High-temperature oxidation behavior of modified 4Al alumina-forming austenitic steel: Effect of cold rolling

The oxidation behavior and mechanism of as-received and 30 % cold-rolled alumina-forming austenitic(AFA) steel were investigated in dry air at 700℃.The results show that the mass gain per unit area curves of as-received and 30 % cold-rolled steels subject to near-parabolic law before 100 h oxidation time.Two samples both show higher high-temperature oxidation resistance due to the formation of dense Al₂O₃ oxide scale.Gradual spallation of outer scale results in the formation of continuous and dense alumina scale.Dislocations can act as short-circuit diffusion channel for the diffusion of Al from alloy matrix to surface,and also provide nucleation sites for B2-NiAl phase,which ensure the continuous formation of Al₂O₃ scale.     

Combining in-situ TEM observations and theoretical calculation for revealing the thermal stability of CeO2 nanoflowers

The thermal stability of Ce₂ nanomaterials can directly impact both the uniformity of the supported catalysts and the catalytic behavior of Ce₂ itself.However,knowledge about the thermal stability of Ce₂ is still deficient.Here,we conduct in-situ transmission electron microscopy experiments and theoretical calculations to elucidate the thermal stability of Ce₂ nanomaterials under different environments.A sinter(<700℃)and a structural decomposition(>700℃)are observed within Ce₂ nanoflowers under O₂.The sinter firstly occurs among the nanoflowers’monomers and then the sintered nanoparticles structurally decompose to tiny nanoparticles from the strain interface.Under a vacuum environment,the Ce₂ nanoflowers firstly undergo a transition from cubic fluorite Ce₂ to hexagonal Ce₂O₃,accompanied by the oxygen release.The Ce₂O₃ nanoparticles further atomically sublimate from the edges to the center under high temperatures.Theoretical calculation results reveal a considerably lower energy barrier for the structural decomposition under O₂ and for the sublimation under vacuum.This work provides a perspective on the structural design and performance optimization of Ce₂-based catalysts.     

Microstructural Evolution and Oxidation Resistance of Multi-walled Carbon Nanotubes in the Presence of Silicon Powder at High Temperatures

The microstructural evolution and oxidation resistance of multi-walled carbon nanotubes(MWCNTs) by directly heating silicon powder and MWCNTs in a coke bed from 1000 to 1500 ℃ are investigated with the aid of X-ray diffraction(XRD),scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM) and thermogravimetry-differential scanning calorimetry(TG-DSC).The results showed that the morphology and microstructure of MWCNTs did not change much after being treated from 1000 ℃ to 1200 ℃.An obvious SiC coating was formed on the surface of MWCNTs from 1300 to 1400 ℃.Up to 1500 ℃,nearly all the MWCNTs transformed into SiC nanowires.The oxidation resistance of the treated MWCNTs was improved compared with as-received ones.Non-isothermal kinetics showed that the oxidation activation energy of the treated MWCNTs reached 208 kJ/mol,much higher than 164 kJ/mol of as-received ones.     

Oxidation Resistance Coatings of Ir – Zr and Ir by Double Glow Plasma

Oxidation resistance coatings of Ir-40 at.% Zr and Ir were produced onto Mo substrates by double glow plasma technology. The oxidation resistances of the coatings were evaluated at high temperature. Ir-Zr coating consisted of two layers： the primary layer close to the substrate was composed of dense columnar grains and the second layer was composed of dense grains of nanometric size. The mass gain of Ir coating above 800℃ was about 1.35% due to the formation of solid IrO2. The mass loss of Ir coating was about 5.3% due to the formation of gaseous oxide IrO3 when being held at 1227 ℃ for 30 min. The substrate was protected more effectively by multilayer than monolayer coating of Ir in oxidizing environment. The Ir-Zr coating was well bonded to the substrate after oxidation at 800℃. After oxidation at 1000℃, the Ir-Zr coating was poorly bonded to the substrate. The oxidation resistance of Ir-Zr coating was poor due to high content of Zr.     

Oxidation behaviors of TA15 titanium alloy and TiBw reinforced TA15 matrix composites prepared by spark plasma sintering

The purpose of this study is to investigate the oxidation behaviors of the TA15 titanium alloy and TiBw/TA15 composite with network microstructure in the temperature range of 873–1073 K. The results show that the oxidation kinetics of the TA15 titanium alloy and TiBw/TA15 composite follows different laws at various oxidation temperatures. Moreover, the effective activation energy Q for oxidation of the TA15 titanium alloy and TiBw/TA15 composite is determined to be 299 ± 19.9 kJ/mol and 339 ± 8.31 kJ/mol at the temperature of 973–1073 K, respectively. The experimental achievements of oxidation kinetics and oxide scales formed in the test temperatures indicate that the TiBw/TA15 composite exhibits a higher oxidation resistance than TA15 titanium alloy. A schematic diagram of oxidation mechanism is established to further reveal the oxidation process for TiBw/TA15 composite at elevated temperatures.     

Temperature Fluctuation Synthesis/Simultaneous Densification and Microstructure Control of Titanium Silicon Carbide (Ti3SiC2) Ceramics

1. IatroductionTitanium Silicon carbide (Ti3SiC2) is a novel ceramic material, which combines the merit of bothmetals and ceramics. It is a good thermal and electrical conductor, not susceptible to thermal shock, andeasy to machine with conventional tools. It is also oxidation resistant at high temperatures, and eXtremelyrefractory. Ti3SiCZ crystallizes in hexagonal structurewith a space group of p.,/mmc['], which is shown inFig.1. The unit cell of Ti3SiCZ consists of alternating layers …     

Inverse single-site Fe1(OH)x/Pt(111)model catalyst for preferential oxidation of CO in H2

Inverse oxide/metal model systems are frequently used to investigate catalytic structure-function relationships at an atomic level.By means of a novel atomic layer deposition process,growth of single-site Fe₁O_x on a Pt(111)single crystal surface was achieved,as confirmed by scanning tunneling microscopy(STM).The redox properties of the catalyst were characterized by synchrotron radiation based ambient pressure X-ray photoelectron spectroscopy(AP-XPS).After calcination treatment at 373 K in 1 mbar O₂.the chemical state of the catalyst was determined as Fe³⁺.Reduction in 1 mbar H₂ at 373 K demonstrates a facile reduction to Fe2+and complete hydroxylation at significantly lower temperatures than what has been reported for iron oxide nanoparticles.At reaction conditions relevant for preferential oxidation of CO in H₂(PROX),the catalyst exhibits a Fe3+state(ferric hydroxide)at 298 K while re-oxidation of iron oxide clusters does not occur under the same condition.CO oxidation proceeds on the single-site Fei(OH)3 through a mechanism including the loss of hydroxyl groups in the temperature range of 373 to 473 K,but no reaction is observed on iron oxide clusters.The results highlight the high flexibility of the single iron atom catalyst in switching oxidation states,not observed for iron oxide nanoparticles under similar reaction conditions,which may indicate a higher intrinsic activity of such single interfacial sites than the conventional metal-oxide interfaces.In summary,our findings of the redox properties on inverse single-site iron oxide model catalyst may provide new insights into applied Fe-Pt catalysis.     

All-inorganic lead-free NiOx/Cs3Bi2Br9 perovskite heterojunction photodetectors for ultraviolet multispectral imaging

Bismuth-based perovskites are considered to be promising candidates to substitute the toxic lead-based perovskite in optoelectronics due to their excellent optoelectronic properties,high environmental friendliness,and(moisture,light,and heat)stability.However,there are still few reports about high performance bismuth-based perovskite ultraviolet photodetectors,and is more lacking in ultraviolet imaging demonstration.Herein,we reported a self-powered NiO_x/Cs₃Bi₂Br₉ heterojunction photodetector with excellent photodetection performance by electrochemical depositing NiOx as the hole transport layer.The optimized NiO_x/CsaBi₂Brg heterojunction photodetector exhibits excellent ultraviolet detection performance with a fast response speed of 3.04/4.65 ms,wide linear dynamic range of 116.6 dB,decent responsivity of 4.33 mA·W^-1 at 0 V bias,and high detectivity of 1.3×10¹¹ jones.The outstanding performance of the optimized NiO_x/Cs₃Bi₂Br₉ heterojunction photodetector is enough to meet the high-quality ultraviolet imaging.Therefore,we further integrated the optimized NiO_x/Cs₃Bi₂Br₉ heterojunction photodetector to the transmission mode ultraviolet multispectral imaging system,achieving admirable imaging results at weak light condition.This work will play a positive role in promoting the development of bismuth-based ultraviolet photodetection and ultraviolet multispectral imaging.     

A mediator-free self-powered glucose biosensor based on a hybrid glucose/MnO2 enzymatic biofuel cell

Self-powered glucose biosensor(SPGB)is of great interest due to the advantages including single configuration,good stability and particularly no need of external power sources.Herein,a mediator-free SPGB with high sensitivity and good selectivity is constructed based on a hybrid enzymatic biofuel cell(EBFC)composed of a glucose oxidase/cobalt phthalocyanine/1-pyrenebutyric acid/buckypaper(GOD/CoPc/PBA/BP)bioanode and a MnO₂/PBA/BP capacitive cathode.The efficient electron transfer from GOD to electrodes is achieved successfully through the anode oxidation of hydrogen peroxide(H₂O₂),one nature product of glucose oxidation catalyzed by GOD,thus avoiding the potential drawbacks posed by the use of redox mediators.CoPc servers as an efficient catalyst to lower the anode potential required by the reaction of H₂O₂ to 0.17 V.The MnO₂/PBA/BP capacitive cathode is utilized because it can not only provide a high discharge potential and adequate capacitance to match the bioanode well,but also exhibit no potential interference to the anodic reaction.The concentration of glucose can be detected simply by measuring the output of the SPGB and a wide linear detection range from 0.5 to 8 mM has been obtained with high sensitivities of 48.66 and 32.12μA·cm^?2·mM^?1 with and without stirring,respectively.The recoveries of glucose in grape juice and human serum are in the range from 99.5%to 101.2%with the relative standard deviation(RSD)less than 8%,indicating the good promise of the SPGB in sensing glucose in real samples.     

Fabrication and oxidation resistance of silicon nitride fiber reinforced silica matrix wave-transparent composites

Wave-transparent ceramic matrix composites for the high temperature use should possess excellent oxidation resistance. In this work, Si_3N_(4f)/SiO_2 composites with different fiber content were fabricated by filament winding and sol gel method. The oxidation resistance was investigated by tracking the response of flexural strength to the testing temperature. The results show that the flexural strength and toughness of the composites with fiber content of over 37% can reach high levels at around 175.0 MPa and 6.2 MPa m1/2, respectively. After 1 h oxidation at 1100?C, the flexural strength drops a lot but can still reach 114.4 MPa, which is high enough to ensure the safety of structures. However, when the oxidation temperature rises to 1200–1400?C, the flexural strengths continue to fall to a relatively low level at 50.0–66.4 MPa. The degradation at high temperatures is caused by the combination of over strong interfacial bonding, the damage of fiber and the crystallization of silica matrix.     

Heterogeneous lamellar-edged Fe-Ni(OH)2/Ni3S2nanoarray for efficient and stable seawater oxidation

Development of efficient non-precious catalysts for seawater electrolysis is of great significance but challenging due to the sluggish kinetics of oxygen evolution reaction(OER)and the impairment of chlorine electrochemistry at anode.Herein,we report a heterostructure of Ni₃S₂nanoarray with secondary Fe-Ni(OH)₂lamellar edges that exposes abundant active sites towards seawater oxidation.The resultant Fe-Ni(OH)₂/Ni₃S₂nanoarray works directly as a free-standing anodic electrode in alkaline artificial seawater.It only requires an overpotential of 269 mV to afford a current density of 10 mA·cm^-2and the Tafel slope is as low as 46 m V·dec^-1.The 27-hour chronopotentiometry operated at high current density of 100 mA·cm^-2shows negligible deterioration,suggesting good stability of the Fe-Ni(OH)₂/Ni₃S₂@NF electrode.Faraday efficiency for oxygen evolution is up to?95%,revealing decent selectivity of the catalyst in saline water.Such desirable catalytic performance could be benefitted from the introduction of Fe activator and the heterostructure that offers massive active and selective sites.The density functional theory(DFT)calculations indicate that the OER has lower theoretical overpotential than Cl₂ evolution reaction in Fe sites,which is contrary to that of Ni sites.The experimental and theoretical study provides a strong support for the rational design of high-performance Fe-based electrodes for industrial seawater electrolysis.     

Corrosion behavior of Al0.4CoCu0.6NiSi0.2Ti0.25 high-entropy alloy coating via 3D printing laser cladding in a sulphur environment

High-entropy alloys(HEAs) are of great interest in materials science and engineering communities owing to their unique phase structure.HEAs are constructed with five or more principal alloying elements in equimolar or near-equimolar ratios.Therefore,they can derive their performance from multiple principal elements ratherthan a single element.In this work,three-dimensional printing laser cladding was applied to produce an Al_0.4CoCu_0.6NiSi_0.2Ti_0.25 HEA coating.The experimental results confirmed that the laser cladding could be used to produce a thin coating of 120 μm in thickness.In the high-temperature laser cladding process,some Fe elements diffused from the substrate to the coating,forming a combination of face-centred cubic and body-centred cubic phase structures.The HEA coating metallurgically bonded well with the substrate.Owing to the increased dislocation density and number of grain boundaries,the HEA coating was harder and had a stronger hydrophobicity than X70 steel.The electrochemistry results showed that the HEA coating had better corrosion resistance than X70 steel.Aluminium oxides formed on the surface of the HEA coating had a certain protective effect.However,because of the laser cladding,the HEA coating generated cracks.In future work,the laser cladding technology will be improved and heat treatment will be implemented to prevent formation of cracks.     

In-situ imaging the electrochemical reactions of Li-CO2 nanobatteries at high temperatures in an aberration corrected environmental transmission electron microscope

Rechargeable lithium-carbon dioxide(Li-CO₂)batteries have attracted much attention due to their high theoretical energy densities and capture of C0₂.However,the electrochemical reaction mechanisms of rechargeable Lo-CO₂ batteries,particularly the decomposition mechanisms of the discharge product Li₂CO₃ are still unclear,impeding their practical applications.Exploring electrochemistry of Li₂CO₃ is critical for improving the performance of Li-C0₂ batteries.Herein,in-situ environmental transmission electron microscopy(ETEM)technique was used to study electrochemistry of Li₂CO₃ in Li-C0₂ batteries during discharge and charge processes.During discharge,Li₂CO₃ was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes(CNTs)and Ag nanowires(Ag NWs),but it was hard to decompose during charging at room temperature.To promote the decomposition of Li2C03,the charge reactions were conducted at high temperatures,during which Li₂CO₃ was decomposed to lithium with release of gases.Density functional theory(DFT)calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li₂CO₃.This study not only provides a fundamental understanding to the high temperature Li-C0₂ nanobatteries,but also offers a valid technique,i.e.,discharging/charging at high temperatures,to improve the cyclability of Li-CO₂ batteries for energy storage applications.     

Moisture-preventing MAPbI3 solar cells with high photovoltaic performance via multiple ligand engineering

Perovskite solar cells present one of the most prominent photovoltaic technologies,yet their stability,and engineering at the molecular level remain challenging.We have demonstrated multifunctional molecules to improve the operating stability of perovskite solar cells while depicting a high-power conversion efficiency.The multifunctional molecule 4-[(trifluoromethyl)sulphanyl]-aniline(4TA)with trifluoromethyl(-CF₃)and aniline(-NH₂)moieties is meticulously designed to modulate the perovskite.The-CF₃ and-NH₂ functional groups have strong interaction with perovskite to suppress surface defects to improve device stability,as well as obtain large crystal grains through delaying crystallization.Moreover,this-CF₃ forms a hydrophobic barrier on the surface of the perovskite to prevent cell decomposition.Consequently,the performance of the perovskite solar cells is remarkably improved with the efficiency increased from 18.00% to 20.24%.The perovskite solar cells with multifunctional molecular maintaining 93% of their original efficiency for over 30 days(-55%humidity)in air without device encapsulation,exhibiting a high long-term stability.Moreover,the lead leakage issue of perovskite solar cells has also been suppressed by the built-in 4TA molecule,which is beneficial to environment-friendly application.Ultimately,we believe this multifunctional small molecule provides an available way to achieve high performance perovskite solar cells and the related design strategy is helpful to further develop more versatile materials for perovskite-based optoelectronic devices.     

Record-high saturation current in end-bond contacted monolayer MoS2 transistors

Monolayer two-dimensional(2D)semiconductors are emerging as top candidates for the channels of the future chip industry due to their atomically thin body and superior immunity to short channel effect.However,the low saturation current caused by the high contact resistance(R_c)in monolayer MoS2 field-effect transistors(FETs)limits ultimate electrical performance at scaled contact lengths,which seriously hinders application of monolayer MoS_(2 )transistors.Here we present a scalable strategy with a clean end-bond contact scheme that leads to size-independent electrodes and ultralow contact resistance of 2.5 kΩ·μm to achieve record high performances of saturation current density of 730μA·μm^-1at 300 K and 960μA·μm^-1at 6 K.Our end-bond contact strategy in monolayer MoS2 FETs enables the great potential for atomically thin integrated circuitry.     

Tunable strength of SiCf/β-Yb2Si2O7 interface for different requirements in SiCf/SiC CMC:Inspiration from model composite investigation

Model composites consisting of Si C fiber embedded inβ-Yb₂Si₂O₇ matrix were processed by Spark Plasma Sintering method and the feasibility of tunable Si Cf/Yb₂Si₂O₇ interface in Si C-based CMCs were estimated.Weak and strengthened Si Cf/Yb₂Si₂O₇ interfaces were achieved by adjusting sintering temperatures.The indentation crack test and fiber push out experiments clearly demonstrated the different debonding mechanisms in the samples.Weak interfaces sintered at 1200 and 1250℃exhibited crack deflection at interface in indentation test.Their low debond energy at the interface,which were comparable to those of Py C or BN,satisfied the well-recognized interfacial debond and crack deflection criteria for CMCs.The interface was strengthened by atomic bonding in model composite sintered at 1450℃,leading to crack penetrating into Si C fiber and high debond energy.The strong interface may be promising in Si Cf/Si C CMC to withstand higher combustion temperature,because Yb₂Si₂O₇ will provide plastic deformation capacity,which would serve as weak interphase for crack deflection and energy dissipation.Therefore,it is possible to design the capability of Si C_f/RE₂Si₂O₇ interface for different requirements by adjusting interfacial strength or debond energy to reach optimal mechanical fuse mechanism in SiC_f/SiC CMC.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.     

Facile synthesis of C3N4-supported metal catalysts for efficient CO2 photoreduction

Facile synthesis of photocatalysts with highly dispersed metal centers is a high-priority target yet still a significant challenge.In this work,a series of Co-C₃N₄ photocatalysts with different Co contents atomically dispersed on g-CaN4 have been prepared via one-step thermal treatment of cobalt-based metal-organic frameworks(MOFs)and urea in the air.Thanks to the highly dispersed and rich exposed Co sites,as well as good charge separation efficiency and abundant mesopores,the optimal 25-Co-C₃N₄,in the absence of noble metal catalysts/sensitizers,exhibits excellent performance for photocatalytic C0₂ reduction to CO under visible.light irradiation,with a high CO evolution rate of 394.4μmol·g^-1·h^-1,over 80 times higher than that of pure g-C₃N₄(4.9μmol·g^-1·h^-1).In:addition,by this facile synthesis strategy,the atomically dispersed Fe and Mn anchoring on g-C₃N₄(Fe-C₃N₄ and Mn-C₃N₄)have been also obtained,indicating the reliability and universality of this strategy in synthesizing photocatalysts with highly dispersed metal centers.This work paves a new way to develop cost-effective photocatalysts for photocatalytic C0₂ reduction.     

Hydrophobic 1-octadecanethiol functionalized copper catalyst promotes robust high-current CO2 gas-diffusion electrolysis

The electrocatalytic reduction of CO₂ presents a promising strategy in addressing environmental and energy crisis.Significant progress has been achieved via CO₂ gas diffusion electrolysis,to react at high selectivity and high rate.However,the gas diffusion layer(GDL)of the gas diffusion electrode(GDE)still suffers from low tolerance and limited active sites.Here,the hydrophobic 1-octadecanethiol molecular was functionalized over the Cu catalyst layer of the GDE,which simultaneously stabilizes the GDL and exposes abundant active solid-liquid-gas three-phase interfaces.The resultant GDE exhibits multi-carbon(C₂₊)product selectivity over faradaic efficiency(FE)of 70.0%in the range of 100 to 800 mA·cm^-2,with the peak FE^c2+of 85.2%at 800 mA·cm^-2.Notably,the strengthened GDE could continuously drive high-current electrolysis for more than 100 h without flooding.This work opens a new way to improve CO₂ gas diffusion electrolysis via surface molecular engineering.     

Highly active multivalent multielement catalysts derived from hierarchical porous TiNb2O7 nanospheres for the reversible hydrogen storage of MgH2

Critical limitations in applying MgH₂ as a hydrogen-storage medium include the high H₂ desorption temperature and slow reaction kinetics.In this study,we synthesized hierarchical porous TiNb₂O₇ spheres in micrometer scale built with 20-50 nm nanospheres,which showed stable activity to catalyze hydrogen storage in MgH₂ as precursors.The addition of 7 wt.%TiNb₂O₇ in MgH₂ reduced the dehydrogenation onset temperature from 300 to 177℃.At 250℃,approximately 5.5 wt.%H₂ was rapidly released in 10 min.Hydrogen uptake was detected even at room temperature under 50 bar hydrogen;4.5 wt.%H₂ was absorbed in 3 min at 150℃,exhibiting a superior low-temperature hydrogenation performance.Moreover,nearly constant capacity was observed from the second cycle onward,demonstrating stable cyclability.During the ball milling and initial de/hydrogenation process,the high-valent Ti and Nb of TiNb₂O₇ were reduced to the lower-valent species or even zero-valent metal,which in situ created multivalent multielement catalytic surroundings.A strong synergistic effect was obtained for hybrid oxides of Nb and Ti by density functional theory(DFT)calculations,which largely weakens the Mg-H bonding and results in a large reduction in kinetic barriers for hydrogen storage reactions of MgH₂.Our findings may guide the further design and development of high-performance complex catalysts for the reversible hydrogen storage of hydrides.