电沉积法制备泡沫Ni-Mo-Co合金

本文以聚氨酯泡沫海绵为基体,经导电层的制备、电镀和热解还原工艺制备出了泡沫Ni-Mo-Co三元合金。采用扫描电子显微镜(SEM)和X射线衍射技术(XRD)分别研究了化学镀镍后及电镀Ni-Mo-Co合金的表面形貌、元素组成和晶态结构,并用稳态极化曲线研究了泡沫Ni-Mo-Co合金电极在30%KOH溶液中的析氢催化性能。结果表明:该泡沫合金具有均匀分布三维网状孔结构及高的孔隙率,析氢过电位比泡沫镍降低了407 mV,其析氢催化活性良好。

石墨烯掺杂对WC(0001)-Co硬质合金晶相界面结合性能的影响

基于第一性原理方法分别计算了WC(0001)-Co、WC(0001)-Co/sGR、WC(0001)-Co/dGR晶相的界面粘附功、断裂韧性,结果表明WC(0001)-Co/sGR中WC(0001)/Co(sGR)界面具有最大粘附功(6.3551 J·m-2),WC相具有最大断裂韧性(6.4376 J·m-2),结构最为稳定,界面结合性能最好。WC(0001)-Co/dGR中GR/GR的界面粘附功仅为0.0057 J·m-2,dGR相的断裂韧性为0.0064 J·m-2,裂纹最易在此处产生。为验证界面结合的分析结果,研究了三种晶相的电子结构和态密度,结果表明掺杂GR增强了界面处原子的电荷分配程度,W-Co之间具有更多电荷转移而相吸,键合作用增强。与掺杂dGR相比,掺杂sGR后的Co-C(sGR)键合作用增强,Co-C(sGR)键强于Co-C(dGR)键,sGR掺杂提高了WC(0001)-Co硬质合金硬质相WC和粘结相Co的界面结合性能。

WC-Ti(C,N)-Co硬质合金表面脱氮后的残余热应力分析

通过定义弹性约束因子和引进塑性约束因子,构造成分梯度硬质合金弹塑性本构方程,根据此方程,采用有限元方法对WC-Ti(C,N)-Co硬质合金脱氮处理后的残余应力分布进行分析。结果表明,WC-Ti(C,N)-Co硬质合金脱氮后从初始无应力的820℃下降到20℃时等效应力最大值出现在表面两相区钴含量最高的位置,从表面两相区到芯部出现很高的应力梯度。表面两相区有拉应力分布,向内逐渐过渡到压应力,两相区的最大静水拉应力约140MPa,而芯部的最大静水压应力为-120MPa。

Oxidation behaviors of electrodeposited nickel-cobalt coatings in air at 960°C

Ni coating and Ni-Co alloy coatings were produced by adjusting the composition of the plating solution using a direct current electrodepositing process. The oxidation behaviors of nickel and nickel-cobalt alloys in air at 960 ℃ were studied by thermogravimetric （TG） analyzer and then the formed oxide scales were examined by scanning electron microscopy/energy dispersive spectroscopy （SEM/EDS）, X-ray diffractometry （XRD）, and Raman spectroscopy. The scale morphologies, composition, grain size and mechanism of oxidation were discussed in detail. The results show that oxidation rates ofNi, Ni-7%Co （mass fraction） and Ni-15%Co generally follow parabolic relationship, whereas that of Ni-30% Co alloy follows cubic relationship. The higher the Co content of the alloys is, the faster the oxidation rate is. Metal concentration profiles reveal cobalt depletion in the alloy surface beneath oxide scales, and a progressive＇enrichment in cobalt towards the outer surface of the scale.

Effect of deposition parameters on micro-and nano-crystalline diamond films growth on WC-Co substrates by HFCVD

The characteristics of hot filament chemical vapor deposition（HFCVD） diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.

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.

Production and fluoride treatment of Mg-Ca-Zn-Co alloy foam for tissue engineering applications

Highly porous Mg-Ca-Zn-Co alloy scaffolds for tissue engineering applications were produced by powder metallurgy based space holder-water leaching method.Mg-Ca-Zn-Co alloy foam can be used as a scaffold material in tissue engineering.Carbamide was used as a space holder material.Fluoride conversion coating was synthesized on the alloy by immersion treatment in hydrofluoric acid(HF).Increasing Zn content of the alloy increased the elastic modulus.Ca addition prevented the oxidation of the specimens during sintering.Electrochemical corrosion behaviour of the specimens was examined in simulated body fluid.Corrosion rate decreased with Zn addition from1.0%up to3.0%(mass fraction)and then increased.Mass loss of the specimens initially decreased with Zn addition up to about3%and then increased.Fluoride conversion coating increased the corrosion resistance of the specimens.

Anodic behavior and microstructure of Al/Pb-Ag-Co anode during zinc electrowinning

In order to study the anodic behavior and microstmctures of A1/Pb-Ag-Co anode during zinc electrowinning, by means of potentiodynamic investigations, scanning electron microscopy （SEM） and X-ray diffraction （XRD） analyses, the mechanism of the anodic processes playing on the surface of A1/Pb-0.8%Ag and A1/Pb-0.75%Ag-0.03%Co anodes prepared by electro-deposition from methyl sulfonic acid bath for zinc electrowinning from model sulphate electrolytes have been measured. On the basis of the cyclic voltammograms obtained, information about the corrosion rate of the composite in PbO2 region has been concluded. The microstructures were also observed by means of SEM and XRD which showed Pb-0.75%Ag-0.03%Co alloy composite coating has uniform and chaotic orientation tetragonal symmetry crystallites of PbSO4, but Pb-0.8%Ag alloy composite coating has well-organized orientation crystallites of PbSO4 concentrated in the certain zones after 24 h of anodic polarization. It is important that Al/Pb-0.75%Ag-0.03%Co anode oxide film consists of non-conductive dense MnO2 and PbSO4 and a, fl-PbO2 penetrated into which, in fact, are the active centers of the oxygen evolution after 24 h of anodic polarization.

Influence of Ni^(2+)/Co^(2+)ratio in electrolyte on morphology,structure and magnetic properties of electrolytically produced Ni-Co alloy powders

Nickel-cobalt(Ni-Co) alloy powders were produced galvanostatically by using sulphate electrolytes with various ratios of Ni2+/Co2+(mole ratios). The morphology, phase structure, chemical composition and magnetic properties were examined by scanning electron microscope(SEM), X-ray diffractometer(XRD), atomic emission spectrometer(AES), and SQUID-based magnetometer, respectively. Morphology of the particles changed from cauliflower-like and dendritic to coral-like and spongy-like ones with increasing Ni2+/Co2+ ratio from 0.25 to 4.0. XRD analysis of the Ni-Co powders revealed that the decrease of Ni2+/Co2+ ratios(the increase of Co content) caused a change of structure from face centered cubic(FCC) obtained for the ratios of 4.0, 1.5 and 0.67 to a mixture of FCC and hexagonal closed-packed(HCP) phases for the ratio of 0.25. The increasing content of nickel led to change of mechanism of electrolysis from irregular(up to 40 wt.% Ni in the electrolytes) to close to equilibrium(between 40 and 60 wt.% Ni in the electrolytes) and anomalous co-deposition(over 60 wt.% Ni in the electrolytes) type. All of the obtained Ni-Co alloy samples behaved as soft magnetic materials while their magnetic parameters showed immediate composition dependence since both coercivity and saturation magnetization almost linearly increased with increase of the Co content.

Synthesis and characterization of Ti-Co alloy foam for biomedical applications

Highly porous Ti-Co alloy specimens for biomedical applications were synthesized by powder metallurgy based space holder technique. Ti alloys have high melting temperature and affinity for oxygen, which makes Ti alloys difficult to be processed. The Co addition reduces the melting temperature and Ti-Co alloy was sintered at lower temperatures. The electrochemical corrosion behaviour of the specimens was examined in the artificial saliva solution. The effects of Co content of the alloy, the p H value and fluoride concentration of the artificial saliva solution on the electrochemical corrosion properties of the specimens were investigated. The microstructure and mechanical properties of the specimens were examined. The electrochemical impedance spectroscopy results indicate that the corrosion resistance of the specimens decreases at high fluoride concentrations and low p H value. The defect density increases with increasing the fluoride concentration and decreasing the p H value of artificial saliva according to Mott-Schottky analysis.

Effects of cryogenic treatment on mechanical properties and microstructure of Fe-Cr-Mo-Ni-C-Co alloy

Fe-Cr-Mo-Ni-C-Co alloy was quenched in liquid nitrogen and held for 24 h.Hardness tester,OM,XRD,SEM were used to investigate the mechanical properties and microstructures of the alloy.The results show that the hardness increases by 1-2(HRC)and the compressive strength decreases slightly after cryogenic treatment.The increase in hardness is attributed to the transformation from austenite to martensite and the precipitation of the very tiny carbideη-Fe2C.The decrease in compressive strength is caused by residual stress.The great amount of carbides,such as Cr7C3 and Fe2MoC,in the alloy and the obvious difference in thermal expansion coefficient between these carbides and the matrix at the cryogenic temperatures lead to this residual stress.The microscopy of cryogenic martensite is different from that of the non-cryogenic martensite.The cryogenic martensite is long and fine;while the non-cryogenic martensite is short and coarse.There is obvious surface relief of the cryogenic martensite transformation.It is not orientational of this kind surface relief and the boundary of this surface relief is smooth and in a shape of butterfly.The surface relief in the non-cryogenic martensite is wide and arranged in parallel,and the boundary of surface relief is not smooth.These characteristics may imply different growth ways of the two kinds of martensite.

Effect of stress ratio on fatigue lifetime and crack growth behavior of WC-Co cemented carbide

Two types of fatigue tests, a rotating bending fatigue test and a three- or four-point bending fatigue test, were carried out on a fine grained WC-Co cemented carbide to evaluate its fatigue crack growth behavior and fatigue lifetime. From successive observations of the specimen surface during the fatigue process, it was revealed that most of the fatigue lifetime of the tested WC-Co cemented carbide was occupied with crack growth cycles. Using the basic equation of fracture mechanics, the relationship between the fatigue crack growth rate(da/dN) and the maximum stress intensity factor(Kmax) was derived. From this relation, both the values of the threshold intensity factor(Kth) and the fatigue fracture toughness(Kfc) of the material were determined. The fatigue lifetime of the WC-Co cemented carbide was estimated by analysis based on the modified linear elastic fracture mechanics approach. Good agreement between the estimated and experimental fatigue lifetimes was confirmed.

Development of black Ni-Co alloy films from modified Watts electrolyte and its morphology and structural characteristics

The electrodeposition of black Ni-Co alloy film from Watts nickel solution and the effects of benzotriaozole and imidazole as the additives were studied. The electrolyte consists of NiSO4, NiC12, H3BO3, COSO4 and KNO3. The cathode current efficiency and the throwing power of the solution and the film adhesion to the mild steel metallic foil were determined by standard methods. The crystal structure, lattice parameter, crystal orientation and crystal size were analyzed by X-ray diffraction （XRD）. Moreover, the surface morphology and elemental composition of the black Ni-Co alloy films were analyzed by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDX） techniques. The darkness of the black films increases with increasing the incorporation of Co ion into the films. The XRD studies reveal that the black Ni-Co alloy films exhibit Ni （11 l） as the preferred orientation.

Possibility of Using Ni-Co Alloy As Catalyst for Oxygen Electrode of Fuel Cell

In recent years, the scale of use of fuel cells （FCs） has been increasing continuously. One of the essential elements that affect their work is a catalyst. Precious metals （mainly platinum） are known for their high efficiency as FC catalysts. However, their high cost holds back the FCs from application on a large scale. Therefore, catalysts that do not contain precious metals are sought. Studies are focused mainly on the search for fuel electrode catalysts, but for the efficiency of FCs also the oxygen electrode catalyst is of great significance. The paper presents an analysis of the possibilitiesof using Ni-Co alloy as a catalyst for the oxygen electrode of the FC.

Solidification process and microstructure evolution of bulk undercooled Co-Sn alloys

A series of Co-Sn alloys with Sn content ranging from 12% to 32%（mole fraction） were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification microstructures.A boundary clearly exists,which separates the coupled growth zone from the decoupled growth zone of eutectic phases for the alloys with Sn content ranging from 14% to 31%（mole fraction）.The other Co-Sn alloys out of this content range are hard to be undercooled into the coupled growth zone in the experiment.It is found that the so-called non-reciprocal nucleation phenomenon does not happen in the solidification of undercooled Co-Sn off-eutectic alloys.

Effects of deep cryogenic treatment on microstructure and properties of WC-11Co cemented carbides with various carbon contents

The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains are refined into triangular prism with sound edges via the process of spheroidization,but WC grain size has no evident change compared with that of untreated alloys.The phase transformation of Co phase from α-Co（FCC） to ε-Co（HCP） is observed in the cryogenically treated alloys,which is attributed to the decrease of W solubility in the binder（Co）.Deep cryogenic treatment enhances the hardness and bending strength of the alloys,while it has no significant effects on the density and cobalt magnetic performance.

Enhanced hydrogen storage kinetics of nanocrystalline and amorphous Mg_2N-type alloy by substituting Ni with Co

In order to improve the hydrogen storage kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted with element Co. The Mg2Ni-type Mg2Ni1-xCox （x=0, 0.1, 0.2, 0.3, 0.4） alloys were fabricated by melt-spinning technique. The structures of the as-spun alloys were characterized by XRD and TEM. The gaseous and electrochemical hydrogen storage kinetics of the alloys was measured. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg2Ni-type alloy. The amorphization degree of the alloys visibly increases with rising of Co content. Furthermore, the substitution of Co for Ni significantly improves the hydrogen storage kinetics of the alloys. With an increase in the amount of Co substitution from 0 to 0.4, the hydrogen absorption saturation ratio of the as-spun （15 m/s） alloy increases from 81.2% to 84.9%, the hydrogen desorption ratio from 17.60% to 64.79%, the hydrogen diffusion coefficient increases from 1.07×10-11 to 2.79×10-11 cm2/s and the limiting current density increases from 46.7 to 191.7 mA/g, respectively.

Effect of germanium on electrochemical performance of chain-like Co-P anode material for Ni/Co rechargeable batteries

Co-P （4.9% P） powders with a chain-like morphology were prepared by a novel chemical reduction method. The Co-P and germanium powders were mixed at various mass ratios to form Co-P composite electrodes. Charge and discharge test and electrochemical impedance spectroscopy （EIS） were carried out to investigate the electrochemical performance, which can be significantly improved by the addition of germanium. For instance, when the mass ratio of Co-P powders to germanium is 5：1, the sample electrode shows a reversible discharge capacity of 350.3 mA·h/g and a high capacity retention rate of 95.9% after 50 cycles. The results of cyclic voltammmetry （CV） show the reaction mechanism of Co/Co（OH）2 within Co-P composite electrodes and EIS indicates that this electrode shows a low charge-transfer resistance, facilitating the oxidation of Co to Co（OH）2.

Non-isothermal reduction kinetics of Fe_2O_3-NiO composites for formation of Fe-Ni alloy using carbon monoxide

The non-isothermal reduction kinetics and mechanism of Fe2O3-NiO composites with different Fe2O3-NiO compacts using carbon monoxide as reductant were investigated. The results show that the reduction degree increases rapidly with increasing the content of NiO, and the presence of NiO also improves the reduction rate of iron oxides. It is found that NiO is preferentially reduced at the beginning of the reactions, and then the metallic Ni acts as a catalyst promoting the reduction rate of iron oxides. It is also observed that the increase of the Ni O content enhances the formation of awaruite(FeNi3) but decreases the percentage of kamacite(Fe,Ni) and taenite(Fe,Ni). The particle size of the materials tends to be uniform during the reduction process due to the presence of metallic nickel, metallic iron and the formation of Fe-Ni alloy. The concentration of CO in the product gas is greater than that of CO2 at the beginning of the reaction and then slows down. The fastest reduction rate of Fe2O3-NiO composites with CO appears at 400-500 °C, and nucleation growth model can be used to elucidate the reduction mechanism. Nucleation growth process is found to be the rate controlling step when the temperature is lower than 1000 °C.

Thermodynamic assessment of Co-Cr-W ternary system

The Co-Cr-W ternary system was critically assessed using the CALPHAD technique.The solution phases including the liquid,γ-Co,ε-Co and α-Cr were described by a substitutional solution model.The σ,μ and R phases were described by three-sublattice models of（Co,W）8（Cr,W）4（Co,Cr,W）18,（Co,Cr,W）7W2（Co,Cr,W）4 and（Co,W）27（Cr,W）14（Co,Cr,W）12,respectively,in order to reproduce their homogeneity ranges.A self-consistent set of thermodynamic parameters for each phase was derived.The calculated isothermal sections at 1 000,1 200 and 1 350 ℃ are in good agreement with the experimental data.A eutectoid reaction of R μ＋γ-Co＋σ in this ternary system was predicted to occur at 1 022 ℃.