# Washcoat Nanoparticle-Driven Microcrack Enlargement in a Coated Catalyst

## TL;DR

This study shows how nanoparticles in coatings can enlarge microcracks in ceramic filters, affecting their long-term durability.

## Contribution

The first investigation into nanoparticle-driven microcrack enlargement in microcracked ceramic filters using novel imaging and mechanical testing methods.

## Key findings

- Nanoparticles from washcoating penetrate microcracks in ceramic substrates.
- Penetration hinders microcrack closure, leading to crack enlargement.
- Structural stability is maintained after three thermal cycles despite crack enlargement.

## Abstract

Nanoparticles are
avoided in coating particulate filters
made from
microcracked ceramics like aluminum titanate (AT) to prevent thermal
stress damage during manufacturing despite limited understanding of
the process. This study, first in this field, investigated the effect
of fines penetration (D
50: 21 nm) from
washcoating on the thermomechanical properties and long-term durability
of a microcracked AT honeycomb filter substrate. Through a combination
of bespoke SEM, FIB-SEM, and TEM methodologies developed, visual evidence
of nanoparticles from the washcoat penetrating microcracks in the
substrate has been obtained. The impact of this penetration upon the
substrate's mechanical properties has been successfully evaluated
using dynamic stiffness measurements through a high-temperature impulse
excitation technique (IET), providing an alternative detection methodology
to time-consuming and expensive microscopy measurements for product
development. The IET measurements revealed that the fines penetration
hinders the closing of microcracks, leading to their enlargement.
These microstructural changes are not indicated by strength testing,
as the coating increased the substrate strength. However, IET experiments
confirmed that the effect of the penetration has been shown to stabilize
after three thermal cycles, ensuring the structural stability of these
substrates even after applying a coating with nanoparticles.