Method of standard porosimetry

The experimental basis of sorption studies includes structural data (SANS, SAXS, USAXS), isopiestic vapor sorption isotherms,i and capillary isotherms, measured by the method of standard porosimetry. i 2-i44 Thermodynamic models for water uptake by vapor-equilibrated PEMs have been suggested by various groupThe models account for interfacial energies, elastic energies, and entropic contributions. They usually treat rate constants of interfacial water exchange and of bulk transport of water by diffusion and hydraulic permeation as empirical functions of temperature. 

The method of standard porosimetry (MSP)41-43 was one of the first approaches used to obtain air-water capillary pressure curves for GDMs.16 In this test, a GDM sample is initially saturated with water and contacted with a water-saturated porous disc, which is a standard with known Pc(Sw) behavior. The capillary pressure of the sample-standard system is varied by allowing the liquid to evaporate from the standard and sample while in contact. If the two media can be assumed to be in capillary equilibrium, their capillary pressures are equal. Saturation is determined by measuring the weights of the sample and standard periodically. The capillary pressure of the system is found by reference to the known capillary pressure curve of the standard. This method is limited to scanning... 

A close set of equations was formulated in Ref. 16, related to the capillary pressure isotherms determined by the method of standard porosimetry [60], In the latter procedure, the equilibrium amount of the wetting liquid is measured in the porous sample under study. Simultaneously, the amount of the wetting liquid is measured in the standard specimen with a genuine porous structure, in which the capillary equilibrium is established. The standards are kept in thermodynamic equilibrium with the sample. The comparison of the amount of wetting liquid in the membrane with the pore-radius distribution in the standards, enables one to record (with a minimum of theoretical assumptions), the volume-size and surface-size distribution curves, specific pore-space surface area, and absorption isotherm in the membrane of interest, for various wetting liquids. 

Volfkovich YM, Bagotzky VS. The method of standard porosimetry 1. Principles and possibilities. J Power Sources 1994 48 327-38. 

To determine the fraction of expanded channels, T and the channel-size distribution must be known. The channel-size distribution gives the fully expanded channel radii and is taken to be the same for different operating conditions and the same as the distribution measured for a liquid-equilibrated membrane. The reasons that this distribution is assumed to be constant are that it should not vary significantly with pressure or temperature xmder typical fuel-cell operating conditions and is used only when there is a separate liquid-water phase. This assumption has been used and proved valid within error tolerances [13, 18, 57]. The pore-size distribution for Nafion has been measured by the method of standard contact porosimetry [29, 58, 59]. In those studies, the distribution included both the channels and the clusters. Since only the channel-size distribution is of interest, only that regime of data is fit using the log-normal distribution [39]. The average channel radius is around 1.5 nm as expected from the physical model and other studies [23, 60, 61). 

MSU. The studies at MSU were supervised by Frumkin much more intently than those at the Institute. On the other hand, Frumkin always thoroughly read all the papers before submitting them for publication. These studies had made fundamental contributions to the theory and practice of electrocatalysis, especially with regard to the dissociative adsorption of organic compounds, the nature of adsorbates, and the rate-determining step of electrooxidation processes. Methods were also developed for optimizing the structure of porous electrodes. The method of standard contact porosimetry was widely used to quantify various materials. Finally, the book by W. Vielstich Brennstojfelemente was translated into Russian with a preface written by Frumkin. 

The aim of this study is to eompare pore structure characteristics of two industrial catalysts determined by standard methods of textural analysis (physical adsorption of nitrogen and mercury porosimetry) and selected methods for obtaining parameters relevant to transport processes (multicomponent diffusion and permeation of gases). 

More national and international standardization procedures for mercury porosimetry and the derivation of pore size distributions from adsorption isotherms are in preparation. Regarding the weakness of the two-parameter BET model for surface area determination in addition the three-parameter BET equation or improved approximations [26] should be considered. Competitive evaluation methods, like the method of Dubinin, Horwath-Kawazoe, Kaganer and Radushkevich are being discussed. 

Another method that should be shortly mentioned here is the standard porosimetry developed by Volfkovich. Based on a well-characterized reference material the pore size distribution of a sample can be determined by making use of a capillary equilibrium between the sample and the reference. This variant of porosimetry is very sensitive and, like capillary flow, a non-destructive method. 

Due to the small solute loading of the particles of less than 500 pg, the experimental porosity cannot be determined with standard methods such as porosimetry. Therefore, the porosity, (p, of the investigated particles is calculated as... 

Catalysts were characterised by two standard textural-analysis methods mercury porosimetry (AutoPore 9200, Micromeritics, USA) and physical adsorption of nitrogen (ASAP2010M, Micromeritics, USA). 

Gas sorption porosimetry is a standard method for the characterization of the pore size distribution (PSD) of porous solids. To interpret the experimental isotherm and obtain the adsorbent PSD, one must adopt a model for the pore structure, and a theory that estimates the adsorption that will occur in pores of a particular size. If the porous solid is represented as an array of independent, noninterconnected pores of uniform geometry and identical surface chemistry, then the excess adsorption, /JP), at bulk gas pressure P is given by the adsorption integral equation... 

Chemical characterization total metal analysis has been performed using atomic adsorption spectroscopy (Varian Techtron analyzer). Metals were reported in % by weight (bulk) of total metal oxides in the support (W, Ni, Pt / Al-Si support). See Table 1. Physical method Surface, pore volume, and average pore diameter were measured using standard nitrogen adsorption and mercury porosimetry methods. See Table 1. 

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