Microscopy particle size determination

The specific surface estimated from particle size determined by electron microscopy was I lOm g . 

Because XPS is a surface sensitive technique, it recognizes how well particles are dispersed over a support. Figure 4.9 schematically shows two catalysts with the same quantity of supported particles but with different dispersions. When the particles are small, almost all atoms are at the surface, and the support is largely covered. In this case, XPS measures a high intensity Ip from the particles, but a relatively low intensity Is for the support. Consequently, the ratio Ip/Is is high. For poorly dispersed particles, Ip/Is is low. Thus, the XPS intensity ratio Ip/Is reflects the dispersion of a catalyst on the support. Several models have been reported that derive particle dispersions from XPS intensity ratios, frequently with success. Hence, XPS offers an alternative determination of dispersion for catalysts that are not accessible to investigation by the usual techniques used for particle size determination, such as electron microscopy and hydrogen chemisorption. 

The size of particles is of great importance, and particle size determinations should be carried out in preformulation as well in formulation functions. For small particle sizes, simple microscopy [41] may be used, but again imaging techniques, particularly with motorized stages, are more representative and much easier to carry out [42],... 

With such a definition, it was found that vfc at 445 K did not change within experimental error as the average Pd particle size, determined by transmission electron microscopy (TEM), was varied between 1.5 and 8.0 nm (Figure 1). Besides, this value of v was also the same as that reported for the ill face of a single crystal of Pd (2), the latter value being itself very much the same on other planes of Pd or on a polycrystalline wire (3). 

Particle-Size Determination Particle-size of the cleaned1 latexes were determined using transmission electron microscopy after freeze-drying the samples and counting the particles with a Quantimet image analyzer. The number average particle diameters ( n) of the homopolymer, the 85/15 VA/BA and 70/30 VA/BA latexes were found to be 0.Q57/ m, 0.062/<.m and 0.073 m, respectively. 

For the first time, TIRE-LII has been successfully applied to the characterization of in liquids suspended nanoparticles. Re-dispersed carbon blacks were investigated in different solvents, whereby a linear correlation between the exponential LII signal decay time and the primary particle size determined by transmission-electron microscopy was found. 

X-ray powder diffraction data may be helpful but are often hard to interpret for complex mixtures use of computer data file search programs (6) and microcamera methods for single particle analysis (7) may be useful for identification. Comparative sample identification is generally less often possible than for metals since the latter are manufactured while the nonmetallic inorganic solids are often unprocessed materials with large property variations. However, where applicable, the following are some examples of determinations which might be made (a) particle size by microscopy (b) microstructure and sub-microstructure characterization... 

The relationship between crystallites and particles with respect to XRD is shown in Figure 2. The morphological "crystal" "c" is composed of anisotropic crystallites with dimensions "a,b". The arrows show the difference in dimension detected by XRD (a,b in two dimensions) and by other methods not requiring coherent scattering methods such as electron microscopy or gas adsorption. It is obvious that there may be little relationship between the particle size determined by microscopy or surface area analysis and the... 

Two main techniques have been used to determine the particle size distribution of colloidal systems PCS and electron microscopy including both SEM and TEM. The QELS technique for Brownian moment measurement, offers an accurate procedure for measuring the size distribution of nanoparticles. The PCS technique does not require any particular preparation for analysis and is excellent due to its efficiency and accuracy. However, its dependency on the Brownian movement of particles in a suspended medium may affect the particle size determination. 

Microspheres intended for nasal administration need to be well characterized in terms of particle size distribution, since intranasal deposition of powder delivery systems is mostly determined by their aerodynamic properties and particle sizes. Commonly used methods for particle size determinations described in the literature are sieving methods [108], light microscopy [58], photon correlation spectroscopy [66], and laser diffractometry [25,41,53,93], The morphology of the microparticles (shape and surface) has been evaluated by optical, scanning, and transmission electron microscopy [66, 95],... 

These processes must be monitored to confirm that the second polymer does not emerge as a separate particle type. Re-nucleation, producing a crop of new particles, may be detected by progressive determination of particle size and comparing actual with the theoretical size calculated on the basis of constant particle number. This is easier to do in those processes where the monomer for the second polymer is added slowly at a steady and known rate and samples can be taken at regular time intervals for particle-size determination by electron microscopy, photon correlation spectroscopy or by disc centrifuge photo-sediometry. For particles prepared by non-aqueous dispersion... 

The obtained latex is then characterized by its coagulum content and its particle size determined by photon correlation spectroscopy or electron microscopy. The results are given in Table V and VI. 

In a recent publication Dumeslc c.s. described adsorption and desorption measurements of H2 on Ni/Ti(>2 and Pt/Ti(>2 catalysts, which showed that a larger amount of H2 could be desorbed (after 15-20 h equilibration of these catalysts under about 40 kPa H2) than could be directly adsorbed (32). In agreement with our conclusions their explanation was that, apart from a fast H2 adsorption on the metal, hydrogen apparently also adsorbed slowly on the Ti02 support via a spillover process from metal to support. These authors noticed that the amounts of H2 desorbed from the M/Ti(>2 catalysts in the SMSI state were in fair agreement with metal particle sizes determined by X-ray line broadening and electron microscopy and suggested that H2 desorption could be used to estimate metal... 

The most difficult part of particle size estimation is related to the determination methods themselves. Particle size determination is complicated by size distribution, the presence of particle associations, and the shape of particles. If particles are not spherical, more than one parameter is needed to describe them and if the shape of the particle is irregular, numerous parameters are needed to express their dimensions. The method used for particle size determination (sieving, light scattering, microscopy, etc.) determines what dimensional aspects are measured. In addi-... 

In other Pt-doped monolithic carbon aerogels, prepared by adding the Pt pre-cnrsor to the initial R/F mixture [41], the Pt particle size determined by H2 chemisorption was mnch higher than that determined by high-resolution transmission electron microscopy (HRTEM). This indicates that some Pt particles were encapsnlated by the carbon matrix and were consequently inaccessible to H2. This can be the main problem of this preparation method when the metal-doped carbon gel is to be used as catalyst, because part of the metal will not be accessible to the reactant molecules. 

Carbon monoxide chemisorption was measured at 25 °C on all catalysts tested. The results were used in calculations of turnover numbers, assuming only rhodium metal atoms chemisorbed CO. While this assumption is naive and probably incorrect (10), results correlated moderately well with rhodium particle size determinations by transmission electron microscopy. 

Synthesized powders were calcined and characterized by standard techniques of thermogravimetric analysis, BET specific surface area measurements, and particle size determination by sedigraphy, as well as X-ray diffraction, and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) for microchemical analyses. To... 

Multiple techniques can be used to measure the particle size distribution, for example electrozone sensing, sedimentation, laser diffraction, and microscopy. With the exception of microscopy, they all require calibration and the results depend on the technique. For example, in a round-robin study reported in Reference 4, the commonly used electrical sensing zone technique (Coulter Counter) was compared to microscopy and sedimentation. The average particle size determined by the electrical sensing zone method was by about 25%... 

Electron Microscopy. The electron microscope provides a direct method for determining dimensions of colloidal particles (Figure 4.7). With improved equipment, individual particles as small as only 1-2 nm can be discerned, but measuring the diameter of particles smaller than 5 nm is difficult. Alexander and Her (142) first demonstrated that the particle size of colloidal silica measured by the electron microscope correlated well with particle size determined by light scattering in solution, and also with the size calculated from the specific surface area of the dried silica powder. 

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