Mechanical Properties and Damage Tolerance of Bulk Yb3Al5O12 Ceramic

Yb₃Al₅O₁₂ has potential applications as thermal barrier coatings（TBCs） because it shows low thermal conductivity and close thermal expansion coefficient to nickel-based superalloys.As a prospective TBC material,besides superior thermal properties,the mechanical properties are also important.In this paper,we present the mechanical properties of Yb₃Al₅O₁₂ including elastic moduli,hardness,strength,and fracture toughness.The Young’s modulus of Yb₃Al₅O₁₂ is 282 GPa.The shear-modulus-to-bulkmodulus ratio of Yb₃Al₅O₁₂ is 0.63,which indicates relatively low shear deformation resistance.In addition,Yb₃Al₅O₁₂ exhibits high strength and fracture toughness but low hardness compared to yttria stabilized zirconia（YSZ）,the most successful TBC material.SEM observation reveals that the fracture surface of Yb₃Al₅O₁₂ displays "layered structure feature",which is caused by crack deflection.Investigation based on Hertzian contact test demonstrates that Yb₃Al₅O₁₂ is a damage-tolerant ceramic.Crack deflection and bridging can arouse shear faults,dissipate the local damage energy,and restrict the crack propagation within the material,which play an important role in enhancing the damage tolerance.The superior mechanical properties and good damage tolerance ensure Yb₃Al₅O₁₂ a promising candidate for TBC applications.     

Growth mechanism of primary Ti5Si3 phases in special brasses and their effect on wear resistance

In the present work, in-situ Ti₅Si₃ reinforced special brasses were prepared by melt reaction method. The synthesized Ti₅Si₃ phase shows various morphologies in brasses with different Ti₅Si₃ content, and the3 D morphological evolution of primary Ti₅Si₃and its growth mechanism were investigated. The Ti₅Si₃ crystal, which bears D8₈ hexagonal crystal structure, grows along <0001> direction and is revealed by{1010} faces during growth. With the increase of Ti₅Si₃ content in the brasses, the morphology of primary Ti₅Si₃significantly changes from fibers to hexagonal prisms to short-rods with hollow. In addition,the influence of Ti₅Si₃ volume fraction and morphology on the wear behavior of special brass was also revealed. It was substantiated that the wear resistance increases with the increasing volume fraction of Ti₅Si₃, and the corresponding wear mechanism changes from delamination to slight adhesive wear and abrasive wear. However, the friction coefficient shows an abnormal increase when most of the Ti₅Si₃ containing hollows appears in the brass. That is mainly due to the fact that the Ti₅Si₃ is easier to break and fall off resulted by the hollow as a crack source, which makes it unable to resist the plastic deformation of the contact surface during the sliding.     

Structural and Physical Property Analysis of ZnO-SnO2—In2O3—Ga2O3 Quaternary Transparent Conducting Oxide System

The increasing demand in the diverse device applications of transparent conducting oxides（TCOs） requires synthesis of new TCOs of n- or p-type conductivity.This article is about materials engineering of ZnO—SnO₂—ln₂O₃—Ga₂O₃ to synthesize powders of the quaternary compound Zn_2-xSn_1-xJn_xGa_xO_4-δ in the stoichiometry of x = 0.2,0.3,and 0.4 by solid state reaction at 1275℃.Lattice parameters were determined by X-ray diffraction（XRD） technique and solubility of ln³⁺ and Ga³⁺ in spinel Zn₂SnO₄ was found at 1275℃.The solubility limit of ln³⁺ and Ga³⁺ in Zn₂SnO₄ is found at below x = 0.4.The optical transmittance approximated by the UV—Vis reflectance spectra showed excellent characteristics while optical band gap was consistent across 3.2 eV with slight decrease along increasing x value.Carrier mobility of the species was considerably higher than the older versions of zinc stannate spinel co-substitutions whereas the carrier concentrations were moderate.     

Effect of sintering temperature on the chemical bonding,electronic structure and electrical transport properties of β-Ga1.9Fe0.1O3 compounds

A model system,which is based on iron(Fe)doped gallium oxide(Ga₂O₃)(Ga_1.9Fe_0.1O₃),has been considered to elucidate the combined effect of transition-metal ion doping and processing temperature on the chemistry,local structure and chemical bonding,and electrical transport properties of a wide band gap oxide(Ga₂O₃).The Ga_1.9Fe_0.1O₃ compounds were synthesized using standard high-temperature solid state reaction method.The effect of processing conditions in terms of different calcination and sintering environments on the structural and electrical properties of Ga_1.9Fe_0.1O₃ compounds is studied in detail.Structural characterization by Raman spectroscopy revealed that Ga_1.9Fe_0.1O₃ compounds exhibit monoclinic crystal symmetry,which is quite similar to the intrinsic parental crystal structure,though Fedoping induces lattice strain.Sintering temperature(T_sint)which was varied in the range of 900-1200℃,has significant impact on the structure,chemical bonding,and electrical properties of Ga_1.9Fe_0.1O₃ compounds.Raman spectroscopic measurements indicate the proper densification of the Ga_1.9Fe_0.1O₃ compounds achieved through complete Fe diffusion into the parent Ga₂O₃ lattice which is evident at the highest sintering temperature.The X-ray photoelectron spectroscopy validates the chemical states of the constituent elements in Ga_1.9Fe_0.1O₃ compounds.The electrical properties of Ga_1.9Fe_0.1O₃ fully controlled by T_sint,which governed the grain size and microstructural evolution.The temperature and frequency dependent electrical measurements demonstrated the salient features of the Fe doped Ga₂O₃ compounds.The activation energy determined from Arrhenius equation is 0.5 e V.The results demonstrate that control over structure,morphology,chemistry and electrical properties of the Ga_1.9Fe_0.1O₃ compounds can be achieved by optimizing T_sint.     

Improvement in the Adhesion Between Electrode of a SOFC and Ag Paste as a Current Collector by Au Deposition

This paper reports the use of Au films to improve the performance of the stacked solid oxide fuel cell(SOFC) based on the characterization of the interface and the adhesion between the electrodes of the SOFCs and the Ag paste. The specimens were manufactured to perform the experiment as follows. A Si O2 wafer with a 300 mm notch was attached to the electrodes of a SOFC by a Ag paste and Au film, which were deposited on the electrodes by sputtering for 1 min or 5 min deposition time and annealed at300 C for 1 h. The four-point bending test was performed, which resulted in the formation of an extended crack at the tip on the wafer notch, and the crack propagation was observed using a stereo microscope equipped with a charge-coupled device(CCD). Consequently, the interfacial adhesion energy and the effect of the Au film between the each electrode and the Ag paste can be evaluated. On the cathode, the interfacial adhesion energy without Au film was 2.59 J/m2(upper value) and the adhesion energy increased to 11.59 J/m2(upper value) and 15.89 J/m2(lower value) with the Au film. On the anode,the interfacial adhesion energy without Au film was 1.74 J/m2(upper value), which increased to 11.07 J/m2(upper value) and 14.74 J/m2(lower value) with the Au film. In addition, the interface areas were analyzed by scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) to estimate the interface delamination.     

硅酸镱环境障涂层抗熔盐腐蚀行为与机制研究

稀土硅酸盐环境障涂层(EBC)是应用于新一代高推重比航空发动机热端部件的重要材料, 但其在高温熔盐环境的腐蚀行为与机制尚不明晰。本工作采用真空等离子喷涂技术(VPS)制备了Yb₂SiO₅/Yb₂Si₂O₇/Si环境障涂层, 并研究了该涂层体系在900 ℃、Na₂SO₄+25% NaCl(质量分数)熔盐环境中的腐蚀行为与机制。研究发现, 所制备的Yb₂SiO₅/Yb₂Si₂O₇/Si涂层体系结构致密, 各层之间结合良好; 涂层体系腐蚀240 h, 熔盐组分渗透Yb₂SiO₅涂层, 在Yb₂Si₂O₇中间层发生富集。涂层中Yb₂SiO₅相具有良好的稳定性, Yb₂O₃第二相与熔盐发生反应, 且随腐蚀时间延长, Yb₂O₃含量减少。中间层Yb₂Si₂O₇相与熔盐反应生成磷灰石相NaYb₉Si₆O₂₆和钠硅酸盐, 并产生Cl₂和SO₂等挥发性物质, 从而影响服役寿命。硅黏结层中未发现熔盐渗透现象, 保持完整。该涂层体系具有良好的抗熔盐腐蚀性能。     

In situ confined vertical growth of Co2.5Ni0.5Si2O5(OH)4 nanoarrays on rGO for an efficient oxygen evolution reactionOA

Rational design of oxygen evolution reaction(OER) catalysts at low cost would greatly benefit the economy.Taking advantage of earth-abundant elements Si, Co and Ni, we produce a unique-structure where cobalt-nickel silicate hydroxide [Co_2.5Ni_0.5Si₂O₅(OH)₄] is vertically grown on a reduced graphene oxide(rGO) support(CNS@rGO). This is developed as a low-cost and prospective OER catalyst. Compared to cobalt or nickel silicate hydroxide@rGO(CS@...     

Continuous dimethyl carbonate synthesis from CO2 and methanol over BixCe1-xOδ monoliths:Effect of bismuth doping on population of oxygen vacancies,activity,and reaction pathway

We evaluated bismuth doped cerium oxide catalysts for the continuous synthesis of dimethyl carbonate(DMC)from methanol and carbon dioxide in the absence of a dehydrating agent.Bi_xCe_1-xO_δnanocomposites of various compositions(x=0.06-0.24)were coated on a ceramic honeycomb and their structural and catalytic properties were examined.The incorporation of Bi species into the CeO₂ lattice facilitated controlling of the surface population of oxygen vacancies,which is shown to play a crucial role in the mechanism of this reaction and is an important parameter for the design of ceria-based catalysts.The DMC production rate of the Bi_xCe_1-xO_δ catalysts was found to be strongly enhanced with increasing Ov concentration.The concentration of oxygen vacancies exhibited a maximum for Bi_0.12Ce_0.88O_δ,which afforded the highest DMC production rate.Long-term tests showed stable activity and selectivity of this catalyst over 45 h on-stream at 140°C and a gas-hourly space velocity of 2,880 mL·g_cat^-1·h^-1.In-situ modulation excitation diffuse reflection Fourier transform infrared spectroscopy and first-principle calculations indicate that the DMC synthesis occurs through reaction of a bidentate carbonate intermediate with the activated methoxy(-OCH₃)species.The activation of C0₂ to form the bidentate carbonate intermediate on the oxygen vacancy sites is identified as highest energy barrier in the reaction pathway and thus is likely the rate-determining step.     

The Role of Particles in Fatigue Crack Propagation of Aluminum Matrix Composites and Casting Aluminum Alloys

Fatigue crack propagation （FCP） behaviors were studied to understand the role of SiC particles in 10 wt pct SiCp/A2024 composites and Si particles in casting aluminum alloy A356. The results show that a few particles appeared on the fracture surfaces in SiCp/Al composites even at high △K region, which indicates that cracks propagated predominantly within the matrix avoiding SiC particles due to the high strength of the particles and the strong particle/matrix interface. In casting aluminum alloy, Si particle debonding was more prominent.Compared with SiCp/Al composite, the casting aluminum alloy exhibited lower FCP rates, but had a slight steeper slope in the Paris region. Crack deflection and branching were found to be more remarkable in the casting aluminum alloy than that in the SiCp/Al composites, which may be contributed to higher FCP resistance in casting aluminum alloy.     

Microstructure and tensile behavior of 2D-C_f/AZ91D composites fabricated by liquid–solid extrusion and vacuum pressure infiltration

2D carbon fiber reinforced AZ91 D matrix composites(2D-C_f/AZ91 D composites) were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique(LSEVI). In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon(Py C) coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition(CVD). Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_(17)Al_(12) precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.     

Enhanced photoresponse of Ti02/MoS2heterostructure phototransistors by the coupling of interface charge transfer and photogating

Two-dimensional(2D)MoS₂with appealing physical properties is a promising candidate for next-generation electronic and optoelectronic devices,where the ultrathin MoS₂is usually laid on or gated by a dielectric oxide layer.The oxide/MoS₂interfaces widely existing in these devices have significant impacts on the carrier transport of the MoS₂channel by diverse interface interactions.Artificial design of the oxide/MoS₂interfaces would provide an effective way to break through the performance limit of the 2D devices but has yet been well explored.Here,we report a high-performance MoS₂-based phototransistor with an enhanced photoresponse by interfacing few-layer MoS₂with an ultrathin Ti0₂layer.The Ti0₂is deposited on MoS₂through the oxidation of an e-beam-evaporated ultrathin Ti layer.Upon a visible-light illumination,the fabricated Ti0₂/MoS₂phototransistor exhibits a responsivity of up to 2,199 A/W at a gate voltage of 60 V and a detectivity of up to 1.67×10¹³Jones at a zero-gate voltage under a power density of 23.2μW/mm².These values are 4.0 and 4.2 times those of the pure MoS₂phototransistor.The significantly enhanced photoresponse of Ti0₂/MoS₂device can be attributed to both interface charge transfer and photogating effects.Our results not only provide valuable insights into the interactions at Ti0₂/MoS₂interface,but also may inspire new approach to develop other novel optoelectronic devices based on 2D layered materials.     

Relationship between Microstructure Evolution and the Luminescent Properties of Eu3+-doped Yttrium Aluminum Garnet and Y2O3 Nano-powders

Eu³⁺-doped yttrium aluminum garnet（YAG） and Y₂O₃ composite phase nanoparticles were synthesized using a modified hydrothermal method.Sintering was performed at 800℃,which is considerably lower than the sintering temperature used in the conventional method.Y³⁺ in YAG and Y₂O₃ was partially substituted with Na⁺ by adding NaNO₃ into the solution during sample synthesis.The microstructures and phase transformation process were characterized through X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.The obtained results verified that the addition of Na⁺ promoted crystallinity and grain growth of the three phases,namely,Y₂O₃,Y₄AI₂O₉,and Y₃AI₅O₁₂.Highly efficient luminescence properties excited by 254 and 365 nm ultraviolet were achieved.In conclusion,the remarkable enhancement of the luminescence intensity with the addition of Na⁺ should be attributed to grain growth and improvement of crystallinity.     

H2O2的高效电合成及其电Fenton在难降解有机物降解中的应用(英文)

Hydrogen peroxide(H₂O₂) in situ electrosynthesis by O₂ reduction reaction is a promising alternative to the conventional Fenton treatment of refractory wastewater.However,O₂ mass transfer limitation,cathodic catalyst selectivity,and electron transfer in O₂ reduction remain major engineering obstacles.Here,we have proposed a systematic solution for efficient H₂O₂ generation and its electro-Fenton(EF)application for refra...     

Effect of Synthesis Technique and Carbonate Content on the Crystallinity and Morphology of Carbonated Hydroxyapatite

The syntheses of nanosized carbonated hydroxyapatite（CHA） were performed by comparing dropwise and direct pouring of acetone solution of Ca（N0₃）₂-4H₂0 into mixture of（NH₄）₂HP0₄ and NH₄HCO₃ at room temperature controlled at pH 11.Direct pouring method was later applied to study the increment of carbonate content in syntheses.The as-synthesized powders were characterized by various characterization techniques.The crystallographic results of the produced powders were obtained from X-ray diffraction analysis,whilst the carbonate content in the produced powders was determined by the CHNS/O elemental analyzer.Fourier transform infrared analysis confirmed that the CHA powders formed were B-type.Field emission scanning electron microscopy revealed that the powders were highly agglomerated in nanosized range and hence energy filtered transmission electron microscopy was employed to show elongated particles which decreased with increasing carbonate content.     

Analytical Modeling to Predict the Strain Energy of Circular GLARE Fiber-Metal Laminates Under Lateral Indentation

This article deals with the strain energy calculation of thin circular clamped Glass Reinforced （GLARE） fiber-metal laminates subjected to static indentation by a lateral hemispherical indentor. Using one-, two- and three-parameter Ritz approximations, analytical equations of the strain energy as a function of the central plate deflection are derived. Previously published analytical formulas, concerning the load-indentation response of circular GLARE plates, are used in order to determine the Ritz parameters and the first failure load and deflection due to tensile fracture of glass-epoxy layers. In this study, the membrane and bending strain energy components of aluminum and prepreg layers are determined. Also, the elastic and plastic strain energy absorbed during the indentation loading are calculated. The derived formulas are applied successfully for GLARE 2-2/1-0.3, GLARE 3-3/2-0.4 and GLARE 31 （special lay-up） circular plates subjected to lateral indentation. The strain energy results converge satisfactorily in all examined cases. The predicted strain energy-indentation response is compared with published experimental data and a good agreement is found. No other solution of this problem is known to the authors.     

Dip Coating of Nano Hydroxyapatite on Titanium Alloy with Plasma Assistedγ-Alumina Buffer Layer:A Novel Coating Approach

This paper reported a novel coating approach to deposit a thin,crack free and nano-structured hydroxyapatite （HA） film on Ti6AI4V alloy with Al₂O₃ buffer layer for biomedical implants.The Al₂O₃ buffer layer was deposited by plasma spraying while the HA top layer was applied by dip coating technique.The X-ray diffraction（XRD） and Raman reflections of alumina buffer layer showedα- toγ-AI₂O₃ phase transformation; and the fractographic analysis of the sample revealed the formation of columnar grains in well melted splats. The bonding strength between Al₂O₃ coating and Ti6AI4V substrate was estimated to be about 40 MPa.The presence of dip coated HA layer was confirmed using XRD,scanning electron microscopy（SEM） and energy dispersive X-ray spectroscopy（EDX） analysis.The SEM images exhibited that HA top layer enveloped homogenously the troughs and crests of the underneath rough（R_a= 2.91 |im） Al₂O₃ surface.It is believed that the novel coating approach adopted might render the implant suitable for rapid cement-less fixation as well as biocompatible for longer periods.     

Compression Molded Ultra High Molecular Weight Polyethylene-Hydroxyapatite-Aluminum Oxide-Carbon Nanotube Hybrid Composites for Hard Tissue Replacement

Ultra high molecular weight polyethylene（UHMWPE） is widely used for articulating surfaces in total hip and knee replacements.In the present work,UHMWPE based polymer composites were synthesized by synergistic reinforcing of bioactive hydroxyapatite（HA）,bioinert aluminum oxide（Al₂O₃）,and carbon nanotubes（CNTs） using compression molding.Phase and microstructural analysis suggests retention of UHMWPE and reinforcing phases in the compression molded composites.Microstructural analysis elicited variation in densification due to the size effect of the reinforcing particles.The hybrid composites exhibited hardness, elastic modulus and toughness comparable to that of UHMWPE.The interfacial effect of reinforcement phases has evinced the effectiveness of Al₂O₃ over HA and CNT reinforcements,depicting synergistic enhancement in hardness and elastic modulus.Weak interfacial bonding of polymer matrix with HA and CNT requires utilization of coupling agents to achieve enhanced mechanical properties without deteriorating cytocompatible properties.     

Phase growth patterns for Al_2O_3/GdAlO_3 eutectics over wide ranges of compositions and solidification rates

Phase selection and growth characteristics of directionally solidified Al₂O₃/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone.Through the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al₂O₃phase,prima ry non-faceted GAP phase and Al₂O₃/GAP eutectic with diffe rent morphologies is detected.Microstructure transitions from wholly eutectic to primary Al₂O₃(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al₂O₃-2 O mol%Gd₂O₃hypoeutectic(Al₂O₃-26 mol%Gd₂O₃hypereutectic)ceramics with the increase of solidification rate.The dendrite growth of faceted Al₂O₃and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of dendrites.Based on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al₂O₃/GAP eutectic ceramics is in good agreement with the experimental results.Besides,the influence of microstructure with these different morphologies on the flexural strength of Al₂O₃/GAP eutectic ceramics is studied.     

Effect of heat treatment on the microstructure and properties of CVD SiC fiber

In this study, the effect of heat treatment on the room temperature strength of W-core Si C fiber produced by chemical vapor deposition(CVD) was investigated. Thermal exposure in the temperature range of 900–1000?C decreases the strength of the Si C fiber. Fracture morphology analysis indicates that failure initiations predominantly take place at the W-core/Si C interface. A reaction layer that formed at the W-core/Si C interface during thermal exposure degraded the fiber strength and an empirical linear relationship of strength vs thickness of the reaction layer can be obtained. The kinetics of the growth of the W-core/Si C reaction layer were determined.     

S-scheme ZnO/WO3 heterojunction photocatalyst for efficient H2O2 production

Designing highly efficient photocatalyst for hydrogen peroxide (H₂O₂) production is an ideal strategy to avoid the shortcomings of traditional H₂O₂ production and to realize the conversion of solar energy to chemical energy.In this work,a step-scheme (S-scheme) heterojunction photocatalyst composed of Zn O and WO₃ is carefully prepared by hydrothermal and calcination method for efficient photocatalytic H₂O₂ production.T...