Preparation of Compositionally Complex Ultra-High Temperature Ceramics via Group IV Metal Functionalized Preceramic Polymers

Materials capable of withstanding ultra-high temperatures are becoming increasingly important for various aerospace applications, ranging from atmospheric re-entry shielding to aircraft brakes. While silicon-based ceramics have proven to be a key class of materials for these harsh applications, introduction of transition metals into these ceramics is required for ultra-high temperatures conditions. Preparation of ultra-high temperature ceramics (UHTCs) using traditional inorganic powder sintering methods limits the structural/compositional designs possible and is challenging for preparing composite components. Preceramic polymers (PCPs) have been used to address these challenges via the synthetic tunability and processing properties of polymers prior to pyrolysis. Following pyrolysis of the PCP, a polymer derived ceramic (PDC) is obtained. By tuning the PCP structure, curing/pyrolysis conditions, and pyrolysis atmosphere, the composition of the PDC can be manipulated for different properties.<br/>Here we report that by functionalizing a commercially available polysilazane-based PCP with transition metal complexes, we have prepared polymer-metal complexes that convert to UHTCs composites when pyrolyzed. In addition to functionalization with the individual group IV metal (Ti, Zr, and Hf) complexes, a blend of the three metals was prepared to understand how the materials blend/separate in PDCs. Following ceramization at different temperatures, X-ray diffraction (XRD) and atomic pair distribution functional (PDF) analysis are used to understand the structural evolution of the material from amorphous to crystalline ceramics. A combination of quantitative energy dispersive X-ray spectroscopy (EDS) and selected area diffraction from transmission electron microscopy (TEM) was utilized to observe the distribution of atomic species within the ceramic. From these various methodologies, the compositions of the PDCs were found to consist of silicone and transition metal carbides, nitrides, and carbonitrides. Ultimately, we report a route to polymer derived compositionally complex UHTC nanocomposites suitable for various high temperature applications.