Non-uniform Pore Size Distribution Research Articles

Agglomeration parameter, aggregation number, and aggregate porosity

Most ceramic powders contain amounts of agglomerates. Hard agglomerates (aggregates) which do not break up during processing may retard compaction leading to a nonuniform pore–size distribution and/or the formation of internal cracks which act as strength–limiting flaws in the sintered product [1]. So far, however, there have been few reports on the quantitative estimation of aggregation. In this study, the aggregation number is correlated with the agglomeration parameter (A) by a simple model relating aggregate density to compact density. The experiments entailed determining the green densities of seeded pellets. Aggregate density was derived from the relation between the porosities and amounts of added seed. The models and experiments permit quantitative investigation of aggregation in ceramic powders.

On the concentration dependence of surface diffusion coefficients in capillary porous materials

The influence of structural heterogeneity, in the form of a non-uniform pore size distribution, on the isotherms and surface diffusion coefficients for monolayer physical adsorption is studied. A pore size dependent langmuirian isotherm is used along with consideration of equality of chemical potentials at the pore mouths at an intersection. The diffusion is modelled by a recently developed random walk formulation. It is found that the surface diffusion coefficients are strongly influenced by the heterogeneity and have a stronger increase with overall coverage than that predicted by the Darken equation. The results are found to match the experimental data of P. C. Carman and F. A. Raal on the diffusion of carbon dioxide in carbon black without the use of a fitting parameter.

Enzyme loading in a solid support with nonuniform pore size distribution

The concept of pore size distribution is incorporated into the Clark model of enzyme immobilization in the present study. This refined model predicted that in the case of small harmonic pore radius with the same surface area and porosity of the support, more enzyme could be loaded in a support with nonuniform pores than that with uniform pores. In comparing the enzyme loading efficiency of the support with two different pore size distributions, the one with Gaussian distribution had the greater amount of enzyme immobilized than the other one with Rajagopalan's distribution. Furthermore, more enzyme could be loaded in a support with wider Gaussian pore size distribution than that with narrower distribution. The immobilized enzyme profile in the solid support with pore size distribution displayed a stepwise pattern which differed appreciably from the sigmoidal profile predicted for the support with uniform pore size. This stepwise enzyme distribution profile became sigmoidal with decreasing h(T) or increasing k. The new model could be used for designing protocols for an enzyme immobilization process.