Fabrication of three-dimensional interconnected hierarchically macroporous SiC by a modified freeze-gelcasting method

In this work, three-dimensional interconnected hierarchically macroporous SiC (HMS) materials with trimodal macropores were fabricated by a modified freeze-gelcasting method. In the HMS, the large and uniform 1st modal macropores up to 1 mm in size form the primary porosity, while the SiC walls contain the 2nd and 3rd modal macropores on different scales. The formation mechanism of the 1st, 2nd and 3rd modal macropores is proposed to be due to the H2O2 foaming process, unidirectional freezing and presence of organic porogens (polyacrylamide (PAM) and polyvinyl alcohol (PVA)), respectively. Both polymerized PAM and PVA cryogel upon freezing together help consolidate the foamed macroporous structures before sintering. The contents of PVA, H2O2 and surfactant all have the influence on the structures of HMS.