High strength sisic ceramics derived from wood powders

A new approach to the manufacture of dense reaction infiltrated silicon carbide (SiSiC) from wood-based composites is presented in a joint project by the German Aerospace Centre (DLR) and the Technical University of Munich (TUM). To produce such ceramics, wood powders of small particle sizes were homogeneously mixed with phenolic resin powder and made into boards (140×140×10 mm³) in an uni-axial thermal pressing process. By varying parameters such as wood species, particle size, amount of binding agent as well as pressure and temperature during the pressing process a wide range of structural modifications in wood composites is possible. These materials were carbonized at temperatures up to 1650°C to obtain porous carbon pre-forms for the final reaction infiltration with liquid silicon. One advantage of this process is the use of cheap raw materials such as wood and phenolic resin powder. Moreover, in contrast to natural solid wood, the isotropy of these wood-based ceramics is much higher and the properties are easily adjustable and reproducible. The micro-structure, phase composition and mechanical properties of these ceramics were investigated. Densities of up to 3070 kg/m3́ with SiC contents in the range of 70-85 vol.-%. and flexural strength values up to 400 MPa were achieved.