Hysteresis In Mercury Porosimetry Research Articles

MF-DFT and Experimental Investigations of the Origins of Hysteresis in Mercury Porosimetry of Silica Materials

In order to be able to make a proper interpretation of mercury porosimetry data, to obtain a structural characterization of a porous solid, a full understanding of the causes of hysteresis in mercury porosimetry is required. Several different theories have previously been proposed, but it is still difficult to make a priori predictions of the level of hysteresis anticipated. In this work, the effect of the degree of smaller scale surface roughness on the hysteresis width has been studied using mean-field density functional simulations and the results obtained confirmed by experiments on silica materials. It has been found that the hysteresis width decreases with increased degree of surface roughness, as characterized experimentally by the surface fractal dimension.

The Physical Significance of Mercury Porosity Hysteresis in the Characterization of Calcined Precipitated Alumina

AbstractActivated alumina, for application as a catalyst support or as an adsorbent, is often obtained industrially via calcination of precipitated aluminum oxide hydrate. Its preparation conditions depend on the ultimate application, which, in turn, dictates its target specifications, e.g., surface area (SA), total pore volume (PV), pore size distribution (PSD) and density. Invariably, some method of porosity characterization is required periodically during manufacture for process control and at the final stage of alumina certification. Although gas and vapor adsorption methods were common in the early days of alumina production, mercury porosimetry (MP) has become the technique of choice in the past 30 years. MP provides valuable information about the meso‐ and macro‐pore structure of the alumina but the hysteresis, seen in each analysis, has been difficult to interpret. In this work the MP porosity of a wide variety of calcined aluminas is contrasted with thermogravimetric (TGA) analyses of the source aluminum oxide hydrates and the precipitation and activation conditions, which generated the aluminas in an attempt to better understand the hysteresis phenomenon. The results imply a “connectivity”, or internal structure, explanation for MP hysteresis in calcined aluminas.

Mercury Porosimetry: Contact Angle Hysteresis of Materials with Controlled Pore Structure

Mercury Porosimetry (MP) hysteresis is a commonly observed phenomenon in which mercury retention disguises further the overall hysteresis picture. This article introduces a new interpretation of the MP hysteresis based on the combined effect of pore structure networking and mercury contact angle variation occurring between the mercury penetration and retraction operations. To distinguish the contribution of each factor the following investigations were carried out. Nitrogen sorption (NP) and MP experiments were performed on samples of an anodic aluminum membrane and the results were interpreted in terms of the Corrugated Pore Structure Model (CPSM), i.e., CPSM-Nitrogen and CPSM-Mercury models, respectively. The simulation of the observed hysteresis data using the CPSM model enabled the evaluation of an identical for the two methods intrinsic pore size distribution (PSD) and cumulative surface area in perfect agreement with the respective BET value. Additionally, the CPSM analysis of data resulted in the evaluation of mercury contact angles, i.e., θp=143° and θr=101.7° for the MP penetration and retraction branches of the hysteresis loop, respectively. Moreover, CPSM-Mercury simulations of literature MP hysteresis data, valid for controlled-pore glasses and nuclepore membranes, led to the evaluation of contact angles, i.e., glasses: θp=143°, θr=100.5–107.5° and nuclepore: θp=143°, θr=118– 121°. The latter values are comparable with relevant literature data and approximate those determined for the anodic aluminum membrane. The CPSM model employed herein proved to be a flexible and reliable model for simulating the pertinent hysteresis loops by combining pore networking and contact angle hysteresis phenomena.

TOMOGRAPHY OF MACRO-MESO-PORE STRUCTURE BASED ON MERCURY POROSIMETRY HYSTERESIS

Mercury porosimetry (MP) hysteresis loop scanning (SHL) data are used in the deduction of pore structure tomography diagrams. Macro and/or meso-pore structure tomography refers to the tracing of intrinsic pore size distributions (psd) of pore structure sections corresponding to specified volume saturation levels. Tomography information may be proved a useful tool e.g., to elucidate mass transfer, heterogeneous reaction phenomena, eic. The contribution of the present work is the simulation of the MP - scanning data, based on the random corrugated pore structure model (CPSM), reported elsewhere and the generation of the pertinent pore structure tomography spectra (i.e., a set of local, as regards saturation, intrinsic psd). The CPSM model has been applied to carry out parametric studies for the generation of theoretical loop scanning diagrams and the construction of the pertinent tomography plots. Additionally the CPSM model have been successfully used in curve fitting applications by using experimental MP hysteresis loop scanning data, taken from literature or produced in this work, and the deduction of the respective tomography diagrams. Part 1 of this work is devoted to pore structure tomography accruing from MP loop scanning along the penetration line while Part II deals with loop scanning along the retraction curve and the derivation of the respective pore structure tomography spectrum. Overall, the CPSM model simulates satisfactorily MP loop scanning data and yields credible pore structure tomography information.

TOMOGRAPHY OF MACRO-MESO-PORE STRUCTURE BASED ON MERCURY POROSIMETRY HYSTERESIS LOOP SCANNING Part II: MP Hysteresis Loop Scanning Along the Overall Retraction Line

The concept of macro-meso-pore structure tomography based on mercury porosimetry hysteresis loop scanning along the retraction curve (MP-SHL-R) is introduced. The random corrugaled pore structure (CPSM) model is used in the simulation of the present loop-scanning variant. The CPSM predicted, distribution (VT) of trapped mercury, reported elsewhere, is employed in the definition of a retraction line‘free of entrapment’(Vr) and hence, a ‘nominal’ MP hysteresis loop scanning (MP-SHL-R(A’)) is constructed. The CPSM model have been used in MP-SHL-R(N)) scanning cycles applications to deduce the relevant intrinsic pore size distributions. These psds drawn on a 2-D and/or 3-D plots, that constitute the pore structure tomography, are compared graphically to those obtained by MP hysteresis loop scanning along the penetration line (Part I), Further the CPSM model, as applied in Part II, has been successfully used in regression trials of experimental MP hysteresis loop scanning data and generated the respective tomography spectra. It is concluded that given an MP overall penetration-retraction experimental data, the CPSM model can be best fitted over these data and hence achieve sensible predictions of pore structure tomography based on both MP scanning modes.

Mercury porosimetry of ordered sphere compacts: Investigation of intrusion and extrusion pore size distributions

Intrusion—extrusion hysteresis in mercury porosimetry is thought to be caused either by mercury contact angle hysteresis or by the domination of extrusion by pore bodies and intrusion by throats to the pore network. Mostly, only the information obtained during the intrusion of mercury has been used in the pore structure characterization of materials via mercury porosimetry. The use of the data obtained during extrusion has been the subject of several recent studies in an attempt to reach a more complete picture of pore structure. In this work, the possible use of both intrusion and extrusion for pore structure characterization have been investigated. Submicron monosize spherical particles of silica and yttrium hydroxycarbonate were synthesized and ordered compacts of these powders have been prepared. Mercury porosimetry tests on these high-density compacts (typically 68 – 70% of sphere density) have shown the presence of two pore peaks for intrusion and extrusion with the exception of one compact. Comparisons of intrusion pore sizes with the theoretical sizes of the constrictions for ordered sphere packings have shown reasonable agreements. Similar comparisons between the sizes of cavities in sphere packings and the extrusion pore sizes did not show the same agreement. Results for one sample did not show a distinct extrusion pore size even at very large pore sizes, most probably due to the domination of mercury extrusion by very few large pores present in the sample. For all other samples, the extrusion pore sizes were close to the actual sphere size and the extrusion was most probably dominated by a few vacant sphere sites in the ] ordered structures. The results of this work have shown that the possibility of using extrusion data for pore body size distribution determination is in serious doubt. The presence of very few larger pores in the porous body may dominate the whole extrusion process and can cause the extraction of inaccurate pore size information from the extrusion data.

Hysteresis caused by dimensional changes of porous solids during mercury porosimetry

Hysteresis in mercury porosimetry is often attributed to differences in contact angle and to inkbottle-shaped pores. In this paper, the contribution to hysteresis from dimensional changes in pores is considered. Empty pores are compressed by the applied external mercury pressure. The mercury penetration pressure is related to the dimensions of the compressed pores. After the pores are filled with mercury, the pressure becomes isotropic throughout the solid and the pores revert to their original dimensions. The pressure at which mercury retracts from the pores is related to the original pore dimensions. Using these concepts, the magnitude of the pore dimension changes was determined as a function of the applied mercury pressure, the modulus of elasticity of the solid and the solid porosity. The effect of dimensional changes on the width of the hysteresis loop (P pen - P ret ) was found to be minimal at pressures less than 70 MPa (10 4 psi). At 350 MPa (5 × 10 4 psi), the width of the hysteresis loop caused by dimensional changes can be significant even when the modulus of elasticity is large. The predicted hysteresis loop widths are compared with experimental data reported for model pore systems.

Postulated role of intrinsic contact-angle hysteresis in mercury porosimetry

Mercury-porosimetry hysteresis, previously recognized to be related to contact-angle hysteresis, is equivalent to the irreversibility of the work cycle of immersion followed by emersion of the surface of a sample by mercury. There are several implications to recognizing that this work cycle is irreversible. For example, the validity of surface areas calculated from this pressure—volume work requires examination. Several past models for mercury-porosimetry hysteresis and for contact-angle hysteresis are also examined. The conclusion reached in the present work is that irreversible work is converted to heat in a manner that is completely analogous to friction. Regardless of the direction of motion, a portion of the mechanical work involved in moving the three-phase boundary is converted to heat, even if the surface is smooth and homogeneous. This intrinsic contact-angle hysteresis may be present not only in the mercury-porosimetry experiment, but also for other contact-angle phenomena, such as measurements involving sessile droplets.

Measurement of the morphology of high surface area solids: hysteresis in mercury porosimetry

The cause of hysteresis between the intrusion and extrusion curves in mercury porosimetry has usually been attributed to (1) the void structure of the solid, (2) a shift in contact angle between intrusion and extrusion, or (3) a combination of both in specific cases. Our studies indicate that all forms of hysteresis can be attributed to structural factors. Intrinsic contact angle shifts in porosimetry are thermodynamically and experimentally inconsistent.

A generalized analysis of hysteresis in mercury porosimetry

Modifications in hardware, including the addition of a computer, and in operating procedures, were made to a commercial mercury porosimeter to facilitate thermal and mechanical equilibration. These modifications reduce temperature changes in the hydraulic fluid which cause an ‘apparent hysteresis’ even in the mercury-only blank. These modifications also allow the allocation of additional time for slow processes such as mercury extrusion from the porous samples analyzed in this work. Hysteresis observed between intrusion and extrusion mercury porosimetry data has been interpreted by a generalized analysis. Without specifying a particular pore shape, detailed features of sample compaction, mercury retention, and contact-angle changes can be identified by this method. The hysteresis in the mercury porosimetry data of the samples analyzed in this work are completely consistent with contact-angle hyteresis.

Volume and contact angle hystereses in mercury porosimetry of ASC-whetlerite

On a sample of ASC-whetlerite, local hysteresis in mercury porosimetry both for reintrusion and extrusion courses was investigated. In this way, some important characteristics of the porous body were evaluated: contact angles and their hysteresis, adhesion tension and its intermediate values, differences of interfacial energies, and line tension.

Hysteresis, entrapment, and wetting angle in mercury porosimetry

Intrusion—extrusion hysteresis in mercury porosimetry is shown to be due to the extrusion wetting angle differing from the intrusion angle. When correct extrusion wetting angles are used, second-cycle intrusion—extrusion curves are coincident and first-cycle intrusion—extrusion curves reflect only the fact that mercury is permanently entrapped. The distribution of the entrapped mercury volume as a function of pore radius is given for two samples. The work corresponding to the entrapment of mercury, the work associated with the change in wetting angle, and the work of extrusion are determined. These work terms were also identified with regions of hysteresis on first-and second-cycle intrusion—extrusion curves.

Continuous scan mercury porosimetry and the pore potential as a factor in porosimetry hysteresis

A new type of very rapid continuous intrusion porosimeter is discussed which has virtually eliminated the need for blank corrections. Also, the influence of the pore potential is offered as a factor which contributes to hysteresis in mercury porosimetry.