Electrochemical Studies on Silicate and Bicarbonate Ions for Corrosion Inhibitors
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INTRODUCTION
THE AISI 4340 steel (UNS G43400) is an ultrahighstrength low-alloy steel that combines deep hardenability with high ductility, toughness, and strength, and is considered as the benchmark for ultrahigh-strength steels.[1] These properties make the steel useful for industrial applications where high strength in heavy sections is required.[1] Yucca Mountain, located on the southwest corner of the Nevada Test Site, in Nye County, Nevada, has been chosen as the potential site for spent nuclear fuel and high-level radioactive waste in the United States.[2] Currently, different types of steels are being considered for tunnel reinforcement applications inside the repository. These include stainless steels, low- and medium-carbon steels, and high-strength lowalloy (HSLA) steels. These materials may see significant amounts of corrosion over the lifetime of the repository. The inhibiting effect of silicate and bicarbonate ions on the surface of AISI 4340 steel was investigated in this study. We measured this steel’s electrochemical and corrosion (CR) behavior in aqueous solutions containing sodium silicate or sodium bicarbonate to determine if either of these chemicals could be used as a suitable corrosion inhibitor for HSLA-candidate steels proposed for use as rock bolts and I-beams inside the repository MICHAEL E. MOHORICH, Graduate Research Assistant, formerly with the Chemical and Metallurgical Engineering Department, University of Nevada, Reno, NV. JOSHUA LAMB, Postdoctoral Scholar and DHANESH CHANDRA, Professor, are with the Chemical and Metallurgical Engineering Department, University of Nevada. Contact e-mail: [email protected] JAAK DAEMEN, Professor, is with the Mining Engineering Department, University of Nevada, Reno, NV 89557. RAUL B. REBAK, Research Scientist, is with GE Global Research, Schenectady, NY 12309. Manuscript submitted September 1, 2009. Article published online June 22, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
tunnels. A significant amount of research has been devoted on stress corrosion cracking of 4340 steel,[3–7] hydrogen embrittlement,[8–10] and hydrogen-induced cracking,[11–14] due to the material’s heavy use in the automotive and aerospace industries[1] and the need to understand the steel’s fracture mechanics and stress behavior under severe loading conditions.[1] However, rather limited studies have been conducted on 4340 steel to understand the corrosion science and relations to engineering applications. Myers and Saxer[15] studied the anodic polarization behavior of 4340 steel in sulfuric acid solutions, and Mansfeld et al.[16] published the effects of 4340 steel using various sodium-based salt solutions in tap water, deionized water, and a mixture of phosphonic/polyacrylic acids with fatty amine as inhibitors. Our current study builds on previous work published by Deodeshmukh;[17,18] however, his studies were limited to room temperature measurements using Rock Bolt Carbon Steel, a medium-carbon resulfurized steel, at a constant pH of 8.5. The electrolytes used in his stud
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