Structure for electro‐spun silk fibroin nanofibers

Electro‐spinning was made using silk fibroin and it was found that silk fibroin nanofibers of partially oriented amorphous structure are producible using HFIP(1,1,1,3,3,3 hexafluoro‐2‐propanol) as a solvent for fibroin via the electro‐spinning setup equipped with parallel electrodes as a collector. Transformation from amorphous to silk I of a highly contracted beta‐turn form or amorphous to silk II of a regular array of antiparallel beta‐sheets occurred preferentially via the treatment with water vapor or ethanol, respectively. In addition the c‐axis of crystallites was oriented parallel to the fiber axis. When the electro‐spinning was made using a dish‐type collector filled with ethanol, a peculiar web texture was obtained. Such a web texture seems to be brought about by the shrinkage of fiber due to the crystallization of fibroin and/or surface tension of ethanol droplets formed between the fibers. In this spinning setup, the c‐axis of crystallites was also oriented parallel to the fiber axis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electroreduction of molecular oxygen on preferentially oriented platinum electrodes in acid solution

The oxygen electroreduction reaction was studied on two different preferentially oriented ((111)-type and (100)-type and on a conventional polycrystalline (PC) platinum rotating disc electrodes in acid solutions at 30 °C. At low overpotentials, Tafel lines of –0.060 V decade^–1 were obtained on the three electrodes in oxygen-saturated 1.0m H₂SO₄ and 1.0m H₂SO₄ + y m K₂SO₄ (0 y 1). At high over-potentials the usual Tafel slope of -0.120V decade^–1 was observed on both (111)-type and PC platinum electrodes in 1.0m H₂SO₄, whereas a slope of –0.165V decade^–1 was found on (100)-type platinum. In oxygen-saturated 1.0m H₂SO₄ the surface coverage by O-containing adsorbates on (100)-type platinum was greater than on both (111)-type and PC platinum. Rotating ring-disc electrode data showed that a higher amount of H₂O₂ was produced on (100)-type platinum than on the other platinum surfaces. The overpotential against current density plots are influenced by the anion concentration depending on the type of preferentially oriented platinum.     

Scanning probe microscopy studies of Ebonex® electrodes

The porosity of Ebonex® electrodes is known to have a marked affect on their electrochemical properties. Atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) have been used to investigate the topography of porous and fully-hardened (nonporous) Ebonex® at high resolution. AFM has also been used to study the early stages of copper electrodeposition on porous Ebonex® electrodes. Initial copper nucleation and growth were found to occur preferentially at surface pores.     

Kinetics and mechanism of the electrochemical reduction of molecular oxygen on platinum in KOH: influence of preferred crystallographic orientation

The oxygen electroreduction reaction has been studied at both preferred oriented and conventional polycrystalline platinum rotating disc electrodes in x m KOH (0.05 ⩽ x ⩽ 3.0) aqueous solutions under oxygen saturation at 25°C. At low current densities, Tafel lines with slope -0.060 V decade⁻¹ have been obtained at all platinum electrodes. At high current densities, higher Tafel slopes ranging from -0.18 to -0.40 V decade⁻¹ have been observed, depending on the type of preferred oriented Pt and KOH concentration. Rotating ring-disc electrode data have shown that a higher amount of H₂O₂ is produced on one type of preferred oriented surface at all KOH concentrations. A complex reaction scheme has been used to evaluate the electrochemical rate constants of the reaction steps at three platinum electrodes.     

Influence of Spray Angle on the Pore and Crack Microstructure of Plasma-Sprayed Deposits

To understand the influence of processing parameters on the microstructure of plasma-sprayed deposits, smallangle neutron scattering measurements were made of the processing-parameter-dependent specific surface area of the voids in gray alumina deposits. These studies indicate that the voids are in the form of pores between the splats and around inclusions or unmelted particles, and are also in the form of cracks within the splats which may develop during cooling. The porous volume increases as the angle between the spray gun and the substrate (the "spray angle") decreases. This study also indicates that the cracks are preferentially oriented, and that the crack orientation also depends on the spray angle. The interlamellar pores, however, are preferentially oriented parallel to the substrate surface, and the orientation of the pore is independent of the spray angle.     

Influence of crystallographic properties on antimony electrode potential—III. Oriented monocrystalline material

Crystallographically oriented monocrystalline antimony electrodes representing close-packed crystallographic planes have been studied in HClSbOCl solutions at pH 1.9. The electrode potentials were found to stabilize in less than 1 min. They then remained stable at that level to within 1 mV for more than 100 h of continuous use unless a surface defect existed or developed. The potentials of the different electrodes were reproducible to within 1 mV and repeatable to within 0.2mV. The typical short-term potential variations were 0.1 mV for long periods of time and no stirring effect was noted during the first 100h of use. All electrodes responded reproducibly to oxygen and nitrogen bubbling and to temperature changes in the solution. The maximum long-term potential drift encountered after the first 100 h period of relative potential stability was ? 0.8mV/day during a total of 800 h use. Sem studies of the surfaces of used electrodes showed only minor corrosion and no signs of a covering surface (oxide) structure. The surfaces also appeared less corroded for electrodes with more close-packed surfaces. These electrodes also possessed the most negative potentials.     

Focused ion beam tomography of zirconia degraded under hydrothermal conditions

Three-dimensional tomography was performed on hydrothermal degraded zirconia by sequential focussed ion beam (FIB) sectioning and field emission scanning electron microscopy (FE-SEM) observation. By means of image analysis the distribution of microcracks produced under the surface was reconstructed and characterized.Results show a microcrack network preferentially oriented parallel to the surface, and a gradient in microcrack density from the surface, which is coherent with other measurements that reveal a decrease in monoclinic phase. The elastic properties of the reconstructed volume are simulated, showing that the deterioration of mechanical properties of degraded zirconia can be mainly attributed to microcracking, with a minor contribution of the phase transformation.     

Electrochemical reactivity at graphitic micro-domains on polycrystalline boron doped diamond thin-films electrodes

This paper deals with the electrochemical reactivity of boron doped diamond (BDD) electrodes. A comparative study has been carried out to show the influence of the presence of graphitic micro-domains upon the surface of these films. Those graphitic domains are sometimes present on as-grown boron doped diamond electrodes. The effect of doping a pure Csp³ diamond electrode is established by highly oriented pyrolytic graphite (HOPG) abrasion onto the diamond surface. In order to establish the effect of doping on a pure Csp³ diamond electrode, the amount of graphitic domains was increased by means of HOPG crystals grafted onto the BDD surface. Indeed that method allows the enrichment of the Csp² contribution of the electrode.The presence of graphitic domains can be correlatively associated with the presence of kinetically active redox sites. The electrochemical reactivity of boron doped diamond electrodes shows a distribution of kinetic constants on the whole surface of the electrode corresponding to different active sites. In this paper, we have studied by cyclic voltammetry and electrochemical impedance spectroscopy the kinetics parameters of the ferri/ferrocyanide redox couple in KCl electrolyte. A method is proposed to diagnose the presence of graphitic domains on diamond electrodes, and an electrochemical “pulse cleaning” procedure is proposed to remove them.     

Electrochemically stable gold nanoclusters in HOPG nanopits

Gold nanoparticles on highly oriented pyrolytic graphite (HOPG) electrodes are synthesized. They are stabilized in nanosized pits of well defined depth in the graphite surface. These pits are created by energetic cluster impact followed by etching under a well controlled oxygen atmosphere. We succeeded in the preparation of highly dispersed and stable Au electrodes with gold particles with a mean diameter smaller than 5 nm. The stability of the gold nanostructures for electrochemical applications has been tested by performing cyclic voltammetric measurements in 0.5 M H₂SO₄. While conventionally prepared sputter deposited electrodes show highly unstable structures in this size range, Au clusters stabilized in the nanosized containers are stable.     

EPR study of preferential orientation of crystallites in N-doped high quality CVD diamond

The directions of preferential growth of free-standing optical-quality CVD diamond wafers have been investigated with the help of electron paramagnetic resonance (EPR). EPR signals of the well-known P1 centre (substitutional nitrogen) have been used as a probe. A computer simulation of EPR spectra of preferentially oriented polycrystalline material allows the estimation of the real orientation and spatial distribution of crystallographic axes of crystallites in the samples oriented preferentially in the [110] direction.     

闪光釉闪光机理的研究

闪光釉的特征是对入射光有金属镜面般的反向，研究表明，这种反射是由釉中心（200）晶面平行于釉面的的CeO2晶粒造成的，晶粒的取向程度越高反射越强，闪光釉只有施在相应的底釉上才具有闪光效果。     

Energetic deposition of carbon clusters with preferred orientation using a new mixed mode cathodic arc - Sputtering process

Carbon films were produced by triggering a cathodic arc from a magnetron glow discharge by the application of a high voltage pulse to the target. The arc is quenched rapidly to prevent the formation of large macroparticles normally produced by cathodic arcs. The films are smooth and, when grown with negative substrate bias, they contain graphitic nano-clusters which are preferentially oriented with their c-axis normal to the film surface. This orientation gives films with high in-plane conduction. We propose a mechanism for the formation of these oriented layers in which the clusters are charged, accelerated electrostatically and flattened on impact onto the growth surface.     

Effect of the boron content on the steam activation of boron-doped diamond electrodes

In order to investigate the initial stages of the steam-activation process of boron-doped diamond (BDD) electrodes, polycrystalline BDD electrodes with different levels of boron doping (800, 2500 and 5000 ppm) and crystal orientation were treated with water vapor at 800 °C. A higher degree of etching was observed for BDD electrodes with higher boron content. Based on scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, it is suggested that the {1 1 1} planes are preferentially etched. Thus, high-boron containing BDD electrodes which have a higher abundance of the {1 1 1} planes are heavily etched, while low-boron containing BDD electrodes with a mixed surface of {1 0 0} and {1 1 1} planes are less corroded. The steam activation of BDD electrodes have a higher electrochemically active surface area and wider potential window compared to pristine BDD electrodes.     

A comparative investigation of chromium deposition at air electrodes of solid oxide fuel cells

Deposition processes of chromium (Cr) species were investigated for the O₂ reduction on (La,Sr)MnO₃ (LSM), Pt and (La,Sr)(Co,Fe)O₃ (LSCF) electrodes in the presence of chromia-forming alloy metallic interconnect at 900^oC under air flow. For the reaction on LSM electrodes, deposition of Cr species preferentially occurred on the zirconia electrolyte surface, forming a distinct deposit ring at the edge of the LSM electrode while at LSCF electrodes, Cr species deposited on the electrode and electrolyte surface, forming isolated Cr particles. In contrast, there was no detectable deposition of Cr species either on the electrode or electrolyte surface for the O₂ reduction reaction on Pt electrodes. The results clearly demonstrated that deposition of Cr species in solid oxide fuel cells is not an electrochemical reduction of high valent Cr vapor species to Cr₂O₃ in competition with O₂ reduction. Cr deposition at SOFC cathodes is basically a chemical dissociation reaction and is controlled by the nucleation reaction between the nucleation agent and the gaseous Cr species. The nature of the nucleation agent strongly depends on the electrode material and impurities which may be introduced during electrode and electrolyte fabrication processes.     

Doubly oriented β-form films of poly(vinylidene fluoride)

PVDF sheets, rapidly quenched, were (1) two-step transversely stretched at various temperatures and (2) stretched at various temperatures, rolled at room temperature and then annealed. The orientation patterns of the β-form crystal (which contains the polar b-axis) in these films were analysed on the basis of X-ray diffraction photographs taken with flat and cylindrical cameras. In the case of (1), when both of the two-step transversely stretching temperatures were below 100°C, a doubly oriented film with the plar b-axis oriented parallel to the film surface was obtained. In the case of (2), when the stretching temperature was below 100°C, the sheets then rolled without annealing, another doubly oriented film with the polar b-axis preferentially oriented at 30° to the film surface was obtained. On the other hand, when these films were annealed above 100°C, or the stretching temperatures were above 100°C, orientation patterns in which the polar b-axis was partially rotated through 60° were obtained. The orientation mechanisms of these films are discussed using the measurements of the lattice spacings of the β-form crystal.     

Nucleation- or Growth-Controlled Orientation Development in Chemically Derived Ferroelectric Lead Zirconate Titanate (Pb(ZrxTi1−x)O3, x= 0.4) Thin Films

The profound influence of low-temperature processing steps, hitherto assumed benign from the viewpoint of texture development, is reported. On inclusion of a 400°C step and further heat treatment at 700°C, PZT (40/60) sol-gel thin films with a strong (111) texture were obtained. When the 400°C step was excluded, the films exhibited a strong (100) texture. The (111) PZT texture development is nucleation-controlled and is attributed to the solid-phase epitaxial effect. The (100) texture is considered growth-controlled in that (100) oriented grains grow preferentially so as to minimize surface energy.     

Electrocatalysis by nanoparticles: Optimization of the loading level and operating pH for the oxygen evolution at crystallographically oriented manganese oxide nanorods modified electrodes

The electrocatalytic evolution of oxygen gas is investigated at manganese oxide nanorods (nano-MnO_x) modified Au, Pt and GC electrodes in a wide range of pH values, ranging from highly acidic to highly basic. Morphological investigation has been carried out by a scanning electron microscopy (SEM), which revealed the deposition of nano-MnO_x in a nanorod morphology. A significant enhancement of the electrocatalytic activity of the Au, Pt and GC electrodes towards the oxygen evolution reaction (OER) was observed upon the electrodeposition of nano-MnO_x onto the aforementioned electrodes. The effect of the surface coverage of the manganese oxide and the pH of the electrolyte was investigated to seek an optimization. The highest cathodic shift in the onset potential of the OER was obtained in 0.5 M KOH irrespective of the substrate whereas the optimum loading (surface coverage) was about ca. 52%. The origin of the enhancement of the OER is addressed with the assistance of an X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The preferential electrodeposition of crystallographically oriented nano-MnOx (in the manganite phase, γ-MnOOH) is thought to play the primary role in the observed enhancement.     

Electrocatalysis of oxygen reduction by quinones adsorbed on highly oriented pyrolytic graphite electrodes

The reduction of oxygen in alkaline solution has been studied on highly oriented pyrolytic graphite (HOPG) electrodes modified with various quinones using a rotating disk electrode (RDE). The electrode surface was modified by adsorption of quinones from a 0.1 M KOH solution. The oxygen reduction activity of these electrodes was considerably higher than that for unmodified HOPG and characteristic current maxima for oxygen reduction was observed. All quinones studied catalysed the two-electron reduction of oxygen to hydrogen peroxide. The peak potentials for oxygen reduction were in good correlation with the redox potentials of the quinones that were found from the cyclic voltammograms in oxygen-free solutions. The results obtained give further evidence that oxygen reduction is catalysed by the semiquinone radical and that the redox potential of the quinone is the most important factor determining its electrocatalytic activity for oxygen reduction.     

Behavior of lithiated graphite electrodes comprising silica based binder

Graphite electrodes comprising silica binder were tested in ethylene carbonate–dimethyl carbonate (EC–DMC), propylene carbonate and tetrahydrofuran solutions. The electrochemical behavior of these electrodes was analyzed using chronopotentiometry, slow-scan rate cyclic voltammetry (SSCV), impedance spectroscopy and potentiostatic intermittent titration technique (PITT). The electrode morphology and integrity were studied by scanning electron microscopy (SEM). Using silica binder, graphite particles are usually embedded in the current collector in an unoriented form. Thus, the electroanalytical study of these electrodes and the comparison of their response with that of highly oriented PVDF based graphite electrodes, provided insight into the effect of particle orientation on the general electrochemical behavior of lithiated graphite anodes. In general, the higher the particle orientation and compact packing in the electrodes' active mass, the better the performance o f the Li–graphite electrodes, as the surface films developed are better passivating and the interparticle electronic contact is also better. The silica binder may have advantages over other binders such as PVDF in its ability to better retain the electrode integrity upon cycling. However, the practical use of such electrodes requires further optimization, especially in connection with particle orientation and compact packing.     

Preparation of cyclodextrin membrane-modified electrodes as sensor materials

Cyclodextrin membrane-modified electrodes as sensor materials have been prepared by dipping platinum electrodes in the water suspensions of an oriented cyclodextrin polymer, followed by drying the polymer layers on the electrodes. The polymer is obtained by the solid-liquid reaction between the crystal of cyclodextrin inclusion complex and hexamethylene diisocyanate in anisole. The thickness (2 ? 80 μm) of the cyclodextrin membrane is satisfactorily controlled by changing the concentration of the water suspension of the polymer. The cyclodextrin membranemodified electrodes show a significant response to p-nitrophenolate in water which is highly in contrast with no measurable response to o- and m-nitrophenolates.