空天往返飞行器以大于第一宇宙速度再入返回大气层时，来流空气受到激波压缩和黏性阻滞减速作用，导致飞行器周围流场压力和温度急剧升高，氧、氮分子发生能量激发、离解、电离等复杂物理化学反应，形成高焓化学非平衡等离子体环境，最高焓值在25 MJ/kg以上。离解的氧、氮原子还会与防热材料在高温界面处发生显著的气固耦合作用，如催化复合、氧化氮化、烧蚀辐射等复杂演化行为，其中高温界面是指边界层内复杂高温环境与防热材料本身之间的气固界面，此过程不仅会释放大量的化学反应热，还可能会因氧化烧蚀破坏飞行器结构，威胁飞行安全。因此加强对高温界面处复杂演化行为的认知对于气动热环境和材料响应的精确预测极为必要。

  具有耐高温、低烧蚀等优良特点的SiC基材料在空天往返飞行器可重复热防护应用中十分具有发展前景。该类材料主要依赖SiC与氧原子发生氧化反应形成致密的保护性氧化层，覆盖在材料表面和填充材料裂缝及孔隙，降低氧氮原子向材料内层的扩散速率，抑制其与内层基体材料的进一步化学反应，实现对内部结构的防护作用。然而在日益严苛的高焓长时再入环境下，氧化层可能会分解或进一步被氧原子侵蚀，此时SiC基防热材料表面物性发生改变，可能会导致被动氧化向主动氧化行为的演化、材料表面温度大幅跃升等现象的发生，造成保护的失效。由此可看出如何精确表征氧、氮原子相关的物理化学反应进程及动态演化规律是开展高温界面处催化氧化等演化行为研究的关键。

  高温界面处物理化学反应的发生常伴随着特征光谱的产生，可通过对特征光谱进行解析获得材料高温界面反应过程中的关键物理量信息，基于此本文围绕易于调控的低压射频等离子体环境开展了光谱方法可行性实验验证，主要包括窄带光谱成像方法在流场轮廓表征方面的应用、发射光谱方法进行多组分辨析和化学反应示踪能力的验证以及激光吸收光谱方法进行氧氮原子双组分同时定量测量的实现；并对不同光谱信息进行标定处理，得到窄带光谱强度响应曲线以及光谱仪光谱响应曲线，从而得到所测量位置的实际辐照度结果；吸收光谱信息经干涉仪标定后将时域信号转换为频域信号，用于平动温度和粒子数密度的计算，同时对温度和数密度测量不确定度进行了评估。等离子体空流场特性及防热材料表面光谱特性分析的实验结果证明了上述光谱方法具备过程中多物理量测量和动态变化规律实时监控的能力。

  在此基础上，结合过程光谱信息与实验前后材料宏观和微观结构组分信息，在1 MW高频感应等离子体风洞提供的高焓环境下开展了SiC材料高温界面催化氧化演化行为及规律的分析研究。以宏观热响应信息材料表面温度作为指引，改变实验热流参数，设计了热流为3.1 MW/m²和热流为3.7 MW/m²的两种状态，以下简称为低热流和高热流，用于产生仅存在被动氧化行为与主被动氧化行为耦合竞争的两种对比实验状态。两种实验状态后的材料表面宏观形貌与微观结构组分存在明显差异，低热流状态下材料表面颜色发生变化，经和实验前材料扫描电镜（SEM）结果对比可看出表面存在白色的团聚状SiO₂颗粒；高热流状态下材料表面出现明显SiO₂氧化层，X射线衍射分析（XRD）检测为方石英，从过程中的发射光谱结果中也可以看到高热流状态下出现特征Si原子谱线。结合发射光谱监测到的具有时序变化特征的氧、氮原子及特征组分的演化信息，可实现不同状态下材料高温界面处物理化学反应路径的初步推断及反应进程的定性表征。吸收光谱则可提供量化的氧氮原子数密度信息和温度等热力学状态参数，用以分析材料高温界面处催化氧化动态行为发展过程及竞争关系。相同状态下吸收光谱轴向空间分辨解析表明近表面的氧和氮的平动温度均低于远表面的平动温度，粒子数密度结果则是近表面要高于远表面，氮原子的平动温度和粒子数密度均高于氧原子。氧氮原子的窄带光谱成像结果中也表明两种组分具有不同的流场分布轮廓。低热流状态下，氧氮原子在过程中平动温度和粒子数密度变化幅度较小，仅发生微弱被动氧化反应；高热流状态下，两种组分的平动温度保持下降趋势，氮原子数密度后期有上升趋势，综合分析可能原因是材料表面通过被动氧化反应生成的氧化层会影响材料催化行为，降低原子的催化复合速率，氧原子受到氧化反应消耗，数密度维持动态平衡，同时SiO₂分解也会吸收大量的热量，导致流场平动温度降低，这也解释了流场中氧氮原子辐射强度呈下降趋势的原因。

  综上可得出多物理量光学诊断研究方案可为材料复杂的高温界面催化氧化演化行为提供可靠的分析视角，本文对于催化氧化反应动态演化规律及耦合竞争趋势的表征可为高温界面处演化行为的研究提供参考价值。

    When the aerospace vehicle reenters the atmosphere at a velocity exceeding the first cosmic velocity, the incoming air is decelerated through shock wave compression and viscous retardation. This process causes sharp increases in both pressure and temperature within the surrounding flow field, leading to a series of complex physical and chemical reactions. These include energy excitation, molecular dissociation, and ionization of oxygen and nitrogen, generating a high-enthalpy, chemically non-equilibrium plasma environment with enthalpy values exceeding 25 MJ/kg. In this extreme environment, dissociated and highly reactive oxygen and nitrogen species interact significantly with the thermal protection materials at the high-temperature interface. These interactions encompass complex processes such as catalysis recombination, oxidation nitridation, and ablation radiation. Here, the high-temperature interface represents the gas-solid layer where the reactive high-temperature plasma meets the thermal protection material. The chemical reactions occurring at this interface release substantial amounts of heat, which can lead to oxidative ablation and structural degradation, posing serious threats to the vehicle’s structural integrity and flight safety. Consequently, advancing our understanding of these complex reactions and the material evolution at the high-temperature interface is critical. Such insights are essential for accurately predicting the aerothermal environment and material response under extreme reentry conditions.

    SiC-based materials exhibit exceptional properties, including high-temperature resistance and low ablation rates, making them highly promising for reusable thermal protection in aerospace applications. Their protective function largely depends on the oxidation reaction between SiC and oxygen atoms, which generates a dense oxide layer that coats the material’s surface. This oxide layer fills surface cracks and pores, effectively slowing the diffusion of oxygen and nitrogen atoms into the material’s interior. By limiting these diffusion processes, the oxide layer inhibits further reactions with the inner matrix, thereby preserving the internal structure. However, under extreme high-enthalpy, long-duration reentry conditions, this oxide layer may degrade due to interactions with oxygen atoms, potentially leading to surface property changes in SiC-based materials. These changes can shift the oxidation process from passive to active oxidation, causing significant surface temperature increases and risking protective failure. Therefore, accurately characterizing the physicochemical reactions and dynamic behaviors of oxygen and nitrogen atoms is essential. This understanding is crucial for studying catalytic oxidation and other complex reactions at high-temperature interfaces.

    Physicochemical reactions at high-temperature interfaces often emit characteristic spectra. Analyzing these spectra provides key physical data on high-temperature interface reactions of materials. To explore this, we conducted feasibility experiments in a controlled low-pressure plasma environment. These experiments included the application of narrow-band spectral imaging for flow field profiling, emission spectroscopy for multi-component resolution and reaction tracing, and laser absorption spectroscopy for the quantitative measurement of oxygen and nitrogen atoms. Each spectral method was calibrated. The narrow-band spectral intensity response and spectrometer response curves enable accurate irradiance measurements. Time-domain signals from absorption spectroscopy were converted to frequency-domain signals after interferometer calibration, facilitating calculations of translational temperature and particle density while also assessing measurement uncertainty. Experimental results provided insights into plasma airflow field characteristics and the spectral behavior of thermal protection material surfaces. The findings demonstrate that these spectral methods can measure multiple physical quantities and monitor real-time dynamic changes.

    Building on this, the SiC materials evolution behavior of catalysis and oxidation at high-temperature interface was studied in a high enthalpy environment. This environment was provided by the 1 MW high-frequency induction plasma wind tunnel. The study combined process spectral information with the macroscopic and microstructure components of the materials pre- and post-experiment. The surface temperature guided adjustments to heat flux, setting low and high heat flux conditions of 3.1 MW/m² and 3.7 MW/m², respectively. These conditions are allowed to compare passive oxidation alone with the combined effects of active and passive oxidation. Significant differences in the macroscopic appearance and microstructure of the material emerged after exposure to these conditions. Unde the low heat flux condition, the surface color changed, with agglomerated sparing SiO₂ particles forming observed by scanning electron microscope. Under the high heat flux condition, a visible SiO₂ oxide layer formed, identified as cristobalite through XRD analysis. The emission spectra during the process also reveal the characteristic spectral lines of Si atoms. The physical and chemical pathways at high temperature interface under different conditions can be preliminarily inferred by time-varying emission spectra. Absorption spectroscopy provided quantitative data on oxygen and nitrogen atoms, including particle density and thermodynamic state parameters such as temperature. Axial spatial resolution analysis revealed that the translational temperature near the material surface was lower than further out, while particle density was higher. The temperature and particle density of nitrogen were consistently higher than those of oxygen. Narrow-band spectral imaging indicated distinct distribution patterns of oxygen and nitrogen atoms in the flow field. Under low heat flux, the translational temperature and particle density remained relatively stable, indicating minimal passive oxidation. Under high heat flux, the translational temperature of both elements declined, while particle density increased in later stages. This increase may be attributed to the passive oxidation layer’s impact on catalytic behavior, reducing recombination rates. Additionally, SiO₂ decomposition absorbs substantial heat, contributing to the observed drop in translational temperature.

    In conclusion, multi-physical optical diagnostic methods offer a reliable framework for analyzing catalysis and oxidation evolution at high-temperature interface. Characterizing the dynamics of these reactions provides insights into competing processes at these interfaces. This research can provide a valuable reference for future studies on the evolution behavior at the high-temperature interface.