A counter-gravity casting system for in situ high-speed synchrotron x-ray imaging characterization.

Counter-gravity casting (CGC) aims to eliminate turbulent melt flow and defect formation during filling and subsequent solidification by pushing high-temperature melt into the mold cavity against gravity with regulated pressure. However, limited by the opaqueness of molten metals and the complexity of the CGC apparatus, it is extremely difficult to directly quantify the high-velocity mold filling and pressurized solidification in real-time. Here, we report the design and characterization of a CGC system capable of in situ monitoring of mold filling and subsequent solidification processes in the synchrotron beamlines by deploying a high-energy, high-speed synchrotron x-ray imaging technique. The high-velocity melt flow and dendrite growth during pressurized solidification have been quantified for systematical process parameter analysis by investigating time-resolved x-ray images of an exemplary Al-Cu alloy. The high-speed imaging results demonstrate that the in situ CGC system provides a useful way to better understand the fundamentals of mold filling, pressurized solidification, and experimental inputs for high-fidelity modeling in scientific and industrial applications.

Air-Stable Binary Hydrated Eutectic Electrolytes with Unique Solvation Structure for Rechargeable Aluminum-Ion Batteries.

Aluminum-ion batteries (AIBs) have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve, light weight, low cost, and good safety of Al. However, the development of AIBs faces challenges due to the usage of AlCl3-based ionic liquid electrolytes, which are expensive, corrosive, and sensitive to humidity. Here, we develop a low-cost, non-corrosive, and air-stable hydrated eutectic electrolyte composed of aluminum perchlorate nonahydrate and methylurea (MU) ligand. Through optimizing the molar ratio to achieve the unique solvation structure, the formed Al(ClO4)3·9H2O/MU hydrated deep eutectic electrolyte (AMHEE) with an average coordination number of 2.4 can facilely realize stable and reversible deposition/stripping of Al. When combining with vanadium oxide nanorods positive electrode, the Al-ion full battery delivers a high discharge capacity of 320 mAh g-1 with good capacity retention. The unique solvation structure with a low desolvation energy of the AMHEE enables Al3+ insertion/extraction during charge/discharge processes, which is evidenced by in situ synchrotron radiation X-ray diffraction. This work opens a new pathway of developing low-cost, safe, environmentally friendly and high-performance electrolytes for practical and sustainable AIBs.

Regulation of Atomic Fe-Spin State by Crystal Field and Magnetic Field for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

Highly-active and low-cost bifunctional electrocatalysts for oxygen reduction and evolution are essential in rechargeable metal-air batteries, and single atom catalysts with Fe-N-C are promising candidates. However, the activity still needs to be boosted, and the origination of spin-related oxygen catalytic performance is still uncertain. Herein, an effective strategy to regulate local spin state of Fe-N-C through manipulating crystal field and magnetic field is proposed. The spin state of atomic Fe can be regulated from low spin to intermediate spin and to high spin. The cavitation of dxz and dyz orbitals of high spin FeIII can optimize the O2 adsorption and promote the rate-determining step (*O2 to *OOH). Benefiting from these merits, the high spin Fe-N-C electrocatalyst displays the highest oxygen electrocatalytic activities. Furthermore, the high spin Fe-N-C-based rechargeable zinc-air battery displays a high power density of 170 mW cm-2 and good stability.

Phenoxazine Polymer-based p-type Positive Electrode for Aluminum-ion Batteries with Ultra-long Cycle Life.

Aluminum-ion batteries (AIBs) are a promising candidate for large-scale energy storage due to the abundant reserves, low cost, good safety, and high theoretical capacity of Al. However, AIBs with inorganic positive electrodes still suffer from sluggish kinetics and structural collapse upon cycling. Herein, we propose a novel p-type poly(vinylbenzyl-N-phenoxazine) (PVBPX) positive electrode for AIBs. The dual active sites enable PVBPX to deliver a high capacity of 133 mAh g-1 at 0.2 A g-1 . More impressively, the expanded π-conjugated construction, insolubility, and anionic redox chemistry without bond rearrangement of PVBPX for AIBs contribute to an amazing ultra-long lifetime of 50000 cycles. The charge storage mechanism is that the AlCl4 - ions can reversibly coordinate/dissociate with the N and O sites in PVBPX sequentially, which is evidenced by both experimental and theoretical results. These findings establish a foundation to advance organic AIBs for large-scale energy storage.

Atomically Dispersed Iron Active Sites Promoting Reversible Redox Kinetics and Suppressing Shuttle Effect in Aluminum-Sulfur Batteries.

Rechargeable aluminum-sulfur (Al-S) batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity, good safety, abundant natural reserves, and low cost of Al and S. However, the research progress of Al-S batteries is limited by the slow kinetics and shuttle effect of soluble polysulfides intermediates. Herein, an interconnected free-standing interlayer of iron single atoms supported on porous nitrogen-doped carbon nanofibers (FeSAs-NCF) on the separator is developed and used as both catalyst and chemical barrier for Al-S batteries. The atomically dispersed iron active sites (Fe-N4) are clearly identified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption near-edge structure. The Al-S battery with the FeSAs-NCF shows an improved specific capacity of 780 mAh g-1 and enhanced cycle stability. As evidenced by experimental and theoretical results, the atomically dispersed iron active centers on the separator can chemically adsorb the polysulfides and accelerate reaction kinetics to inhibit the shuttle effect and promote the reversible conversion between aluminum polysulfides, thus improving the electrochemical performance of the Al-S battery. This work provides a new way that can not only promote the conversion of aluminum sulfides but also suppress the shuttle effect in Al-S batteries.

In situ atomic-scale observation of dislocation climb and grain boundary evolution in nanostructured metal.

Non-conservative dislocation climb plays a unique role in the plastic deformation and creep of crystalline materials. Nevertheless, the underlying atomic-scale mechanisms of dislocation climb have not been explored by direct experimental observations. Here, we report atomic-scale observations of grain boundary (GB) dislocation climb in nanostructured Au during in situ straining at room temperature. The climb of a edge dislocation is found to occur by stress-induced reconstruction of two neighboring atomic columns at the edge of an extra half atomic plane in the dislocation core. This is different from the conventional belief of dislocation climb by destruction or construction of a single atomic column at the dislocation core. The atomic route of the dislocation climb we proposed is demonstrated to be energetically favorable by Monte Carlo simulations. Our in situ observations also reveal GB evolution through dislocation climb at room temperature, which suggests a means of controlling microstructures and properties of nanostructured metals.

Challenges and Strategies of Low-Cost Aluminum Anodes for High-Performance Al-Based Batteries.

The ever-growing market of electric vehicles and the upcoming grid-scale storage systems have stimulated the fast growth of renewable energy storage technologies. Aluminum-based batteries are considered one of the most promising alternatives to complement or possibly replace the current lithium-ion batteries owing to their high specific capacity, good safety, low cost, light weight, and abundant reserves of Al. However, the anode problems in primary and secondary Al batteries, such as, self-corrosion, passive film, and volume expansion, severely limit the batteries' practical performance, thus hindering their commercialization. Herein, an overview of the currently emerged Al-based batteries is provided, that primarily focus on the recent research progress for Al anodes in both primary and rechargeable systems. The anode reaction mechanisms and problems in various Al-based batteries are discussed, and various strategies to overcome the challenges of Al anodes, including surface oxidation, self-corrosion, volume expansion, and dendrite growth, are systematically summarized. Finally, future research perspectives toward advanced Al batteries with higher performance and better safety are presented.

Ultrasound cavitation induced nucleation in metal solidification: An analytical model and validation by real-time experiments.

Microstructural refinement of metallic alloys via ultrasonic melt processing (USMP) is an environmentally friendly and promising method. However, so far there has been no report in open literature on how to predict the solidified microstructures and grain size based on the ultrasound processing parameters.In this paper, an analytical model is developed to calculate the cavitation enhanced undercooling and the USMP refined solidification microstructure and grain size for Al-Cu alloys. Ultrafast synchrotron X-ray imaging and tomography techniques were used to collect the real-time experimental data for validating the model and the calculated results. The comparison between modeling and experiments reveal that there exists an effective ultrasound input power intensity for maximizing the grain refinement effects for the Al-Cu alloys, which is in the range of 20-45 MW/m2. In addition, a monotonous increase in temperature during USMP has negative effect on producing new nuclei, deteriorating the benefit of microstructure refinement due to the application of ultrasound.

First-Principles Study on the Cu/Fe Interface Properties of Ternary Cu-Fe-X Alloys.

The supersaturated Fe in Cu is known to reduce the electrical conductivity of Cu severely. However, the precipitation kinetics of Fe from Cu are sluggish. Alloying is one of the effective ways to accelerate the aging precipitation of Cu-Fe alloys. Nucleation plays an important role in the early stage of aging. The interface property of Cu/γ-Fe is a key parameter in understanding the nucleation mechanism of γ-Fe, which can be obviously affected with the addition of alloying elements. In this paper, first principles calculations were carried out to investigate the influence of alloying elements on the interface properties, including the geometric optimizations, interfacial energy, work of adhesion and electronic structure. Based on the previous research, 14 elements including B, Si, P, Al, Ge, S, Mg, Ag, Cd, Sn, In, Sb, Zr and Bi were selected for investigation. Results showed that all these alloying elements tend to concentrate in the Cu matrix with the specific substitution position of the atoms determined by the binding energy between Fe and alloy element (X). The bonding strength of the Cu/γ-Fe interface will decrease obviously after adding Ag, Mg and Cd, while a drop in interfacial energy of Cu/γ-Fe will happen when alloyed with Al, B, S, P, Si, Ge, Sn, Zr, Bi, Sb and In. Further study of the electronic structure found that Al and Zr were not effective alloying elements.

Design of high-ductile medium entropy alloys for dental implants.

Developing new materials with high strength and ductility, low modulus and high biocompatibility is a continuing demand in the field of surgical implants. Inspired by the high-entropy design philosophy, two medium entropy alloys (MEAs), i.e. equiatomic TiZrHf and equi-weight Ti40Zr20Hf10Nb20Ta10 were designed and their mechanical properties and biocompatibility were assessed. Both the single-phase hexagonal close-packed (HCP) structured TiZrHf alloy and the single-phase body-centered cubic (BCC) structured Ti40Zr20Hf10Nb20Ta10 alloy show high strength-ductility combinations close to commercial Ti-6Al-4V wrought alloy and remarkably lower young's modulus than commercial pure titanium (CP-Ti) and Ti-6Al-4V. From the aspects of adhesion, proliferation, toxicity and related gene expression of human gingival fibroblasts (HGFs), the Ti40Zr20Hf10Nb20Ta10 alloy exhibits distinctively better biocompatibility than that of CP-Ti while the TiZrHf shows only slightly better biocompatibility as compared with CP-Ti. These results indicate that these two ductile MEAs are potential candidates for dental application.

Microstructure and properties of TC4/TNTZO multi-layered composite by direct laser deposition.

In this work, TC4/TNTZO multi-layered composite as well as TNTZO and TC4 alloys were prepared by direct laser deposition (DLD) to investigate the microstructure, mechanical properties and in vitro bioactivity. The microstructure characterization shows that the multi-layered material is free of cracks and intermetallics while the interface is metallurgically bonded. The fine microstructure was observed in TC4 layer of the TC4/TNTZO multi-layered material, and a large amount of α' martensite exists in the transition zone. Different from the single ß phase cellular arrays in the DLD-ed TNTZO alloy, α″ martensite with high volume content formed at the cellular grain boundary in TNTZO zone of DLD-ed TC4/TNTZO. The elastic modulus of the DLD-ed TC4/TNTZO is 64 GPa, decreased about 45% compared to the DLD-ed TC4. The tensile yield strength and elongation along the printing direction are up to 789 MPa and 7%, which are 12% higher than the tensile yield strength of DLD-ed TNTZO and 61% higher than the elongation of DLD-ed TC4 respectively. Moreover, the DLD-ed TC4/TNTZO shows good in vitro bioactivity. The TC4/TNTZO multi-layered composite fabricated by DLD can be regarded as a potential candidate to integrate the advantages of the two Ti-base alloys for application in the biomedical field.

Reversible Photodriven Droplet Motion on Ti3C2 MXene Film for Diverse Liquids.

The manipulation of liquid droplets on a specific surface with reversible wettability is of great importance for various applications from science to industry. Herein, the concept of a smart, flexible photodriven droplet motion (PDM) device with programmable wettability is designed using the 2D material of MXene film. Because of the MXene photothermal property, the Vaseline layer in the device is in transition between solid and liquid states under the heat transformation due to light illumination, thus attractively producing a reversible wettability for liquid motion with respect to sliding and pinning. Multifarious pathways for liquid motion could be designed through the flexibility of light illumination, which is a revolutionary enhancement in diverse liquid motion to form the desired pathways. In addition, we demonstrated liquid motion under illumination of the back face, which has a profound influence on applications, such as microfluidic systems, microengines, and liquid manipulation.

Integrated and Binder-Free Air Cathodes of Co3 Fe7 Nanoalloy and Co5.47 N Encapsulated in Nitrogen-Doped Carbon Foam with Superior Oxygen Reduction Activity in Flexible Aluminum-Air Batteries.

All-solid-sate Al-air batteries with features of high theoretical energy density, low cost, and environmental-friendliness are promising as power sources for next-generation flexible and wearable electronics. However, the sluggish oxygen reduction reaction (ORR) and poor interfacial contact in air cathodes cause unsatisfied performance. Herein, a free-standing Co3 Fe7 nanoalloy and Co5.47 N encapsulated in 3D nitrogen-doped carbon foam (Co3 Fe7 @Co5.47 N/NCF) is prepared as an additive-free and integrated air cathode for flexible Al-air batteries in both alkaline and neutral electrolytes. The Co3 Fe7 @Co5.47 N/NCF outperforms commercial platinum/carbon (Pt/C) toward ORR with an onset potential of 1.02 V and a positive half-wave potential of 0.92 V in an alkaline electrolyte (0.59 V in sodium chloride solution), which is ascribed to the unique interfacial structure between Co3 Fe7 and Co5.47 N supported by 3D N-doped carbon foam to facilitate fast electron and mass transfer. The high ORR performance is also supported by in-situ electrochemical Raman spectra and density functional theory calculation. Furthermore, the fabricated Al-air battery displays good flexibility and delivers a power density of 199.6 mW cm-2 , and the binder-free and integrated cathode shows better discharge performance than the traditionally slurry casting cathode. This work demonstrates a facile and efficient approach to develop integrated air cathode for metal-air batteries.

Effects of the γ″-Ni3Nb Phase on Fatigue Behavior of Nickel-Based 718 Superalloys with Different Heat Treatments.

The effects of the γ″-Ni3Nb phase on fatigue behavior of nickel-based 718 superalloys with standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging were investigated by scanning electron microscope, transmission electron microscopy, and fatigue experiments. The standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging resulted in the formation of more and smaller γ″ phases in the matrix in the nickel-based 718 superalloys. However, the grain boundaries of the hot isostatic pressing + direct aging sample showed many relatively coarse disk-like γ″ phases with major axes of ~80 nm and minor axes of ~40 nm. The hot isostatic pressing + direct aging sample with a stress amplitude of 380 MPa showed the longest high cycle fatigue life of 5.16 × 105 cycles. Laves phases and carbide inclusions were observed in the crack initiation zone, and the cracks propagated along the acicular δ phases in the nickel-based 718 superalloys. The precipitation of fine γ″ phases in the matrix and relatively coarse γ″ phases in the grain boundaries of the hot isostatic pressing + direct aging sample can hinder the movement of dislocation.

Investigation of Fused Alumina Based-Mold Facecoats for DZ22B Directionally Solidified Blades.

The interaction between alloy melt and mold facecoats is the main factor affecting the surface quality of investment casting nickel-based superalloys. An investigation was undertaken to develop suitable refractories as facecoat materials for the directionally solidified blades of DZ22B nickel-based superalloys in order to avoid a sand-burning defect. The wettability and interface reactions between alloy melt and various facecoats were studied by using a sessile drop experiment and the real investment casting method, respectively. The results show that by adding Cr2O3 powder with the amounts of 2 wt.%, 5 wt.% and 10 wt.% in the fused alumina-based facecoats, the wetting angles between the alloy melt and facecoats decreased from 105.40° to 100.37°, 99.96° and 98.11°, respectively, while the sand-burning defect on the casting blade surfaces still formed during the process of directional solidification. However, by adding h-BN powder in the fused alumina-based facecoats, the wetting angles between the alloy melt and facecoats dramatically increased, the sand-burning defect on the casting blade surfaces was effectively inhibited and a metallic luster on the directionally solidified blades could be obviously observed. In this study, the suitable composition of mold facecoats for the investment casting of blades is 2 wt.% h-BN added fused alumina.

Effects of the γ″-Ni3Nb Phase on Mechanical Properties of Inconel 718 Superalloys with Different Heat Treatments.

The effects of the γ″-Ni3Nb phase on the mechanical properties of Inconel 718 superalloys, with standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging, were characterized by morphological observation, X-ray diffraction, and tensile experiments. The results of the morphological observation revealed that many fine γ″ precipitates of ~26.49 ± 1.82 nm in mean size were formed in all samples. However, the relatively coarser γ″ precipitates formed in the grain boundaries were only observed in the sample treated with hot isostatic pressing + direct aging. The yield strengths of the hot isostatic pressing + direct aging sample at room temperature and at 650 °C both exhibited the maximum values about 993 ± 5.7 and 811 ± 12.6 MPa, respectively. The γ″ precipitate was considered to be the dominant strengthening phase in the sample according to the lattice misfits (ε) of γ/γ″. The strengthening mechanism of the samples can be explained as the coherency strain strengthening of fine γ″ precipitates. Moreover, due to the coarser γ″ precipitates in the grain boundaries, dislocation-cut ordered particle strengthening also occurred in the sample after hot isostatic pressing + direct aging treatment.

Design and production of a novel antimicrobial fusion protein in Escherichia coli.

In recent years, antimicrobial peptides (AMPs) have attracted increasing attention. The microbial cells provide a simple, cost-effective platform to produce AMPs in industrial quantities. While AMP production as fusion proteins in microorganisms is commonly used, the recovery of AMPs necessitates the use of expensive proteases and extra purification steps. Here, we develop a novel fusion protein DAMP4-F-pexiganan comprising a carrier protein DAMP4 linked to the AMP, pexiganan, through a long, flexible linker. We show that this fusion protein can be purified using a non-chromatography approach and exhibits the same antimicrobial activity as the chemically synthesized pexiganan peptide without any cleavage step. Activity of the fusion protein is dependent on a long, flexible linker between the AMP and carrier domains, as well as on the expression conditions of the fusion protein, with low-temperature expression promoting better folding of the AMP domain. The production of DAMP4-F-pexiganan circumvents the time-consuming and costly steps of chromatography-based purification and enzymatic cleavages, therefore shows considerable advantages over traditional microbial production of AMPs. We expect this novel fusion protein, and the studies on the effect of linker and expression conditions on its antimicrobial activity, will broaden the rational design and production of antimicrobial products based on AMPs.

Cost-effective downstream processing of recombinantly produced pexiganan peptide and its antimicrobial activity.

Antimicrobial peptides (AMPs) have significant potential as alternatives to classical antibiotics. However, AMPs are currently prepared using processes which are often laborious, expensive and of low-yield, thus hindering their research and application. Large-scale methods for production of AMPs using a cost-effective approach is urgently required. In this study, we report a scalable, chromatography-free downstream processing method for producing an antimicrobial peptide, pexiganan, using recombinant Escherichia coli (E. coli). The four helix bundle structure of the unique carrier protein DAMP4 was used to facilitate a simple and cheap purification process based on a selective thermochemical precipitation. Highly pure fusion protein DAMP4var-pexiganan was obtained at high yield (around 24 mg per 800 mL cell culture with a final cultivation OD600 ~ 2). The purification yield of DAMP4var-pexiganan protein is increased twofold with a 72.9% of the protein recovery in this study as compared to the previous purification processes (Dwyer in Chem Eng Sci 105:12-21, 2014). The antimicrobial peptide pexiganan was released and activated from the fusion protein by a simple acid-cleavage. Isoelectric precipitation was then applied to separate the pexiganan peptide from the DAMP4var protein carrier. The final yield of pure bio-produced pexiganan was 1.6 mg from 800 mL of bacterial cell culture (final cultivation OD600 ~ 2). The minimum bactericidal concentration (MBC) test demonstrated that the bio-produced pexiganan has the same antimicrobial activity as chemically synthesized counterpart. This novel downstream process provides a new strategy for simple and probable economic production of antimicrobial peptides.

Effect of Mg on the Microstructure and Corrosion Resistance of the Continuously Hot-Dip Galvanizing Zn-Mg Coating.

The microstructure of continuously hot-dip galvanizing Zn-Mg coating was investigated in order to obtain the mechanism of the effects of Mg on the corrosion resistance. In this paper, the vertical section of the Zn-0.20 wt % Al-Mg ternary phase diagram near the Al-low corner was calculated. The results indicates that the phase composition of the Zn-0.20 wt % Al-Mg ternary phase diagram near the Al-low corner is the same as Zn-Mg binary phase diagram, suggesting Al in the Zn-Mg (ZM) coatings mainly concentrates on the interfacial layer between the coating and steel substrate. The microstructure of continuously hot-dip galvanizing ZM coatings with 0.20 wt % Al containing 1.0-3.0 wt % Mg was investigated using tunneling electron microscopy (TEM). The morphology of Zn in the coating changes from bulk to strip and finally to mesh-like, and the MgZn2 changes from rod-like to mesh-like with the Mg content increasing. Al in the ZM coatings mainly segregates at the Fe2Al5 inhibition layer and the Mg added to the Zn bath makes this inhibition layer thinner and uneven. Compared to GI coating, the time of the first red rust appears increases by more than two-fold and expansion rate of red rust reduces by more than four-fold in terms of salt spray experiment. The ZM coating containing 2.0 wt % Mg has the best corrosion resistance. The enhanced corrosion resistance of ZM coatings mainly depends on different corrosion products.

Microstructure Evolution in High Purity Aluminum Single Crystal Processed by Equal Channel Angular Pressing (ECAP).

Aluminum single crystal with 99.999% purity was deformed at room temperature by equal channel angular pressing (ECAP) up to 16 passes. Grain size and misorientation of processed samples were quantitatively characterized by TEM and EBSD. The results show that the refinement efficiency of high purity aluminum single crystal was poor in the initial stage. Extrusion by fewer ECAP passes (n ≤ 8) resulted in only elongated grains containing a large number of subgrains and small misorientations between grains. Stable microstructures of nearly equiaxed grains with high misorientations were obtained by 15 passages, indicating that the initial extremely coarse grains and highly uniform grain orientation are not conducive to the accumulation of strain energy. The initial state of high purity aluminum has a significant effect on the refining efficiency of the ECAP process.