3D printing of porous low-temperature in-situ mullite ceramic using waste rice husk ash-derived silica

•In-situ mullite foam is fabricated by 3D printing (direct ink writing) technique.•RHA nano-silica contains ink shows a low solid-loading with higher dispersant need.•The ink exhibited good printability and started mullitization reaction at ∼1200 °C.•1400 °C fired printed structure retained complete mullite phase with ∼75 % porosity.•Nano-silica enhances the properties of mullite foam than commercial silica.