Unusual Nature of NanoDomains in Ultrahigh Temperature Polymer Derived Ceramics.

摘要

This grant has the objective of explaining the unusual properties of polymer-derived-ceramics (PDCs), so called because they are made directly from cross-linked polymers by controlled pyrolysis. The PDCs have unusual properties: (i) They remain structurally and chemically stable up to 1500 degrees C, (ii) They are amorphous in Bragg diffraction although small-angle-x ray-scattering shows the presence of nanodomains, (iii) POCs do NOT show steady state creep despite their amorphous structure, and (iv) PDCs exhibit viscoelasticity at high temperatures. The critical advance made in this grant is the development of a nanodomain model for the PDCs, which is validated by the experimental findings. The model consists of a graphene network interconnected in the form of nanodomains, about 1-5 nm in size. The graphene network stabilizes the amorphous structure of the ceramic. The unusual properties of PDCs are successfully explained by the nanodomain model. The PDCs are a new class of metastable ceramics that are likely to lead to revolutionary new technologies for high temperatures. Their amorphous nature is similar to that of polymers and metallic glasses. However, the chemical and structural stability of the PDCs at ultrahigh temperatures is unique.