Controlling Mechanical Properties of Porous Mullite/Alumina Mixtures Via Precursor‐Derived Alumina

This study focuses broadly on synthesis and characterization of porous mullite/alumina mixtures for use as matrices in oxide fiber composites. Specifically, an assessment is made of the utility of a precursor‐derived alumina (PDA) in controlling both the modulus and the toughness of mullite‐rich particle mixtures. Property changes are probed through models of the mechanical behavior of bonded particle aggregates. Consideration of the conditions needed to cause crack deflection at a fiber–matrix interface yields an upper allowable limit on the concentration of PDA to ensure damage tolerance in a fiber composite. The predicted critical concentration lies in the range of about 7–9%, depending on the mullite/alumina ratio in the particle slurry and the subsequent aging treatment. Values slightly below this limit should yield composites that exhibit a desirable balance between fiber‐ and matrix‐dominated properties.