Product properties powder technologies

In spite of the presence of ECC, the sample exhibiting a domain structure remains unoriented on the macroscopic level. Figure 3 c shows a great difference in the structures obtained, if molecular orientation exists and if hydrostatic compression is applied. Although the method of hydrostatic compression of the melt is of paramount importance from the scientific view point just for samples crystallized under pressure it was possible to prove unequivocally the existence of ECC), it does not allow a direct preparation of oriented samples of high strength (they are brittle and readily crumble to powder under minimum strain). However, the material obtained in this way can probably serve as a semi-finished product for further technological treatment that would improve its mechanical 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. 

The physical and mechanical properties of all the final products made of nitride UFPs depend intimately on the smallness and uniformity of its particle size and also on the purity of nitride particles used. For three decades the major efforts have been related to the development of powder synthesis technology. 

Since the properties of these particulate materials are basically determined by their mean size, size distribution, external shape, internal structure, and chemical composition, the science in the mechanistic study of particle formation and the fundamental technology in their synthesis and characteristic control may constitute the background for the essential development of colloid science and pertinent industries. Scientists have now learned how to form monodispersed fine particles of different shapes of simple or mixed chemical compositions, and, as a result, it is now possible to design many powders of exact and reproducible characteristics for a variety of uses. These achievements are especially important in the manufacture of high-quality products requiring stringent specification of properties. 

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