Thermal diffusivity of kaolinite–mullite ceramic matrix composite with silicon nitride nanoparticle filler

•Silicon nitride nanopowder was inserted into a mullite matrix composite.•Increasing sintering temperature up to 1200°C produces higher thermal diffusivity for pure mullite.•Silicon nitride nanopowder suppresses thermal diffusivity of the composites at 1200°C sintering temperature.•Low thermal diffusivity suggests pore formation but FESEM image indicate glass-like morphology within the composites.•Silicon nitride nanopowder could cause heat transfer interruption within the composite, thus resulting in low thermal diffusivity values.