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Enhanced oxidation of the 9%Cr steel P91 in water vapour containing environments

机译：在含水蒸气的环境中增强9％Cr P91钢的氧化

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The short term (～100 h) oxidation behaviour of the 9%Cr steel P91 was studied at 650 ℃ in N_2-O_2-H_2O gas mixtures containing a relatively low oxygen level of 1%. The oxidation kinetics were measured thermogravimetrically and the oxide scale growth mechanisms were studied using H_2~(18)O-tracer with subsequent analyses of oxide scale composition and tracer distribution by MCs~+-SIMS depth profiling. The corrosion products were additionally characterised by light optical microscopy, SEM-EDX and XRD. It was found that the transition from protective, Cr-rich oxide formation into non-protective mixed oxide scales is governed by the ratio H_2O~((g))/O_2 ratio rather than the absolute level of H_2O~((g)). The results of the tracer studies in combination with the data obtained from experiments involving in situ gas changes clearly illustrated that under the prevailing conditions the penetration of water vapour molecules triggers the enhanced oxidation and sustains the high growth rates of the poorly protective Fe-rich oxide scale formed in atmospheres with high H_2O~((g))/O_2 ratios. The experimental observations can be explained if one assumes the scale growth to be governed by a competitive adsorption of oxygen and water vapour molecules on external and internal surfaces of the oxide scales in combination with the formation of a volatile Fe-hydroxide during transient oxidation. The formation of the non-protective Fe-rich oxide scales is suppressed in atmospheres with low H_2O~((g))/O_2 -ratios, and the healing of any such scale is promoted.
机译：研究了9％Cr钢P91在650℃，氧含量相对较低的1％的N_2-O_2-H_2O混合气体中的短期（〜100 h）氧化行为。热重法测量了氧化动力学，并使用H_2〜（18）O-示踪剂研究了氧化皮的生长机理，随后通过MCs〜+ -SIMS深度剖析分析了氧化皮的组成和示踪剂的分布。腐蚀产物还通过光学显微镜，SEM-EDX和XRD表征。已经发现，从保护性富铬氧化物形成过渡到非保护性混合氧化物水垢是由比例H_2O〜（（g））/ O_2的比例而不是由H_2O〜（（g））的绝对水平决定的。示踪剂研究的结果与从涉及现场气体变化的实验中获得的数据相结合，清楚地表明，在普遍条件下，水蒸气分子的渗透会触发增强的氧化作用并维持保护性差的富铁氧化物的高生长速率H_2O〜（（g））/ O_2比高的大气中形成氧化皮。如果假设氧化皮的生长受氧化皮的内外表面上氧气和水蒸气分子的竞争性吸附以及在瞬态氧化过程中形成挥发性氢氧化铁的结合，则可以解释实验观察结果。在低H_2O〜（（g））/ O_2-比例的气氛中抑制了非保护性富铁氧化物水垢的形成，并促进了任何此类水垢的修复。

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