Mercury porosimetry hysteresis

A. Tsetsekou and G. Androutsopoulos, Mercury porosimetry hysteresis and entrapment predictions based on a corrugated random pore model, Chem. Eng. Comm., 110 (1991) 1. 

Lowell S. and J. E. Shields (1984). Theory of mercury porosimetry hysteresis . Powder Technology 38 121-124. 

In their original work Drake and Ritter found that the curves of volume against pressure for the penetration and withdrawal did not coincide. Numerous investigations since then have confirmed that hysteresis is a general feature of mercury porosimetry. 

Perhaps the best known explanation of reproducible hysteresis in mercury porosimetry is based on the ink bottle model already discussed in connection with capillary condensation (p. 128). The pressure required to force mercury with a pore having a narrow (cylindrical) neck of radius r, will be... 

Experimental techniques commonly used to measure pore size distribution, such as mercury porosimetry or BET analysis (Gregg and Sing, 1982), yield pore size distribution data that are not uniquely related to the pore space morphology. They are generated by interpreting mercury intrusion-extrusion or sorption hysteresis curves on the basis of an equivalent cylindrical pore assumption. To make direct comparison with digitally reconstructed porous media possible, morphology characterization methods based on simulated mercury porosimetry or simulated capillary condensation (Stepanek et al., 1999) should be used. 

Two methods are used to measure the pore size distribution in a powder mercury porosimetry and adsorption-desorption hysteresis. Both methods utilize the same principle capillary rise. A nonwetting liquid requires an excess pressure to rise in a narrow capillary. The pressure difference across the interface is given by the Young and Laplace equation [15]. 

Gas adsorption Is most widely used to assess porosity, especially by analyzing the hysteresis loops appearing in the isotherms due to capillary condensation in pores (fig. 1.13 types IV and V). However, there are a number of alternatives. Including mercury porosimetry, neutron and X-ray scattering. 

The texture properties of the ultrathin porous glass membranes prepared in our laboratory were initially characterized by the equilibrium based methods nitrogen gas adsorption and mercury porosimetry. The nitrogen sorption isotherms of two membranes are shown in Fig. 1. The fully reversible isotherm of the membrane in Fig. 1 (A) can be classified as a type I isotherm according to the lUPAC nomenclature which is characteristic for microporous materials. The membrane in Fig. 1 (B) shows a typical type IV isotherm shape with hysteresis of type FIl (lUPAC classification). This indicates the presence of fairly uniform mesopores. The texture characteristics of selected porous glass membranes are summarized in Tab. 1. The variable texture demanded the application of various characterization techniques and methods of evaluation. 

The mercury porosimetry intrusion-extrusion data is shown in Fig. 3. Two types of behaviour can be observed. In the case of mN2 and mEl the pores are filled at relatively low pressure and the extrusion curve is horizontal with negligible hysteresis. mVT4 and mlO show intrusion at higher pressures and hysteresis on extrusion - reintrusion corresponding to this high pressure region. 

Mercury porosimetry is governed in each pore by an equilibrium force/surface tension balance (the Washburn equation) that relates the diameter of a cylindrical pore to the pressure needed to force mercury into it. The pressured step-by-step invasion of a pore network is then controlled by a pattern of pone accessibly at each given pressure. Systematic penetration, starting from an empty network surrounded by mercury, can be readily performed. Results for the network in Fig. 5 are given in Fig. 6, showing both the penetration curve and the retraction curve. Stochastic pore networks implicitly predict hysteresis between penetration and retraction as well as a residual final entrapment of mercury. In Fig. 6, the final entrapment is about 45%, with much of the retained mercury entrapped in the larger pores [11]. More details of the pore-by-pore calculation have been published [4]. 

Ioannidis, M.A., and I. Chatzis. 1993. A mixed-percolation model of capillary hysteresis and entrapment in mercury porosimetry. J. Colloid Interface Sci. 161 278-291. 

The use of complementary experimental techniques as a numerical and visual basis in the formulation of more realistic and applicable pore structure characterisation models has become widespread. Examples of the use of these techniques include mercury porosimetry [9] in the study of entrapment hysteresis in porous media, and in the characterisation of permeable solids [7], the use of NMR (nuclear magnetic resonance) in the heterogeneous and hierarchical stractural modelling of porous media [8,10], and flie use of SEM imaging techniques [7,11]. 

H. Giesche, K.K. Unger, U. Muller, and U. Esser Hysteresis in nitrogen sorption and mercury porosimetry on mesoporous model adsorbents made of aggregated monodisperse silica spheres, CoUoids Surf., 37 (1989) 93-113... 

H. Giesche Interpretation of hysteresis fine-structure in mercury-porosimetry measurements, in Materials Research Society Symposium Proceedings, Volume 371, Advances in Porous Materials (Komarneni S., Smith D.M. Beck J.S., eds) Materials Research Sodety, Pittsburgh, PA (1995) 505-510... 

Liabastre and Orr [52] examined graded series of controlled pore glasses and Nuclepore membranes by electron microscope and mercury porosimetry in o er to determine compressibilities and explore the reason for hysteresis. 

It is not common practice to measure the contact angle and, indeed, there is some evidence that its value is affected by surface roughness. The hysteresis encountered in mercury porosimetry may be completely removed by the use of different contact angles for intrasion and extrusion. On this basis the use of hysteresis to predict pore shape may lead to erroneous and misleading data. 

Microporosity (< 20 A) is best examined using nitrogen ad/desoiptioa While diffinent physics are at work in characterizing sorption data, the effects of network stroctuie yielding hysteresis in the adsorption and desorption profiles is similar to that found from mercury porosimetry (ref. 12) for mesopores. 

W.C. Conner, A.M. Lane, and A.J. Hoffman, Measurement of the Morphology of High Surface Area Solids Hysteresis in Mercury Porosimetry, Journal of Coll, and Int. Sci., 100(1) (1984) 185-193. 

It is evident that the permeability of the heated and rehydrated cements was not simply controlled by the pore volume as determined by mercury porosimetry. Howeveri the shape of some of the mercury intrusion curves in Figures 1-4 indicates that at the maximum attainable pressure mercury did not penetrate into the narrowest pores of the heated or rehydrated samples. Furthermore the extensive intrusion-extrusion hysteresis and the large entrapment of mercury are features generally associated with complex pore networks made up of interconnecting channels and cavities of different dimensions. 

Salmas C. and G. Androutsopoulos (2001). Mercury porosimetry Contact angle hysteresis of materials with controlled pore structure . Journal of Colloid and Interface Science 239 178-189. 

Being able to identify the necessary properties to define a porous medium in no way implies that there are analytical methods to evaluate them. Using porosimetry and sorption, it is possible to measure 6 properties of the porous medium structure (refe. 5-7). It is not clear that these measures are independent. These properties are obtained by analyzing both mercury intrusion and retraction profiles (i.e., the nature of the hysteresis commonly found with most porous materials). These properties are enumerated below ... 

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