Platelet-type particles

Sugimoto,T. Waki, S. Itoh, H. Muramatsu, A. (1996) Preparation of monodisperse platelet type particles from a highly condensed K-FeOOH suspension. Colloids Surfaces 109 155-165. 

A high barrier nylon film has been developed by Bayer, also using nanoadditives and Nanocor, USA, has developed an aluminosilicate with platelet-type particles in the nanometer (0.001 pm) size range has been shown to reduce permeability to gases by up to 45 times in polyolefin, PET, or EVOH films. Correctly added, the platelets overlap and present a difficult path to migration of molecules through the film. 

Figure 6 shows transmission electron micrographs of Au particles supported by (a) monocrystalline ellipsoidal (B), (b) monocrystalline pseudocubic, and (c) monocrystalline platelet-type hematite particles (see also Figure 5 for Au particles on polycrystalline ellipsoidal (A) particles). Figure 7 shows Au particles deposited on (a) a-FeOOH, (b) P-FeOOH, (c) ZrOj (A), (d) ZrOj (B), and (e) Ti02 (anatase). 

Fig. 1.3.10 SEM images of (a) pseudocubic, (b) ellipsoidal, (c) peanut-type, and (d) platelet-type hematite particles. The particles of (a), (b), and (c) were prepared under the same conditions as those of the particles in Fig. 1.3.7 but with 10-2 and 3.0 X 10-2 mol dm-3 Na2S04 for (b) and (c), respectively. The platelet particles in (d) were prepared by aging a P-FeOOH suspension ( 0.9 mol dm-3) at 70°C for 8 days in a medium of 2 mol dm-3 NaCl and 7.5 mol dm-3 NaOH. (From Refs. 16 and 20.)...

Okada, I., Ozaki, M., and Matijevid, E., Magnetic interactions between platelet-type colloidal particles, J. Colloid Interface Sci, 142, 251, 1991. 

Shindo, D., Lee, B.T., Waseda, Y, Muramatsu, A., and Sugimoto, T., Crystallography of platelet-type hematite particles by electron microscopy, Mater Trans. JIM, 34, 580, 1993. 

Properties Platelet-type crystalline structure. High porosity, high void volume to surface area ratio, low density, large range of particle size. Insoluble in water and organic solvents soluble in hot concentrated sulfuric acid. Water vapor adsorption capacity of expanded vermiculite less than 1%, liquid adsorption dependent on conditions and particle size, ranges 200-500%. Noncombustible. 

There are basically only three types of platelet-type fillers which can be considered for use in thin barrier films. These are aluminum flake, mica and talc (Table II). Other types of platelets, such as glass, stainless steel or brass flakes and certain aluminum silicate minerals, such as kaolin clay, are either too large in particle size or have too low an aspect ratio to be useful. With these three... 

The toughness induced in ceramic matrices reinforced with the various types of reinforcements, that is, particles, platelets, whiskers, or fibers, derives from two phenomena crack deflection and crack-tip shielding. These phenomena usually operate in synergism in composite systems to give the resultant toughness and noncatastrophic mode of failure. 

More than 20 different types of clay can be actually distinguished. Those most appreciated for making ceramics, for example, kaolinite, are built up of combinations of the basic structural units described above. The particles of most consist of platelets (very small, flat sheets) that, when stacked together, form layered arrangements having extensive surface areas, much like the pages of a book. Other common clay particle shapes are fibrous or tubular. 

Concerning the Fischer-Tropsch synthesis, carbon nanomaterials have already been successfully employed as catalyst support media on a laboratory scale. The main attention in literature has been paid so far to subjects such as the comparison of functionalization techniques,9-11 the influence of promoters on the catalytic performance,1 12 and the investigations of metal particle size effects7,8 as well as of metal-support interactions.14,15 However, research was focused on one nanomaterial type only in each of these studies. Yu et al.16 compared the performance of two different kinds of nanofibers (herringbones and platelets) in the Fischer-Tropsch synthesis. A direct comparison between nanotubes and nanofibers as catalyst support media has not yet been an issue of discussion in Fischer-Tropsch investigations. In addition, a comparison with commercially used FT catalysts has up to now not been published. 

Figure 1.4 SEM images and EDX data from a Mo9V3W12Ox catalyst after activation during the oxidation of acrolein [35], The pictures indicate that needle-like (A), platelet-like (B), and spherical (not shown) particles are formed during exposure to the reaction mixture. EDX analysis at different spots, two of which are exemplified here, point to V, Mo, and W contents that vary from 19 to 29, 60 to 69, and 11 to 13 atom%, respectively. It was determined that the in situ formation of a (MoVW)5014-type phase accounts for the increase in acrolein conversion observed during the initial reaction stages. (Reproduced with permission from Elsevier.)...

In this type of system, the polymer chains are constrained by a surface. They can lie between two hard surfaces such as in the galleries within two parallel clay platelets (as is illustrated in Figure 7), have one layer absorbed on to a hard surface as a coating, with the other free (as in Figure 8), they can be absorbed by the surfaces of exfoliated clay platelets (Figure 9), or by the surface of a solid reinforcing particle completely surrounded by an elastomeric phase (Figure 10). 

Mesostructured materials are granules containing individual platelets (crystals) associated in a fairly random manner. This type of configuration is always associated with a bi-porous structure, in which small particles (platelets) have pores, usually mesopores, different from the composite particle (secondary mesopores and macropores). The secondary pore structure controls access to the individual crystal mesoporosity. As a result, different mass transfer resistances to diffusion through bi-porous structures could be present. In order to evaluate the relative significance of both primary and secondary pore diffusion, usually two different particle sizes are employed in diffusion measurements. 

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