Effects of Neodymium and Calcium on the Thermal Stability of AZ71 Magnesium Alloys

The effects of an addition of 0–2 wt% Nd on thermal stability of 0–3 wt% Ca-containing modified AZ71 magnesium alloys was investigated. The ignition temperature was found to increase from that of AZ71, 574, to 825 °C with the addition of 0.5 wt% Ca and 1 wt% Nd. The ignition temperature was further increased to 1114 °C when 3 wt% Ca was added. The Ca- and Nd-added AZ71 was isothermally maintained at a temperature of 500 °C in air for 12 h. The MgO–CaO–Nd₂O₃ formed on the surface to improve the thermal stability of the AZ71–xCa–yNd alloys. While both the tensile strength and ductility decreased with the Ca concentration in the alloy, an addition of 1 wt% Nd was found able to alleviate the degradation effects of Ca on the tensile strength and ductility at 170 °C. Both solid solution formation and precipitation strengthening contributed to the increase in toughness. AZ71 containing 0.5–2 wt% Ca and 1 wt% Nd provides the optimum combination of ignition resistance and mechanical properties.     

High-temperature behavior of oxide dispersion strengthening CoNiCrAlY

To fabricate oxide dispersion strengthened bond coatings, commercial Co–30wt-%Ni–20Cr–8Al–0?4Y powder was milled with 2% additions of Al₂O₃, Y₂O₃ or Y₂O₃ + HfO₂. Low-pressure plasma sprayed, free-standing specimens were oxidised in air + 10%H2O at 1100 °C both isothermally (100 h) and in 500, 1?h cycles. Dry air cyclic testing conducted at both ORNL and FZJ showed remarkably similar results. In general, the water vapour addition caused more scale spallation. Two LPPS specimens without oxide additions were tested for comparison. The specimens with 2%Al₂O₃ addition exhibited the best behaviour as the powder already contained 0?4%Y. Additions of 2%Y₂O₃ and especially 1%Y₂O₃ + 1%HfO₂ resulted in over-doping as evidenced by high mass gains and the formation of Y- and Hf-rich pegs. Scanning transmission electron microscopy of the isothermal specimens showed no Hf and/or Y segregation to the alumina scale grain boundaries in the over-doped specimens.     

Fabrication of 3D Ni nanosheet array on Crofer22APU interconnect and NiO-YSZ anode support to sinter with small-size Ag nanoparticles for low-temperature sealing SOFCs

A novel low-temperature sealing method was developed to seal solid oxide fuel cells. The 3D Ni nanosheet array was pre-fabricated on faying surfaces of Crofer22APU interconnect and NiO-YSZ anode-support. Then it was covered with Au film without changing its morphology. This special nanostructure improved sintering efficiency between Ag nanoparticles and substrates. A dense joint was obtained at the low-temperature between 250 °C–300 °C. This method effectively avoided the oxidation of interconnect during sealing. When joints were sealed at 300 °C, the shear strength reached 16 MPa. The fracture was mainly located in the central Ag layer, presenting a significant plastic deformation. Due to the effective protection of Ni layer, joints also possessed excellent oxidation resistance in oxidizing atmosphere at 800 °C for 400 h. After high-temperature oxidation, the shear strength was increased to 23 MPa, revealing an increasement of 43.8% compared with the as-sealed condition (16 MPa). This sealing method has great potential in sealing solid oxide fuel cells. It also can be extended to seal other energy-conversion devices.     

An easy and scalable approach to synthesize three-dimensional sandwich-like Si/Polyaniline/Graphene nanoarchitecture anode for lithium ion batteries

A new three-dimensional (3D) sandwich-like Si/Polyaniline/Graphene nanoarchitecture anode for lithium ion batteries (LIBs) is successfully fabricated through an easy approach. In this nanoarchitecture, the in-situ polymerized electronic conductive polyaniline (PAni) hydrogel, acting as “glue”, agglutinates tightly to both the silicon nanoparticles (SiNPs) and graphene sheets, forming efficient conductive networks with high elastic modulus and high tensile strength. This mechanically robust nanoarchitecture can endure the great volume change of silicon and retain structural stability during Li-ion insertion/extraction. The electrodes consisting of this 3D sandwich-like Si/Polyaniline/Graphene nanoarchitecture reveal excellent electrochemical performance. The progress made in this work provides an easy and scalable route for preparing Si-based anode materials with high performance for advanced LIBs.     

Failure Analysis of Authentic Stainless Steel Tubes in a Vertical Fixed Shell–Tube Heat Exchanger

Journal of Failure Analysis and Prevention - The vertical fixed shell–tube heat exchanger failed to work in one chemical plant, and the leakage of the heat exchanger tubes were found after...     

A comparison study of Taiwanese He-Yuan Architecture between the ethically spatial order and the condition of physical environment

Since the 21st century, problems such as global warming and energy depletion have become important issues to scientists and architects. The architectural design nowadays often relies on large amount of mechanical equipment to create a comfortable environment for the users. However, it burdens and deteriorates the nature. On the other hand, some of the traditional architecture in the past can cope with the local humid and hot climate, achieving good passive heat control for the environment. Therefore, this study explores the relation between traditional residents in Taiwan’s use of space and the external environment and climate through modern environment measurement technique, restores and conducts quantitative analysis on the interior thermal environment and light environment of Lin-An-Tai Historical House in the past through Ecotect Analysis, and analyzes the results of the calculation in terms of its spatial allocation, openings, and outer walls, etc. This study also evaluates the effects of lighting and user’s sense of comfortable temperature under its environmental conditions according to the standards of residential quality nowadays. It further studies the ancestor of traditional architecture by reviewing its spatial order and compares to the current situation in order to feedback the modern architecture design. Part of the results of the simulation show that the variation of temperature indoors in each space is less dynamic than that of outdoors. The temperature in the space at the right of the main hall (northwestern side) is generally higher than that in the left (southeastern side). The highest temperature in the space farther away from the interior patio is usually higher than that in the space closer to the interior patio. The temperature near the outer side of the space above Hulong is higher than that in the middle. Accordingly, the location is closely related to the interior temperature. As to human’s sense of comfortable temperature, the results show that in summer, the Predicted Mean Vote (PMV) in the space at the left of the main hall (southeastern side) is generally higher than that in the right (northwestern side). In winter, the sense of comfortable temperature in the rooms in the corner is lower than that in other rooms at the inner side, the comparison between the space ethical order and the evaluation result did not show any obvious relationship. For the evaluation of lighting, the main hall and the restaurant at the outer left Hulong have better lighting while other space does not have sufficient and even lighting. Artificial lighting is needed to make the space more functional, the results shows that lighting conditions of space did not metaphor to the space ethical order.     

Test sample allocation method for testability verification test

An extended failure mode effect and criticality analysis (FMECA)-based sample allocation method for testability verification is presented in this study to deal with the poor representativeness of test sample sets and the randomness of the testability evaluation results caused by unreasonable selection of failure samples. First, the fault propagation intensity is introduced as part of the extended information of FMECA, and the sample allocation impact factors of component units and failure modes are determined under this framework. Then, the failure mode similarity and impact factor support are defined, and the game decision method for weighing the relationship between similarity and support is proposed to obtain the weight of failure mode impact factor. Finally, a two-step allocation framework of test samples is formulated to realize the sample allocation of component units and failure modes. This method is applied to the testability verification test of a launch control system. Results show that this method can obtain more representative test samples compared with the traditional sample allocation method while effectively reducing randomness of single testability evaluation result.     

An Artificial Skyrmion Platform with Robust Tunability in Synthetic Antiferromagnetic Multilayers

Magnetic skyrmions are topologically nontrivial spin structures, and their existence in ferromagnetically coupled multilayers has been widely reported with a disordered arrangement. Here, a nucleation scenario of ordered skyrmions in nanostructured synthetic antiferromagnetic (SAF) multilayers is proposed and experimentally demonstrated using direct magnetization imaging, indirect magnetometer and magnetoresistance measurement, and micromagnetic simulation. Instead of relying on Dzyaloshinskii–Moriya interaction, the antiferromagnetic interlayer exchange coupling in the SAF multilayers fulfills the role of nucleation and stabilization of skyrmions. The robustness of the proposed skyrmion nucleation scenario is examined against temperature from 4.5 to 300 K and device size from 400 to 1200 nm. Interestingly, these synthetic skyrmions still behave well with a size less than 100 nm. The higher stability than generic magnetic domains can be attributed to topological protection. The results thus provide an artificial skyrmion platform to meet the functional needs of high density and designable arrangement in magnonic and spintronic applications.