Band Formation during Gaseous Diffusion in Aerogels

TL;DR

This paper investigates the diffusion and reaction of gases within silica aerogels, revealing unique sheet-like solid deposit structures influenced by aerogel inhomogeneities through experimental and numerical methods.

Contribution

It provides new insights into gas diffusion and reaction patterns in aerogels, highlighting the effects of boundary conditions and material inhomogeneities.

Findings

Formation of sheet-like NH4Cl structures in aerogels

Significant differences from previous studies due to boundary conditions

Influence of nucleation centers and inhomogeneities on pattern formation

Abstract

We study experimentally how gaseous HCl and NH_3 diffuse from opposite sides of and react in silica aerogel rods with porosity of 92 % and average pore size of about 50 nm. The reaction leads to solid NH_4Cl, which is deposited in thin sheet-like structures. We present a numerical study of the phenomenon. Due to the difference in boundary conditions between this system and those usually studied, we find the sheet-like structures in the aerogel to differ significantly from older studies. The influence of random nucleation centers and inhomogeneities in the aerogel is studied numerically.