Kinetics of the Thermal Decomposition of Ethylsilane: Shock-Tube and Modeling Study

The thermal decomposition of ethylsilane (H3SiC2H5, EtSiH3) is investigated behind reflected shock waves and the gas composition is analyzed by gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) in a temperature range of 990–1330 K and pressure range of 1–2.5 bar. The unimolecular decomposition of EtSiH3 is considered to be initiated via a molecular elimination of H2 (H3SiC2H5 → H2 + HSiC2H5) followed by reactions of cyclic silicon-containing species. The main observed stable products were ethylene (C2H4) and silane (SiH4). Measurements are performed with a large excess of a silylene scavenger (C2H2) to suppress bimolecular reactions caused by silylene (SiH2) and to extract unimolecular rate constants. A kinetics mechanism accounting for the gas-phase chemistry of EtSiH3 is developed, which consists of 24 Si-containing species, 31 reactions of Si-containing species, and a set of new thermochemical data. The derived unimolecular rate constant is represented by the Arrhenius expression kuni(T) = 1.96 × 1012 s–1 exp­(−205 kJ mol–1/RT). The experimental data is reproduced very well by simulations based on the mechanism of this work and is in very good agreement with literature values. It is shown that EtSiH3 is a promising precursor for the synthesis of SiC nanoparticles.

本研究在反射激波后环境下对乙基硅烷（ethylsilane，分子式H₃SiC₂H₅，缩写EtSiH₃）的热分解过程开展了实验探究，实验温度区间为990~1330 K、压力区间为1~2.5 bar，采用气相色谱-质谱联用（gas chromatography/mass spectrometry, GC/MS）与高重复率飞行时间质谱（high-repetition-rate time-of-flight mass spectrometry, HRR-TOF-MS）对气相产物组分进行分析。EtSiH₃的单分子分解反应被认为以H₂分子消去为起始步骤（H₃SiC₂H₅ → H₂ + HSiC₂H₅），后续伴随含硅环状物种的反应。实验观测到的主要稳定产物为乙烯（C₂H₄）与硅烷（SiH₄）。为抑制由甲硅烯（silylene, SiH₂）引发的双分子反应并提取单分子反应速率常数，实验中引入了大量过量的甲硅烯捕获剂（C₂H₂）。本研究构建了描述EtSiH₃气相反应动力学的机理模型，该模型包含24种含硅物种、31个含硅基元反应以及一套全新的热化学数据。推导得到的单分子反应速率常数可通过阿伦尼乌斯（Arrhenius）表达式表示为：k_uni(T) = 1.96 × 10^12 s^-1 exp(−205 kJ·mol^-1/RT)。基于本研究机理开展的模拟结果可很好地复现实验数据，且与已有文献报道的数值吻合度极佳。研究表明，EtSiH₃是一种极具应用前景的碳化硅（SiC）纳米颗粒合成前驱体。