Porosity characterization

Walker, P L., Jr., Davis, A., Verina, S. K., Rivera-Utrilia, J., and Khan, M. R., Interaction of Gases, Vapors, and Liquids with Coals and Minerals at Ambient Temperatures—Their Use to Characterize Porosity, The Pennsylvania State University, DOE-30013-19, Under Contract No. DE-AC22-80PC30013 (1984). 

Kastelan-Kunst, L., et al. (1997). ET30 membranes of characterized porosities in the reverse osmosis organics removal from aqueous solutions. Water Res. 31, 11, 2878-2884. 

The follow-up of the time dependence of the total pressure and the H2 partial pressure, supplemented by a complete analysis of the gas space by chromatography, allows comparison between experiment and simulation reasonably under well-defined operating conditions. One should keep in mind that a badly characterized porosity or an inaccurate dose rate constitute the most common causes of divergence, with the strongest impact. 

Various calorimetric methods can be used to characterize carbon surfaces from different viewpoints the application of these techniques to carbons has been recently reviewed in detail [35], and only a brief outline will be presented here. Adsorption calorimetry has been used to investigate surface chemical properties more irequently than to characterize porosity in carbons. Terzyk et al. [36] have compared a number of techniques, including benzene adsorption calorimetry, to characterize the microporosily of cellulose-derived carbonaceous films where the majority of micropores possessed the same diameter. The determination of pore size based on the enhancement of potential energy in micropores... 

There are several key ideas in this chapter. PBs are present wherever we have a second phase, particle, or precipitate in a matrix we treat pores as a special particle. (The surface is actually a special PB.) Like GBs, PBs are everywhere in ceramics we could develop a notation similar to the Z for GBs but rarely use it. When a phase transformation occurs, the mechanism is the movement of a PB. Particles can be different in structure and/or composition in a ceramic matrix precipitates are particles that have developed by a specific process. Pores are present in most ceramics and play important roles in determining properties. We have developed special methods for characterizing porosity and ceramics in which the pores are actually the major phase—porous ceram-... 

Porosity, with the dimensions of nanometers or less, cannot be precisely imaged even in the most recent of transmission and scanning electron microscopes and recourse has to be made to the powerful experimental techniques of physical adsorption of gases, of immersion calorimetry and of small-angle scattering of X-rays (SAXS) and neutrons (SANS) to characterize porosity. Microporosity has the dimensions of molecules and such molecules, as adsorbates, become the experimental probes providing significant information about the adsorption site. Hence, the phenomena of porosity and adsorption are inseparable. 

In order to further characterize porosity in activated carbon, to assess if pores with dimensions <0.7 nm existed in activated carbons, Setoyama et al. (1996) studied activated carbons from olive stones, 19-80wt% bum-off in CO2 by adsorption of helium at 4K and nitrogen at 77 K. Micropore volumes, determined from the s analysis of the helium... 

The contents of this chapter summarize the several methodologies used to characterize the porosity of activated carbon. The isotherms of the N2 (77 K), CO2 (273 K), H2O (298 K), making use of DR and BET equations, together with a-plots, in association with enthalpies of immersion, characterize porosity in activated carbon. Equilibria data are complemented by the kinetic data from breakthrough curves. 

The use of adsorption methods to characterize porosity in carbons, and the (then considered) undisputable position of the N2 BET isotherm appeared to be permanent. However, the advent of immersion calorimetry and its application to carbon chemistry, together with the availability of commercial calorimeters, presented a significant challenge to the supremacy of the N2 (77 K) adsorption isotherm. The School of Adsorption, University of Alicante, made use of immersion calorimetry and reviewed their work over several years (Rodrfguez-Reinoso et al., 1997 Silvestre-Albero et al., 2001). Immersion calorimetry, as a method of characterization, is discussed at length in Section 4.7. 

Much that has been written earlier, about the properties of AC, finds relevance to the understanding of the use of carbon as a catalyst support and as a catalyst in its own right (Rodriguez-Reinoso, 1998). Section 4.2 characterizes porosities in carbons, with special reference to the dominant importance of microporosity. The chemistry of functionality attached to the graphene layer, both in-plane and at edges, is immediately relevant to the use of carbons in catalytic processes (Section 4.3). The amphoteric nature of the graphene layer, for example, as discussed with reference to adsorption of anions from aqueous solution, has a role in catalytic processes (Section 8.1.3). 

Although not routinely used to characterize porosity, nuclear magnetic resonance (NMR) can also be used to study porous materials. The method relies on the fact that the difference in t and t2 relaxation times of protons in water (or other fluid) in porous materials will decrease with the average pore diameter. 

Table 5.3 summarizes the general approaches to characterizing porosity of materials together with the information each is likely to provide. Those that do not apply to electrospun nanofibers are also included for completion. 

The effect of compression on the structure of MCM-41 with the template within the pores was examined by N2 adsorption. Fig. 6 shows the N2 adsorption/desorption isotherms for the as-synthesized MCM-41 before and after compression. The nitrogen adsorption/desorption isotherm for as-synthesized sample and samples after hydrostatic pressure experiment exhibit over the relative pressine p/po = 0.9 hysteresis loop which is characteristic of the c illary condensation between silica particles. Some parameters characterizing porosity of the investigated samples are collected in Table 1. Two samples with the template do not exhibit porosity of MCM-41 silica. Only for MCM-41 after compression in argon the specific surface area and pore volume are little higher in comparison to the as-synthesized sample. 

Otherwise, the porosity of the electrode needs to be determined by diagnostic methods. So far, several methods have been proposed and implemented to comprehensively characterize porosity, including mercury or gas porosimetry, capillary flow porosimetry, and standard contact porosimetry. 

One of the common methods of characterizing porosity is finding the apparent porosity. This corresponds to the amount of open pores. The total porosity includes both open and closed pores. Open pores affect permeability, vacuum tightness, and the surface available for catalytic reactions and chemical attacks. Permeability increases with porosity, vacuum tightness decreases with it, and the surface available for catalytic reactions and chemical attacks increases. Before the firing process starts, almost the entire pores are open. 

The best method to characterize porosity is by the use of polished sections with lineal or area analysis. Difficulties in the characterization of porosity by this method arise in the following instances ... 

Kosutic, K. and B. Kunst. 2002. Removal of organics from aqueous solutions by commercial RO and NF membranes of characterized porosities. Desalination 142 47-56. 

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