Methods of Phase Identification

In practice, nearly the entire array of characterization tools has been employed to determine the identities of unknown phases. The ensuing discussion begins by addressing the microstructural examination of phase distributions. Full identification of any particular phase in the microstructure requires knowledge of both crystal structure and chemical content each of these topics is discussed with respect to the types of analyses best suited to obtaining the necessary information. Both elementary techniques and advanced analytical approaches are mentioned one should 

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Other excellent methods of phase identification include TEM and electron diffraction. These may be more useful for low-Z materials, ultrathin films, and for characterizing small areas, including individual grains. For multiphase films with incomplete texture, these methods and XRD are complementary, since in commonly used geometries, they probe atomic planes perpendicular and parallel to the thin film surface, respectively. 

Miscibility is a very useful method often used in conjunction with microscopy. The simplest use of the technique is to bring two materials together on the cover slip in their mesophases in a contact preparation the identity of the mesophase of one of the materials should already be known. If the two materials are co-miscible, then both have the same mesophase (at the temperature in question) and this can then be a useful method of phase identification. Unfortunately, if the two materials are immiscible then no information is obtained as two materials in the same phase are not necessarily miscible (e.g., water and chloroform which are both isotropic). 

The various microstructural features discussed above are presented in further detail below, and a number of illustrative examples are provided. The following section specifically addresses methods of phase identification with respect to both crystal structure and chemical composition. Finally, the chapter concludes with a brief description of stereology—the quantitative extraction of information about a three-dimensional solid from the two-dimensional images of sections or surfaces that are normally available. 

Chapter 13 surveys methods of system identification in physiology, the process of extracting models or model components from experimental data. Identification typically refers to model specification or model estimation, where unknown parameters are estimated within the specified model using experimental data and advanced computational techniques. Estimation may be either parametric, where algebraic or difference equations represent static or dynamic systems, or nonparametric, where analytical (convolution), computational (look-up tables), or graphical (phase-space) techniques characterize the system. This chapter closes with a recent hybrid modular approach. 

At room temperature the y- and /3-phases may coexist due to the large hysteresis in the y /3 transition. The two phases do not differ sufficiently in their magnetic or transport properties to determine relative percentages from these measurements therefore the best method for phase identification is by diffraction methods. One can, however, make use of the fact that y-Ce will always transform to a-Ce when cooled below 100 K and from resistance or magnetic susceptibility measurements one can detect small amounts of y-Ce in jS-Ce (see below). As mentioned previously (sections 2.4 and 3.3) the surface of the sample may contain more of a particular phase than the bulk hence neutron diffraction methods are more reliable than X-ray methods. However, neutron diffraction may require a significantly larger sample. 

Infrared (IR) spectroscopy is one of the most versatile, fast, inexpensive, and conclusive methods of molecular identification available to the instrumental ly-oriented analytical chemist. Samples can usually be examined with ease and are not limited to one or two phases gases, liquids, and solids can usually be examined with equal facility, a feature available in few other instrumental techniques. Specialized techniques have been developed to handle all but the most stubborn samples. Some of these techniques are... 

As indicaled above, the PHA may ser c as a precursor lo further hazard analyses. It is included in lliis chapter because it can pro ide a cost effective, early-on plant method for hazard identification. As its title indicates, the PHA is really intended for use only in the preliminary phase of plant development for cases where past e.spcriencc provides little or no insight into any potential safety problems, e g., a new plant with a new process. 

If small or medium libraries for lead optimization are demanded and all synthetic products are to be screened individually, most often parallel synthesis is the method of choice. Parallel syntheses can be conducted in solution, on solid phase, with polymer-assisted solution phase syntheses or with a combination of several of these methods. Preferably, parallel syntheses are automated, either employing integrated synthesis robots or by automation of single steps such as washing, isolation, or identification. The latter concept often allows a more flexible and less expensive automation of parallel synthesis. 

Various synthetic routes to isocyanides have been reported since their identification over 100 years ago.8 Until now, the useful synthetic procedures all required a dehydration reaction8-11 Although the carbylamine reaction involving the dichlorocarbene intermediate is one of the early methods,8 it had not been preparatively useful until the innovation of phase-transfer catalysis (PTC).4 5... 

Berger [340] has examined the use of pSFC in polymer/additive analysis. As many polymer additives are moderately polar and nonvolatile SFC is an appropriate separation technique at temperatures well below those at which additives decompose [300,341,342], SFC is also a method of choice for additives which hydrolyse easily. Consequently, Raynor et al. [343] and others [284,344] consider that SFC (especially in combination with SFE) is the method of choice for analysing polymer additives as a relatively fast and efficient sample preparation method. Characterisation of product mixtures of nonpolar to moderately polar components encompassing a wide range of molecular masses can be accomplished by cSFC-FID. Unknown polymer additives may be identified quite adequately by means of cSFC-FID by comparison with retention times of standards [343], However, identification by this method tends to be time-consuming and requires that all the candidate compounds are on hand. SFC-FID of some low-to-medium polarity additives on reversed-phase packed columns... 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Determining the potential for hazards to result in an accident (risk assessment) is frequently part of the identification step (see chapter 11). This list of potential hazards and their risk is used during the evaluation and control phase of the project. Resources for evaluating the hazards and developing control methods are allocated on a priority basis, giving the appropriate time and attention to the most significant hazards. 

In environmental analytical applications where analyte concentrations, e.g. surfactants or their metabolites, are quite low, extraction and concentration steps become essential. Solid phase extraction (SPE) with cartridges, disks or SPME fibres (solid phase micro extraction) because of its good variety of SP materials available has become the method of choice for the analysis of surfactants in water samples in combination with FIA as well as LC—MS analysis. SPE followed by sequential selective elution provides far-reaching pre-separations if eluents with different polarities and their mixtures are applied. The compounds under these conditions are separated in the MS spectrometer by their m/z ratios providing an overview of the ionisable compounds contained in a sample. Identification in the sense it has been mentioned before, however, requires the generation of fragments. 

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