Structure and properties of short fibre reinforced silica matrix composite foams

Glass (GFC) and silica (SFC) fibre reinforced silica matrix composite foams with 84–90% porosity content have been developed through slurry-based processing, involving random dispersion of 10 wt.% fibres with aspect ratios of >1000 in hydrophobized silica-based suspensions, and direct foaming for air entrapment. Fibre entanglement has not been found either in the suspensions or in the sintered composite foams. Microstructural and mercury porosimetry studies of the composite foams have shown a trimodal size distribution with small (4–8 μm), medium (40–200 μm), and large (∼1 mm or more) pores. The pores appear spherical and interconnected, with the fibres embedded in cell-walls or struts. The dynamic Young's modulus of the silica-coated GFCs is found to be ∼3.5 and ∼5.2 times that of the coated and uncoated monolithic silica foams, respectively, confirming that both fibre-reinforcement and the presence of surface coating are beneficial for increase in stiffness of the composite foams.