Surface Chemical Analysis Technical

The Versailles Project on Advanced Materials and Standards (VAMAS) established a Surface Chemical Analysis Technical Working Area (SCATWA) in 1984 to conduct the collaborative international research needed for the subsequent... 

X-ray photoelectron spectroscopy (XPS) is widely used for surface characterization and analysis of polymers, biomedical materials and paper. The technique was developed by Kai Siegbahn in the 1960s, who realized that technical development had come to a point where the photoelectric effect discovered by Einstein could be used for surface chemical analysis. The photoelectric effect is the phenomenon that occurs when a material is exposed to photons with sufficiently high energy and electrons contained in the material with a lower binding energy are emitted. Therefore, we can write ... 

The surface chemical analysis made possible by XPS has proved useful in a number of areas. Simple detection of surface contamination has already been mentioned another technically important area is the detection of changes in surface functionality introduced by treatments such as plasma and flame modification and chemical etching. These treatments are extensively used in practice to modify surface properties such as adhesion and wettability and the use of XPS and other surface analysis techniques permits one to associate these changes with the introduction of specific chemical functionality at the surface. Excellent entries into the extensive literature in this area may be found in the monograph by Garbassi et al. (1994) and the review by Briggs (1990). 

The ISO Technical Committee 201 Surface Chemical Analysis , the second body that is active in this area, is dedicated to the standardization in the field of surface chemical analysis in which beams of electrons, ions, neutral atoms or molecules, or photons are incident on the specimen material and scattered or emitted electrons, ions, neutral atoms or molecules, or photons are detected. Valid ISO standards on surface chemical analysis with relevance to AES are (January 2004, see ISO TC 201 at http //www. iso.ch) ... 

Under the NAMAS (National Measurement Accreditation Service) quality system, detailed procedures are written by a particular analytical laboratory which apply only to the instrumentation in that laboratory. Unfortunately, these in-house procedures are not made available to the wider analytical community. However, in 1991, ISO technical committee 201 on surface chemical analysis (TC20I) was set up specifically to develop documentary standards for the most industrially developed surface analytical techniques. The standards written by this technical committee are targeted directly at the requirements of the average industrial user, and, since they are ISO standards, are available to any analyst upon request [ I ]. 

Reference procedures (i.e., documentary standards) for sinface analysis have been published by ASTM International [8] and the ISO [9]. Tables 3.2.3.1 and 3.2.3.2 list selected standards prepared by ASTM International Committee E-42 on Surface Analysis and by ISO Technical Committee (TC) 201 on Surface Chemical Analysis that are relevant to AES and XPS. These standards provide recommended terminology and definitions, procedures for handling and mounting specimens. 

The chemical analysis showed the presence of phosphoric acid and, surprisingly, also traces of vanadium containing species in the condensate. This finding is explained by decomposition of vanadyloligophosphate structures on the catalyst surface which are assumed to be formed under the influence of adsorbed water molecules. It is assumed that this also occur during the technical process but on a much longer time scale. However, after some hundreds of hours time on stream of an industrial reactor the loss in phosphorus leads to a decline in... 

If we set out to unravel surface chemical functionalities with high spatial resolution down to atomic detail, we also encounter various practical (technical) problems. It is fair to say that the technique development for direct space analysis (again, we exclude Fourier space methods) is still lagging much behind. Chemical force microscopy can be considered as a first step in the direction of a true description of surface chemical functionalities with high spatial resolution in polymers, primarily based on the chemically sensitive analysis of AFM data via adhesion mapping. At this point the detailed theory for force spectroscopy is not developed beyond the description of London forces. The consideration of the effect of polar functional groups in force spectroscopy (similar to difficulties with solubihty parameter and surface tension approaches for polar forces, as well as specific interactions) is still in its infancy. Instead, one must still rely on continuiun contact mechanics to couple measured forces and surface free energies. 

Many instrumental methods have been developed and are still evolving for the characterization of catalyst surfaces. These instruments are capable of revealing information of value on various aspects of catalysis. Electron spectroscopy for chemical analysis (ESCA), which is also known as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), the electron microprobe, electron microscopy, and X-ray diffraction crystallography are better-developed techniques that have been of particular value in working with technical catalysts. AES has... 

Laser desorption methods (such as LD-ITMS) are indicated as cost-saving real-time techniques for the near future. In a single laser shot, the LDI technique coupled with Fourier-transform mass spectrometry (FTMS) can provide detailed chemical information on the polymeric molecular structure, and is a tool for direct determination of additives and contaminants in polymers. This offers new analytical capabilities to solve problems in research, development, engineering, production, technical support, competitor product analysis, and defect analysis. Laser desorption techniques are limited to surface analysis and do not allow quantitation, but exhibit superior analyte selectivity. 

The technical synthesis of graphite, diamond and a variety of other forms of sp2 carbons (Fig. 3) is described in a review [39] and is not covered here. As the unintended formation of carbon in deactivation processes and the modification of primary carbon surfaces during chemical treatment (in catalytic service and during oxidative reactivation) and their chemical properties arc frequent problems encountered in catalytic carbon chemistry, it seems appropriate to discuss some general mechanistic ideas which mostly stem from the analysis of homogeneous combustion processes (flame chemistry) and from controlled-atmosphcre electron microscopy. 

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