Electrodeposition of Ni-SiC nanocomposite film

The point of zero charge(PZC) of SiC nanoparticles was determined by means of standard potentiometric titration method, while the influences of the main technological parameters on the microstructure of electrodeposited Ni-SiC composite film were studied and optimized. The results show that high bath pH value favors SiC nanoparticles negatively charged and high bath temperature promotes them positively charged. Under the experimental conditions, sodium dodecyl-glycol is proven to be an effective surface modification anionic surfactant for SiC nanoparticles. The results also show that the optimized Ni-SiC composite film is composed of the nanoparticles with the average grain size in the nanometer range (100 nm), and SiC nanoparticles disperse into the nickel matrix uniformly.     

Electrodeposition and characterization of nano-structured Ni-SiC composite films

Ni-SiC nano-composite coating, which simultaneously composed of both nanocrystalline consecutive Ni matrix and dispersed inert SiC nano-particles, has been fabricated by ultrasonic electroplating technique from a modified Watts bath containing SiC nano-particles. The influence of mechanical stirring and ultrasonication on the surface morphology of the nanocrystalline Ni-SiC nano-composite film has also been investigated. The surface morphology, microstructure, anti-corrosion property and electrocatalytic activity for hydrogen evolution of the obtained nanocrystalline Ni-SiC nano-composite film, are characterized using scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) system, atomic force microscopy (AFM), transmission electron microscope (TEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) techniques. The results find that, mechanical stirring mainly prevents the sedimentation of the inert particles suspended in solutions, while ultrasonication mainly prevents the particles agglomeration. In the case of only mechanical stirring to disperse the SiC nano-particles, the composite surface is cauliflower alike. While in the case of both mechanical stirring and ultrasonication, the obtained Ni-SiC composite film is much smoother and composes of particles with the mean diameter of 42.9 nm, and SiC particles are uniformly dispersed into Ni matrix. Meanwhile, the results obtained by polarization curves and EIS methods show that, when compared with the traditional polycrystalline Ni film, the obtained Ni-SiC nano-composite film exhibits the enhanced corrosion resistance in NaCl solutions, possesses much higher electrocatalytic activity for hydrogen evolution in KOH solutions.     

SiC颗粒尺寸对镍基复合镀层耐磨性和耐蚀性的影响

在正交实验基础上,对比研究微米SiC(平均粒径1.5 μm)和纳米SiC(平均粒径20 nm)增强复合镍基镀层的摩擦磨损行为和耐腐蚀性能.通过TEM、SEM、EDX和XRD等手段研究颗粒分散状态以及复合镀层的表面和截面形貌、成分及相结构.采用球-盘滑动摩擦磨损试验机研究复合镀层的耐磨性.电化学阻抗谱测量在3.5%的NaCl水溶液中进行.结果表明:微米级颗粒增强复合镀层可以获得更高的表面硬度,两种增强复合镀层具有相似的摩擦磨损行为.电化学阻抗谱分析表明:SiC颗粒的加入可以提高镀层的耐腐蚀性,且纳米颗粒复合镀层具有更好的耐蚀性.     

MB8镁合金阴极电沉积Ni-SiC纳米复合镀层微观结构及性能

采用以硫酸镍为主盐的电沉积技术,在MB8形变镁合金表面制备纳米复合镀层。利用扫描电镜和透射电镜观察复合镀层的显微形貌和微观结构,利用X射线衍射仪和能谱仪对复合镀层进行物相分析,利用显微硬度计测定镀层显微硬度,利用快速磨损试验机测试复合镀层的耐磨性能,利用电化学测试仪测定复合镀层在3.5%NaCl（质量分数）溶液中的极化曲线。结果表明：在MB8形变镁合金表面可以获得结晶均匀、结构致密的纳米复合镀层,该复合镀层的显微硬度最高达HV 682,其耐磨性能超过硬铬镀层,且具有较好的耐蚀性能,自腐蚀电位较镁合金基体提高677 mV。     

Preparation of composite electroheat carbon film

1INTRODUCTIONThe electroheat carbon fil mis a newfunction-al electroheat fil m developed based on the electro-heat coating.Due to its good electroheat propertyand equivalent volume resistivity as nickel at roomtemperature,it can be widely used in electroheator relevant advanced technological fields such asportable low-voltage electric food warmer,ricecooker and heater,as a kind of lowvoltage electro-heat material[15].The existing electroheat coatingdeveloped by Acme chemicals&Insulating o…     

Nucleation and growth of titanium aluminide in an explosion-welded laminate composite

Processes of nucleation and growth of titanium aluminide in a 23-layer aluminum-titanium composite produced by explosion welding have been studied. In the vortex zones of seven upper welds, microvolumes of melted metal whose microhardness is ??5500 MPa have been revealed, which corresponds to the microhardness of the intermetallic compound Al₃Ti. No formation of titanium aluminide in welded junctions that were not subjected to additional heat treatment has been revealed by X-ray diffraction. The holding of the composites at 630°C is accompanied by the formation of interlayers of intermetallic compounds of the Al₃Ti type. Intermetallic compounds of two morphological types are formed in the welds. In the regions of vortex zones, compact precipitates of Al₃Ti are formed; in the other regions of the welds, intermetallic compounds in the form of a film are precipitated. The intermetallic compounds of the first type grow more rapidly and in final account absorb the precipitates of the film type. The activation of diffusion in the upper junctions that occurs upon heating of the welded composites is favored by the nonequilibrium state of the material caused by the strain hardening of the initial samples. In the welds located deeper than the 13th layer, no signs of the formation of compact intermetallic compounds have been revealed upon the annealing for 5 h and less.     

Dissolution kinetics and thermodynamic analysis of vanadium trioxide during pressure oxidation

The dissolution kinetics of vanadium trioxide in sulphuric acid-oxygen medium was examined. It was determined that the concentration of sulphuric acid and stirring speed above 800 r min 1 did not significantly affect vanadium extraction. The dissolution rate increased with increasing temperature and oxygen partial pressure, but decreased with increasing particle size. The dissolution kinetics was controlled by the chemical reaction at the surface with the estimated activation energy of 43.46 kJ·mol-1. The l...     

Nucleation mechanism of a nickel-base superalloy during dynamic recrystallization

Hot compression test was carried out at 1000℃ to investigate the dynamic recrystallization nucleation mechanism of a nickel-base superalloy. It was found that the bulging of original grain boundaries was inhibited by carbides and deformation twins at the boundaries. Recrystallized nuclei evolved from the subgrains of dislocation reconfiguration along original grain boundaries, and the growth of the potential nuclei was carried out by the coalescence of subgrains. The necklace structure of recrystallized gra...     

Thermodynamic effects on the kinetics of vacancy-generating processes

The inhibiting effect of vacancies on the very process in which they are generated is considered from a thermodynamic viewpoint. Examples of such processes treated here in some detail are grain growth and pore dissolution. It is shown that these processes are inhibited due to vacancy generation. A particular scenario discussed implies intermittent “locking”. After a period of uninhibited kinetics the process comes to a halt due to a thermodynamic back force “locking” it. It can only re-start once the vacancies produced are removed by diffusion. This repetitive cycle leads to an overall reduction in the rate of the kinetic process in question. Specific predictions with regard to grain growth in fine-grained (particularly nanocrystalline) materials and void dissolution kinetics in sintering are made. A third example considered is vacancy drag on a moving individual grain boundary. The magnitude of the drag is re-assessed by taking into account the Gibbs free energy of the vacancies generated.