Work of adhesion in ZrO2-liquid metal systems

Using the sessile drop technique for the measurement of contact angles, the work of adhesion of polycrystalline cubic ZrO₂ in contact with various liquid metals was determined. Based on these experimental values, a model for the evaluation of the work of adhesion is proposed. According to this model the wetting of ZrO₂ by the metals indium, tin, bismuth and lead is established by Van der Waals dispersion binding forces. For the transition metals silver, copper, nickel, cobalt and iron a chemical equilibrium bond between the liquid metal and the oxygen ion of the surface oxide is created at the interface. In this case the value of the work of adhesion is related to the enthalpy of formation of the oxide of the metal.     

镀钴泡沫镍基板界面机理研究

研究了泡沫镍镀钴镍电极的初期化成行为,发现在电池端电压0.2V附近出现一个充电电压平台,1.0V附近出现第二个充电电压平台,而纯泡沫镍做基板的镍电极无此现象.循环伏安和XRD测试验证了两个电压平台对应的反应是Co氧化为Co(OH)2和Co(OH)2氧化为CoOOH反应.EPMA线扫描显示,镍电极化成后基板表面钴元素呈梯度分布.结果表明,泡沫镍表面的金属钴通过电化学溶解沉淀机理,在基板附近生成梯度分布的CoOOH.     

Metal ion release from metal implants

Metal ion release from metallic materials, e.g. stainless steel, cobalt–chromium alloy, titanium, and titanium alloys, implanted into human body was reviewed in this paper. Surface oxide films on metallic materials play an important role as an inhibitor of ion release and they change with the release in vivo. Low concentration of dissolved oxygen, inorganic ions, proteins, and cells may accelerate the metal ion release. The regeneration time of the surface oxide film after disruption also governs the amount of released ion. In addition, preferential release of specific elements during wear and fretting of metallic materials occurs. The behavior of metal ion release into biofluid is governed by the electrochemical rule. Released metal ions do not always combine with biomolecules to appear toxicity because active ion immediately combine with a water molecule or an anion near the ion to form an oxide, hydroxide, or inorganic salt. Thus, there is only a small chance that the ion will combine with biomolecules to cause cytotoxicity, allergy, and other biological influences.     

Atomic layer deposition of transition metals

Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable.     

Cathodic electrophoretic deposition of barium titanate films from aqueous solution

Cathodic electrophoretic deposition (EPD) of barium titanate from aqueous suspensions was performed on nickel substrate. Cathodic deposition allows preparation of thin layers from aqueous solution on base metal electrodes, such as Ni or Cu, without creating an intermediate oxide layer during the deposition. This opens the opportunity to prepare complex shapes of dielectric layers onto base metals for co-firing, using relatively cheap and environmentally benign aqueous EPD. Stable barium titanate colloidal suspension with a concentration of 10 g/100 mL at pH of 9.2 has been prepared for the deposition. The characteristics of electrophoretic deposition of those positively charged particles onto cathode were investigated. A uniform and dense layer was obtained for films deposited at 3 V for 2 min. The calculated film thickness for the sintered layer at these conditions was ∼1 μm. The morphology can be controlled, and in particular the pore size and distribution can be controlled via the applied voltage. At low voltage a uniform layer can be obtained whereas at high voltage a large number of macropores appears in the deposit and their size increase with the increasing of the voltage due to gas bubble formation.     

Electroplating of zirconium and aluminum hydroxide thin films following anodic dissolution of corresponding metal anodes in organic medium

Zirconium (IV) hydroxide or hydrate oxide films, which are typically difficult to prepare by electrochemical methods using aqueous solutions, are easily fabricated in an acetone bath using Zr anodes as the metal sources and a metal-free solvent containing halide ions as the supporting electrolyte. This method is also confirmed to be applicable to aluminum anodes. In the early stage of electrolysis, anodic oxidation of the metal anode proceeds in the presence of water as an impurity in the solvent. Subsequently, pitting corrosion of the oxide film on the metal anode occurs as a result of the action of halide ions. The corrosiveness of the halogen additive appears to be an important factor determining the dissolution or deposition of metal species in this stage. That is, Br^– is more active for electrochemical dissolution of a passive oxide film on the anode compared to I^–. Finally, Zr species are deposited on the cathode surface via reactions with cathodically generated hydroxide ions. In these processes, the metal plate acts as a soluble anode and as a metal source for electrodeposition. The coating of Zr (IV) hydroxide film on a stainless steel substrate is shown to act as an effective barrier against electrolytic corrosion.     

Metallization of cross-linked epoxy resins by reduction of polymer-incorporated metal ions

The metallization behavior of the poly(ethylene glycol) diglycidyl ether films cured with 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride (DMCDA) by reduction of polymer-incorporated cobalt chloride or nickel chloride was investigated by means of infra-red spectroscopy, dynamic viscoelastic measurement, X-ray photoelectron spectroscopy, scanning electron microscopy and electron probe microanalysis. For the film containing the metal chloride cured at finally 200 °C for 5 h, the metal ion was homogeneously distributed in the inner part of the film, except that the film surface at the air side had a higher metal ion concentration because of the chelation of the metal ion with carboxylic acid group generated by the reaction of DMCDA with water in air. By the reduction treatment in aqueous sodium borohydride at 20–50 °C, the metal ion migrated to both sides of the film and then reduced to pure metal. The metal layer generated at the air side was thicker than the one at the side of a polypropylene plate used in the preparation of film. The X-ray diffraction analysis of the reduced films revealed that the generated cobalt and nickel were almost amorphous.     

Photo-stability of TiO2 particles coated with several transition metal oxides and its measurement by rhodamine-B degradation

Titanium dioxide is the best white pigment, but it does not have good photo-stability if it is not properly coated. As a change from the conventional coating with silicon or aluminum oxide, its photo-stability after coating with zirconium, cerium as well as some other transition metal oxides was investigated. The function of the coated film was to capture electrons and holes of the TiO₂ particles produced by the ultraviolet irradiation that otherwise could produce free radicals on the TiO₂ surface. A new more efficient, easier and more accurate method that used rhodamine-B degradation was used to evaluate the photo-stability of the coated TiO₂ particles. TiO₂ particles coated with the oxides of zirconium, cerium, cobalt or nickel had excellent weather durability, even with only a small amount of coating.     

Role of metal ions of Langmuir–Blodgett film in hydrophobic to hydrophilic transition of HF-treated Si surface

Hydrophobic to hydrophilic transition of HF-treated Si surface strongly depends upon the metal ions, which are present in the headgroups of the deposited Langmuir–Blodgett (LB) film. Structure of LB films studied by X-ray reflectivity technique and chemical analysis of LB film–substrate interfaces studied by X-ray photoelectron spectroscopy combinedly suggest that the partial transition or partial oxidation of the HF-treated Si surface takes place under the subphase water but further transition or oxidation is possible only in the presence of metal ions. Electrovalent and covalent natures of the metal ions tune this transition or oxidation. Ni ions, for which bonding with headgroups are electrovalent in nature, are favorable for such transition/oxidation and as a result, complete transition/oxidation takes place when nickel arachidate LB film is deposited. On the other hand, Cd ions, for which bonding with headgroups show covalent nature, is not favorable for such transition and can not oxidize the underlying H-passivated Si substrate totally when cadmium arachidate LB film is deposited on such HF-treated Si surface. This ion-specific hydrophobic to hydrophilic transition is visualized by X-ray reflectivity, contact angle and X-ray photoelectron spectroscopy measurements.     

Carbon nanotube-nanocrystal heterostructures fabricated by electrophoretic deposition

Alternating layer, carbon nanotubes-nanocrystal composite films, comprising multi-walled carbon nanotubes (MWCNTs) and iron oxide (Fe(3)O(4)) nanocrystals, have been fabricated via electrophoretic deposition (EPD) on stainless steel and gold substrates. Low field-high current and high field-low current EPD schemes were integrated to produce the composite films. The low field-high current EPD approach produced porous mats from an aqueous suspension of the MWCNTs, while the high field-low current EPD approach produced tightly packed nanocrystal films from a dispersion of the nanocrystals in hexane. Large electric fields applied during the nanocrystal EPD and strong van der Waals interactions among the nanocrystals facilitated the formation of tightly packed nanocrystal films atop the MWCNT mats to create CNT mat-nanocrystal film composites. The surface coverage and homogeneity of the nanocrystal films improved with repeated deposition of the nanocrystals on the same mat. The assembly of nanotube mats on top of the CNT mat-nanocrystal film composite confirmed the feasibility of multilayered CNT mat-nanocrystal film heterostructures suitable for a range of devices. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were employed to characterize the surface coverage, homogeneity, and topology of these composite films.     

Materials for solar-transmitting heat-reflecting coatings

A coating for solar energy applications which combines heat reflection with transparency to solar radiation may be of four different types: a metallic film which is sufficiently thin to be transparent; a metal-based multilayer coating; a wide band gap heavily doped semiconductor such as SnO₂ or In₂O₃; a conducting microgrid. We prepared such coatings on glass by evaporating thin films of silver, copper, gold, aluminium, cobalt, iron, chromium and nickel of various thicknesses and by spraying SnO₂ films. The spectral variations in the transmittance, and the front side and back side reflectances were measured in the wavelength range 0.4–15 μm. The properties of a three-layer coating of the dielectric/metal/dielectric type were calculated with a multilayer program using known bulk optical constants. The effect of these films when coated onto a domestic window was demonstrated with a heat transfer calculation using an equivalent thermal net. When a large transmittance over a broad range of the solar spectrum is required, gold is an equally good, or a slightly better, choice than silver as the metal in a three-layer coating. In general, an SnO₂ film exhibits a higher solar transmittance as well as a higher emittance than a coating containing metals. This implies that the oxide is to be preferred as a coating on a window when the maximum passive solar heating is sought. However, a metal-based coating could be better when a very low U_L value is the most important requirement.     

镍氢电池掺钴镍正极的研究进展

对镍氢电池的镍正极覆钴改性的研究进展进行了综述,系统归纳了添加剂Co、CoO、Co(OH)2、CoOOH对电池镍正极性能的改善及覆钴工艺的研究进展,并对覆钴工艺的前景提出了新的展望.     

Metal and mixed-metal (oxy)-hydroxide ceramic precursor materials prepared by cathodically-induced precipitation using a hydrogen-sorbing palladium electrode

The electrochemical reduction of several metal and mixed-metal sulfate aqueous solutions at a palladium electrode has been studied. For magnesium, lanthanum, yttrium and scandium sulfates, metal (oxy)-hydroxide films are produced by cathodically-induced precipitation of the metal cations, following the local generation of hydroxide ions at the hydrogen-sorbing cathode. Mixed-metal (oxy)-hydroxide films are prepared from yttrium/lanthanum and yttrium/scandium sulfate solutions. For mixed yttrium/indium sulfate solutions, the amorphous yttrium/indium (oxy)-hydroxide films initially contain indium dendrites. On calcination, a metastable yttrium/indium oxide phase is observed between 600-1000 °C, followed by the separation of the indium and yttrium oxides above 1000 °C. No films are accessible from the sulfate solutions of electropositive metals such as sodium and potassium, where the corresponding metal oxides and hydroxides are highly soluble. Metals are electrodeposited from separate sulfate solutions of zinc, nickel and indium, in preference to the cathodically-induced precipitation of the metal (oxy)-hydroxide.     

Nanostructured copper and copper oxide thin films fabricated by hydrothermal treatment of copper hydroxide nitrate

Metallic copper and copper oxide thin films were fabricated on surface of glass slide substrates. Copper oxide thin films were prepared by a hydrothermal method using an α-phase layered hydroxide, copper hydroxide nitrate as a precursor. Morphology, thickness and crystallite size of the obtained copper oxide thin films changed by changing the time of hydrothermal treatment. Accordingly, the copper oxide thin films showed various water contact angles and optical band gaps. As, the optical band gap of the nanostructured copper oxide thin films increased with an increase in hydrothermal time from 1.85 to 2.95 eV. Moreover, the water contact angles changed from 16.4 to 38.8° by changing the hydrothermal time. By a reductive hydrothermal-treatment route, the copper oxide thin film was reduced to metallic copper thin film without any particle growth.     

Synthesis and electrophoretic deposition of magnetic nickel ferrite nanoparticles

Powders with particle size ∼5–15 nm of nickel ferrite have been synthesized chemically from aqueous precursor solutions. From the structural and magnetic properties, it is determined that the synthetic material possesses high NiFe₂O₄ phase purity and controllable particle size. The optimum calcination temperature is found to be ∼500 °C, at which the NiFe₂O₄ particles exhibit a saturation magnetization of 2800 G, and a particle size of about 10 nm. The particles are then deposited onto silicon substrates by electrophoretic deposition (EPD) process. The Ni ferrite particles are suspended in a medium of isopropyl alcohol with magnesium nitrate and lanthanum nitrate salts as charging agents. The transportation of particles to the substrate surface is assisted by applied electric field and particles adhere to the substrate surface by a glycerol based surfactant. The magnetic response of the EPD film has been investigated by vibrating sample magnetometer (VSM) measurements.     

Formation and characterization of cobalt oxide layers on polyimide films via surface modification and ion-exchange technique

Polyimide (PI) films with thin cobalt oxide (Co₃O₄) layers on both film sides have been prepared via a surface modification and ion-exchange technique. The method works by hydrolyzing the PI film surfaces in aqueous potassium hydroxide solution and incorporating Co²⁺ into the hydrolyzed layers of PI film via subsequent ion exchange, and followed by thermal treatment in ambient atmosphere. The PI composite films were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractions, scanning electron microscopy, transmission electron microscopy and thermogravimetric analyses, as well as surface resistance and mechanical measurements. By varying the absorbed cobalt ion content, a series of PI/Co₃O₄ composite films with insulative to semiconductive surfaces were obtained. The room temperature surface resistances of the semiconductive composite films reached to about 10⁷ Ω. The Co₃O₄ particle formed on PI film surfaces was in the range of 10-40 nm. The final composite films maintained the essential mechanical properties and thermal stability of the pristine PI films. The adhesion between surface Co₃O₄ layers and PI matrix was acceptable.     

Evolution of potential distributions during the charging of nano-structured metal oxide films in air as response to sudden voltage application

Using metal oxide film structures, which were originally designed for gas sensing applications, we measured the charging and discharge currents and potential distributions on several metal oxide coatings after the application of an electrical potential against earth. The potential distributions show a specific charging of the surface with oxygen ions through the gas phase. The accumulated charge corresponds to that of the pseudocapacitors. Influence of air humidity has been found to be low, voltaic and temperature dependences of the charge are presented. The activation energy of discharge indicates a weak chemisorption of the charging oxygen species on the metal oxide surface.     

Incorporation of cobalt and nickel metal nano-particles in nano-grain zirconia film matrix by solution route

Precursor solutions of cobalt/nickel incorporated nano-grain zirconia films were prepared from aquo-organic solutions of zirconium oxychloride octahydrate and corresponding transition metal nitrate. The films were deposited onto silica glass substrate by the dipping technique. Annealing was made at different temperatures from 450°C to 1200°C ± 5°C in air atmosphere. The range of thickness of the films baked at 450°C was 1800–1870 å. For cobalt system Co₃O₄ was formed initially at 450°C which gradually transformed to alpha cobalt and next to cubic cobalt along with a non-stoichiometric compound (Zr_0.71Co_0.23O_0.06) with increasing annealing temperature. On the other hand, for nickel system nickel metal of nano-size was observed in the nano-grain zirconia film matrix at 450°C. By increasing annealing temperature to 1200°C, a compound, ZrNi₄O, was formed which was found to be stable for ～ 30 days.     

Dispersion of metal nanoparticles on carbon nanotubes with few surface oxygen functional groups

Homogeneous dispersion of metal oxide nanoparticles was achieved on carbon nanotubes (CNTs) even with a very small amount of surface oxygen functional groups (SOFGs) aided by using ethylene glycol (EG) and sodium hydroxide during the process. Similar particle size distributions were obtained for iron deposited on CNTs containing various amounts of SOFGs. We proposed that formation of hydrogen bonds between EG on the CNT surface and sodium hydroxide is likely responsible, which creates precipitating sites for iron ions on the CNT surface. This facile method is expected to find applications not only for catalysis but also in the fields such as sensors and magnetic materials in particular where a perfect sp² hybridized carbon structure is preferred.     

Synthesis,characterization and photoresponse study of undoped and transition metal (Co,Ni, Mn) doped ZnO thin films

The synthesis, characterization and photoresponse studies of undoped and transition metal doped zinc oxide thin films are carried out in this work, in prospect of visible light photo detection and sensor applications. The undoped and transition metal ions such as, Co, Ni and Mn doped ZnO films in this study were synthesized by chemical solution deposition, involving spin-coating. We have characterized the deposited films using X-ray diffraction, scanning electron microscopy, photoluminescence and UV–vis spectroscopy studies. The devices of the films for photoresponse study were fabricated by top Ag contacts on the film surface in metal–semiconductor–metal configuration. The current–voltage characteristics and switching measurements of these devices were studied under the illumination of an incandescent lamp. We found a high ON/OFF ratio of 8 and highest photocurrent density of 0.7 mA/cm² for Ni doped ZnO film.