Uniting tensile ductility with ultrahigh strength via composition undulation.

Metals with nanocrystalline grains have ultrahigh strengths approaching two gigapascals. However, such extreme grain-boundary strengthening results in the loss of almost all tensile ductility, even when the metal has a face-centred-cubic structure-the most ductile of all crystal structures1-3. Here we demonstrate that nanocrystalline nickel-cobalt solid solutions, although still a face-centred-cubic single phase, show tensile strengths of about 2.3 gigapascals with a respectable ductility of about 16 per cent elongation to failure. This unusual combination of tensile strength and ductility is achieved by compositional undulation in a highly concentrated solid solution. The undulation renders the stacking fault energy and the lattice strains spatially varying over length scales in the range of one to ten nanometres, such that the motion of dislocations is thus significantly affected. The motion of dislocations becomes sluggish, promoting their interaction, interlocking and accumulation, despite the severely limited space inside the nanocrystalline grains. As a result, the flow stress is increased, and the dislocation storage is promoted at the same time, which increases the strain hardening and hence the ductility. Meanwhile, the segment detrapping along the dislocation line entails a small activation volume and hence an increased strain-rate sensitivity, which also stabilizes the tensile flow. As such, an undulating landscape resisting dislocation propagation provides a strengthening mechanism that preserves tensile ductility at high flow stresses.

Improvements of Corrosion Resistance and Antibacterial Properties of Hydroxyapatite/Cupric Oxide Doped Titania Composite Coatings on Degradable Magnesium Alloys.

The excellent biocompatibility of calcium phosphate (CaP) coatings makes them widely used in magnesium (Mg) alloy orthopedic implant materials. However, the porous morphology of CaP coatings limits their corrosion resistance. A cupric oxide (CuO) doped titania (TiO2) sol-gel coating is prepared on a porous hydroxyapatite (HA) coating. According to electrochemical test results, the HA/CuO-TiO2 coating obtains a current density of 6 × 10-4 mA/cm2, lower than that of the Mg alloy (2.6 × 10-2 mA/cm2). The hydrogen evaluation of the HA/CuO-TiO2 coating is only 1/12 that of the Mg alloy after immersion for 7 days. In addition, the HA/CuO-TiO2 coating has an antibacterial rate of 99.5 ± 0.4% against Staphylococcus aureus, significantly higher than that of the HA coating (19.8 ± 0.3%) and HTC0 coating (38.4 ± 0.5%). The CuO doped composite coating has no adverse effect or cytotoxicity on cell proliferation (cell viability ≥79.6%). Hence, the HA/CuO-TiO2 composite coating is useful for enhancing the corrosion resistance and antibacterial properties of Mg alloys while ensuring cytocompatibility. The HA/CuO-TiO2 coated AZ60 Mg alloy can meet the requirements of clinical application.

Ni Foam-Ni3 S2 @Ni(OH)2 -Graphene Sandwich Structure Electrode Materials: Facile Synthesis and High Supercapacitor Performance.

A novel Ni foam-Ni3 S2 @Ni(OH)2 -graphene sandwich-structured electrode (NF-NN-G) with high areal mass loading (8.33 mg cm-2 ) has been developed by sulfidation and hydrolysis reactions. The conductivity of Ni3 S2 and Ni(OH)2 were both improved. The upper layer of Ni(OH)2 , covered with a thin graphene film, is formed in situ from the surface of the lower layer of Ni3 S2 , whereas the Ni3 S2 grown on Ni foam substrate mainly acts as a rough support bridging the Ni(OH)2 and Ni foam. The graphene stabilized the Ni(OH)2 and the electrochemical properties were effectively enhanced. The as-synthesized NF-NN-G-5mg electrode shows a high specific capacitance (2258 F g-1 at 1 A g-1 or 18.81 F cm-2 at 8.33 mA cm-2 ) and an outstanding rate property (1010 F g-1 at 20 Ag-1 or 8.413 F cm-2 at 166.6 mA cm-2 ). This result is around double the capacitance achieved in previous research on Ni3 S2 @Ni(OH)2 /3DGN composites (3DGN=three-dimensional graphene network). In addition, the as-fabricated NF-NN-G-5mg composite electrode has an excellent cycle life with no capacitance loss after 3000 cycles, indicating a potential application as an efficient electrode.

Role of edge geometry and magnetic interaction in opening bandgap of low-dimensional graphene.

By using a size-dependent cohesive energy formula for two-dimensional coordination materials, the bandgap openings of ideal graphene quantum dots (GQDs) and nanoribbons (GNRs) have been investigated systematically regarding dimension, edge geometry, and magnetic interaction. Results demonstrate that the bandgap openings in GQDs can be dominated by the change of atomic cohesive energy. Relative to zigzag GQDs, the openings in the armchair ones are more substantial, attributed to its edge instability. The change of cohesive energy can also lead to bandgap openings in zigzag and armchair GNRs. The contribution from the interedge magnetic interaction in zigzag GNRs is negligible, while the cohesive-energy induced openings in armchair GNRs can oscillate according to the so-called full-wavelength effect, depending on the width. The model prediction provides physicochemical insight into the bandgap openings in graphene.

Synthesis of a thin-layer MnO2 nanosheet-coated Fe3O4 nanocomposite as a magnetically separable photocatalyst.

A facile hydrothermal method combined with a mild ultrasonic means has been developed for the fabrication of a magnetically recyclable thin-layer MnO2 nanosheet-coated Fe3O4 nanocomposite. The photocatalytic studies suggest that the MnO2/Fe3O4 nanocomposite shows excellent photocatalytic efficiency and stability simultaneously for the degradation of methylene blue under UV-vis light irradiation. Moreover, its good acid resistance and stable recyclability are very important for its future practical application as a photocatalyst. Magnetic measurements verify that the MnO2/Fe3O4 nanocomposite possesses a ferromagnetic nature, which can be effectively separated for reuse by simply applying an external magnetic field after the photocatalytic reaction. This novel composite material may have potential applications in water treatment, degradation of dye pollutants, and environmental cleaning.

Effect of Strontium-Substituted Calcium Phosphate Coatings Prepared by One-Step Electrodeposition at Different Temperatures on Corrosion Resistance and Biocompatibility of AZ31 Magnesium Alloys.

As potential degradable biomaterials, magnesium (Mg) alloys have development prospects in the field of orthopedic load-bearing, whereas the clinical application has encountered a bottleneck due to a series of problems caused by its rapid corrosion. In this study, strontium-substituted calcium phosphate (CaP) coatings with different structures were prepared on the surface of the Mg matrix by a simple one-step electrodeposition method at different temperatures, which enhanced the poor corrosion resistance of the Mg matrix. The coated sample prepared at 65 °C reduced the corrosion current density by 3 orders of magnitude and increased the impedance by nearly 2 orders of magnitude compared with bare Mg alloy, thanks to its dense fibrous structure similar to that of natural bones. Although the coating composition varies with different preparation temperatures, CaP, as an inorganic component similar to natural bone, has good cytocompatibility. Doping the right amount of strontium, which is a trace element in human bones, is beneficial to stimulate osteoblast differentiation, inhibit the activity of osteoclasts, and induce the formation of bone tissues. This provides a new option for modifying the Mg alloy with CaP coatings as a base.

Stearic Acid Treatment Enhancing Corrosion Resistance of Biomimetic-Deposited Calcium Phosphate Dihydrate Coating on Medical Degradable Magnesium Alloy.

Magnesium (Mg) alloys, a degradable material, have been studied for medical applications due to their excellent mechanical and chemical properties. However, their applications are limited by rapid corrosion. In this work, stearic acid and sodium stearate were used to treat the silane-induced calcium phosphate dihydrate coating to improve its protection for the Mg alloy further without changing the bone-like structure of calcium phosphate. The different effects of stearic acid treatment and sodium stearate treatment were compared. Electrochemical test and immersion test results confirmed that the corrosion resistance of the stearic acid-treated composite coating was greatly enhanced with a reduced corrosion current density by 3 orders of magnitude and hydrogen evolution reduced to 1/25 after 14 days. The stearic acid-treated coating also exhibited improved in vitro biocompatibility corroborated by promoted cell viability and better cell morphology.

Corrosion Resistance and Biocompatibility of Calcium Phosphate Coatings with a Micro-Nanofibrous Porous Structure on Biodegradable Magnesium Alloys.

Magnesium (Mg) and its alloys have exhibited great potential for orthopedic applications; however, their poor corrosion resistance and potential cytotoxicity have hindered their further clinical applications. In this study, we prepared a calcium phosphate (Ca-P) coating with a micro-nanofibrous porous structure on the Mg alloy surface by a chemical conversion method. The morphology, composition, and corrosion performance of the coatings were investigated by scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), immersion tests, and electrochemical measurements. The effects of the preparation temperature of the Ca-P coatings were analyzed, and the results confirmed that the coating obtained at 60 °C had the densest structure and the best corrosion resistance. In addition, a systematic investigation into cell viability, ALP activity, and cell morphology confirmed that the Ca-P coating had excellent biocompatibility, which could effectively promote the proliferation, differentiation, and adhesion of osteoblasts. Hence, the Ca-P coating demonstrates great potential in the field of biodegradable Mg-based orthopedic implant materials.

Interface Engineering of CoP3/Ni2P for Boosting the Wide pH Range Water-Splitting Activity.

Developing electrocatalysts with low price, high energy efficiency, and universal pH value for hydrogen/oxygen evolution reaction (HER and OER) is very important for the wide application of electrochemical water splitting in hydrogen production. The results of density functional theory show that the interface region of CoP3/Ni2P heterostructures can significantly boost all of the catalytic performances. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the abundant structural defects and the corresponding adjustment of the electronic state, thus ameliorating the activation energy, conductivity, and active area of the catalyst. Benefiting from these, CoP3/Ni2P heterostructures exhibit superior performance of both HER and OER in a wide pH range. CoP3/Ni2P can also be used for water splitting (1.557 V at 10 mA cm-2) more than 40 h, superior to benchmark pairs of Pt/C and RuO2 on Ni foam.

The microstructure, mechanical properties, corrosion performance and biocompatibility of hydroxyapatite reinforced ZK61 magnesium-matrix biological composite.

Magnesium (Mg)-based composites, as biomaterials, have attracted widespread attention due to their adjustable mechanical properties like elastic modulus, ductility, ultimate tensile strength, and corrosion resistance. In this study, hydroxyapatite (HA) reinforced ZK61 Mg-matrix composites were prepared by powder metallurgy and hot extrusion methods. The influence of the content of HA (10 wt%, 20 wt%, and 30 wt%) on the microstructure, density, mechanical properties, corrosion property and biocompatibility were investigated. The results showed that the density and yield strength of the composites match those of natural bone. Moreover, the composite with 10 % HA (ZK61-10HA) exhibited the best corrosion resistance, as determined by the electrochemical measurement and immersion test in simulated body fluid (SBF) at 37 °C. In addition, the ZK61-10HA composite significantly enhanced the cell viability (≥78 %) compared with ZK61 alloy in vitro testing. It is demonstrated that the mechanical properties, corrosion resistance and biocompatibility of Mg alloy can be effectively controlled by adjusting the content of HA, which suggested that the ZK61-HA composites were promising candidates for degradable implant materials.

Thermodynamic analysis on wetting states and wetting state transitions of rough surfaces.

Determining the equilibrium wetting states and exploring the conditions and mechanisms of the wetting state transition from the Cassie-Baxter (CB) state to the Wenzel (W) state (CB-W transition) have been a central topic in the study of superhydrophobic behavior on rough or textured surfaces. Although considerable progress has been made, some issues regarding this topic are still not completely understood. In this study, a systematic thermodynamic analysis has been performed to address several key issues related to this topic. Generalized theoretical expressions for determining the equilibrium wetting states (the threshold Young contact angle of the CB region) and evaluating the stability of the CB state (the energy barrier separating the CB and W states and the critical pressure for the CB-W transition) have been derived. Applying these expressions to four types of surfaces built with protrusions in paraboloid, truncated cone, inverted truncated cone and flat-top pillar shapes, the wetting equilibrium and resultant wetting states have been studied. The physical meanings of the threshold Young contact angle, the roles and mechanisms of the energy barrier and critical pressure in stabilizing the CB state have been discussed. Finally, a general guidance for achieving robust superhydrophobicity on the studied surfaces has been given.

A multifunctional polypyrrole/zinc oxide composite coating on biodegradable magnesium alloys for orthopedic implants.

Magnesium (Mg) and its alloys exhibit great potential in clinical applications owing to the outstanding biological performance and excellent mechanical properties, whereas the quick corrosion rate in the physiological environment has limited their further clinical application. In this work, we designed and developed a multifunctional polypyrrole/zinc oxide (Ppy/ZnO) composite coating by cyclic voltammetry method, aiming to enhance the biocorrosion resistance, biocompatibility and antibacterial property of the Mg alloys. The electrochemical and immersion tests indicated that the corrosion resistance of the Mg alloy was improved significantly by the composite coating. A systematic in vitro investigation of cellular response confirmed that the composite coating significantly promoted the adhesion and proliferation of cells. In addition, the composite coating showed a remarkable antibacterial ability of 96.5 ±â€¯2.6 % against Escherichia coli (E.coli). The enhanced corrosion resistance, cytocompatibility, and antibacterial property of the Ppy/ZnO coated Mg alloy makes it a promising candidate as orthopedic implants material.

Charge Storage by Electrochemical Reaction of Water Bilayers Absorbed on MoS2 Monolayers.

It is well-known that in neutral and acidic aqueous electrolytes, MoS2 monolayers can store charges by adsorption of cations on to the electrode-electrolyte interface as its analog of graphene. Restricted by its low conductivity and the charge storage mechanism, the electrochemical performance of MoS2 monolayer supercapacitor electrode is not satisfactory. It is reported here that water bilayers absorbed on MoS2 monolayers can be involved in charge storage. One proton of each absorbed water molecule can intercalate/de-intercalate the water bilayers during charging/discharging in the alkaline aqueous electrolyte. For two water molecules are present for every Mo atom, the water bilayers can endow MoS2 monolayers an ultrahigh specific capacitance. In this paper, 1T phase MoS2 nanosheets with three monolayers were synthesized by hydrothermal reaction. It presents a specific capacitance of 1120 F g-1 at a current density of 0.5 A g-1 in KOH. As it is assembled with active carbon into a hybrid supercapacitor, the device has an energy density of 31.64 Wh kg-1 at a power density of 425 W kg-1, and gets a specific capacitance retention of 95.4% after 10,000 cycles at 2 A g-1.

Dual Superlyophobic Copper Foam with Good Durability and Recyclability for High Flux, High Efficiency, and Continuous Oil-Water Separation.

Traditional oil-water separation materials have to own ultrahigh or ultralow surface energy. Thus, they can only be wetted by one of the two, oil or water. Our experiment here demonstrates that the wettability in oil-water mixtures can be tuned by oil and water initially. Hierarchical voids are built on commercial copper foams with the help of hydrothermally synthesized titanium dioxide nanorods. The foams can be easily wetted by both oil and water. The water prewetted foams are superhydrophilic and superoleophobic under oil-water mixtures, meanwhile the oil prewetted foams are superoleophilic and superhydrophobic. In this paper, many kinds of water-oil mixtures were separated by two foams, prewetted by corresponding oil or water, respectively, combining a straight tee in a high flux, high efficiency, and continuous mode. This research indicates that oil-water mixtures can be separated more eco-friendly and at lower cost.

High Density Arrayed Ni/NiO Core-shell Nanospheres Evenly Distributed on Graphene for Ultrahigh Performance Supercapacitor.

A novel NiO/Ni/RGO three-dimensional core-shell architecture consisting of Ni nanoparticles as core, NiO as shell and reduced graphene oxide (RGO) as conductivity layer, has been constructed by redox reactions with hydrothermal method and heat treatment. High density arrayed nickel nanoparticles (20 nm diameter) semi-coated by a 3 nm thick layer of NiO are evenly distributed on the surface of graphene. This elaborate design not only uses abundant NiO surfaces to provide a wealth of active sites, but also bridges electrochemical active NiO shell and graphene by Ni core to construct an interconnected 3D conductive network. Since both electrochemical activity and excellent conductivity are reserved in this Ni/NiO core-shell/graphene layer 3D structure, the as-prepared electrode material exhibits an extremely high specific capacitance (2048.3 F g-1 at current density of 1 A g-1) and excellent cycle stability (77.8% capacitance retention after 10000 cycles at current density of 50 A g-1). The novel method presented here is easy and effective and would provide reference for the preparation of other high performance supercapacitor electrodes.

Facile Synthesis ZnS/ZnO/Ni(OH)2 Composites Grown on Ni Foam: A Bifunctional Materials for Photocatalysts and Supercapacitors.

A facile one-step hydrothermal reaction was employed to synthesis an integrated bifunctional composite composed by a network structure of ZnS/ZnO/Ni(OH)2 nanosheets with ZnS/ZnO nanospheres in situ growing on Ni foam. The synergistic effect of these three substances make the composite having both improved electrochemical performances and photocatalytic activity. The ZnS/ZnO/Ni(OH)2-4mmol shows a high specific capacitance of 1173.8 F g-1 at 1 A g-1, as well as good rate capability and relatively stable cyclability. Using as photocatalyst, the methyl orange dye in solution can be completely decomposed under ultraviolet-visible radiation in about 80 min. And the composite is easy to be repeatedly used because bulk Ni foam was used as a carrier. Such a bifunctional composite material provides a new insight for energy storage and utilization as well as the water pollution treatment.

A Strategy for Synthesis of Nanosheets Consisting of Alternating Spinel Li4Ti5O12 and Rutile TiO2 Lamellas for High-Rate Anodes of Lithium-Ion Batteries.

Ultrathin dual phase nanosheets consisting of alternating spinel Li4Ti5O12 (LTO) and rutile TiO2 (RT) lamellas are synthesized through a facile and scalable hydrothermal method, and the formation mechanism is explored. The thickness of constituent lamellas can be controlled exactly by adjusting the mole ratio of Li:Ti in the original reactants. Alternating insertion of the RT lamellas significantly improves the electrochemical performance of LTO nanosheets, especially at high charge/discharge rates. As anodes in lithium-ion batteries (LIBs), the dual phase nanosheet electrode with the optimized phase ratio can deliver stable discharge capacities of 178.5, 154.9, 148.4, 142.3, 138.2, and 131.4 mA h g-1 at current densities of 1, 10, 20, 30, 40, and 50 C, respectively. Meanwhile, they inherit the excellent cyclic stability of pure spinel LTO and exhibit a capacity retention of 93.1% even after 500 cycles at 50 C. Our results indicate that the alternating nanoscaled lamella structure is a good alternative to facilitate the transfer of both the Li ions and electrons into the spinel LTO, giving rise to an excellent cyclability and fast rate performance. Therefore, the newly prepared carbon-free LTO-RT nanosheets with high safety provide a new opportunity to develop high-power anodes for LIBs.

Robust superhydrophobic surface on Al substrate with durability, corrosion resistance and ice-phobicity.

Practical application of superhydrophobic surfaces is limited by the fragility of nanoscale asperities. Combining chemical etching and anodization, microscale pits and nanoscale pores, instead of the micro and nano protrusions on traditional superhydrophobic surfaces mimicking Lutos leaves, were fabricated on commercially pure aluminum surfaces. After modified by FDTS, the surfaces were superhydrophobic and self-cleaning. The ultrahigh hardness and electrochemical stability of Al2O3 coating endowed the surface excellent mechanical durability and good corrosion resistance. Because the method is scalable, it may find practical application on body panels of automobiles and aircrafts and so on.

High Efficient Photo-Fenton Catalyst of α-Fe2O3/MoS2 Hierarchical Nanoheterostructures: Reutilization for Supercapacitors.

A novel three-dimensional (3D) α-Fe2O3/MoS2 hierarchical nanoheterostructure is effectively synthesized via a facile hydrothermal method. The zero-dimensional (0D) Fe2O3 nanoparticles guide the growth of two-dimensional (2D) MoS2 nanosheets and formed 3D flower-like structures, while MoS2 facilitates the good dispersion of porous Fe2O3 with abundant oxygen vacancies. This charming 3D-structure with perfect match of non-equal dimension exhibits high recyclable photo-Fenton catalytic activity for Methyl orange pollutant and nice specific capacity in reusing as supercapacitor after catalysis. The synergistic effect between Fe2O3 and MoS2, the intermediate nanointerfaces, the 3D porous structures, and the abundant oxygen vacancies both contribute to highly active catalysis, nice electrochemical performance and stable cycling. This strategy is simple, cheap, and feasible for maximizing the value of the materials, as well as eliminating the secondary pollution.

Improvement of the Biodegradation Property and Biomineralization Ability of Magnesium-Hydroxyapatite Composites with Dicalcium Phosphate Dihydrate and Hydroxyapatite Coatings.

The application of calcium phosphate reinforced magnesium matrix composites has not achieved the expected effect to control the degradation rate of magnesium so far. Therefore, in order to enhance the corrosion resistance and further develop the surface bioactivity of the composites to meet specific requirements of bone tissue engineering applications, biocompatible dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HA) coatings have been deposited on homemade HA/Mg composites using a simple conversion coating method and a subsequent alkali post-treatment, respectively. The conversion coating mechanism was studied by comparing coating processes on the composites, pure Mg, and an AZ60 Mg alloy. Electrochemical results showed that polarization resistance of the optimum DCPD and HA coatings was about 15 and 65 times higher than that of the composites, respectively. Immersion tests in simulated body fluid revealed that both coatings could supply improved corrosion resistance and biomineralization ability for the HA/Mg composites.