Ceramic powder characterization distribution

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. 

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. 

Characterization. Ceramic bodies are characterized by density, mass, and physical dimensions. Other common techniques employed in characterizing include x-ray diffraction (XRD) and electron or petrographic microscopy to determine crystal species, stmcture, and size (100). Microscopy (qv) can be used to determine chemical constitution, crystal morphology, and pore size and morphology as well. Mercury porosknetry and gas adsorption are used to characterize pore size, pore size distribution, and surface area (100). A variety of techniques can be employed to characterize bulk chemical composition and the physical characteristics of a powder (100,101). 

The driving force behind the rapid development of powder diffraction methods over the past 10 years is the increasing need for structural characterization of materials that are only available as powders. Examples are zeolite catalysts, magnets, metal hydrides, ceramics, battery and fuel cell electrodes, piezo- and ferroelectrics, and more recently pharmaceuticals and organic and molecular materials as well as biominerals. The emergence of nanoscience as an interdisciplinary research area will further increase the need for powder diffraction, pair-distribution function (PDF) analysis of powder diffraction pattern allows the refinement of structural models regardless of the crystalline quality of the sample and is therefore a very powerful structural characterization tool for nanomaterials and disordered complex materials. 

The extent to which the characterization process is taken depends on the application. In the case of traditional ceramics, which do not have to meet exacting property requirements, a fairly straightforward observation, with a microscope, of the size, size distribution, and shape of the powdCTs may be sufficient. For advanced ceramics, however, detailed knowledge of the powder characteristics is required for adequate control of the microstructure and properties of the fabricated material. Commercial powders are used in most applications. Normally, the manufacturer has carried out most of the characterization experiments and provides the user with the results, generally referred to as powder specifications. The manufacturer s specifications combined with a straightforward observation of the powder with a microscope are sufficient for many applications. 

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... 

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