Porous structure characterisation

Measurements of BET nitrogen surface area at 77 K are frequently used as a standard procedure for characterisation of porous materials. Studies suggested that BET surface area correlates with MOE surface areas determined from crystallographic data. However, heterogeneous surfaces are found in MOEs and it is best to describe the BET surface area as an apparent surface area. If a Type I isotherm has a plateau at high relative pressure, the micropore volume is given by the amount adsorbed (converted to a liquid volume) since the mesopore volume and external surface are both relatively small. Porous structure characterisation parameters (Eangmuir and BET surface areas and pore volumes) obtained from gas adsorption studies of MOEs have interrelated correlations. 

The values of the Michaelis-Menten kinetic parameters, Vj3 and C,PP characterise the kinetic expression for the micro-environment within the porous structure. Kinetic analyses of the immobilised lipase in the membrane reactor were performed because the kinetic parameters cannot be assumed to be the same values as for die native enzymes. 

N. Eisenreich, A. Geifiler, E. Geigler, J. Gotz 2004, (Structure characterisation of foams and filled polymers by means of MRI), Proceedings of the 8 International Conference on Magnetic Resonance in Porous Media, Palaiseau, France, July 7- 9, J. Magn. Reson. 

Both Ksec <1 pore size distribution have been measured experimentcilly for hard-sphere column packing materials (9), but for soft gel packing materials there does not seem to be ciny reliable information presumably because the accepted method of pore structure characterisation in porous materials, mercury porosime-try, cannot be used. However, Ep Ccin be measured for gels without great difficulty from the column calibration curve (as is mcinife-st from Equation 12) provided the calibration is made on the basis of the peak mean position, i.e. the first moment of the peak... 

Wheeler s treatment of the intraparticle diffusion problem invokes reaction in single pores and may be applied to relatively simple porous structures (such as a straight non-intersecting cylindrical pore model) with moderate success. An alternative approach is to assume that the porous structure is characterised by means of the effective diffusivity. (referred to in Sect. 2.1) which can be measured for a given gaseous component. In order to develop the principles relating to the effects of diffusion on reaction selectivity, selectivity in isothermal catalyst pellets will be discussed. 

For pores smaller than 10 m, a molecular sieving effect can be present and the movement of one or more species inside the porous solid occurs due to the molecular interactions between the species and the network of the porous body here, for the description of species displacement, the theory of molecular dynamics is frequently used. The affinity between the network and the species is the force that controls the molecular motion at the same time, the affinity particularities, which appear when two or more species are in motion inside the porous structure, explain the separation capacity of those solids. We can use a diffusive characterisation of species motion inside a porous solid by using the notion of conformational diffusion. 

The dispersion of a liquid that flows inside a porous medium is the macroscopic result of some individual motions of the liquid determined by the pore network of the solid structure. These motions are characterised by the local variations of the velocity magnitude and direction. Accepting the simplified structure of a porous structure shown in Fig. 4.31, the liquid movement can be described by the motion of a liquid element in a +x direction (occurring with the probability p) compared to the opposite motion or —x displacement (here q gives the probability of evolution and Ax represents the length portion of the pore which is not in contact with the nearby pores). Indeed, the balance of probability that shows the chances for the liquid element to be at time t in x position can be written as follows ... 

Characterising the porous structure of Egyptian mortars using thermoporometry, mercury intrusion porometry and gas adsorption manometry... 

In the present study we have had access to various mortars obtained from the Sphinx and the Kephren Valley Temple. The characterisation of the porous structure of these mortars was carried out using thermoporometry, mercury intrusion porometry and gas adsorption. The aim of this communication is to discuss the relevance of these techniques to the study of Egyptian mortars and to compare the superposition of the results thus obtained. 

Thin alumina membranes (Anodise ) with two different nominal pore diameters (20 nm and 200 nm) were obtained commercially (Whatman International Ltd., Maidstone, Kent, UK). These two types of membranes, designated subsequently as A20 and A200 respectively, had a thickness of 50 pm and an overall diameter of either 25 of 47 mm. X-ray diffraction analysis showed that the alumina in the as received membranes was almost amorphous. Subsequent thermal treatment up to 950 °C produced a crystalline structure (y-alumina), without any significant collapse in the porous structure. Here we describe, in general, the characterisation of the untreated membranes. 

Methods for the characterisation of porous structure in membrane materiais... 

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