Particle size distribution visual methods

To account for scale-up effects, especially using dissimilar equipment, formulators have employed a variety of approaches. Typically, trial and error adjustments, empirical correlations between known machines, and several geometric rules of thumb have been devised. Usually, trial and error approaches will alter the amount of granulation liquid used, the post-liquid addition mixing time kneading, or the liquid addition rate to arrive at an acceptable formulation upon scale-up. Although particle size distribution and bulk/tap density measurements may be used to establish equivalence in these methods, often visual judgments are made by experienced operators on the floor with a feel for proper appearance and manual consistency. 

As an economical and rapid method to control the quality of portland cement, the value of routine clinker microscopy should be an inescapable conclusion from the numerous observations and interpretations given on previous pages. Quality control of clinker without microscopy of raw feed, in the writer s opinion, is less than adequate. Profound cause-effect relationships exist between the raw feed/particle size distribution, energy required for grinding and burning, clinker quality, and cement performance. Visually appreciating the characteristics of raw feed via microscopical examination gives additional comprehension to quality control. 

To avoid these problems, polymer dispersions are routinely tested for mechanical and storage stability and, for certain applications, also subjected to freeze-thaw cycles. After testing, any changes can be inspected visually or quantified using the methods available for assessing the coagulum, the viscosity or the particle size distribution. 

Other measurements important to visual air quality are pollutant related, i.e., the size distribution, mass concentration, and number concentration of airborne particles and their chemical composition. From the size distribution, the Mie theory of light scattering can be used to calculate the scattering coefficient (20). Table 14-2 summarizes the different types of visual monitoring methods (21). 

Microscopy is often referred to as an absolute method for the determination of size and size distribution of small particles because it allows direct visualization and measurements of individual particles. Three commonly used types are optical microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). 

Refined methods for combining the Kelvin relationship with adsorption equations for obtaining pore size distribution have recently been suggested (Barrett and Joyner, 2 Shull, Elkin, and Roess, 57 Wheeler, 64, 64a). With some experience, however, simple visual inspection of the isotherms proper provides a reasonable impression of the relative pore size distributions. It must be borne in mind when considering pore structure and particularly the structure of high area gels that the shape of the ultimate particles and thus the shape of the pores is not known. It remains to be established whether the particles are platelets, fibers, spheres, or complex combinations of many structures. 

SEM has been a primary tool for characterizing the fundamental physical properties of oxide materials for some time. For example, SEM is particularly useful for determining the particle shape and approximate size distribution of various silica materials used as supports in chemically bonded stationary phases for chromatography [8]. The visual images provide resolution at the micron to in some cases the submicron level so that surface morphology can be determined. This information is especially useful when evaluating a new synthetic approach to the formation of oxide materials. For example, a recently developed method... 

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