X-Ray Photoelectron Spectroscopy Study of LaMn1-xFexO3 (x=0-1) Oxides

The redox potential, surface composition and oxygen species of a series of complex oxides LaMn1-xFexO3 (x=0-1) having perovskite structure (ABO(3)) have been investigated by means of XI'S. The variation of binding energies referring to Mn2p and Fe 2p under different treatment offerred an obvious evidence of redox between Mn and Fe, which could be expressed as Mn4+ + Fe(3-delta)+ Mn(4-delta)+ Fe3+ Feat Through computer fit three kinds of adsorbed oxygen species (O-I, O-II, O-III) have been evaluated based on the XPS spectra of O1s. From the variation of contents of different oxygen species, it could be concluded that. the redox occuring in the surface might be related with the adsorbed oxygen species O-I and O-II, furthermore the possibility of transfer of electron between adsorption site and oxygen was also discussed.

XPS STUDY OF CORROSION BEHAVIOUR OF TITANIUM IN H2C2O4 SOLUTION

The corrosion behaviour of titanium substance and the XPS characterization of Ti surface in the H2C2O4 solution have been first studied by X-ray photoelectron spectroscopy, The experimental results show that there am mile Ti-2 and Ti2+ on sample surface in 10% H2C2O4 solution for two boars corrosion at 80 degrees C, but if corrosion is extended to 4 hones, the surface composition is mainly TiO2 with a small amount of Ti2+. This result corresponds to the structure of TiH1.642 composion in sample surface found by XRD analysis. Since bath TiO2 and the surface coating RuO2 are of Gald-Redstone structure, therefore electrode materials of Ti-Ru are stable in chemical industry.

基于IGES的卷曲类工件结构光测量路径规划研究

本文通过对卷曲类工件IGES文件的分析,本文提出了一种新的基于IGES文件的测量路径规划策略。根据张量积曲面的性质,提出了一种曲面组合算法,运用了张量积曲面的性质,将曲面操作转化为多次曲线操作,将IGES文件中存储的多片曲面片组合为一整片曲面,从而为自由曲面测量路径的提取提供了数学模型。运用二次逼近原理,提出了一种B样条曲线上的等距采样算法。通过在实际系统进行实验,上述策略及算法得到了验证,并在自主开发的智能测量建模加工一体化装备中得到了应用。

An in-situ modified sol-gel process for monolith catalyst preparation used in the partial oxidation of methane

An in-situ modified sol-gel method for the preparation of a Ni-based monolith-supported catalyst is reported. With the presence of a proper amount of plasticizer and binder, and at an optimized pH value, the stable boehmite sol was modified with metal ions (Ni, Li, La) successfully without distinct growth of the particle size. Monolith-supported Ni-based/gamma-Al2O3 catalysts were obtained using the modified sol as the coating medium with several cycles of dip-coating and calcination. Combined BET, SEM-EDS, XRD and H-2-TPR investigations demonstrated that the derived monolith catalysts had a high specific surface area, a relatively homogeneous surface composition, and a high extent of interaction between the active component and the support. These catalysts showed relatively stable catalytic activities for partial oxidation of methane (POM) to syngas under atmospheric pressure. The monolith catalysts prepared by this sol-gel method also demonstrated an improved resistance to sintering and loss of the active component during the reaction process.

XPS and XRD studies of fresh and sulfided Mo2N

Mo surface species of molybdenum nitride and their changes under sulfiding conditions were investigated by XRD and XPS. Mo2N was synthesized by temperature-programmed reaction of MoO3, with NH3. The decomposition of the Mo3d spectra gave a Mo3d doubler which corresponded to Modelta+ (2 less than or equal to delta < 4), Mo4+ and Mo5+ Or Mo6+ species. The BE of the Mo species of passivated Mo2N shifted to higher energy level compared with the freshly prepared Mo2N due to the oxidation of Mo nitride during passivation. When Mo2N was contacted for 4 h with a 15% H2S-H-2 mixture at 400 degrees C, the XRD spectra did not reveal any new phase, which indicates a high stability of Mo2N against sulfidation, but XPS data showed the presence of sulfur, including S-0 and S2- species, and a decrease of the N/Mo atomic ratio revealed some changes in surface composition. More than one monolayer of Mo2N was transformed to sulfide. It is probable that the oxygen incorporated during passivation reacted with sulfur and formed a thin layer of molybdenum sulfide on the Mo2N surface. (C) 1998 Elsevier Science B.V. All rights reserved.

Preparation and characterization of multi-walled carbon nanotubes supported PtRu catalysts for proton exchange membrane fuel cells

A series of PtRu nanocomposites supported on H2O2-oxidized multi-walled carbon nanotubes (MWCNTs) were synthesized via two chemical reduction methods - one used aqueous formaldehyde (HCHO method) and the other used ethylene glycol (EG method) as the reducing agents. The effects of the solvents (water and ethylene glycol) and the surface composition of the MWCNTs on the deposition and the dispersion of the metal particles were investigated using N-2 adsorption. TEM. ICP-AES. FTIR and TPD. The wetting heats of the MWCNTs in corresponding solvents were also measured. The characterizations suggest that combination of the surface chemistry of the MWCNTs with the solvents decides the deposition and the dispersion of the metal nanoparticles. These nanocomposites were evaluated as proton exchange membrane fuel cell anode catalyts for oxidation of 50 ppm CO contaminated hydrogen and compared with a commercial PtRu/C catalyst. The data reveal superior performances for the nanocomposites prepared by the EG method to those by the HCHO method and even to that for tile Commercial analogue. Structure performance relationship of the nanocomposites was also studied. (C) 2005 Elsevier Ltd. All rights reserved.

Bimetallic effects in the liquid phase hydrogenation of 2-butanone

A series of bimetallic Ru-containing monometallic and bimetallic catalysts were prepared and tested for their activity for the hydrogenation of 2-butanone to 2-butanol at 30 °C and 3 bar H2. RuPt bimetallic catalysts were the most active for the reaction, with a ratio of 5 wt% Ru:1 wt% Pt on activated carbon (AC) found to be optimum. The activity of this bimetallic catalyst was more than double that of the sum of the activities of the monometallic Ru and Pt catalysts, providing evidence of a “bimetallic” effect. Structural analysis of the bimetallic catalysts revealed that they consisted of clusters of particles of the order of 1–2 nm. Extended X-ray absorption fine structure analysis showed that there were two types of particle on the surface of the bimetallic RuPt catalyst, specifically monometallic Ru and bimetallic RuPt particles. For the bimetallic particles, it was possible to fit the data with a model in which a Ru core of 1.1 nm is enclosed by two Pt-rich layers, the outer layer containing only 13 at% Ru. Pretreatment of the monometallic and bimetallic catalysts in hydrogen had a significant effect on the activity. Both the bimetallic and monometallic Ru-based catalysts showed a trend of decreasing activity with increasing temperature of prereduction in hydrogen. This loss of activity was almost fully reversible by exposure of the catalysts to air after reduction. The changing activity with exposure to different gas phase environments could not be attributed to changes in particle size or surface composition. It is proposed that the introduction of hydrogen results in a gradual smoothing of the surface and loss of defect sites; this process being reversible on introduction of air. These defect sites are particularly important for the dissociative adsorption of hydrogen, potentially the rate-determining step in this reaction.

The Y-procedure: How to extract the chemical transformation rate from reaction-diffusion data with no assumption on the kinetic model

The paper presents a new method to extract the chemical transformation rate from reaction–diffusion data with no assumption on the kinetic model (“kinetic model-free procedure”). It is a new non-steady-state kinetic characterization procedure for heterogeneous catalysts. The mathematical foundation of the Y-procedure is a Laplace-domain analysis of the two inert zones in a TZTR followed by transposition to the Fourier domain. When combined with time discretization and filtering the Y-procedure leads to an efficient practical method for reconstructing the concentration and reaction rate in the active zone. Using the Y-procedure the concentration and reaction rate of a non-steady state catalytic process can be determined without any pre-assumption regarding the type of kinetic dependence. The Y-procedure is the basis for advanced software for non-steady state kinetic data interpretation. The Y-procedure can be used to relate changes in the catalytic reaction rate and kinetic parameters to changes in the surface composition (storage) of a catalyst.

Effect of post-weld heat-treatment on the oxide film and corrosion behaviour of laser-welded shape memory NiTi wires

Post-weld heat-treatment (PWHT) was applied to NiTi weldments to improve the corrosion behaviour by modifying the microstructure and surface composition. The surface oxide film on the weldments is principally TiO2, together with some Ti, TiO, and Ti2O3. The surface Ti/Ni ratio of the weldments after PWHT is increased. The oxide film formed in Hanks’ solution is thicker on the weldments after PWHT. The pitting resistance of the weldments is increased by PWHT. The galvanic effect in the weldments is very small. The weldment with PWHT at 350 °C shows the best corrosion resistance among other heat-treated weldments in this study.

Interpretation of electrochemical measurements made during micro-scale abrasion-corrosion

This paper brings together and analyzes recent work based on the interpretation of the electrochemical measurements made on a modified micro-abrasion-corrosion tester used in several research programmes. These programmes investigated the role of abradant size, test solution pH in abrasion-corrosion of biomaterials, the abrasion-corrosion performance of sintered and thermally sprayed tungsten carbide surfaces under downhole drilling environments and the abrasion-corrosion of UNS S32205 duplex stainless steel. Various abrasion tests were conducted under two-body grooving, three-body rolling and mixed grooving-rolling abrasion conditions, with and without abrasives, on cast F75 cobalt-chromium-molybdenum (CoCrMo) alloy in simulated body fluids, 2205 in chloride containing solutions as well as sprayed and sintered tungsten carbide surfaces in simulated downhole fluids. Pre- and post-test inspections based on optical and scanning electron microscopy analysis are used to help interpret the electrochemical response and current noise measurements made in situ during micro-abrasion-corrosion tests. The complex wear and corrosion mechanisms and their dependence on the microstructure and surface composition as a function of the pH, abrasive concentration, size and type are detailed and linked to the electrochemical signals. The electrochemical versus mechanical processes are plotted for different test parameters and this new approach is used to interpret tribo-corrosion test data to give greater insights into different tribo-corrosion systems. Thus new approaches to interpreting in-situ electrochemical responses to surfaces under different abrasive wear rates, different abrasives and liquid environments (pH and NaCl levels) are made. This representation is directly related to the mechano-electrochemical processes on the surface and avoids quantification of numerous synergistic, antagonistic and additive terms associated with repeat experiments. (C) 2010 Elsevier Ltd. All rights reserved.

Histomorphologic evaluation of Ti-13Nb-13Zr alloys processed via powder metallurgy. A study in rabbits

This study presents the in-vivo evaluation of Ti-13Nb-13Zr alloy implants obtained by the hydride route via powder metallurgy. The cylindrical implants were processed at different sintering and holding times. The implants` were characterized for density, microstructure (SEM), crystalline phases (XRD), and bulk (EDS) and surface composition (XPS). The implants were then sterilized and surgically placed in the central region of the rabbit`s tibiae. Two double fluorescent markers were applied at 2 and 3 weeks, and 6 and 7 weeks after implantation. After an 8-week healing period, the implants were retrieved, non-decalcified section processed, and evaluated by electron, UV light (fluorescent labeling), and light microscopy (toluidine blue). BSE-SEM showed close contact between bone and implants. Fluorescent labeling assessment showed high bone activity levels at regions close to the implant surface. Toluidine blue staining revealed regions comprising osteoblasts at regions of newly forming/formed bone close to the implant surface. The results obtained in this study support biocompatible and osseoconductive properties of Ti-13Nb-13Zr processed through the hydride powder route. (c) 2007 Published by Elsevier B.V.

XPS characterization of sensitized n-TiO2 thin films for dye-sensitized solar cell applications

TiO2 thin films, employed in dye-sensitized solar cells, were prepared by the sol-gel method or directly by Degussa P25 oxide and their surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The effect of adsorption of the cis-[Ru(dcbH(2))(2)(NCS)(2)] dye, N3, on the surface of films was investigated. From XPS spectra taken before and after argon-ion sputtering procedure, the surface composition of inner and outer layers of sensitized films was obtained and a preferential etching of Ru peak in relation to the Ti and N ones was identified. The photoelectrochemical parameters were also evaluated and rationalized in terms of the morphological characteristics of the films. (c) 2007 Elsevier B.V. All rights reserved.

Treatment of PVC using an alternative low energy ion bombardment procedure

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

X-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and x-ray diffraction characterization of CuO-TiO2-CeO2 catalyst system

X-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and x-ray absorption spectroscopy (XAS) techniques have been applied to characterize the surface composition and structure of a series of CuO-TiO2-CeO2 catalysts. For a small loading of cerium, ceria was mainly dispersed on the titania surface and a minor amount of CeO2 crystallite appeared. At higher loading of cerium, the CeO2 phase increased and the atomic Ce/Ti ratio values were smaller than the nominal composition, as a consequence of cerium agglomeration. This result suggests that only a fraction of cerium can be spread on the titania surface. For titanium-based mixed oxide, we observed that cerium is found as Ce3+ uniquely on the surface. The atomic Cu/(Ce+Ti) ratio values showed no influence from cerium concentration on the dispersion of copper, although the copper on the surface was shown to be dependent on the cerium species. For samples with a high amount of cerium, XPS analysis indicated the raise of second titanium species due cerium with spin-orbit components at higher binding energies than those presented by Ti4+ in a tetragonal structure. The structural results obtained by XAS are consistent with those obtained by XRD and XPS. (C) 2001 American Vacuum Society.

Electrodeposited thin mercury films on Pt-Ir alloy electrodes

Mercury thin films prepared by electrochemical deposition on Pt-Ir alloy and after partial removing of mercury at different temperatures were studied by means of an interferometric surface mapping microscope and by X-ray photoelectronic spectroscopy. Mercury film samples having mercury partially removed by anodic stripping at a potential more positive than the corresponding peak in the voltammogram were also studied using the same techniques. For blank samples the surface topographic studies showed well defined grain boundaries. Mercury film samples when heated up to different temperatures showed as material is removed and that the surface roughness decreases as the temperature increases. For samples heated up to 800 degrees C the surface roughness is approximately the same that for the blank. A model for the interphase of volumetric mercury electrodeposited on a Pt-Ir alloy has been proposed using samples both electrochemically and thermally removed of their Hg coatings. The model includes a layered three-region structure, containing at least two Pt-Hg intermetallics: PtHg4 and PtHg2. A substrate modified region, iridium rich, has also been detected. (C) 1999 Elsevier B.V. S.A. All rights reserved.