Impact of doping on the mechanical properties of acicular mullite

Acicular mullite (ACM) is a highly porous ceramic with a needlelike microstructure. Next-generation ACM-based diesel particulate filters will require porosities >60%, making optimizing ACMʹs mechanical properties a key area of interest. A prior study determined that, for the range of microstructures evaluated, the elastic modulus, strength, and fracture toughness were largely functions of total porosity and not needle or pore size, consistent with the Gibson–Ashby foam model. Therefore, alternate strengthening and toughening methods were sought. Doping the ACM precursor with either MgO or Nd2O3 produced ACM microstructures that appeared similar but had differing bulk mechanical properties. The mechanical properties of the mullite needles, the intergranular glassy phase, and the mullite–glass interface of the ACMs were investigated, but no major differences were found. Using X-ray computed tomography, a 3D imaging technique, it was found that MgO-doping of the ACM created a less uniform, and thus weaker, microstructure than Nd2O3-doping.