Hg Porosimetry

Mercury (Hg) porosimetry is a method that is able to probe about six orders of magnitude in accessible pore size ranging from about 400 pm down to a few Angstroms [76]. Hereby isostatic pressure is applied to force nonwetting hquid mercury into the pores to be quantified. The external pressure required to access a cylindrical pore with radius Rpore is given by the Washburn equation  

Prior to the measurement, the sample is introduced into a sample cell that allows for degassing under vacuum. Usually the same port also provides the coimections to the low pressure system of the mercury porosimeter, where air pressure is applied onto the pool of mercury to force it into the sample in contrast, the high pressure port uses a hydraulic system to provide pressure up to 400 or even 600 MPa. The amount of mercury vanishing from the mercury reservoir, AVmercury. is recorded together with the net applied pressure and converted into a pore size distribution. 

Care has to be taken to choose the rate of pressurization or the time allowed for equilibration (when pulse wise pressurizing) such that the sample is in quasi equilibrium at each pressure otherwise artifacts will be introduced due to kinetic effects, shifting the calculated pore size to smaller values compared to the actual pore sizes. 

Depending on the average pore size, the modulus of compression, and the type of aerogel under investigation, the compression of the sample can be in part or totally irreversible. In particular, sUica-based aerogels without organic surface modification are irreversibly deformed. 

When compressional effects occur, one can either try to correct for their contribution or to exploit them to determine the mechanical characteristics of the aerogel under investigation. Pirard compared two intrusion/extrusion curves taken for two different pieces of monolithic precipitated silica taken from the same batch [80] hereby one sample was wrapped into a mercury impermeable membrane. The experimental curves showed that the first flat slope of the intmsion curve can exclusively be related to compression of the sample while the subsequent steep increase of the intmsion volume with increasing pressure applied is actually dominated by intmsion of the pores. Upon extmsion, the volume detected for the unwrapped sample was not fully recovered it could be shown that the missing volume upon extmsion was equivalent to the volume compressed in the first stage of pressurization (intmsion). 

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B) Pore size distribution (solid line) obtained from DDIF, in comparison with mercury (Hg) porosimetry (dashed line). The peak in the... 

Hg Porosimetry Fractional Volume of Carbon Densities Particle which is ... 

The first task was to produce carriers from different recipes and in different shapes as shown schematically in Fig. 8. The raw materials diatomaceous earth, water and various binders are mixed to a paste, which is subsequently extruded through a shaped nozzle and cut off to wet pellets. The wet pellets are finally dried and heated in a furnace in an oxidising atmosphere (calcination). The nozzle geometry determines the cross section of the pellet (cf. Fig. 3) and the pellet length is controlled by adjusting the cut-off device. Important parameters in the extrusion process are the dry matter content and the viscosity of the paste. The pore volume distribution of the carriers is measured by Hg porosimetry, in which the penetration of Hg into the pores of the carrier is measured as a function of applied pressure, and the surface area is measured by the BET method, which is based on adsorption of nitrogen on the carrier surface [1]. 

NaY of Si02/Al203 = 5.6 was dealuminated by ion exchanges in NH NO solution, calcination and HC1 treatment. The final Si02/Al203 ratio was 680 by chemical analysis. The pore size distribution was measured by N2 adsorption, Hg porosimetry and electron microscopy. The details have been described previously [3]. 

The rehydrated products were characterized by chemical analysis (ICP Plasma 400 Perkin Elmer), powder-XRD measurements (URD 63 Seifert) in a range from 4° to 40° (20), N2-Adsorption (Sorptomatic 1900 Porotec), Hg-porosimetry, He-density and Scanning Elektron Microscopy (SEM). 

The chemical composition can be measured by traditional wet and instrumental methods of analysis. Physical surface area is measured using the N2 adsorption method at liquid nitrogen temperature (BET method). Pore size is measured by Hg porosimetry for pores with diameters larger than about 3.0 nm (30 A) or for smaller pores by N2 adsorp-tion/desorption. Active catalytic surface area is measured by selective chemisorption techniques or by x-ray diffraction (XRD) line broadening. The morphology of the carrier is viewed by electron microscopy or its crystal structure by XRD. The active component can also be measured by XRD but there are certain limitations once its particle size is smaller than about 3.5 nm (35 A). For small crystallites transmission electron microscopy (TEM) is most often used. The location of active components or poisons within the catalyst is determined by electron microprobe. Surface contamination is observed directly by x-ray photoelectron spectroscopy (XPS). 

FIGURE 13.29 (a) Compaction of spray-dried alumina at 92% relative humidity, (b) Cumulative pore size distributions by Hg porosimetry for spray dried AI2O3 (Alcoa A-17-1) for different pressing pressures. Data taken from Reed [6, p. 337]. 

We prepared two carbons by pyrolysis of saccharose followed by heat treatment at two different temperatures 400 C (CS400) and 1000"C (CSIOOO). We performed X-ray diffraction and SAXS on each of these porous materials and obtained the structure factors, S q), following the procedure described by Franklin [14]. The resulting S(q) s are shown in Figure 1 (bold line). We performed Hg porosimetry to obtain the density of both carbons, accounting for the volume occupied by C atoms, closed pores and smaller open pores. We also measured the H/C and the O/C ratios by combustion experiments. The results are summarized in Table 1. 

The surface area, total pore volume, and microporc volume (in pores <7..S nm) were determined by CO adsorption and Hg porosimetry. 

We are indebted to Mr. El Mansouri for the measurements of Hg porosimetry, and the CNRS for access to neutron scattering facilities at LLB. S.K. acknowledges financial support by the European Community under the Industrial and Materials Technologies Programme (Contract No BRPR-CT96-313). 

Silicalite-1 membranes, supported on porous alumina ceramic discs, have been prepared by two different routes. In the first the zeolite membrane has been formed by in situ hydrothermal synthesis. Secondly a layer has been formed by controlled filtration of zeolite colloids. To optimise membrane stability, conditions have been established in which penetration of zeolite into the support sublayer occurs. The pore structure of these membranes has been characterised by a combination of SEM and Hg-porosimetry. The permeabilities of several gases have been measured together with gas mbeture separation behaviour. 

Hg porosimetry provided a detailed insight into the mechanism of the growth of zeolite phase in the macropore structure of the alumina support. Investigations were made using supports with different pore sizes for different reaction conditions (time, temperature). Typical results showing Hg porosimetry before and after synthesis at two different temperatures (150 and 190 °C) are shown in Figures 3. 

The pore properties of cast bulk porous material and coating layers from the same suspension become different above sinter temperatures where intermediate stage sintering in the bulk starts (see Section 6.2.5). At lower temperatures pore properties of free casts determined with Hg porosimetry can be used to compare the pore properties of consolidated dispersion coatings. 

In Fig. 6.48 the porosity of free cast layers as a function of the suspension pH is given and in Fig. 6.49 the pore size distributions as determined with Hg porosimetry for free cast layers at pH 3.6 and 8.1 are given. It is shown that the porosity difference between consolidated coatings obtained from stable and coagulated suspensions is only 10% and the median pore diameter decreases from 210 nm to 160 nm going from instable to stable suspensions. The decrease... 

Fig. 6.48. Porosity of free cast coatings of a-Al203 as a function of the suspension pH after drying and sintering (Hg porosimetry, cylinder model).

Fig. 6.49. Pore size distributions of unsupported a-A Os coatings obtained by Hg porosimetry of...

In the water retention (e.g., Childs, 1940 d Hollander, 1979) and Hg porosimetry (e.g., Washburn, 1921 Nagpal et al., 1972) methods, length is measured as an equivalent cylindrical radius, rc, that is calculated according to the following relationship,... 

Froment discusses pore network influences in deactivation. He concludes that, "Evidently, the parameters associated with the pore and network structure should be determined from independent physical measurements adsorption, mercury porosimetry, electron microscopy..." Unfortunately, no experimentally based studies have been published that have employed one or a combination of techniques to determine the pore network structure and its changes during deactivation. The few experimental determinations of pore structure are limited to determination of pore dimensions usually from the intrusion data in Hg porosimetry or the desorption data from nitrogen physical sorption (often incorrectly referred to as BET analyses). 

All catalysts have been characterized in previous studies by N2 adsorption-desorption, Hg porosimetry. He pycnometry. X-ray diffraction, CO chemisorption as well as by static electron microscopy (SEM, TEM and STEM-EDX) [4,6,15]. Before describing below the TEM analysis technique, called rotating TEM, allowing to rotate the sample in situ and thus to take pictures at various angles, as well as XPS measurements, the procedure used to examine the catalysts by classical static TEM is briefly reminded. 

In this work, we report on the preliminary results from the fabrication and characterization of Ni-AbOs membranes. The effect of sintering temperatures on membrane support was investigated. The fabricated membranes were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer including X-ray mapping (EDS). In addition, the pore size and porosity were determined by Hg porosimetry. 

Figure 7.47. Comparison of pore size distributions obtained by using Hg porosimetry. (Taken from ref. (66))...

BET analysis of the system Ni catalyst and [BMIMKOCSO4] indicates that both the pore volume (meso- and micropores only) and the surface area decrease with increasing filHng degree (Figures 5.3 and 5.4). The values of the total residual pore volume of the SCILL catalysts measured by BET analysis in combination with Hg-porosimetry agree well with calculations based on the IL volume used for the SCILL catalysts and on the initial pore volume [2, 3]. 

Analysis of the hquid samples was done with a Varian GC CP-3800 with 15 and 30 m CP-SIL 8CB columns. BET measurements were carried out with a Micromeritics Gemini 539 and Hg porosimetry measurements with a Micromerit-ics AutoPore 111. 

The authors would like to thank Slid Chemie for kindly providing the Ni catalyst, and Christoph Kern and Bastian Etzold for fmitful discussions on the SCILL concept, and the Chair of Materials Processing (University Bayreuth) for the Hg porosimetry measurements. 

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