Particle size, measurement microscopy

ASTM (1976), Annual Book of Standards, Part 4. Particle Size Measurement, Microscopy, E20-69, Reapproved 1984, 148... 

For the particle size measurements of boron and barium dichromate, components of pyrotechnic delay compns, Freeman (Ref 46) evaluated the MSA. Particle Size Analyzer versus microscopy, gravitational liq sedimentation,... 

Particle Size Measurement. The best way to evaluate an emulsion s stability is probably to measure its particle size distribution. A number of methods are available for droplet size determination (see Sec. VIII.A). Optical microscopy, although a time-consuming technique, is a direct way of measuring droplets larger than 1 pm. Nowadays, laser lightscattering, diffraction, and transmission methods are becoming popular for routine determination of particle size [151, 152],... 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

Particle size measurement is one of the essential requirements in almost all uses of colloids. However, our discussion in Section 1.5 makes it clear that this is no easy task, especially since even the definition of particle size is difficult in many cases. A number of techniques have been developed for measuring particle size and are well documented in specialized monographs (e.g., Allen 1990). Optical and electron microscopy described in the previous section can be used when ex situ measurements are possible or can be acceptable, but we also touch on a few nonintrusive methods such as static and dynamic light scattering (Chapter 5) and field-flow fractionation (see Vignette II Chapter 2) in other chapters. 

Particle-size measurements were accomplished with light-scattering techniques. Typical particle-size distributions were established for each polymer by electron microscopy (5). All polymerizations were conducted at 60.0° C in a thermostated bath having a temperature fluctuation of less than 0.03°C. 

Theoretical models based on first principles, such as Langmuir s adsorption model, help us understand what is happening at the catalyst surface. However, there is (still) no substitute for empirical evidence, and most of the papers published on heterogeneous catalysis include a characterization of surfaces and surface-bound species. Chemists are faced with a plethora of characterization methods, from micrometer-scale particle size measurement, all the way to angstrom-scale atomic force microscopy [77]. Some methods require UHV conditions and room temperature, while others work at 200 bar and 750 °C. Some methods use real industrial catalysts, while others require very clean single-crystal model catalysts. In this book, I will focus on four main areas classic surface characterization methods, temperature-programmed techniques, spectroscopy and microscopy, and analysis of macroscopic properties. For more details on the specific methods see the references in each section, as well as the books by Niemantsverdriet [78] and Thomas [79]. 

Bulk chemical analyses of the products were determined by atomic absorption spectroscopy (Al) and gravimetric analysis (Si). The two samples of ZSM-5 were distinguished by noting the nominal Si Al ratio in parentheses as shown in Table I. The average particle sizes measured by electron microscopy are also shown in Table I. 

By electron microscopy the size of the primary particles in the aggregates is estimated to be about 10 nm. Particle size measurements using a nanosizer show the size of aggregates dispersed in a well wetting solvent to be in the range of 100 nm. Laser diffraction of fumed silica dispersed in air provides sizes of agglomerates larger than 5 pm. 

In view of the problems involved with the particle size measurement of soft particles by electron microscopy and the uncertainty In surface coverage by oleate soap molecules which were discussed in the introduction, agreement between the V/S average electron microscope measurements and polymerization rate measurements for these latexes Is quite acceptable. 

In some cases particle size measurements were also performed by electron microscopy and nitrogen adsorption. 

Particle Size Measurements Using Optical Microscopy... 

Washington (1992) has discussed the concepts and techniques of particle size analysis and its role in pharmaceutical sciences and other industries. There are many different methods available for particle size analysis. The techniques most readily available include sieving, optical microscopy in conjunction with image analysis, electron microscopy, the Coulter Counter and laser diffractometers. Size characterization is simple for spherical particles, but not for irregular particles where the assigned size will depend on the method of characterization used. Table 6.2 lists particle size measurement methods commonly used and the corresponding approximate useful size range (Mullin 1993). 

Particle size measurement with microscopy is a direct observation method, where individual particles are observed directly, so that their shape and the degree of agglomeration can be identified at the same time. It provides straightforward information on a ceramic powder. There are three types of microscopies optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Optical microscopes can be used for particle sizes larger than... 

For mica minerals, aspect ratio is defined as the average ratio of the average diameter of all particles to the average thickness of all particles. Until recently it has been impossible to accurately determine aspect ratios of different products. Attempts at predicting aspect ratio were made by measurement of diameters and thickness of individual particles using scanning electron microscopy. It is now possible to make this measurement with modern particle size measurement equipment. Research is currently underway to determine and develop a correlation of the aspect ratio of mica in processed polypropylene composites to observed mechanical properties. 

Dodecyl acrylate microspheres, crosslinked with hexanediol diacrylate, were prepared by emulsion polymerisation and characterised by scanning electron microscopy, particle size measurement, and differential scanning calorimetry. The microspheres were doped with 9-(diethylamino)-5-(octadecanoylimino)-5H-benzo(alpha)phenoxazine (ETH 5294), a chromoionophore whose fluorescence emission spectrum is sensitive to pH. These microspheres adsorb anions selectively according to their lipophilicity, and therefore can be used as anion-selective optical sensors. The responses of the microspheres to chloride, nitrate and perchlorate ions were reported. 27 refs. 

Particle size measurements are usually made from micrographs. The method is extremely tedious if it is done manually. Automatic image analysis of micrographs or an electronic display can reduce the amount of work considerably. Normally a large number of particles (a few hundred) need to be measured. As would be apparent, microscopy produces a particle size distribution based on the numbCT of particles within an appropriate size range. 

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