Real Powder

This is the size of each particle of an artificial mono-disperse powder such that the same number of particles to equal the mass of the real powder. 

This is the size at whieh eaeh partiele of a mono-disperse representation would have for the saiue number of partieles to have equal surfaee area as the real powder. 

Note that mosaic artifacts can also occur physically in real spectra when a real powder sample of a model compound exhibits microcrystallinity and thus contains too few different molecular orientations. This phenomenon is rare in X-band EPR and is usually easily solved by grinding the sample in a mortar it is, however, not at all uncommon even for extensively ground samples in high-frequency EPR with single-mode resonators where the sample size is orders of magnitude less than that of an X-band sample. 

In any real powder, there will be a range of void sizes fiUed at different rates. This means that the overall volume compaction will be a sum of all the rates for the different sizes of holes. 

Tsubaki et. al. [44,45] argue that many of the proposed shape factors have little practical relevance to the analysis of real powders until the advent of electronic equipment and the computer. They define six shape indices based on the following diameters (see Table 2.1) d, d dp, dp. The shape... 

The characteristics of ideal powders and real powders produced by hydrothermal processing are shown in Table 1.6 and Table 1.7. Hydrothermal powders are close to ideal powders. 

The complex nature of the sintering process in real powder systems coupled with the drastic simplifications assumed in the models means that quantitative testing of the sintering models is seldom meaningful. Nevertheless, the models clearly indicate the parameters that must be controlled to promote densification. Because of the strong... 

Figure 1.9 Illustration of the reciprocal lattice associated with a single crystal lattice (left) and a large number of randomly oriented crystallites (right). A real powder consists of so many grains that the dots of the reciprocal lattice form into continuous lines.

To prepare it, use one, two, or ten pounds of Real Powder zhensha, cinnabar), in the desired amount according to your wealth. 

Real Powder is a secret name of cinnabar. In the Liquid Pearl, 1.4b, the ingredient of this elixir is called Vermilion Child zhu er), an abbreviated form of Vermilion Child Who Descends on the Mound (jiangling zhu er), which the Shiyao erya (Synonymic Dictionary of the Materia Medica ... 

Most industrial mixtures fail to conform to the statistically ideal pattern of equi-sized particles distinguishable only by colour. It is for this reason that equations (2.5) and (2.6) are so important in establishing the best attainable limits of mixture quality. The statistically precise work of Stange was applied to real powder mixtures by Poole, Taylor and Wall . This application involved assumptions and estimations which in view of the central value of the equation are worthy of investigation. 

Numerical simulations of sintering with diffusion mechanisms, such as surface diffusion and rain boundary diffusion, have been conducted and reported in the literature [39 3]. In such simulations, the three-dimensional real powder systems are simplified to two-dimensional geometrical models. 

Explain why the shrinkage equation derived from a two-particle model cannot be applicable to the prediction of the shrinkage of a real powder compact with a particle size distribution. 

In real powder compacts where the dihedral angle is, in general, around 150°(j/, (l/3)j/ y-(l/2)3/ ), the pores smaller than the average grain satisfy the... 

What does a high dihedral angle mean in the initial and final stage of sintering of real powder compacts ... 

A brush of many thin wires, oriented in a parallel way and constrained to be in lateral contact, provides a useful and geometrically weU-deflned model of a porous electrode. Of course, the model pores are linear and of anticyUndrical cross section while pores in a real powder electrode, or an electrode made from unoriented carbon fibers, are of random size and geometry. 

The analytical models assume a relatively simple, idealized geometry for the powder system, and for each mechanism, the mass transport equations are solved analytically to provide equations for the sintering kinetics. A problem is that the microstructure of a real powder compact changes continuously as well as drasti-... 

The microstructure in the final stage can develop in a variety of ways, and we shall consider this in detail in Chapter 9. In one of the simplest descriptions, the final stage begins when the pores pinch off and become isolated at the grain corners, as shown by the idealized structure in Fig. 8.8d. In this simple description, the pores are assumed to shrink continuously and may disappear altogether. As outlined in Chapter 1, the removal of almost all of the porosity has been achieved in the sintering of several real powder systems. 

Some of the main parameters associated with the three idealized stages of sintering are summarized in Table 8.4, and examples of the microstmctures (planar section) of real powder compacts in the initial, intermediate, and final stages are shown in Fig. 8.9. 

The other simplifying assumptions of the models must also be remembered. The extension of the two-sphere geometry to real powder compacts is valid only if the particles are spheres of the same size arranged in a uniform pattern. In practice, this system is, at best, approached only by the uniform consolidation of monodisperse powders by colloidal methods (see, for example, the work of Barringer and Bowen discussed in Chapter 1). Coble (17) considered the effect of a particle size distribution on the initial stage of sintering by considering a linear array of spheres. 

For polycrystalline materials, the sintering phenomena are considerably more dependent on the structural details of the powder system. Because of the drastic simplifications made in the models, they do not provide an adequate quantitative representation of the sintering behavior of real powder systems. The models do, however, provide a good qualitative understanding of the different sintering mechanisms and the dependence of the sintering kinetics on key processing parameters such as particle size, temperature, and, as we shall see later, applied pressure. 

The assumptions made in the models must be remembered. The models assume a geometry that is a drastic simplification of a real powder system. They also assume that each mechanism operates separately. Although attempts have been made to develop analytical models with more realistic neck geometries [e.g.. 

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