[理学]lecture_8_Corrosion.pdf

Corrosion issues for nuclear reactor materials Key words for this part •corrosion; gereral corrosion; local corrosion; pitting; crevice corrosion; galvanic corrosion SCC; • What are the main corrosion environment for nuclear reactor materials? Corrosion: the environmental degradation of materials The disintegration of an material into its constituent atoms due to chemical reactions with its surroundings. Erosion of the carbon steel reactor head, caused by a persistent leak of borated water. 2002年3月6日，Davis-Besse USA • According to corrosion mechanism: • Physical corrosion: physical solution induced • Chemical corrosion: chemical reaction induced. Oxidation • 酸性气体腐蚀： H S + Fe FeS + H 2 2 • 在800℃以 上高温下进 行迅速 n M + O MO 2 n 2 • 金属氧化的热力学判据 – 金属被氧化的化学腐蚀表现为氧化膜逐渐增厚，体积不 断变化，但温度和压力不变。 – 根据热力学第二定律，从等温等压的吉布斯（Gibbs ）自 由能的 △G值可判断金属是否自发氧化。即 • △G＜0时，氧化反应能自发进行， • △G＞0时则不能， △ ＝ 时为平衡状态。 • G 0 R为普适气体常数， 1 1 P R=1.198717Cal/K.mol； O ΔG =−RT ln +RT ln RT ln 2 T P P / P / PO2为标准氧分压 O O O 2 2 2 P O2为体系中的氧分压 当环境体系氧分压P O2大于氧化物分解压PO2 时，氧化反应自 发进行 • Electrochemical corrosion: chemical reaction involving the trans