I. Sutherland

On the oxide formation on stainless steels AISI 304 and incoloy 800H investigated with XPS

The influence of cold work on the initially formed oxide layer on the stainless steels AISI 304 and Incology 800H has been studied by XPS. Oxidations were performed at pressures of 10-6-10-4 Pa and temperatures of 300–800 K. All samples showed a similar oxidation behaviour. The oxidation rates of iron and chromium are of the same order of magnitude at temperatures below 650 K. Subsequent oxidation results in an iron oxide on top of a chromium oxide layer. At temperatures above 650 K the metal surface becomes enriched in chromium, which is preferentially oxidized at these temperatures and pressures. Even prolonged oxidation does not result in an iron-rich oxide surface. Nickel has never been found in its oxidized form. The binding energy of oxygen, in the various oxide layers, is independent of the extent of oxidation and is 530.6 eV.

Pretreatment of poly(vinyl fluoride) and poly(vinylidene fluoride) with potassium hydroxide

Abstract Treatment of poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVdF) with hot aqueous solutions of potassium hydroxide resulted in large increases in adhesion. With PVF, the addition of small quantities of tetrabutylammonium bromide to an aqueous solution or the replacement of an aqueous with an alcoholic solution resulted in much more rapid treatment under a given set of conditions. Effective treatments of just 30 and 10s were developed for PVF and PVdF, respectively. Substantial changes in surface chemistry were observed using XPS for most of the pretreatment conditions used; the changes were mainly in the form of defluorination plus introduction of oxygen. The changes were most marked for PVdF treated with solutions containing a small amount of TBAB. Elimination reactions are likely to be of particular importance with PVdF, a view supported by the existence of CC and CC bonds. Substantial chemical modification of PVF did not necessarily result in large increases in adhesion. This is attributed to the chemical modification of a weak boundary layer without its removal.

An investigation of carbon fibre surface chemistry and reactivity based on XPS and surface free energy

Abstract The surface effects of anodic oxidation on high and low modulus PAN-based carbon fibres are interpreted in terms of surface composition, chemistry, and free energy. High-energy resolution X-ray photoelectron spectroscopy has been used to investigate changes in surface chemistry. Data for low modulus oxidised fibres indicate marked inreases in surface oxygen compared to untreated fibres. This is shown to be due to increases in surface C-O-, CO and COOH. An increase in carbon-nitrogen bonding is also detectable. These changes in chemistry are reflected in an increase in the polar contribution (γsp) to the surface free energy of the fibre. For high-modulus fibre surfaces, the effects of oxidation are less marked, indicating a more graphitic, less reactive surface. The changes observed for low-modulus materials are consistent with a less ordered structure, with a higher degree of exposed basal plane edge area than the high-modulus fibre surfaces.

Analysis of the laser-induced reduction mechanisms of medieval pigments

This study is concerned with the effect of infrared Q-switched laser radiation on four of the most commonly used medieval pigments. Vermilion, red lead (minium), white lead and yellow lead (massicot) have been irradiated with Nd:YAG laser radiation at 1064 nm. Visual observation, reflectance spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy analyses have been employed to study the colour alteration, identity the chemical composition and observe the surface of the irradiated pigments. It was shown that, contrary to what was generally accepted, the mechanism responsible for the discoloration is reduction. It was suggested that under the intense laser ablation conditions and the plasma formation, oxidation is not favourable and instead the pigments decompose to their constituent elements. This scenario can also explain the temporary blackening on red and white lead as it is a well established tendency for metallic lead to become oxidised as soon as favourable conditions are obtained. Recovery mechanisms are currently being studied to prove the model.

Effects of ozone oxidation on carbon black surfaces

Surface effects of ozone treatment with a fluidized bed-type reactor on carbon black have been studied. It has been observed that the surface oxygen level is proportional to the total volume of ozone supplied per unit area of carbon black surface. The ozone treatment increases the acidity of the carbon black surface. A limiting pH value has been obtained at a surface oxygen concentration of around 6 at %. The surface oxygen introduced on the carbon black is most likely present as carboxylic acid groups as indicated by both high-resolution X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy results. The ozone treatment of a carbon black decreases the tensile strength for a natural rubber (non-polar), but increases the tensile strength for a nitrile butadiene rubber (polar).

Studies of the composition, ion-induced reduction and preferential sputtering of anodic oxide films on Hg0.8Cd0.2Te by XPS

Abstract Angle-resolved studies of anodic oxide films on Hg 0.8 Cd 0.2 Te, and on cadmium and tellurium bulk oxides, by X-ray photoelectron spectroscopy (XPS) have revealed the formation of a discrete altered overlayer, containing reduced tellurium (Te 0 ) species, following inert gas ion bombardment. In the presence of Cd 2+ species, recombination is shown to occur, to yield a Te 2− (telluride) species, in the form of CdTe. Only Te 2− is observed on ion-induced reduction of CdTeO 3 , whereas there is no evidence for significant Te 2− formation on either TeO 2 or anodic oxides on CMT, reflecting the low cadmium content of these latter two oxides. In addition, preferential cation sputtering leads to a homogeneous (within the XPS sampling depth) Te 4+ -depleted layer in Cd-Te mixed oxides. The phenomenon is characterised by an effective sputter yield ratio ( S Te 4+ / S Cd 2+ ) of 1.83 (±0.06). The anodic oxide on CMT, when corrected for preferential Te 4+ sputtering, yields a (Te 4+ ):(Cd 2+ ) ratio of 4.6 (±0.5), in excellent agreement with the bulk Te:Cd ratio in Hg 0.8 Cd 0.2 Te. An anodic oxide film composition of approximately 2 O 5 and > 75 mol% TeO 2 and/or mixed Hg-Te oxides is proposed.

Characterization of coated particulate fillers

Stearic acid coated samples of porous and non-porous grades of magnesium hydroxide and calcium carbonate have been characterized using diffuse reflectance infra red (DRIFT), and X-ray photoelectron spectroscopy (XPS). Using DRIFT, the signal due to the reacted coating reached a plateau at a coating level dependent on the filler surface area. XPS showed that coating thickness increased with the amount of coating, slope changes being observed in plots at lower levels of applied coating than those observed by DRIFT. The differences between the measurements for the two techniques is attributed to their different sampling depths. The FTIR having a greater sampling depth probes the internal surface area of the agglomerates present in the porous material, whereas XPS does not. The surface chemistry of the two types of coated filler is compared.

Effects of a multifunctional additive on bound rubber in carbon black and silica filled natural rubbers

The effects of a multifunctional additive (MFA), i.e. a diamine salt of a carboxylic acid, on the bound rubber in carbon black and silica filled natural rubber compounds in o-xylene, have been studied. For the carbon black filled compound, the bound rubber initially decreases with the MFA concentration and then does not change significantly above an MFA concentration which approximately corresponds to the monolayer surface coverage of the carbon black. This phenomenon has been explained in terms of the release of immobilised rubber within the carbon black agglomerates. Bound rubber measured at high temperatures indicated that the MFA did not improve the chemical interaction between the carbon black and the rubber in an unvulcanised rubber mix. The MFA has no pronounced effects on the bound rubber for silica. This may be caused by the combined effects of improved filler dispersion and silica-rubber interfacial interaction. The ozone oxidation of the carbon black significantly increases its surface oxygen concentration but has little effect on its specific surface area. The oxidation has been found to decrease the bound rubber.

Effects of the chromic acid etching on propylene polymer surfaces

The chromic acid etching of three propylene polymers has been investigated by contact angle measurement, X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR), scanning electron microscopy (SEM), and an adhesion test. It has been shown that etching with such an oxidative acid has a much more significant effect on the receding contact angle than on the advancing contact angle of a test liquid. Significant water and diiodomethane contact angle hystereses were found and were attributed mainly to surface chemical heterogeneity caused by the acid etching. Surface roughness resulting from the etching may also account for the contact angle hystereses in some cases. The acid etching significantly increased the surface oxygen concentration of all three polymers. Chemical derivatisation with trifluoroacetic anhydride (TFAA) and hydrazine have indicated that the acid etching introduced C=O/COOH but there is no evidence of -OH groups on the polymer surfaces. The adhesion level of the p...

A quantitative XPS study of spherically shaped powders coated with an overlayer

Effects of the spherical shape of a small size (< 1 μm) powder and the thickness of a uniform overlayer on the surface elemental compositions measured by X-ray photoelectron spectroscopy (XPS) have been studied. The angular and radial dependence of the path length of photoelectrons generated within the substrate and the overlayer was taken into account in the calculation. The difference in photoelectron inelastic mean free path (IMFP) between the substrate and the overlayer was also considered in calculating the photoelectron intensity. Spherically shaped zinc oxide powder coated with a hydrocarbon overlayer was taken as an example.