MECHANISM OF SIEAM OXIDATION OF IRON-CHROM ALLLYS FOR POWER TENERATION ULTRA-SUPERCRITICAL CONDITION AND SUPPERESION OF

铁铬合金已被用作发电锅炉炉管材料，许多数据在使用条件下进行了修正。然而，水蒸气氧化的机理尚不清楚，需要抑制保护性氧化膜的剥落。超超临界水操作是提高能效的关键问题，本项目的研究目的是阐明水蒸气氧化机理和抑制剥落。通过透射电子显微镜观察早期氧化膜的发展。少量硅的加入对内氧化区(IOZ)有很大影响。IOZ的生长和消失对氧化膜起到了保护作用。氧化膜中存在许多空洞，它们可能控制着剥落。通过计算化学势在标度上的分布和质量守恒，可以定量地解释空洞的形成。结果表明，溶解在氧化膜中的质子可能会影响空穴的形成。质子在膜中的渗透研究仍在进行中。

Iron-chromium alloys have been used as materials for boiler tubes in power generation and many data were corrected in service conditions. However, the mechanism of steam oxidation has not been clarified yet and the suppression of exfoliation of protective oxide scales is required. The operation with ultra-supercritical water is a key issue to improve energy efficiency and the objects of this project area clarification of the steam oxidation mechanism and suppression of the exfoliation.The development of the oxide scale at the early stage was observed by transmission electron microscopy. The internal oxidation zone (IOZ) was strongly affected by small amount of added silicon. The growth and disappearance of IOZ contributed to the protectiveness of oxide scales. Many voids, which may govern the exfoliation, existed in the oxide scales. It was revealed that the formation of voids was quantitatively explained by calculation of chemical potential distribution in the scale and of mass conservation. It was suggested that the proton dissolved in the oxide scale might affect the void formation. The study on the permeation of proton through the scale is still in progress.