Powder compaction data, analysis

Perhaps the most definitive result to come from the early nickel-aluminia synthesis work was the thermal analysis investigation of Hammetter [88HO 88W01], which showed explicit data on substantial changes in the shockec-but-unreacted mixtures. Differential thermal analysis was carried out on th -starting powder compacts of both the mechanically mixed and composite powders. Shocked and unreacted powders were compared to provide direc evidence for substantial changes introduced by the shock process. 

Particle size is one of the principal determinants of powder behavior such as packing and consolidation, flow ability, compaction, etc., and it is therefore one of the most common and important areas of powder characterization. Typically, one refers to particle size or diameter as the largest dimension of its individual particles. Because a given powder consists of particles of many sizes, it is preferable to measure and describe the entire distribution. While many methods of size determination exist, no one method is perfect (5) two very common methods are sieve analysis and laser diffraction. Sieving is a very simple and inexpensive method, but it provides data at relatively few points within a distribution and is often very operator dependent. Laser diffraction is a very rapid technique and provides a detailed description of the distribution. However, its instrumentation is relatively expensive, the analytical results are subject to the unique and proprietary algorithms of the equipment manufacturer, and they often assume particle sphericity. The particle size distribution shown in Figure 1 was obtained by laser diffraction, where the curves represent frequency and cumulative distributions. 

The most basic analysis is the presentation of force versus time or displacement versus time. These curves are different for eccentric and rotary tableting machines. The data given in Figures 12 and 13 are valid for the contact time of the compaction cycle of one single tablet. Due to the eccentric-driven movement of the punches, the force-time curve can be described by a sharp peak at the maximum force evolving at the punches and the displacement-time curve can be described with a sharp peak at the minimum height of the powder bed. For curves of eccentric tableting... 

A digitized representation of powder data is quite compact and is especially convenient for comparison with other patterns, provided a suitable database is available. In addition to a digitized pattern, each entry in such a database may (and usually does) contain symmetry, imit cell dimensions, and other useful information phase name, chemical composition, references, basic physical and chemical properties, etc. Powder diffraction databases find substantial use in both simple identification of compounds (qualitative analysis) and in quantitative determination of the amounts of crystalline phases present in a mixture (quantitative analysis). 

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