Characterization techniques specimen preparation method

Applications showing the range of microscopy techniques and specimen preparation methods used on commercial impact polymers will be described. Changes in polymer morphology are expected upon addition of an elastomer for instance, such addition is expected to cause a decrease in the spherulite size as the elastomer domains can act as nucleating sites [219]. This has been observed for many polymers including modified nylon [220]. Characterization of an EPDM impact modified nylon 6,6 has been... 

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

Microscopy in Food Science is in an exciting state of flux. Traditional techniques of specimen preparation and observation will continue to give essential data on the structure of foods. However, the emphasis in the future will probably lie in the development of faster methods and in the quantification of individual components, both aiming at definition of structre /function relationships. This will be true of particulates as they relate to sensory scores and to the characterization of dispersed phases in emulsions and foams. At the same time, the use of microchemical methods should become more common as a means of... 

The powder diffraction experiment is the cornerstone of a truly basic materials characterization technique - diffraction analysis - and it has been used for many decades with exceptional success to provide accurate information about the structure of materials. Although powder data usually lack the three-dimensionality of a diffraction image, the fundamental nature of the method is easily appreciated from the fact that each powder diffraction pattern represents a one-dimensional snapshot of the three-dimensional reciprocal lattice of a crystal. The quality of the powder diffraction pattern is usually limited by the nature and the energy of the available radiation, by the resolution of the instrument, and by the physical and chemical conditions of the specimen. Since many materials can only be prepared in a polycrystalline form, the powder diffraction experiment becomes the only realistic option for a reliable determination of the crystal structure of such materials. 

Before the advent of the SEM (Johari, 1971), several tools, such as the optic microscope, the transmission electron microscope, the electron microprobe analyzer, and X-ray fluorescence, were employed to accomplish partial characterization this information was then combined for a fuller description of materials. Each of these tools has proficiency in one particular aspect and complements the information obtained with other instruments. The information is partial because of the inherent limitations of each method, such as the invariably cumbersome specimen preparation, specialized observation techniques and interpretation of results. 

The majority of work done on VGCF reinforced composites has been carbon/carbon (CC) composites [20-26], These composites were made by densifying VGCF preforms using chemical vapor infiltration techniques and/or pitch infiltration techniques. Preforms were typically prepared using furfuryl alcohol as the binder. Composites thus made have either uni-directional (ID) fiber reinforcement or two-directional, orthogonal (0/90) fiber reinforcement (2D). Composite specimens were heated at a temperature near 3000 °C before characterization. Effects of fiber volume fraction, composite density, and densification method on composite thermal conductivity were addressed. The results of these investigations are summarized below. 

In the past, most solids were prepared on a large scale by standard ceramic techniques, in which accurate control of the composition, as well as uniform homogeneity of the product, were not readily achieved. Unfortunately, this has sometimes led to uncertainty in the interpretation of the physical measurements. In recent years more novel methods have been developed to facilitate the reaction between solids. This is particularly true for the preparation of polycrystalline samples, on which the most measurements have been made. It is of utmost importance to prepare pure single-phase compounds, and this may be very difficult to attain. Even for a well-established reaction, careful control of the exact conditions is essential to ensure reproducible results. For any particular experiment, it is essential to devise a set of analytical criteria to which each specimen must be subjected. It will be seen from the solid-state syntheses included in this volume that one or more of the following common tests of purity are used to characterize a product. 

Until recently it was common to view any breakup of the structure as being independent of laboratory methods of preparation and even the extent of polymorphism was not well understood. However, as a result of numerous investigations described previously [3,6] and in this volume, it has become recognized that some of the more subtle responses of azides to external stimulation (particularly of a gentler kind) are quite sensitive to the preparative techniques. Hence, the techniques themselves have been the subject of investigation (Chapters 1 and 2), and it has been increasingly important to characterize specimens in terms of their precise chemical constituents, their crystal structure (Chapter 3), and the form and perfection of crystals (Chapters 4 and 5). Thus,... 

Several polymer studies have been reported where the specimens were prepared by freeze fracture techniques. A modification of the freeze fracture method was used by Singleton et ah [432] in the preparation of plasticized PVC. The sample was notched, cooled and fractured and then immediately replicated with platinum-carbon. Replicas were stripped after warming to room temperature. The authors noted that the preparation was not highly reproducible, perhaps due to nonuniform cooling of large specimens. The results of such a study must be compared with other characterizations for accurate analysis. 

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