Particle size, measurement properties

A-11 Particle Size Measurement, 434 A-l 2 Viscosity Conversions, 435 A-13 Viscosity Conversions, 436 A-14 Commercial Wrought Steel Pipe Data, 437 A-15 Stainless Steel Pipe Data, 440 A-16 Properties of Pipe, 441 A-17 Equation of Pipes, 450 A-l 8 Circumferences and Areas of Circles, 451 A-19 Capacities of Cylinders and Spheres,... 

Suspensions are generally evaluated with respect to their particle size, electrokinetic properties (zeta potential), and rheological characteristics. A detailed discussion on the methods/techniques and relevant instrumentation is given in Sec. VII. A number of evaluating methods done specifically with suspension dosage forms, such as sedimentation volume, redispersibility, and specific gravity measurements, will be treated in this section. 

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]. 

With the development of powder metallurgy a vast new field has recently been opened in which the value of particle-size measurements and packing behavior will play an important role. Selection of the proper combination of sizes and their relation to void structure will be fundamental considerations. A knowledge of the electrical and gas adsorption properties of fine powders should also prove of inestimable value in this field. 

Powder properties and behavior, sampling, numerous potential particle size measuring devices, available equipment as well as surface and pore size are his principal themes. 

The measurement of particle size is a key issue in the formulation of many pharmaceutical products. Particle size distribution is known to directly influence physical properties of powders, such as dissolution rate, powder flow, bulk density, and compressibility. Conventional methods of particle size measurement include sieve analysis and laser diffractometry. ... 

There is a wide variety of methods for particle size measurement which measure different types of particle size. When selecting a method, it is best to take one that measures the type of size which is most relevant to the property or the process which is under study. Thus, for example, in powder elutriation, pneumatic conveying or gas cleaning, it is most relevant to use one of the sedimentation methods which measure the Stokes diameter, i.e. the diameter of a sphere of the same density as the particle itself, which would fall in the gas at the same velocity as the real particle (assuming Stokes law). In flow through packed or fluidized beds, on the other hand, it is the surface-volume diameter (or diameter... 

It is well known that particle shape affects many secondary properties relevant to powder handling such as the bulk density, failure properties or particle-gas interaction. For non-spherical particles, the results obtained with different methods of particle size measurement are, in general, not comparable. From the point of view of powder handling, flaky or stringy particles like wood shavings, mica or asbestos fibres are known to be difficult because they interlock and form obstructions to flow. 

Based on the above-mentioned six key properties of reversed phases, the stationary phases can be characterized. A wide variety of literature exists on this subject [9-15]. Of course, the synthesized stationary phases can be subjected to a full physicochemical examination (nitrogen adsorption measurements to determine the specific surface area, the pore volume and the pore size, CHN analysis to determine the surface coverage of the stationary phase, particle size measurements, etc.). However, all these characterizations are not really to the point, because in the end only the chromatographic separation counts. As a result, chromatographic tests for the characterization and classification of reversed phases have established themselves, from which a representative few, without any claim to being exhaustive, are presented here (Figures 4.1—4.3). 

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. 

The particle size measurement of the raw materials is usually done by the supplier or the manufacturer. For the interpretation of those results it is necessary to know the principles of some methods. In the design phase, during in-process controls and at final testing, it is important to choose the particle size measurement method that is relevant to the property for which the particle size is investigated. Next to the determination of the particle size, a description of the nature of particles (crystals, agglomerates or aggregates) may be recommended. 

Appendix 1. Particle size range of aerosol particle properties and measurement instruments (a) Application range for aerosol particle size measuring instruments, and (b) size range of aerosol particle properties. 

At the simplest level we use particle size measurements to monitor their concentration or to control the reproducibility of a product. Thus, we compare what we find with what we expect and if the two do not coincide we reject the product. The science of powder technology, however, is concerned to use the microscopic properties of the system, for example the particle size distribution, to interpret the bulk behaviour of the powder. If it is to be used in dilute circumstances, then the bulk behaviour can be derived by integrating the behaviour of the individual particles but usually this is not so and the relationship between the microscopic and macroscopic properties must take account of the particle interactions. By observing the difference in particle size distribution of samples which exhibit a different bulk behaviour, we begin to make a "correlation" between the two which, whether empirical or theoretical, quantitative or qualitative, involves interpretation of the mechanisms involved. Somewhere between these two purposes usually lies the purpose of a particle size measurement. There is, however, a far more ambitious level at which powder technology must eventually operate and, as yet, rarely does. That is to design the particles and the particle mixture to produce required properties, to use the relationships between microscopic and macroscopic properties in a predictive manner. It is the more rigorous use of particle size measurements which introduces the real diversity and which requires the measurements to be carefully matched to the problem. The increased diversity does not alter the basic needs which Heywood described. 

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