查看更多>>摘要：This study reports on the effect of the addition of Glycine to Hank's solution on the in-vitro corrosion behavior of AZ31 magnesium (Mg) alloy at 37 ℃ and a pH of 7.4 studied by using potentiodynamic polarization (PDP),hydrogen collecting techniques and electrochemical impedance spectroscopy (EIS) in combination with surface characterization techniques such as optical microscopy (OM),scanning electron microscopy(SEM),energy dispersive spectroscopy (EDS),X-ray diffraction (XRD) and X-ray photoelectron spectroscopy analysis (XPS).The results reveal that adsorption of glycine initially subdues the dissolution ofAZ31 Mg alloy while in long run it enhances the dissolution of the alloy due to the commencement of the chelation effect ofglycine with Ca2+ released from hydroxyapatite.The chelation ofglycine with Ca2+induces the formation of cracks in the surface film which further promotes the dissolution ofAZ31 Mg alloy thereby forming a porous corrosion products layer on the surface of the alloy.As a result,both the continuous dissolution of AZ31 magnesium alloy and the hydrogen evolution rate (HER) are enhanced with increasing the immersion time in Hank's solution.
查看更多>>摘要：Since titanium has high affinity for hydrogen and reacts reversibly with hydrogen,the precipitation of titanium hydrides in titanium and its alloys cannot be ignored.Two most common hydride precipitates in α-Ti matrix are γ-hydride and δ-hydride,however their mechanisms for precipitation are still unclear.In the present study,we find that both γ-hydride and δ-hydride phases with different specific orienta-tions were randomly precipitated in the as-received hot forged commercially pure Ti.In addition,a large amount of the titanium hydrides can be introduced into Ti matrix with selective precipitation by using electrochemical treatment.Cs-corrected scanning transmission electron microscopy is used to study the precipitation mechanisms of the two hydrides.It is revealed that the γ-hydride and δ-hydride precipita-tions are both formed through slip + shuffle mechanisms involving a unit of two layers of titanium atoms,but the difference is that the γ-hydride is formed by prismatic slip corresponding to hydrogen occupy-ing the octahedral sites of α-Ti,while the δ-hydride is formed by basal slip corresponding to hydrogen occupying the tetrahedral sites of cα-Ti.
查看更多>>摘要：To develop an ultra-high-temperature resistant coating for a reusable thermal protection system,the preparation of a tantalum-based MoSi2-Mo coating by a new two-step process of multi-arc ion plating and halide activated pack cementation is presented.The coating has a dense structure and is well compatible with the tantalum substrate,which can be thermally shocked from room temperature to 1750℃ for 360 cycles without failure.The mechanism of the coating's excellent resistance to high-temperature thermal shocks is that a strong-binding gradient interface and a dense SiO2 oxide scale with good oxygen resistance are formed by the high-temperature self-diffusion of Si.
查看更多>>摘要：The structure-property relationship,one of the central themes in materials science,is far from being well understood for metallic glasses (MGs) due to the great complexity of their amorphous structures.Based on the analysis of published experimental data for 165 MGs from more than 15 different alloy systems,the present study reveals a universal dependence of mechanical properties (Young's moduli,shear moduli and yield strength) on simple structural parameters (the inter-atomic distance and/or valence electron density) originating from the interatomic potential and Fermi sphere-Brillouin zone interaction.This work establishes a structure-property relationship for metallic glasses and provides insights into the fundamentals of the mechanical properties of disordered systems.
查看更多>>摘要：Oxygen evolution and oxygen reduction are considered as essential processes in the energy conversion devices.The progress of cost-effective bifunctional catalysts has become a critical issue to be solved.Here,we report that Co(OH)2@N-doped carbon (NC) was facilely synthesized through the impregnation strat-egy of metal-organic frameworks derived carbon and cobalt ions.N-doped carbon with porous structure and cobalt hydroxide nanosheets play a synergistic effect role,representing excellent catalytic perfor-mance toward oxygen evolution and reduction reactions.The obtained Co(OH)2@NC exhibits remarkable activity in terms of a lower overpotential of 330 mV@10 mA cm-2 for OER and a more positive half-wave potential (E1/2 =0.84 V) for ORR in alkaline medium,outperforming lrO2 and Pt/C.Due to its superior bifunctional catalytic performance,Co(OH)2@NC catalyst is applied into a promising air electrode of Zn-air battery.This presented strategy of impregnation synthesis in this work provides a new design direction for practical electrochemical energy devices.
查看更多>>摘要：Monolithic bulk metallic glass and glass matrix composites with a relative density above 98 ％ were produced by processing Cu46Zr46Al8 (at.％) via selective laser melting (SLM).Their microstructures and mechanical properties were systematically examined.B2 CuZr nanocrystals (30-100 nm in diameter) are uniformly dispersed in the glassy matrix when SLM is conducted at an intermediate energy input.These B2 CuZr nanocrystals nucleate the oxygen-stabilized big cube phase during a remelting step.The presence of these nanocrystals increases the structural heterogeneity as indirectly revealed by mircrohardness and nanoindentation measurements.The corresponding maps in combination with calorimetric data indicate that the glassy phase is altered by the processing conditions.Despite the formation of crystals and a high overall free volume content,all additively manufactured samples fail at lower stress than the as-cast glass and without any plastic strain.The inherent brittleness is attributed to the presence of relatively large pores and the increased oxygen content after selective laser melting.
查看更多>>摘要：Bacterial attachment is a complex process affected by flow conditions,imparted stresses,and the sur-face properties and structure of both the supporting material and the cell.Experiments on the initial attachment of cells of the bacterium Streptococcus gordonii (S.gordonii),an important early coloniser of dental plaque,to samples of stainless steel (SS) have been reported in this work.The primary aim motivating this study was to establish what affect,if any,the surface roughness and topology of sam-ples of SS would have on the initial attachment of cells of the bacterium S.gordonii.This material and bacterium were chosen by virtue of their relevance to dental implants and dental implant infections.Prior to bacterial attachment,surfaces become conditioned by the interfacing environment (salivary pellicle from the oral cavity for instance).For this reason,cell attachment to samples of SS pre-coated with saliva was also studied.By implementing the Extended Derjaguin Landau Verwey and Overbeek(XDLVO) theory coupled with convection-diffusion-reaction equations and the surface roughness infor-mation,a computational model was developed to help better understand the physics of cell adhesion.Surface roughness was modelled by reconstructing the surface topography using statistical parame-ters derived from atomic force microscopy (AFM) measurements.Using this computational model,the effects of roughness and surface patterns on bacterial attachment were examined quantitatively in both static and flowing fluid environments.The results have shown that rougher surfaces (within the sub-microscale) generally increase bacterial attachment in static fluid conditions which quantitatively agrees with experimental measurements.Under flow conditions,computational fluid dynamics (CFD) simula-tions predicted reduced convection-diffusion inside the channel which would act to decrease bacterial attachment.When combined with surface roughness effects,the computational model also predicted that the surface topographies discussed within this work produced a slight decrease in overall bacterial attachment.This would suggest that the attachment-preventing effects of surface patterns dominate over the adhesion-favourable sub-microscale surface roughness;hence,producing a net reduction in adhered cells.This qualitatively agreed with experimental observations reported here and quantitatively matched experimental observations for low flow rates within measurement error.
查看更多>>摘要：To overcome the disadvantages of traditional powder electrodes,such as the insufficient performance,the aggregation of active materials,and the complex fabrication process,rationally constructing free-standing electrode materials with hierarchical architecture is an effective and promising method,which could further improve the electrochemical properties.Herein,using metal-organic framework nanoar-rays (MOFNAs) as self-sacrificial templates and SiC nanowires (SiCNWs) network as nanoscale conductive skeletons,we successfully fabricated the hierarchical core-shell SiCNws@NiCo2O4NAs on carbon cloth (CC)substrate.Taking advantages of structural merits,such as hierarchical porous triangle-like NiCo2O4NAs,the interwoven SiCNWs network and conductive CC substrate,when evaluated as a binder-free superca-pacitor electrode,the CC/SiCNWs@NiCo2O4NAs shows a high specific capacitance of 1604.7 F g-1 (specific capacity of 222.9 mA h g-1) at 0.5 A g 1,good rate performance,and excellent cycling stability.Signifi-cantly,the hybrid supercapacitor assembled with CC/SiCNWs@NiCo2O4NAs as the cathode and MOF derived CC/SiCNWs@CNAs as the anode,could deliver a high specific density of 49.9 W h kg-1 at a specific power of 800 W kg-1,stable cycling performance,and good flexibility.Impressively,this feasible strategy for fabricating hierarchical structure displays great potential in the field of energy storage.
查看更多>>摘要：In this work,the beneficial effect of Sn addition on the corrosion resistance mechanism of Cr-Mo low alloy steel was studied.Results demonstrated that Sn improves the corrosion resistance of the steel matrix mainly by influencing the microstructural transformation.Sn addition and the synergistic effect of Sn,Cr,and Mo promote the formation of α-FeOOH,SnO2,SnO,Cr(OH)3,and molybdates,lead to the improved protection and stability of the rust layer.This synergistic effect also endows the inner rust layer with cation selectivity,preventing the further penetration of Cl-and inhibiting the localized corrosion of steel.
查看更多>>摘要：Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave (EMW),but versatile designs including crystal transformation,heterogeneous structures and magnetic exchange coupling to further contribu-tion are even not designed or stressed together in previous literatures.In this article,rational design on the hollow CoFe2O4/CoFe@C architecture has been conducted by a sequential process of self-sacrifice by combustion,in-suit polymerization and calcination.Results of morphology observation exhibit that heterogeneous CoFe2O4/CoFe@C composites were generated via crystal transformation from CoFe2O4 to CoFe alloys with encapsulated carbon,together with ultimate growth of crystal particles.As for three carbon-based architectures,relatively low-graphitization carbon layers are favorable for enhancing impedance matching and polarization relaxation,but suppressing the conductive loss essentially.Mod-erate carbon content endows sample S2 with the maximum magnetic saturation (Ms) of 152A emu g-1.The optimized RL of sample S3 is up to-51 dB with 30 wt％ loading,and the effective absorption band(EAB) is of 5.9 GHz at the thickness of 2.17 mm,while 6.0 GHz can be reached at 2.5 mm.Therefore,this hollow multi-interfaces design definitely shed light on novel structure for new excellent absorbers.
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