Porous mullite ceramics with enhanced mechanical properties prepared by SLS using MnO2 and phenolic resin coated double-shell powders

Novel double-shell mullite powders with good flowability and formability for selective laser sintering (SLS) were prepared for the fabrication of porous mullite ceramics with enhanced mechanical properties. The inner MnO 2 shell was prepared by the co-precipitation reaction between MnC 4 H 6 O 4 ·4H 2 O (Mn(Ac) 2 ·4H 2 O) and KMnO 4 , and the outer phenolic resin shell was obtained via the solvent evaporation method. The influence of Mn(Ac) 2 ·4H 2 O solution content on phase composition, microstructure, pore size distribution and mechanical properties of porous mullitie ceramics was investigated. With increasing Mn(Ac) 2 ·4H 2 O content from 0 to 48 mL, the compressive strength and fracture toughness of porous mullite ceramics increased from 0.8 ± 0.1 MPa to 22.1 ± 1.0 MPa and from 0.03 ± 0.01 MPa m 1/2 to 0.53 ± 0.01 MPa m 1/2 , respectively. It was found from TEM analysis that the remarkable mechanical property enhancement was attributed to the pinning effect of the presence of MnO 2 sintering additive precipitated between the interwoven mullite grains. Correspondingly, the shrinkage increased sharply from 5.27 ± 1.3% to 23.5 ± 1.4%, while the open porosity decreased dramatically from 64.1 ± 0.6% to 48.7 ± 1.2% with the gradual reduction of open pore size distribution from 17.25 to 11.33 μm. Finally, the honeycomb mullite ceramics with very complex shapes of intersecting pore tunnels were successfully prepared by SLS. This paper provide a novel and feasible route to dramatically improve the mechanical properties of SLS-formed porous ceramic products.