Sintering particle size distribution effect

The characteristics of a powder that determine its apparent density are rather complex, but some general statements with respect to powder variables and their effect on the density of the loose powder can be made. (/) The smaller the particles, the greater the specific surface area of the powder. This increases the friction between the particles and lowers the apparent density but enhances the rate of sintering. (2) Powders having very irregular-shaped particles are usually characterized by a lower apparent density than more regular or spherical ones. This is shown in Table 4 for three different types of copper powders having identical particle size distribution but different particle shape. These data illustrate the decisive influence of particle shape on apparent density. (J) In any mixture of coarse and fine powder particles, an optimum mixture results in maximum apparent density. This optimum mixture is reached when the fine particles fill the voids between the coarse particles. 

In addition to the use of composite anodes and cathodes, another commonly used approach to increase the total reaction surface area in SOFC electrodes is to manipulate the particle size distribution of the feedstock materials used to produce the electrodes to create a finer structure in the resulting electrode after consolidation. Various powder production and processing methods have been examined to manipulate the feedstock particle size distribution for the fabrication of SOFCs and their effects on fuel cell performance have also been studied. The effects of other process parameters, such as sintering temperature, on the final microstructural size features in the electrodes have also been examined extensively. 

Effect of Particle Size Distribution on Sintering Kinetics... 

The effect of the particle size distribution on shrinkage rates has been considered previously for the initial stage sintering [46]. The problem was treated for the linear shrinkage of a pair of different size spherical particles in contact. These results were extended to distributions of a few discrete sizes by a weighting of all possible contacts. For a continuous distribution in size, this pairwise interaction can be... 

In this case, the "fine" particles and the "coarse" particles were separated so that the difference in size between individual particles was minimized. That is, most of the individual particles in each fraction were almost the same size. Both the fine and coarse particles have a sintering slope of 1/2 but it is the coarse particles which sinter to form a solid having a density closest to theoretical density. This is an excellent example of the effect of pore volume, or void formation, and its effect upon the final density of a solid formed by powder compaction and sintering techniques. Quite obviously, the fine particles give rise to many more voids than the coarser particles so that the attained density of the final sintered solid is much less than for the solid prepared using coarser particles. It is also clear that if one wishes to obtain a sintered product with a density close to the theoretical density, one needs to start with a particle size distribution having particles of varied diameters so that void volume is minimized. 

Coble RL (1973) Effects of particle-size distribution in initial-stage sintering. J Am Ceram Soc 56 461 66... 

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. 

The elegant work of Yeh and Sacks (1988b) emphasized the effect of particle size distribution on the sintering of AI2O3. They used commercial alkoxide derived powders with controlled particle size distribution—one with a narrow size distribution (NSD) and the other with a broad size distribution (BSD). Green compacts with high packing density... 

Table IV and Table V give coke breeze and limestone particle size distribution based on size analysis and the mean particle size of coke breeze and limestone was taken into consideration for analysis of the experiment results. In the pot grate sintering experiments, the mean particle size of coke breeze varied from 2.33 to 0.89 mm while the mean particle size of limestone varied from 2.38 to 1.10 mm to understand the effect of the mean particle on productivity and sinter properties. In each experiment, we just changed the mean particle size of coke breeze and limestone in the sinter mix and kept the taw material proportion constant. The pot grate sintering experimental program is shown in Table VI.

Variants of preparation have been proposed [135, 248] including sintering [391] or co-electrodeposition of the precursors [138, 407], and aluminization of the surface of Ni at high temperature whose nature has a definite effect on the resulting electrocatalytic activity [408]. The main features of Raney Ni have been evaluated, including the pore size distribution and the real surface area [93, 135]. It has been found that the composition of the precursor alloys and their particle size have important influence on the adsorption properties of the resulting Raney metal, hence on its electrocatalytic properties [409]. 

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