Phase field simulation of grain refinement in silver-based filler metal

Numerical simulation is one of the important auxiliary methods for studying materials-related problems. In this study, phase field simulation was employed to investigate the refinement behavior of BAg55CuZn-x B brazing alloys. Simulation and experimental studies were conducted for B contents ranging from 0 wt.% to 0.2 wt.%. The results demonstrated that the addition of 0.05 wt.% B in the brazing alloy leads to a significant refinement effect. As the B content increases, the grain size further reduces, and a refinement stagnation phenomenon occurs after exceeding 0.15 wt.%. The solidification process of brazing alloys with different B content was predicted by simulation, and the simulation results showed that with the increase of B content, the initial number of nucleation increased, and the radius of the dendrite tip decreased. The simulation results are in good agreement with the experimental findings, providing further evidence of the refining effect of the B element and the reliable predictive capability of the phase field model.

Research on arc erosion of silver-based alloy contact materials under low voltage,resistive load and small current at 400 Hz and 50 Hz

By using a self-developed IF power and a ASTM contact material experimental system of small-capacity and variable frequency,the value of arcing characteristics and the welding force of the silver-based contact material are acquired under low voltage,resistive load and small current at 400 Hz and 50 Hz. By means of an electricity-ray analytical balance,SEM and EDAX,the weighing values of the contact materials and the changes of AgCdO,AgNi,AgC and AgW contact material surface profile and micro-area constituent are obtained and analyzed. The arc erosion causes of silver-based alloy contact materials at 400 Hz and 50 Hz are also discussed.

Fabrication and properties of silver-based composites reinforced with carbon-coated Ti_(3)AlC_(2)

Ti_(3)AlC_(2)-reinforced Ag-based composites,which are used as sliding current collectors,electrical contacts,and electrode materials,exhibit remarkable performances.However,the interfacial reactions between Ag and Ti_(3)AlC_(2) significantly degrade the electrical and thermal properties of these composites.To diminish these interfacial reactions,we fabricated carbon-coated Ti_(3)AlC_(2) particles(C@Ti_(3)AlC_(2))as reinforcement and prepared Ag–10wt%C@Ti_(3)AlC_(2) composites with carbon-layer thicknesses ranging from 50–200 nm.Compared with the uncoated Ag–Ti_(3)AlC_(2) composite,Ag–C@Ti_(3)AlC_(2) was found to have a better distribution of Ti_(3)AlC_(2) particles.With increases in the carbon-layer thickness,the Vickers hardness value and relative density of Ag–C@Ti_(3)AlC_(2) gradually decreases.With a carbon-layer thickness of 150 nm,we obtained the lowest resistivity of Ag–C@Ti_(3)AlC_(2) of 29.4135.5×10^(−9)Ω·m,which is half that of Ag–Ti_(3)AlC_(2)(66.7×10^(−9)Ω·m).The thermal conductivity of Ag–C@Ti_(3)AlC_(2) reached a maximum value of 135.5 W·m^(−1)·K^(−1) with a 200-nm carbon coating(~1.8 times that of Ag–Ti_(3)AlC_(2)).These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti_(3)AlC_(2) composites.

Effects of Ga and In on the properties of cadmium-free Ag-Cu-Zn filler metal

Melting temperature, spreadability, mechanical properties and the microstructures of joints brazed with silver-base filler metals including different amounts of Ga and/or In were studied respectively in this paper, and the results show that the melting temperature of the silver-base filler metals is decreased, spreadability of the silver-base filler metals is improved, and the microstructures of silver-base filh, r metals are refined obviously with the addition of Ga and/or In. Using copper and brass plates as base metal and brazing with flame method, the mechanical properties of the lap-joint and butt joint were also examined and analyzed respectively, and the results indicate that the fracture position of two kinds of brazed joints occurred on the base metal, except for the lap-joint of brass, which shows better mechanical properties of the joints brazed with the silver- based filler metals including Ga. For the lap-joint of brass, the tensile strength gradually increased with the increase of Ga content, while the addition of In has little effect on mechanical properties. It is also found that the best comprehensive properties of cadmium-free Ag-Cu-Zn filler metals are obtained when Ga content is about 3.0 wt. % and In content is between 1.5 wt. % and 2. 0 wt. %.

Solar-Driven Hydrogen Peroxide Production Using Polymer-Supported Carbon Dots as Heterogeneous Catalyst

Safe, sustainable, and green production of hydro gen peroxide is an exciting proposition due to the role of hydrogen peroxide as a green oxidant and energy carrier for fuel cells. The current work reports the development of carbon dot-impregnated waterborne hyperbranched polyurethane as a heterogeneous photo-catalyst for solar-driven production of hydrogen peroxide. The results reveal that the carbon dots possess a suitable band-gap of 2.98 eV,which facilitates effective splitting of both water and ethanol under solar irradiation. Inclusion of the carbon dots within the eco-friendly polymeric material ensures their catalytic activity and also provides a facile route for easy catalyst separation, especially from a solubilizing medium.The overall process was performed in accordance with the principles of green chemistry using bio-based precursorsand aqueous medium. This work highlights the potential of carbon dots as an effective photo-catalyst.

Development and high-gradient test of a two-half accelerator structure

This paper reports on the design,fabrication,RF measurement,and high-power test of a prototype accelerator—such as 11.424 GHz with 12 cells—and a traveling wave of two halves.It was found that the unloaded gradient reached 103 MV/m during the high-power test and the measured breakdown rate,after 3.17×10^(7) pulses,was 1.62×10^(-4)/pulse/m at 94 MV/m and a 90 ns pulse length.We thus concluded that the high-gradient two-half linear accelerator is cost-effective,especially in high-frequency RF linear acceleration.Finally,we suggest that silverbased alloy brazing can further reduce costs.

Recent Progress,Challenges,and Prospects in Two‑Dimensional Photo‑Catalyst Materials and Environmental Remediation

The successful photo-catalyst library gives significant information on feature that affects photo-catalytic performance and proposes new materials.Competency is considerably significant to form multi-functional photo-catalysts with flexible characteristics.Since recently,two-dimensional materials(2DMs)gained much attention from researchers,due to their unique thickness-dependent uses,mainly for photo-catalytic,outstanding chemical and physical properties.Photo-catalytic water splitting and hydrogen(H2)evolution by plentiful compounds as electron(e−)donors is estimated to participate in constructing clean method for solar H2-formation.Heterogeneous photocatalysis received much research attention caused by their applications to tackle numerous energy and environmental issues.This broad review explains progress regarding 2DMs,significance in structure,and catalytic results.We will discuss in detail current progresses of approaches for adjusting 2DMs-based photo-catalysts to assess their photo-activity including doping,hetero-structure scheme,and functional formation assembly.Suggested plans,e.g.,doping and sensitization of semiconducting 2DMs,increasing electrical conductance,improving catalytic active sites,strengthening interface coupling in semiconductors(SCs)2DMs,forming nano-structures,building multi-junction nano-composites,increasing photo-stability of SCs,and using combined results of adapted approaches,are summed up.Hence,to further improve 2DMs photo-catalyst properties,hetero-structure design-based 2DMs’photo-catalyst basic mechanism is also reviewed.

Kinetics Study on Photocatalytic Degradation of Methyl Orange Catalyzed by Sea Urchin-Like Cu2O

Sea urchin-like cuprous oxide with hollow glass microsphere as core was prepared using sodium sulfite as the reducing agent and sodium acetate-acetic acid as buffer solution in copper sulfate solution. Methyl orange was selected as degradation target for photocatalytic experiments. The photocatalytic activities were investigated by visible spectro- photometer. Photocatalytic kinetics parameters were studied by the Langmuir-Hinshelwood model and Arrhenius formula. It was observed that the sea urchin-like morphology dramatically improved the photocatalytic activity of cuprous oxide. The photo-degradation belongs to the first-order reaction and the maximum degradation rate could reach 94.37%. The activation energy and pre-exponential factor are 41.18 KJ·mol-1 and 1.07 × 106, respectively. After seven times recycling, the sample still showed high photo-catalytic efficiency and stability.

Amino-Functionalized Reduced Graphene-Oxide-Copper (I) Oxide Composite: A Prospective Catalyst for Photo-Reduction of CO2

In the present article, an easy synthetic strategy of a novel composite photo-catalyst comprising of amino-functionalized reduced graphene oxide and Cu2O has been proposed. Role of this composite catalyst in photo reduction of CO2 has been analyzed and it is shown that both amino groups and reduced grapheme oxide, participate in enhancing quantum yield of the photo reduction process.

Ozonation of ibuprofen in presence of SrWO4/ZnO photo-catalyst

The study was performed for removing ibuprofen from water using ozonation with visible light SrWO4/ZnO catalyst.For the removal of Ibuprofen,the overall reaction was carried out in a glass reactor in the presence of UV light and constant supply of ozone.The maximum removal efficiency of Ibuprofen was 93%at 0.1 mg/L initial Ibuprofen concentration,and 0.35 g/L catalyst concentration keeping the contact time 30 min.After a certain value,an increase in a concentration of doping agent,catalyst as well as initial Ibuprofen concentration results in a decrease of efficiency of the process.The prepared photo catalysts were characterized by X-ray diffraction,FTIR spectra and SEM analysis.XRD peaks and FTIR spectra has clearly shown that the doping of SrWO4 with ZnO showed better result as compared to individual.SEM analysis showed that they spherical nano-composite crystals were dominant in character.BOD character was found to reduce after ozonation of solution.Various by products were formed and were identified through GC-MS analysis.From results,it was found that combination of SrWO4/ZnO was able to remove 93%of ibuprofen and 0.4%dopping of ZnO on SrWO4 was found to be sufficient.Degradation pattern of by products were identitified in GC-MS with various mass ratios as 177,92,57,44.Nearly 55%removal of BOD was observed in this study.This study was found to be useful for removal of pharmaceuticals and other similar pollutants from water effectively.

Atypical BiOCl/Bi_2S_3 hetero-structures exhibiting remarkable photo-catalyst response

We demonstrate the fabrication of BiOCl/Bi_2S_3 which is well defined at a large scale. The BiOCl/Bi_2S_3 heterostructures exhibit an enhanced photo-catalytic degradation of methyl orange（MO） compared to BiOCl and Bi_2S_3, attributed to the interface between Bi_2S_3 and BiOCl, which effectively separate the photo-induced electron-hole pairs and suppress their recombination.

Hetero-structured ZnIn_(2)S_(4)-NiO@MOF photo-catalysts for efficient hydrogen evolution

To obtain a high-performance heterogeneous photo-catalyst, herein, the hetero-structured Zn In_(2)S_(4)-Ni O@MOF(ZNM) nano-sheets are designed and prepared by partial pyrolysis of nickel-based MOFs(NiMOF) combined with the low-temperature solvo-thermal method. The results indicate that the NiO nanoparticles, produced by partial pyrolysis of the Ni-MOF, have a high density of the surface active sites with limited aggregation, which act as a co-catalyst to capture photo-induced charge carriers. In addition, the morphology and structure of Ni-MOF nano-sheets were preserved in ZNM, which is beneficial to the reduction of the conduction barrier for the photo generated electron-hole pairs. With the synergetic advantages of co-catalyst and unique two-dimensional hetero-structure, ZNM nano-sheets exhibited significantly improved activity for photo-catalytic hydrogen production.

Structure Engineered g-C3N4 Nano-Sheets by Switching the Pyrolysis Gas Atmosphere for Enhanced Photo-Catalytic Degradation

We developed a new one step approach to synthesize g-C3N4 nano-sheets by direct thermal pyrolysis process of urea in NH3 atmosphere. For the first time, the influence of the preparation gas atmosphere on the composition, crystalline and polymerization degree, and the activity of the g-C3N4 synthesized from thermal condensation of urea was investigated. Impressively, the g-C3N4 nano-sheets obtained under NH3 gas atmosphere exhibited much superi- or photo-catalytic activities to the prepared g-C3N4 in air or N2, and the rate of the g-C3N4-NH3 was about 5 times higher than that on g-C3N4-N2 sample. The detailed characterization analysis revealed that NH3 thermal pyrolysis atmosphere contributed to the polymerization degree and the formation of the layer with a more regular structure due to the efficiently extending of the conjugated π-conjugative system, which was favorable to the transfer of the photo-induced charge carriers. Furthermore, we studied in depth the structure-performance relationship in the sys- tem, and it was found that the synergistic effect of the larger surface area, the adjusted band energy structure and the well crystallization may be conductive to the higher separation of the electron-hole pair, thus leading to the won- derful performance for the g-C3N4-NH3. Notably, the method has the merits of low cost, scalable production and environmental friendliness.