Elastic scanning electron microscopy

For surface structure studies, perhaps the most popular technique has been LEED (373). Elastically diffracted electrons from a monoenergetic beam directed to a single-crystal surface reveal structural properties of the surface that may differ from those of the bulk. Some applications of LEED to electrocatalyst characterization were cited in Section IV (106,148,386). Other, less specific, but valuable surface examination techniques, such as scanning electron microscopy (SEM) and X-ray microprobe analysis, have not been used in electrocatalytic studies. They could provide information on surface changes caused by reaction, some of which may lead to catalyst deactivation (256,257). Since these techniques use an electron beam, they can be coupled with previously discussed methods (e.g. AES or XPS) to obtain a qualitative mapping of the structure and composition of a catalytic surface. 

The inherent ability of the powder to reduce its volume during compression could affect the amount of interparticulate attraction in the final compact. A decrease in compact porosity with increasing compression load is normally attributed to particle rearrangement elastic deformation, plastic deformation, and particle fragmentation. Scanning electron microscopy (SEM) for the qualitative study of volume-reduction mechanisms has been presented in the literature. 

SEM (scanning electron microscopy)—an electron beam is focused onto a small region of a sample contained within a vacuum. The beam is scanned across the sample and the backscattered electrons (those undergoing elastic collisions) and the secondary electrons (those electrons released through inelastic collisions) are collected on a positively charged detector to obtain an image on a scintillation screen or electronic detector. 

BSE Backscattered scanning electron microscopy. Backscattered electrons are the result of elastic collisions between energetic beam electrons and atoms within the target, for example athin-section. 

The polymers, whose characteristics are summarized in Table 1, were melt mixed in a Brabender-like apparatus at 200 C and at two residence times 6 min, at 2 r.p.m. and further 10 min. at 32 r.p.m. The blend compositions are listed in Table 2. After premixing, cylindrical specimens were obtained directly by extrusion using a melting-elastic miniextruder (CSI max mixing extruder mod. CS-194), Thermal and tensile mechanical tests were performed on these specimens by an Instron Machine (mod. 1122) at room temperature and at cross-head speed of 10 mm/min. Also made were morphological studies by optical microscopy of sections microtomed from tensile samples and scanning electron microscopy of fractured surfaces of samples broken at liquid nitrogen temperature. Further details on the experimental procedures and on the techniques used are reported elsewhere . 

Radioactive tracers were utilized by Bueche (1962) to measure self diSusion coefficients for polymer systems above their glass-transition temperature, Tg. Price et al. (1978) described a novel approach that used scanning electron microscopy (SEM) and dispersive energy X-ray fluorescence analysis to measure the interdiffusion (D Kh cmVsec) of compatible polymer/polymer systems. Quasi-elastic light scattering (QELS) is an unusual technique due to its ability to measure both the mutual and self diffusion coefficients. Patterson et al. (1981) and Amis s. (1983) have demonstrated the apphcahon of this technique to polymeric gels. 

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