Electron microscopy microdiffraction

A comparative study has been made by optical and electron microscopy of the anisotropic texture of several cokes from caking coals and pitches carbonized near their resolidification temperature. A simple technique made it possible to examine, by both methods, the same area of each sample and to identify the corresponding zones of the two very similar images. The anisotropy observed in polarized light appears in electron microscopy as differences in contrast resulting not from inequalities in electron absorption, but, as revealed by microdiffraction and dark Reid examinations, from diffraction phenomena depending on the general orientation of the carbon layers within each anisotropic area. 

We shall first examine the microscopic techniques which allowed us to study these transformations and to show the striking analogy between the images obtained by optical microscopy in polarized light and by electron microscopy with ultrathin sections, despite the difference of the absorption mechanisms of light and electrons. Once this analogy was established, we sought to use electron microscopy and electron microdiffraction to learn more about the texture and structure of the anisotropic areas. 

Transmission Electron Microscopy. An electron microdiffraction technique was employed to identify crystal structures developed in two Pt-Sn-alumina catalysts (47). One catalyst was prepared by co-precipitating Sn and A1 oxides and then impregnating the calcined material with chloroplatinic acid to give... 

The atomic structure of the films was studied by transmission electron microscopy (TEM) using a JEM lOOC electron microscope in the microdiffraction mode. The diffraction patterns were obtained at a low electron beam intensity using the CCD high-sensitive registration system to prevent the films from radiation damage by the electron beam. 

These data lead us to the conclusion that the usual explanations for structure sensitivity, which are valid in particular for particles of less than 5 nm, do not apply for these silver systems. The great sensitivity of the catalyst to the nature of the support, chlorine, and alkaline earth elements makes it clear that the chemical state of silver is greatly varied in these different environments. The morphology of the silver particles has been invoked as an explanation of its unusual behavior (325, 327), but the data are not convincing. Studies on model catalysts by modern methods of electron microscopy and microdiffraction would be of value for this particular system. 

The catalyst used must be characterized at the various particle sizes by a number of chemical and physical methods. For example, if TOF is supposed to increase because the fraction of (110) faces exposed is said to increase, then the shapes of the particles should be studied by appropriate electron microscopy and microdiffraction techniques, and perhaps by EXAFS. Further comments follow. 

The process starts with the preparation of polymer solutions, for instance, polyvinyl alcohol (PVA), and metal compounds, for instance, 3d-metal chlorides. Afterwards, the solutions with a certain concentration are mixed in the ratio PVA-metal chloride equals to 20 1-1 5 (better 5 1). Then the prepared solutions are dried till they obtain gel-like colored films with further temperature elevation up to 100°C. The films obtained are controlled by spectral photometry, and also with help of transmission optical microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. When the film color changes to black, the films are heated in the furnace according to the following program 100-200-300-400°C. As a result, the dark porous semiproduct with many microcracks is formed, that is milled in spherical or jet mill. The nanopowder obtained is steamed and dispersed in hot water. After filtration, the powder is dried and tested with the help of Raman spectroscopy. X-ray photoelectron spectroscopy, transmission electron microscopy and electron microdiffraction. 

In the following, we discuss cross-sectional scanning and transmission electron microscopy study of Sn whisker, the effect of surface oxide on whisker growth, synchrotron radiation microdiffraction study of Sn whisker, and kinetic model of Sn whisker growth. 

Thermotropic aromatic copolyesters have a major advantage over the lyotropes, as the former can be melt processed. Temperature affects the orientation and the mechanical properties, and the copolyesters have been shown to be biphasic by SEM [694-696], optical, and TEM [697-699] techniques. The biphasic structure of X7G has been reported [699] for extruded fibers by optical and EM imaging and microdiffraction. Transmission electron microscopy micrographs of ultrathin longitudinal sections reveal a dense dispersed phase elongated along the fiber axis (Fig. 5.147). Microdiffraction from regions 20-100 nm across show the... 

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