Preparation of Si3N4 Porous Ceramics via Combined Foam-gelcasting and Catalytic Nitridation with Fe Powder as Catalyst

Si3N4 porous ceramics were fabricated by a combined foam-gelcasting and catalytic nitridation method at 1473-1623 K using silicon powder as the starting material,hexadecyl trimethyl ammonium bromide(CTAB)as the foaming agent,and different amounts of micron Fe powder as the catalyst.The effects of the nitridation temperature and the Fe powder addition on the phase composition,the mechanical properties,and the microstructure of the samples were researched.The results show that when nitriding at 1573 K for 5 h and adding 1 mass%Fe powder(with respect to the Si powder),the sample has a high porosity and suitable mechanical properties:the porosity of 76.5%,the compressive strength of 16.2 MPa,and the specific strength of 22.7 MPa•cm3•g^-1.

Foam-gelcasting preparation of porous Si C ceramic for high-temperature thermal insulation and infrared stealth

Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the development of new military equipment.However,the controllable synthesis of PSCs with both hierarchical pore structure and thermal/mechanical stability remains challenging.In this work,such PSCs were prepared by a facile foam-gelcasting/solid-state reaction method,using silicon powders and glucose-derived carbon as starting materials.The favorable dispersibility and wettability of hydrophilic carbon microspheres and the in-situ formed SiC guarantee the highly porous structure(92.8%porosity),comparable bulk density(0.20 g·cm^(-3))and reasonable mechanical property of the product.The designed PSCs performed outstanding high-temperature performance,especially thermal insulation in both oxidizing and inert atmospheres.More importantly,the composite architecture of PSCs and low emissivity layer(Al foil)exhibited desirable infrared stealth property(at a temperature up to 1100℃),significantly extending the operating temperature range of thermal camouflage material.The unique combination of excellent properties would make PSCs a potential candidate material for future thermal protection and infrared stealth applications in an extreme environment.