Chemical state determinations

The particular strengths of XPS are semi-quantitative elemental analysis at surfaces without standards, quantitative analysis with standards, and chemical state determination for materials as diverse as biological to metallurgical. 

The u.se of well-defined reference materials is crucial with regard to chemical-state determination by XPS. However, it is very difficult to prepare well-defined surfaces for many chemical compounds due to the pre.sence of surface contaminants and multiple chemical states and to the fact that the surface compo.sition is seldom similar to the bulk composition. This point is illustrated by the use of an AgO powder sample to obtain reference BEs and peak shapes for AgO and AgO (45, 46]. The AgO was heated in vacuum in order to decompose first the contaminating carbonate and hydroxyl species and then the AgO it.self to Ag O and finally to Ag metal. The XPS Ag id spectra recorded after heating the sample to various temperatures are shown in Fig. 14. The spectral changes are complex because several Ag species are present and their BEs are separated by only a few tenths of an eV (Table 1.2). Heating at 100°C results in the loss of carbonate and hydroxyl species, at 200°C in the decomposition of AgO to Ag 0. and at 400°C in the decomposition of Ag 0 to Ag metal. Spectrum f was recorded from a clean... 

The bulk of the literature shows that the energy of the Ti 2p doublet exhibits large chemical shifts (up to 4 eV) and considerable alterations of peak. shape due to changes in the chemical environment around the Ti atoms, e.g.. due to partial oxidation. This has led to the erroneous conclusion that chemical-state determination can be performed in a quantitative manner with relative ea.se by using a simple peak-synthesis procedure on the Ti 2p envelope. As will be shown, a complex evaluation procedure should be applied to the quantitative analysis and the assignment of the chemical states of Ti, making the characterization of TiN more reliable. 

The Unction of this chapter is to summarize some of the general approaches to the determination of the physical and chemical state in both of the types of adsorption systems described. 

The composition and chemical state of the surface atoms or molecules are very important, especially in the field of heterogeneous catalysis, where mixed-surface compositions are common. This aspect is discussed in more detail in Chapter XVIII (but again see Refs. 55, 56). Since transition metals are widely used in catalysis, the determination of the valence state of surface atoms is important, such as by ESCA, EXAFS, or XPS (see Chapter VIII and note Refs. 59, 60). 

Polymer Composition. The piopeities of foamed plastics aie influenced both by the foam stmctuie and, to a gieatei extent, by the piopeities of the parent polymer. The polymer phase description must include the additives present in that phase as well. The condition or state of the polymer phase (orientation, crystallinity, previous thermal history), as well as its chemical composition, determines the properties of that phase. The polymer state and cell geometry are intimately related because they are determined by common forces exerted during the expansion and stabilization of the foam. 

AT the path length, and P (A) the mass absorption coefficient at wavelength A. Between absorption edges, P (A) is proportional to Z A and is nearly independent of physical or chemical state. An absorption measurement on each side of an absorption edge is required for each element analyzed. X-ray absorption is especially useful in determining heavy elements in mixed materials of lower Z, such as lead in gasoline and uranium in aqueous solution. 

SORPTION-CATALYTIC DETERMINATION OF MICRO-AMOUNT AND CHEMICAL STATE OF PALLADIUM ON SURFACE OF CARBON ADSORBENT... 

It was found that sorbed palladium might catalyse reaction of Mn(III) reduction by Cf not only after it s removing from coal, but AC with palladium, Pd/AC, has also his own catalytic effect. On the base of dependence between characteristics of AC, chemical state of palladium on AC surface and catalytic action of Pd/AC in indicator reaction it might establish, that catalytic action concerns only to non-reduced or partly reduced palladium ions connected with chloride ions on coal surface. The presence or absence of catalytic action of Pd/AC in above-mentioned reaction may be proposed for determination of chemical state of palladium on AC surface. Catalytic effect was also used for palladium micro-amounts determination by soi ption-catalytic method. 

The results shown in Figure 6 above are an example of this mode of analysis, but include additional information on the chemical states of the Si. The third most frequently used mode of analysis is the Auger mapping mode, in which an Auger peak of a particular element is monitored while the primary electron beam is raster scanned over an area. This mode determines the spatial distribution, across the surface, of the element of interest, rather than in depth, as depth profiling does. Of course, the second and third modes can be combined to produce a three-dimensional spatial distribution of the element. The fourth operational mode is just a subset of the third mode a line scan of the primary beam is done across a region of interest, instead of rastering over an area. 

Determination of surface functional groups, e.g., —OH, —C - C—, and >C = O, and identificadon of adsorbed molecules comes principally from comparison with vibrational spectra (infixed and Raman) of known molecules and compounds. Quick qualitative analysis is possible, e.g., stretching modes involving H appear for v(C—H) at 3000 cm and for v(0—H) at 3400 cm L In addition, the vibrational energy indicates the chemical state of the atoms involved, e.g., v(C=C) " 1500 cmT and v(C=0) " 1800 cm"L Further details concerning the structure of adsorbates... 

The element sensitivity is determined by the ionization probability of the sputtered atoms. This probability is influenced by the chemical state of the surface. As mentioned above, Cs" or OJ ions are used for sample bombardment in dynamic SIMS, because they the increase ionization probability. This is the so-called chemical enhancement effect. 

The results for the chemical potential determination are collected in Table 1 [172]. The nonreactive parts of the system contain a single-component hard-sphere fluid and the excess chemical potential is evaluated by using the test particle method. Evidently, the quantity should agree well with the value from the Carnahan-Starling equation of state [113]... 

As AOS is a mixture of different chemical species, determination of its composition by modern analytical techniques is perhaps even more important than for most other surfactants this chapter therefore also describes the state of the art of the analysis of AOS. The chapter also contains a brief review of the biodegradability and the toxicity of AOS. 

Determination of surface chemical states of CoOj/TiOi catalysts for continuous wet TCE oxidation... 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

The chemical formula of a compound contains essential information about its composition. The formula identifies which elements are present, and it states the number of atoms of each kind present in one unit of the compound. We need the chemical formula of a substance to calculate its molar mass. In fact, almost all chemical calculations require the correct chemical formula. How are chemical formulas determined in the first place ... 

C20-0003. The following compounds can be purchased from chemical companies. Determine the oxidation state of the transition metal In each of them. 

Besides this iron meteorite, there have been four other rocks identified to be probably of meteoritic origin. These centimeter-sized pebbles, named Barberton, Santa Catarina, Santorini and Kasos, show troilite and/or kamacite signatures in the corresponding Mossbauer spectra [359]. The range of Fe oxidation states suggests the presence of a fusion cmst. The four cobbles have a very similar chemical composition determined by the APXS, and therefore they may be fragments of the same impactor that created Victoria Crater [361]. 

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