The characterisation of irregularly-shaped particles: a re-consideration of finite-sized, porous and fractal grains

TL;DR

This paper critically examines the usefulness of porosity and fractal dimension in characterizing irregular particles, proposing alternative measures 'inflation' and 'dimensionality' for finite-sized aggregates.

Contribution

It introduces new parameters 'inflation' and 'dimensionality' to better characterize finite-sized, irregular particles, addressing limitations of traditional porosity and fractal dimension.

Findings

Porosity and fractal dimension have limited usefulness for finite-sized aggregates.

Highly porous aggregates (>80%) may be physically unconstructable.

Proposed parameters 'inflation' and 'dimensionality' effectively characterize particle shape and structure.

Abstract

Context. A porous and/or fractal description can generally be applied where particles have undergone coagulation into aggregates. Aims. To characterise finite-sized, porous and fractal particles and to understand the possible limitations of these descriptions. Methods. We use simple structure, lattice and network considerations to determine the structural properties of irregular particles. Results. We find that, for finite-sized aggregates, the terms porosity and fractal dimension may be of limited usefulness and show with some critical and limiting assumptions, that highly-porous aggregates (porosity > 80%) may not be constructable. We also investigate their effective cross-sections using a simple cubic model. Conclusions. In place of the terms porosity and fractal dimension, for finite-sized aggregates, we propose the readily-determinable quantities of inflation, I (a measure of the solid filling factor and size), and dimensionality, D (a measure of the shape). These terms can be applied to characterise any form of particle, be it an irregular, homogeneous solid or a highly-extended aggregate.