Mercury pycnometry

In order to identify the volume variation mechanisms on the precipitated silica sample, experiments were performed at various maximum pressure below and near the point of slope change P,.. A monolithic sample of high dispersive precipitated silica was weighted and its specific volume (2.04 cm /g) was determined using mercury pycnometry. It has been submitted to mercury porosimetry until a pressure (40 MPa) just below the characteristic transition... 

The porous texture of the dried gels and the pyrolyzed gels was characterised by the analysis of nitrogen adsorption-desorption isotherms, performed at 77 K. The analysis of the isotherms was performed according to the methodology proposed by Lecloux [19]. Samples bulk density was obtained by mercury pycnometry. Infrared and X-ray spectra analysis allowed to obtain data about the elementary composition of the samples and the aggregation state of the metals. 

The apparent density is also badly defined. It actually uses volumes of a polymer sample measured either by microscopy or by mercury pycnometry under 1 atm pressure. With pores large enough, these methods can provide different results. From this consideration it follows that the most reliable method of measuring the pore volume W, of a porous material, by comparing its apparent and true densities, bears serious uncertainty. 

Figure 26.7. Monolithic silicaaerogelmonolith synthesized by a two-step catalytic process from TEOS [30], presenting a density of 0.18 g cm and an effective thermal conductivity of 0.015 W m (as respectively measured by mercury pycnometry and with the hot-wire method at room temperature) with couite of Rigacci A. and Achard P.

Weighing of the sample before and after the porosimetry experiment can quantify the mercury which has intruded pores and is subsequently entrapped within the sample. In the case of pure intrusion, the full detected mercury volume remains within the sample, as revealed by the depressurization branch in Fig. 5.9a. If no mercury is found in the porous solid after porosimetry, the volume change of the sample may be measured (by mercury pycnometry as explained below) to confirm the assumed extent of irreversible shrinkage. 

Another useful technique is mercury pycnometry which can be used to determine the geometrical volume of the dry gel (pores and solid), hence giving complementary data to helium pycnometry which measures only the pore volume. In this characterization method, a volume-calibrated chamber containing the sample is filled with mercury the mercury volume (or weight) is measured to compute the sample volume. Unlike mercury porosimetry, no pressure is exerted so that mercury neither enters the pores nor crushes the sample. 

In order to characterize the structure of RF and carbon xerogels, a combination of nitrogen adsorption (for micro- and meso-pores) and mercury porosimetry (for pore diameters from 7.5 to 150 nm) was used to obtain the BET surface area and pore volume (microporous and total) helium and mercury pycnometry were applied to determine the skeletal and bulk density. 

The apparent specific volume, V wUch is foe revase of the bulk daisity, was measured by mercury pycnometry. After placing a fiiam sample of wei w, in a pycnometer, it is completely filled with mercury and weighed (w, ). F, is calculated arxxmding to foe expression wh e wj is foe weight of the pycnometer filled with... 

The microstructure of the reactants and products have been investigated by scanning electron microscopy (SEM), coupled with energy dispersive X ray microanalysis (XMA), on initially polished surfaces, and by mercury intrusion porosimetry (ME ) and mercury pycnometry on small lumps. 

Mercury pycnometry experiments allowed to explain these discrepancies by revealing a strong swelling of the CSOs especially in nitrogen. The phenomenon was first strictly established for both ores by comparing the mercury intrusion curves before and after treatment at 700 C in nitrogen the results are given in table 2. 

Results of exact measurement of swelling by mercury pycnometry Ore / Treatment Initial volume (ccl Final volume (cc) Swelling... 

Cylindrical pellets of four industrial and laboratory prepared catalysts with mono- and bidisperse pore structure were tested. Selected pellets have different pore-size distribution with most frequent pore radii (rmax) in the range 8 - 2500 nm. Their textural properties were determined by mercury porosimetry and helium pycnometry (AutoPore III, AccuPyc 1330, Micromeritics, USA). Description, textural properties of catalysts pellets, diameters of (equivalent) spheres, 2R, (with the same volume to geometric surface ratio) and column void fractions, a, (calculated from the column volume and volume of packed pellets) are summarized in Table 1. Cylindrical brass pellets with the same height and diameter as porous catalysts were used as nonporous packing. 

A comparison of true particle density, apparent particle density, and bulk density can provide information on total porosity, interparticle porosity, and intraparticle porosity. Methods include true particle density measurements via helium pycnometry, mercury intrusion porosimetry, and poured and tapped bulk density. 

The bulk densities were calculated from weight and volume measurements. Skeletal densities were measured by He pycnometry N2 adsorption-desorption isotherms were determined at 77 K on a Carlo Erba Sorptomatic 1900 and their analysis was done using a set of well-known techniques [5], Mercury porosimetry up to a pressure of 200 MPa is performed on a Carlo Erba Porosimeter 2000. Samples were examined using a transmission electron microscope to obtain particle and aggregate sizes [2]. 

The bulk density of materials was measured by Hg pycnometry from independent measurements of the mass and the volume of monolithic samples. The geometrical volume of the sample is determined fi om the weight difiference between a flask (calibrated volume) filled up with mercmy and the same flask filled up with the sample and mercury. As mercury is a non-wetting liquid and as no pressure is exerted, mercury does not enter in the porosity of the sample or crush it. 

The accuracy of pycnometry depends on the size and type of pores as well as the wettability of the solids—how well does the fluid envelope the solid and at what time frame. Mercury as a fluid minimizes these limitations and many instruments are available commercially. 

The porosity and pore stmcture can be also determined with mercury porosim-etry, as well as with helium flow method proposed by Feldman [48]. However, a more adequate method of the total porosity measmement is helium pycnometry [57]. The applicability of the mercury intmsion porosimetry covers the pore diameters from 3 nm to about 10 nm, while the capillary condensation— from 4 to 50 nm respectively. 

Bulk and apparent density Helium pycnometry Mercury porosimetry Liquid displacement Surface energy Thermal analysis tests Tempera ture-progra m med desorption and reaction Calorimetry... 

Although more labor-intensive and less efficient, information on the densification kinetics and densification can also be obtained from density measurements on different individual samples as a function of time for otherwise identical sintering conditions. Bulk density measurements on <92% dense sintered samples containing open porosity can be determined from the measured mass and dimensions of the compact, while Archimedes method works well for closed pore, >92% dense bodies. The density of closed pore samples can also be determined by pycnome-try (e.g., helium pycnometry),, 37 mercury porosimetry, and by the sink-float method (i.e., whereby the buoyancy of the sample is assessed and compared in different density liquids). Density can also be estimated from micrographs using quantitative stereology. 

The bulk and skeletal densities estimated from mercury and helium pycnometry,... 

Two standard methods (mercury porosimetry and helium pycnometry) together with liquid expulsion permporometry (that takes into account only flow-through pores) were used for determination of textural properties. Pore structure characteristics relevant to transport processes were evaluated fiom multicomponent gas counter-current difhision and gas permeation. For data analysis the Mean Transport-Pore Model (MTPM) based on Maxwell-Stefan diffusion equation and a simplified form of the Weber permeation equation was used. 

All porous materials were chosen to cover as wide as possible range of pore sizes and to represent both monodisperse and bidisperse PSD. Textural properties were determined by mercury porosimetry (AutoPore 111, Micromeritics, USA) and helium pycnometry (AccuPyc 1330, Micromeritics, USA) are summarized in Table 1. 

Textural properties of six porous materials with mono- and bidisperse porous structure and a range of pore radii from nanometers to microns were determined by mercury porozimetry and helium pycnometry. The obtained pore-size distributions were compared with transport characteristics obtained independently from diffusion and permeation measurements. For three chosen samples the distribution of transport-pores was obtained from LEPP. 

Table 14.8 Results of mercury intrusion porosimetry of mannitol samples spray dried at different outlet temperatures (mean (n = 3) SD) and helium pycnometry (mean (n = 3) SD) [32]...

Mean (n = 3) SD Helium pycnometry Mercury intrusion porosimetry (MIP) ... 

If all the inner voids are accessible via pores the density obtained at 20(X) bar should be equal to the apparent density measured by helium pycnometry. Results shown in Table 14.8 showed slightly higher densities for helium pycnometry measurements, indicating that not all pores, which are permeable for helium, are accessible by mercury intrusion [32]. 

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