查看更多>>摘要：Amorphous metal-based catalysts(AMCs)have sparked intense research interests in the field of electro-catalysis elicited by their hallmark features such as unlimited volume and morphology,manipulated elec-tronic structures,enriched defects,and unsaturated surface atom coordination.Nevertheless,the manip-ulation of the amorphous phase in metal-based catalysts is so far impractical,and thus their electrocat-alytic mechanism yet remains ambiguous.In this review,the latest advances in AMCs are systematically reviewed,covering amorphous-phase engineering strategy,structure manipulation,and amorphization of various material categories for electrocatalysis.Specifically,a series of applications of AMCs in electro-catalysis for the oxygen reduction reaction(ORR),hydrogen evolution reaction(HER),and oxygen evo-lution reaction(OER)are summarized based on the classification criteria of substances.Finally,we put forward current challenges that have not yet been clarified in the field of AMCs,and propose possible solutions,particularly from the perspective of the evolution of electron microscopy.It is expected to pro-mote the understanding of the amorphization-catalysis relationship and provide a guideline for designing high-performance electrocatalysts.
查看更多>>摘要：Grain refinement is a well-recognized method to simultaneously increase the strength and ductility of metallic materials.Fabrication of ultrafine-grained metals in bulk using a simple low-cost approach is a long-term goal for material scientists.In this work,based on the chemical composition of a biomedical Ti-15Zr alloy,a series of novel Ti-15Zr-xCu(x=0,3,5,7 wt.％)alloys were designed and fabricated.The alloys were quenched in the single β phase region to obtain a martensitic microstructure and deformed in the temperature range of 710-750℃to obtain an ultrafine-grained microstructure through marten-site decomposition under thermomechanical coupling conditions.Experimental results showed that Cu alloying could increase the dynamic recrystallization(DRX)nucleation rate due to its role in both re-fining martensitic lath width and increasing dislocation density.Cu alloying could also suppress grain growth due to the precipitated Ti2Cu particles exerting pinning forces on the grain boundaries.The op-timal Cu content in the Ti-15Zr-xCu alloy was determined to be 5 wt.％.After being subjected to a com-pression leading to a 70％height reduction at 730℃and 1 s-1,the grain size of the Ti-15Zr-5Cu alloy was only 180±70 nm.The tensile strength of the as-prepared alloy reached 975±10 MPa,which was 45％higher than that of the conventional Ti-15Zr alloy(673±16 MPa).This increase in strength was achieved without any reduction in ductility.The comprehensive mechanical properties of the ultrafine-grained Ti-15Zr-5Cu alloy are better than that of the Roxolid Ti-Zr alloy currently used for dental implants.
查看更多>>摘要：Additive manufacturing(AM),also called three-dimensional(3D)printing,has been developed to obtain energetic materials within the past decade.3D printing represents a family of flexible manufacturing techniques that enable fast and accurate fabrication of structures with complex 3D features and a broad range of sizes,from submicrometer to several meters.Various methods have already been explored,in-cluding templating,melting extrusion,inkjet printing and electrospray methods.It was demonstrated that the structure achieved by AM could be used to manipulate the reactivity of energetic or reactive mate-rials by changing the flow of gases and entrained particles via architecture.By employing different AM techniques,energetic materials with controllable nanostructures and uniformly dispersed ingredients can be prepared.It is exciting to tailor the energy release without defaulting to change the formulation of the conventional method.The combustion and mechanical properties of conventional energetic materials can be retained at the same time.In this review,the preparation and characterization of AM energetic materials that have been developed in the last decade are summarized.Various AM techniques used in the fabrication of energetic materials are compared and discussed.In particular,formulations of energetic materials applied in AM,metallic fuels,binders and energetic fillers and their advantages in terms of combustion efficiency and other properties are proposed.
查看更多>>摘要：Environment and energy are the eternal hot topics in the world,multiloculated microscale materials have attracted great attention in the field of electromagnetic interference(EMI)shielding and lithium ions storage.Herein,a novel flower-like NiFe2O4/graphene composite with adjustable structure was fabricated as EMI shielding material and anode material of lithium-ion batteries.NiFe2O4/graphene composite is a potential green EMI shielding material.The EMI shielding effectiveness(SE)increases with the increase of graphene content in NiFe204/graphene composite,and the total EMI SE of NiFe204/graphene with 73.6 wt.％graphene increases from 26.5 to 40.6 dB with the increase of frequency in 2-18 GHz.Furthermore,it exhibits long-life and large capacity lithium storage performance at high current density.The capacity reaches 732.79 mAh g-1 after 100 cycles at 0.1 A g-1,recovering to more than 139％from the minimum capacity value.After 300 cycles at 0.5 A g-1,the capacity increases to 688.5 mAh g-1.The initial capacities at 2 and 5 A g-1 are 704.9 and 717.8 mAh g-1,and remain 297.9 and 203.2 mAh g-1 after 1000 cycles.The distinguished EMI shielding performance and electrochemical performance are mainly ascribed to the structure regulation of NiFe2O4/graphene composite,as well as the synergistic effect of graphene and NiFe2O4.This research opens up infinite opportunities for the application of multifunctional and interdisciplinary materials.
查看更多>>摘要：The selective laser melting(SLM)with subsequent cold rolling and annealing is used to produce high-density lattice defects and grain refinement in the CoCrNi medium-entropy alloys(MEAs).The superior comprehensive mechanical properties have been achieved in the as-SLMed CoCrNi alloy after rolling and annealing.The as-SLMed alloys delivered the yield strength of 693.4 MPa,the ultimate tensile strength of 912.7 MPa and the fracture strain of 54.4％.After rolling with 70％reduction in thickness and annealing at 700℃for 2 h.the yield strength,ultimate tensile strength and fracture strain reached 1161.6 MPa,1390.8 MPa and 31.5％,respectively.The exceptional strength-ductility synergy is mainly attributed to the refined hierarchical microstructures with coarsening grains at a level of 30 pm and ultrafine grains at a level of 1 pm,and the heritage of dislocation-formed sub-grains and other lattice defects.This investi-gation demonstrates that the SLM with subsequent rolling and annealing is beneficial to fabricate high strength and ductile MEAs with single face-centered cubic(fcc)structure.
查看更多>>摘要：Ti3C2Tx MXenes with excellent metallic conductivity and flexibility have shown a promising prospect as electromagnetic interference(EMI)shielding materials.Ultrathin,hierarchical hybrid films were fab-ricated by using C6o intercalating Ti3C2Tx MXenes with the assistance of water-soluble y-cyclodextrin(CD).The C60/CD complex was obtained by high-speed vibration milling using hydrophilic CD as dispers-ing agent.After thermal annealing treatment,the obtained hybrid film exhibited excellent EMI shielding(53.52±0.43 dB),hydrophobicity(water contact angle:93.7°)and mechanical stability(over 0.9 million bending times).Taking advantage of the antioxidant of C60,the chemical durability of Ti3C2Tx MXenes based hybrid films was also improved as expected.These results indicate that the well-designed hier-archical hybrid films with the intercalation of C60 have promising potential for high-performance EMI shielding applications.
查看更多>>摘要：Yttrium tantalate(YTa04)is the next generation of higher service temperature thermal barrier coatings(TBCs)materials due to its smaller volume effect in phase change,lower thermal conductivity and unique ferroelastic domain structure.However,the low fracture toughness limits its application.We first char-acterized the diffraction patterns of variants,and two variants(M1 and M2)observed in transmission electron microscopy(TEM)results were determined from four possible variants by mechanical deriva-tion.The role of Zr4+doping in ferroelastic toughening was explained in detail.With the increase of Zr4+doping concentration,the monoclinic angle β and the domain rotation angle α decrease,respectively.The spontaneous strain component and the principal strain in the main space also have a similar decreasing trend.The decrease of the ferroelastic domain inversion energy barrier is beneficial to the improvement of fracture toughness.Combining the results of Vickers indentation,we found that Zr4+could be enriched at the domain boundary to inhibit the generation of cracks.An appropriate amount of Zr4+is conducive to the improvement of fracture toughness,and the excessive Zr4+will reduce the fracture toughness due to the generation of by-product t-ZrO2.So,the optimal composition is Y0.44Ta0.44Zr0.1202 and the best fracture toughness(2.9-3.8MPa m1/2)is equivalent to the commercial 8YSZ.This result will promote the application of a new generation of TBCs.
查看更多>>摘要：Aerogels have shown great potential as oil adsorbents but their application to the removal of microscale oil from water and their recycling remains problematic.The present work proposed a freeze-shaping method for fabricating carbon nanofiber aerogels(CNFAs)based on the direct use of one-dimensional(1D)carbon nanofibers(CNF)rather than carbonization of polymer aerogels.This technique greatly re-duces volume shrinkage and increases the three-dimensional(3D)structural stability of the material.Car-bon nanotubes(CNT)and gelatinized starch were incorporated in these aerogels as a conductive enhance-ment agent and binder,respectively,forming a"vine(CNT)-wrapped tree(CNF)"structure that improved mechanical and Joule-heating performance.The effects of glutaraldehyde added to aerogels as a cross-linking agent on mechanical properties and microstructure were also systematically investigated.The optimized CNFAs combined with low density,high porosity,good elasticity,and superior Joule-heating efficiency along with suitable adsorption capacity,excellent selectivity,and cycling stability.This mate-rial was able to selectively remove 87％and 92％of microscale acetone and dimethylformamide(DMF),respectively,from the water after nine cycles of adsorption and Joule-heating.The present work demon-strates a novel means of designing and fabricating a low shrinkage CNFA with outstanding Joule-heating performance having potential practical applications in the remediation of organic pollution.
查看更多>>摘要：The incipient plasticity and dislocation behavior in a nanocrystalline(NC)CrCoNi medium-entropy alloy were systematically investigated in terms of pop-in events during instrumental nano-indentation tests.Quantitative statistical analysis and molecular dynamic simulations were performed to reveal the effects of grain boundaries(GBs)on initial st(a)ges of plastic deformation.Multiple pop-in events appeared dur-ing loading on the NC CrCoNi.The first pop-in that represents the initial yielding was identified to be controlled by dislocation nucleation,which is in sharp contrast to the continuous elastic-plastic transi-tion mediated by GB mechanisms in NC pure metals.This can be attributed to the sluggish kinetics of the chemically complex GBs(CCGBs)in the NC CrCoNi that hinders diffusive GB activities but facilitates dislocation nucleation.Subsequent pop-ins were also found to be closely related to the extra dragging effects imposed by the CCGBs on dislocation propagation in the NC alloy.Moreover,the extremely small grain sizes and the consequent high-volume fraction of GBs in the NC alloy severely restrict the lengths of dislocation source and the radii of dislocation loop,giving rise to a higher critical stress,smaller ac-tivation volume and lower pop-in width as compared with its coarse-grained counterpart.These results provide new insights into the onset of nano-plasticity in concentrated multi-principal element alloys.
查看更多>>摘要：Mg-based thermoelectric materials have attracted more and more attention because of their rich com-position elements,green environmental protection,and lower price.In recent years,the thermoelectric properties of n-type Mg3Sb2 materials have been optimized by doping chalcogenide elements(S,Se,and Te)at the anionic position.In this work,n-type Mg3.2AxSb1.5Bi0.5(A=Gd,Ho;x=0.01,0.02,0.03,and 0.4)samples were prepared by the cation site doping of lanthanide elements(Gd and Ho).The research re-sults show that Gd and Ho doped n-type Mg3.2Sb1.5Bio.5 samples are entirely comparable to the S,Se,and Te doped n-type Mg3.2Sb1.5Bi0.5 samples,demonstrating more excellent thermoelectric properties.Dop-ing with lanthanides(Gd and Ho)at the Mg site increases the carrier concentration of the material to 8.161 x 1019 cm-3.Doping induces the contribution of more electron,thus obtaining higher conductiv-ity.The maximum zT value of the Mg3.2Gd0.02Sb1.5Bi0.5 and the Mg3.2HO0.02Sb1.5Bi0.5 samples reaches 1.61 and 1.55,respectively.This work theoretically and experimentally demonstrates Gd and Ho are efficient n-type dopants for Mg3.2Sb1.5Bi0.5 thermoelectric material.
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