Kossel diffraction

Another optical technique, called the back-light scattering (Kossel-diffraction) method can also be used to investigate structure in food emulsions and foams. In this method, the emulsion (or foam) in a transparent vessel is illuminated by a collimated laser beam (See... 

The third chapter, by Wasan and Nikolov, discusses fundamental processes in emulsions, i.e., ereaming/sed-imentation, flocculation, coalescence, and final phase separation. A number of novel experimental facilities for characterization of emulsions and the above-mentioned processes are presented. This chapter highlights recent techniques such as film rheometry for dynamic film properties, capillary force balance in eonjunetion with differential microinterferometry for drainage of curved emulsion films, Kossel diffraction, imaging of interdroplet interactions, and piezo imaging spectroscopy for drop-homophase coalescence rate processes. 

The X-rays generated when an electron beam strikes a crystal also can be diffracted by the specimen in which they are produced. If a photograph is made of this diffracdon pattern (the Kossel pattern) using a special camera, localized crystallographic information can be gleaned. 

While Werner s ideas of primary and secondary valence were not well received during his lifetime, shortly after his death (1920) they were confirmed by Kossel, who laid the foundation for the electronic theory of valence. Furthermore, at about the same time, Wyckoff and Dickinson both confirmed Werner s theory by x-ray diffraction studies of these types of compounds. 

Striking confirmation of the cubic structures of BP I and BP II was obtained by Onusseit and Stegemeyer and others, who succeeded in growing beautiful single crystals of up to a few hundred microns in size (fig. 4.8.2(a)). Optical Kossel diagrams, analogous to the Kossel lines observed in X-ray diffraction from crystals, have confirmed their symmetry (fig. 4.8.2(f))). 

In 1939 Kossel and Mollenstedt demonstrated the possibility of obtaining CBED patterns from crystals with more information than obtained from the more conventional focused patterns for special beam directions. Later, in 1940, it was demonstrated that the intensity of a reflection is a function of the excitation error, and the thickness, t, of a plane parallel crystal slab [3]. Lately, more advances in CBED became possible with the introduction of field emission guns and scanning TEM (STEM) techniques. Thus, the STEM instrument has electron optics similar to CBED for obtaining diffraction results from areas as small... 

In the b) variant the convergence angle is increased by using a very large limiting aperture or none. Thus, the individual round diffraction spots produce large overlap and superimposed black and white lines are obtained, similar to the Kossel or the Kikuchi lines formed from electrons diffusely scattered in thick crystals. The separation of these line pairs can be used as a measure of crystal curvature. 

In a single crystal, the excited X rays are Bragg diffracted at the lattice plane, and their isotropic angular characteristics show defect and excess Kossel lines of apex angle 90°-0b. which can be used for accurate measurement of lattice parameters and strains when the Kossel pattern is recorded on a photographic emulsion. 

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