Insights into electric- and thermal-induced decomposition and gas evolution of silicone rubber through experiments and molecular simulations

This study investigates the degradation state of silicone rubber (SiR) under electric and thermal fields by analyzing its gas-evolution characteristics. The goal is to provide a new diagnostic approach for high-voltage cable accessories. Thermogravimetry-infrared spectroscopy (TG-IR) was used to trace the thermal decomposition products. Electrical breakdown was simulated through discharge experiments. Density functional theory (DFT) calculations and reactive force field (ReaxFF) molecular dynamics simulations were employed to verify the reaction mechanisms and decomposition pathways. The results show that under electric field, SiR mainly produces CH₄, C₂H₂, and silane (SiH₄), accompanied by CO and CO₂. Under thermal field, the main products are CH₂O, CH₄, hexamethylcyclotrisiloxane (D3), and octamethylcyclotetrasiloxane (D4), along with oxidative gases such as CO₂. Molecular simulations revealed differences in microscopic decomposition pathways. A normalized infrared spectral database was also established based on DFT calculations. Overall, this work links macroscopic gas-evolution behavior with microscopic mechanisms and diagnostic applications. It systematically elucidates the decomposition behavior of SiR under electric and thermal fields and provides a theoretical foundation for gas-infrared-based fault diagnosis in cable accessories.