Cluster size effects on hydrazine decomposition on Irn/Al2O3/NiAl(1 1 0)

A series of planar model catalysts were prepared by deposition of size-selected on Al₂O₃/NiAl(1 1 0), and hydrazine decomposition chemistry was used to probe their size-dependent chemical properties. Small Ir_n (n ? 15) on Al₂O₃/NiAl(1 1 0) are able to induce hydrazine decomposition at temperatures well below room temperature, with significant activity first appearing at Ir₇. Both activity and product branching are strongly dependent on deposited cluster size, with these small clusters supporting only the simplest decomposition mechanism: dehydrogenation and N₂ desorption at low temperatures, followed by H₂ recombinative desorption at temperatures above 300 K. For Ir₁₅, we begin to see ammonia production, signaling the onset of a transition to clusters able to support more complex chemistry.     

Influence of long-term aqueous exposure on surface properties of plasma sprayed oxides Al2O3, TiO2 and their mixture Al2O3-13TiO2

The surface properties of plasma sprayed Al₂O₃- and TiO₂-based coating materials were characterized in order to investigate the influence of surface strain and phase inhomogenity. The materials were water exposed up to 8 months. The bulk crystallographic structure, dissolution behaviour, effective charge (zeta potential, isoelectric point), surface compositions and oxidation states were determined. In addition, the properties of the aging solutions, such as conductivity, supernatant pH (point of zero charge), and redox potential, were monitored during aging.It was shown that the materials were stable under aging conditions, but that considerable surface rearrangements, such as dissolution-reprecipitation and surface site redistributions may occur. However, overall only minor changes in surface properties results from this restructuring process.     

MAO-synthesized Al2O3-supported V2O5 nano-porous catalysts: Growth, characterization, and photoactivity

V₂O₅-loaded Al₂O₃ layers were successfully grown via micro-arc oxidation (MAO) process for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). It was found that the composite layers had a porous structure with a rough surface which is suitable for catalytic applications. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS) techniques were also employed to study phase structure and chemical composition of the composite layers. The layers consisted of γ-alumina, α-alumina, and vanadium pentoxide phases in which their relative contents varied with the applied voltage. Meanwhile, optical properties of the composite layers were investigated using UV-vis spectrophotometry technique, and the band gap energy was calculated as 3.15 eV. Furthermore, photocatalytic performance of the synthesized composite layers was determined by measuring the decomposition rate of methylene blue solution, as a model compound, on the surface of the layers under ultra violet photo-irradiation. It was found that more than 91% of the methylene blue was degraded after 120 min with a rate constant of k = 0.0192 min⁻¹.     

MoO3/Al2O3催化剂中Mo分散的正电子研究

用浸渍法制备了一系列不同Mo含量的MoO₃/Al₂O₃催化剂.测量了这些样品的正电子湮没寿命谱(PALS)与符合多普勒展宽(CDB)谱,以研究其孔洞结构以及Mo分散.正电子寿命测量结果表明,Al₂O₃载体中存在两种不同尺寸的孔洞.掺入MoO₃之后,Mo原子主要进入Al₂O₃的大孔中,使孔洞体积减小.符合多普勒展宽谱结果表明,当MoO 关键词： 3/Al₂O₃催化剂')" href="#">MoO₃/Al₂O₃催化剂 正电子湮没寿命谱 符合多普勒展宽 Mo 分散     

Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

Fe₂O₃/Al₂O₃ catalysts were prepared by solid state reaction method using α-Fe₂O₃ and γ-Al₂O₃ nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ₃ and τ₄ are attributed to positronium annihilation in two types of pores distributed inside Al₂O₃ grain and between the grains, respectively. With increasing Fe₂O₃ content from 3 wt% to 40 wt%, the lifetime τ₃ keeps nearly unchanged, while the longest lifetime τ₄ shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe₂O₃ content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ₄ is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.     

Hydrogenolysis of methylcyclopentane over the bimetallic Ir-Au/γ-Al2O3 catalysts

The gas-phase hydrogenolysis of methylcyclopentane (MCP) was investigated over the bimetallic Ir-Au/γ-Al₂O₃ catalysts. The bimetallic systems containing the atomic Au/Ir ratios in the range of 0.125-8 and a fixed total metal content of 8 wt.%, were prepared by the sequential impregnation (SI) and co-impregnation (CI) methods. The corresponding monometallic Ir/γ-Al₂O₃ and Au/γ-Al₂O₃ catalysts were also prepared. The materials were characterized by ICP, XRD, N₂ adsorption, TEM, and H₂ chemisorption. Highly dispersed Ir nanoparticles were obtained in all cases, while the size of Au nanoparticles increased (up to 50 nm) upon the increasing Au content in the catalyst. The monometallic gold catalyst did not adsorb H₂. The incorporation of Au increased the amount of irreversible adsorbed H₂ in the Ir-Au/γ-Al₂O₃ catalysts with respect to the monometallic ones. The products obtained in the MCP hydrogenolysis were 2-methylpentane (2-MP), 3-methylpentane (3-MP) and n-hexane (n-H). The initial rate (molecules of MCP reacted s⁻¹ g_Ir⁻¹) increased with the Au content. The deactivation was lower for bimetallic catalysts, particularly for the CI ones. The addition of Au played a significant effect on chemisorption and catalytic properties of Ir.     

Effects of CeO2-ZrO2 present in Pd/Al2O3 catalysts on the redox behavior of PdOx and their combustion activity

The ceria-zirconium-modified alumina-supported palladium catalysts are prepared using impregnation method with H₂PdCl₄ as Pd source, hydrazine hydrate as reducing agent. The physicochemical properties of these catalysts are characterized by BET surface area (BET), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (H₂-TPR) and temperature programmed oxidation (O₂-TPO) techniques, and their catalytic activities for the combustion of methane are examined. The results show that the palladium mainly exist in a highly dispersed PdO species on Ce-Zr-rich grains as well as Al₂O₃-rich grains surfaces, and a stable PdO species due to the strong interaction between PdO and CeO₂-ZrO₂ on the Ce-Zr/Al₂O₃ surfaces. The catalytic activity is strongly related to the redox behavior of PdO species highly dispersed on Ce-Zr-rich grains and Al₂O₃-rich grains surfaces, and the higher the reducibility of the PdO species, the higher the catalytic activity. The presence of Ce-Zr in Pd/Al₂O₃ catalyst would inhibit the site growth of PdO_x particles and decomposition of PdO to Pd⁰, and the reoxidation property of Pd⁰ to PdO_x is significantly improved, which obviously increases thermal stability and catalytic activity of Pd/Ce-Zr/Al₂O₃ catalyst for the methane combustion.     

石墨烯在Al_2O_3(0001)表面生长的模拟研究

基于密度泛函理论的广义梯度近似法,对用化学气相沉积法在蓝宝石(α-Al_2O_3)(0001)表面上生长石墨烯进行理论研究.研究结果表明:CH_4在α-Al_2O_3(0001)表面上的分解是吸热过程,由CH_4完全分解出C需要较高能量及反应能垒,这些因素不利于C在衬底表面的存在.在α-Al_2O_3(0001)表面,石墨烯形核的活跃因子并不是通常认为的C原子,而是CH基团.通过CH基团在α-Al_2O_3(0001)表面上的迁移聚集首先形成能量较低的(CH)_x结构.模拟研究(CH)_x对揭示后续石墨烯的形核生长机理具有重要意义.     

Laser treatment of Si-Al2O3 two-layer target

The laser treatment of two-layer Si-Al₂O₃ target at λ=1064 nm and P=170 W in a N₂+O₂ atmosphere by electron microscopy, atomic force microscopy, X-ray microanalysis, and IR-spectroscopy was investigated. It is established that in the stage of fracture of a silicon plate, the ablation products were silicon clusters into which, when passing over, oxygen and nitrogen diffused. On collective plate, a SiO_xN composite film formed. In the stage of fracture of an alumina plate, the oxidation of silicon in the channel zone and the interaction of Al and Si oxides, accompanied by their nitration, occurred. In this stage, evolved oxide vapors and ejected mullite drops deposit on the SiO_xN film. On collective plate, mullite nanowhiskers grew from mullite drops by the vapor-liquid-solid body mechanism.     

Characteristics of sandwich-structured Al2O3/HfO2/Al2O3 gate dielectric films on ultra-thin silicon-on-insulator substrates

Sandwich-structure Al₂O₃/HfO₂/Al₂O₃ gate dielectric films were grown on ultra-thin silicon-on-insulator (SOI) substrates by vacuum electron beam evaporation (EB-PVD) method. AFM and TEM observations showed that the films remained amorphous even after post-annealing treatment at 950 °C with smooth surface and clean silicon interface. EDX- and XPS-analysis results revealed no silicate or silicide at the silicon interface. The equivalent oxide thickness was 3 nm and the dielectric constant was around 7.2, as determined by electrical measurements. A fixed charge density of 3 × 10¹⁰ cm⁻² and a leakage current of 5 × 10⁻⁷A/cm² at 2 V gate bias were achieved for Au/gate stack /Si/SiO₂/Si/Au MIS capacitors. Post-annealing treatment was found to effectively reduce trap density, but increase in annealing temperature did not made any significant difference in the electrical performance.     

Influence of the transparency of tunnel barriers in Nb/Al2O3/Al/Al2O3/Nb junctions on transport properties

The transparency of the tunnel barriers in double-barrier junctions influences the critical current density and the form of the current–voltage characteristics (IVC). Moreover, the barrier asymmetry is an important parameter, which has to be controlled in the technological process. We have performed a systematic study of the influence of the barrier transparency on critical current, I_C, and normal resistance, R_N, by preparing SIS and SINIS junctions under identical technological conditions and comparing their transport properties. We have fabricated Nb/Al₂O₃/Nb and Nb/Al₂O₃/Al/Al₂O₃/Nb devices with different current densities using a conventional fabrication process, varying pressure and oxidation time. The thickness of the Al middle electrode in all Nb/Al₂O₃/Al/Al₂O₃/Nb junctions was 6 nm. Patterning of the multilayers was done using conventional photolithography and the selective niobium etching process. The current density of SIS junctions was changed in the range from 0.5 to 10 kA/cm². At the same conditions the current density of SINIS devices revealed 1–100 A/cm² with non-hysteretic IVC and characteristic voltages, I_CR_N, of up to 200 μV. By comparing the experimental and theoretical temperature dependence of the I_CR_N product we estimated the barrier transparency and its asymmetry. The comparison shows a good agreement of experimental data with the theoretical model of tunneling through double-barrier structures in the dirty limit and provides the effective barrier transparency parameter γ_eff≈300. A theoretical framework is developed to study the influence of the barrier asymmetry on the current–phase relationship and it is proposed to determine the asymmetry parameter by measuring the critical current suppression as function of applied microwave power. The theoretical approach to determine the non-stationary properties of double-barrier junctions in the adiabatic regime is formulated and the results of calculations of the I–V characteristics are given in relevant limits. The existence and the magnitude of a current deficit are predicted as function of the barrier asymmetry.     

Influence of treating frequency on microstructure and properties of Al2O3 coating on 304 stainless steel by cathodic plasma electrolytic deposition

Alumina ceramic coatings were fabricated on 304 stainless steel by cathodic plasma electrolytic deposition (CPED). Influence of treating frequency of the power supply on the microstructure and properties of the coatings were studied. The results indicated that coatings obtained at various frequencies on 304 stainless steels were all composed of α-Al₂O₃ and γ-Al₂O₃, and α-Al₂O₃ was the dominant phase. The contents of α-Al₂O₃ decreased gradually in a very small rate with increasing the frequency and γ-Al₂O₃ gradually increased. The surface of alumina ceramic coating was porous. With increasing the frequency, the coating surface gradually became less rough and more compact, resulting in low surface roughness. The bonding strength of Al₂O₃ coating was higher than 22 MPa and was not strongly affected by treating frequency. With increasing the frequency, the alumina coated steels showed better and gradually increasing corrosion resistance than the uncoated one in 3.5% NaCl solution. The coating steel with desirable corrosion resistance was obtained at 800 Hz whose corrosion current potential and corrosion density were −0.237 V and 7.367 × 10⁻⁸ A/cm², respectively.     

Preparation of well-adhered γ-Al2O3 washcoat on metallic wire mesh monoliths by electrophoretic deposition

Washcoat deposited on metallic wire mesh monoliths was prepared using γ-alumina powders by electrophoretic deposition under a relatively low electric voltage. The microstructure, phase structure and adhesion of washcoat were investigated by SEM, XRD, ultrasonic vibration and thermal shock. The results showed that the loading and adhesion of washcoat were affected obviously by the properties of suspension, such as the zeta potential and the amount of adding binders. A small quantity of aluminum isopropoxide could promote the cohesive affinity of washcoat in thermal shock. The adhesion of washcoat in ultrasonic vibration could be reinforced by increasing calcined temperature and adding a certain aluminum particles. It was also found that the washcoat immersed metal nitrate has excellent vibration-resistant ability.     

Magnetic properties of a cermet on the base of Al2O3

The zero-field-cooled and field-cooled magnetizations, magnetization versus field, and remanent magnetization were measured for a cermet on the base of Al₂O₃ using a SQUID magnetometer in the temperature range of 2–360 K. It was shown that magnetic properties of the cermet are determined by independent ferromagnetic, paramagnetic and spin-glass contributions. The spin-glass behavior was studied.     

Electronic properties of thin films of laser-ablated Al2O3

Laser ablation coupled to mass quadrupole spectrometry (LAMQS) has been used to prepare thin films of aluminum oxide deposited on Si substrates starting from commercial Al₂O₃ polycrystalline targets. X-ray photoemission (XPS) and reflection electron energy loss spectroscopy (REELS) have allowed the investigation of the electronic properties of the produced films. In particular, it was found that the Al/O atomic ratio assumes a value very near to 0.7 (stoichiometric ratio) only for films deposited normally with respect to the target surface, while films grown at larger deposition angles are more rich in oxygen content.The composition, the mass density, the optical energy gap, the complex dielectric function and refraction index of the films have been calculated and compared with the results obtained from our starting target material and with the literature. The morphology of the deposited samples has been analyzed by the AFM technique.     

Al2O3增强的Co2-C98/Al2O3/Si异质结的光伏效应

随着能源危机的加剧,太阳能电池作为开发和利用太阳能的一种普遍形式, 日益受到世界各国的重视.随着太阳能电池向着高效率、薄膜化、无毒性和原材料丰富的方向发展, 单纯的硅系太阳能电池已经无法达到这样的要求,因此新的材料和工艺的开发利用迫在眉睫. 本文研究了碳材料在硅异质节上实现光伏效应的改善及其可能在太阳能电池上的应用. 采用脉冲激光沉积方法制备的Co₂-C₉₈/Al₂O₃/Si异质结构在标准日光照射 (AM1.5, 100 mW/cm²)条件下,可获得0.447 V的开路电压和18.75 mA/cm²的电流密度, 转换效率可达3.27%.通过电容电压特性和暗条件下的电输运性能测量, 证明了氧化铝层的引入不但对单晶硅的表面起到了物理钝化作用,减小了反向漏电流, 使异质结界面缺陷、界面能级和复合中心减少,还起到了场效应钝化作用, 增加了异质结界面的势垒高度,增加了开路电压,使异质结的光伏效应显著增强.     

XPS, FTIR and TPR characterization of Ru/Al2O3 catalysts

The properties of Ru/Al₂O₃ catalysts prepared using RuCl₃ as precursor and subjected to different treatments after impregnation, were studied using different techniques: XPS, FTIR, hydrogen chemisorption and thermal programmed reduction. Differences in the Ru species (Ru⁰, ruthenium oxides and ruthenium oxychloride), metal dispersion and chlorine content in the catalysts as well as in their catalytic activity and selectivity during benzene selective hydrogenation to cyclohexene, were found according to the preparation procedure used.     

Size-dependent magnetic properties of FeGaB/Al2O3 multilayer micro-islands

Recently, micrometer-size patterned magnetic materials have been widely used in MEMS devices. However, the self-demagnetizing action is significantly influencing the performance of the magnetic materials in many MEMS devices. Here, we report an experimental study on the magnetic properties of the patterned micro-scale FeGaB/Al₂O₃ multilayers. Ferromagnetic hysteresis loop, ferromagnetic resonance (FMR), permeability and domain behavior have been demonstrated by complementary techniques. Magnetic annealing was used to enhance the performance of magnetic multilayers. The comparisons among micro-islands with different sizes in the range of $200\mathrm{\mu }\text{m}～500\mathrm{\mu }\text{m}$ as well as full film show a marked influence of size-effect, the exchange coupling effect, and the different domain structures inside the islands.     

Mesoporous (ZrO2-TiO2)/Al2O3 ternary carriers as hydrodesulfurization catalysts support

Ternary systems at various compositions were synthesized by coprecipitating Zr and Ti (to get a ZrO₂-TiO₂ 40-60 mol%) chlorides in aqueous basic media (provided by urea thermal decomposition) over an alumina substrate. Materials characterization included N₂ physisorption, X-ray diffraction, thermal analysis, high-resolution electron microscopy and Raman and UV-vis spectroscopies. High interaction among components was clearly evidenced by various techniques. Textural properties of ternary oxides could be tuned depending on composition of formulations. Mixed oxides with 10 or 20 mol% of ZrO₂-TiO₂ (at 40-60% mol, in turn) had the most suitable combination of textural properties (surface area, average pore diameter and pore volume) for the intended application (support of catalyst for hydrodesulfurization de oil-derived middle distillates). The suitability of those ternary supports was demonstrated in the dibenzothiophene hydrodesulfurization where the corresponding supported MoS₂ catalysts (at 2.8 atom Mo nm⁻²) were much more active (on a per mass of catalyst basis) than when impregnated over either alumina or zirconia-titania oxides.