Oxygen evolution in the organic–inorganic transformation of polycarbosilane fibers via temperature‐programmed analysis

Abstract During the process of preparing SiC fibers by oxidation curing method, the chemical bonding form of oxygen and its content undergo significant changes, and oxygen plays a crucial role in the process of organic–inorganic–polycrystalline structure transformation. Currently, there are certain difficulties in specifically studying the evolution of oxygen chemical structure and the variation regularity of its content during the process of organic–inorganic transformation of precursor fibers. In this work, a novel research strategy, temperature‐programmed oxygen–nitrogen analyzer, is proposed to study the evolution of oxygen chemical structure and its content during the organic–inorganic transformation of polycarbosilane (PCS) precursor fibers. Three oxygen partial peaks of different oxygen chemical structures are separated by this method, oxygen is identified as Si–OH, low‐oxygen silicon groups (SiOC₃ + SiO₂C₂), and high‐oxygen silicon groups (SiO₃C + SiO₄). Fourier transform infrared (FTIR) and solid‐state 29 Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) validated these assignments, showing Si–OH depletion above 700°C and progressive conversion of low‐ to high‐oxygen groups with temperature. In addition, after 600°C, the number of high‐oxygen silicon groups in the system began to increase significantly. The oxygen content introduced in the low‐temperature preoxidation stage significantly affects the evolution of oxygen structure and the change of oxygen content after 700°C. Higher oxygen content (>6%) promotes the formation of more high‐oxygen silicon groups in the high‐temperature decomposition stage. The method demonstrated reliability for oxygen content below 20%, offering insights into structural evolution critical for optimizing SiC fiber properties.