Ceramica celular

J Porous Mater (2008) 15:419–425 DOI 10.1007/s10934-007-9101-y

Synthesis of porous biomorphic a/b-Si3N4 composite from sea sponge
C. R. Rambo Æ H. Sieber Æ L. A. Genova

Received: 25 July 2006 / Revised: 17 November 2006 / Published online: 12 May 2007 Ó Springer Science+Business Media, LLC 2007

Abstract Biomorphic a/b-Si3N4 composites were produced from natural sea sponge via replication method. The sponges were impregnated with a Si-containing slurry via dip-coating. After coating, the sponges were submitted to oxidation at 600°C for 1 h to decompose the bio-polymers followed by burning out of carbon, leading to a Si-skeleton. Subsequent thermal treatment at 1,450°C for 5 h under flowing nitrogen promoted the nitridation of the Si resulting in a/b-Si3N4 with an a/b fraction of 67%. The ceramic composite maintained the original morphology of the sea sponge and exhibited a porosity of 88%. The microstructure comprised whiskers, small irregular shaped particles and rod-like hexagonal grains.

1 Introduction 1.1 Silicon nitride ceramics Silicon nitride is a very interesting structural ceramic due to its excellent properties, such as high fracture toughness, low thermal expansion coefficient (3 · 10-6 per °C), high strength at high temperatures, high elastic modulus (320 GPa), and high corrosion resistance [1, 2]. These properties make Si3N4 ceramics potential candidates for applications at severe conditions [3]. Two well-known crystal structures of silicon nitride are of engineering interest: a-Si3N4 and b-Si3N4. The mechanical properties of silicon nitride-based-ceramics are strongly dependent on their microstructure. It is well know that the presence of large, elongated b-Si3N4 grains with high aspect ratio enhances the toughness, by deflecting the propagation of cracks. However, for the toughness mechanisms to be effective, the energy of the grain/liquid interface should be adapted and in that way the composition of the liquid phase (and therefore, of the