高温高压水环境中锆合金腐蚀的原位阻抗谱特征

IN SITU IMPEDANCE CHARACTERISTICS OF ZIRCONIUM ALLOY CORROSION IN HIGH TEMPERATURE AND PRESSURE WATER ENVIRONMENT

利用电化学阻抗谱等技术研究了360℃/18.6 MPa的0.01 mol/L LiOH水溶液中退火态Zr-4合金在转折前后的腐蚀演化过程.结果表明,腐蚀转折前,锆合金氧化增重缓慢.当Zr氧化生成ZrO_2时,由于体积发生膨胀而在氧化膜中产生压应力,随着氧化膜逐渐增厚,氧化膜外层的压应力因微观缺陷凝聚而得到松弛,使得氧化膜由均匀致密的单层结构演化为外层疏松、内层致密的双层结构,阻抗谱也由单一容抗弧演变为双容抗弧,并出现高频弧减小而低频弧增大的现象.当氧化膜形成裂纹等宏观缺陷后,腐蚀发生转折,氧化增重加快,阻抗谱的2个容抗弧均快速减小.腐蚀电位和电化学阻抗谱均能原位获得腐蚀转折点的突变信息.

The electrochemical impedance spectroscopy（EIS） was used to analyze the corrosion evolution of pre- and post-transition of the annealed Zr-4 alloy in 0.01 mol/L LiOH aqueous solution at 360℃/18.6 MPa.The results show that oxidation weight gain of Zr-4 alloy increases slowly before corrosion transition.When Zr is oxidized into ZrO2,the stress appears in the oxide film due to volume expansion.With gradually thickening of the oxide film,accumulation of micro-defects will relax the stress in outer layer of oxide film.As a result,the uniform and compact oxide layer turns into double layer with a porous outer layer and a dense inner one.Meanwhile the impedance spectra evolve from single arc into double capacitive arcs.When the oxide film forms macro-defects such as cracks,corrosion transition takes place,giving rise to an acceleration of oxidation weight gain and the rapid drop of impedance and corrosion potential.Corrosion potential and electrochemical impedance spectroscopy are able to obtain in situ some information of the transition point.