Development of Advanced Electrochemical Emission Spectroscopy for Monitoring Corrosion in Simulated DOE Liquid Waste

Macdonald, Digby D. ; Liu, Sue ; Sikora, Elizbieta ; Liu, Jun

Pennsylvania State University, University Park, PA (United States)

关键词: 08 Hydrogen;    Corrosion;    Crack Propagation;    Fractures;    Cathodes;   

DOI  :  10.2172/829897
RP-ID  :  EMSP-60219--2001
RP-ID  :  FG07-97ER62515
RP-ID  :  829897

美国|英语

来源: UNT Digital Library

【 摘 要 】

Fracture of AISI 4340 steel in concentrated sodium hydroxide solution has been monitored by measuring the coupling current that flows between the crack and the external surfaces. The results clearly demonstrate that positive current flows from the crack to the external cathodes (through the solution) during crack growth of AISI 4340 steel in concentrated (6 to12 M) sodium hydroxide solution at 70 C. The (electron) coupling current contains periodic noise that is attributed to fracture events occurring at the crack front, with the amplitude of the noise and the mean current increasing with crack growth rate. The characteristic shape of the individual transients in the noise at lower SCC crack growth rate is a rapid drop followed by slow recovery. The form of the noise in the coupling current during SCC at high NaOH concentration (8 M and 12 M) is attributed to overlap of many cracks propagating simultaneously through micro fracture events along grain boundaries. The discrete events, which have a dimension of about 49 {micro}m, are postulated to be hydrogen induced, and the mechanism of caustic cracking of AISI 4340 steel is considered to be hydrogen embrittlement along grain boundaries. Measurement of the electrochemical noise is shown to be capable of detecting and distinguishing between uniform corrosion and stress corrosion cracking in the steel/NaOH system. The coupling current data are consistent with a hydrogen embrittlement mechanism for crack advance.