Microstructure characterization tools

Recent progress in electron diffraction has significantly broadened its applications from a primary a microstructure characterization tool to an accurate structure analysis technique that traditionally belongs almost exclusively to the domain of X-ray and neutron diffraction. This development is timely since the focus of modem materials feature size is increasingly on nanoscale stmctures, where the electron high spatial... 

Powder diffraction studies can provide a wealth of structural and nonstriictural information. Powder diffraction studies can provide quantitative information on multiphasic samples, atoinic coordinates similar to those from single-crystal studies, and give microstructural information on the properties of individual crystallites. The ease with which nonambient experiments can be performed makes powder diffraction one of the more powerful characterization tools available to the supramolecular chemist. 

Figure 2.5 depicts the bivariate distribution of molecular weight and chemical composition of another LLDPE resin. This rather appealing tri-dimensional plot summarizes the complexity inherent to most commercial polyolefin resins. It also shows that microstruc-tural characterization techniques, such as the ones used to generate Figures 2.4 and 2.5, are indispensable tools to understand polyolefins. The most important techniques for polyolefin microstructural characterization will be reviewed later in this section. 

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... 

T. VeckoPirtovsek, G. Kugler, M. Godec, M. Tercel], Microstructural characterization during the hot deformation of 1.17C-11.3Cr-1.48V-2.24W-1.35Mo ledeburitic tool steel, Materiais Characterization, 62 (2011), 189-197. 

Evaluation of bulk industrial material is best done by microtomy for OM, TEM, and SPM and by fracture of bulk molded or extruded samples for SEM and FESEM for determining microstructure. A brief literature review with examples of microscopy characterization of copolymers follows, but this review is not intended to reflect the thousands of studies and references on this important topic. Transmission electron microscopy is by far the most widely used characterization tool for the assessment of copolymers, and it has been used for several decades to uncover and provide understanding of copolymer microstructure. 

Characterization and understanding of the microstructure become important after hydrogenation and hydroformylation of the nitrile rubber since the amount and distribution of the residual double bonds influence the properties of modified rubber. The conventional analytical tools have been used to characterize the elastomers. Spectroscopy is the most useful technique for determination of the degree of hydrogenation in nitrile rubber. 

In the past three decades, industrial polymerization research and development aimed at controlling average polymer properties such as molecular weight averages, melt flow index and copolymer composition. These properties were modeled using either first principle models or empirical models represented by differential equations or statistical model equations. However, recent advances in polymerization chemistry, polymerization catalysis, polymer characterization techniques, and computational tools are making the molecular level design and control of polymer microstructure a reality. 

Using solid-state physics and physical metallurgy concepts, advanced non-destructive electronic tools can be developed to rapidly characterize material properties. Non-destructive tools operate at the electronic level, therefore assessing the electronic structure of the material and any perturbations in the structure due to crystallinity, defects, microstructural phases and their features, manufacturing and processing, and service-induced strains.1 Electronic, magnetic, and elastic properties have all been correlated to fundamental properties of materials.2 5 An analysis of the relationship of physics to properties can be found in Olson et al.1... 

Micro structures in heterogeneous catalysts are closely related to the catalytic properties. TEM and related microanalytic techniques are powerful tools in characterising catalysts at atomic level. The obtained structural information is essential to the understanding of correlations between microstructures and catalytic properties. In this lecture note, the general principle of characterization of catalysts by TEM is introduced and the applications on Pt/Si02 model system and on VPO catalysts are intensively described. 

In FIB-SEM, such milling and imaging can be performed in a sequential manner thus a series of images (often called "slices") can be collected at well-defined distances. This opens up the third dimension by making a SEM combined with a FIB a well suited tool for characterizing micron and sub-micron size microstructural features in three dimensions via serial-sectioning procedures (94). 

In terms of characterizing the microstrac-ture of polymer chains, the two most useful techniques are infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectroscopy. Commercial infrared spectrometers were introduced after the end of the second world war and quickly became the workhorse of all polymer synthesis laboratories, providing a routine tool for identification and, to a certain degree, the characterization of microstructure (e.g., the detection of short chain branches in polyethylene). In this regard it can no longer compete with the level of detail provided by modem NMR methods. Nevertheless, IR remains useful or more convenient for certain analytical tasks (and a powerful tool for studying other types of problems). So here we will first describe both techniques and then move on to consider how they can be applied to specific problems in the determination of microstructure. 

Although infrared spectroscopy was one of the first tools applied to the characterization of polymer microstructure, for many tasks it has been supplanted by NMR spectroscopy. In about a page or so briefly outline why this is so. 

An important future objective in the present field of research evidently concerns surface characterization during and after the anodic and open-circuit processes under consideration, not only as far as the surface composition is concerned, but also from the viewpoint of the surface microstructure and defect structure. Recently developed in-situ techniques such as FTIR, photocurrent imaging by laser scanning and STM may constitute excellent tools for this purpose. 

The most frequently used technique for the determination of crystal structures is single crystal analysis. However, if no single crystals of suitable size and quality are available, powder diffraction is the nearest alternative. Furthermore, single crystal analysis does not provide information on the bulk material and is not a routinely used technique for the determination of microstructural properties. Neither is it often used to characterize disorder in materials. Studies of macroscopic stresses in components, both residual from processing and in situ under load, are studied by powder diffraction, as is the texture of polycrystalline samples. Powder diffraction remains to this day a crucial tool in the characterization of materials, with increasing importance and breadth of application as instrumentation, methods, data analysis and modeling become more powerful and quantitative. 

Metastability. Much of the use and analysis of real materials involves systems that are metastable. Unlike the robust tools that are available for the evaluation of systems that are in terminal privileged states (i.e. equilibria), the study of metastable systems is presently characterized by ideas that are based upon perturbations about the equilibrium state, or else ad hoc hypotheses that remain, as yet, unjustified. Our discussion of microstructure and its evolution was based upon a range of clever and fascinating ideas, but I at least am unable to escape the feeling that the treatment of the material s history was implicit and present primarily by virtue of initial conditions, whereas a more fundamental treatment of such metastable systems might demand a more detailed accounting for that history. 

The Digital Material is a material description based on measurable quantities that provides the necessary link between simulation and experiment. Critical components of the Digital Material, a feature based material description with a statistical description of attributes, include 1) experimental methods that provide initial data for simulations and simulation methods to evolve the material attributes, 2) simulation tools that can be used to build virtual specimens, characterize them and compute material properties, 3) coordinated experiments to verify simulations and to supplement critical data and 4) accuracy assessment techniques for both simulation and experiment. Development of this program will itself require simulations and experiments of a fundamental nature. The output will be a model that will permit virtual experiments to be conducted on a two-phase material of previously selected and characterized microstructure. 

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