ESCA Studies Research Articles

ESCA study of the oxidation of DHP copper

AbstractThe surface composition of deoxidized high phosphorus (DHP) copper sheets was investigated by ESCA with the aim of verifying the role of phosphorus in oxide formation. While no surface segregation of phosphorus was observed on samples cleaned by ion bombardment and annealing in ultrahigh vacuum, the presence of large amounts of phosphorus was found after the formation of the oxide by exposure to 0.1 Torr oxygen at 770 K. The surface enrichment in P with the same binding energy was found after annealing a sheet of DHP copper coated with a layer of Cu2O deposited by sputtering. The binding energy of the P 2p peak as well as the analysis of the components of O 1s can be interpreted with the formation of a metaphosphate. Experiments performed at intermediate temperatures showed that the segregation of phosphorus is appreciable above 600 K and appears to be related to oxygen diffusion into the bulk.

ESCA studies of Fe-Ti alloys

Fe-Ti alloys containing 5 to 47% Ti have been studied by ESCA. The alloys were exposed to 0.1 M NaCl for 24 h under open-circuit potential (OCP) during which passive films were formed. The passive film consisted of FeO and TiO2 in the inner layer while Fe2O3, water, and hydroxyl groups were present in the outermost monolayers, irrespective of composition. The thickness of the passive layer was reduced from 4.4 nm to 1.0 nm with increasing Ti content. The amount of iron oxide in the passive layer also decreased with increasing Ti. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate of the alloys. Alloys with 5–28% Ti showed a relatively high corrosion rate but that with 47 wt.% Ti had a much lower corrosion rates.

ESCA studies of Ni-Cr alloys

ESCA examination on Ni-Cr alloys has shown that a thin passive film was formed after 24 h immersion in 0.1 M NaCl. The film contained only chromium oxide in the form of Cr2O3. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate of the alloys. Both Ni-10 wt. % Cr and Ni-20 wt. % Cr alloys showed a slightly higher corrosion rate than the Ni-40 wt. % Cr alloy.

Preparation of hydrogenated nitrile rubber using palladium acetate catalyst: Its characterization and kinetics

AbstractHydrogenated nitrile rubber was prepared by using palladium acetate as the homogeneous catalyst system. The effect of different reaction parameters on the level of hydrogenation was studied. The extent of hydrogenation increased with increase in reaction time, temperature, pressure, and catalyst concentration. A maximum conversion of 96% could be achieved. The degree of hydrogenation was estimated from IR and NMR spectroscopy. The selectivity of the catalyst in reducing CC in presence of CN was supported by IR and 13C‐NMR spectra. ESCA studies further confirmed this observation. Properties of hydrogenated nitrile rubber were investigated by various techniques such as gel permeation chromatography (GPC), glass transition temperature (Tg), stress‐strain behavior and rheological measurements. GPC studies showed no significant change in molecular weights of the products after the reaction. Tg value decreased with an increase in the level of hydrogenation. The ultimate stress improved significantly with the increase in the extent of hydrogenation. The die swell decreased with hydrogenation at a particular shear rate. The kinetics of the NBR hydrogenation were investigated. With the increase of the hydrogen pressure and catalyst concentration, the rate of the reaction increased. The reaction was apparently first order with respect to olefinic substrate at higher hydrogen pressure. The apparent activation energy, enthalpy, and entropy of the reaction were calculated as 29.9 kJ/mol, 27.42 kJ/mol, and –0.20 kJ mol−1 K−1, respectively.

ESCA studies of phase transfer catalysts in solution. 2. Surface ion pairing and salting-out effects

The surface segregation or tetrabutylammonium bromide and tributyl(bromomethyl)ammonium bromide in formamide is studied by means or angular resolved photoelectron spectroscopy. The results are discussed in terms or surface ion pairs as well as electric double layers. By use or a cation marked with an atom or the same element as the anion, it is shown that ion-pairing occurs at the solution surface. A salting-out effect is observed when ammonium chloride is added, and it is found that the chloride ions also take part in the surface ion-pairing

ESCA studies of Cr-Co alloys

ESCA examination of films formed on Cr-Co alloys after immersion in 0.1M NaCl for 24 h has shown that the thickness of passive films decreased with an increase in chromium content. Surface films consisted of chromium and cobalt oxides as Cr2O3 and CoO. The amount of CoO in the surface film of the alloy was decreased with an increase in chromium but Cr2O3 was found at a greater depth in the passive film at any composition. Cr2O3 was a major component of the surface film when the chromium content in the alloy was 10% or higher. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate. Both Co-10 wt.% Cr and Co-30 wt.% Cr alloys investigated showed a lower corrosion rate than the Co-5 wt.% Cr alloy. Corrosion rate measured could be correlated to the surface film composition and structure as determined by ESCA.

ESCA and electrochemical studies on pyrolysed iron and cobalt tetraphenylporphyrins

Catalysts for the reduction of O 2 have been prepared by pyrolysis of CoTPP and FeClTPP in their crystalline state as well as in different mixtures with carbon black. ESCA measurements on these pyrolysed porphyrins have been correlated to their catalytic properties. When porphyrins are pyrolysed with carbon black, sublimed chelates re-adsorb on the surface of carbon black forming a stable chelate—carbon support bond, which is believed to increase the activity and stability of the catalyst. Porphyrins pyrolysed without carbon black become electrically conducting after pyrolysis as a result of a polymerization reaction with the chelates intact. For porphyrins pyrolysed without carbon black the main active site is believed to be a metal chelate but for the Co-catalyst there is evidence that other surface components, formed as a result of decomposition of the chelate, influence the activity.

Surface modification of UHSPE fibers through allylamine plasma deposition. I. Infrared and ESCA study of allylamine plasma formed polymers

AbstractAllylamine (CH2CHCH2NH2) was polymerized through rf generated plasma at varying powers and times. Chemical groups and elemental compositions in the polymers were studied using ESCA and infrared spectroscopy. It was observed that plasma derived polymers contained a significant number of primary amines, along with some secondary and tertiary amines, imines, and nitrile groups. Plasma derived polymers had a complex structure and contained unsaturated groups. A considerable amount of oxygen, primarily from residual air in the plasma reaction chamber, and possibly from atmosphere when plasma polymers were exposed to air, was responsible for carbonyl, amide, ether, and hydroxyl groups found in the polymer structure. Some silicon was also detected in the plasma deposited films.

Wettability of kraft pulps-effect of surface composition and oxygen plasma treatment

Wettability and ESCA studies have been carried out using unextracted and extracted kraft pulps with different amounts of lignin. The effect of oxygen plasma treatment was investigated. The wettability was studied by placing a drop of water on a sheet made from the pulp and following the decrease in drop volume and apparent contact angle with time. The first reading is taken after about 0.1 s. Extrapolation to zero time gives the initial contact angle. The initial absorption rate was also determined. Good correlation between the initial contact angle and the oxygen to carbon atomic ratio was found for the pulps without extractives. Pulps containing extractives are very hydrophobic, but an oxygen plasma treatment renders these pulps as hydrophilic as the purest pulps. It is concluded that the oxygen plasma treatment oxidizes the lignin and the extractives but reduces the pure cellulose surface. The oxidized extractives appear to act as wetting agents. The initial absorption rate is strongly dependent on the...

Surface characterization of microtextured silicone

A set of microtextured silicone surfaces was manufactured using the technique of photolithography. The textures consist of a uniform array that imparts anisotropy to the surfaces. Processing the material required multiple steps which may have altered the surface characteristics. This project aimed to determine if a surface texture on implant grade silicone would affect the material characteristics. ESCA and contact angle studies revealed no measurable alteration of the surface chemistry or surface energy due to the texturing procedure or the presence of the texture. Both analytical techniques confirmed the material was silicone. The actual dimensions of the surface textures, size, spacing, depth and orientation of the textures were found to be close to the design values, using SEM and quantitative two- and three-dimensional profilometry. Standard 2D profilometry was not sufficient to characterize the surfaces, as a direct result of the uniformity of the arrays. A method of characterizing regular surface periodic structures is presented.

Study of Blood Compatible Polymers I. Modification of Poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) has been modified by the graft copolymerization of methyl methacrylate and acrylamide. These polymers have been characterized by FT IR, ESCA, and SEM. Angle dependent ESCA studies have been carried out to determine the surface homogeniety. The in vitro blood coagulation tests have shown that the modified polymers possess an enhanced antithrombogenicity compared to PVA. Protein adsorption on these polymers from rabbit plasma has been followed by electrophoresis and ELISA. The ratio of albumin to fibrinogen adsorbed on the modified polymers increases with increase of incubation time while that on PVA decreases as the incubation time increases. Cell proliferation studies using L929 cells revealed that in contrast to PVA the modified polymers are good matrices for cell attachment and growth.

ESCA studies of charge transfer interactions in electroactive polymers

X-ray photoelectron spectroscopy (XPS) data suggest that proton modifications of nitrogens in polypyrrole (PPY) give rise to a number of intrinsic redox states analogous to those observed in polyaniline (PAN). The behavior of the corresponding oxidation states in both polymers towards oxidation/reduction, deprotonation/reprotonation or charge transfer (CT) interactions are grossly similar. For the thiophene polymers, such as the poly(2,2′-bithiophene) (PBT) complexes and poly(3-methylthiophene) (P3MT) complexes, XPS results reveals the simultaneous presence of neutral and polarized (or partially charged) species in both carbon and sulfur. The relative amounts of the neutral and polarized species vary in accordance with the oxidation level of the polymer. These results suggest that each dopant anion is associated with a thiophenium ion in the polymer chain. Substantially lower extent of CT is observed in the complexes involving photoconductive substituted polyacetylenes, such as polyphenylacetylene (PPA) and poly[[o-(trimethylsilyl)phenyl] acetylene] or poly(o-Me3SiPA).

Angular-Resolved ESCA Studies of Cadmium Arachidate Monolayers on Si (100): Inelastic Mean-Free Path and Depth Profile Analysis

AbstractAngular-resolved ESCA was used to study single cadmium arachidate monolayers transferred to Si (100) wafers by the Langmuir-Blodgett technique. We find the monolayers to be of high integrity with respect to those defects which enhance the escape probability of substrate photoelectrons through the overlayer. The inelastic mean-free pathlengths of Si (2p) and C (1s) electrons were calculated to be 49±6 Å and 45±6 Å for the kinetic energies of 1388 eV and 1202 eV, respectively. The overall ordering of the hydrocarbon chains is less than for alkane thiols assembled on noble metals. We find that the precision of the Tyler algorithm to deconvolute angular-resolved ESCA data into depth profiles is accurate within 10% for predicting the thickness of the hydrocarbon overlayer but less precise for intermediate layers.

Ground state vs. transition state substituent effects on reactions of aziridinium salts

AbstractThe possibility that the similarity of Hammett ρ values for several very different reactions of 2‐arylaziridinium salts is due to ground state effects was investigated by MO methods and ESCA. Minimum energy structures of p‐nitrophenyl‐, phenyl‐, and p‐methoxyphenyl‐substituted ions, however, have the same C2N bond lengths. This result shows that substituent effects are primarily a transition state phenomenon, even in the three‐membered ring heterocycles. In agreement, the ground state does not have significant amino carbocation character based on similar charge distributions of 2‐phenyl‐N,N‐dimethylaziridinium ion and N,N,N‐trimethylbenzylammonium ion as well as the same nitrogen ls binding energies by ESCA studies on corresponding salts.

ESCA spectroscopy of poly(methyl methacrylate) grafted onto wood fibers

AbstractThe incompatibility of hydrophilic wood fiber and hydrophobic polymers is the main difficulty with wood thermoplastic polymer composites. To overcome this issue, many researchers suggest grafting polymer onto wood fiber for improving the interfacial adhesion during mixing. A systematic ESCA study of chemi‐thermo‐mechanical pulp (CTMP) grafted fiber has been performed to provide chemical information about surface composition modification. The material analyzed included initial CTMP fiber, the pure polymer i.e., poly(methyl methacrylate) (PMMA) as reference material, and grafted fiber at different polymer loadings. Interest is focused on the carbon and oxygen spectra. Samples at high polymer loading or high grafting level have an O/C, C1, C2, C4, O1, and O2 intensities much similar to those of the PMMA but a little different since some wood fiber sites have still not fixed the polymer. ESCA spectra provide information on about 1–5 nm depth. The ESCA technique allows the monitoring of grafting polymer onto wood fiber as a surface phenomenon.

ESCA studies of Si-Fe alloys

ESCA examination of films formed on Si-Fe alloys after immersion in 0.1 M NaCl for 24 h has hown that the thickness of passive films decreased with an increase in silicon content. A thick passive film containing oxidized silicon and oxidized iron was formed on Fe-20 wt% Si and the oxidized iron was about three times higher than the oxidized silicon in the passive film. However, an obvious reduction in the oxidized iron in the film on Fe-30 wt % Si was observed. Oxidized iron was detected up to a depth of 1.0 nm and at a depth greater than 1.0 nm from the surface, the film was exclusively in oxidized silicon. The film was exclusively silicon oxide when the silicon content was increased to 50 wt %. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate. Fe-50 wt % Si was found to have a corrosion rate smaller than those lower silicon alloys. This relates to the surface film composition and structure as determined by ESCA.

ESCA study of modifying effect by potassium carbonate on Pd/γ−Al2O3 catalysts

ESCA studies of the state of Pd/γ−Al2O3 catalysts modified by potassium carbonate show that such catalysts differ from unmodified samples in much greater changes of a positive charge of palladium ions under redox conversions. This is ascribed to the lower interaction of Pd with the support in modified samples.

ESCA study on tribochemical characteristics of filled PTFE

ESCA analyses were performed on the frictional tracks on metal blocks covered with the transfer films of PTFE-based composites containing zinc, copper, and lead powders. Results show that the tribochemical reactions between PTFE and an aluminum or an iron counterface as well as between PTFE and zinc filler were found to occur under experimental conditions. Compounds of iron or aluminum fluoride were detected at the interface between the transfer film and the steel or aluminum substrate when PTFE composite pins rub against a steel or an aluminum counterface. This means that a chemical reaction between them has occurred. But the formation of a chemical bond between the transfer film of the composite and the substrate is not the real reason why metallic fillers reduce the wear of the PTFE, because the chemical reaction can also be detected when a pure PTFE pin rubs against a steel or an aluminum disk under these test conditions. The consumption of fluorine in PTFE at the interface between the films and the substrate is much more serious than that on the surface of the transfer films. It was found that the chemical reaction of the PTFE to the steel or aluminum substrate is by means of the fluorinc atom and not the carbon atom in the PTFE.

An ESCA study of the interaction of oxygen with the surface of ruthenium

The interaction of oxygen with the surface of a Ru wafer in the range of room temperature to 600°C was investigated by ESCA. Ru3d,3p,MVV, valence band and 01s spectra were recorded. Three different states of oxygen were observed on the Ru wafer surface. Definitive identification of two of the three states was achieved according to the multiplet structure in the photoemission spectra of oxygen and the binding energy of various states of oxygen. The oxygen species identified are O 2- and dissolved atomic oxygen. The third oxygen state which gives rise to the peak at a BE of 532.3 eV in the O1s spectrum and 11.7 eV in the photoemission spectrum is tentatively assigned to a chemisorbed hydroperoxy radical. A discussion of the Ru oxidation process is also given.

ESCA study of the effect of hydrocarbon contamination on poly(tetrafluoroethylene) exposed to atomic oxygen plasma

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTESCA study of the effect of hydrocarbon contamination on poly(tetrafluoroethylene) exposed to atomic oxygen plasmaMorton A. Golub, Theodore. Wydeven, and Robert D. CormiaCite this: Langmuir 1991, 7, 5, 1026–1028Publication Date (Print):May 22, 1991Publication History Published online1 May 2002Published inissue 22 May 1991https://doi.org/10.1021/la00053a034RIGHTS & PERMISSIONSArticle Views103Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (332 KB) Get e-Alerts Get e-Alerts