Surface Analysis Results

DISCUSSION OF THE SURFACE ANALYSIS RESULTS 2.8.1. The Catalyst Surface 

Only few descriptions of the surface constitution of technical ammonia synthesis catalysts can be found in the literature.An extensive investigation of such a catalyst, similar to one of the samples used in this study, was carried out by Ertl and Thiele who employed a similar activation process to the dry method used in the present investigation. Although there is good general agreement between the two studies, some differences will be discussed. 

the authors stated that the reduced catalyst surface contained only zero-valent iron. This is based on the analysis of the raw data from the Fe 2p 3/2 spectra. It has been found, however, that it is impossible to identify small levels of oxidized iron in the presence of a large fraction of metallic iron. This is due to the wide distribution of intensity for iron compounds caused by their satellite structure. It is therefore believed that the catalyst described in Ref. 19 contained a similar fraction of iron oxide to the present samples activated with the dry method (see Fig. 2.40). This is in line with the expectation that the presence of the spinel-forming aluminum oxide prevents complete reduction. It should be pointed out that Mossbauer spectroscopy, thermogravimetric reduction, and energy dispersive X-ray analysis all showed a small fraction of oxidized iron to be present within the bulk of fully reduced samples. 

in both studies significant amounts of surface carbon impurities have been observed. Ertl and Thiele attributed the presence of the carbon to contamination, which occurred during handling of the samples. Analysis of the carbon Is spectra in the present samples led to the conclusion that at least some of the carbon is an intrinsic impurity of the iron compounds. On the other hand, the carbonate species found in the catalyst precursor is attributed to uptake of carbon dioxide by the alkaline promoter phases during storage of the catalyst. Therefore, the 

In a subsequent study, Ertl et al reported on the overall surface composition of a reduced catalyst which had a bulk composition similar to catalyst 1 in the present study. The surface composition of the two samples is, however, vastly different. In particular, the iron content is lower than the iron content of the present sample, in the unreduced state. The levels of potassium and aluminum are, on the other hand, much larger. It was pointed out that the surface composition as determined was consistent with earlier chemisorption experiments, and led to the conclusion that ca 40% of the accessible surface should be covered with potassium oxide. If the potassium and aluminum oxides were indeed present, as suggested, in the form of surface films, then the bulk of the catalyst would consist predominantly of metallic iron. If a sampling depth of 2-4 nm for XPS is assumed, then the analysis presented in Ref. 19 would represent a catalyst which is largely covered by a multilayer of promoter oxides. Consequently, a very much smaller fraction than 60% of the surface would consist of free iron. In accordance with the SEM and Auger map images the activation procedure of Ertl et led to a surface of elemental iron, which is covered almost entirely by a layer of promoter oxides that contain occasional crystals of embedded ternary oxides. 

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Figure 6. XPS surface analysis results for debonded SAA 7075-T6 aluminum specimens.

From the standpoint of environmental pollution, the surface analysis results discussed above have a number of ramifications ... 

PMDA-ODA on Al 0,. A minor improvement is noticed in the peel force of PMDA-ODA on Al20, when APS is applied to the surface. From the surface analysis results one can see that the APS was not retained on the IPA cleaned sapphire surface to any detectable level, which is likely the cause for no significant improvement in the peel force. The minor improvement in the results may have to do with a possible surface cleaning effect of the sapphire surface with APS solution. The data in Table 3 show that the failure locus has not changed significantly by the APS or T H exposure, being essentially in the polyimide film close to the polyimide/ceramic interface. 

The XPS analysis of the samples primed at 34% RH indicated that there was a consistent failure of the wedge samples which occurred mainly within the alkoxide layer in all systems. Partial hydrolysis may have resulted in the formaton of a weak hydrated oxide layer and was the zone through which the crack propagated to debond the samples. Based on the relative humidity in the chamber during the priming process and the failure surface analysis results, it was concluded that this level of 34% RH was not sufficient to complete the hydrolysis of the alkoxides and produce a stabilized oxide structure. As noted above, however, the wedge crack results did not indicate any instability. 

The surface analysis results of the two minerals by Quantachrome Autosorb 1-C system using with multipoint BET analysis are given in Table 2. 

For very short chains, the surface analysis results point clearly at a pullout of the shorter PVP block from the PVP homopolymer. For all block copolymers where NpVP < NePVp the FRES results showed that all the dPS was on the PS side after fracture. Although the same result could have been obtained, in principle, if the copolymer fractured exactly at the joint, in reality when fracture does occur near the joint, a small amount of dPS is always found on the wrong side. Also the results with PS-PMMA diblocks clearly demonstrate chain pullout for short chains. 

Surface analysis results from XPS (ESCA) and SIMS as well as IEPS of samples with a coverage corresponding to 0.3-5.9-wt% SiC>2 are shown in Table II. At higher silica levels, the surface of the alumina particles is completely covered by a multilayer of silica and the thickness can be measured by TEM. Figure 7 shows, as an example, a micrograph of the coated edge of an alumina particle. These measurements are plotted in Figure 8 and included in Table III with BET results. 

Surface analysis results from XPS (ESCA) and SIMS as well as EPS of samples with a coverage corresponding... 

H. Fischmeister, U. RoU, Passive layers on stainless steels a survey of surface analysis results, Fresenius Z. Anal. Chem. 319 (1984) 639-645. 

The structures of PL membranes are currently being elucidated. Surface analysis results have suggested the presence of networks of nano-sized channels filled with the liquid extractant and diluent. The small size of these channels explains the facts that PL... 

From the surface analysis results it seems that the PAS surface was fully covered with PDMS blocks and that the in vitro bioinertness of PASs resulted from the outermost PDMS layer, similar to PDMS itself (SILASTIC ... 

The detection of impurities or surface layers (e.g., oxides) on thick specimens is a special situation. Although the X-ray production and absorption assumptions used for thin specimens apply, the X-ray spectra are complicated by the background and characteristic X rays generated in the thick specimen. Consequently, the absolute detection limits are not as good as those given above for thin specimens. However, the detection limits compare very favorably with other surface analysis techniques, and the results can be quantified easily. To date there has not been any systematic study of the detection limits for elements on surfaces however, representative studies have shown that detectable surface concentrations for carbon and... 

In a molded polymer blend, the surface morphology results from variations in composition between the surface and the bulk. Static SIMS was used to semiquan-titatively provide information on the surface chemistry on a polycarbonate (PC)/polybutylene terephthalate (PBT) blend. Samples of pure PC, pure PBT, and PC/PBT blends of known composition were prepared and analyzed using static SIMS. Fn ment peaks characteristic of the PC and PBT materials were identified. By measuring the SIMS intensities of these characteristic peaks from the PC/PBT blends, a typical working curve between secondary ion intensity and polymer blend composition was determined. A static SIMS analysis of the extruded surface of a blended polymer was performed. The peak intensities could then be compared with the known samples in the working curve to provide information about the relative amounts of PC and PBT on the actual surface. 

Initial results prove the high potential of LA-based hyphenated techniques for depth profiling of coatings and multilayer samples. These techniques can be used as complementary methods to other surface-analysis techniques. Probably the most reasonable application of laser ablation for depth profiling would be the range from a few tens of nanometers to a few tens of microns, a range which is difficult to analyze by other techniques, e. g. SIMS, SNMS,TXRE, GD-OES-MS, etc. The lateral and depth resolution of LA can both be improved by use of femtosecond lasers. 

Table 8 shows results obtained from the application of various bulk and surface analysis methods to lithium metal at rest or after cyclization experiments, as well as at inert and carbon electrodes after cathodic polarization. The analytical methods include elemental analysis, X-ray photoelectron spectroscopy (XPS or ESCA), energy-dispersive analysis of X-rays (X-ray mi-... 

His researches and those of his pupils led to his formulation in the twenties of the concept of active catalytic centers and the heterogeneity of catalytic and adsorptive surfaces. His catalytic studies were supplemented by researches carried out simultaneously on kinetics of homogeneous gas reactions and photochemistry. The thirties saw Hugh Taylor utilizing more and more of the techniques developed by physicists. Thermal conductivity for ortho-para hydrogen analysis resulted in his use of these species for surface characterization. The discovery of deuterium prompted him to set up production of this isotope by electrolysis on a large scale of several cubic centimeters. This gave him and others a supply of this valuable tracer for catalytic studies. For analysis he invoked not only thermal conductivity, but infrared spectroscopy and mass spectrometry. To ex-... 

Dehydration reactions. In early studies of dehydration reactions (e.g. of CuS04 5 H20 [400]), the surfaces of large crystals of reactant were activated through the incorporation of product into surfaces by abrasion with dehydrated material. An advantage of this pretreatment was the elimination of the problems of kinetic analysis of the then little understood relationship between a and time during the acceleratory process. Such surface modification resulted in the effective initiation of reaction at all boundary surfaces and rate studies were exclusively directed towards measurement of the rate of interface advance into the bulk. 

The resulting data of the Box-Behnken design were used to formulate a statistically significant empirical model capable of relating the extent of sugar 3deld to the four factors. A commonly used empirical model for response surface analysis is a quadratic polynomial of the type... 

The surface analyses of the Co/MgO catalyst for the steam reforming of naphthalene as a model compound of biomass tar were performed by TEM-EDS and XPS measurements. From TEM-EDS analysis, it was found that Co was supported on MgO not as particles but covering its surface in the case of 12 wt.% Co/MgO calcined at 873 K followed by reduction. XPS analysis results showed the existence of cobalt oxide on reduced catalyst, indicating that the reduction of Co/MgO by H2 was incomplete. In the steam reforming of naphthalene, film-like carbon and pyrolytic carbon were found to be deposited on the surface of catalyst by means of TPO and TEM-EDS analyses. 

We have studied the steady-state kinetics and selectivity of this reaction on clean, well-characterized sinxle-crystal surfaces of silver by usinx a special apparatus which allows rapid ( 20 s) transfer between a hixh-pressure catalytic microreactor and an ultra-hixh vacuum surface analysis (AES, XPS, LEED, TDS) chamber. The results of some of our recent studies of this reaction will be reviewed. These sinxle-crystal studies have provided considerable new insixht into the reaction pathway throuxh molecularly adsorbed O2 and C2H4, the structural sensitivity of real silver catalysts, and the role of chlorine adatoms in pro-motinx catalyst selectivity via an ensemble effect. 

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