Precipitates, photomicrographs

Figure 12.6. Polarization photomicrograph showing dislocation Awith Burgers vector parallel to the c-axis, which is generated from a tube-like liquid inclusion (U in (b)) formed behind foreign mineral grains (arrows in (a)), which were precipitated on a growing surface. The X symbols in (b) denote the banding of successive stages of formation of a negative crystal [1].

Figure 3. Scanning electron photomicrographs of fly ash particulates collected on alundum thimbles used to sample the precipitator inlet and outlet and the stack...

This photomicrograph shows the crystalline structure of precipitated boiler scale. 

Figure 8-2 shows a selection of electron photomicrographs of barium sulfate and nickel dimethylglyoxime precipitates formed under a variety of conditions. The size and shape of precipitate particles clearly varies widely with the nature of the precipitate and the mode of precipitation. The perfection of crystals of the same size also varies with conditions. Particle size as reflected by a linear dimension may be misleading. 

Figure 2 A high-resolution TEM photomicrograph of the amorphous altered layer (lower left) developed on crystalhne lahradorite (hulk material, upper right) after dissolution at pH 1. The hlurry lattice fringes at the interface reflect the varying boundary orientation with respect to the ultrathin section. Interface thickness is 0.5-2 nm. Energy filtered (EE) TEM was also used to chentically characterize the alteration zone, which was found to he depleted in Ca, Na, K, and Al, and enriched in H, O, and Si. The sharp structural interface shown here and the sharp chemical interface observed with EFTEM are interpreted by the authors to indicate that the alteration layer is formed by dissolution-precipitation. Such amorphous altered layers are often high in porosity and yield high BET surface areas (reproduced by permission of Springer from Phys.

Figure 12 Quartz precipitation that overlaps the timing of fracture opening results in dramatic crack-seal fabrics. Here, a pale blue-luminescing quartz grain has been repeatedly fractured to yield rafted grain slivers encased in blue- and red-luminescing authigenic quartz. Quartz precipitation ultimately did not keep pace with fracture opening as considerable fracture porosity survives (green). Cozzette Sandstone, lies Formation (upper Cretaceous), Eastern Piceance Basin, Colorado. Photomicrograph by Rob Reed.

Figure 11. Photomicrograph (plane polarized light) of the crystal morphology characteristic of folia. Note the dendritic habit and the very porous nature of the precipitate. The dark material surrounding the crystals is opaque epoxy resin used to impregnate the sample before thin sectioning.

After fixation, precipitated preservative salts can be seen in the wood structure. Comparison of photomicrographs of untreated southern pine (Figure 22a) and southern pine treated with 2.5 lb CCA/ft (Figure 22b) reveals that the salts in the treated wood form a rough coating on the lumen walls. The exact final location of these fixed salts is still subject to discussion. Undoubtedly, most of these injected hydrolytic preservatives remain in the cell lumen, but the extent to which these preservatives enter the cell wall and react with the cell wall substance dictates the preservative s effect on strength. 

Fig. 6. (Opposite) Thin-section photomicrographs of textural occurrences of diagenetic carbonates in the Oseberg Formation. (A) Spherulitic precipitates of early diagenetic siderite (S) embedded in late poikilotopic calcite (C).

A photomicrograph, of barium carbonate formed by precipitation using pure soda ash (eq. 9), is shown in Figure 3. The average particle size is 1.2 pm. The exclusive use of soda ash results in a barium carbonate having included sodium that cannot be reduced below a certain level by repeated washings. The sodium can be detrimental if the BaCCL is to be used for barium titanate production. 

The above outlined measurements of the solution property change to determine the induction period may be complemented by the count of the number of nuclei formed within unit solution volume to assess nucleation rates. The simplest but somewhat tedious method of nuclei count is that via a hematocytometer (Burker cell) (Nielsen and Sohnel 1971). Sampling, sample handling, and sample quenching are critical in order to obtain a reliable count. A particle counter with a well-defined optical volume (sensing zone) can also be used. A less accurate procedure is based on determination of the number of nuclei from the mean size of a known mass of precipitate. In such experiments, size can be determined either from optical or electron photomicrographs or measured by an appropriate partiele sizer. 

Figure 1. Light microscopy photomicrograph of radial section of white oak (Quercus alba group) from unidentified marine wreck from New Brunswick Canada. Iron salts have precipitated inside pits (5-p.m diameter) on the radial walls of small vessels and in ray parenchyma cells.

Figure 23.8. Fe° aggregates (from Connelly-GPM Inc., USA) after 6 days of use for treating Cr(VI). (a) SEM photomicrograph of Fe° aggregate with surface precipitates (1500x magnification). (b) Energy dispersive X-ray spectroscopy (EDS) spectra shown for the entire used Fe° aggregate. The semiquantitative results indicate Si 5.28 wt %, Fe 79.86 wt %, O 6.65 wt %, Cr 8.22 wt %.

In addition to particle size distribution obtained from the particle size analyzer, some photomicrographs were obtained to characterize further the nature of the suspensions. As can be seen in Figure 9, the precipitated dye solids are aggregates of small spherical shaped particles. The size of the individual particles making up the aggregates ranges from 0.01 to 0.3pm . 

Figure 9. Photomicrographs of quench slurry, a, b thionyl chloride precipitation, c, d phosphorus oxychloride based precipitation...

FIG. 12—Photomicrograph showing a phase precipitation along austenitic grain boundaries in a type 310 stainiess steei (magnification 500 x). 

FIG. 1—Photomicrograph of severely hydrided unalloyed titanium at 200x. Note the acicular (needle-like) titanium hydride precipitate. 

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