Elemental characterization techniques

Instrumental Methods for Bulk Samples. With bulk fiber samples, or samples of materials containing significant amounts of asbestos fibers, a number of other instmmental analytical methods can be used for the identification of asbestos fibers. In principle, any instmmental method that enables the elemental characterization of minerals can be used to identify a particular type of asbestos fiber. Among such methods, x-ray fluorescence (xrf) and x-ray photo-electron spectroscopy (xps) offer convenient identification methods, usually from the ratio of the various metal cations to the siUcon content. The x-ray diffraction technique (xrd) also offers a powerfiil means of identifying the various types of asbestos fibers, as well as the nature of other minerals associated with the fibers (9). 

The STEM Is Ideally suited for the characterization of these materials, because one Is normally measuring high atomic number elements In low atomic number metal oxide matrices, thus facilitating favorable contrast effects for observation of dispersed metal crystallites due to diffraction and elastic scattering of electrons as a function of Z number. The ability to observe and measure areas 2 nm In size In real time makes analysis of many metal particles relatively rapid and convenient. As with all techniques, limitations are encountered. Information such as metal surface areas, oxidation states of elements, chemical reactivity, etc., are often desired. Consequently, additional Input from other characterization techniques should be sought to complement the STEM data. 

ISO/TR 7073 1988 Recommended techniques for the installation of unplasticized poly (vinyl chloride) (PVC-U) buried drains and sewers ISO 7387-1 1983 Adhesives with solvents for assembly of PVC-U pipe elements -Characterization - Part 1 Basic test methods ISO 7508 1985 Unplasticized polyvinyl chloride (PVC-U) valves for pipes under pressure -Basic dimensions - Metric series... 

Elemental and Structural Characterization Many oxidation reactions occur on mixed oxides of complex composition, such as SbSn(Fe)0, VPO, FePO, heteropolycompounds, etc. Very often the active surfaces are not simple terminations of the three dimensional structure of the bulk phases. There is need to extensively apply structural characterization techniques to the study of catalysts, if possible in their working state. 

Table 3. Comparison of primary elemental surface characterization techniques used to determine the locus of failure in adhesion systems 159). (Reprinted from Ref. 59, p. 136, by courtesy of Plenum Press)...

It is well known that ferromagnetism favors reentrant behaviour (see subsection 1.3). The formation of such secondary phases is supported by nonstoichiometry. Therefore the chemical characterization of the sample is of prime importance. However, due to the presence of the two light elements B and C the various classical characterization techniques as chemical analysis, intensity analysis of x-ray or neutron diffraction, transition electron... 

Direct Characterization Techniques. The in situ analysis of elemental composition of coals by ion microprobe was first demonstrated by Dutcher t al. (85). Raymond (86) has applied this technique to examine the variation in composition of coal macerals which has been especially effective for looking at sulfur distribution. An example of the organic sulfur distribution for two bituminous coals is shown in Table II which is taken from reference (86). Note that the liptinites contain the... 

The abihty of these gases to form true chemical compounds with other atoms is limited to the heavier members of the group, krypton, xenon, and radon, where the first ionization energies are reduced to a level comparable with other chemically active elements. Theoretical studies, however, have indicated that it may be possible to isolate helium derivatives, such as MeBeHe. Many of the compounds are prepared at low temperature and characterized through spectroscopic techniques. More recently, multinuclear NMR has emerged as an extremely useful characterization technique. ... 

Theories and principles of the characterization techniques are not described here. For consistenc), all the catatysts described in this review are referred to with the same nomenclature, although a different nomenclature is sometimes used in the cited publications. Each catalyst component (element) separated by the symbol indicates the sequence of its introduction into the catalyst formulation from right to left. Those separated by the symbol 7 between right and left belong to the support material and the elements on the support, respectively. For example, NiMo-P/Al refers to a catalyst prepared such that the phosphorus-containing precursor is loaded on the alumina support first, followed by nickel and molybdenum, which are introduced simultaneously. CoMo/Al — P refers to a catalyst in which cobalt and molybdenum are introduced simultaneously onto an alumina support doped with phosphorus-containing species. Each element may represent its oxide or sulfide forms. In all cases, A1 refers to the alumina-based support or to its hydroxide precursor. 

In the preceding chapter it had already been discussed that it is less the synthesis itself which may be the bottleneck in high-throughput zeolite science but rather the analysis of the solids formed in a high-throughput program. There are several standard characterization techniques which are typically employed to characterize zeolitic materials. These include powder XRD for phase identification, X-ray fluorescence analysis (XRF) or atomic absorption spectrometry to analyze elemental composition, sorption analysis to study the pore system, IR-speclroscopy, typically using adsorbed probe molecules to characterize the acid sites, NMR spectroscopy and many others. For some of these techniques parallelized solutions have been developed and described in the literature, other properties are more difficult to assess in a parallelized or even a fast sequential fashion. 

---