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Polymer-derived ceramic foams with hierarchical porosity from polymer-demixing processesWednesday (07.10.2020) 13:20 - 13:40
Polymer-derived ceramic foams were generated by the combination of Schwartzwalder´s reticulation process for the manufacturing of open cellular foams and a demixing process of two immiscible preceramic polymers. As a template a 20 ppi polyurethane foam was coated with dispersion containing two different preceramic polymers (Silres H62C and Silres MK, both Wacker Silicones) and two fillers: silicon carbide and a mixture of silicon carbide and silicon. After template coating, additional pores were generated within the coating layer due to a demixing process of the H62C and MK polymers during dispersant evaporation. The resulting structure consisting of foam cell pores and of strut pores originating from this demixing process, remained unaffected after drying, cross-linking, template removal and pyrolysis. Polymer-derived ceramic foams with an open strut porosity of 33 % to 36 % and a total porosity, exceeding 92 %, were obtained; the compressive strength is ~0.2 MPa. As a result of the strut porosity generated by the demixing process, the specific surface area of the pyrolyzed foams increased from 55 cm² g-1 for samples without additional strut pores to ~145 cm² g-1 for samples with additional strut porosity.