Low melting point alloy impregnation

In conclusion it would appear that the combination of 3-D stochastic pore networks with mercury porosimetry and low melting point alloy impregnation offers a new framework for the description and calculation of the role of pore spaces in typical porous catalyst particles. 

Figure 17 Low-melting-point alloy impregnation of FCC catalyst panicles.

The technique of impregnation with low melting point alloy results in a freezing of the state of penetration in 3-dimensions amongst the pore spaces. An impregnated sample of powder can then be sectioned and polished and, if viewed on an SEM, affords a view of a 2-D random plane through the 3-D pore spaces. The alloy used melts at 47 C. Impregnation has been performed at around 60 C (in a hot water bath) so that samples are solid at room temperature. 

Figure 8 shows a part of a section of an impregnated powder sample with a field size of approximately 500 pm x 500 pm. This field contains sections through about 250 powder particles, and it is clear that the extent of penetration amongst individual particles shows a very great variance. Indeed, about 50 particles (around l/5th of the total) show negligible penetration of low melting point alloy For the purposes of the present analysis, attention will be focused on the typical particle shown in Figure 9. This particle is the one located just lower than, and left of the centre of Figure 8. It has a typical penetrated porosity of 0.33 and an apparent diameter of about 60 pm. The section in Figure 9 probably passes close to the particle centre, since particles are of this order of diameter.

Figure 8. Low melting point alloy (LMPA) impregnation at 50 atmos (Reproduced with permission. Copyright 1993 Institution of Chemical Engineers.)...

In this section, two examples are presented for the application of a technique of low-melting-point alloy (LMPA) impregnation that provides for a visualization of the invasion of a nonwetting fluid into the pore spaces in a typical porous article. The visualization can be linked to the modeling of mercury porosimeter curves using 3-D stochastic pore networks. This makes the quantification of pore structure more direct. Quantified structures can be visually examined against sample particle sections. The visual comparison can be made more precise by image analysis of the accessible porosity made visible by metal penetration over a series of pressures. 

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