Plasma electrolytic ceramic-like aluminum oxide coatings on iron

The process characteristics of plasma-assisted electrochemical treatment of iron in aluminate electrolyte consisted of aqueous 0.1 M NaAlO₂ + 0.05 M NaOH have been studied. It has been shown that in the range of DC voltages from 260 to 340 V, it is possible to deposit dense ceramic-like coatings with the thickness increased from 0.3–0.5 μm after 1 min deposition time to 25–30 μm for 1 h of deposition. The coatings were examined by X-ray diffractometry, Fourier-transformed infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, and an electrochemical potentiodynamic voltammetry. It is shown that in pre-spark conditions (100–200 V) and on the initial stages of micro-arc anodizing the forming films contain, along with amorphous aluminum oxide/hydroxide, a substantial amount of iron oxide/hydroxide. The coatings obtained by micro-arc anodizing at 260–360 V for 10–60 min represent amorphous aluminum oxide with inclusions of crystalline corundum phase. The films with a thickness of 4–15 μm deposited at the anodizing voltage of 320–360 V exhibited the uniformity and good corrosion protection properties after sealing with common agents.     

Electrodeposition and characterization of nickel–copper metallic foams for application as electrodes for supercapacitors

Nickel–copper metallic foams were electrodeposited from an acidic electrolyte, using hydrogen bubble evolution as a dynamic template. Their morphology and chemical composition was studied by scanning electron microscopy and related to the deposition parameters (applied current density and deposition time). For high currents densities (above 1 A cm^?2) the nickel–copper deposits have a three-dimensional foam-like morphology with randomly distributed nearly-circular pores whose walls present an open dendritic structure. The nickel–copper foams are crystalline and composed of pure nickel and a copper-rich phase containing nickel in solid solution. The electrochemical behaviour of the material was studied by cyclic voltammetry and chronopotentiometry (charge–discharge curves) aiming at its application as a positive electrode for supercapacitors. Cyclic voltammograms showed that the Ni–Cu foams have a pseudocapacitive behaviour. The specific capacitance was calculated from charge–discharge data and the best value (105 F g^?1 at 1 mA cm^?2) was obtained for nickel–copper foams deposited at 1.8 A cm^?2 for 180 s. Cycling stability of these foams was also assessed and they present a 90 % capacitance retention after 10,000 cycles at 10 mA cm^?2.     

Electrochemical determination of dissolved oxygen based on three dimensional electrosynthesis of silver nanodendrites electrode

In this paper, a highly sensitive electrochemical sensor for dissolved oxygen was prepared. A glassy carbon electrode was modified with silver nanodendrites that were synthesized by electrochemical deposition on the electrode without the use of a surfactant or template. The electrode displayed efficient electrocatalytic reduction of dissolved oxygen to form hydroxy ions via a four-electron reduction pathway, and a significant decrease in the respective overvoltage. The sensor responded linearly to dissolved oxygen in the 1.0–66.7 μM concentration range, and had a remarkably good sensitivity (0.169 μA μM^?1) at an applied potential of ?300 mV (vs. Ag/AgCl). The lower detection limit was 0.043 μM (at the signal-to-noise ratio of 3), and the response time was 5 s. The good performance was attributed to the enlarged electro-active surface of the dendritic silver nanostructures and to the efficiency of electron transfer between dissolved oxygen and the electrode. The sensor also showed good reproducibility, long-term stability, and relative good selectivity.     

Electrophoretic deposition of nanocrystalline hydroxyapatite on Ti6Al4V/TiO2 substrate

Hydroxyapatite is a bioactive material that is the main inorganic constituent of human hard tissue (Ca/P ratio of 1.67) whose coatings provide requisite surface bioactivity to the bone implants. In the current work, the characteristics of nanocrystalline hydroxyapatite (HA) coatings, electrophoretically deposited on Ti6Al4V substrate, have been investigated. To enhance the coating’s compatibility, a 0.75 μm thick TiO₂ layer was thermally grown as a diffusion barrier prior to electrophoretic deposition of HA. Subsequently, HA was electrophoretically deposited (EPD) at different deposition voltages (100–250 V) while keeping the deposition time as 10 s. Both anodic oxidation during EPD for 10 s and thermal oxidation during sintering at 1000°C for 2 h resulted in the growth of a TiO₂ layer thickness of more than 25 μm. Enhancement of voltage also has shown significant influence on the mechanism of the evolution of biphasic microstructures, attributed to the simultaneous growth of TiO₂ and HA phases. Optimized distribution of HA and TiO₂ phases was evidenced at 200 V, with explicit HA retention as observed via transmission electron microscopy. An empirical relationship is developed to relate the voltage with the suppression of cracking in the deposited coatings.     

Inert substrate-supported microtubular solid oxide fuel cells based on highly porous ceramic by low-temperature co-sintering

Inert substrate-supported microtubular solid oxide fuel cells (MT-SOFCs) are attractive due to their advantages, including high reduction–oxidation (redox) cycling stability and thermal cycling tolerance. A method involving sequential dip-coating, leaching, and co-sintering was developed and applied to fabricate inert substrate-supported MT-SOFCs through acid leaching nickel from the conventional Ni–yttria-stabilized zirconia (YSZ) anode. A thin current collector was deposited onto the support surface to minimize the current collection losses by collecting current from the entire surface area of the anode. A dense electrolyte could be obtained at a co-sintering temperature of 1250?°C. The produced MT-SOFC with the configuration of porous zirconia support/Ni–Scandia-stabilized zirconia (SSZ) anode current collector/Ni-SSZ anode/SSZ electrolyte/strontium-doped lanthanum manganite (LSM)-SSZ cathode/LSM cathode current collector was evaluated by electrochemical characterization tests. The inert substrate-supported MT-SOFC exhibited the maximum power densities of 616, 542, 440, and 300?mW?cm^?2 at 800, 750, 700, and 650?°C, respectively using dry hydrogen and air. In addition, the thermal cycling stability of the MT-SOFC was evaluated. The cell survived from thermal cycling tests and came out intact after 50 thermal cycles between 700?°C and 400?°C during an operation time of 50?h.     

Electroreductlon of cyclohexanone oxime

An electrochemical method for preparing cyclohexylamine from cyclohexanone oxime has been developed. Cyclohexanone oxime underwent smooth reduction in an aqueous ethanolic ammonium sulphate medium on nickel black deposited on graphite. The oxime is not reducible at ordinary copper or nickel electrodes. Nickel black deposited on copper or nickel was also found to be ineffective due to poor adhesion of the nickel black.     

Electroreduction of phenyl cyanide and benzyl cyanide on nickel cathode

An electrochemical method for preparation of primary amines from organic cyanides using nickel black deposited over graphite substrate as cathode has been studied. It has been observed that it is possible to reduce benzyl cyanide both in ethanolic sulphuric acid and in aqueous ethanolic ammonium sulphate media. But with phenyl cyanide, the reduction is efficient only in ethanolic sulphuric acid medium. Both in laboratory and 75 A scale experiments 62–66% yield has been obtained at a current efficiency of 36–44% for benzylamine. Similarly a yield ranging from 60–80% with a current efficiency of 36–52% has been obtained for β-phenylethylamine both in laboratory scale and also in large scale experiments. Results of operation of a 500 A cell for the preparation of β-phenylethylamine are also presented.     

In Situ Hydrothermal Synthesis of Nickel Oxide Nanostructures by Thermal Decomposition and its Electrochemical Property

NiO nanorods composed of nanoparticles with diameter of 25–65 nm were synthesized on a nickel foam substrate by an in situ hydrothermal process in an aqueous solution containing only oxalic acid and subsequent calcination treatment. The nickel foam acted both as a substrate and nickel source. The calcination of the nickel foam substrate before the hydrothermal process played a crucial role in the formation of NiO nanostructures with different morphologies. Cyclic voltammetry and constant current charge–discharge measurements were used to evaluate the electrochemical properties of NiO. The results indicated a maximum specific capacitance as high as 126 F/g at a current density of 0.4 A/g.     

The influence of organization of LbL films containing a silsesquioxane polymer on the electrochemical response of dopamine

This paper describes the construction, evaluation, and application of an electrochemical sensor for the determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). Satisfactory results were achieved for the simultaneous determination of DA and UA, it was verified that it is possible to detect AA in the presence of DA, but high concentrations of AA interfere in detection of DA. The sensor was constructed using the layer-by-layer (LbL) technique with the modification of the surface of indium tin oxide coated glass (ITO) substrate with nanostructured films comprising a 3-n-propylpyridinium silsesquioxane polymer (SiPy⁺Cl^?) and nickel(II) tetrasulfophthalocyanine (NiTsPc). Using the square wave voltammetry technique (SWV), the LbL modified electrodes produced at different pHs (pH 2 and 8) were used to determine DA in the presence UA, and the electrochemical responses of the electrodes were compared. It was observed that the electrodes with the highest concentration of monomeric species showed the highest current intensity and the lowest peak potential for the DA and UA analytes in analysis of DA and UA, individually and simultaneously, with peak potential separation of 460 mV versus Ag/AgCl. Applying SWV, a linear dynamic range of 10–99 μmol L^?1 and 100–900 μmol L^?1 with detection limit of 16.8 μmol L^?1 and 58.3 μmol L^?1 was obtained for DA and UA, respectively. The method has good selectivity and sensitivity, and it was successfully applied to the simultaneous determination of DA and UA in spiked human urine sample.     

Oxytetracycline nanosensor based on poly-ortho-aminophenol/multi-walled carbon nanotubes composite film

Poly-ortho-aminophenol (PoAP) and multi-walled carbon nanotubes (MWCNTs) were deposited on the platinum electrode using cyclic voltammetry technique to form the Pt/PoAP/MWCNTs nanosensor for the electrochemical determination of oxytetracycline as analyte. This electrochemical nanosensor with good uniformity and high surface area was prepared in the presence of an ionic surfactant (sodium dodecyl sulfate) as electrolyte to suspend carbon nanotubes within the PoAP and improve the stability and electroactivity of the composite film. The surface morphology of the prepared nanosensor was characterized by scanning electron microscopy and showed a three-dimensional network structure. The influence of several parameters such as number of potential cycles, scan rate and pH of the solution on the electrochemical response of the resultant electrode was investigated. The prepared electrode functioned as a selective recognition element for oxytetracycline determination. It showed excellent electrochemical response to oxytetracycline at low oxidative potential in buffer solution of pH 2.0, with good stability and sensitivity. Under the optimal experimental conditions, the electrochemical response of the sensor was linear with respect to the concentration of oxytetracycline in a dynamic range of 0.2 μM–0.25 mM. The detection limit of the fabricated nanosensor was calculated as 0.10 μM (signal/noise = 3). This sensor was used successfully for the oxytetracycline determination in real samples with recoveries of 96.9–103.5 %.     

Effect of porous properties on self-cooling of fired clay plate by evaporation of absorbed water

Porous ceramic plates were prepared from clay and wood charcoal powder at 900 and 1100?°C and their porous properties, water absorption and the cooling effect of porous plates were investigated to produce eco-friendly porous ceramics for cooling by the evaporation of absorbed water. Porous properties were dependent on the firing temperature, and total pore volume, average pore size and porosity, which were 0.38–0.39 cm³/g, 0.15–0.17 μm and 49–50%, respectively at 900?°C and 0.31–0.33 cm³/g, 2.47–2.59 μm and 43–44%, respectively at 1100?°C. By the addition of wood charcoal powder, the cooling rate of porous plate fired at 1100?°C was 1.7 times faster than that of the plate fired at 900?°C and the cooling temperature difference (?T) was around 2.3?°C at 22.5?°C and 52–54% of relative humidity and around 3.2?°C at 29?°C and 77–80% of relative humidity. The porous ceramic plates developed here are potential materials for cooling buildings.     

Effect of Scanning Speed on Copper Line Deposition Using Nanoparticle Deposition System (NPDS) for Direct Printing Technology

Cu nanoparticles (100 nm) were deposited on a silicon substrate using Nanoparticle Deposition System (NPDS) at 300 μm of stand-off distance (SoD). It was found that the lines deposited at a scanning speed below 5 μm/s showed ohmic contact; their resistivities were 1.68 × 10^?4 Ω·cm at 5 μm/s, 3.91 × 10^?5 Ω·cm at 2 μm/s, 1.70 × 10^?5 Ω·cm at 1 μm/s, and 1.28 × 10^?5 Ω·cm at 0.5 μm/s, respectively. However, samples fabricated at scanning speed of 8 and 10 μm/s showed schottky contact behavior. To study relationship between resistances of the deposited copper lines at various scanning speeds and density of the line, porosity of the deposited copper lines and SEM images of Cu lines were studied. As a result, average porosity of the copper lines was found to be 16% at 5 μm/s, 8% at 2 μm/s, 2% at 1 μm/s, and 6% at 0.5 μm/s. The porosity values are closely related to the resistance of the deposited copper lines. Therefore, the deposited copper line at 1 μm/s of scanning speed was shown to be the best one with the lowest porosity and resistance with its maximum thickness. This indicates that both the resistance and density of the deposited line improved at low scanning speed.

Copyright 2013 American Association for Aerosol Research     

Ni-doped TiO2 hollow spheres as electrocatalysts in water electrolysis for hydrogen and oxygen production

This work represented the electrocatalytic properties of Ni-doped titania hollow sphere materials in hydrogen and oxygen evolution during water electrolysis from acidic media. Titania hollow sphere particles were synthesized using poly(styrene-methacrylic acid) latex as template material, and various amount of nickel were doped over the sphere using nickel (II) sulfate as the precursor of nickel. The presence of rutile TiO₂ and NiO phases were revealed during XRD analysis, indicating the critical growth of nickel on the surface of the hollow sphere catalysts. BET surface area results also shown the 166.76 m² g^?1 value for 30 wt% Ni/TiO₂ hollow sphere sample. The SEM and TEM images were confirmed the hollow sphere structure of the catalysts with diameter of 0.8–0.9 μm. The cyclic voltammetric studies proved the presence of both hydrogen and oxygen evolution peaks for all the hollow sphere samples. The anodic peak current density value, which usually represents the oxygen evolution phenomenon, was revealed as 13 mA cm^?2 for 25 wt% Ni-loaded sample; whereas, the hydrogen evolution peak was most intense for 30 wt% Ni/TiO₂ material with cathodic peak current density of 32 mA cm^?2. The average value of ?1.42 were determined as the reaction order of the system irrespective of the nickel loading and heating duration in the synthesis of hollow sphere materials. During photocatalytic water splitting, 30 wt% Ni/TiO₂ hollow sphere sample yielded the highest amount of hydrogen in all irradiation time span.     

Residual stress control in CrAlN coatings deposited on Ti alloys

In order to control residual stress of CrAlN coatings on Ti substrates, ~70 nm CrAl interlayer was deposited at different temperatures. Residual stress and coatings’ structure were characterized by X-ray diffraction. Residual stress in the coatings was compressive and increased with CrAl interlayer deposition temperature. Residual stress in 1.5 µm, 2 µm and 2.6 µm thick CrAlN films on TC21 with the interlayer deposited at 100 °C (?47.43 MPa, ?25.57 MPa and ?855.77 MPa, respectively) was smaller than with the interlayer deposited at 300 °C (?1.39 GPa, ?1.95 GPa and ?1.62 GPa, respectively). The coatings on the TC4 substrate showed the same trend (?1.02 GPa, ?389.91 MPa and ?1.03 GPa for the interlayer deposited at 100 °C, respectively, and ?921.42 MPa, ?2.31 GPa and ?1.80 GPa for the interlayer deposited at 100 °C, respectively). Changing the interlayer deposition temperature can influence the coatings’ residual stress and crystal structure, and improve mechanical properties of the coatings. CrAlN deposition is a convenient and efficient way to improve mechanical properties of Ti alloys.     

Intercalation of lithium in r.f.-sputtered vanadium oxide film as an electrode material for lithium-ion batteries

Vanadium oxide films were prepared by r.f.-sputtering using an argon sputter gas and a V2O5 target. The films were characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical techniques. The oxide film as deposited is amorphous; they are heat-treated in the range 300–700°C in oxygen atmosphere and are composed of orthorhombic V2O5 crystals. At higher heat-treatment temperatures (600–700°C) the crystallization of the oxide proceeded significantly with ab-direction parallel to the substrate. The oxide film undergoes a reversible lithium intercalation and deintercalation process. The kinetics of the intercalation process of lithium into amorphous V2O5 film was studied using an a.c. impedance method. Furthermore, a rocking-chair type V2O5 film/LixV2O5 film cell could be charge–discharge cycled over 300 times at a current of 10μA at 25°C.     

Performance of the silicon carbide coating under erosion wear by erosion by solid particles

In this article, the phenomenon of erosion by solid particles on the silicon carbide coating (SiC) deposited on AISI 304 stainless steel substrates was analyzed. The specimens used were 25 mm square and 3 mm thick, using 300–450 μm silicon carbide as abrasive particles. Experimental tests were performed on an apparatus developed in accordance with some parameters of the ASTM G76-95 standard. Four angles of impact at 30°, 45°, 60°, and 90° are contemplated with an approximate particle velocity of 25 ± 2 m/s with a maximum exposure time of 10 min per specimen, taking measurements of weight intervals every 2 min to determine the mass loss. The wear mechanisms that were identified to small angles were: plastic deformation, displacement of material, and plow mechanisms. While at higher impact angles, the mechanisms were mainly: cutting, pitting, fractures, and cracks. It was observed that the rate of erosion depends on the angle of incidence of the abrasive particles. The results indicated that a higher damage zone was obtained at 30° of impact angle; on the other hand, at an angle of 90° there was less damage.     

Preparation of Yttria-Stabilized Zirconia Microtube by Electrochemical Vapor Deposition

A microtube of yttria-stabilized zirconia of ca. 100 μm diameter was prepared. An yttria-stabilized zironia film was formed over a surface-oxidized nickel wire with a diameter of 10 μm by electrochemical vapor deposition using zirconium tetrachloride and yttrium trichloride as metal sources, and nickel oxide as an oxygen source for the reaction. The YSZ-coated wire was then immersed in aqueous 11.5 mol.L^-1 hydrochloric acid to dissolve the nickel and nickel oxide, and a microtube of 80 mol? yttria-stabilized zirconia with a cubic crystal structure was obtained. The surface of the microtube was rough, but was pinhole-free, from SEM observation. The thickness of the zirconia layer was about 3 μm.     

Surface topography and tribological properties of coatings prepared from microparticle size polyurethane dispersions studied by atomic force microscopy

The surface topography and mechanical properties of coatings prepared using large particle size polyurethane dispersions (PUD) are investigated using atomic force microscopy (AFM) imaging, AFM-based force measurements, and friction force microscopy. PUD coatings, which are prepared from dispersions containing particles of micron size, have surface roughness of 250–300 nm and waviness of 2.5–3 μm resulting from the particle size. The surface moduli of the PUD coatings are varied by tuning the ratio of hard-to-soft segmentation in the polyurethanes and are found to be between 40 and 100 MPa. The friction coefficient obtained in the study is found to be correlated with both the surface modulus of the coatings and the adhesion between the probe and the samples and is well in line with the perceived feel of an experienced human panel. The data are very well behaved and clearly show the utility of this technique in characterizing these types of surfaces.     

Improving electrochemical performance of NiO films by electrodeposition on foam nickel substrates

NiO films for lithium-ion batteries were deposited on copper plates and foam nickel substrates by electrodeposition and subsequent heat treatment at 300 °C. At a discharge/charge rate of 0.1 C, foam NiO films delivered reversible capacity larger than 650 mAh g⁻¹ and capacity retention over 93% after 50 cycles. NiO films deposited on foam nickel exhibited higher reversible capacity, better cyclability, as well as higher rate capability than those on copper plates. The unique three-dimensionally porous morphologies of foam NiO films were responsible for the better electrochemical performance, which provided not only high electrode/electrolyte contact area but also a good electronic conduction matrix. The present finding offers a new pathway for the large scale fabrication of high-energy-density electrodes for lithium-ion batteries.     

Characterization of An Open-Pored Nickel Foam with Respect to Aerosol Filtration Efficiency by Means of Measurement and Simulation

The deposition of micron and submicron particles in metallic, ceramic, or synthetic open-pored foams is a special field of aerosol filtration in porous media. This is due to the more complicated pore structure than, for example, fibrous filter media. Therefore, the measurement as well as the simulation of aerosol filtration in open-pored foams involves certain custom-built techniques.

The filter efficiency for micron and submicron particles can be measured by differential electrical mobility analyser systems (DEMAS) or optical particle counters (OPC). Empirical formulas are available in literature for open-pored polyurethane foams to determine their aerosol filtration efficiency and pressure drop. An additional method for characterization is direct numerical simulation (DNS) by means of a three-dimensional (3D) model of the pore structure. These models can be obtained either by tomography or by mathematical generation.

In this work, the filter efficiency of an open-pored nickel foam with a cell diameter of 450 μm is determined by the methods previously mentioned. The experimental results are in good agreement with the results of the 3D simulation and a semi-empirical approach for polyurethane foams is adapted for a nickel foam.

Copyright 2015 American Association for Aerosol Research