Particle mounts

The choice of the mounting medium usually obviates the need for any new instmmental technique for enhancing contrast. A particle mounted in a... 

Conversely, transmission geometry requires that the sample is minimally absorbing. This is usually not a problem if the studied specimen is a molecular substance. However, when the material is a dense alloy or intermetallic compound containing heavy elements, the preparation of a high quality specimen for transmission powder diffraction may be problematic. With flat transmission samples the best approach is to try to arrange no more than a single layer of particles mounted on the film. When cylindrical specimens are employed, the radius of the capillary should be reduced to a practical minimum. Unfortunately, these measures usually reduce the... 

While it might seem surprising that rather large (/xm-scale) particles can be characterized as slurries in solution by electrochemical techniques, there have been many papers concerned with the dark electrochemistry of suspended solids. For example, voltammetric studies of suspensions of AgBr are possible (84). In addition, there have been numerous studies of solid particles mounted on electrode surfaces (85). 

Samples in any form (solid, liquid, gas) can be analyzed and, with hard X-ray microprobes, the technique is particularly well suited for studies of wet materials because no vacuum chamber is required. In practice, most samples consist of individual particles mounted on thin plastic films or conventional thin sections with pure silica as the substrate. 

The material under test is mounted in a liquid of known refractive index and examined in monochromatic light with the condenser adjusted to give a narrow axial beam. When the test pieces and the liquid have different refractive indices, each particle is surrounded by a narrow luminous halo (the Becke line), which moves as focus is adjusted. If the focus is lowered, then the Becke line moves towards the medium having the lower refractive index. The test is repeated with particles mounted in other immersion liquids until a match is found or until the index of the test sample lies between two known indices in the series of liquid standards. If the Becke line phenomenon does not appear, then the refractive index of the material being examined is equal to that of the immersion liquid. 

Figure 5.5a and b presents scanning electron microscopic (SEM) images of Barton pot oxide particles and Fig. 5.5c and d shows micrographs of these particles mounted in resin and polished in cross-section [13]. Particles of two sizes can be identified in the pictures fine lead oxide particles and coarse agglomerates of roughly spherical shape. When these particles are mounted in resin and polished, the unoxidized lead becomes visible. These are the large-sized particles obtained by solidification of the lead droplets and by surface oxidation of flie lead particles. The pure lead oxide particles are small and fairly equal in size. 

Preparation of Polished Sections, Thin Sections, and Particle Mounts... 

Methods making use of epoxy resins, resulting in polished sections in only a few minutes, are discussed first, followed by details of impregnation and encapsulation. Equipment and techniques for grinding and polishing, including thin-section procedures, are described. The use of Hyrax , a synthetic resin with an index of refraction of 1.70, is discussed, followed by a description of a recommended method for refractive-index determination of particles mounted on a thin film of epoxy. 

Particle mounts in which the particles are attached to a thin film of substrate epoxy on a glass microscope slide are quite useful for repeated examination of the same grain with various refractive-index (RI) liquids and for the application of various stains as in raw feed analysis. An epoxy not soluble in acetone or xylene... 

According to Ono, Kawamura, and Soda (1968), alite birefringence is a function of maximum temperature in the kiln load the higher the temperature, the larger the birefringence. Birefringence in Ono s method is measured on alite crystals in clinker particles mounted in RI oil and observed in transmitted, polarized light. 

Mineral characteristics in transmitted and reflected light are clearly described in standard optical mineralogy texts (Heinrich, 1965 Kerr, 1977). The optical properties of almost all known minerals, with a concise description of optical theory and technique, are given by Fleischer, Wilcox, and Matzko (1984) who emphasize particle-mount analysis. 

The present writer uses particle mounts and thin sections for determination of component percentages in raw feeds. Raw feed examination using powder mounts is described first, followed by analysis with thin sections. 

The steady state diffusion cell is composed of a porous medium bound by two chambers. The porous medium can be either a particle or a collection of particles mounted in parallel as shown in Figure 13.1-1. The advantages and disadvantages of the steady state diffusion cell are listed in the following table. 

Particles of plastic or rubber are often recovered from crime scenes or from victim s and suspect s clothing. Occasionally, these have forensic significance and must be identified and compared as described above. Rubber particles mounted on a microscope slide are recognizable because they can be compressed when pressure is applied to the coverslip with a needle, and recover fully when the pressure is released. Plastics are more easily recognized by an experienced eye by ruling out other types of particles. Particles of plastic are readily identified today by FT-IR analysis. 

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