution of a-Al2O3 columnar dendrites has the effect of increasing the strength of the matrix. Under current process conditions, the prepared sample with 10 wt.per cent TiO2 has micro-hardness of 21.05 GPa and flexural strength of 170 MPa. Originality/value This paper provides a new method and inspiration for direct additive manufacturing of large-sized crack-free ceramics, which has the potential to promote practical application of the technology.

Gold (Au) is a noble metal that has been widely researched due to its high catalytic performance-to-cost ratio. The catalysis could be improved by fabrication of nanostructured arrays on Au thin film with a large area. In the present paper, a facile NSL-RIE approach comprising of nanosphere lithography followed by oxygen plasma reactive ion etching has been developed to fabricate ordered Au nano-ring arrays with almost 100% substrate coverage. The preferential etching of {1 1 1} lattice planes of Au gives rise to the formation of a number of Au nano-pyramids across the entire surface of the nano-ring arrays. The sharp tips along with the Au atoms around the edges of these nano-pyramids provide active sites that perform strong catalysis. Meanwhile, Moire fringes are observed over the etched Au surface which is caused by the rotation of the partial Au lattice with respect to the original Au lattice. This lattice distortion provides high surface energy allowing the significant improvement of the catalysis of Au nano-ring arrays. The direct evidence is proven by the enhanced electrochemical properties of the as-produced Au nano-ring array, which has high efficiency in ethanol oxidation reactions (EORs) with low energy input requirement. Electrochemical testing with varying physical parameters shows that the detecting limit of ethanol is ∼5.0 mM and strong signals come with high concentrations of mobile charge carriers at extreme pH values. Long continuous CV scans reveal that in alkaline medium, C1 pathway could become increasingly preferential over C2 pathway, and thus making the Au nano-ring array structure useful in the field of direct ethanol fuel cell.

Treatment of glycerol, the byproduct from biodiesel production, calls for a more efficient and cost-effective approach. In this work, in situ hybrid induced oxidation method was proposed, involving the advanced oxidation process and electro-catalytic process. Generally, these highly active species in the plasma region is helpful to degrade the organic products. In addition, numerous CuO nanoparticles with oxygen defects that were induced by the plasma, could improve the catalytic performances. In the plasma discharge process, those CuO catalysts and plenty of hydrogen bubbles which were generated around the copper cathode, also resulted in the high efficiency dehydration of glycerol. The effects of discharge status of liquid plasma and glycerol volume on conversion rate were discussed in detail. It was found that a lower discharge voltage 70 V in the normal glow discharge period is beneficial to dehydration of glycerol. Combined with the FTIR analysis for products composition, the degradation products and the conversion rate were illustrated using the HPLC. The experimental results showed it can achieve a conversion rate of 81.27% after 40 min and the energy yield was 10.02 g/(kW h).

Dielectric fluids affect not only the discharge status but also the structure and composition of recast layer in the electrical discharge machining (EDM) process. In order to reduce the thickness of recast layer and improve the surface quality of film cooling holes of nickel alloy, in this paper, the effects of four different types of dielectric fluids on surface integrity of the recast layer formed during high speed EDM drilling process were investigated; the formation mechanism of the recast layer on nickel alloy was discussed by comparing the surface characters of the bulk and those of the recast layer using various characterization methods. The dielectric fluids with larger electric conductivity (emulsion and water solution) were found to have higher sensitivity to the single pulse discharge energy. With the increase in electric conductivity of dielectric fluids, the recast layer became thicker accordingly. The thickness of the recast layer when using kerosene fluid was the smallest (4.8 μm), which was nearly one third of the that of using water-based fluid. The cooling rate of the dielectric fluid affected the microstructure of the recast layer, where the surface of recast layer was apt to form fine grain zone and the bottom formed columnar grain.

The hollow mesoporous Co(PO3)2@carbon nanocomposite (H–Co(PO3)2@C) was synthesized using ZIF-67 as the template by a facile one-step thermal decomposition reaction. As an anode for lithium ion batt...

Melt growth Al2O3–ZrO2 eutectic ceramic has excellent high-temperature strength, creep resistance, oxidation resistance and ultra-high-temperature microstructural stability, which is expected to become one of the ideal high-temperature structural materials. Directed laser deposition (DLD) is a new technology for fabrication of melt growth eutectic ceramics, which can rapidly fabricate net-shaped ceramics. Aiming at decreasing crack and pore defects in samples prepared by DLD, different proportions of SiC particles (SiCp) are doped into Al2O3–ZrO2. Results show that SiCp distributes uniformly in Al2O3–ZrO2 eutectic ceramic matrix. Interfacial reaction occurs between SiCp and matrix. Two kinds of white phases rich in C, Si, Zr elements are formed around SiCp, and they are closely bonded with SiCp and matrix. The number and the maximum length of cracks in sample decrease obviously with the addition of SiCp. When the content of SiCp increases from 0 to 25 wt%, the number of cracks decreases 93% and the maximum cracks length decreases 92%. Some energy dissipation mechanisms such as crack pinning, transgranular fracture, crack deflection and bifurcation have remarkable effect on crack suppression. In addition, SiCp plays a significant role in eliminating pores, which reduces the porosity from 11.71 to 0.20%. Doping SiCp can increase the temperature and enhance the convection and disturbance of melt pool. Also, it can provide discharge channels for bubbles in melt pool.

As flexible joint is a typical low-rigidity micro part, which have four narrow neck structures evenly distributed around its central axis, it is necessary to strictly control the dimensional accuracy of the narrow necks to improve the consistency of stiffness. However, the radius of the arc of the narrow necks is less than 2mm, and the thickness of thinnest part of the necks formed by two adjacent arcs is only tens of microns, which also has sub-micron accuracy requirement. These cross-scale dimensional characteristics and accuracy requirements give rise to extremely difficulty on the measuring process. In this paper, an on-machine measurement method for the semicircular narrow necks was presented and a measuring device was developed based on the comparative principle by making full use of the high linearity characteristic in the small measuring range of the sensor probes. Meanwhile, the on-machine measurement process based on ultra-precision machine tools was also introduced in details. The experiments results show that the uncertainty of the measurement method proposed is less than 0.2µm, and the repeatability is less than 0.1μm, which meet the measuring requirement of flexible joint. Furthermore, the effect of probe position, measurement force, environmental factor and the accuracy of the sensor on total measuring accuracy was analyzed, which could provide further evidences to improve the measuring accuracy. of micro-scale hybrid surface texture.

The measurement of resonator’s frequency splitting is a critical issue in vibratory gyroscopes, which would be elaborately treated in practical applications. The high-precision measurement of frequency splitting plays a significant role in frequency tuning control. A novel time-domain method of frequency splitting measurement for hemispherical resonator based on the standing wave swing effect was proposed. The frequency splitting value of the resonator can be directly obtained by taking the reciprocal of the one cycle time of standing wave swings, rather than through the frequency difference between two resonant modes. To begin with, the method was analyzed theoretically, and the measurement resolution and accuracy of the method were researched in detail. Simulation and experimental results showed that the frequency splitting value can be effectively obtained by measuring the period of the standing wave swings, improving the fine measurement resolution and high accuracy. The frequency splitting of lower than 0.007 Hz has to be effectively obtained in the experiment. It is found that the measurement error is a small proportional part of frequency splitting value, so the measurement accuracy is very high when the frequency splitting is very low. Therefore, this time-domain method would contribute to the measurement of ultralow-frequency splitting for high-Q resonators.

Transition metal oxides CuO-ZnO nano-flowers have been simultaneously synthesized by the low voltage liquid plasma discharge method using brass cathode. The effects of discharge statue (normal and abnormal glow discharge) on the nanostructures were investigated. It was found that a lower discharge voltage 52 V in the normal glow discharge period is beneficial to produce homogeneous nano-flower structures while a higher voltage tend to result in inhomogeneous products including larger particles. The obtained products were characterized by SEM, XRD, high-resolution TEM, Raman and XPS. Moreover, the nano-flowers exhibit a favorable electrocatalytic activity of glucose oxidation. This research was funded by the Chinese Natural Science Foundation (Grant number: 21504025 and 51305230).

The present paper reports a rapid and cost-effective bifunctional approach to the degradation of organic pollutants in the aqueous solution. This in situ hybrid induced photocatalytic method involves the advanced oxidation process, and photocatalytic process induced by ultraviolet radiated from the plasma discharge to improve the degradation efficiency. This powerful plasma allows the organic molecules to be cleaved either in the plasma zone or on the plasma/solution interface through hydrogen abstraction and electron transfer. Four parallel metal foil electrodes (i.e. Ta, Cu, Ti and Au coated Ti), used as cathodes in the two-electrode system, were evaluated in terms of their degradable performance to organic pollutants. It was found that the degradation rates are dependent on the electrical conduction of metal cathodes. During the discharge process, the Ti-based foil produces TiO2 particles, which then act as catalyst in the electrolyte and perform the photocatalytic process along with the plasma discharge process to degrade organic pollutants. It is of particular interest that gold nanoparticles, generated from Au coated Ti foil film during electrode discharging, are less than 5 nm in size and further enhance the TiO2 photocatalytic activity. In fact, this bifunctional plasma discharge process to the degradation of water pollutant provides an insight into more applications such as chemical conversion, water purification and dust pollution. Ministry of Education (MOE) This work was supported by Tier 1 (AcRF grant MOE Singapore M4011648 and M4011528) and the National Natural Science Foundation of China (Grant 51271031).