Pore Width Distribution Research Articles

Determination of the pore widths of highly porous materials with NMR microscopy

The quantitative characterization of macro-porous materials with regard to pore width and pore width distribution was accomplished for the first time by using 1H-NMR microscopy in combination with suitable methods of digital image analysis. Here we present the newly developed algorithm and discuss the first experimental results. Large-pored glass filter systems filled with silicon oil as intrusion fluid were used as references. Silicates of unknown pore width were analyzed both with the new method and with Hg intrusion. NMR image data were recorded using a 3D spin echo sequence, which gave 128 slice images with a spatial resolution of 14.5 μm × 14.5 μm within each slice, with a slice-thickness of 37 μm or 48 μm. A quantitative evaluation of the 3D NMR data, with regard to pore width and pore width distribution, was done using the appropriate image processing function of the HORUS program. Individual slice evaluation was performed first, followed by an analysis of the binding elements between the slices. Pore widths of the glass filters determined using this analytical algorithm were in accordance with the manufacturer’s values, and silicate pore widths were in good agreement with the values determined by Hg intrusion.

Flocculation Control of Ceramic Powder Slurries by Water Soluble Polymers with Different Ionicities

The factors for the flocculation control of ceramic powder (alumina and alumino-silicate) slurries by various water soluble polymers with different ionicities were investigated through floc size, porosimetry, and polymer adsorption. The results are summarized as follows; (1) Floc size depends on the sign and the strength of charged sites on ceramic particles, ionicities of polymers, solid loading, and slurry pH. (2) Cationic polymers make mainly particles containing SiO sites flocculate, and the floc size increases with increasing pH and solid loading. Anionic and nonionic polymers make particles containing Al (O, OH) sites flocculate, and the floc size increases with decreasing pH and increasing solid loading. (3) The peak pore diameter in a dried floc obtained at high pH is smaller than that at low pH which shows a wide pore distribution. The high pH floc is denser than the low pH floc. (4) It was found that there are two systems showing different floc size behavior. In one system the floc size increases with increasing polymer adsorption, while in the other system it increases with decreasing adsorption. The former is anionic and nonionic polymer systems, the latter is cationic polymer system. This behavior suggests the difference in the mechanisms of polymer adsorption and/or flocculation.

Correct form of the equation of capillary condensation in porous bodies in application to the separation of adsorption and capillary condensation in slits and porous bodies of known structure and determination of their structure by adsorption and sorption isotherms

A line of thermodynamic reasoning of a very general nature is presented. It does not depend on any special pore shape or any pore width distribution. It does not require the use of the ‘disjoining pressure’ but leads to the precise equation of capillary condensation in porous bodies of any kind, applicable for any adsorption isotherm in the simplest case when the influence of the pore wall curvature on the adsorption equilibrium may be neglected.

RANDOM NETWORKS AND MIXING LAWS

Random networks are investigated as models of heterogeneous media. A general approximate structure is used where the networks are described as a system of embedded networks, and the critical behavior and averaging behavior of such networks are developed. These results are applied to a study of the electrical conductivity of porous media, with special attention to an Archie's law behavior. It appears that the wide range of crack and pore widths in rocks makes the resulting conductivity relatively insensitive to the topology of their interconnections and allows one to make reasonable predictions of rock conductivities, given the distribution of crack and pore widths. It also appears that with low porosity rocks the conductivity is controlled by the microcrack population which only accounts for a fraction of the total porosity. It would seem, therefore, that Archie's law is a feature of some general trend between porosity and crack and pore width distributions rather than a fundamental property of porous media. The law of the geometric mean is an accurate predictor of the physical properties of a mixture of different materials. This mixing law can result from an equal balance of series and parallel arrangements which can be produced by an appropriate distribution of shapes. A brief look is given to problems of anisotropic distributions for the conductivity problem and it is shown how the averaging process greatly dilutes the microscopic anisotropy in producing the macroscopic properties.