Particle Size and Distribution

Several techniques are commonly used to measure the size distributions of metal colloid particles. Electron microscopy. X-ray diffi ction, and small angle X-ray scattering are the most commonly used, although dassical methods such as sedimentation rates are sometimes reported. The techniques whidi have been extensively applied to the sizing of polymer colloids and emulsions, [183] such as light scattering and neutron scattering, have been only rarely applied to the characterization of metal sols. [103, 151, 153, 184] 

Sample preparation for TEM analysis of colloidal metals is usually a simple procedure, involving the evaporation of a drop of suitably diluted colloid suspension onto a microscope grid. For polymer stabilized colloids, the polymer forms a thin transparent film by this procedure. Thin films can be alternatively prepared by ultramicrotomography of thick polymer/metal samples produced by evaporation of the liquid suspension. 

The resolution limits of modern transmission electron microscopes are more than sufficient for the imaging of metal particles in the 1-10 nm size range of interest here. The images obtained vary in their degree of precision, whereby the information content of the image is set by the needs of the analyst. Although atomic resolution and lattice imaging are required for detailed structural analysis, a particle size distribution can be obtained at moderately low resolution for a sol 

The available literature on metal colloids contains size distributions which span the range from monodispersity to severe agglomeration. Strictly speaking, the term monodispersed means absolutely homogeneous in size, however, in the context of colloid chemistry, a monodispersed sol contains a distribution of partide sizes with a standard deviation from the mean of less than 10 % (i. e. a polydis-persity of 1.1). Although this may seem to be a relatively generous definition of the term, it is the one in common use. 

There is significant evidence that small metal partides, and espedally those in polymer films, can undergo structural change and even aggregation when under the influence of the electron beam during TEM analysis. [185, 186] This is not always observed, but the recognition of this potential problem is a prerequisite in TEM analysis of colloidal metals. 

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The value of pigments results from their physical—optical properties. These ate primarily deterrniaed by the pigments physical characteristics (crystal stmcture, particle size and distribution, particle shape, agglomeration, etc) and chemical properties (chemical composition, purity, stabiUty, etc). The two most important physical—optical assets of pigments are the abiUty to color the environment in which they ate dispersed and to make it opaque. 

It may sometimes by necessary to supplement the properties of the drug so that it compresses more easily, and these needs have been realized by several manufacturers of excipients. Materials described as compression aids are now commercially available. Ideally, such adjuvants should develop mechanical strength while improving, or at least not adversely affecting, release characteristics. Among the most successful at meeting both these needs have been the microcrystalline celluloses (partially acid-hydrolyzed forms of cellulose). A number of grades are available based upon particle size and distribution. 

The electrical conductivity of a Ni-YSZ cermet anode depends on the composition (i.e., Ni to YSZ volume ratio), the microscopic features of the starting materials (e.g., particle size and distribution of NiO and YSZ powders), and the sintering and reduction conditions (e.g., temperature and atmosphere), as will be discussed in detail in the following sections. 

Similar to the percolation threshold, the effective electrical conductivity of a porous Ni-YSZ cermet anode depends on the morphology, particle size, and distribution of the starting materials as well. In general, the effective conductivity increases as the NiO particle size is reduced when other parameters are kept constant. As shown in Figure 2.4 (samples 1 and 2), the cermet conductivity increased from -10 S/cm to 103 S/cm as the NiO particle size was decreased from 16 to 1.8 pm while using the same YSZ powder (primary particle size of -0.3 pm) and the same Ni to YSZ volume fraction [30],... 

The particle size and distribution in soils can be easily determined by the sedimentation method. It is based on the fact that large particles will settle faster than smaller ones. No special equipment is needed. 

An evaluation of numerous clays, including kaolins and bentonites of comparable particle size and distribution, revealed a wide variation in the properties of LDEE-clay composites prepared under identical conditions with similar loadings. This may be attributed to the interference with the radical reactions involved in the coupling sequence. This is confirmed, in part, by the finding that the most effective clays were those which were reported to have been treated with sodium polyphosphate to improve their dispersibility in water during papermaking processes. Solomon reported (1) that treatment of the clays which inhibited radical reactions with sodium polyphosphate reduced the inhibition. 

The solvent-mediated transformation of o -L-glutamic acid to the S-form was quantitatively monitored over time at a series of temperatures [248]. The calibration model was built using dry physical mixtures of the forms, but still successfully predicted composition in suspension samples. Cornel et al. monitored the solute concentration and the solvent-mediated solid-state transformation of L-glutamic acid simultaneously [249]. However, the authors note that multivariate analysis was required to achieve this. Additionally, they caution that it was necessary to experimentally evaluate the effect of solid composition, suspension density, solute concentration, particle size and distribution, particle shape, and temperature on the Raman spectra during calibration in order to have confidence in the quantitative results. This can be a substantial experi-... 

This need is addressed in part by NIR-CI, in that it offers the ability to obtain high fidelity, spatially resolved pictures of the chemistry of the sample. The ability to visualize and assess the compositional heterogeneity and structure of the end product is invaluable for both the development and manufacture of solid dosage forms. NIR chemical images can be used to determine content uniformity, particle sizes and distributions of all the sample components, polymorph distributions, moisture content and location, contaminations, coating and layer thickness, and a host of other structural details. "... 

Combustion of aluminum particle as fuel, and oxygen, air, or steam as oxidant provides an attractive propulsion strategy. In addition to hydrocarbon fuel combustion, research is focussed on determining the particle size and distribution and other relevant parameters for effectively combusting aluminum/oxygen and aluminum/steam in a laboratory-scale atmospheric dump combustor by John Foote at Engineering Research and Consulting, Inc. (Chapter 8). A Monte-Carlo numerical scheme was utilized to estimate the radiant heat loss rates from the combustion products, based on the measured radiation intensities and combustion temperatures. These results provide some of the basic information needed for realistic aluminum combustor development for underwater propulsion. 

We are developing a new method for preparing heterogeneous catalysts utilizing polyamidoamine (PAMAM) dendrimers to template metal nanoparticles. (1) In this study, generation 4 PAMAM dendrimers were used to template Pt or Au Dendrimer Encapsulated Nanoparticles (DENs) in solution. For Au nanoparticles prepared by this route, particle sizes and distributions are particularly small and narrow, with average sizes of 1.3 + 0.3 nm.(2) For Pt DENs, particle sizes were around 2 nm.(3) The DENs were deposited onto silica and Degussa P-25 titania, and conditions for dendrimer removal were examined. 

Particle Size and Shape. The polymerization process for producing macroporous synthetic polymers (539) leads to the formation of spherical particles whose size can be controlled within certain limits. The popular XAD polymers are usually sold with approximately 90 of the total weight encompassing smooth beads with 20-50-mesh sizes. Most users incorporate a suspension step to remove the fines in their purification of the polymer, but they do not remove the small number of particles larger than 20 mesh. The particle size and distribution vary with different polymer batches, and it is advisable to mechanically sieve polymer beads and choose only those within the 20-50-mesh size for preparation of the adsorption columns. 

The effective viscosity depends on the solid hold-up, on particle size and distribution, on the surface properties, on the particle shape and density, on the properties of the liquid (p, p, d), on temperature, and the shear stress in the column. Depending on the solid concentration encountered in BSCR, we can classify the suspensions into "dilute" and "concentrated" groups. 

Figure 16 may also be used to illustrate the problem of polydispersity. For simplicity, consider a small polydispersity in particle size at constant refractive index. The theoretical surface shown in Figure 16 must be modified with a running integration over the size distribution which tends to fill in the minima and round off the maxima so that some of the structure is averaged out. Graphical illustrations of the effect have been reported (9) and the effect has been exploited to obtain both particle size and distribution width (10). It should be realized that both very narrow or very broad distributions tend... 

Figure 5 shows a plot of TOFs for the partial hydrogenation of 1,3-COD by PdRh DENs compared to TOFs for physical mixtures of Pd and Rh monometallic DENs as a function of mol % Rh. As the mol % of Rh in the bimetallic DENs was increased, an increase in the TOF was observed that was greater than that of the physical mixtures. Importantly, the average particle size and distribution did not change as the mol % Rh increased, which was used to rule out the possibility that the TOF enhancement was a consequence of a systematic decrease in particle size. This allows for the conclusion that the bimetallic DENs are truly intimately mixed bimetallic nanoparticles and that a synergistic effect is responsible for the catalytic rate enhancement. 

Binder fluid temperature Particle size and distribution... 

The individual graphitic layers are the basic building blocks of carbon black particles. The morphology and particle size distribution of carbon black is dependent on the source material and the process of its thermal decomposition. Particle size and distribution determine directly the specific surface area (SSA) which is one of the most important properties of carbon black for fuel cell applications. High surface area (ranging from a few hundreds to 2000-3000m2 g-1) carbon blacks suitable for fuel cell applications can be obtained from Cabot Corporation (Vulcan XC-72R, Black Pearls BP 2000), Ketjen Black International, Chevron (Shawinigan), Erachem and Denka. 

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