DESIGNING OF SI3N4 SIC COMPOSITE-MATERIALS

The influence of dopants on the microstructure of quaternary Si-C-N-M- ceramics (M=B,P) is investigated Monolithic amorphous ceramics are obt ained by the polycocondensation of polysilazanes ((RR'SiNH)(y)) with t he appropriate alkyl amide (M(NRR')(x)) of boron or phosphorus and sub sequent pyrolysis in argon atmosphere at 1000 degrees C. The electron spectroscopic imaging method (ESI) in TEM reveals a homogeneous distri bution of the elements Si, C, N and M. Upon annealing in nitrogen atmo sphere at temperatures around 1400 degrees C, crystallisation of the a ppropriate thermodynamically stable phases occurs. Heat treatment at t emperatures up to 1800 degrees C results in micro/nano-, nano/nano- or micro/microcrystalline microstructures with design-tailored propertie s which depend on the element M. Boron as dopant forms turbostratic bo ron nitride which coats the crystalline phases, inhibits the further c rystal growth and thus leads to nanosize composite structure of the ce ramics.