Surface Separation Research Articles

S-type Bi2S3/BiOBr heterojunction with robust piezo-photocatalytic dye removal activity: degradation performance and mechanism investigation

In this work, an efficient S-type Bi2S3/BiOBr piezo-photocatalysts was prepared by the decoration of Bi2S3 nanorods on the surface of BiOBr nanosheets. The piezo/photo/piezo-photocatalytic performance of samples were evaluated under the irradiation of ultrasonic and/or simulated-sunlight employing methyl orange (MO) as a target reactant, indicating that above catalytic activity of BiOBr is able to be elevated after Bi2S3 attachment. Particularly, the 10%Bi2S3/BiOBr sample exhibits the optimal catalytic performance. It is worth noting that the 10%Bi2S3/BiOBr sample achieves much higher piezo-photocatalytic MO removal efficiency than its photocatalysis and piezocatalysis, demonstrating a remarkable synergistic improvement between piezocatalysis and photocatalysis with a synergistic enhancement factor (SF) of ∼1.29. The formation of S-type heterojunction in the Bi2S3/BiOBr composite was directly confirmed by the combination of density functional theory (DFT) calculation and in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) measurement, elevating the surface separation of generated charges. Meanwhile, the ultrasonic-excited piezoelectric polarization field in BiOBr nanosheets excited by ultrasonic irradiation promotes the bulk segregate of generated charges. Benefiting from above two aspect effects, the overall separation of generated charges can be effectively achieved, leading to outstanding piezo-photocatalytic degradation activity of Bi2S3/BiOBr composite.

Numerical investigation of the influence of suction surface synthetic jet on the performance of transonic axial flow compressor

In order to investigate the effect of suction surface synthetic jet on the aerodynamic performance of transonic axial compressor, Rotor35 was used for numerical simulation. The results show that at four different positions, the stability margin of the compressor is slightly reduced by suction surface excitation, but there is an optimal position that can improve the compressor total pressure ratio and efficiency. At this position, there is little change in the total pressure ratio at the peak efficiency, and the efficiency is improved by 0.58%. The total pressure ratio and efficiency of the design point are increased by 0.18% and 0.55%, respectively. The periodic excitation of synthetic jet can effectively separate the suction surface and reduce the separation loss, which is the reason for the improvement of compressor efficiency. However, for the transonic compressor, synthetic jet on the suction surface obstructs the radial migration vortex that reaches the tip to the exit, but cause it to gather in the tip channel, resulting in the blockage and reduction of the stability margin of the compressor. In order to take into account the stability margin of the compressor, the coupled flow control is carried out by combining the casing treatment with synthetic jet on the suction surface. The results show that the flow margin of the compressor is increased by 8.76%, the total pressure ratio is increased by 1.76%, and the efficiency is only decreased by 0.13%. In coupled flow control, the suction and injection effects of the casing treatment can make up for the negative influence of synthetic jet on the tip flow, effectively improve the tip flow and expand the stable working range of the compressor. Compared with flow control that only carries out casing treatment, coupled flow control can exert the advantages of synthetic jet suppressing suction surface separation, reduce shock loss, outlet loss and casing treatment loss, and make up for the shortage of excessive efficiency reduction after casing treatment, which is the main reason for the improvement of compressor performance.

Comprehensive investigation of flue gas component separation and CO2 sequestration in water-saturated porous media of subsurface formation

Flue gas poses subsurface direct storage inefficiency due to its high non-CO2 content, while surface separation, desulfurization and denitrification processes require additional equipment and financial resources. To address these challenges, flue gas subsurface component separation and CO2 sequestration within aquifer were proposed in this paper. CO2 migrates notably slower than N2, leading to the gathering of N2 at gas flooding front and the occurrence of CO2 hysteresis during flue gas filtration within the aquifer. The phenomenon, characterized by gas composition deviations from the original injection mole fractions of N2 and CO2, is referred to as the flue gas component separation. Numerical simulation results indicate that the solubility difference between N2 and CO2 is the primary force driving the separation of components, and the asynchronous filtration velocities of the gas and aqueous phases further promote the separation. Thus, simultaneous N2 separation and CO2 storage can achieve by the optimized gas-water alternate injection, and the efficiencies of N2 separation and CO2 storage are inversely correlated. Increasing N2 mole fraction within the injected flue gas enhances the efficiency of N2 separation, while having a slight effect on CO2 storage. Water vapor in flue gas condenses and integrates into the liquid phase, while O₂ component is produced slightly later than N₂, leading to a marginal reduction in N₂ separation efficiency. The synergistic influences of aquifer temperature and pressure exhibit bidirectionality, stemming from the shift between the dominant factors between CO2 dissolution and gas sweep efficiency. Conditions of relatively lower aquifer temperatures and moderate pressures, particularly in medium permeability aquifers, are more favorable for enhancing N₂ separation and CO₂ storage. This proposal method holds the potential for efficient subsurface separation of flue gas components and concurrent underground storage of CO2, thereby contributing to the reduction of greenhouse gas emissions and mitigation of climate change.

Design of CdZnS/BiOCl heterostructure as a highly-efficient piezo-photocatalyst for removal of antibiotic

Facilitating the surface and bulk photocarrier separation in semiconductors is crucially important for enhancing their photocatalytic activities. In this study, we have immobilized CdxZn1−xS (x = 0.7) nanoparticles on the surface of (001)-facet-exposed BiOCl (BOC) nanosheets to form heterostructured CZS/BOC piezo-photocatalysts. Experiments and theories were performed to unveil the piezo-photocatalytic performances of the CZS/BOC heterostructures and involved mechanisms. It is corroborated that the CZS/BOC heterostructures exhibit efficient transfer/separation of photocarriers, and hence possess excellent photocatalysis for eliminating tetracycline hydrochloride (TC). When irradiated by simulated sunlight, the 20 %CZS/BOC heterostructure manifests a photocatalytic activity with η(40 min)/kapp = 95 %/0.06825 min−1, which is enhanced by 6.9 (or 1.9) times over that of bare BOC (or Cd0.7Zn0.3S). While exerting ultrasonic vibration during the simulated-sunlight illumination, i.e., for the piezo-photocatalysis, a further improvement in the TC degradation rate is observed. The synergistic factor is calculated to be 1.5, quantifying the enhancement degree achieved by piezo-photocatalysis collaboration. The enhanced piezo-photocatalysis can be interpreted by the accelerated separation of the bulk photoelectrons and photoholes in the photocatalysts resulted from ultrasonic-induced polarization field, thus elevating their utilization for redox reactions. This work could advance the application of piezo-photocatalysts in environmental remediation.

Dynamics of phase separation of metastable crystal surfaces by surface diffusion: A phase-field study.

A new phase-field approach is designed to model surface diffusion of crystals with strongly anisotropic surface energy. The model can be shown to asymptotically converge toward the sharp-interface equationfor surface diffusion in the limit of vanishing interface width. It is employed to investigate the dynamical evolution of a thermodynamically metastable crystal surface. We find that nucleation and growth by surface diffusion of the newly formed surface induce the formation of additional stable surfaces at its wake. This induced nucleation mechanism is found to produce domains composed of several stable surfaces of prescribed width. The domains propagate on the crystal surface and then coalesce to form a hill-and-valley structure. The resulting morphology is more regular than the typical hill-and-valley surface produced by random thermal nucleation, i.e., when motion-by-curvature controls the phase separation dynamics. Moreover, the induced nucleation mechanism is found to be peculiar to surface diffusion and to dominate the phase separation at high degree of metastability. Once the hill-and-valley structure is formed, coarsening operates by motion and elimination of facet junctions, points where two facets merge to form one and we find the following scaling law L∼t^{1/6}, for the growth in time t of the characteristic length scale L during this coarsening stage. The density of junctions is found to exhibit a t^{-2/3} regime. Our results elucidate the role of the induced nucleation mechanism on the dynamics of interfacial phase separation and corroborate surface faceting experiments on ceramics.

Comparisons between full molecular dynamics simulation and Zhang's multiscale scheme for nanochannel flows.

In a very small surface separation, the fluid flow is actually multiscale consisting of both the molecular scale non-continuum adsorbed layer flow and the intermediate macroscopic continuum fluid flow. Classical simulation of this flow often takes over large computational source and is not affordable owing to using molecular dynamics simulation (MDS) to model the adsorbed layer flow, if the flow field size is on the engineering size scale such as of 0.01-10mm or even bigger like occurring in micro or macro hydrodynamic bearings. The present paper uses full MDS to validate Zhang's multiscale flow model, which yields the closed-form explicit flow equations respectively for the adsorbed layer flow and the intermediate continuum fluid flow. Here, full MDS was carried out for the pressure-driven flow of methane in the nano slit pore made of silicon respectively with the channel heights 5.79nm, 11.57nm, and 17.36nm. According to the number density distribution, the flow areas were respectively discriminated as the adsorbed layer zone and the intermediate fluid zone. The values of the characteristic parameters for Zhang's multiscale scheme were extracted from full MDS and input to Zhang's multiscale flow equations respectively for calculating the flow velocity profile and the volume flow rates of the adsorbed layers and the intermediate fluid. It was found that for these three channel heights, the flow velocity profiles calculated from Zhang's model approximate those calculated from full MDS, while the total flow rates through the channel calculated from Zhang's model are close to those calculated from full MDS. The accuracy of Zhang's multiscale flow model is improved with the increase of the channel height. The recent modification of the optimized potential for liquid simulation (MOPLS) model was used to calculate the interaction force between two methane molecules. In order to calculate the interaction force between the wall atoms and the methane molecules accurately, our previous non-equilibrium multiscale MDS was used. The interaction forces between the methane molecule and the wall atom were obtained from the coupled potential function by the L-B mixing rule when the fluid molecules arrived at near wall. The methane molecule diameter was obtained from the radial distribution function by using equilibrium MDS under the same initial conditions. The local viscosities across the adsorbed layer were obtained from the local velocity profile by using the Poiseuille flow method. The motion equation of the methane molecule was solved by the leapfrog method. The temperature of the simulation system was checked by Bhadauria's method, i.e., the system temperature was rectified by the velocities in the y- and z-directions. The flow velocity distributions across the channel height and the volume flow rates through the channel were also calculated from Zhang's closed-form explicit flow equations respectively for the adsorbed layer flow and the intermediate fluid flow. The results respectively obtained from full MDS and Zhang's multiscale flow equations were then compared.

Nanoscale Surface Tension, Adsorption Isotherms and Separation of Water–Ethanol Mixtures Confined between Graphene-Based Slit Pores

Nanoscale Surface Tension, Adsorption Isotherms and Separation of Water–Ethanol Mixtures Confined between Graphene-Based Slit Pores

Photosensitive and high temperature resistant polyamide composite nanofiltration membranes with high flux and stable retention

Currently, most commercial membranes are used at temperatures below 50 °C. For high temperature water treatment, nanofiltration membranes with good thermal stability are highly sought after. In order to construct a novel polyamide thin-film composite nanofiltration (TFC NF) membrane, Congo red (CR) as monomer was introduced to the aqueous phase and the chemical structure of the selective layer was changed. Next, a thorough investigation was conducted into the impacts of the piperazine (PIP) to CR ratio on the surface morphology, separation efficiency and chemical structure of the membranes. The TFC NF membrane prepared after parameter optimization exhibited high retention (Na2SO4, >98 %) and flux up to 30 L·m−2·h−1·bar−1 at room temperature. Moreover, the Na2SO4 retention of the TFC NF membrane decreased by less than 1 % when used at 90 °C, demonstrating excellent heat resistance. Meanwhile, the incorporation of CR allowed the structure of the TFC NF membranes to be altered under UV irradiation conditions, which provided new insights into the optical modulation of the composite membrane properties. A promising and reproducible methodology for the development of high flux TFC NF membrane with thermal stability was offered, achieving a breakthrough in water treatment technology under high-temperature conditions.

The formation mechanism of fracture surface separations and their effects on the toughness for ferrite-pearlite steels

The formation mechanism of fracture surface separations for ferrite-pearlite steels is investigated by combining experimental testing and numerical simulation, and the effects of fracture surface separations on the toughness are discussed. The fracture surface of Charpy impact samples for both the as-rolled and the normalized ferrite-pearlite steel were compared. The fracture surface separations occur in the as-rolled plate above the ductile-brittle transition temperature instead of the normalized plate. The fracture surface separations are triggered by transverse tensile stress, which is supported by band-shaped pearlite with poor deformability. It is demonstrated that the formation of fracture surface separations is not only dependent on band-shaped pearlite and temperature but also on the stress state. The normal stress S11 in the X-direction is the largest, and the normal stress S33 distribution concentrates on the plate center, which can explain the location of the fracture surface separations. In contrast to the dispersed distribution of the normal stress S33 for the as-rolled plate, the large normal stress in the normalized plate is in a linear arrangement, resulting in a layered crack. The effects of fracture surface separations on the materials toughness are highly dependent on the number, length, depth and location of the separations.

Multiscale Mixed Elastohydrodynamics in Inclined Fixed Pad Thrust Bearing Involving Surface Roughness and Low Clearance

The film pressures, surface separation profiles and carried loads of the hydrodynamic inclined fixed pad thrust bearing with the sandwich films were calculated by the multiscale approach when the bearing clearance was low and the combined effects of the adsorbed layer, the surface roughness and the surface elastic deformation were incorporated; The sandwich film consists of two physically adsorbed layers respectively on the coupled bearing surfaces and the intermediate continuum fluid film. The results show that the surface roughness intrinsically generates the film pressure ripples, but the rough surface is somewhat flattened and the film pressure ripples are a bit reduced by the surface elastic deformation. For a given sliding speed and a given original bearing clearance, the surface elastic deformation results in the significant reductions of both the maximum film pressure and the carried load of the bearing especially for a strong fluid-bearing surface interaction. In spite of this, the slope of the increase of the bearing load with the magnitude () of the surface roughness is nearly the same for the elastic surfaces with that for the rigid surfaces. The presence of the surface roughness does not qualitatively alter the influence of the surface elastic deformation on the performance of the bearing.

Incorporation of zeolitic imidazolate framework-8 (ZIF-8) in the polyamide and polysulfone layers of forward osmosis membranes for enhancing aquaculture wastewater recovery and PPCPs removal

Wastewater recovery is essential to alleviate water resource shortages, and this can be achieved through a high-energy-efficient forward osmosis (FO) process combined with an emerging material, zeolitic imidazolate framework-8 (ZIF-8). Here, we create thin-film composite FO membranes (TF-CFOMs) by incorporating ZIF-8 into the active polyamide (PA) and/or support polysulfone (PSf) layers to address the challenges of low water flux and loss of draw solutes during operation. Experimental factors included the dosage of ZIF-8 nanoparticles in PA preparation solutions and the dosages of 2-methylimidazole (2-Hmim) and zinc nitrate hexahydrate (ZNH) in n-methyl-2-pyrrolidone (NMP) to fabricate the PSf casting solutions with in-situ formed ZIF-8 nanoparticles. Successful ZIF-8 incorporation on the TF-CFOM surface was confirmed, and the ZIF-8 TF-CFOMs exhibited increased surface hydrophilicity and separation performance. Only modifying the PA layer by adding 0.025 wt% ZIF-8 nanoparticles in trimesoyl chloride (TMC) resulted in the membrane (PA0.025T-PSf0) with water flux 2.3 times higher than the pristine TF-CFOM (4.9 LMH). The pristine and modified TF-CFOMs were further applied for aquaculture wastewater (AWW) recovery and removal of pharmaceuticals and personal care products (PPCPs). Results of water recovery demonstrated that the recovery rate reached 89.1% in 3.5 days when using the dual-layer modified TF-CFOM. Results of PPCP removal indicated that both pristine and modified TF-CFOMs can achieve high PPCP rejection efficiency (>90%), with the modified TF-CFOM (PA0.025T-PSf2.0) performing the best. Overall, the PA0.025T-PSf2.0 TF-CFOM achieved high and stable separation efficiency in long-duration AWW recovery, making it well-suited for practical field applications.

Experimental and theoretical investigations into the surface chemical properties and separation of serpentine from quartz using xanthomonas campestris as a selective flocculant

Separation of fine serpentine (SPT) from quartz (QZ) both of d80 close to 20 µm using an eco-friendly microbial exo-polysaccharide, xanthomonas campestris (XCT), as a selective flocculant for SPT was conducted experimentally and substantiated theoretically. The adsorption of XCT onto SPT was observed to decrease with increase in pH, whereas that of QZ was nearly nil beyond pH 2.1. Zeta potential of SPT in presence of XCT decreased with increase in pH further attesting to the adsorption and anionicity of XCT. The FTIR studies confirmed the interaction of XCT with SPT in presence of sodium hexametaphosphate. The nature of intermolecular interactions present in complexes formed on SPT surface was revealed by quantum theory of atoms in molecules to be non-covalent. The electron density difference plot conducted on formed complexes indicated that electrons drifted from XCT to the surface of SPT. Selective flocculation SPT-QZ (1:1) mixture conducted at pH 6 and pH 7.5 in presence of 4 mg/L and 2 mg/L of sodium hexametaphosphate coupled with 100 mg/L of XCT yielded separation efficiency and selectivity ratio of 96.5 % and 71.2, respectively, after three desliming stages. Therefore, XCT is a potential selective flocculant for serpentine.

Surface nitrogen defect modified crystalline carbon nitride spheres with boosted carrier dynamics for efficient solar hydrogen production

Engineering of the defective structure and crystallinity of semiconductor photocatalysts to promote carrier dynamics has attracted considerable attention. This study presents the design of surface nitrogen defect modified crystalline carbon nitride spheres (QCN) with synergistically boosted surface and bulk carrier separation through a rapid thermal treatment coupled with a flux assisted strategy. Using supramolecular self-assembled polymer as the precursor, spherical crystalline CN heterojunctions are firstly prepared by a molten salt method to improve the separation of bulk carriers. Abundant nitrogen defects are then introduced onto the surface of crystalline CN through the following quick thermal treatment in air, which can generate a higher exciton density and drive rapid migration of surface carriers by acting as effective electron sinks. Furthermore, the defect level also improves the visible light utilization and provides more active centers for reactant adsorption and activation. As a result, QCN samples exhibit excellent performance in photocatalytic hydrogen evolution, with an optimal hydrogen production rate 4.3 times higher than that of pristine bulk CN under visible light irradiation. Moreover, the photocatalytic activities of QCN are dependent on the concentration of nitrogen defects, which can be flexibly adjusted via thermal treatment temperature. Such a two-step regulation strategy combining the distinctive advantages of surface defect structure and high crystallinity is beneficial for synergistic enhancement of photocatalytic performance, and provides new insights for sustainable energy production in the future.

Separation of Surface Grafted Microparticles via Light and Temperature

Separation of equally sized particles distinguished solely by interfacial properties remains a highly challenging task. Herein, a particle fractioning method is proposed, which is suitable to differentiate between polymer‐grafted microparticles that are equal in size. The separation relies on the combination of a pressure driven microfluidic flow, together with simultaneous light illumination and temperature control. Heating the solution forces thermo‐responsive surface grafts to undergo a volume phase transition and therefore locally changing the interfacial properties of the microparticles. Light illumination induces the phoretic/osmotic activity of the microparticles and lifts them into a higher plane, where hovering particles experience a different shear stress proportional to the height. The light‐induced hovering height depends on the interfacial properties, and this complex interaction leads to different movements of the microparticles as a function of their surface grafting. The concepts are visualized in experimental studies, where the complex physical principle provides a simple method for fractioning a binary mixture with at least one thermo‐responsive polymer graft.

Step-by-Step Implementation of Three-Dimensional Print Technology in Preoperative Neurosurgery Planning.

This study presents a detailed methodology for integrating three-dimensional (3D) printing technology into preoperative planning in neurosurgery. The increasing capabilities of 3D printing over the last decade have made it a valuable tool in medical fields such as orthopedics and dental practices. Neurosurgery can similarly benefit from these advancements, though the creation of accurate 3D models poses a significant challenge due to the technical expertise required and the cost of specialized software. This paper demonstrates a step-by-step process for developing a 3Dphysical model for preoperative planning using free, open-source software. A case involving a 62-year-old male with a large infiltrating tumor in the sacrum, originating from renal cell carcinoma, is used to illustrate the method. The process begins with the acquisition of a CT scan, followed by image reconstruction using InVesalius 3, an open-source software. The resulting 3D model is then processed in Autodesk Meshmixer (Autodesk, Inc., San Francisco, CA), where individual anatomical structures are segmented and prepared for printing. The model is printed using the Bambu Lab X1 Carbon 3D printer (Bambu Lab, Austin, TX), allowing for multicolor differentiation of structures such as bones, tumors, and blood vessels. The study highlights the practical aspects of model creation, including artifact removal, surface separation, and optimization for print volume. It discusses the advantages of multicolor printing for visual clarity in surgical planning and compares it with monochromatic and segmented printing approaches. The findings underscore the potential of 3D printing to enhance surgical precision and planning, providing a replicable protocol that leverages accessible technology. This work supports the broader adoption of 3D printing in neurosurgery, emphasizing the importance of collaboration between medical and engineering professionals to maximize the utility of these models in clinical practice.

Solvation Forces Near Hydrophobic Surfaces: A Classical Density Functional Theory Study.

We use classical density functional theory (DFT) to model solvation interactions between hydrophobic surfaces, which we show to be characterized by depletion attraction at small surface to surface separations and a slowly decaying bipower law interaction at large separations. The solvation interaction originates from van der Waals (vdW) and Coulombic interactions between molecules in the polar solvent, e.g., water, and from the molecules thermal motion and finite volume. We investigate model hydrophobic surfaces represented by bubbles and nonpolar solids, e.g., aliphatic particles, and calculate in a DFT fashion the distribution of molecules in the interlaying solvent between two such surfaces and the hydrophobic excess force resulting from it. The interactions are largely attractive, which is well-known in measurement, albeit vdW attraction between molecules in solids and in the solvent may cause repulsion at certain interface to interface separations. We commence our analysis by suggesting an asymptotic analytical bipower law expression for the solvation interaction at large separations. Thereafter we present a full numerical solution, which is in good agreement with the analytical prediction and further explores the interaction at small surface to surface separations. Our theoretical results yield adhesion energies which agree with previous experiments.

An Improved Vibration Multi Mode-Based Technique for the Characterization of Metallic Adhesion Impulses

Adhesion impulses generated at the separation of metallic surfaces significantly impact the functionality and performance of launch-lock and release space mechanisms. The testing concept adopted here consists of a suspended plate set into contact with an end-effector, which is retracted to simulate an in-flight release. At the retraction, the bonds are stretched up to failure, transferring an impulse to the plate. The proposed technique focuses on plate-free vibration: if at least two amplitudes of the excited vibration modes are measured, it is possible to estimate the impulse intensity and duration. This technique is developed by exploiting the plate multimode response with redundant outputs to the same dynamic input to characterize adhesion dynamics with improved measurement performance.

Sustainable adhesives: Exploring boronic ester vitrimers containing lignin microparticles

The market of epoxy resin-based adhesives is constantly growing in the automotive, electronics, and healthcare industries thanks to their unique features such as high bonding strength, durability, and corrosion resistance. In this work, alternative sustainable vitrimer adhesives, containing from 20 to 50 wt% of lignin microparticles, were prepared from epoxidized linseed oil (ELO) and a boronic ester dithiol crosslinker (DBEDT), in the absence of solvents and catalysts. The addition of unmodified commercial Kraft lignin to the composites directly influences their thermal and mechanical properties and determines their bonding capacity between several adherent substrates, also affecting the rewelding potential. The lignin-vitrimer composites and the corresponding neat vitrimer matrix exhibited values of lap shear strengths in the range of 9 to 17 MPa, when tested as adhesives with aluminum, stainless steel, and wood specimens, and good to excellent rewelding capability. The amount of lignin microparticles influences the balance between cohesive and adhesive forces during the separation of the adhered aluminum surfaces and the eventual joint failure. In the case of the composites with 20 wt% of lignin, lap shear strength remains constant even after four cycles of rebonding via compression molding, indicating that the best rewelding performance is associated with previous cohesive failure when the adhesive remains on both aluminum sheets' surfaces. In addition, the adhesion was preserved for 83 % of the initial value after 24 h immersed in water. Importantly, biodegradability in both soil and seawater was enhanced by the presence of the lignin filler. In summary, the simple preparation strategy of bio-based vitrimer composites coming from two natural sources could pave the way to green alternatives for industrial applications, such as epoxy-based adhesives.

Effects of substrate materials and electrodeposition parameters on hydrogen evolution reaction of Ni–Cu–Fe coatings

In this study, the effects of substrate materials and electrodeposition parameters on the hydrogen evolution reaction (HER) of Ni–Cu–Fe coatings were studied. For this purpose, different materials, including carbon steel (CS), stainless steel 304 (SS), and pure commercial graphite (G) were used as substrates, while the coating process was done in both modes of constant current density (CC) and variable current density, the latter to produce a functionally-graded (FG) coating. Microstructural investigations were done by using scanning electron microscopy, while the HER behavior was analyzed by electrochemical tests, including cyclic voltammetry (CV), linear scanning voltammetry (LSV), and electrochemical impedance (EIS) measurements. The morphology of the produced Ni–Cu–Fe coatings was completely affected by the coating parameters in the deposition bath and the type of substrates. In samples with micro/nano-cone morphology, deposited at a constant current density of 2.5 A/dm2, better HER behavior was obtained due to the highly effective surface and easier separation of hydrogen bubbles. Besides, the best electrocatalytic activity and the lowest overpotential (110 mV at 10 mA/cm2 in CC mode) were related to the samples coated on G. The proper selection of the substrate material plays an important role in improving the electrocatalytic behavior of composite coatings.

Investigation on passive suppression method of hump characteristics in a large vertical volute centrifugal pump: Using combined diffuser vane structure

The hump characteristic is one of the unique hydraulic instability of the large vertical volute centrifugal pump (LVVCP) under part-load conditions, which is extremely detrimental to the safe and stable unit operation. To suppress the hump characteristic of LVVCP, a passive suppression method with a combined diffuser vane structure is proposed in this paper. This diffuser vane structure consists of a combination of large and small hydrofoil vanes, with the special 6 small hydrofoil vane B are arranged within 150° range of the small volute section side. To investigate the key reasons for suppression, detached eddy simulations are performed for LVVCP with original diffuser vane (Diffuser A) and combined diffuser vane (Diffuser B), and the energy loss and flow patterns are analyzed. The hump region of LVVCP with Diffuser B is narrower, the positive slope of Q-H curve is decreased and the hump margin is increased. The reduced conversion of kinetic energy to turbulent kinetic energy and the decreased Reynolds stress diffusion loss in the Diffuser B and volute are main reasons for the hump characteristic suppression. The energy loss in the volute small section side region and its corresponding diffuser region increases significantly under hump conditions, and Diffuser B can obviously reduce the energy loss in these regions. The flow pattern analysis in the diffuser shows that the weakened rotating stall in Diffuser B leads to a more regular Qm variation with time in D1∼D6. The reduced chord length and thickness of vane B results in a significant decrease of pressure surface separation vortex (PSV) and suction surface separation vortex (SSV) scales and a weakened vortex merging phenomenon, which causes a considerable drop of ΔSPRO in the Diffuser B. The Diffuser B provides a more uniform α distribution to the volute inlet, and decreases the vortex scale and vortex-induced energy loss on the volute small section side.