Influence Of Surface Oxidation Research Articles

Effect of the structure of smooth copper surfaces on the accuracy of determination of the optical constants of copper

The accuracy of determination of the optical constants of smooth copper surfaces produced by different technologies is analyzed, with particular attention paid to the consideration of the influence of scattered radiation (which is ignored by many authors) on the retrieval of the optical constants of copper surfaces from reflected radiation. The neglect of scattered radiation can lead to errors as high as 50% in determining the optical constants for bulk copper. For thin films, the errors are much lower. The influence of surface oxidation during measurements in air and surface features of studied objects on the parameters to be determined is analyzed as well. It is shown that errors in determination of the constants are maximal in the plasma resonance region of copper.

Influence of the Surface Properties of SiC Particles on Their Codeposition with Nickel

The electrolytic codeposition of SiC with nickel from a nickel Watts bath was investigated by codeposition experiments of SiC particles on a rotating disk electrode and by thin-film rupture experiments. From the rotating disk experiments it was found that the codeposition of SiC depends strongly on the presence of a surface oxide. A few monolayers of oxide impede the codeposition. Removing the surface oxide by HF or NaOH greatly increases the codeposition of SiC particles with nickel. The influence of surface oxidation on the codeposition of SiC particles with Ni was correlated with thin-film rupture results. Thin liquid films of nickel Watts solutions on SiC were investigated by microinterferometry. The effect of surface pretreatment on the stability and rupture of the thin films was studied. It was found that the stability of thin films on SiC is strongly influenced by the solvation force. A strong correlation was established between the stability of the thin films and the codeposition results. Our results demonstrate that thin-film rupture experiments can be used to analyze and even predict the codeposition behavior of a material. © 2003 The Electrochemical Society. All rights reserved.

Influence of surface oxides on the adhesion of a wild strain of Pseudomonas sp. to aluminium brass

Abstract The adhesion of a wild strain of Pseudomonas sp. to aged aluminium brass was evaluated modifying the pH and ionic strength of the electrolyte solution. Ionic strengths of 0.1 and 0.6 M NaCl, and pH values of 2, 4, 6, and 8 were tested. The surface oxides composition was analysed in situ by reflectance spectroscopy and the water contact angle of oxides under n-hexane was determined. At low ionic strength the adhesion of bacteria increased as pH values raised. The occurrence of adhesion was correlated to the formation of an oxide layer on the samples. The presence of copper and zinc oxides was detected in the layer at pH values⩾4 at both ionic strengths. At low ionic strength the formation of (hydro)oxides was also observed. At high ionic strength (0.6 M ) , the adhesion was strongly diminished throughout the range of pH values tested. No evidences of hydration of the oxide layer were found at this condition. The acid–base interaction capacity of the metal surface was observed to increase with the raising of pH accounting for both, the bacterial adhesion increase and the oxides hydration.

Influence of surface oxides on the impedance behavior of carbon-based electrochemical capacitors

Electrochemical capacitors made of activated carbon fabrics containing different compositions of surface oxides are analyzed using ac impedance spectroscopy. The oxides are introduced and controlled via HNO 3 treatment followed by thermal treatment at different temperatures within 150–900 °C. The impedance spectra showed that the overall resistance mainly came from the fiber contact resistance, which was an increasing function of oxide number, while the overall capacitance was contributed by the interface inside micropores. Oxidation enhanced the specific capacitance of the electrodes, but it was found that a thermal treatment temperature of 450 °C gave the highest capacitance. Constant phase element (CPE) analysis of the capacitive behavior showed insignificant deviation from ideality, indicating the low resistance in the carbon micropores as well as the domination of the double layer mechanism in energy storage. Thus, the capacitance increase from oxidation resulted mainly from the double layer mechanism as well. The deviation from ideality was more obvious for lower temperature treated electrodes, indicating that the surface oxides that desorb as CO 2 upon heat treatment may enhance formation of aggregates to retard the charge process, while the surface oxides that desorb as CO are responsible for the promotion of the double layer capacitance.

Adsorption of cadmium by activated carbon cloth: influence of surface oxidation and solution pH

The surface of activated carbon cloth (ACC), based on polyacrylonitrile fibre as a precursor, was oxidised using nitric acid, ozone and electrochemical oxidation to enhance cadmium ion exchange capacity. Modified adsorbents were physically and chemically characterised by pH titration, direct titration, X-ray photoelectron spectroscopy, elemental analysis, surface area and porosimetry, and scanning electron microscopy. BET surface area decreased after oxidation, however, the total ion exchange capacity increased by a factor of approximately 3.5 compared to the commercial as-received ACC. A very significant increase in cadmium uptake, by a factor of 13, was observed for the electrochemically oxidised ACC. Equilibrium sorption isotherms were determined at pH 4, 5 and 6 and these showed that cadmium uptake increased with increasing pH. There was clear evidence of physical damage to ozone-oxidised fibre, however, acid and electrochemically oxidised samples were completely stable.

Influence of Combined Treatment before Activation on the Development of Pore Structure of Anthracite

The influence of surface oxidation of anthracite with humid air, followed by impregnation with alkali metal compounds and calcination in inert atmosphere before activation, on the efficiency of steam-gas activation and on the development of the pore structure of the resulting carbon adsorbents was studied.

Low-temperature direct bonding of silicon and silicon dioxide by the surface activation method

We have investigated low-temperature bonding of Si and SiO 2 by the surface activation method in vacuum. In the method, Ar beam etching is used to create a clean surface which has strong bonding ability. The specimens are bonded in the vacuum without exposing them to the atmosphere. The strength of Si/Si bonding prepared at room temperature by the method is equivalent to the bulk strength. SiO 2/SiO 2 bonding by the method is twice as strong as conventional bonding before annealing. In addition, the bonding prepared by Ar beam is stronger than that prepared by reactive molecule beam etching such as H 2O and NH 3. The influence of surface oxidation was examined by exposing an etched Si surface to residual gas in the vacuum chamber. Adsorption of reactive molecules such as H 2O on the etched surface causes reduction of bonding strength, whereas Ar gas does not affect the bonding. These results mean that a clean surface etched by Ar beam has strong bonding ability even at room temperature.

Influence of Surface Oxides on Ethanol Regeneration of Spent Carbonaceous Adsorbents

Activated carbon (AC) and activated carbon fiber (ACF) that adsorbed aromatic compounds were regenerated by ethanol. The influence of their acidic surface oxides on ethanol regeneration was studied based on the frontier orbital theory. It is found that the regeneration efficiency can be correlated by the energy difference between HOMO of aromatic compounds and LUMO of adsorbents |EH−EL|. The regeneration efficiency is improved by oxidizing AC or ACF because the adsorptive interaction becomes weak as the energy difference |EH−EL| increases. The influence of the oxides on repeating ethanol regeneration of the carbons that adsorbedp-cresol was then experimentally elucidated. Although the regeneration efficiency of oxidized AC or ACF is kept higher than that of original AC or ACF even after the 16th regeneration, the oxidation has no practical use because the adsorption capacity is decreased by the oxidation.

Influence of surface oxidation on the photoelectron diffraction intensities from InP single crystals

Abstract The Monte Carlo method was used to calculate the influence of amorphous overlayers on the angle-dependent intensity distribution due to photoelectron diffraction (XPD) in monocrystalline substrates. The influences of the overlayer thickness, the elastic and inelastic mean free paths in the amorphous overlayer, the shape of the initial intensity distribution, as well as the overlayer chemical composition, on XPD is discussed and some trends are formulated. The simulated P 2p intensities of oxidized InP agree with the experimental data. The effect of elastic scattering on the intensity minimum around the detection angle 18° is stronger than that of inelastic scattering. A new method for the thickness determination of thin overlayers on single ecrystals is discussed.

The influence of surface oxidation on the reactions of methanol on Fe(110)

The thermal decomposition of methanol occurs via adsorbed methoxy on clean and oxidized Fe(110). Methoxy is detected following adsorption of CH 3OH at 100 K using X-ray photoelectron spectroscopy. On clean Fe(110), methoxy dehydrogenates at ∼400 K, yielding gaseous H 2 and CO. The hydroxyl hydrogens leave the surface as H 2 at slightly lower temperature, 375 K, based on isotopic labeling experiments. Carbon-oxygen bond scission competes with CO evolution at 400 K, accounting for ca 25% of the CO yield on clean Fe(110). Surface oxygen inhibits OH and CH bond dissociation in methanol leading to a decrease in the total amount of reaction and an increase in the amount of methanol desorbed from the surface with increasing oxygen coverage. At coverages greater than one monolayer (ML), there is no detectable reaction of methanol. In addition, the temperature required for CH bond activation in methoxy increases to 475 K for an initial oxygen coverage of 0.75 ML. Surprisingly, the ratio of CO bond dissociation to retention increases as a function of initial oxygen coverage. The increase in C—O bond dissociation is tentatively attributed to defects in mixed phases of FeO(111) and Fe(110)-c(3 × 1)-O, based on comparison with STM data taken from the literature. The potential implications of the different reactivity of methanol as a function of oxygen coverage with regard to the function of lubricant additives is discussed.

Influence of surface oxidation on thermal shock resistance and flexural strength of SiC/Al2O3 composites

It is known that SiC whisker/Al2O3 matrix composites can oxidize in air at high temperature and then form oxidation layers on their surfaces. Oxidation treatment has been experimentally performed in air at 1450 °C for a pre-determined time. The results show that the surface layer is in a state of compressive residual stress. The oxidized specimens have better resistance to thermal shock damage than the non-oxidized specimens. However, the surface oxidation can degrade the room-temperature flexural strength.

Studies of Ru(001) electrodes in aqueous electrolytes containing silver ions and methane: LEED, HREELS, Auger spectroscopy and electrochemistry

Potent catalysis by Ru electrodes has been reported by various workers. Reported here are studies of chemisorption, surface vibrational spectroscope and electrochemical reactivity at Ru(001) single-crystal electrode surfaces. Electrochemical oxidation of methane on these Ru electrode surfaces in aqueous electrolytes was investigated. The influence of surface oxide and electrodeposited silver on methane oxidation were explored. Immersion of Ru(001) into pure water at open circuit forms a layer of adsorbed hydrous oxides with an ordered (2 × 2) structure as measured by Auger spectroscopy and low energy electron diffraction (LEED). Anodization of Ru(001) in 1 M HClO 4 produces a disordered Ru O/OH film consisting of several atomic layers. The high resolution energy electron loss spectrum of this O/OH layer exhibits RuO and OH stretching bands, and the layer is not removed by subsequent electrolysis at negative potentials. Various submonolayer and multiple-layer amounts of silver were electrodeposited on Ru(001). A continuous film is formed, based upon attenuation of the substrate Auger signal. The silver layer lacks long-range order, as judged by LEED. Under the present conditions, namely Ru(001) single-crystal surfaces with or without the O/OH and/or silver layers in aqueous electrolytes, the faradaic current due to oxidation of methane is generally less than 1 μA cm −2. Experiments were performed with Ru(001) surfaces brought to an atomically clean ordered state by Ar + ion bombardment and annealing in UHV. Immersion of Ru(001) into water at open circuit formed a submonolayer of oxide/hydroxide with an ordered (2 × 2) structure and HREELS vibrational bands attributable to RuO and OH libration and traces of adsorbed CO. Cyclic voltammetry of Ru(001) in aqueous KF and HClO 4 electrolytes illustrated the substantial irreversibility of oxide formation—reduction and the near reversibility of hydrogen adsorption—desorption. Electrochemical oxidation of CH 4 in 10 mM KF electrolyte at pH 3 produced an increase in current density equal to 1 μA cm −2 at potentials between − 0.1 and 0.2 V vs. Ag/AgCl. Electrodeposition of Ag onto the bare Ru(001) surface did not alter the current density for CH 4 oxidation significantly. Electrochemical oxidation of the Ru(001) surface to form a (1 × 1) oxide/hydroxide layer decreased the activity of the surface for anodic oxidation of CH 4 in aqueous KF electrolyte. Electrodeposition of a fractional monolayer or multilayer of Ag onto the electrochemically pre-oxidized surface did not detectably influence the rate of CH 4 electrochemical oxidation. The clearly demonstrated catalytic activity of metal-doped Ru oxide electrodes [1–4] is all the more intriguing in the light of the present results which suggest that the observed catalytic behavior is not due primarily to the metallic Ru surface, layers of adsorbed oxide on Ru or electrodeposited metallic Ag.

The reactive chemisorption of formic acid at A1(111) surfaces and the influence of surface oxidation and coadsorption with water: a combined XPS and HREELS investigation

In a combined photoelectron-vibrational spectroscopic study of the chemistry of formic acid interaction with A1(111) surfaces the influence of temperature, surface oxidation and coadsorption with water have been investigated. At the clean surface adsorption at low temperatures leads to deprotonation and on warming to room temperature the major species is formate. On the other hand direct interaction with A1(111) at room temperature leads to more extensive bond cleavage including the formation of chemisorbed oxygen, and carbidic carbon. At the preoxidized A1(111) surface deprotonation is facile at 80 K but there is no evidence for further reaction on warning to room temperature. When formic acid is coadsorbed with water at 295 K, HREEL and XP spectra confirm the formation of surface formate together with hydroxyl and chemisorbed oxygen species.

The influence of surface conditions and subcooling on film-transition boiling

The influence of surface oxidation, liquid subcooling and surface roughness on pool boiling from a 1.27-cm copper sphere is reported in the present study. The sphere was specially designed to minimize support interference with vapor formation and removal; the surface was carefully prepared so that surface roughness and oxidation could be controlled. Experiments were conducted for four different surface roughness levels and subcooling up to 22°C for Freon-113 and up to 50°C for water. Experiments were also conducted with oxidized spheres in Freon-113. In general, the data and observations show that increased subcooling, roughness, and oxidation increase the heat flux during the stage of film boiling near the minimum heat flux where liquid-solid contact is possible. Such increases carry over into transition boiling as well. Vapor bubble detachment frequencies and diameters are reported. A curious “parent-son” detachment mode was observed. Such behavior is explained by a recirculating liquid flow pattern behind the parent bubble that entrains the son bubble. Oscillation amplitudes and frequencies of the vapor envelope during transition boiling are also reported. The heat flux data for subcooled water exhibit the dual maxima reported by other investigators. An explanation is given that relies on the idea of Witte and Lienhard that a quenching system can choose either a “film-transition” or a “nucleate-transition” curve.

Carburized steel-update on a mature composite

This review of properties and applications of carburized steel provides an historical perspective from which to examine current efforts to improve this important ferrous composite. The carbon-rich case, useful for its wear resistance, also interacts with the low carbon core during quenching to generate favorable residual stresses which enhance the load carrying ability of the composite. The paper will review the control of core and case microstructure, the importance of case hardenability, and the influence of surface oxidation. Fatigue behavior, with and without superimposed overloads, will be summarized, and a relationship between overload fatigue and impact fracture will be reviewed. The review presents good evidence that the performance of carburized steel can be optimized by alloying, and that alloy selection can have a significant effect on engineering properties. Metallurgical data can aid the processing of carburizing steel; available data, and their effect on machinability and distortion control, are reviewed.

Thermal degradation of Timahdit oil shales: behaviour in inert and oxidizing environments

Most previous work has examined the thermal degradation of oil shales only in inert atmospheres. Therefore, the important implications of oxidation by O 2, and any connections with combustion have not been considered. This study investigated the thermal degradation, in both inert and oxidizing environments (five N 2-O 2 atmospheres), of two oil shales from the Timahdit site in Morocco. The influence of surface oxidation and its impact on the degradation mechanism were examined. Results indicate that atmospheres containing increasing amounts of O 2 significantly enhance the degradation process. It was assumed that in the presence of O 2, two processes develop simultaneously: a simple thermal degradation process, and a thermochemical process combining temperature and O 2 effects. This theory appears to agree well with experimental data.

The influence of surface oxidation on prebreakdown electron emission processes

Electron spectroscopy and optical imaging techniques have been used to study changes in the current-voltage (I-V) characteristics of individual emission sites that result from the growth of 50- to 500-nm-thick layers of surface oxide. It has been established that while there is only a small effect on the I-V characteristic both the spectral shift and half-width exhibit a greatly enhanced field dependence. The fundamental implications of the results are very significant, since they can be discussed in terms of the most recently proposed nonmetallic models of the emission mechanism.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The influence of surface oxidation and sliding speed on the unlubricated wear of 316 stainless steel at low load

The effect of sliding speed on the unlubricated wear of 316 stainless steel at a low load was investigated at room temperature. A threefold to twentyfold reduction in wear rate occurred at a sliding distance which increased with increasing speed. The time to the transition, however, was approximately independent of sliding speed. The transition was associated with the appearance of a reddish brown phase in the wear debris, thought to be a hydrated form of haematite. It is proposed that in the pre-transition stage the surface and subsurface properties of prows, the main contact regions, become modified by oxidation effects. This leads to an elastic component being introduced into the surface interactions with a reduction in the plastic deformation of prows. Prow breakdown then becomes the rate-limiting step in wear debris formation.

Water and cyclohexane vapour adsorption on oxidized porous carbon

Changes in cyclohexane and water vapour adsorptions and enthalpies of immersion for a series of progressively oxidized porous carbons have been measured. The adsorption and thermal results are discussed in terms of the pore-filling mechanism of Dubinin and the influence of surface oxides on the water adsorption is examined. It is concluded that the important enthalpic contribution for cyclohexane comes from pore-filling while for water, the hydrogen bonding-like interaction around surface oxide sites plays the major role.

The influence of surface oxidation on the electron tunnelling mechanism of microparticle charge reversal during a bouncing impact on a charged conductor

Carbonyl iron microspheres 0.1-2 mu m diameter, with velocities of 10-100 m s-1 and positive charges of (0.5-5)*10-15 C have been used for a comparative study of the charge reversal that occurs during a bouncing impact with negatively charged copper and stainless steel high-voltage electrodes that are either atomically clean or have approximately 30 AA and approximately >or approximately=150 AA surface oxide films. Argon ion etching and electron bombardment heating were available for in-situ surface cleaning, while an ellipsometric facility was used for characterizing electrode surfaces. Experimental results show that the efficiency of charge reversal is strongly dependent on both the thickness and electrical properties of surface oxide films.