Nanostructure and Calorimetry of Amorphous SiCN and SiBCN Ceramics

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Intellectual Merit: Polymer derived ceramics (PDCs) are a broad group of x-ray amorphous but nanoscopically heterogeneous materials obtained by careful thermal decomposition of organic polymers which provide silicon, carbon, oxygen, nitrogen, and/or boron in controlled proportions. They are lightweight, have excellent mechanical properties, and persist without crystallization or degradation to near 1500 oC. This project brings together groups in the U.S.A. and Germany with expertise in PDC synthesis, characterization by spectroscopic, scattering, and imaging tools, thermochemical measurements, and theory to provide systematic data and generate fundamental understanding of the structure, bonding, and stability of these materials, with an emphasis on new materials in the SiBCN system, as well as PDCs in the SiCO, SiCN, and SiOCN systems. A specific goal is to understand the origin of the recently observed thermodynamic stability (exothermic heats of formation of ternary amorphous ceramics from binary crystalline end-members) over a large range of compositions in the SiCO and SiCON systems. The nature of the nanophase domains and their interfaces which contain silicon bonded to more than one type of anion may be the origin of such stability, but much more detailed structural models must be developed. These models must be consistent with nanostructural, spectroscopic and thermochemdynamic data, and must be guided by first principles calculations of structure and interactions at the nanodomain interfaces. Specifically, Riedel at Darmstadt will concentrate on synthesis, Navrotsky at UC Davis on calorimetric measurements and thermodynamic analysis, Kleebe at Darmstadt on electron microscopy, Sen at UC Davis on nuclear magnetic resonance and vibrational spectroscopy and x-ray and neutron scattering, and Galli at UC Davis on theoretical calculations.Broader Impacts: As a Materials World Network project, this brings together researchers in the U.S.A. and Germany and provides students and postdocs an opportunity to participate in both interdisciplinary and international materials research. A structured set of exchanges of researchers and workshops is planned. A number of women (including two of the three faculty from Davis) will participate in the project and young scientists from other underrepresented groups are being recruited. Because PDCs have a wide range of potential uses, ranging from automotive and aircraft engines to coatings, the results of this fundamental study will help advance ceramic science with practical applications.