Preparation of cellular SiBOC foams by precipitating methylvinylborosiloxane oligomers within melamine formaldehyde foam scaffold

Abstract

SiBOC cellular ceramic foams were realized by precipitating methylvinylborosiloxane (MVBS) oligomers within reticulated poly(melamine-formaldehyde) (PMF) foam followed by drying and ceramization. The conventional method of impregnation-squeezing-drying exhibited MVBS starvation at the foam-core as the MVBS oligomers migrate to the surface due to its high solubility in ethanol and small cell size (200 ppi) of the PMF foam. In contrast, the precipitation of the MVBS oligomers on the web of the PMF foam prevents their migration to the surface. Ceramization by heat treatment at 1500 °C in inert atmosphere resulted in amorphous SiBOC cellular foams with cells in the size range of 20–400 μm. The density, compressive strength and thermal conductivity of the SiBOC foams were modulated in the ranges of 0.18−0.39 gcm−3, 0.3 to 0.87 MPa and 0.08−0.13 Wm-1 K-1, respectively, by using MVBS solution of concentrations in the range of 37–73 wt.%. The SiBOC foams remain amorphous up to 1600 °C beyond which extensive crystallization and phase separation occurs. Exposure of the SiBOC foam bodies at 1300 °C in air atmosphere showed negligible (∼ 0.2 wt.%) weight gain due to oxidation, indicating its potential as thermal protection material in oxidizing atmosphere.