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The origin of the hysteresis, obtained from mercury porosimetry analyses of diatomite filter aids DFA powders and DFA-kaolin based extrudates for fluidized bed applications, is used for fundamental description of the porous network. Pore sizes calculated from the depressurization step, corrected with contact angle of 101.4° and with Kloubek semi-empirical equations, were compared to pores size evaluated with a conventional contact angle of 140.0°. Interestingly same behaviour is observed for DFA powders and extrudates: a hysteresis is observed at 800 °C, while no mercury is removed during the extrusion step for samples heat treated at 1300 °C. These results indicate that the pore structure for extrudates is mainly dominated by the structure of DFA in comparison to the interconnected pores coming from the removal of the organic binders. The presence of contact angle hysteresis was observed by comparing Kloubek and Washburn equations. Similar mesopore size distributions were obtained with using Barret–Joyner–Halenda model and Kloubek equations. This work allows confirming the interest of using Kloubek equations on the whole range of pore size distribution (from the macro- to the mesopores) for siliceous based materials, composed of low cristobalite, quartz and mullite. In case of multi-cycle studies, because of the overestimated pore sizes determined by Washburn equations during extrusion step, Kloubek equations seem to give a better description of the microstructure. |
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