Processing, microstructure and elastic properties of mullite-based ceramic foams prepared by direct foaming with wheat flour

摘要

Mullite-based ceramic foams with bulk densities as low as 0.4 g/cm(3), porosities between 49 and 88% and average foam cell sizes in the range 100-320 mu m are fabricated by direct foaming from suspensions containing wheat flour and partial sintering at 1600 degrees C. Stereology-based image analysis is used to determine a complete set of global microstructural descriptors, i.e. the porosity from foam cells (8-88%), interface density, mean curvature integral density and the related pore size measures (mean chord length and Jeffries size). Elastic constants are determined via impulse excitation (Young's moduli 2.3-21.4 GPa, shear moduli 0.9-8.8 GPa, bulk moduli 1.5-12.9 GPa, Poisson ratios 0.193-0.234). Elastic moduli obey the power-law prediction (Gibson Ashby relation for open-cell foams) for foams with porosities higher than 70%, but for lower porosities they are significantly lower, due to concave pores in the partially sintered matrix. (C) 2015 Elsevier Ltd. All rights reserved.