Isothermal oxidation behavior of a thermal barrier coating prepared using EB‐PVD

A novel two‐layer structural thermal barrier coating (TBC) system with a ~150‐µm‐thick CoCrAlY bond coat (BC) and a ~60‐µm‐thick yttria stabilized zirconia (YSZ) ceramic top coat (TC) was prepared on superalloy K444 matrix using electron beam physical vapor deposition (EB‐PVD). This deposited coating was characterized using isothermal oxidation tests (1000 °C × 200 h). The results indicated that the deposited coating had a dense structure and close bonding between the layers. The thermally grown oxide (TGO) layer (predominantly alumina) that formed at the interface between the TC and the BC as a consequence of the oxidation process was effective in preventing the further oxidation of the BC. In the later stages of the oxidation process, embedded oxides of chromium/cobalt were observed among the TC's columnar grains, and the TGO underwent densification thinning. Through observations of the growth behavior of the TGO, the element diffusion, displacement reaction, and volatilization of the oxides were found to be related to the weight loss in the coating and the densification thinning of the TGO. These coatings displayed superior high‐temperature oxidation resistance properties. Copyright © 2014 John Wiley & Sons, Ltd.     

SNMS and XRD investigations of laser deposited YSZ buffer layers

Summary Secondary Neutral Mass Spectrometry (SNMS) and X-Ray Diffraction (XRD) were used to find optimum parameters for the in-situ pulsed laser deposition of ZrO₂/Y₂O₃ (YSZ) buffer layers on silicon (100) substrates. Homogeneous and nearly stoichiometric concentration depth profiles were found by SNMS for the laser deposited YSZ films. A peak of the SiO intensity during profiling of the YSZ/Si interface points to a SiO₂ intermediate layer. An increasing Y-deficit of the YSZ films was found by decreasing the laser energy density at the target. Epitaxial growth of the YSZ thin films was observed at an oxygen partial pressure lower than 10^–3 mbar, a substrate temperature of 600–800°C and a laser energy density at the target of about 8 J/cm².     

Influence of rapid thermal annealing on structure and interfacial characteristic of ZnO thin films

Highly C‐axis oriented ZnO thin film was manufactured by radio‐frequency magnetron sputtering technique on Si (111) substrate. The main objective was to study the influence of rapid thermal annealing (RTA) temperature on the structure and interfacial characteristic of ZnO thin films. X‐ray diffraction results showed that the ZnO thin films annealed at 600 °C by RTA technique had a perfect C‐axis preferred orientation compared to the other ZnO thin films, and the full width at half maximum of ZnO (002) rocking curve measurements indicted that the RTA‐annealed ZnO thin films possessed better crystal structure. Atom force microscopy displayed that the grain size of RTA‐annealed ZnO thin films was fine and uniform compared with the as‐deposited ZnO thin films, although the grains grew in RTA process and the root meant square roughness was smaller than that of as‐deposited films. High‐resolution transmission electron microscopy showed that there was an obvious amorphous layer between ZnO thin films and Si substrate, but the RTA‐annealed ZnO thin films exhibited larger and denser columnar structure and a preferred orientation with highly c axis perpendicular to the amorphous layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Nitridation of V5Al8 films with NH3 by Rapid Thermal Processing (RTP)

V₅Al₈ films (thickness about 100 nm) were deposited on sapphire substrates by RF‐sputtering and nitridated with NH₃ at 600‐1250 °C (1 min) in a RTP system. The as deposited and nitridated films were investigated by ESCA (electron spectroscopy for chemical analysis), XRD (X‐ray diffraction), XRR (X‐ray reflectometry), AFM (atomic force microscopy) and SEM (scanning electron microscopy). Formation of an aluminum nitride layer at the surface and precipitation of V(Al) in the bulk was found. In the temperature regime from 600 °C to 900 °C a considerable amount of oxygen is incorporated in the aluminum nitride layer. The roughness of the surface increased with increasing temperature and at 1250 °C a partially detaching of the AlN layer could be observed.     

Formation of NiO/YSZ functional anode layers of solid oxide fuel cells by magnetron sputtering

The decrease in the polarization resistance of the anode of solid-oxide fuel cells (SOFCs) due to the formation of an additional NiO/(ZrO₂ + 10 mol % Y₂O₃) (YSZ) functional layer was studied. NiO/YSZ films with different NiO contents were deposited by reactive magnetron sputtering of Ni and Zr–Y targets. The elemental and phase composition of the films was adjusted by regulating oxygen flow rate during the sputtering. The resulting films were studied by scanning electron microscopy and X-ray diffractometry. Comparative tests of planar SOFCs with a NiO/YSZ anode support, NiO/YSZ functional nanostructured anode layer, YSZ electrolyte, and La_0.6Sr_0.4Co_0.2Fe_0.8O₃/Ce_0.9Gd_0.1O₂ (LSCF/CGO) cathode were performed. It was shown that the formation of a NiO/YSZ functional nanostructured anode leads to a 15–25% increase in the maximum power density of fuel cells in the working temperature range 500–800°C. The NiO/YSZ nanostructured anode layers lead not only to a reduction of the polarization resistance of the anode, but also to the formation of denser electrolyte films during subsequent magnetron sputtering of electrolyte.     

On the influence of strain on ion transport: microstructure and ionic conductivity of nanoscale YSZ|Sc2O3 multilayers

Multilayer samples of the type (YSZ|Sc2O3) × n with layer thicknesses between 8 nm (n=100) and 250 nm (n=5) were prepared on (0001) sapphire substrates by pulsed laser deposition (PLD). The samples were characterised using X-ray diffraction (XRD), scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM/HRTEM, SAED (selected-area electron diffraction) and quantitative EELS (electron energy-loss spectroscopy)). The polycrystalline layers show a columnar microstructure, which is typical for the used preparation technique. The layers are highly textured and only one axial orientation relation is found between yttria-stabilised zirconia (YSZ), scandium oxide and the substrate: (0001) Al2O3‖(111) Sc2O3‖(111) YSZ. A preferred orientation relationship also exists for the azimuthal rotation of the crystallites, which was demonstrated by SAED, XRD pole figure measurements and fast Fourier transformation (FFT) of HRTEM micrographs. The interfaces between YSZ, Sc2O3 and the substrate are sharp and do not contain diffuse transition regions. Dislocations appear not to be arranged in regular arrays. With increasing interface density (thinner individual layers in the multilayer), the conductivity of the multilayers decreases. We relate this to the negative nominal misfit present at the YSZ|Sc2O3 interfaces (compressive stress in YSZ at the phase boundaries). This observation agrees well with the previously investigated case of YSZ|Y2O3 (A. Peters et al., Phys. Chem. Chem. Phys., 2008, 10, 4623), where tensile misfit strain was present in YSZ at the phase boundaries, leading to a conductivity increase.     

锰酸镧和氧化钇稳定的氧化锆复合阴极的研究

用交流阻抗,强极化和电导测量等方法考察了一系列不同氧化钇稳定氧化锆(YSZ)含量的锶掺杂锰酸镧(LSM)复合阴极的电化学性能,发现随着掺入YSZ量的增大,阴极性能大幅度提高,当YSZ质量分数为40%时,电极性能最好,电化学极化电阻约为1.18Ω/cm².通过分析发现,YSZ的掺杂使电极反应过程的控制步骤发生了变化.同时发现,随着YSZ含量的增加,电极的接触电阻增大.以Pt为电流收集层和40%的YSZ+LSM的复合电极形成的二层电极可有效地消除接触电阻,进一步提高了复合电极的性能.在1223K极化电阻从1.18Ω/cm²下降到0.41Ω/cm².     

A Procedure for Transforming Impedance Spectra for the Determination of Mechanism of Electrochemical Reactions

Transformation of impedance spectra into relaxation time spectra (RTS) is used for determining contributions of individual processes of the oxygen electroreduction reaction (OER) to the polarization resistance of the electrochemical cell. The transformation technique involves the solution of the convolution equation found with the aid of a modified Van Cittert iteration algorithm checked on model impedance spectra. The technique, when used to analyze impedance spectra of electrochemical cells air|Pt|YSZ|YSZ + Pt|air, shows that the conversion of a globular structure of the YSZ + Pt cermet layer to a columnar one is accompanied by a change of peak amplitudes in RTS. The revealed RTS dynamics when heated to 750°C is compared with peculiarities of individual processes in OER.     

Characterisation and properties of magnetron sputtered nanoscale bi‐layered Ni/Ti thin films and effect of annealing

Single‐bi‐layer of Ni–Ti thin film was deposited using DC and RF magnetron sputtering technique by layer‐wise deposition of Ni and Ti on Si(100) substrate in the order of Ni as the bottom layer and Ti as the top layer. The deposition of these amorphous as‐deposited thin films was followed by annealing at 300 °C, 400 °C, 500 °C, and 600 °C temperature with 1‐h annealing time for each to achieve crystalline thin films. This paper describes the fabrication processes and the novel characterization techniques of the as‐deposited as well as the annealed thin films. Microstructures were analysed using FESEM and HRTEM. Nano‐indentation and AFM were carried out to characterize the mechanical properties and surface profiles of the films. It was found that, for the annealing temperatures of 300 °C to 600 °C, the increase in annealing temperature resulted in gradual increase in atomic‐cluster coarsening with improved ad‐atom mobility. Phase analyses, performed by GIXRD, showed the development of silicide phases and intermetallic compounds. Cross‐sectional micrographs exhibited the inter‐diffusion between the two‐layer constituents, especially at higher temperatures, which resulted either in amorphization or in crystallization after annealing at temperatures above 400 °C. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrically conductive acrylonitrile–butadiene rubber elastomers prepared by dopamine‐induced surface functionalization and metallization

A novel method for the preparation of electrical conductive surface silvered acrylonitrile–butadiene rubber (NBR) was developed. Dopamine was spontaneously oxide polymerized and deposited onto the surface of NBR. Electroless plating of silver was carried out on the poly(dopamine) (PDA)‐functionalized NBR surface. The composition of the NBR surface was studied by X‐ray photoelectron spectroscopy (XPS). XPS results showed that PDA was successfully deposited onto the NBR surface. The morphology of the NBR surface was observed by scanning electron microscopy (SEM). The SEM images showed that PDA had formed a distinctive layer ready for electroless deposition of silver. The catechol/quinone groups on the PDA molecular structure can be used as binding sites for silver ions. The silvered NBR showed high surface conductivity of 1.4 Ω. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural Characteristics at the Adductor Muscle and Shell Interface in Mussel

The structure, organic matrix, and mineral structure of the scar (the interface between the adductor muscle and the shell) in Mytilus galloprovincialis were investigated. The scar was found to be a hierarchically multilayered structure composed of organic matrix and structurally different minerals. Different from the aragonite structure of the nacre, we have identified the top layer of the scar to contain structurally organized columnar calcite. This is the first report on calcite-containing scar. Study of the organic matrix showed that there was at least one protein that seemed to be preferentially localized in this columnar layer. Since the scar is the most important stress distribution site in the mussel, the function of the columnar structure and the matrix protein was discussed in relation to a similar structure at the tendon–bone connection site.     

Development of electrospun metallic hybrid nanofibers via metallization

The metallized hybrid nanofiber webs were prepared by using a combined technology of electrostatic spinning and metallization. The electrospun polyurethane (PU) nanofibers were metallized with different thicknesses of copper layer via metal vapor deposition technique. The thickness of the copper layer, which ranges from 10 to 100 nm, was monitored and controlled. The resultant metallized hybrid nanofiber webs were characterized using field emission scanning electron microscopy (FE‐SEM), wide angle X‐ray diffraction (WAXD), and thermogravimetric analysis (TGA). FE‐SEM images demonstrated that the nanoscaled copper layers are well deposited on the surface of the PU nanofibers. TGA result indicated that the thermal stability of the metallized hybrid PU nanofibers was dramatically enhanced due to the barrier effects of thin metallic copper layer. WAXD data confirmed that the crystalline copper layers were well deposited onto the PU nanofibers. Moreover, the mechanical properties of the metallized hybrid PU nanofiber webs were increased with increase in the thickness of deposited copper layer. Unlike the organic PU nanofiber webs, it was observed that the metallized hybrid PU nanofiber webs showed higher conductive properties depending on the thickness of the deposited copper layer. Copyright © 2009 John Wiley & Sons, Ltd.     

TEM investigations on PECVD-titanium carbide layers

TiC_x-PECVD-layers were characterized by TEM. EDX analysis and electron diffraction. TiC_x-layers deposited using benzene showed a columnar structure, at which the column size decreases with rising excess carbon content. TiC_x-layers deposited using n-heptane presented a lamellar structure, at which the lamellar thickness diminishes with an increasing excess carbon content. In dependence on the layer thickness a periodic progress of the element contents was observed, at which a maximum for Ti and Cl correlates with a minimum for C. It was found that the incorporated chlorine is bonded to titanium. The lattice parameter depends on the chlorine content. Using TiCl₄/H₂/Ar-gas mixtures without any hydrocarbon, layers containing TiH₂ are formed.     

单一混合固态源PE-MOCVD法制备YSZ薄膜及其表征

采用等离子体增强的MOCVD技术,以均匀混合的金属β-二酮鳌合物固态源Y(DPM)₃和Zr(DPM)₄作为前驱物,在NiO/SDC多孔阳极和多孔-αAl₂O₃衬底上制备了氧化钇稳定的氧化锆(YSZ)薄膜.研究了两种衬底对成膜过程和膜的结构以及微结构的影响,讨论了源区输运机制及薄膜生长动力学.XPS分析结果表明,薄膜中Y和Zr元素的摩尔比低于原始混合源中的Y和Zr元素的摩尔比,当混合源中的Y和Zr元素的摩尔比约为0.35:1时,可以获得无定形态的8%YSZ薄膜,经高温焙烧转化为单一立方相,其晶粒大小约为100nm,薄膜的生长速率约为7nm/min.     

Interfacial oxidation of ultrathin nickel and chromium films on yttria-stabilized zirconia

The substrate-induced oxidation upon prolonged annealing in UHV of ultrathin films of Ni and Cr vapor deposited on yttria-stabilized zirconia YSZ(100) was studied by X-ray photoelectron spectroscopy (XPS) to obtain information about the oxidation mechanism, determine the available quantity of reactive oxygen in YSZ, and investigate the thermal stability of the thin oxide films. Up to about 0.8 ML of Ni deposited at room temperature was oxidized to NiO at a constant rate at 650 K via the substrate, whereas at slightly higher coverage, the oxidation rate under identical conditions was drastically reduced. In contrast to Ni, up to 4.8 ML of Cr deposited at 275 K could be oxidized via the substrate to Cr2O3 upon extensive UHV annealing at increasing temperature up to 820 K, indicating a reactive oxygen content of at least 4 x 10(-6) with respect to the lattice oxygen in the YSZ specimen. The Cr2O3 decomposed to metallic Cr above about 800 K, whereas NiO was stable up to the maximum temperature of 875 K. These results indicate that the oxidation via the substrate is kinetically analogous to the gas-phase oxidation of bulk Ni and Cr. The reactive oxygen content of the single-crystal YSZ is larger than expected, and part of it is accommodated at the surface of the substrate. The thermal stability of the thin oxide films is determined by the oxygen exchange with YSZ and not by the respective bulk oxide thermodynamic decomposition temperature.     

A Multiple Evaluation Approach of Commercially Available Screen‐Printed Nanostructured Carbon Electrodes

Commercially available carbon‐based screen‐printed electrodes were studied by cyclic voltammetry and electrochemical impedance spectroscopy in their behavior towards electron transfer to the soluble fast redox probes hexacyanoferrate(III), hexaammineruthenium(III) and methyl‐viologen. Semi‐infinite linear diffusion was observed for hexacyanoferrate(III) probe, with heterogeneous electron transfer rate constants significantly favored on nanotubes‐modified surfaces. Finite diffusion was observed for methyl‐viologen on graphene electrodes, which was reflected in the enhancement of the faradic currents by 4‐folds. Hexaammineruthenium(III) showed mixed diffusion behavior. These characteristics are reflected in the voltammetric behavior of lead(II) and cadmium(II) stripping from in‐situ deposited bismuth layer.     

TiO2修饰La0.6Sr0.4Co0.2Fe0.8O3-δ用于中温固体氧化物燃料电池的阴极

纳米TiO2修饰的La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF)阴极被直接应用于YSZ电解质电池上. TiO2可阻止LSCF和YSZ间的化学反应,抑制SrZrO3的形成. LSCF-0.25 wt% TiO2阴极电池在0.7 V和600°C下的电流密度是LSCF阴极电池的1.6倍.电化学阻抗谱结果表明, TiO2修饰显著加快了氧离子注入电解质的过程,这可能与TiO2抑制了阴极/电解质界面处高电阻SrZrO3层的形成有关.本文为在ZrO2基电解质上使用高性能的(La,Sr)(Co,Fe)O3阴极材料提供了一种简单有效的方法.     

Influence of YSZ buffer layer on the electric properties of compositionally graded (Ba,Sr)TiO<Subscript>3</Subscript> thin film

Compositionally graded Ba_1−x Sr _x TiO₃ (BST) (0 ≤ x ≤ 0.4) thin films were fabricated on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by a modified sol–gel technique. The YSZ buffer layer was prepared by RF magnetron sputtering. The microstructure of the graded BST films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that all the films have uniform and crack-free surface with a perovskite structure. The graded BST film with an YSZ buffer layer has larger dielectric constant and lower dielectric loss. The leakage current density of the graded BST film with an YSZ buffer layer lowers two orders than the film without buffer layer. The improved electric properties of the graded films with an YSZ buffer layer was attributed to the YSZ buffer layer act as an excellent seeding layer to enhance the graded BST film growth.     

Influence of thermal annealing on the microstructure,hardness and corrosion behavior of TiAlSiCuN nanocomposite films

Nanocomposite TiAlSiCuN films were deposited on high speed steels by filtered magnetic arc ion plating. Detailed properties of the films annealed at various temperatures are studied. After thermal annealing at different temperatures ranging from 400 to 800 °C, changes in the film micro‐structure, chemical and phase composition, surface morphology, hardness and polarization curve properties were systematically characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, nano‐indenter and electrochemical workstation, respectively. It was found that the TiAlSiCuN films could be fully oxidized at 800 °C, Al and Ti atoms all diffused outwards and formed dense protective Al₂O₃ and TiO₂ layer. Simultaneously, the TiAlN phase gradually disappeared. The films annealed at 400 °C obtained the highest hardness because of the certain grain growth and little generated oxides. Besides, the certain formation of dense protective Al₂O₃ layer made the TiAlSiCuN film annealed at 600 °C present the least corrosion current density and the corrosion voltage. Copyright © 2016 John Wiley & Sons, Ltd.     

Remarkable Enhancement of O2 Activation on Yttrium‐Stabilized Zirconia Surface in a Dual Catalyst Bed

Yttrium‐stabilized zirconia (YSZ) has been extensively studied as an electrolyte material for solid oxide fuel cells (SOFC) but its performance in heterogeneous catalysis is also the object of a growing number of publications. In both applications, oxygen activation on the YSZ surface remains the step that hinders utilization at moderate temperature. It was demonstrated by oxygen isotope exchange that a dual catalyst bed system consisting of two successive LaMnO₃ and YSZ beds without intimate contact drastically enhances oxygen activation on the YSZ surface at 698 K. It can be concluded that LaMnO₃ activates the triplet ground‐state of molecular oxygen into a low‐lying singlet state, thereby facilitating the activation of the O₂ molecule on the YSZ oxygen vacancy sites. This phenomenon is shown to improve the catalytic activity of the LaMnO₃‐Pd/YSZ system for the partial oxidation of methane.