Ceramic powder characterization particle size

This chapter has described the various techniques of ceramic powder characterization. These characteristics include particle shape, surface area, pore size distribution, powder density and size distribution. Statistical methods to evaluate sampling and analysis error were presented as well as statistical methods to compare particle size distributions. Chemical analytical characterization although veiy important was not discussed. Surface chemical characterization is discussed separately in a later chapter. With these powder characterization techniques discussed, we can now move to methods of powder preparation, each of which 3uelds different powder characteristics. 

To characterize a ceramic powder, a representative sample must be taken. Methods of sampling and their errors therefore are discussed. Powder characteristics, including shape, size, size distribution, pore size distribution, density, and specific surface area, are discussed. Emphasis is placed on particle size distribution, using log-normal distributions, because of its importance in ceramic powder processing. A quantitative method for the comparison of two particle size distributions is presented, in addition to equations describing the blending of several powders to reach a particular size distribution. 

The topic of this chapter is how to produce particles of a particular shape, chemistry, and size and then how to characterize them. We are going to describe the methods used to produce ceramic powders, from the traditional ball-milling technique to more recent vapor-phase approaches that can produce nanometer-sized particles. It is worth remembering that powder processing is used to produce some special metals (e.g., tungsten filaments for incandescent lamps), it is used in the pharmaceutical industry, for making catalysts, and it is used to prepare many food ingredients. 

Ceramic powders usually consist of particles with different sizes that are distributed over a certain range. Some powders have a very narrow size distribution, such as those prepared by chemical precipitation under well-controlled conditions, whereas others may exhibit a broad size distribution, such as those made through mechanical milling or solid-state reaction. Some particles have spherical, near spherical, or equiaxial shapes, while there are many cases where the powders are irregular in shape, including rod, wire, fiber, disk, plate, and so on. The importance of characterizing size and size distribution of ceramic particles is due to their effects in the consohdation and sintering behaviors of the powders. 

Surface area of a powder increases geometrically with decreasing particle size, so that the volume fraction of the outermost layer of ions on the surface increase significantly, which has a significant effect on properties of the powder. With the development of nanotechnology, it is readily to synthesize powders with nanosized particles (1-100 nm). Therefore, characterization of surface properties becomes more and more important. Specifically for ceramics or transparent ceramics, the consolidation of fine ceramic powders with liquid suspensions to produce more uniform green bodies has been shown to play an important role in the fabrication ceramics, especially when special or complex structures are required. Because the quality of microstructure of the consolidated body is determined by the dispersion behavior of the powder and the interaction between the particles in the suspension, which is closely related to the surface properties of the particles, controlling the physical and chemical properties of particles is a critical to ceramics fabrication. 

Microscopy is a fairly straightforward technique that offers the advantage of direct measurement of the particle size coupled with simultaneous observation of the individual particles, their shape, and the extent of agglomeration. It usually forms the first step in the characterization of ceramic powders. Optical microscopes can be used for particle sizes down to 1 p.m, while electron microscopes... 

Virtually all of the chemical characterization techniques described in the first volume of this series have been applied to ceramic powders. " The only limitation is in the difficulty of dealing with the small size of the particles. For example, when using surface analysis techniques it is not always possible to characterize individual particles instead, groups of particles are simultaneously analyzed. It would be redundant to discuss the application of these techniques to ceramic powders here. 

Most physical properties of a particulate system are ensembles or statistical values of the properties from their individual constituents. Commonly evaluated particle geometrical properties are counts, dimension (size and distribution), shape (or conformation), and surface features (specific area, charge and distribution, porosity and distribution). Of these properties, characterization of particle size and surface features is of key interest. The behavior of a particulate system and many of its physical parameters are highly size-dependent. For example, the viscosity, flow characteristics, filterability of suspensions, reaction rate and chemical activity of a particulate system, the stability of emulsions and suspensions, abrasiveness of dry powders, color and finish of colloidal paints and paper coatings, strength of ceramics, are all dependent on particle size distribution. Out of necessity, there are many... 

The final properties of the ceramic product will depend upon the powder characteristics. The important characteristics are shape, composition, and size of the powder particles. The characterization techniques also will be described in this chapter. 

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