Polished Nickel Research Articles

STUDIES ON CORROSION BEHAVIOR OF POLISHED NICKEL SURFACE WITH RESIN WETTED BY DEEP EUTECTIC SOLVENT

As a material widely used in aerospace and energy development, the surface quality of nickel and its alloy will need to be improved urgently. Electrochemical polishing, as a surface treatment method, can smoothen the metal surface and improve its corrosion resistance. Strict environmental regulations have given rise to new electrochemical polishing techniques. In this paper, the electrochemical polishing of nickel was carried out using resin particles wetted by deep eutectic solvent (DES) as polishing medium. The surface morphology and roughness of polished nickel were characterized by scanning electron microscopy (SEM) and optical profilometer. In addition, electrochemical polarization curve and electrochemical impedance spectroscopy (EIS) were used to test the corrosion behavior of polished specimens in 3.5[Formula: see text]wt.% NaCl solution. The results show that the surface morphology of polished nickel shows grain boundary characteristics. The surface roughness Ra can be reduced from 0.612[Formula: see text][Formula: see text]m to 0.0913[Formula: see text][Formula: see text]m (under 30[Formula: see text]V voltage polishing 1[Formula: see text]h), and the corrosion current density can be reduced from 27.30[Formula: see text][Formula: see text]A[Formula: see text]cm[Formula: see text] to 12.15[Formula: see text][Formula: see text]A[Formula: see text]cm[Formula: see text]. Pitting potential in the polarization curve indicates that the pits at the grain boundaries are corroded due to the influx of corrosive chloride ions. This polishing method combines the resin with DES which can reduce the production of polishing liquid waste while avoiding the use of harmful acid-base electrolytes and effectively reduce the surface geometry uneven degree, improving the surface corrosion resistance.

Determination of Surface Intrinsic Resilience against Bubble Coverage Using Localized Electrochemical Impedance Spectroscopy Time Domain Information

Bubble coverage on electrode surfaces presents challenges for the wide application of water electrolysis technology. Earlier experimental studies on superaerophobic electrode surfaces indicated that surface roughness of microscale morphologies can greatly increase the surface’s resilience against bubble coverage at high current densities. Localized electrochemical impedance spectroscopy (LEIS) is used in this paper to assess this surface conductance under bubbles. The local impedance of the bubble-shielded area and the contour around the bubble were investigated on polished nickel and dynamic hydrogen bubble templating (DHBT) nickel surfaces with different porosities and pore distributions. This study demonstrated that porosity could reduce the resistivity caused by bubble coverage, and an evenly distributed porous surface is more resilient to bubble coverage.

Elaboration and characterisation of plasma sprayed alumina coatings on nickel with nickel oxide interlayer

A process implying the pre-oxidation of nickel substrates was proposed alternatively to the usual Atmospheric Plasma Spraying (APS) of alumina on sandblasted substrates. This process comprised two steps, the substrate pre-oxidation (instead of the sandblasting of the substrate) followed by APS. The pre-oxidation formed a thin layer of the NiO oxide, 0.7–3.5 μm thick, which entirely covered the nickel substrate. During APS, the deposit did not react with NiO due to the very high cooling rate of the alumina splats at the surface of the substrates. The characterisation of the interfacial zone showed the crystallographic continuity of the different lattices, from the nickel substrate (f.c.c.) to the NiO interlayer (f.c.c.) and to the monoclinic γ-Al2O3 coating. The NiO interlayer played the role of a buffer zone that adapted the crystal lattices of the three phases. The adhesion of the coatings was determined according to the ASTM C633 test modified by reducing the contact area substrate/coating, in order to quantify the adhesion of strongly-linked coatings. The coating adhesion reached 105 MPa for the pre-oxidized samples when NiO was 1.8 μm thick, instead of 48.5 MPa for the sandblasted samples and only 8 MPa for the simply polished nickel.

Helium plasma induced nanostructure formation in copper and nickel

Copper and nickel samples were exposed to helium plasma to investigate surface nanostructure formation and associated helium nano-bubble growth. Plasma fluences from 3.9 × 1023 He m−2 to 3.1 × 1024 He m−2 were used for this study. For copper with an unpolished surface finish 50–100 nm wide nanoscale pillars were formed, with more complex structures observed at higher plasma fluences. This is due to the uneven topography providing nucleation sites that stabilises the growth of these features. For polished copper surfaces nano-scale pillars formed on some crystal grains but not others, indicating strong crystal orientation effects on nano-structure formation. The formation of nano-scale islands and pillars was also observed in both polished and unpolished nickel samples, with nano-structure formation occurring across all crystal grains.Nanostructures that formed on nickel samples exposed to helium plasma at controlled temperatures from 200 °C to 325 °C showed significant sensitivity to the sample temperature. Dense fields of 50 nm diameter nanostructures formed at 300 °C, larger but sparse nanostructures formed at 325 °C, and little change was observed at and below 250 °C.Sub-surface helium bubbles were measured and displayed similar sizes for bubbles formed in both copper and nickel samples.

High temperature thermal radiation property measurements on large periodic micro-structured nickel surfaces fabricated using a femtosecond laser source

Microstructures enable many kinds of surface modifications with unique physical characteristics. The difficulties in fabricating microstructures on large metallic surfaces, however, may limit their wide use. This work measured the thermal radiation characteristics of large, three-dimensional microstructured metal surfaces where the microstructures were fabricated by a femtosecond laser to investigate the influence of the surface microstructures on the thermal radiation properties at elevated temperatures. The microstructured nickel surfaces with the microholes having the periods of 100 μm (aligned array) and 71 μm (staggered array) were fabricated by different femtosecond laser pulses (200 and 2000) and fluences (0.138 J/cm2 and 0.276 J/cm2). The microhole diameter was close to 20 μm and the depth was 50–120 μm with large aspect ratios above 2.5. Measurements of the thermal radiation properties of a polished bare nickel surface and surfaces with microholes showed that the topography greatly affected the surface radiation properties with increased emissivities (maximum increase of 55%) at temperatures from 700 K to 1200 K. It mainly arises from the multiple reflections inside the microholes and even cavity resonance inside some of the microholes. The work provides a valuable reference for fabricating 3D periodic microstructures on large metallic surfaces and shows how the engineered microstructure surfaces affect the thermal radiation at elevated temperatures.

Surface features and energy considerations related to the erosion processes of Cu and Ni electrodes in a spark discharge nanoparticle generator

In the present study, the erosion of polished nickel and copper electrode surfaces (with an average roughness of ca. 4.5 nm) exposed to a low number (1−3) of sparks in a spark discharge nanoparticle generator were investigated with the purpose of better understanding the utilization of the energy pumped into the electrodes as well as the processes leading to the generation of aerosol nanoparticles. It was shown that even a single oscillatory discharge creates complex morphological changes on the electrode surfaces. Three main erosion features were identified (referred to as craters, undulated areas and dendritic areas) and characterized by optical, confocal laser scanning and atomic force microscopy. Their potential formation mechanisms are also discussed. By estimating the total energy needed to melt the electrode material corresponding to the volume of the craters individually identified and associated with the first half-cycle of the discharge, it was shown that the electric energy pumped into the electrodes in the form of Joule heating is mostly consumed by the melting of the electrode material, which is followed by re-solidification. Hence, only a small fraction of the electrode material is actually evaporated into the ambient gas. This explains the very low value of the energy-efficiency in the commonly used Jones model.Our results indicate that only a part of the material that leaves the electrode surface is actually converted into an aerosol. The input to the aerosol formation is either vapor or molten material ejected from craters. Ejected molten material can lead to the formation of micrometer-sized aerosol particles (“splashing particles”). Some of the metal vapor is deposited on the surface in the vicinity of craters forming dendritic areas, whereas only a fraction of the metal vapor is carried away by the ambient gas and may form aerosol nanoparticles. This study clearly indicates that erosion processes in spark discharge nanoparticle generators are very complex and can not be reasonably described by simplified erosion models.

Effect of surface finishing on the formation of nanostructure and corrosion behavior of Ni–Ti alloy

In the present work, we have investigated the formation of nanostructured oxide layers by anodic oxidation on different surface finished (mirror finished, 600 and 400 grit polished) nickel–titanium alloy (Ni–Ti) in electrolyte solution containing ethylene glycol and NH4F. The anodized surface has been characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X‐ray photoelectron spectroscopy (XPS). The corrosion behaviors of the Ni–Ti substrate and anodized samples have been investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated body fluid (Hanks' solution). The results show that the native oxide on the substrate is replaced by nanostructures through anodization process. XPS of Ni–Ti substrate shows the presence of Ni0, NiO, Ti0 and TiO2 species, whereas Ni2O3 and Ni(OH)2 and TiO2 are observed in the samples after anodization. Corrosion resistance of the anodized sample is comparable with that of the untreated sample. Copyright © 2016 John Wiley & Sons, Ltd.

Spectral enhancement of thermal radiation by laser fabricating grating structure on nickel surface**Project supported by the National Natural Science Foundation of China (Grant No. 51275012).

Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared (FTIR) spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance (SPR) and Kirchhoff’s law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis (RCWA) to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.

Kinetics of the hydrogen evolution on nickel in alkaline solution: new insight from rotating disk electrode and impedance spectroscopy analysis

Nickel catalysts were characterized for the hydrogen evolution reaction (HER) using rotating disk electrode (RDE) and electrochemical impedance spectroscopy (EIS). The theoretical Levich slope was calculated on the basis of the HER mechanism in alkaline solution. Kinetic and thermodynamic parameters of the reaction were obtained for fresh polished nickel electrode (Nif), and for nickel after a quick chronoamperometric aging procedure (Nipc). Koutecky-Levich analysis indicated that the rate determining step on Nif is the one-electron Volmer reaction, while for Nipc decreases from one to 0.68 and exhibits a strong temperature dependence. A loss of catalytic activity, corresponding to an increase of 0.3V of the HER onset potential, was observed after aging. Furthermore, from the EIS-Tafel analysis we concluded that the H adsorption changes from a Langmuir type for Nif, to a Temkin type for Nipc.

Mass transfer to a nanostructured nickel electrodeposit of high surface area in a rectangular flow channel

Nanostructured nickel was electrodeposited on a stainless steel plate. The convective-diffusion mass transfer to this nanostructured electrode was compared to that of a planar, mirror polished solid nickel electrode using the limiting current technique, for the reduction of ferricyanide, hexacyanoferrate (III) ion in an undivided cell. The effect of introducing a turbulence promoter into the electrolyte channel was also evaluated for each electrode under steady state conditions. At a Reynolds number of 700, the product of mass transfer coefficient and active electrode area, kLA for the nanostructured nickel electrode increases over 11 times compared to the mirror polished planar nickel electrode. In the presence of a turbulence promoter, the nanostructured nickel electrode shows an approximately 23 times increase in kLA compared to the planar mirror polished nickel electrode. The dimensionless mass transfer correlations Sh=aRebScdLee are compared to others in the literature.

Friction and wear behaviors of dental ceramics against natural tooth enamel

Abstract The friction and wear behaviors of dental ceramics against the natural tooth enamel were investigated. In this study three dental ceramics, namely zirconia with both polished and rough surfaces, hot-forged lithium disilicate glass ceramics and silicates based veneer porcelain were involved with two metallic materials, gold–palladium alloy and Nickel–chromium alloy, as references. The tribological tests were carried out under artificial saliva lubrication condition by using freshly extracted natural teeth and samples with controlled surface roughness. The frictional coefficients versus reciprocating cycles were recorded. Scanning Electron Microscopy was used to observe the topography of worn teeth enamel surfaces and antagonists. The frictional coefficient of enamel against gold palladium alloy or Nickel–chromium alloy was the smallest. The frictional coefficient of enamel against polished zirconia or porcelain was between that of metal and glass-ceramic. Upon surface polishing, frictional coefficient between zirconia and enamel was radically decreased. Furrows and granular debris were observed on the worn surfaces of enamel while sliding against the rough zirconia or glass ceramic, indicating a abrasive wear mechanism. While chipping flake and pit-like structure after stripping and crack were observed on the enamel surface while sliding against polished zirconia or Nickel–chromium alloy, indicating a type of fatigue wear. It appeared that the friction and wear performances of zirconia could be improved significantly by adequate surface polishing. This observation indicated that attention must be paid to carefully design proper occlusal surface contours and correctly choose dental materials in clinical practice.

Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates.The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements.We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature.

Effects of annealing time on infrared emissivity of the Pt film grown on Ni alloy

Platinum films were sputter-deposited on polished nickel alloy substrates. The platinum thin films were applied to serve as low-emissivity layers to reflect thermal radiation. The platinum-coated samples were then heated in the air at 600 °C to explore the effects of annealing time on the emissivity of platinum films. The results show that the grain size of the Pt films increased with the increasing annealing time while their dc electrical resistivity decreased. Besides, the IR emissivitiy of the films gradually decreased with the increasing annealing time. Especially, when the annealing time reached 150 h, the average IR emissivity at the wavelength of 3–14 μm was only about 0.1. Moreover, the chemical analysis indicated that the Pt films on Ni-based alloy exhibit a good resistance against oxidation at 600 °C.

Surface orientation effects on initial carbon deposition and metal dusting of nickel

Polished polycrystalline nickel was first characterised by orientation imaging microscopy to search for grains with low index faces, and then reacted in a gas of 25%CO– 25%H2–0.5%H2O–49.5%Ar at 650°C for different times. Carbon deposition on and metal dusting of these grains were examined by scanning electron microscopy and cross-section observations made by focused ion beam milling. Carbon deposition was found to be the fastest on nickel (111) face, slowest on nickel (001), and somewhere in between on other faces. The carbon morphology varied from a featureless uniform layer on (111) face to aligned needles or leaves on (101) and other faces. This phenomenon can be explained in terms of a graphite-nickel epitaxial relationship.Initial metal dusting was affected by nickel surface orientation in a more complicated way. The (001) face produced initially little or no carbon deposition, and therefore no carbon attack in most area, but dusted locally after 22 h reaction. Local dusting attack was also found to correspond well with localised graphite nucleation. Different surface nickel grains were found to change height with reaction time, a difference attributed to varying extents of carbon dissolution.

Low temperature diffusion bonding of Pd-based composite membranes with metallic module for hydrogen separation

A diffusion-bonding procedure at a low temperature, i.e. 500 °C, based on the high mobility of silver atoms was developed with a newly designed plate-and-frame type hydrogen purification membrane module consisting of a unit cell and a housing. Two membranes made of palladium and copper sputtered on polished porous nickel supports (PNS) followed by Cu-reflow at 750 °C, respectively, were assembled in a unit cell to verify that the low temperature diffusion-bonding method could be applied to gas-tight membranes. Ring-shaped silver foils with a thickness of 50 μm were placed between the membranes and the unit cell body made of nickel plate. A pair of membranes, a pair of silver foils and the unit cell body were compressed with a pair of covers and eight screws by a 17 cm long torque wrench at 12 N m. The diffusion-bonded unit cell was welded in a module housing comprised of a feed port and a retentate port by a laser-operated welder. After the module was constructed, gas-tightness tests were carried out using helium and the measured helium leakage was 8 × 10 −5 mol m −2 s −1 at 0.7 MPa, which is the same as the value detected before diffusion bonding with a Viton O-ring. The hydrogen permeation test and durability test consisting of three cycles of alternately changing the temperature and transmembrane pressure difference were carried out using a single gas, hydrogen, and it was found that the hydrogen permeation flux remained constant during the durability test and that the helium leakage did not increase after the durability test.

Growth of HT-LiCoO 2 thin films on Pt-metalized silicon substrates

Layered LiCoO 2 (HT-LiCoO 2) films were grown on Pt-metalized silicon (PMS) substrates and polished bulk nickel (PBN) substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO 2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO 2 films. The HT-LiCoO 2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [00l] preferential orientated triangular shaped grains with the average grain size less than 100 nm. Electrochemical measurements show that the highly [00l] preferentially orientated nanostructured HT-LiCoO 2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45 μA·h·cm −2·μm −1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5 C.

Formation of a defect-free Pd–Cu–Ni ternary alloy membrane on a polished porous nickel support (PNS)

In order to decrease its resistance we enlarged the pore size of a porous nickel support (PNS) by using nickel powder with a larger particle size. The gas permeation test showed that this increased the gas permeation flux compared with the previous support. To make up for the various disadvantages, such as the enlarged surface roughness and pore size, a polishing process was introduced with sandpaper, followed by wet polishing with alumina powder. The polishing treatment was very effective in leveling off the surface of the porous nickel support, but it almost completely plugged the pores. Those pores blocked by the polishing process could be regenerated during Cu-reflow at 973 K by the upward diffusion of nickel and in this way a 12 μm defect-free Pd–Cu–Ni ternary alloy film was formed on the polished porous nickel support. Furthermore, we were able to obtain a three times higher hydrogen permeability than that reported in previous studies, because of the decreased support resistance of the porous nickel support.

Efficiency of the Horizontal Single Pin Fin Subjected to Free Convection and Radiation Heat Transfer

In this communication, the results of numerical calculations of the heat transfer coefficient and temperature distribution along the horizontal single pin fin in still ambient air, as well as the fin efficiency, are presented and compared with classical analytical results in the case of the constant heat transfer coefficient fin theory. The measured temperature distributions along the two low carbon steel pin fins having a length-to-diameter ratio of 35—one covered with the polished nickel and the other painted mat black—agree very well with the numerical results and are higher than the classical results. The analytically calculated fin efficiency does not differ significantly from the results of the numerical calculations if they are compared for the same dimensionless fin parameter in which the heat transfer coefficient is determined for the fin base temperature. More extended numerical calculations showed that beyond the fin parameter of five, the analytical results of the fin efficiency are higher than the numerical results by no more than about 1%. The largest difference between the classical and numerical fin base efficiencies is about 3.5%, and it was observed at a fin parameter of about 1, where the length of the pin fin has the optimal value based on the classical theory.

Transition Boiling Heat Transfer of Droplet Streams and Sprays

An experimental study was performed to characterize the transition boiling heat transfer rate from a surface to a stream of impinging water droplets and to extrapolate this information to predict the transition boiling heat transfer of a dilute spray. First, transition boiling heat transfer data were gathered for a continuous stream of monodispersed water droplets striking a polished nickel surface. From these data, empirical correlations were developed to describe the heat transfer rate and heat transfer efficiency for droplet velocities between 1.0ms−1 and 7.1ms−1, droplet diameters ranging from 0.250×10−3mto1.002×10−3m, and surface temperatures covering 110–240°C. By properly accounting for the hydrodynamic differences between a spray and a single droplet stream, the empirical single droplet stream heat transfer correlations were effectively extrapolated into a model for predicting the transition boiling heat flux of dilute sprays (Q″≈0.5×10−3m3s−1m−2).

Studies on the morphologies of LiCoO 2 films prepared by soft solution processing

Lithium cobalt oxide films were prepared on nickel plates and foam nickel by soft solution processing method. The films were characterized by chemical analysis, X-ray diffraction, scanning electron microscopy, and atomic force microscopy. It was found that growth of LiCoO 2 crystal on polished nickel plates and foam nickel led to different morphologies of LiCoO 2. A compact LiCoO 2 film was formed on smooth nickel plates while some grassy LiCoO 2 crystals formed and scattered on the surface of foam nickel, which indicates different mechanism of films growth. Formation of LiCoO 2 crystal on nickel plates shows the characteristic of two-dimensional nucleation while on foam nickel shows the characteristic of preferential nucleation. Further, increase of LiOH concentration in the soft solution results in morphological change of LiCoO 2 film from hexagonal platelets to spherical grains. In addition, the larger the current density, the less the grain size and the porosity inside grains are.