Mercury porosimetry scanning

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

Nitrogen sorption measurements were performed on a Quantachrome Autosorb 6B (Quantachrome Corporation, Boynton Beach, FL, USA). All samples were degassed at 423 K before measurement for at least 12 hours at 1 O 5 Pa. Mercury-porosimetrie has been measured on a Porosimeter 2000 (Carlo Erba Instruments) Scanning electron micrographs were recorded using a Zeiss DSM 962 (Zeiss, Oberkochen, Germany). The samples were deposited on a sample holder with an adhesive carbon foil and sputtered with gold. 

The new composite (SC-155) and some of its precursors and derivatives were characterized by LOI (loss on ignition), XRD ( X ray diffraction), 1R (infrared spectra), BET specific surface area, nitrogen adsorption desorption isotherms, pore size distribution (mercury porosimetry), dynamic methylene blue adsorption and SEM (Scanning Electron... 

Since the porosity of carbons is responsible for their adsorption properties, the analysis of the different types of pores (size and shape), as well as the PSD, is very important to foresee the behavior of these porous solids in final applications. We can state that the complete characterization of the porous carbons is complex and needs a combination of techniques, due to the heterogeneity in the chemistry and structure of these materials. There exist several techniques for the analysis of the porous texture, from which we can underline the physical adsorption of gases, mercury porosimetry, small angle scattering (SAS) (either neutrons—SANS or x-rays—SAXS), transmission and scanning electron microscopy (TEM and SEM), scanning tunnel microscopy, immersion calorimetry, etc. 

Keywords tissue scaffolds, mercury porosimetry, capillary flow porometry, scanning electron microscopy, image analysis... 

Three methods have been used in this investigation to estimate the porosity of PCL tissue scaffolds, namely weight determination, mercury porosimetry and analysis of scanning electron micrographs. The results are shown in Figure 4. 

We found the latter factor-voids to be important. Experimental results showed that when green coke was calcined under the new methods, and the derived calcined coke was observed by scanning electron microscopy (Figure 2) and its pore size distribution was measured by mercury porosimetry (Figure 3), microcracks of significant sizes (1 to 60 microns) were developed. This was an important contribution to the reduction of the thermal expansion coefficients of the calcined coke processed under the new method. 

The porous structure of active carbons can be characterized by various techniques adsorption of gases (Ni, Ar, Kr, CO ) [5.39] or vapors (benzene, water) [5,39] by static (volumetric or gravimetric) or dynamic methods [39] adsorption from liquid solutions of solutes with a limited solubility and of solutes that are completely miscible with the solvent in all proportions [39] gas chromatography [40] immersion calorimetry [3,41J flow microcalorimetry [42] temperature-programmed desorption [43] mercury porosimetry [36,41] transmission electron microscopy (TEM) [44] and scanning electron microscopy (SEM) [44] small-angle x-ray scattering (SAXS) [44] x-ray diffraction (XRD) [44]. 

Alumina membranes containing monodispersed cylindrical pores have been characterised by a combination of three ditferent techniques Field emission scanning electron microscopy, mercury porosimetry and small angle neutron scattering (SANS). SANS is a method which can provide details of the highly anisotropic texture in such model porous materials. 

Several determination methods of a porous texture can be used for characterizing the supports. Certain of these methods (i.e., scanning electron microscopy, mercury porosimetry) are described in other chapters of this book. We shall only report here the specific methods of support characterization. 

After fabrication, the density of membrane was measured by dimension calculation. The crystalline phases of cermet membrane were investigated by using X-ray diffraction (XRD model JEOL, JDX-3530). Scanning electron microscope (SEM JEOL, JSM-6301F) was used to investigate the microstructure of Ni/AbOj membrane. For analysis of nickel dispersion of Ni/AbOj membrane, energy dispersive X-ray spectroscope (EDS Oxford Inca 300 and 350) with X-ray dot mapping was used. In addition, the pore size and porosity were determined by mercury porosimetry. 

The basical theories, equipments, measurement practices, analysis procedures and many results obtained by gas adsorption have been reviewed in different publications. For macropores, mercury porosimetry has been frequently applied. Identification of intrinsic pores, the interlayer space between hexagonal carbon layers in the case of carbon materials, can be carried out by X-ray dififaction (XRD). Recently, direct observation of extrinsic pores on the surface of carbon materials has been reported using microscopy techniques coupled with image processing techniques, namely scarming tunneling microscopy (STM) and atomic force microscopy (AFM) and transmission electron microscopy (TEM) for micropores and mesopores, and scanning electron microscopy (SEM) and optical microscopy for macropores [1-3],... 

Gravimetric measurement (70°F, 65Vo RH), thermogram method Colorimeter, visible spectroscopy in solution Polymer dye site content, dye saturation value, dye diffusion rate Scanning and transmission electron microscopy, mercury porosimetry Instron (in United States)... 

The specific surface area of the activated catalyst was found to increase with alumina content up to about 20 m /g at around 2% AI2O3 and then to remain constant (10), demonstrating the role of this additive as structural promoter that (together with other nonreducible phases such as hercynite and calcium ferrite) prevents sintering of the metallic iron particles into low surface area material. These values are compatible with the mean particle sizes of around 30 nm, as determined by mercury porosimetry and seen directly in the scanning electron microscope (Fig. 2) (11). This agreement further shows that the texture of the catalyst permits the N2 molecules of the BET analysis to reach essentially the whole internal surface. 

The density is measured from the mass and external volume. For a body with a regular shape, the external volume can be measured from the dimensions. Porosity and pore size distribution are normally measured by mercury porosimetry or, for very fine pores, by gas adsorption. Scanning electron microscopy (SEM) of a fracture surface provides a rough visual guide of the packing homogeneity and is also easy to perform. The techniques of mercury porosimetry, gas adsorption, and SEM are also commonly used for powder charactaization and have been described in Chapter 3. 

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