A hybrid model for estimation of pore size from ortho-positronium lifetimes in porous materials

Abstract

The present paper proposes a novel model for estimating the free-volume size of the porous materials based on the analysis of the experimental ortho-positronium (o-Ps) lifetimes collecting within more than four decades. The model is derived by combining the semi-classical (SE) physics model, which works in the region of large pores (pore size R > 1 nm), with the conventional Tao-Eldrup (TE) model, which is applicable only for the small-pore region (R < 1 nm). Thus, the resulting model, called the hybrid (HYB) model, is able to smoothly connect the o-Ps lifetimes in the two regions of the pore. Moreover, by introducing the o-Ps diffusion probability parameter (D), the HYB model has reproduced quite well the experimental o-Ps lifetimes in the whole region of pore sizes. It is even in a better agreement with the experimental data than the most up-to-date rectangular TE (RTE) and Tokyo models. In particular, by adjusting the value of D, * Corresponding Author the HYB model can also describe very well the two defined sets of experimental o-Ps lifetime in the pores with spherical and channel geometries. The merit of the present model, in comparison with the previously proposed ones, is that it is applicable for the pore size in the universal range of 0.2 − 400 nm for most of porous materials with different geometries.

Exploring the Sub-nanoscale Structure of Cobalt Molybdenum Sulfide and the Role of a Cobalt Promoter in Catalytic Hydrogen Evolution

“…Meanwhile, the presence of the third positron lifetime components τ 3 in CoS and MoS 2.46 and their mixtures indicated the existence of nanoporous structure in these samples. We can estimate the sizes of these nanopores by using the latest hybrid model, and the results are shown in table . Here, one can see that the nanopore size of mixed samples (∼0.47–0.65 nm) fell in between the nanopore size of single MoS 2.46 (∼0.45 nm) and single CoS (∼0.67 nm) samples.…”

High-yield thermalized positronium at room temperature emitted by morphologically tuned nanochanneled silicon targets

“…The Ps emission energy into the vacuum depends on the number of collisions with the walls and the energy-loss rate per collision that is determined by the characteristics of the surface of the pores [13,16,[23][24][25][26][27]. The number of collisions is decided by the depth at which Ps is formed and by the morphology of the pores (namely shape, length, diameter, interconnection and tortuosity) [13,16,[23][24][25][26]28]. In large pores, the rate of interaction with the inner surfaces is reduced and the cooling time required to reach a given temperature is consequently extended [27,29].…”