Single-atom Pt on carbon nanotubes for selective electrocatalysis

Utilizing supported single atoms as catalysts presents an opportunity to reduce the usage of critical raw materials such as platinum,which are essential for electrochemical reactions such as hydrogen oxidation reaction(HOR).Herein,we describe the synthesis of a Pt single electrocatalyst inside single-walled carbon nanotubes(SWCNTs)via a redox reaction.Characterizations via electron microscopy,X-ray photoelectron microscopy,and X-ray absorption spectroscopy show the single-atom nature of the Pt.The electrochemical behavior of the sample to hydrogen and oxygen was investigated using the advanced floating electrode technique,which minimizes mass transport limitations and gives a thorough insight into the activity of the electrocatalyst.The single-atom samples showed higher HOR activity than state-of-the-art 30%Pt/C while almost no oxygen reduction reaction activity in the proton exchange membrane fuel cell operating range.The selective activity toward HOR arose as the main fingerprint of the catalyst confinement in the SWCNTs.

Genetic dissection and origin of pleiotropic loci underlying multilevel fiber quality traits in upland cotton(Gossypium hirsutum L.)

Cotton fiber quality is a persistent concern that determines planting benefits and the quality of finished textile products.However,the limitations of measurement instruments have hindered the accurate evaluation of some important fiber characteristics such as fiber maturity,fineness,and neps,which in turn has impeded the genetic improvement and industrial utilization of cotton fiber.Here,12 single fiber quality traits were measured using Advanced Fiber Information System(AFIS)equipment among 383 accessions of upland cotton(Gossypium hirsutum L.).In addition,eight conventional fiber quality traits were assessed by the High Volume Instrument(HVI)System.Genome-wide association study(GWAS),linkage disequilibrium(LD)block genotyping and functional identification were conducted sequentially to uncover the associated elite loci and candidate genes of fiber quality traits.As a result,the previously reported pleiotropic locus FL_D11 regulating fiber length-related traits was identified in this study.More importantly,three novel pleiotropic loci(FM_A03,FF_A05,and FN_A07)regulating fiber maturity,fineness and neps,respectively,were detected based on AFIS traits.Numerous highly promising candidate genes were screened out by integrating RNA-seq and qRT-PCR analyses,including the reported GhKRP6 for fiber length,the newly identified GhMAP8 for maturity and GhDFR for fineness.The origin and evolutionary analysis of pleiotropic loci indicated that the selection pressure on FL_D11,FM_A03 and FF_A05 increased as the breeding period approached the present and the origins of FM_A03 and FF_A05 were traced back to cotton landraces.These findings reveal the genetic basis underlying fiber quality and provide insight into the genetic improvement and textile utilization of fiber in G.hirsutum.

KCNQ1 rs2237895 gene polymorphism increases susceptibility to type 2 diabetes mellitus in Asian populations

BACKGROUND The association of single nucleotide polymorphism of KCNQ1 gene rs2237895 with type 2 diabetes mellitus(T2DM)is currently controversial.It is unknown whether this association can be gene realized across different populations.AIM To determine the association of KCNQ1 rs2237895 with T2DM and provide reliable evidence for genetic susceptibility to T2DM.METHODS We searched PubMed,Embase,Web of Science,Cochrane Library,Medline,Baidu Academic,China National Knowledge Infrastructure,China Biomedical Literature Database,and Wanfang to investigate the association between KCNQ1 gene rs2237895 and the risk of T2DM up to January 12,2022.Review Manager 5.4 was used to analyze the association of the KCNQ1 gene rs2237895 polymorphism with T2DM and to evaluate the publication bias of the selected literature.RESULTS Twelve case–control studies(including 11273 cases and 11654 controls)met our inclusion criteria.In the full population,allelic model[odds ratio(OR):1.19;95%confidence interval(95%CI):1.09–1.29;P<0.0001],recessive model(OR:1.20;95%CI:1.11–1.29;P<0.0001),dominant model(OR:1.27.95%CI:1.14–1.42;P<0.0001),and codominant model(OR:1.36;95%CI:1.15–1.60;P=0.0003)(OR:1.22;95%CI:1.10–1.36;P=0.0002)indicated that the KCNQ1 gene rs2237895 polymorphism was significantly correlated with susceptibility to T2DM.In stratified analysis,this association was confirmed in Asian populations:allelic model(OR:1.25;95%CI:1.13–1.37;P<0.0001),recessive model(OR:1.29;95%CI:1.11–1.49;P=0.0007),dominant model(OR:1.35;95%CI:1.20–1.52;P<0.0001),codominant model(OR:1.49;95%CI:1.22–1.81;P<0.0001)(OR:1.26;95%CI:1.16–1.36;P<0.0001).In non-Asian populations,this association was not significant:Allelic model(OR:1.06,95%CI:0.98–1.14;P=0.12),recessive model(OR:1.04;95%CI:0.75–1.42;P=0.83),dominant model(OR:1.06;95%CI:0.98–1.15;P=0.15),codominant model(OR:1.08;95%CI:0.82–1.42;P=0.60.OR:1.15;95%CI:0.95–1.39;P=0.14).CONCLUSION KCNQ1 gene rs2237895 was significantly associated with susceptibility to T2DM in an Asian population.Carriers of the C allele had a higher risk of T2DM.This association was not significant in non-Asian populations.

Genetically predicted fatty liver disease and risk of psychiatric disorders: A mendelian randomization study

BACKGROUND Non-alcoholic fatty liver disease(NAFLD)and alcohol-related liver disease(Ar-LD)constitute the primary forms of chronic liver disease,and their incidence is progressively increasing with changes in lifestyle habits.Earlier studies have do-cumented a correlation between the occurrence and development of prevalent mental disorders and fatty liver.AIM To investigate the correlation between fatty liver and mental disorders,thus ne-cessitating the implementation of a mendelian randomization(MR)study to elu-cidate this association.METHODS Data on NAFLD and ArLD were retrieved from the genome-wide association studies catalog,while information on mental disorders,including Alzheimer's disease,schizophrenia,anxiety disorder,attention deficit hyperactivity disorder(ADHD),bipolar disorder,major depressive disorder,multiple personality dis-order,obsessive-compulsive disorder(OCD),post-traumatic stress disorder(PTSD),and schizophrenia was acquired from the psychiatric genomics consor-tium.A two-sample MR method was applied to investigate mediators in signifi-cant associations.RESULTS After excluding weak instrumental variables,a causal relationship was identified between fatty liver disease and the occurrence and development of some psychia-tric disorders.Specifically,the findings indicated that ArLD was associated with a significantly elevated risk of developing ADHD(OR:5.81,95%CI:5.59-6.03,P<0.01),bipolar disorder(OR:5.73,95%CI:5.42-6.05,P=0.03),OCD(OR:6.42,95%CI:5.60-7.36,P<0.01),and PTSD(OR:5.66,95%CI:5.33-6.01,P<0.01).Meanwhile,NAFLD significantly increased the risk of developing bipolar disorder(OR:55.08,95%CI:3.59-845.51,P<0.01),OCD(OR:61.50,95%CI:6.69-565.45,P<0.01),and PTSD(OR:52.09,95%CI:4.24-639.32,P<0.01).CONCLUSION Associations were found between genetic predisposition to fatty liver disease and an increased risk of a broad range of psychiatric disorders,namely bipolar disorder,OCD,and PTSD,highlighting the significance of preven-tive measures against psychiatric disorders in patients with fatty liver disease.

The role of cAMP-dependent protein kinase A in the formation of long-term memory in Bactrocera dorsalis

The cAMP-dependent protein kinase A(PKA)signaling pathway has long been considered critical for long-term memory(LTM)formation.Previous studies have mostly focused on the role of PKA signaling in LTM induction by multiple spaced conditioning with less attention to LTM induction by a single conditioning.Here,we conducted behavioral-pharmacology,enzyme immunoassay and RNA interference experiments to study the role of the PKA signaling pathway in LTM formation in the agricultural pest Bactrocera dorsalis,which has a strong memory capacity allowing it to form a two-day memory even from a single conditioning trial.We found that either blocking or activating PKA prior to conditioning pretreatment affected multiple spaced LTM,and conversely,they did not affect LTM formed by single conditioning.This was further confirmed by enzyme-linked immunosorbent assay(ELISA)and silencing of the protein kinase regulatory subunit 2 and catalytic subunit 1.Taken together,these results suggest that activating PKA during memory acquisition helps to induce the LTM formed by multiple spaced conditioning but not by a single conditioning.Our findings challenge the conserved role of PKA signaling in LTM,which provides a basis for the greater diversity of molecular mechanisms underlying LTM formation across species,as well as possible functional and evolutionary implications.

Study of leakage current degradation based on stacking faults expansion in irradiated SiC junction barrier Schottky diodes

A comprehensive investigation was conducted to explore the degradation mechanism of leakage current in SiC junction barrier Schottky(JBS)diodes under heavy ion irradiation.We propose and verify that the generation of stacking faults(SFs)induced by the recombination of massive electron-hole pairs during irradiation is the cause of reverse leakage current degradation based on experiments results.The irradiation experiment was carried out based on Ta ions with high linear energy transfer(LET)of 90.5 MeV/(mg/cm^(2)).It is observed that the leakage current of the diode undergoes the permanent increase during irradiation when biased at 20%of the rated reverse voltage.Micro-PL spectroscopy and PL micro-imaging were utilized to detect the presence of SFs in the irradiated SiC JBS diodes.We combined the degraded performance of irradiated samples with SFs introduced by heavy ion irradiation.Finally,three-dimensional(3D)TCAD simulation was employed to evaluate the excessive electron-hole pairs(EHPs)concentration excited by heavy ion irradiation.It was observed that the excessive hole concentration under irradiation exceeded significantly the threshold hole concentration necessary for the expansion of SFs in the substrate.The proposed mechanism suggests that the process and material characteristics of the silicon carbide should be considered in order to reinforcing against the single event effect of SiC power devices.

Metal-organic framework-based single-atom electro-/ photocatalysts: Synthesis, energy applications, and opportunities

Single-atom catalysts(SACs)have gained substantial attention because of their exceptional catalytic properties.However,the high surface energy limits their synthesis,thus creating significant challenges for further development.In the last few years,metal–organic frameworks(MOFs)have received significant consideration as ideal candidates for synthesizing SACs due to their tailorable chemistry,tunable morphologies,high porosity,and chemical/thermal stability.From this perspective,this review thoroughly summarizes the previously reported methods and possible future approaches for constructing MOF-based(MOF-derived-supported and MOF-supported)SACs.Then,MOF-based SAC's identification techniques are briefly assessed to understand their coordination environments,local electronic structures,spatial distributions,and catalytic/electrochemical reaction mechanisms.This review systematically highlights several photocatalytic and electrocatalytic applications of MOF-based SACs for energy conversion and storage,including hydrogen evolution reactions,oxygen evolution reactions,O_(2)/CO_(2)/N_(2) reduction reactions,fuel cells,and rechargeable batteries.Some light is also shed on the future development of this highly exciting field by highlighting the advantages and limitations of MOF-based SACs.

Advances of Synergistic Electrocatalysis Between Single Atoms and Nanoparticles/Clusters

Combining single atoms with clusters or nanoparticles is an emerging tactic to design efficient electrocatalysts.Both synergy effect and high atomic utilization of active sites in the composite catalysts result in enhanced electrocatalytic performance,simultaneously provide a radical analysis of the interrelationship between structure and activity.In this review,the recent advances of single-atomic site catalysts coupled with clusters or nanoparticles are emphasized.Firstly,the synthetic strategies,characterization,dynamics and types of single atoms coupled with clusters/nanoparticles are introduced,and then the key factors controlling the structure of the composite catalysts are discussed.Next,several clean energy catalytic reactions performed over the synergistic composite catalysts are illustrated.Eventually,the encountering challenges and recommendations for the future advancement of synergistic structure in energy-transformation electrocatalysis are outlined.

Cooperation between single atom catalyst and support to promote nitrogen electroreduction to ammonia:A theoretical insight

The co-catalysis between single atom catalyst(SAC)and its support has recently emerged as a promising strategy to synergistically boost the catalytic activity of some complex electrochemical reactions,encompassing multiple intermediates and pathways.Herein,we utilized defective BC_(3)monolayer-supported SACs as a prototype to investigate the cooperative effects of SACs and their support on the catalytic performance of the nitrogen reduction reaction(NRR)for ammonia(NH_(3))production.The results showed that these SACs can be firmly stabilized on these defective BC_(3)supports with high stability against aggregation.Furthermore,co-activation of the inert N_(2)reactant was observed in certain embedded SACs and their neighboring B atoms on certain BC3 sheets due to the noticeable charge transfer and significant N–N bond elongation.Our high-throughput screening revealed that the Mo/DV_(CC)and W/DV_(CC)exhibit superior NRR catalytic performance,characterized by a low limiting potential of−0.33 and−0.43 V,respectively,which can be further increased under acid conditions based on the constant potential method.Moreover,varying NRR catalytic activities can be attributed to the differences in the valence state of active sites.Remarkably,further microkinetic modeling analysis displayed that the turnover frequency of N_(2)–to–NH_(3)conversion on Mo/DV_(CC)is as large as 1.20×10^(−3)s^(−1)site^(−1) at 700 K and 100 bar,thus guaranteeing its ultra-fast reaction rate.Our results not only suggest promising advanced electrocatalysts for NRR but also offer an effective avenue to regulate the electrocatalytic performance via the co-catalytic metal–support interactions.

Preparation of single atom catalysts for high sensitive gas sensing

Single atom catalysts(SACs)have garnered significant attention in the field of catalysis over the past decade due to their exceptional atom utilization efficiency and distinct physical and chemical properties.For the semiconductor-based electrical gas sensor,the core is the catalysis process of target gas molecules on the sensitive materials.In this context,the SACs offer great potential for highly sensitive and selective gas sensing,however,only some of the bubbles come to the surface.To facilitate practical applications,we present a comprehensive review of the preparation strategies for SACs,with a focus on overcoming the challenges of aggregation and low loading.Extensive research efforts have been devoted to investigating the gas sensing mechanism,exploring sensitive materials,optimizing device structures,and refining signal post-processing techniques.Finally,the challenges and future perspectives on the SACs based gas sensing are presented.

Enhancing thermodynamic stability of single-crystal Ni-rich cathode material via a synergistic dual-substitution strategy

Nickel(Ni)-rich cathode materials have become promising candidates for the next-generation electrical vehicles due to their high specific capacity.However,the poor thermodynamic stability(including cyclic performance and safety performance or thermal stability)will restrain their wide commercial application.Herein,a single-crystal Ni-rich Li Ni_(0.83)Co_(0.12)Mn_(0.05)O_(2) cathode material is synthesized and modified by a dual-substitution strategy in which the high-valence doping element improves the structural stability by forming strong metal–oxygen binding forces,while the low-valence doping element eliminates high Li^(+)/Ni^(2+)mixing.As a result,this synergistic dual substitution can effectively suppress H2-H3 phase transition and generation of microcracks,thereby ultimately improving the thermodynamic stability of Ni-rich cathode material.Notably,the dual-doped Ni-rich cathode delivers an extremely high capacity retention of 81%after 250 cycles(vs.Li/Li+)in coin-type half cells and 87%after 1000 cycles(vs.graphite/Li^(+))in pouch-type full cells at a high temperature of 55℃.More impressively,the dual-doped sample exhibits excellent thermal stability,which demonstrates a higher thermal runaway temperature and a lower calorific value.The synergetic effects of this dual-substitution strategy pave a new pathway for addressing the critical challenges of Ni-rich cathode at high temperatures,which will significantly advance the high-energy-density and high-safety cathodes to the subsequent commercialization.

Highly Sensitive Ammonia Gas Sensors at Room Temperature Based on the Catalytic Mechanism of N,C Coordinated Ni Single-Atom Active Center

Significant challenges are posed by the limitations of gas sensing mechanisms for trace-level detection of ammonia(NH3).In this study,we propose to exploit single-atom catalytic activation and targeted adsorption properties to achieve highly sensitive and selective NH3 gas detection.Specifically,Ni singleatom active sites based on N,C coordination(Ni-N-C)were interfacially confined on the surface of two-dimensional(2D)MXene nanosheets(Ni-N-C/Ti_(3)C_(2)Tx),and a fully flexible gas sensor(MNPE-Ni-N-C/Ti_(3)C_(2)Tx)was integrated.The sensor demonstrates a remarkable response value to 5 ppm NH3(27.3%),excellent selectivity for NH3,and a low theoretical detection limit of 12.1 ppb.Simulation analysis by density functional calculation reveals that the Ni single-atom center with N,C coordination exhibits specific targeted adsorption properties for NH3.Additionally,its catalytic activation effect effectively reduces the Gibbs free energy of the sensing elemental reaction,while its electronic structure promotes the spill-over effect of reactive oxygen species at the gas-solid interface.The sensor has a dual-channel sensing mechanism of both chemical and electronic sensitization,which facilitates efficient electron transfer to the 2D MXene conductive network,resulting in the formation of the NH3 gas molecule sensing signal.Furthermore,the passivation of MXene edge defects by a conjugated hydrogen bond network enhances the long-term stability of MXene-based electrodes under high humidity conditions.This work achieves highly sensitive room-temperature NH3 gas detection based on the catalytic mechanism of Ni single-atom active center with N,C coordination,which provides a novel gas sensing mechanism for room-temperature trace gas detection research.

Purification of copper foils driven by single crystallization

High-purity copper(Cu) with excellent thermal and electrical conductivity, is crucial in modern technological applications, including heat exchangers, integrated circuits, and superconducting magnets. The current purification process is mainly based on the zone/electrolytic refining or anion exchange, however, which excessively relies on specific integrated equipment with ultra-high vacuum or chemical solution environment, and is also bothered by external contaminants and energy consumption. Here we report a simple approach to purify the Cu foils from 99.9%(3N) to 99.99%(4N) by a temperature-gradient thermal annealing technique, accompanied by the kinetic evolution of single crystallization of Cu.The success of purification mainly relies on(i) the segregation of elements with low effective distribution coefficient driven by grain-boundary movements and(ii) the high-temperature evaporation of elements with high saturated vapor pressure.The purified Cu foils display higher flexibility(elongation of 70%) and electrical conductivity(104% IACS) than that of the original commercial rolled Cu foils(elongation of 10%, electrical conductivity of ~ 100% IACS). Our results provide an effective strategy to optimize the as-produced metal medium, and therefore will facilitate the potential applications of Cu foils in precision electronic products and high-frequency printed circuit boards.

Cryptanalysis of efficient semi-quantum secret sharing protocol using single particles

In paper[Chin.Phys.B 32070308(2023)],Xing et al.proposed a semi-quantum secret sharing protocol by using single particles.We study the security of the proposed protocol and find that it is not secure,that is,the three dishonest agents,Bob,Charlie and Emily can collude to obtain Alice's secret without the help of David.

Single crystal growth and transport properties of narrow-bandgap semiconductor RhP_(2)

We report the growth of high-quality single crystals of RhP_(2),and systematically study its structure and physical properties by transport,magnetism,and heat capacity measurements.Single-crystal x-ray diffraction reveals that RhP_(2) adopts a monoclinic structure with the cell parameters a=5.7347(10)A,b=5.7804(11)A,and c=5.8222(11)A,space group P2_(1)/c(No.14).The electrical resistivityρ(T)measurements indicate that RhP_(2) exhibits narrow-bandgap behavior with the activation energies of 223.1 meV and 27.4 meV for two distinct regions,respectively.The temperaturedependent Hall effect measurements show electron domain transport behavior with a low charge carrier concentration.We find that RhP_(2) has a high mobilityμ_(e)~210 cm^(2)·V^(-1)·s^(-1)with carrier concentrations n_(e)~3.3×10^(18)cm^(3) at 300 K with a narrow-bandgap feature.The high mobilityμ_(e) reaches the maximum of approximately 340 cm^(2)·V^(-1)·s^(-1)with carrier concentrations n_^(e)~2×10^(18)cm^(-3)at 100 K.No magnetic phase transitions are observed from the susceptibilityχ(T)and specific heat C_(p)(T)measurements of RhP_(2).Our results not only provide effective potential as a material platform for studying exotic physical properties and electron band structures but also motivate further exploration of their potential photovoltaic and optoelectronic applications.

Atomically dispersed calcium as solid strong base catalyst with high activity and stability

Solid strong base catalysts are highly attractive for diverse reactions owing to their advantages of neglectable corrosion,facile separation,and environmental friendliness.However,their widespread applications are impeded by basic components aggregation and low stability.In this work,we fabricate single calcium atoms on graphene(denoted as Ca1/G)by use of a redox strategy for the first time,producing solid strong base catalyst with high activity and stability.The precursor Ca(NO_(3))_(2)is first reduced to CaO at 400℃ by the support graphene,forming CaO/G with conventional basic sites,and the subsequent reduction at 850℃results in the generation of Ca1/G with atomically dispersed Ca.Various characterizations reveal that Ca single atoms are anchored on graphene in tetra-coordination(Ca-C_(2)-N_(2))where N is in situ doped from Ca(NO_(3))_(2).The atomically dispersed Ca,along with their anchoring on the support,endow Ca1/G with high activity and stability toward the transesterification reaction of ethylene carbonate with methanol.The turnover frequency value reaches 128.0 h^(-1)on Ca1/G,which is much higher than the traditional counterpart CaO/G and various reported solid strong bases(2.9-46.2 h^(-1)).Moreover,the activity of Ca1/G is well maintained during 5 cycles,while 60%of activity is lost for the conventional analogue CaO/G due to the leaching of Ca.

Achieving Negatively Charged Pt Single Atoms on Amorphous Ni(OH)_(2)Nanosheets with Promoted Hydrogen Absorption in Hydrogen Evolution

Single-atom(SA)catalysts with nearly 100%atom utilization have been widely employed in electrolysis for decades,due to the outperforming catalytic activity and selectivity.However,most of the reported SA catalysts are fixed through the strong bonding between the dispersed single metallic atoms with nonmetallic atoms of the substrates,which greatly limits the controllable regulation of electrocatalytic activity of SA catalysts.In this work,Pt-Ni bonded Pt SA catalyst with adjustable electronic states was successfully constructed through a controllable electrochemical reduction on the coordination unsaturated amorphous Ni(OH)_(2)nanosheet arrays.Based on the X-ray absorption fine structure analysis and first-principles calculations,Pt SA was bonded with Ni sites of amorphous Ni(OH)_(2),rather than conventional O sites,resulting in negatively charged Pt^(δ-).In situ Raman spectroscopy revealed that the changed configuration and electronic states greatly enhanced absorbability for activated hydrogen atoms,which were the essential intermediate for alkaline hydrogen evolution reaction.The hydrogen spillover process was revealed from amorphous Ni(OH)_(2)that effectively cleave the H-O-H bond of H_(2)O and produce H atom to the Pt SA sites,leading to a low overpotential of 48 mV in alkaline electrolyte at-1000 mA cm^(-2)mg^(-1)_(Pt),evidently better than commercial Pt/C catalysts.This work provided new strategy for the control-lable modulation of the local structure of SA catalysts and the systematic regulation of the electronic states.

Effect of surface modification on the radiation stability of diamond ohmic contacts

The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.

Oxidation behavior of 4774DD1 Ni-based single-crystal superalloy at 980℃ in air

The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980℃ and discontinuous oxidation weight gain methods.The phase constitution and morphology of surface oxides and the characteristics of the crosssection oxide film were analyzed by XRD,SEM and EDS.Results show that the oxidation kinetics of the 4774DD1 superalloy follows the cubic law,indicating its weak oxidation resistance at this temperature.As the oxidation time increases,the composition of the oxide film evolves as following:One layer consisting of a bottom Al_(2)O_(3)sublayer and an upper(Al_(2)O_(3)+NiO)mixture sublayer after oxidized for 25 h.Then,two layers composed of an outermost small NiO discontinuous grain layer and an internal layer for 75 h.This internal layer is consisted of the bottom Al_(2)O_(3)sublayer,an intermediate narrow CrTaO_(4)sublayer,and an upper(Al_(2)O_(3)+NiO)mixture sublayer.Also two layers comprising an outermost relative continuous NiO layer with large grain size and an internal layer as the oxidation time increases to 125 h.This internal layer is composed of the upper(Al_(2)O_(3)+NiO)mixture sublayer,an intermediate continuous(CrTaO_(4)+NiWO_(4))mixture sublayer,and a bottom Al_(2)O_(3)sublayer.Finally,three layers consisting of an outermost(NiAl2O_(4)+NiCr2O_(4))mixture layer,an intermediate(CrTaO_(4)+NiWO_(4))mixture layer,and a bottom Al_(2)O_(3)layer for 200 h.

Comparative analysis of single-crater parameters in ultrasonic-assisted and unassisted micro-EDM of Ti6Al4V using discharge plasma imaging

Ultrasonic-assisted micro-electro-discharge machining(EDM)has the potential to enhance processing responses such as material removal rate(MRR)and surface finish.To understand the reasons for this enhancement,the physical mechanisms responsible for the individual discharges and the craters that they form need to be explored.This work examines features of craters formed by single discharges at various parameter values in both conventional and ultrasonic-assistedEDM of Ti6Al4V.High-speed imaging of the plasma channel is performed,and data on the individual discharges are captured in real-time.A 2D axisymmetric model using finite element software is established to model crater formation.On the basis of simulation and experimental results,a comparative study is then carried out to examine the effects of ultrasonic vibrational assistance on crater geometry.For every set ofEDM parameters,the crater diameter and depth from a single discharge are found to be higher in ultrasonic-assistedEDM than in conventionalEDM.The improved crater geometry and the reduced bulge formation at the crater edges are attributed to the increased melt pool velocity and temperature predicted by the model.