Photochemical and thermal conversion of boron-based polymer precursor to boron carbide ceramic

Boron-based preceramic polymers are essential precursors for the synthesis of advanced boron carbide ceramic materials valued for their exceptional thermal and chemical stability. The conversion of these polymers into a dense ceramic network through pyrolysis is a complex process involving intricate bond rearrangements, cross-linking, and gas evolution, which ultimately dictate the microstructure and properties of the final material. However, a detailed atomistic understanding of these transformations remains elusive. In this work, we utilize first-principles adiabatic and non-adiabatic quantum molecular dynamics simulations to investigate the initial stages of conventional and photochemical pyrolysis of a boron-based polymer system respectively. Our simulations explicitly track the dynamic evolution of atomic bonds, revealing the primary reaction pathways, including dehydrogenation, ring-opening of decaborane units, and the formation of B-C networks. We identify key transient species and chart the temperature-dependent evolution of gaseous byproducts like H_₂. This fundamental understanding of pyrolysis at the quantum level provides a foundation for the rational design of preceramic polymers to synthesize advanced BC-based ceramics with tailored functionalities.