Porous powder grains, structure

When the pore size of a packed powder bed or of the structure of porous powder grains is of interest. 

The simplest way of introducing Che pore size distribution into the model is to permit just two possible sizes--Tnlcropores and macropotes--and this simple pore size distribution is not wholly unrealistic, since pelleted materials are prepared by compressing powder particles which are themselves porous on a much smaller scale. The small pores within the powder grains are then the micropores, while the interstices between adjacent grains form the macropores. An early and well known model due to Wakao and Smith [32] represents such a material by the Idealized structure shown in Figure 8,2,... 

The supported layers obtained after treating at 500°C exhibited crystallized structures (anatase for titania and a tetragonal metastable form for zirconia) and revealed a very fine texture from TEM observation. For Ti with a Ti/acac ratio = 1, grains with defined faces can be observed whose size is around 20 nm. For Zr with a Zr/acac ratio = 2, a finer texture was obtained than with titania, with a mean grain size of around 4 nm. In the two cases, powder x-ray diffraction (Sherrer formula) was used to measure an individual crystal size, which is in good accordance with TEM observations. For the zirconia membrane the N2 adsorption and desorption isotherm in Fig. 18a shows a micro-porous domain with a 1.7 nm centered pore size distribution (Fig. 18b). 

TTie specification M1L-P-223B (1962 with Amendment 1—1963) is mandatory for all Department of Defense uses. Its formula is given under No. 146. Black powder is not strictly a mechanical mixture of potassium nitrate, sulfur, and charcoal. During the ball-milling phase of mixing the charcoal and sulfur, the latter is forced into the porous structure of the carbon. This makes the individual grain very dense. Hard compressed larger pellets or columns are relatively nonporous, so that they burn in orderly fashion. 

Fig. 1 XRD patterns of Cu-Cr-0 powder prepared at various GN ratios Fig. 2 shows the SEM images of as-self-combusted CuCrO powders synthesized at various GN ratios. The powders exhibited a porous structure with a cotton-like shape however, as observed in Figs. 3(k) and 3(i), large grains were formed because the high GN ratio caused excessive heat, which promoted grain growth.

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