Mercury porosimetry experimental results

We found the latter factor-voids to be important. Experimental results showed that when green coke was calcined under the new methods, and the derived calcined coke was observed by scanning electron microscopy (Figure 2) and its pore size distribution was measured by mercury porosimetry (Figure 3), microcracks of significant sizes (1 to 60 microns) were developed. This was an important contribution to the reduction of the thermal expansion coefficients of the calcined coke processed under the new method. 

Whereas from nitrogen sorption data a size distribution can only be extracted for mesopores (with pore diameter 2 nm < dp < 50 nm), standard mercury porosimetry is used to obtain complete pore size distributions in the pore diameter range from 7.5 nm to 150 [im. During the characterization experiment, the sample is first surrounded and then progressively intruded by mercury, as the pressure is increased. Experimental results are commonly plotted as invaded pore volume versus applied pressure (see Fig. 5.9a). The Washburn equation describes at which (capillary) pressure a cylindrical pore of diameter dp is invaded... 

A new experimental procedure based on the isothermal desorption of vapour is proposed to extend the domain of characterisation of porous solids and powders by capillary condensation until the macropore range. The set-up is based on the use of a Tian-Calvet type microcalorimeter that insures a lull control of temperature gradients around the sample and allows the desorption isotherm to be determined very close to the saturation pressure. The principle of the experiment is described and the first results obtained for water desorption are compared to measurements based on gravimetry as well as to pore size distributions obtained by mercury porosimetry. 

In Table 2, results obtained by image analysis and by mercury porosimetry are reported for plate shape slabs calcined at 1100-1200 and 1300°C (TP2). The agreement between the results obtained by the two methods is encouraging. These results were determined in the same pore radius range (tp > 7.5 nm). In our experimental conditions, it may be computed that one pixel is equivalent to a pore diameter of 15 nm. 

Drug Substance (DS) Specific Surface Area (SSA) has been estimated by permeabilimetry, gas adsorption, laser light scattering and Mercury Intrusion Porosimetry (MIP). Because of the simplifying and different assumptions made, none of these experimental methods can provide the absolute SSA value and a perfect agreement between the values obtained by each technique is not found However, differences in theoretical assumptions made for each technique and observed results have been useful for understanding and interpreting the texture of the powder studied. 

It has been found that models for the structure of sol-gel silica spheres, constructed foom spin density and spin-spin relaxation time images, give rise to good predictions for tiie point of separation of mercury intrusion and retraction curves, and the level of mercuiy entrapment, found for experimental porosimetry data for the same material. This finding suggests that the MR images contain sufficient information to determine the level of mercury entrapment. Hence, this result supports the view that mercury intrusion and retraction within this material is determined by macroscopic (0.01-1 mm) heterogeneities in the spatial distribution of porosity and pore size. 

---