Particles, transmission electron samples, preparation

MgO-supported model Mo—Pd catalysts have been prepared from the bimetallic cluster [Mo2Pd2 /z3-CO)2(/r-CO)4(PPh3)2() -C2H )2 (Fig. 70) and monometallic precursors. Each supported sample was treated in H2 at various temperatures to form metallic palladium, and characterized by chemisorption of H2, CO, and O2, transmission electron microscopy, TPD of adsorbed CO, and EXAFS. The data showed that the presence of molybdenum in the bimetallic precursor helped to maintain the palladium in a highly dispersed form. In contrast, the sample prepared from the monometallie precursors was characterized by larger palladium particles and by weaker Mo—Pd interactions. ... 

Figure 10.6. Transmission electron micrographs of polystyrene particles prepared by dispersion polymerization in Freon 113 and stabilized by Fluoro-PSB-IV (a) Sample 2 (b) Sample 3.

Transmission electron microscopy micrographs (Fig. 13.24) also indicate an important characteristic of the supported particles. As in the case of suspensions, they are either aggregated or isolated. Support surface properties may he an important factor governing this aggregation. After deposition on the support, we observed that samples prepared from acidic hydrosols are characterized by the presence of aggregated particles constituting flocculates ranging from 10 to 200 nm, whereas samples prepared via basic hydrosols contain only isolated particles. The opposite was observed when hydrosols were concerned. These final states of the supported particles may be controlled... 

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

To etch away silica, carbonization product samples were treated with a mixture of concentrated sulfuric and hydrofluoric acids (5 drops of H2S04 and 1 mL of HF), boiled dry and washed with water. From the precipitate obtained were prepared dispersions in acetone, which were used to determine the size and shape of particles on a JEM100CX-II transmission electron microscope by a commonly used procedure[10]. 

The colloidal metals prepared in the manner described above were characterized by transmission electron microscopy. The solutions, as prepared, were diluted to a concentration adequate to allow for the formation of a film of aluminoxane on a sample grid of sufficient thinness for adequate imaging of the metal particles. 

The preparation, which is rapid if it concerns dispersing the crushed catalyst on an amorphous carbon film, may take several hours for microtomy. The analysis of a sample in transmission electron microscopy requires several hours of observation if the aim is to ensure that the results are representative. This is particularly important when subsequently seeking to determine particle size distribution histograms. Reliable values of the average size and of the width of the distribution can only be obtained taking into account a number of particles greater than 100. 

The morphology of the BT powders was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A small amount of the BT powders were pressed on a carbon tape, which attached to the brass sample stub for SEM. To prepare TEM samples, a tiny amount of the BT particles was dispersed in isopropanol by grinding in an agate mortar before placing it on a copper grid. 

Einally, europium oxide nanorods have been prepared by the sonication of an aqueous solution of europium nitrate in the presence of ammonia [85]. The particle sizes measured from transmission electron micrographs and HRSEM are about 50 X 500 nm (W x L). Sonication of an aqueous solution of europium nitrate in the presence of ammonia results in the precipitation of europium hydroxide The as-prepared material is europium hydroxide, as confirmed by TGA, DSC, XPS, and Mossbauer spectroscopy measurements, as well as by PXRD of the as-prepared sample assisted by microwave irradiation... 

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