Protecting the MoSi2 healing particles for thermal barrier coatings using a sol-gel produced Al2O3 coating

A successful sol-gel process to encapsulate molybdenum di-silicide MoSi₂ particles with a closed and thermally stable Al₂O₃ layer using aluminium tri-sec-butoxide as a precursor is presented. The processing conditions such as precursor selection and temperature were optimized through analysing the interaction of the MoSi₂ particles with the sol. The application of the sol-gel based coating was followed by calcining the coated particles at temperatures between 900 and 1200?°C in Ar. The shell composition and the mechanical stability of the microcapsule were analysed by means of X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. Upon calcining at 1200?°C in Ar, the MoSi₂ core remains intact as it is, covered by an α - alumina shell with a thickness of about 0.6?μm. The stability tests proved that the encapsulate particles are about five times more oxidation resistant than the uncoated MoSi₂ particles.     

Residual stress and electrical properties of Pb(Zr0.52,Ti0.48)O3 thin films RF sputtered directly on Cu foils

Polycrystalline Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films between 250 and 1000 nm thick were deposited on Cu foils via RF magnetron sputtering. Samples were crystallized ex situ between 550°C and 750°C in a low oxygen partial pressure atmosphere, pO₂, in order to avoid oxidation of the substrate. These were compared to films made on more common Pt/TiO_x/SiO₂/Si substrates also crystallized under low pO₂ conditions. The mismatch of the coefficients of thermal expansion for Cu and PZT caused large compressive residual stresses to develop in the films, whereas films on Pt‐Si experienced more moderate tensile stresses. Stress was measured using the sin²ψ method. In addition to mechanical implications, i.e., film cracking and delamination, the effect of residual stress on electrical properties is discussed. Dielectric constants of PZT were lower on Cu than on Pt/TiO_x/SiO₂/Si. This could be due either to a dead layer effect or to the residual stress imposed by the substrate. The remanent polarizations for films on Cu were between 18 and 41 μC/cm², while coercive fields were between 37 and 54kV/cm. Rayleigh analysis was used to describe the role of defects affecting domain wall mobility, as they act as pinning centers and decrease the extrinsic polarization response.     

The preparation of Al2O3 based organic/inorganic composite films and the application in agricultural greenhouse

The work presented herein focuses on developing the Al₂O₃ based organic/inorganic multifunctional composite films via an internal addition method in the presence of dripping agent, antifogging agent, light stabilizer and insulation barrier agent. The resulting composite films were systematically characterized using scanning electron microscope, FTIR, differential scanning calorimetry, UV, and tensile testing machine. The morphology changed obviously after introducing the inorganic fillers. In addition, the results indicated that the contact angle of the activated Al₂O₃–10 film had the best stability and the film with ultrafine Al₂O₃ possessed the best anti-dripping performance. The time of the first water drop of the film containing 10 g activated Al₂O₃ (the activated Al₂O₃–10) was 7 min and 18 s, and the time of each ten-drops was less than 120 s. The simulated anti-aging period of the films with anti-aging agent was up to 423 days, which is superior to many other reported organic/inorganic composite films and can be applied to those extreme climate areas (such as Xinjiang, China).     

High temperature electrode‐electrolyte interface formation between LiMn1.5Ni0.5O4 and Li1.4Al0.4Ge1.6(PO4)3

All‐solid‐state lithium‐ion electrolytes offer substantial safety benefits compared to flammable liquid organic electrolytes. However, a great challenge in solid electrolyte batteries is forming a stable and ion conducting interface between the electrolyte and active material. This study investigates and characterizes a possible solid‐state electrode‐electrolyte pair for the high voltage active cathode material LiMn_1.5Ni_0.5O₄ (LMNO) and electrolyte Li_1+xAl_xGe_2‐x(PO₄)₃ (LAGP). In situ X‐ray diffraction measurements were taken on pressed pellets comprised of a blend of LMNO and LAGP during exposure to elevated temperatures to determine the product materials that form at the interface of LMNO and LAGP and the temperatures at which they form. In particular, above 600°C a material consistent with LiMnPO₄ was formed. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy were used to image the morphology and elemental compositions of product materials at the interface, and electrochemical characterization was performed on LMNO‐coated LAGP electrolyte pellet half cells. Although the voltage of Li/LAGP/LMNO assembled batteries was promising, thick interfacial phases resulted in high electrochemical resistance, demonstrating the need for further understanding and control over material processing in the LAGP/LMNO system to reduce interfacial resistance and improve electrochemical performance.     

An Investigation on the Thermal Effusivity of Nanofluids Containing Al(2)O(3) and CuO Nanoparticles

The thermal effusivity of Al(2)O(3) and CuO nanofluids in different base fluids, i.e., deionized water, ethylene glycol and olive oil were investigated. The nanofluids, nanoparticles dispersed in base fluids; were prepared by mixing Al(2)O(3), CuO nanopowder and the base fluids using sonication with high-powered pulses to ensure a good uniform dispersion of nanoparticles in the base fluids. The morphology of the particles in the base fluids was investigated by transmission electron microscopy (TEM). In this study, a phase frequency scan of the front pyroelectric configuration technique, with a thermally thick PVDF pyroelectric sensor and sample, was used to measure the thermal effusivity of the prepared nanofluids. The experimental results of the thermal effusivity of the studied solvents (deionized water, ethylene glycol and olive oil) showed good agreement with literature values, and were reduced in the presence of nanoparticles. The thermal effusivity of the nanofluid was found to be particularly sensitive to its base fluid and the type of nanoparticles.     

An efficient method for enhancing adhesion and uniformity of Al2O3 coatings on nickel micro-foam used in micropacked beds

Methods of coating Al₂O₃ on nickel micro-foam were compared and screened, aiming to overcome the capillary force and prepare the micro-foam monolithic catalyst coatings. The surface of micro-foam substrate was pretreated by a chemical etching method to improve the adhesion of the coatings on the substrate. The results showed that the slurry circulation at 162 ml·min^-1 was evaluated as the optimal method. The pore size on the substrate surface can be controlled by changing the pretreatment conditions. An empirical correlation was also proposed, showing an excellent practicality for predicting the pore size. The adhesion of the coatings with substrate pretreatment was significantly better than that without substrate pretreatment. The minimum value of mass loss after ultrasonic vibration was 3.9%. This mainly attributes to the squeezing of Al₂O₃ particles in the pores of substrate surface. The coatings on nickel micro-foam are hopefully used in micropacked beds for catalytic reactions.     

t-ZrO2 toughened Al2O3 free-standing films and as oxidation mitigating thin films on silicon nitride via colloidal processing of flame made nanopowders (NPs)

Zirconia toughened aluminas (ZTAs) are one of the most important engineering ceramics with high melting points, excellent mechanical strength, and chemical stability, and are commonly used as wear resistant and high-temperature components, as prosthetic implants, and electric circuit substrates. In this work, we explore methods of processing fine-grained, dense, thin, free-standing (ZrO₂)_x(Al₂O₃)_1−x films (x = 0-50 mol%, ~40 μm thick) by sintering flame made nanopowders (NPs) to optimize the t-ZrO₂ content, sinterability, and microstructures under select conditions (1120°C-1500°C/5 h in O₂ or 95%N₂/5%H₂). In all cases, the final sintered products retain t-ZrO₂ with average grain sizes (AGSs) of 0.1-1 μm. ZTA film thicknesses were increased to ~200 μm to assess potential as electronic substrates. Excellent fracture toughness (24 MPa m^1/2) and small AGSs of 0.7 μm were found for ~200 μm thick ZTA films sintered at 1500°C/5 h/N₂/H₂ using a three-step binder burnout process. Furthermore, we show that homogeneous ZTA thin films (<5 μm thick) can be sintered on Si₃N₄ substrates (thickness ≈ 300 μm) to provide physical protection against oxidation under extreme conditions (1500°C/1 h/O₂), offering additional practical utility for high-temperature ceramics and power electronic substrates.     

Enhanced voltage endurance capability of Ba(Zr0.2Ti0.8)O3 thin films induced by atomic-layer-deposited Al2O3 intercalations and the application in electrostatic energy storage

Ultrathin Al₂O₃ insulating intercalations with different thicknesses and numbers, prepared by atomic layer deposition technology, were introduced into Ba(Zr_0.2Ti_0.8)O₃ (BZT) relaxor ferroelectric films as the dielectric for electrostatic energy storage capacitors. The phase structure, microstructure and electrical properties were investigated in detail. Due to the insertion of insulating layers, the films show less leakage current and enhanced voltage endurance capability when the thickness of single Al₂O₃ intercalation exceeds a threshold (0.45–0.9 nm). The voltage endurance capability can be more enhanced by increasing the number of Al₂O₃ intercalations. For energy storage applications, the energy storage density and efficiency obtained from the polarization-electric field loops are significantly improved owing to the suppressed leakage and enhanced voltage endurance ability. The results promote the application of BZT-based films in electrostatic energy storage. It is demonstrated that the introduction of atomic-layer-deposited insulating intercalations with controllable thickness, such as those fabricated by ALD method, is an effective way to improve the electrical performance of devices based on composite materials.     

Adjustable amine–epoxy composition in a stratified thin film with a spin‐coating process: A useful tool for establishing relationships between the local glass‐transition temperature at the interface and the network structure

An easy method for preparing supported homogeneous epoxy–amine thin films on a silica surface consisting of two distinct layers was developed via spin coating from epoxy–amine solutions. Because of these two layers had the controlled properties of the upper layer, we showed that it was possible to precisely control the epoxy–amine stoichiometry in the sublayer through the initial epoxy–amine ratio, the spin‐cast process, and the overall film thickness. First, in the thin films, the primary amine–epoxy conversion was constant, whatever the thickness and initial epoxy–amine stoichiometry for a given curing schedule. As the primary amine conversion can be independently tuned in thin films, it thus provided a rather unique and easy method for better understanding the relationship between the network structure curing at the interface and the resulting properties, such as the glass‐transition temperature (T_g) and elastic modulus. Here, we also showed that we could access the local T_g; this implied a potential application of these experimental data in predictive composite material properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42078.     

Conventional and wet proofed CuO/Al2O3 catalysts for phenol oxidation: deactivation studies in a trickle bed reactor

A large variety of catalytic systems have been studied for the catalytic wet air oxidation of phenolic solutions. Most of them show good activity, but serious stability problems. In this contribution, stability studies were performed over CuO/Al₂O₃ conventional (CNT) and polytetrafluorethylene coated (C3T) catalysts used for the oxidation of 5 g L^?1 phenol solutions in a trickle bed reactor (140 °C and 7 atm of oxygen pressure). For the hydrophilic catalyst, phenol conversion decreased with usage due to the formation of Cu₂O and copper oxalate phases. For the wet proofed catalyst, the hydrophobic layer prevented the appearence of those phases, and conversion levels remained practically constant with reaction time. After usage, both catalysts were oxidized at 400 °C and tested for reaction: in the case of the C3T catalyst, the phenol conversion was increased over its initial level; for CNT catalyst, the phenol conversion was also increased, but initial levels were not completely restored. The deactivation mechanism of the CNT catalyst is associated with the formation of the Cu₂O and copper oxalate phases during reaction. For catalyst C3T, practically no deactivation was observed. Copyright © 2007 Society of Chemical Industry     

Studies on nanotribological and oxidation resistance properties of yttria stabilized zirconia (YSZ), alumina (Al2O3) based thin films developed by pulsed laser deposition

The present study aims at a detailed evaluation of mechanical, tribological, and high temperature oxidation resistance (at 1000 °C under isothermal condition) properties of YSZ, and Al₂O₃ based thin films developed by pulsed laser deposition technique. The mechanical and tribological properties of YSZ and Al₂O₃ thin films showed significant improvement with increasing the deposition temperature during pulsed laser deposition process. The kinetics of oxidation was reduced due to pulsed laser deposition and Al₂O₃ coating offered a superior oxidation resistance property as compared to YSZ coating. However, the deposition temperature has no significant effect in reducing the TGO growth rate of the pulsed laser deposited thin films.     

Nanoscale observation of surface potential and carrier transport in Cu2ZnSn(S,Se)4 thin films grown by sputtering-based two-step process

Stacked precursors of Cu-Zn-Sn-S were grown by radio frequency sputtering and annealed in a furnace with Se metals to form thin-film solar cell materials of Cu₂ZnSn(S,Se)₄ (CZTSSe). The samples have different absorber layer thickness of 1 to 2 μm and show conversion efficiencies up to 8.06%. Conductive atomic force microscopy and Kelvin probe force microscopy were used to explore the local electrical properties of the surface of CZTSSe thin films. The high-efficiency CZTSSe thin film exhibits significantly positive bending of surface potential around the grain boundaries. Dominant current paths along the grain boundaries are also observed. The surface electrical parameters of potential and current lead to potential solar cell applications using CZTSSe thin films, which may be an alternative choice of Cu(In,Ga)Se₂.PACS number: 08.37.-d; 61.72.Mm; 71.35.-y     

Effect of Constant‐Rate Reduction on the Performance of a Ternary Cu/ZnO/Al2O3 Catalyst in Methanol Synthesis

A multi‐functional flow set‐up was developed for the rate‐ and temperature‐controlled reduction of copper catalysts, their application in high‐pressure methanol synthesis and the determination of the copper surface area by N₂O frontal chromatography. The influence of constant‐rate reduction on the catalytic properties of a ternary Cu/ZnO/Al₂O₃ catalyst was investigated. The temperature during the constant‐rate reduction was found to decrease, indicating autocatalytic kinetics, but no significant catalytic effect of the milder reduction conditions was observed compared with a slow linear heating ramp.     

Relationship between distortion of crystal structure and dielectric properties of complex perovskite oxide Ba(Co,Zn)1/3Nb2/3O3 thin films

The oxygen octahedral can be distorted by epitaxial strain due to the lattice mismatch. The epitaxial strain (ε_yy) linearly decreases from ? 0.244% to ? 0.445% with the growth temperature. Thin films grow along c axis on the SrTiO₃ substrate and exhibit the epitaxial relationship of Ba(Co,Zn)_1/3Nb_2/3O₃ (001) // SrTiO₃ (001). The superlattice reflections arising from in-phase tilting of the oxygen octahedra are clearly visible along [010] and [111] zone axis. The IR modes at 330 cm^?1 and 390 cm^?1 related to in-phase tilting are observed in far-infrared reflectivity spectroscopy. The calculated Q×f values from far-infrared reflectivity spectra of films grown at 550 °C to 700 °C increases from 51,000 GHz to 91,000 GHz mainly due to the enhancement of crystalline quality. The intrinsic quality factor (Q) is mainly contributed by O-(Co, Nb)-O and O-(Zn, Nb)-O bonding modes, while in-phase tilting in BCZN films may result in enhanced dielectric constants.     

Evaluation of the phase stability,and mechanical and thermal properties of Ba(Sr1/3Ta2/3)O3 as a potential ceramic material for thermal barrier coatings

Ba(Sr_1/3Ta_2/3)O₃ (BST) ceramic was synthesized by a solid-state reaction method. The phase stability, microstructural evolution, and mechanical and thermal properties of the BST ceramic were investigated and characterized to evaluate the potential application of BST as a top coating material for thermal barrier coatings (TBCs). The results show that BST can maintain a stable hexagonal perovskite structure up to 1600 °C. Anisotropic growth of the grains above 1400 °C was observed. Its low elastic modulus and high fracture toughness suggest a high damage tolerance for the BST ceramic. In addition, the moderate coefficient of thermal expansion and superior heat insulation capability of the BST ceramic provide this ceramic the potential to serve as a top coating material of TBCs at higher temperature.     

Interfacial structure in vulcanized EPDM filled with mercaptosilane-treated Al(OH)3 and its influence on the mechanical properties

The reactivity of the alkoxy group in a silane coupling agent toward inorganic surfaces was investigated, and the structure of a silane-treated layer on the particle surface was analyzed. For this purpose, the various inorganic filler particles, SiO₂, Al(OH)₃, Mg(OH)₂, Al₂O₃, and CaCO₃ were treated with γ-mercaptopropyltrimethoxysilane. A strong interaction between the particle surface and the silane due to the hydrogen bonding and ionic interaction was confirmed except for CaCO₃ by electron spectroscopy for chemical analysis (ESCA). The structure of the silane layer on the particle surface was affected significantly by both the amount of added silane and the treatment conditions. Different silane structures, such as monolayer- or network-like, were formed on the particle surface. Their influences on the mechanical properties of filled vulcanized rubber were also investigated. The silane-treated filler particles, except CaCO₃, showed ability as a semi-reinforcing filler for vulcanized rubber. However, the structure of the silane-layer on the particle surface hardly affected the mechanical properties.     

NO Reduction with CO in the Presence of O2 over Cu/Al2O3 (3) – Structural Analysis of Active Species by Means of XAFS and UV/VIS/NIR Spectroscopy

The local structure around Cu supported on Al₂O₃ was determined by UV/VIS/NIR and XAFS spectroscopic techniques. The relationship between catalytic performance for NO–CO–O₂ reaction and the state of supported Cu species is discussed. A new method for estimating the fraction of aggregated to isolated Cu species is proposed.     

Interfacial tension between aluminum and cryolite melts during electrolysis of the systems Na3AlF6–AlF3 (NaF)–Al2O3

The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured by the capillary depression method. The technique is based on the measurement of the capillary depression occurring when the capillary, which is moved vertically down through the molten salt layer, passes through the salt/metal interface. The depression is measured by simultaneous video recording of the immersion height of the alumina capillary. The interfacial tension was found to be strongly dependent on the n(NaF)/n(AlF₃) ratio (cryolite ratio, CR). At the cryolite ratio 2.28 (80 wt.% Na₃AlF₆ + 10 wt.% AlF₃ + 10 wt.% Al₂O₃ // Al, t = 1000 °C) the interfacial tension was 546 mN m⁻¹, while it was 450 mN m⁻¹ at the cryolite ratio 4.43 (80 wt.% Na₃AlF₆ + 10 wt.% NaF + 10 wt.% Al₂O₃ // Al, t = 1000 °C). Experiments under current flow conditions were also performed. During the electrolysis the interfacial tension at n(NaF)/n(AlF₃) ratio 2.28 decreased from 546 mN m⁻¹ at zero current to 518 mN m⁻¹ at 0.112 A cm⁻². The same trend was observed in the system with a cryolite ratio 4.43. The interfacial tension decreased from 450 mN m⁻¹ at zero current to 400 mN m⁻¹ at 0.112 A cm⁻². The consequent increase in interfacial tension of these systems caused by interruption of electrolysis was observed. Electrolysis of the system 25 wt.% NaF + 75 wt.% NaCl (eutectic mixture)/Al indicated no influence of applied current on the interfacial tension at 850 °C.     

The growth mechanism of nickel in the preparation of Ni/Al2O3 catalysts studied by LEIS,XPS and catalytic activity

A series of Ni/Al₂O₃ catalysts prepared from vapor phase by the atomic layer epitaxy (ALE) technique have been studied. A model is proposed for the growth mechanism of nickel in its oxidic form on alumina, from sequences of treatments with Ni(acac)₂ and air. In the study activity measurements were combined with surface analysis by LEIS and XPS. During the first preparation sequence (< 5 wt% Ni) atomically dispersed nickel is obtained on the alumina support. The nickel atoms are catalytically inactive, but act as nuclei for the growth of the catalytically active Ni-species during the subsequent preparation sequences. The highest utilization of nickel atoms in the hydrogenation of toluene was obtained when the nickel nuclei were covered with one layer of active nickel species.     

Inductively coupled plasma etching of Pb(ZrxTi1-x)O3 thin films in Cl2/C2F6/Ar and HBr/Ar plasmas

Pb(Zr_xTi_1-x)O₃ thin films were etched in an inductively coupled plasma by using various etch gases such as Cl₂/Ar, C₂F₆/Ar, Cl₂/C₂F₆/Ar and HBr/Ar. The etch rates and etch profiles for each etch gas were investigated. Fast etch rates were obtained in chlorine-containing etch gases (e.g., Cl₂/Ar and Cl₂/C₂F₆/Ar), and clean and steep etch profiles were achieved in Cl₂/Cv₂F₆/Ar or HBr/Ar gases. The gas mixture of Cl₂ and C₂F₆ was proposed to give a fast etch rate and a steep sidewall angle of etched patterns. The optimum gas mixture of Cl₂C₂F₆/Ar was found by varying the gas ratio of Cl₂ to C₂F₆. On the other hand, HBr/Ar gas as an alternative for etching of the Pb(Zr_xTi_1-x)O₃ films was examined. Cl₂/C₂F₆/Ar and HBr/Ar etch gases were compared with respect to etch rate, etch profile and electrical properties.