Reactive air wetting and brazing of Al_(2)O_(3) ceramics using Ag-Nb_(2)O_(5) filler: Performance and interfacial behavior

We firstly performed the reactive air wetting and brazing of Al_(2)O_(3) ceramics using Ag-(0.5-12)Nb_(2)O_(5) fillers,where Nb_(2)O_(5) can react with liquid Ag and O2 from air to generate AgNbO_(3).The contact angle of the Ag-Nb_(2)O_(5)/Al_(2)O_(3) system almost linearly decreases from~71.6°to 32.5°with the Nb_(2)O_(5) content increasing,and the joint shear strength reaches the maximum of~65.1 MPa while employing the Ag-4Nb_(2)O_(5) filler,which are mainly related to the formation and distribution of the AgNbO_(3) phase at the interface.Moreover,the interfacial bonding and electronic properties of related interfaces were investigated by first-principles calculations.The calculated works of adhesion(Wa)of Ag(111)/Ag-O-AgNbO_(3)(001)and AgNbO_(3)(001)/Al_(2)O_(3)(100)interfaces are higher than that of the Ag(111)/Al_(2)O_(3)(110)interface,indicating good reliability of the Ag/AgNbO_(3)/Al_(2)O_(3) structure.The relatively large interfacial charge transfer indicates the formation of Ag-Ag,Al-O,and Ag-O bonds in the Ag/AgNbO_(3)/Al_(2)O_(3) structure,which can contribute to the interfacial bonding.

Revisiting traditional and modern trends in versatile 2D nanomaterials: Synthetic strategies, structural stability, and gas-sensing fundamentals

Two-dimensional nanomaterials(2DNMs)have attracted significant research interest due to their outstanding structural properties,which include unique electrical nanostructures,large surface areas,and high surface reactivity.These adaptable materials have outstanding physicochemical characteristics,making them useful in a variety of applications such as gas-sensing,electronics,energy storage,and catalysis.Extensive research has been conducted in the pursuit of high performance room-temperature(RT)gas sensors with good selectivity,high sensitivity,long-term stability,and rapid response/recovery kinetics.Metal oxides,transition metal chalcogenides,MXenes,graphene,phosphorene,and boron nitride have all been discovered as 2DNMs with strong potential for gas sensors.This review presents an in-depth analysis of current advances in 2DNM research.It includes synthetic techniques,structural stabilities,gas-sensing mechanisms,critical performance parameters,and factors influencing gas-sensing capabilities of 2DNMs.Furthermore,the present study emphasizes structural engineering and optimization methodologies that improve gas-sensing performance.It also highlights current challenges and outlines future research directions in the domain of tailoring 2DNMs for advanced RT gas sensors.This systematically designed comprehensive review article aims to provide readers with profound insights into gas detection,thereby inspiring the generation of innovative ideas to develop cutting-edge 2DNMs-based gas sensors.

Recent advances in joining of SiC-based materials(monolithic SiC and SiC_f/SiC composites):Joining processes,joint strength, and interfacial behavior

Silicon carbide(SiC) has been widely concerned for its excellent overall mechanical and physical properties, such as low density, good thermal-shock behavior, high temperature oxidation resistance, and radiation resistance; as a result, the SiC-based materials have been or are being widely used in most advanced fields involving aerospace, aviation, military, and nuclear power. Joining of SiC-based materials(monolithic SiC and SiCf/SiC composites) can resolve the problems on poor processing performance and difficulty of fabrication of large-sized and complex-shaped components to a certain extent, which are originated from their high inherent brittleness and low impact toughness.Starting from the introduction to SiC-based materials, joining of ceramics, and joint strength characterization, the joining of SiC-based materials is reviewed by classifying the as-received interlayer materials, involving no interlayer, metallic, glass-ceramic, and organic interlayers. In particular, joining processes(involving joining techniques and parameter conditions), joint strength,interfacial microstructures, and/or reaction products are highlighted for understanding interfacial behavior and for supporting development of application-oriented joining techniques.

Brazing of WC–8Co cemented carbide to steel using Cu–Ni–Al alloys as filler metal: Microstructures and joint mechanical behavior

Three novel Cu-Ni-A1 brazing filler alloys with Cu/Ni weight ratio of 4：1 and 2.5-10 wt% Al were developed and characterized, and the wetting of three Cu-Ni-Al alloys on WC-8Co cemented carbide were investigated at 1190-1210 ℃ by the sessile drop technique. Vacuum brazing of the WC-8Co cemented carbide to SAE1045 steel using the three Cu-Ni-Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5 °and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu-Ni-A1/WC-8Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions （such as diffusion and solid solution） of WC-8Co/Cu-Ni-Al/steel sys- tem. Compared with the other two brazed joints, the WC-8Co/Cu-19Ni-SAl/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 rain, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu-Ni-A1/WC-8Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Efficient photocatalytic hydrogen evolution coupled with benzaldehyde production over 0D Cd_(0.5)Zn_(0.5)S/2D Ti_(3)C2 Schottky heterojunction

Converting water into hydrogen fuel and oxidizing benzyl alcohol to benzaldehyde simultaneously under visible light illumination is of great significance,but the fast recombination of photogenerated carriers in photocatalysts seriously decreases the conversion efficiency.Herein,a novel dual-functional 0D Cd_(0.5)Zn_(0.5)S/2D Ti_(3)C2 hybrid was fabricated by a solvothermally in-situ generated assembling method.The Cd_(0.5)Zn_(0.5)S nano-spheres with a fluffy surface completely and uniformly covered the ultrathin Ti_(3)C2 nanosheets,leading to the increased Schottky barrier(SB)sites due to a large contact area,which could accelerate the electron–hole separation and improve the light utilization.The optimized Cd_(0.5)Zn_(0.5)S/Ti_(3)C2 hybrid simultaneously presents a hydrogen evolution rate of 5.3 mmol/(g·h)and a benzaldehyde production rate of 29.3 mmol/(g·h),which are~3.2 and 2 times higher than those of pristine Cd_(0.5)Zn_(0.5)S,respectively.Both the multiple experimental measurements and the density functional theory(DFT)calculations further demonstrate the tight connection between Cd_(0.5)Zn_(0.5)S and Ti_(3)C2,formation of Schottky junction,and efficient photogenerated electron–hole separation.This paper suggests a dual-functional composite catalyst for photocatalytic hydrogen evolution and benzaldehyde production,and provides a new strategy for preventing the photogenerated electrons and holes from recombining by constructing a 0D/2D heterojunction with increased SB sites.

Electrospun Cu-doped In_(2)O_(3) hollow nanofibers with enhanced H2S gas sensing performance

One-dimensional nanofibers can be transformed into hollow structures with larger specific surface area, which contributes to the enhancement of gas adsorption. We firstly fabricated Cu-doped In_(2)O_(3) (Cu-In_(2)O_(3)) hollow nanofibers by electrospinning and calcination for detecting H2S. The experimental results show that the Cu doping concentration besides the operating temperature, gas concentration, and relative humidity can greatly affect the H2S sensing performance of the In_(2)O_(3)-based sensors. In particular, the responses of 6%Cu-In_(2)O_(3) hollow nanofibers are 350.7 and 4201.5 to 50 and 100 ppm H2S at 250 ℃, which are over 20 and 140 times higher than those of pristine In_(2)O_(3) hollow nanofibers, respectively. Moreover, the corresponding sensor exhibits excellent selectivity and good reproducibility towards H2S, and the response of 6%Cu-In_(2)O_(3) is still 1.5 to 1 ppm H2S. Finally, the gas sensing mechanism of Cu-In_(2)O_(3) hollow nanofibers is thoroughly discussed, along with the assistance of first-principles calculations. Both the formation of hollow structure and Cu doping contribute to provide more active sites, and meanwhile a little CuO can form p–n heterojunctions with In_(2)O_(3) and react with H2S, resulting in significant improvement of gas sensing performance. The Cu-In_(2)O_(3) hollow nanofibers can be tailored for practical application to selectively detect H2S at lower concentrations.