Current and future power systems require chromia-forming alloys compatible with high-temperature CO₂. Important questions concerning the mechanisms of oxidation and carburization remain unanswered. Herein we shed light onto these processes by studying the very initial stages of oxidation of Fe22Cr and Fe22Ni22Cr model alloys. Ambient-pressure X-ray photoelectron spectroscopy enabled in situ analysis of the oxidizing surface under 1 mbar of flowing CO₂ at temperatures up to 530 °C, while postexposure analyses revealed the structure and composition of the oxidized surface at the near-atomic scale. We found that gas purity played a critical role in the kinetics of the reaction, where high purity CO₂ promoted the deposition of carbon and the selective oxidation of Cr. In contrast, no carbon deposition occurred in low purity CO₂ and Fe oxidation ensued, thus highlighting the critical role of impurities in defining the early oxidation pathway of the alloy. The Cr-rich oxide formed on Fe22Cr in high purity CO₂ was both thicker and more permeable to carbon compared to that formed on Fe22Ni22Cr, where carbon transport appeared to occur by atomic diffusion through the oxide. Alternatively, the Fe-rich oxide formed in low purity CO₂ suggested carbon transport by molecular CO₂.

当前和未来的电力系统需要与高温 CO ₂兼容的氧化铬合金。关于氧化和渗碳机制的重要问题仍未得到解答。在此，我们通过研究 Fe22Cr 和 Fe22Ni22Cr 模型合金氧化的初始阶段来阐明这些过程。环境压力 X 射线光电子能谱能够在高达 530 °C 的温度下在 1 mbar 流动的 CO ₂下对氧化表面进行原位分析，而曝光后分析则揭示了氧化表面在近原子尺度上的结构和组成。我们发现气体纯度在反应动力学中起着关键作用，其中高纯度 CO ₂促进了碳的沉积和 Cr 的选择性氧化。相比之下，在低纯度 CO _{2 中}没有发生碳沉积，随后发生了 Fe 氧化，从而突出了杂质在定义合金早期氧化途径中的关键作用。与在 Fe22Ni22Cr 上形成的相比，在高纯度 CO _{2 中的}Fe22Cr 上形成的富含 Cr 的氧化物更厚，对碳的渗透性更强，其中碳传输似乎是通过通过氧化物的原子扩散发生的。或者，在低纯度 CO _{2 中}形成的富铁氧化物表明通过分子 CO ₂传输碳。