Science and Technology on Advanced Ceramic Fibers and Composites Laboratory , National University of Defense Technology , Changsha 410073 , PR China.
ACS Appl Mater Interfaces. 2018 Jun 13;10(23):19712-19720. doi: 10.1021/acsami.8b04497. Epub 2018 May 29.
Amorphous SiBCN fibers possessing superior stability against oxidation have become a desirable candidate for high-temperature aerospace applications. Currently, investigations on the high-temperature corrosion behavior of these fibers for the application in high-heat engines are insufficient. Here, our polymer-derived SiBCN fibers were corroded at 1400 °C in air and simulated combustion environments. The fibers' structural evolution after corrosion in two different conditions and the potential mechanisms are investigated. It shows that the as-prepared SiBCN fibers mainly consist of amorphous networks of SiNC, SiN, B-N hexatomic rings, free carbon clusters, and BNC units. High-resolution transmission electron microscopy cross-section observations combined with energy-dispersive spectrometry/electron energy-loss spectroscopy analysis exhibit a trilayer structure with no detectable cracks for fibers after corrosion, including the outermost SiO layer, the h-BN grain-contained interlayer, and the uncorroded fiber core. A high percentage of water vapor contained in the simulated combustion environment triggers the formation of abundant α-cristobalite nanoparticles dispersing in the amorphous SiO phase, which are absent in fibers corroded in air. The formation of h-BN grains in the interlayer could be ascribed to the sacrificial effects of free carbon clusters, Si-C, and Si-N units reacting with oxygen diffusing inward, which protects h-BN grains formed by networks of B-N hexatomic rings in original SiBCN fibers. These results improve our understanding of the corrosion process of SiBCN fibers in a high-temperature oxygen- and water-rich atmosphere.
非晶态 SiBCN 纤维具有优异的抗氧化稳定性，成为高温航天应用的理想候选材料。目前，对于这些纤维在高热发动机应用中的高温腐蚀行为的研究还不够充分。在这里，我们的聚合物衍生的 SiBCN 纤维在 1400°C 的空气中和模拟的燃烧环境中进行了腐蚀。研究了纤维在两种不同条件下腐蚀后的结构演变和潜在机制。结果表明，所制备的 SiBCN 纤维主要由 SiNC、SiN、B-N 六元环、游离碳簇和 BNC 单元的非晶态网络组成。高分辨率透射电子显微镜横截面观察结合能量色散谱/电子能量损失谱分析表明，腐蚀后纤维具有无明显裂纹的三层结构，包括最外层的 SiO 层、含有 h-BN 晶粒的中间层和未腐蚀的纤维芯。模拟燃烧环境中含有高比例的水蒸气会促使大量α-方石英纳米颗粒在非晶态 SiO 相中分散，而在空气中腐蚀的纤维中则没有。中间层中 h-BN 晶粒的形成可归因于游离碳簇、Si-C 和 Si-N 单元与向内扩散的氧反应的牺牲效应，这保护了由原始 SiBCN 纤维中的 B-N 六元环网络形成的 h-BN 晶粒。这些结果提高了我们对 SiBCN 纤维在高温富氧和富水气氛中的腐蚀过程的理解。
