A Direct Method for the Fabrication of Macro-Porous SiOC Ceramics from Preceramic Polymers

Cellular ceramics, possessing both open or closed porosity, find use in several demanding engineering applications because of their favorable set of properties.[1] Several processing methods have been proposed for their fabrication, including the replication of the structure of polymeric foams, direct blowing, the use of sacrificial fillers, extrusion through special dies (for honeycombs), solid freeform techniques, the mimicking of natural templates (e.g. wood) or the assemblage of fibers or hollow bodies.[2,3] Preceramic polymers, in particular silicones, have been successfully used for obtaining ceramic components (such as foams and membranes) possessing a large amount of porosity, in the micro-, meso- and macro-size scale.[4, and references therein] However, some of the fabrication methods have some limitations: for instance, direct foaming techniques often lead to a gradient in the porosity amount and pore size along the main expansion axis;[5,6] the infiltration of a silicone resin within organic sacrificial fillers requires a burn out step that has to be carried out in a very controlled fashion in order to produce components without defects (besides often requiring warm pressing – depending on the rheological characteristics of the preceramic polymer – to obtain a well controlled morphology), thus limiting the size and shape of the component that can be produced;[7] the use of supercritical CO2 is regulated by the diffusion within the solid polymer, and works well only for components of limited thickness.[8] In recent years, it has been shown that blending preceramic polymers with different characteristics (molecular weight, molecular architecture, ceramic yield) allows to produce cellular ceramics.[9,10] This paper further explores this possibility, with the specific aim of directly developing a large amount of porosity within the resulting ceramic body during a one-step pyrolysis treatment.