Effects of ZrO_2 Nanoparticles on the Microstructure and Thermal-protective Properties of PEO Coating on Al-12.5%Si Alloy

PEO ceramic coatings including ZrO_2-Al_2O_3-SiO_2 in three phases were prepared on an Al-12.5%Si alloy in electrolyte solutions containing ZrO_2 nanoparticles. The microstructures and phases of the coatings were analyzed by SEM and XRD, and the heat insulation performance and the thermal shock resistance of the coatings were investigated. The compactness of the coating increased significantly and the hindrance of the Si element on plasma electrolytic oxidation process was effectively weakened. The growth rate of the coating was improved substantially with the addition of ZrO_2 nanoparticles. The PEO ceramic coatings are primarily composed of SiO_2 and high temperature steady phases such as a-Al_2O_3 and c-ZrO_2. Both the content of c-ZrO_2 and the heat-insulating property of the coating increased significantly. The ceramic coatings with special microstructure and composition formed in the solutions containing ZrO_2 nanoparticles possess excellent heat insulation performance and thermal shock resistance.

Tribological and corrosion behavior of PEO coatings with graphite nanoparticles on AZ91 and AZ80 magnesium alloys

The effect of the addition of graphite nanoparticles into the electrolyte used to produce plasma electrolytic oxidation（PEO） coatings on AZ91 and AZ80 magnesium alloys was studied. The corrosion and wear resistances of the obtained coatings were investigated. A solution that contained both phosphates and silicates was used as electrolyte. Moreover, two different PEO treatment times were studied. The corrosion resistance was analyzed with potentiodynamic polarization and EIS tests; the wear resistance was investigated with a flat on ring tribometer. The results were related to the morphology, microstructure, elemental composition and thickness evaluated with SEM analysis. The presence of the graphite nanoparticles increased the thickness, produced a densification of the coating and sealed the pores on the surface, thus improving both the corrosion and wear resistance. The increase in the corrosion and wear resistances was more evident for AZ91 than for AZ80 due to the higher aluminum content.

Investigation of ZrO2 nanoparticles concentration and processing time effect on the localized PEO coatings formed on AZ91 alloy

AZ91 Mg alloy was treated through a new localized PEO(Plasma Electrolytic Oxidation)coating approach,using electrolyte solutions with varying ZrO2 nanoparticles concentration(2-8 g/L)and processing times.With increase in the ZrO2 concentration,several microstructural changes were observed including;formation of cluster-type structure,damage to the inner layers(∼30 min)and sealing of defects.Corrosion analysis of the final coatings was carried out using potentiodynamic polarization,electrochemical impedance spectroscopy and post-corrosion analysis.It was explored that highest corrosion resistance(Rp∼81.17 kΩcm^2)of the coatings was obtained for ZrO2∼2 g/L.However,higher concentration of the ZrO2 nanoparticles caused weak crystalline coating structure,due to unstable and lower intensity discharges,thus failed to offer high corrosion resistance performance.

Improved hydrogen oxidation reaction under alkaline conditions by Au–Pt alloy nanoparticles

This work demonstrates the outstanding performance of alloyed Au1 Pt1 nanoparticles on hydrogen oxidation reaction(HOR)in alkaline solution.Due to the weakened hydrogen binding energy caused by uniform incorporation of Au,the alloyed Au1Pt1/C nanoparticles exhibit superior HOR activity than commercial PtRu/C.On the contrary,the catalytic performance of the phase-segregated Au2Pt1/C and Au1Pt1/C bimetallic nanoparticles in HOR is significantly worse.Moreover,Au1Pt1/C shows a remarkable durability with activity dropping only 4% after 3000 CV cycles,while performance attenuation of commercial PtRu/C is high up to 15% under the same condition.Our results indicate that the alloyed Au1Pt1/C is a promising candidate to substitute commercial PtRu/C for hydrogen oxidation reaction in alkaline electrolyte.

Structure and magnetic properties of Cu-Ni alloy nanoparticles prepared by rapid microwave combustion method

Cu-Ni alloy nanoparticles were prepared by a microwave combustion method with the molar ratios of CU2＋ to Ni2＋ as 3：7, 4：6, 5：5, 6：4 and 7：3. The as-prepared samples were characterized by XRD, HR-SEM, EDX and VSM. XRD and EDX analyses suggest the formation of pure alloy powders. The average crystallite sizes were found to be in the range of 21.56-33.25 nm. HR-SEM images show the clustered/agglomerated particle-like morphology structure. VSM results reveal that for low Ni content （CusNis, Cu6Ni4 and Cu7Ni3）, the system shows paramagnetic behaviors, whereas for high Ni content （Cu3Ni7 and Cu4Ni6）, it becomes ferromagnetic.

Microstructure and Thermal-protective Property of CPED Coating with ZrO2 Nanoparticles Addition on Al-12Si Alloy

A novel thermal-protective coating has been successfully prepared by CPED process on a cast Al-12%Si alloy with the addition of ZrO2 nano-particles in the electrolyte. The microstructures and phase composition of the coatings were analyzed by SEM and XRD, and the heat insulation performance and the thermal shock resistance of the coatings were investigated. With ZrO2 nanoparticles addition, the cathode plasma discharge on the coating surface is more obvious than that without ZrO2 nanoparticles addition, the coating is more uniform and compact, and the thickness of the coating increases. Furthermore, the content of Zr and Y elements increases and the degree of crystallization of the coating is more complete. The formation of the solid solution of yttrium stabilized zirconia is promoted by cathode plasma discharge. In addition, the thermal insulation temperature increases as ZrO2 nano-particles are added to the electrolyte. After 1 000 cycles of thermal shock, there was no cracking in the coating surface layer, which indicated that the CPED coating with ZrO2 nanoparticles addition possessed a good thermal shock resistance.

Au-Ag alloy nanoparticles with tunable cavity for plasmon-enhanced photocatalytic H2 evolution

Au-Ag alloy nanoparticles with different cavity sizes have great potential for improving photocatalytic performance due to their tunable plasmon effect.In this study,galvanic replacement was combined with co-reduction with the reaction kinetics processes regulated to rapidly synthesize Au-Ag hollow alloy nanoparticles with tunable cavity sizes.The position of the localized surface plasmon resonance(LSPR)peak could be effectively adjusted between 490 nm and 713 nm by decreasing the cavity size of the Au-Ag hollow nanoparticles from 35 nm to 20 nm.The plasmon-enhanced photocatalytic H2 evolution of alloy nanoparticles with different cavity sizes was investigated.Compared with pure P25(TiO2),intact and thin-shelled Au-Ag hollow nanoparticles(HNPs)-supported photocatalyst exhibited an increase in the photocatalytic H2 evolution rate from 0.48μmol h^−1 to 4μmol h^−1 under full-spectrum irradiation.This improved photocatalytic performance was likely due to the plasmon-induced electromagnetic field effect,which caused strong photogenerated charge separation,rather than the generation of hot electrons.

Influence of TiB_2 nanoparticles on elevated-temperature properties of Al-Mn-Mg 3004 alloy

Two contents(1.5%and3%)of TiB2nanoparticles were introduced in Al?Mn?Mg3004alloy to study their effects on theelevated-temperature properties.Results show that TiB2nanoparticles were mainly distributed at the interdendritic grain boundarieswith a size range of20?80nm,which is confirmed by transmission electron microscopy(TEM)and X-ray diffraction(XRD).Therefore,the volume fraction of the dispersoid free zones is greatly reduced and the motion of grain boundaries and dislocations isinhibited more effectively at elevated temperature.After peak precipitation heat treatment,the yield strengths in the alloy with3%TiB2addition at room temperature and300°C were increased by20%and13%respectively,while the minimum creep rate at300°Cwas reduced to only1/5of the base alloy free of TiB2,exhibiting a considerable improvement of elevated-temperature properties inAl?Mn?Mg alloys.

Low temperature synthesis and thermal properties of Ag-Cu alloy nanoparticles

Ag-Cu alloy nanoparticles were synthesized by simple low temperature chemical reduction method using metal salts（acetate/sulphates） in aqueous solution with sodium borohydride as reducing agent.The chemical reduction was carried out in the presence of nitrogen gas in order to prevent the oxidation of copper during the reaction process.The alloy nanoparticles were characterized by XRD,UV-Vis,particle size analysis,EDS,TG-DTA and SEM analysis.From the XRD analysis,the crystallite sizes of the prepared samples were calculated using Scherrer formula and the values were found to be in the range of 15 nm.UV-Vis studies conform the formation of alloy nanoparticles.EDS analysis shows the presence of silver and copper in the samples.The SEM observation reveals that the samples consist of grains with average grain size up to 40 nm,and the particle size dependant melting point was studied by TG-DTA.

Structural optimization and segregation behavior of quaternary alloy nanoparticles based on simulated annealing algorithm

Alloy nanoparticles exhibit higher catalytic activity than monometallic nanoparticles, and their stable structures are of importance to their applications. We employ the simulated annealing algorithm to systematically explore the stable structure and segregation behavior of tetrahexahedral Pt–Pd–Cu–Au quaternary alloy nanoparticles. Three alloy nanoparticles consisting of 443 atoms, 1417 atoms, and 3285 atoms are considered and compared. The preferred positions of atoms in the nanoparticles are analyzed. The simulation results reveal that Cu and Au atoms tend to occupy the surface, Pt atoms preferentially occupy the middle layers, and Pd atoms tend to segregate to the inner layers. Furthermore, Au atoms present stronger surface segregation than Cu ones. This study provides a fundamental understanding on the structural features and segregation phenomena of multi-metallic nanoparticles.

Encapsulated Ni-Co alloy nanoparticles as efficient catalyst for hydrodeoxygenation of biomass derivatives in water

Catalytic hydrodeoxygenation(HDO)is one of the most promising strategies to transform oxygen-rich biomass derivatives into high value-added chemicals and fuels,but highly challenging due to the lack of highly efficient nonprecious metal catalysts.Herein,we report for the first time of a facile synthetic approach to controllably fabricate well-defined Ni-Co alloy NPs confined on the tip of N-CNTs as HDO catalyst.The resultant Ni-Co alloy catalyst possesses outstanding HDO performance towards biomass-derived vanillin into 2-methoxy-4-methylphenol in water with 100%conversion efficiency and selectivity under mild reaction conditions,surpassing the reported high performance nonprecious HDO catalysts.Impressively,our experimental results also unveil that the Ni-Co alloy catalyst can be generically applied to catalyze HDO of vanillin derivatives and other aromatic aldehydes in water with 100%conversion efficiency and over 90%selectivity.Importantly,our DFT calculations and experimental results confirm that the achieved outstanding HDO catalytic performance is due to the greatly promoted selective adsorption and activation of C=O,and desorption of the activated hydrogen species by the synergism of the alloyed Ni-Co NPs.The findings of this work affords a new strategy to design and develop efficient transition metal-based catalysts for HDO reactions in water.

Microstructure and abrasive wear behaviour of anodizing composite films containing Si C nanoparticles on Ti6Al4V alloy

Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.

Sustainable solid-state synthesis of uniformly distributed PdAg alloy nanoparticles for electrocatalytic hydrogen oxidation and evolution

New sustainable syntheses based on solid-state strategies have sparked enormous attention and provided novel routes for the synthesis of supported metallic alloy nanocatalysts(SMACs).Despite considerable recent progress in this field,most of the developed methods suffer from either complex operations or poorly controlled morphology,which seriously limits their practical applications.Here,we have developed a sustainable strategy for the synthesis of PdAg alloy nanoparticles(NPs)with an ultrafine size and good dispersion on various carbon matrices by directly grinding the precursors in an agate mortar at room temperature.Interestingly,no solvents or organic reagents are used in the synthesis procedure.This simple and green synthesis procedure provides alloy NPs with clean surfaces and thus an abundance of accessible active sites.Based on the combination of this property and the synergistic and alloy effects between Pd and Ag atoms,which endow the NPs with high intrinsic activity,the PdAg/C samples exhibit excellent activities as electrocatalysts for both the hydrogen oxidation and evolution reactions(HOR and HER)in a basic medium.Pd9Ag1/C showed the highest activity in the HOR with the largest j0,m value of 26.5 A g Pd^–1 and j0,s value of 0.033 mA cmPd^–2,as well as in the HER,with the lowest overpotential of 68 mV at 10 mA cm^–2.As this synthetic method can be easily adapted to other systems,the present scalable solid-state strategy may open opportunity for the general synthesis of a wide range of well-defined SMACs for diverse applications.

Effect of nano-CaO particle on the microstructure,mechanical properties and corrosion behavior of lean Mg-1Zn alloy

The effects of nano-CaO contents on the microstructure,mechanical properties and corrosion resistance of lean Mg-1Zn alloy were investigated.The results showed that the addition of nano-CaO significantly refined the grain size and improved mechanical properties of the Mg-1Zn alloy.At the same time,CaO reacted with molten Mg in situ to form nano-MgO,whose corrosion product in SBF solution was the same with the degradation product of Mg matrix,resulting in the enhanced compactness of the Mg(OH)_(2) layer and reduced corrosion rate of matrix.The Mg-1Zn alloy had lower corrosion resistance due to excessively large grain size and shedding of corrosion products.The composite with 0.5 wt.%CaO had the best corrosion resistance with a weight loss of 9.875 mg·y^(-1)·mm^(-2)due to the small number of Ca_(2)Mg_(6)Zn_(3) phase and suitable grain size.While for composites with high content of CaO(0.7 wt.%and 1.0 wt.%),they had lower corrosion resistance due to the coexistence of large number of Ca_(2)Mg_(6)Zn_(3) and Mg_(2)Ca at grain boundaries,especially for 1.0 wt.%CaO composite,resulting from the strong micro-galvanic corrosion.

Mechanical alloying of platinum with 5% ZrO_2 nanoparticles for glass making tools

Synthesis and characterization of mechanically alloyed Pt-5%ZrO2(volume fraction) for structural components in the glass industry were described. Zirconia(ZrO2) nanoparticles(<100 nm) were produced by the electrical explosion of zirconium(Zr) wires, and blended with platinum(Pt) powders(<44 ?m) for 2-72 h in ambient atmosphere. The Pt particle size followed the typical decreasing trend of the normal ball milling process up to 48 h, but particle agglomeration was observed at 72 h. The grain size evolution was similar to that of the particle size, dropping down to around 50 nm at 48 h. The root mean square strain of the Pt crystallites showed the opposite behavior, maximizing at 48 h with a subsequent relaxation process. For the 48 h ball milled powders, spark plasma sintering was carried out to form a bulk disk. The measured mass loss of the sintered bulk sample shows a decent thermal stability despite its relatively low density.

Facile fabrication of ultrafine nickel-iridium alloy nanoparticles/graphene hybrid with enhanced mass activity and stability for overall water splitting

Developing active and durable electrocatalysts for overall water splitting is desirable but challenging to realize sustainable hydrogen production.Here,we report a facile and general method to prepare ultrafine nickel(Ni)-iridium(Ir)alloy nanoparticles/graphene hybrids for overall water splitting.The optimized hybrid with 4.9 wt%Ir exhibits much higher catalytic activity and durability than commercial 20 wt%Ir/C for both oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).Theoretical simulations reveal that the incorporation of Ir in metallic Ni lattice regulates hydrogen adsorption free energy to the optimum level,thus improving HER activity,while in situ generated amorphous Ir-Ni hydr(oxy)oxides around metallic Ni-Ir core have been demonstrated to be the active species under OER conditions,which switches OER rate-determining step to energy-favorable pathway.The overall water splitting electrolyzer assembled by the optimized electrocatalyst shows a low cell voltage of only 1.52 V and excellent stability to deliver a current density of 10 m A cm-2.This work provides a powerful strategy toward general synthesis of ultrafine alloy nanoparticles for high-performance overall water splitting.

Unraveling the role of iron on Ni-Fe alloy nanoparticles during the electrocatalytic ethanol-to-acetate process

The anodic electrooxidation of ethanol to value-added acetate is an excellent example of replacing the oxygen evolution reaction to promote the cathodic hydrogen evolution reaction and save energy.Herein,we present a colloidal strategy to produce Ni-Fe bimetallic alloy nanoparticles(NPs)as efficient electrocatalysts for the electrooxidation of ethanol in alkaline media.Ni-Fe alloy NPs deliver a current density of 100 mA·cm^(-2) in a 1.0 M KOH solution containing 1.0 M ethanol merely at 1.5 V vs.reversible hydrogen electrode(RHE),well above the performance of other electrocatalysts in a similar system.Within continuous 10 h testing at this external potential,this electrode is able to produce an average of 0.49 mmol·cm^(-2)·h^(-1) of acetate with an ethanol-to-acetate Faradaic efficiency of 80%.A series of spectroscopy techniques are used to probe the electrocatalytic process and analyze the electrolyte.Additionally,density functional theory(DFT)calculations demonstrate that the iron in the alloy NPs significantly enhances the electroconductivity and electron transfer,shifts the rate-limiting step,and lowers the energy barrier during the ethanol-to-acetate reaction pathway.

Bioinspired Hollow Mesoporous Silica Nanoparticles Coating on Titanium Alloy with Hierarchical Structure for Modulating Cellular Functions

3D-printed Porous Titanium Alloy Implants(pTi),owing to their biologically inertness and relatively smooth surface morphology,adversely affect the biological functions of surrounding cells.To address the challenges,constructing a bioinspired interface that mimics the hierarchical structure of bone tissue can enhance the cellular functions of cells.In this context,Hollow Mesoporous Silica Nanoparticles(HMSNs),renowned for their unique physicochemical properties and superior biocompatibility,offer a promising direction for this research.In this research,the initially synthesized HMSNs were used to construct a“hollow-mesoporous-macroporous”hierarchical bioinspired coating on the pTi surface through the Layer-by-Layer technique.Simultaneously,diverse morphologies of coatings were established by adjusting the deposition strategy of PDDA/HMSNs on the pTi surface(pTi-HMSN-2,pTi-HMSN-4,pTi-HMSN-6).A range of techniques were employed to investigate the physicochemical properties and regulation of cellular biological functions of the diverse HMSN coating strategies.Notably,the pTi-HMSN-4 and pTi-HMSN-6 groups exhibited the uniform coatings,leading to a substantial enhancement in surface roughness and hydrophilicity.Meantime,the coating constructed strategy of pTi-HMSN-4 possessed commendable stability.Based on the aforementioned findings,both pTi-HMSN-4 and pTi-HMSN-6 facilitated the adhesion,spreading,and pseudopodia extension of BMSCs,which led to a notable upsurge in the expression levels of vinculin protein in BMSCs.Comprehensive analysis indicates that the coating,when PDDA/HMSNs are deposited four times,possesses favorable overall performance.The research will provide a solid theoretical basis for the translation of HMSN bioinspired coatings for orthopedic implants.

Effects of in-situZrB_2 nanoparticles and scandium on microstructure and mechanical property of 7N01 aluminum alloy

In this study, the in-situ synthesized ZrB_(2) nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoids. The microstructure and mechanical property evolution of the prepared composites and the interaction between ZrB_(2) and Sc were studied in detail. The microstructure investigation shows that the introduction of rare earth scandium(Sc) can promote the distribution of ZrB_(2) nanoparticles, by improving their wettability to the Al melt. Meanwhile, the addition of rare earth Sc also modifies the coarse Al Zn Mg Mn Fe precipitated phases, refines the matrix grains and generates high-melting Al_3(Sc,Zr)/Al_3Sc nanodispersoids. Tensile tests of the composites show that with the combinatorial introduction of ZrB_(2) and Sc, the strength and ductility of the composites are improved simultaneously compared with the corresponding 7N01 alloy, ZrB_(2) /7N01 composite and Sc/7N01 alloy. And the optimum contents of ZrB_(2) and Sc are 3 wt% and 0.2 wt% in this study. The yield strength, ultimate strength and elongation of(3 wt% ZrB_(2) +0.2 wt% Sc)/7N01 composite are 477 MPa, 506 MPa and 9.8%, increased about 18.1%, 12.2%and 38% compared to 7N01 alloy. Furthermore, the cooperation strengthening mechanisms of ZrB_(2) and Sc are also discussed.

SiC nanoparticles reinforced magnesium matrix composites fabricated by ultrasonic method

SiC nanoparticles reinforced magnesium matrix composites were fabricated by ultrasonic method.The AZ91 alloy and SiC nanoparticles with the average diameter of 50 nm were used as the matrix alloy and the reinforcement,respectively.The addition of nanoparticles was 0.1%,0.3%,and 0.5%(mass fraction) of the composites.The results of microstructural evaluation and mechanical properties indicate that the nanoparticles can be dispersed into magnesium alloys efficiently and uniformly with the aid of ultrasonic vibration.As compared with the matrix alloys,the grains of composites were refined and the mechanical properties of composites were improved significantly.The SEM and DSC analyses show that the SiC nanoparticles can act as the heterogeneous nucleation of α-Mg.Also,the strengthening mechanism responsible for the composites reinforced with SiC nanoparticles was discussed.