High-strength and Low-Thermal-Conductivity Porous Multi-Principal Cation Mullite Ceramic

Abstract

The secret of porous mullite as a thermal insulation material lies in its excellent mechanical properties and lower thermal conductivity. The optimization of performance often depends on the structure design. Herein, via NH4HCO3 as a sacrificial material to fabricate porous multi-principal cation mullite (MPCM) ceramics that have not been reported for 4 doping elements (Mg, Ti, Zr, and Cr) by a sacrificial template method. The novelties of the present work are: (1) The multiple components cause a serious lattice distortion at the microscopic scale, which increases the mechanical properties of porous MPCM ceramics. (2) Porous MPCM (total porosity ≈ 54%) exhibits superior compressive strength (≈ 93 MPa), and the compressive strength with porosity was well modeled based on the Balshin and Rice equations. (3) As a proof-of-concept, we predict the thermal conductivity of pure mullite (PM) with the same porosity as MPCM ceramics. Here it proved the superiority of MPCM (0.67 W∙m-1∙K-1, 1,000 °C) as a thermal insulation material over conventional PM. Porous MPCM prepared by NH4HCO3 will pave a new path for the design of advanced thermal-insulation materials.