A single-step synthesis of nitrogen-doped graphene sheets decorated with cobalt hydroxide nanoflakes for the determination of dopamine

Nitrogen-doped reduced graphene oxide(NrGO)sheets decorated with Co(OH)_2nanoflakes were prepared by a single-step hydrothermal process.The morphological and structural characterizations of as synthesized Nr GO@Co(OH)_2nanoflakes were performed by field emission scanning electron microscopy(FESEM),EDX-mapping and X-ray diffraction(XRD).Nr GO@Co(OH)_2nanoflakes modified glassy carbon electrode(GCE)was used for electrochemical sensing of dopamine in neutral medium.The nanocomposite modified electrode showed enhanced electrochemical sensing ability for the detection of dopamine and the limit of detection(Lo D)was found to be 0.201μM with a sensitivity value of 0.0286±0.002 m A m M~(-1).Interference studies revealed that Nr GO@Co(OH)_2─GCE endow excellent selectivity for DA detection even in the presence of higher concentration of common co-existing physiological interfering analytes.Additionally,proposed sensor demonstrated excellent performance in urine samples with promising reproducibility and stability.     

Effect of pickling processes on the microstructure and properties of electroless Ni–P coating on Mg–7.5Li–2Zn–1Y alloy

The electroless plating Ni–P is prepared on the surface of Mg–7.5Li–2Zn–1Y alloys with different pickling processes.The microstructure and properties of Ni–P coating are investigated.The results show that the Ni–P coatings deposited using the different pickling processes have a different high phosphorus content amorphous Ni–P solid solution structure,and the Ni–P coatings exhibit higher hardness.There is higher phosphorus content of Ni–P amorphous coating using 125 g/L Cr O3and 110 ml/L HNO3(w68%)than using 180 g/L Cr O3and 1 g/L KF during pre-treatment,and the coating structure is more compact,and the Ni–P coatings exhibit more excellent adhesion with substrate(Fcup to22 N).The corrosion potential of Ni–P coating is improved and exhibits good corrosion resistance.As a result,Mg-7.5Li-2Zn-1Y alloy is remarkably protected by the Ni–P coating.     

Corrosion study of resorbable Ca60Mg15Zn25 bulk metallic glasses in physiological fluids

The corrosion activity of amorphous plates of Ca_(60)Mg_(15)Zn_(25)alloy was investigated.The biocompatible elements were selected for the alloy composition.The electrochemical corrosion and immersion tests were carried out in a multi-electrolyte fluid and Ringer's solution.Better corrosion behavior was observed for the samples tested in a multi-electrolyte fluid despite the active dissolution of Ca and Mg in Ringer's solution.The experimental results indicated that reducing concentration of NaCl from 8.6 g/dm~3for Ringer's solution to 5.75 g/dm~3caused the decrease of the corrosion rate.The volume of the hydrogen evolved after 480 min in Ringer's solution(40.1 ml/cm~2)was higher in comparison with that obtained in a multi-electrolyte fluid(24.4 ml/cm~2).The values of opencircuit potential(E_(OCP))for the Ca_(60)Mg_(15)Zn_(25)glass after 1 h incubation in Ringer's solution and a multielectrolyte fluid were determined to be-1553 and-1536 m V vs.a saturated calomel electrode(SCE).The electrochemical measurements indicated a shift of the corrosion current density(j_(corr))from 1062μA/cm~2for the sample tested in Ringer's solution to 788μA/cm~2for the specimen immersed in a multi-electrolyte fluid.The corrosion products analysis was conducted by using the X-ray photoelectron spectroscopy(XPS).The corrosion products were identified to be CaCO_3,Mg(OH)_2,CaO,MgO and Zn O.The mechanism of corrosion process was proposed and described based on the microscopic observations.The X-ray diffraction and Fourier transform infrared spectroscopy(FTIR)also indicated that Ca(OH)_2,CaCO_3,Zn(OH)_2and Ca(Zn(OH)_3)_2·2H_2O mainly formed on the surface of the studied alloy.     

Hot corrosion behavior of nanostructured Gd2O3 doped YSZ thermal barrier coating in presence of Na2SO4 + V 2O5 molten salts

Nickel-based superalloy DZ125 was first sprayed with a NiCrAlY bond coat and followed with a nanostructured 2 mol% Gd_2O_3-4.5 mol% Y_2 O_3-ZrO_2(2 GdYSZ) topcoat using air plasma spraying(APS). Hot corrosion behavior of the as-sprayed thermal barrier coatings(TBCs) were investigated in the presence of 50 wt%Na_2SO_4 + 50 wt% V_2O_5 as the corrosive molten salt at 900 ℃ for 100 h. The analysis results indicate that Gd doped YVO_4 and m-ZrO_2 crystals were formed as corrosion products due to the reaction of the corrosive salts with stabilizers(Y_2O_3, Gd_2O_3) of zirconia. Cross-section morphology shows that a thin layer called TGO was formed at the bond coat/topcoat interface. After hot corrosion test, the proportion of m-ZrO_2 phase in nanostructured 2GdYSZ coating is lower than that of nano-YSZ coating. The result reveals that nanostructured 2GdYSZ coating exhibits a better hot corrosion resistance than nano-YSZ coating.     

Facile synthesis of nanosized sodium magnesium hydride, NaMgH3

The ternary magnesium hydride NaMgH 3 has been synthesised via reactive milling techniques.The method employed neither a reactive H2 atmosphere nor high pressure sintering or other post-treatment processes.The formation of the ternary hydride was studied as a function of milling time and ball:powder ratio.High purity NaMgH 3 powder(orthorhombic space group Pnma,a 5.437(2),b 7.705(5),c 5.477(2) ;Z 4) was prepared in 5 h at high ball:powder ratios and characterised by powder X-ray diffraction(PXD),Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy(SEM/EDX).The products formed sub-micron scale(typically 200-400 nm in size) crystallites that were approximately isotropic in shape.The dehydrogenation behaviour of the ternary hydride was investigated by temperature programmed desorption(TPD).The nanostructured hydride releases hydrogen in two steps with an onset temperature for the first step of 513 K.     

Activated carbon derived from rice husk by NaOH activation and its application in supercapacitor

Four activated carbon(AC) samples prepared from rice husk under different activation temperatures have been characterized by N2adsorption–desorption isotherms, thermogravimetric analysis(TGA–DTA), Fourier transform infrared spectroscopy(FTIR) and scanning electron microscopy(SEM). The specific surface area of AC sample reached 2681 m2 g 1under activation temperature of 800 1C. The AC samples were then tested as electrode material; the specific capacitance of the as-prepared activated carbon electrode was found to be 172.3 F g 1using cyclic voltammetry at a scan rate of 5 mV s 1and 198.4 F g 1at current density 1000 mA g 1in the charge/discharge mode.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Composition design of superhigh strength maraging stainless steels using a cluster model

The composition characteristics of maraging stainless steels were studied in the present work investigation using a cluster-plus-glue-atom model. The least solubility limit of high-temperature austenite to form martensite in basic Fe–Ni–Cr corresponds to the cluster formula [NiFe12]Cr3,where NiFe12is a cuboctahedron centered by Ni and surrounded by 12 Fe atoms in FCC structure and Cr serves as glue atoms. A cluster formula [NiFe12](Cr2Ni) with surplus Ni was then determined to ensure the second phase(Ni3M) precipitation,based on which new multicomponent alloys [(Ni,Cu)16Fe192](Cr32(Ni,Mo,Ti,Nb,Al,V)16) were designed. These alloys were prepared by copper mould suction casting method,then solid-solution treated at 1273 K for 1 h followed by water-quenching,and finally aged at 783 K for 3 h. The experimental results showed that the multi-element alloying results in Ni3M precipitation on the martensite,which enhances the strengths of alloys sharply after ageing treatment. Among them,the aged [(Cu4Ni12)Fe192](Cr32(Ni8.5Mo2Ti2Nb0.5Al1V1)) alloy(Fe74.91Ni8.82Cr11.62Mo1.34Ti0.67Nb0.32Al0.19V0.36Cu1.78wt%) has higher tensile strengths with YS?1456 MPa and UTS?1494 MPa. It also exhibits good corrosion-resistance in 3.5 wt% NaCl solution.     

Minor-alloyed Cu-Ni-Si alloys with high hardness and electric conductivity designed by a cluster formula approach

Cu-Ni-Si alloys are widely used due to their good electrical conductivities in combination with high strength and hardness. In the present work, minor-alloying with M =(Cr, Fe, Mo, Zr) was conducted for the objective of further improving their hardness while maintaining their conductivity level. A cluster-plus-glue-atom model was introduced to design the compositions of M-alloyed Cu-Ni-Si alloys, in which an ideal composition formula[(Ni,Si,M)-Cu_(12)]Cu_3(molar proportion) was proposed. To guarantee the complete precipitation of solute elements in fine δ-Ni_2 Si precipitates, the atomic ratio of(Ni,M)/Si was set as 2/1. Thus the designed alloy series of Cu_(93.75)(Ni/Zr)_(3.75)Si_(2.08)(Cr/Fe/Mo)_(0.42)(at%) were arc-melted into ingots under argon atmosphere, and solidsolutioned at 950 ℃ for 1 h plus water quenching and then aged at 450 ℃ for different hours. The experimental results showed that these designed alloys exhibit high hardness(HV 1.7 GPa) and good electrical conductivities(≥ 35% IACS). Specifically, the quinary Cu_(93.75)Ni_(3.54)Si_(2.08)(Cr/Fe)_(0.42)Zr_(0.21) alloys(Cu-3.32 Ni-0.93 Si-0.37(Cr/Fe)-0.30 Zr wt%) possess both a high hardness with HV = 2.5-2.7 GPa, comparable to the highstrength KLFA85 alloy(Cu-3.2 Ni-0.7 Si-1.1 Zn wt%,HV= 2.548 GPa),and a good electrical conductivity(35-36% IACS).     

Preparation of electroless Ni–P composite coatings containing nano-scattered alumina in presence of polymeric surfactant

Ni–P electroless coating was applied on low carbon steel with the incorporation of different amounts of nano Al2O3 powder (ranging from 3 g/l to 30 g/l) in electroless bath. Corrosion properties and microstructures of the coating were studied. The dispersion stability of alumina colloidal particles stabilized by polymeric (non-ionic) surfactants in an electroless bath was also investigated. The surface morphology and the relevant structure were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results showed that increasing alumina concentration not only changed the surface morphology, but also promoted the corrosion resistance. Addition of surfactants has an indirect effect on the amount of the incorporated particles. Meanwhile, in the presence of surfactant, corrosion resistance of Ni–P coating containing even a small quantity of alumina was improved since a stabilized bath was obtained.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Joining of Si3N4 ceramic using PdCo(Ni SiB)–V system brazingfi ller alloy and interfacial reactions

The wettability of V-active PdCo-based alloys on Si3N4ceramic was studied with the sessile drop method. And the alloy of Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6(wt%),was developed for Si3N4ceramic joining in the present investigation. The rapidly-solidified brazing foils were fabricated by the alloy Pd50.0–Co33.7–Ni4.0–Si2.0–B0.7–V9.6. The average room-temperature three-point bend strength of the Si3N4/Si3N4joints brazed at 1453 K for 10 min was 205.6 MPa,and the newly developed braze gives joint strengths of 210.9 MPa,206.6 MPa and 80.2 MPa at high temperatures of 973 K,1073 K and 1173 K respectively. The interfacial reaction products in the Si3N4/Si3N4joint brazed at 1453 K for10 min were identified to be VN and Pd2Si by XRD analysis. Based on the XEDS analysis result,the residual brazing alloy existing at the central part of the joint was verified as Co-rich phases,in which the concentration of element Pd was high up to 18.0–19.1 at%. The mechanism of the interfacial reactions was discussed. Pd should be a good choice as useful alloying element in newer high-temperature braze candidates for the joining of Si-based ceramics.     

Synthesis of dental resins using diatomite and nano-sized SiO2 and TiO2

The mechanical properties of dental composites were improved by porous diatomite and nano-sized silica (OX-50) used as co-fillers.The resin composites,filled with silanized OX-50 and silanized diatomit...     

La2O3–Al2O3 –SiO2 glass-infiltrated 3Y-TZP all-ceramic composite for the dental restora tive application

The 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) powder had three particle size distributions, while the fine one was lower than 100 nm. The 3Y-TZP compact was prepared by dry-pressing under pressures ranged from 10 to 30 MPa and then presintered at 1250°C for 2 h. The matrix dry-pressed under the pressure of 20 MPa had a porosity of 16.7% and could be easily processed by computer aided design and computer aided manufacturing (CAD/CAM), and which had been infiltrated by the La2O3–Al2O3–SiO2 glass at 1200°C for 4 h. The flexural strength and fracture toughness of the composite were 710.7 MPa and 6.51 MPa m^1/2, respectively. The low shrinkage (0.3%) of the composite can satisfy the net-shape fabrication standard. XRD results illustrated that zirconia in the La2O3–Al2O3–SiO2 glass-infiltrated 3Y-TZP all-ceramic composite was mainly in the tetragonal phase. SEM and EDS results indicated that the pores of the matrix were almost filled by the La2O3–Al2O3 –SiO2 glass     

In-situ secondary growth of nanocube-based Prussian-blue film as an ultrasensitive biosensor

A regular nanostructure has been widely confirmed to result ina marked improvement in material performance in biosensing applications.In the present study,a regular nanostructured Prussian blue(PB) film with two heterogeneous crystal layers was synthesized in-situ using a secondary growth method.A PB seed layer was first controlled to form uniform cube-like crystal nuclei through an ultrasonic reaction with a single reactant.Then,well-defined 100 nm PB nanocubes were further crystallized on this seed layer using a self-assembly approach.In order to accelerate the electron transfer rate during the enzyme reaction for glucose detection,the graphene was used as the main cross-linker to immobilize glucose oxidase on the PB film.The as-prepared biosensor exhibited high electrocatalysis and electron conductivity for the detection of trace glucose with a sensitivity of141.5 μA mM~(-1) cm~(-2),as well as excellent anti-interference ability in the presence of ascorbic acid and uric acid under a low operation potential of-0.05 V.     

The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel for USC power plant application

Copper has been used as a strengthening element in newly developed Fe–Cr–Ni type austenitic heat resistant steel for inducing Cu-rich phase precipitation to meet high temperature strength requirement for 60°C Ultra Super-Critical (USC) coal fired power plants for many years. However, the precipitation behavior and strengthening mechanism of Cu-rich phase in these advanced austenitic heat resistant steels is still unclear. In order to understand the precipitation strengthening behavior of Cu-rich phase and to promote high strength austenitic heat resistant steel development, 18Cr9 NiCuNb steel which is a Cu-added Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel has been selected for this study to be aged at 650°C till to 10,000 h. Micro-hardness and room temperature tensile test were conducted after long-time aging. SEM,TEM, HRTEM and three dimensional atom probe (3DAP) technology accompanying with thermodynamic calculation have been used to investigate the Cu-rich phase precipitation behavior during 650°C aging. The experimental results showed that Cu atoms can quickly concentrate in clusters at very early precipitation stage to form the fine nano-size Cu-rich ‘‘segregation areas’within less than 1 h at 650°C. With increasing aging time at 650°C Cu atoms continuously concentrate to Cu-rich segregation areas (clusters) and simultaneously other kinds of atoms such as Fe, Cr and Ni diffuse away from Cu-rich segregation areas to austenitic matrix, and finally to complete the transformation from Cu-rich segregation areas to Cu-rich phase. However, there is only Cu atoms concentration but not crystallographic transformation from early stage of Cu-rich clusters forming to the final Cu-rich phase formation. Even the Cu atom becomes the main composed element after 500 h aging at 650°C the Cu-rich phase still keeps coherent relationship with austenitic matrix. According the experimental results in this study, Cu-rich phase precipitation sequence which starts from the Cu atom segregation followed by the Cu diffusing from matrix to segregation areas and Fe, Cr and Ni atoms diffuse out from Cu-rich areas to matrix without crystallographic transformation is proposed. The Cu-rich phase is the most dispersed phase and contributes the most important strengthening effect among all precipitated phases (M23C6, MX and Cu-rich phase). It has been found that Cu-rich phase is very stable and still keeps in nano-size even for 10,000 h aging at 650°C. The unique precipitation strengthening of Cu-rich phase in combination with nano-size Nb-rich MX phase and grain-boundary M23C6carbide contributes excellent strengthening effect to 18Cr9 NiCuNb austenitic heat resistant steel.     

Preparation and catalytic effect of porous Co3O4 on the hydrogen storage properties of a Li-B-N-H system

A porous Co_3O_4 with a particle size of 1–3 μm was successfully prepared by heating Co-based metal organic frameworks MOF-74(Co) up to 500 °C in air atmospheric conditions. The as-prepared porous Co_3O_4 significantly reduced the dehydrogenation temperatures of the LiBH_4-2LiNH_2 system and improved the purity of the released hydrogen. The LiBH_4-2LiNH_2-0.05/3Co_3O_4 sample started to release hydrogen at 140 °C and released hydrogen levels of approximately 9.7 wt% at 225 °C. The end temperature for hydrogen release was lowered by 125 °C relative to that of the pristine sample. Structural analyses revealed that the as-prepared porous Co_3O_4 is in-situ reduced to metallic Co, which functions as an active catalyst, reducing the kinetic barriers and lowering the dehydrogenation temperatures of the LiBH_4-2LiNH_2 system. More importantly, the porous Co_3O_4-containing sample exhibited partially improved reversibility for hydrogen storage in the LiBH_4-2LiNH_2 system.     

Structural and dielectric study of nano-crystalline single phase Sn1−xNixS (xNi=0–10%) showing room temperature ferromagnetism

SnS is a promising Ⅳ-Ⅵ semiconductor,which is very less explored for diluted magnetic semiconducting and dielectric applications.In this study,the Ni doping(x_(Ni)=0-10mol%) effects on SnS host lattice were investigated.A simple and low cost co-precipitation technique was employed to grow Ni doped SnS powders.The X-ray diffraction confirmed single phase orthorhombic structure with a nano-crystalline nature that was further verified through the surface structure observed by scanning electron microscopy.Near edge x-ray absorption fine structure spectroscopy revealed a shift in the Ni absorption edge towards higher energy,depicting the formation of Ni~(+3) oxidation state.The impedance measurements,in the frequency range 1 kHz to 20 MHz,depict that owing to the excellent sensitivity to the electromagnetic radiations at the low energy,the Ni doped SnS finds potential applications in various energy related devices.Vibrating sample magnetometer measurements have elucidated room temperature ferromagnetism,which depicts potential memory device applications.     

The enhanced corrosion resistance of UMAO coatings on Mg by silane treatment

The surface silanization was carried out on ultrasonic micro-arc oxidation(UMAO) coatings on pure magnesium using KH550 as silane coupling agent(SCA). The surface morphology, chemical bonds and corrosion resistance of the silane films were investigated by scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FTIR) and electrochemical workstation, respectively. The results showed that hybrid coatings were successfully prepared on pure magnesium by UMAO-Na OH(1 mol/L, 2 mol/L, 3 mol/L)-SCA processing. The organic films with Si–O–Mg bonds are helpful for the reduction of the pores in UMAO coatings. The pores decreased with increasing Na OH concentration. Compared with single UMAO treatment, the corrosion potentials(Ecorr) of magnesium plates with UMAO-Na OH(1 mol/L,2 mol/L, 3 mol/L)-SCA treatment increased by 29 m V, 53 m V and 75 m V, respectively, meanwhile the corrosion current density(Icorr) reduced one to two orders of magnitude. It indicated that the corrosion resistance of the coatings was improved by silane treatment.     

Effect of La0.8Sr0.2Co0.2Fe0.8O3-δ morphology on the performance of composite cathodes

In the present work,one dimensional La0.8Sr0.2Co0.2Fe0.8O3 δ(LSCF) nanofibers with the mean diameter of about 100 nm prepared by electrospinning were deposited on Gd0.2Ce0.8O1.9(GDC) electrolyte followed by sintering to form one dimensional LSCF nanofiber cathode. And LSCF/GDC composite cathodes were formed by introducing GDC phases into LSCF nanofiber scaffold using infiltration method. The polarization resistances for the composite cathode with an optimal LSCF/GDC mass ratio of 1/0.56 are 0.27,0.14 and 0.07 Ω cm2at 650,700 and750 1C,respectively,which are obviously smaller than 2.26,0.78 and 0.29 Ω cm2of pure LSCF nanofiber cathode. And the activation energy is1.194 eV,which is much lower than that of pure LSCF nanofiber cathode(1.684 eV). These results demonstrate that the infiltration of GDC into LSCF nanofiber scaffold is an effective approach to achieve high performance cathode for solid oxide fuel cells(SOFCs). In addition,the performance of composite cathode in this work was also compared with that of our previous nanorod structured LSCF/GDC composite cathode.     

Microstructure and growth kinetics of Ce and Y jointly modified silicide coatings for Nb–Ti–Si based ultrahigh temperature alloy

In order to protect Nb-Ti-Si based ultrahigh temperature alloy from oxidation, pack cementation processes were utilized to prepare Ce and Y jointly modified silicide coatings. The Ce and Y jointly modified silicide coating has a double-layer structure: a relatively thick (Nb, X)Si2 (X represents Ti, Cr and Hf elements) outer layer and a thin (Ti, Nb)5Si4 transitional layer. The pack cementation experiments at 1150 ℃ for 8 h proved that the addition of certain amounts of CeO2 and Y2O3 powders in the packs distinctly influenced the coating thickness, the contents of Si, Ce and Y in the (Nb, X)Si2 outer layers, and the density of cavities in the coatings. In order to study the effects of Ce and Y joint modification in the silicide coatings, both only Ce and only Y modified silicide coatings were also prepared for comparison. The mechanisms of the beneficial effects of Ce and Y are discussed. A pack mixture containing 1.5CeO2-0.75Y2O3 (wt%) powders was employed to investigate the growth kinetics of the Ce and Y jointly modified silicide coating at 1050, 1150 and 1250 ℃. It has been found that the growth kinetics obeyed parabolic laws and the parabolic rate constants were 109.20 mm2/h at 1050 ℃, 366.75 mm2/h at 1150 ℃ and 569.78 mm2/h at 1250 ℃, and the activation energy for the growth of the Ce and Y jointly modified silicide coating was 197.53 kJ/mol.