Pore size measurement

Porosity and surface area are routinely measured by nitrogen absorption-desorption, mercury intrusion, and low-angle X ray. The electron microscope (EM) provides direct visual evidence of pore size and pore-size distribution. Thus, a combination of EM and conventional methods of pore-size measurement should provide reliable information on the pore structure of polymers. 

NMR Pore Size Measurements Using an Internal Magnetic Field in Porous Media... 

Instead of the classical approaches, a molecular-based statistical thermodynamic theory can be applied to allow a model of adsorption to be related to the microscopic properties of the system in terms of fluid-fluid and fluid-solid interactions, pore size, pore geometry and temperature. Using such theories the whole range of pore sizes measured can be calculated using a single approach. Two simulation... 

The rapid growth of interest in powders and their surface properties in many diverse industries prompted the writing of this book for those who have the need to make meaningful measurements without the benefit of years of experience. It is intended as an introduction to some of the elementary theory and experimental methods used to study the surface area, porosity and density of powders. It may be found useful by those with little or no training in solid surfaces who have the need to quickly learn the rudiments of surface area, density and pore-size measurements. 

Bechhold prepares collodion membranes of graded pore size, measures bubble points and uses the term ultrafilter -1907... 

In many papers, an oversimplified expression known as the Kelvin equation Rp = AjAT + t, where A is a constant, has been used. In Figure 10.3, two examples clearly demonstrate that this could lead to large errors in pore size measurement. The data are adapted from [29] for water (a) and from work performed in our group [28] for acetone (b). 

The deactivation of a Fischer-Tropsch precipitated iron catalyst has been investigated by means of a novel reactor study. After use of the catalyst in a single or dual pilot plant reactor, sections of the catalyst were transferred to microreactors for further activity studies. Microreactor activity studies revealed maximum activity for catalyst fractions removed from the region situated 20 - 30% from the top of the pilot plant reactor. Catalyst characterization by means of elemental analyses, XRD, surface area and pore size measurements revealed that (1 deactivation of the catalyst in the top 25% of the catalyst bed was mainly due to sulphur poisoning (2) deactivation of the catalyst in the middle and lower portions of the catalyst bed was due to catalyst sintering and conversion of the iron to Fe304, Both these latter phenomena were due to the action of water produced in the Fischer-Tropsch reaction. 

The comparison of the pore size measured on non-supported membranes by N2 absorption-desorption with that on supported silica membranes measured with gas permeation and separation with molecules of greatly different sizes indicates that the average pore diameter of supported silica layers is slightly smaller (0.40-0.45 nm). See Chapter 9 on gas transport. 

BUous and Counas [B17] recommend for the parameter A a value of 3 Otni cmHg) as providing an adequate correlation between their pore size measurements and barrier separation performance on UFe at temperatures between 35 and 85 C. Hence the upstream pressure p" = Pc in torr at which the barrier would have an efficiency of Eg = 0.500 at a downstream pressure p = 0.00 is... 

Equation 71 is the basic equation that relates permeability of a porous medium to its other properties. However, equation 71 contains the hydraulic diameter of the passage (pore), tortuosity, and areal porosity of the medium, which may not be easily accessible. For example, sandstones or rock formations have irregular pore structure and often have inconsistent pore size measurement values (see previous section). It is rather difficult to measure the average hydraulic pore diameter. On the other... 

The aim of the pore size measurement was not to produce an absolute value for pore size or molecular weight cut off, but rather to determine which of the four membranes is more open, A dextran 1000 standard was chosen and rejection experiments were carried out at a dextran concentration of about 50 mgL and pH 8. The feed DOC was 19.4 mgL k Dextran was chosen as it is not expected to interact strongly with membrane material (Combe et al. (1999)). 

From these data we have aU reasons to expect that the size of the pores characteristic of aU hypercrossHnked polystyrene networks will be in the range of few nanometers. Estimation of such small pore sizes presents special problems, particularly since the very term pore becomes a rather loose concept for an open framework structure. Let us now consider the results of pore size measurements of hypercrossHnked polystyrene by the available different experimental methods. 

For catalysts 12CoRe/Ti02 and 20CoRe/a-Al2O3, the pore size measurements were performed using a Carlo Erba Porosimeter 2000 by mercury intrusion. Each sample was evacuated and dried at 423 K prior to analysis. A cylindrical pore model was assumed. 

The association of several techniques to study the same system is always advantageous. For the specific case of surfaces, techniques like XPS, contact angle, diffuse reflectance infrared with Fourier transform, surface area and pore size measurements, scanning electron microscopy appear frequently associated. This is the case for the study of carbon or glass fibers [ 105-109], activated carbons [110], and polymeric films obtained by plasma polymerization [111]. In Section 5, the specific combination of diffuse reflectance spectroscopies in the region of UVA is and XPS will be emphasized. 

Allen, T. (1997) Particle Size Measurements. Volume 1 Powder Sampling and Particle Size Measurements. Volume 2 Surface Area and Pore Size Determination, 5th. edition. Chapman Hall, London. Comprehensive guides to particle size, surfaee area, and pore size measurements covering experimental methods and data analysis. 

CTOss-link density through the addition of CB[8] to the system allowed control over the microstructure as changes in the pore sizes measured in SEM images were proportional to the cross-link density of the network. 

Results from pore size measurements on unmodified and APTS-modified silica substrates using a Micromeritics ASAP 2020 surface area and porosity analyzer are shown in Fig. 7.8 and Table 7.1. As reported in literature [35], the N2... 

Price, M., Bird, M.J. and Foster, S.S.D. 1976. Chalk pore size measurements and their significance. Water Services, 80, 596-600. 

Surface area, micropore volume, and pores size measurement was done by using N2 with Micromeritics ASAP 2000 equipment and ASAP 2010 software. Surface acidity was determined from temperature programmed desorption of ammonia (TPD-NH3) and equipment used was Micromeritics 2000. Prior to starting tests, catalyst was dried under 30 ml/min Helium continuous flow at 300 C. The temperature at a rate of lO C/min was increased from 27 C to 650°C under a continuous flow of 30 ml/min Helium. Surface groups were determined using diffuse reflectance fourier transform infra red (FTIR) spectroscopy with Nicolet Magna-IR 560 Spectrometer. The catalyst was dewatered at... 

Ji [8] and Hu [7] also studied the NMR spectra and found that the role of chitosan in the aerogels is somewhat modified from the pure material by its interaction with the silica framework. They also analyzed the Xe NMR spectra of Xe in Si02-X aerogels as a function of temperature and pressure, and they showed that the Xe behavior in pores is consistent with the pore size measurements. 

Other important parameters in particle analysis are surface area, pore size, and volume. The basic method for measuring surface area involves determining the quantity of an inert gas, usually nitrogen, required to form a layer one molecule thick on the surface of a sample at cryogenic temperature. Many techniques are used for pore size measurement impregnation with molten metal, particle beam transmission, water absorption, freezing point depression, microscopy, mercury intrusion, and gas condensation and evaporation. The last three techniques are most often utilized. 

---