Processing and mechanical properties of mullite and mullite–alumina composites reinforced with carbon nanofibers

In the present work homogeneous mullite and mullite–alumina composites reinforced with carbon nanofibers (CNFs) were prepared. The stability of aqueous mullite and mullite–CNFs suspensions was studied through zeta potential and rheological behaviour of concentrated slurries. Slurries were optimised in terms of dispersant concentration and solids content and further used for the preparation of homogeneous mixtures of powders by freeze drying. The obtained powders were characterised through the determination of particle size distribution and morphology by Field Emission Scanning Electron Microscopy (FSEM) and Laser Scattering. The freeze dried powders were used to obtain dense composites by spark plasma sintering. Their microstructure and mechanical properties were evaluated. It was found that mullite and mullite–alumina composites reinforced with 2 vol.% CNFs maintain the strength and hardness of the ceramic matrix and presents higher values of toughness. The results indicated the homogeneous distribution and the survival of CNFs after consolidation.