Polysilsesquioxane derived ceramic foams with gradient porosity

Ceramic foams with a gradient porosity were manufactured using a self foaming process of a Si/SiC filled silicone resin in the temperature range of 220–270 °C. Subsequent pyrolysis at 1000 °C resulted in Si–O–C micro composite foams with a pronounced structural anisotropy. The porosity gradient in the foam was controlled by adjusting the polymer melt viscosity during foaming via temperature. The porosity varied from 40% to 90% within 35 mm. The gradient of the porosity caused variations of the connectivity density, structure model index and surface-to-volume ratio and influenced the gas permeability and fracture strength.