Effects of Environmental and Metallurgical Conditions on the Passive and Localized Dissolution of Ti-0.15%Pd

• Published in: Corrosion (Houston, Tex.) Vol. 57; no. 9; pp. 768 - 776
• Main Authors: Brossia, C.S., Cragnolino, G.A.
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.09.2001; NACE
• Subjects: Anodic polarization; Applied sciences; Breakdown; Calomel electrode; Corrosion; Corrosion environments; Current density; Electrode polarization; Environmental effects; Exact sciences and technology; Fluorides; High temperature; Metallurgy; Metals. Metallurgy; pH effects; Repassivation; Titanium; Weldments; Chlorides; Concentration effect; Temperature effect; Repassivation; pH; Localized corrosion; Palladium alloy; Fluorides; Titanium base alloys; Passivation; Passivity breakdown
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3280611

ABSTRACTThe safety strategy adopted by the U.S. Department of Energy (DOE) for the proposed high-level nuclear waste (HLW) repository at Yucca Mountain (YM) relies on several key attributes for the unsaturated repository system, one of which is the integrity of the drip shield (DS) to divert incoming water away from the waste packages.1 Primary materials being considered by the DOE for construction of the DS are Pd-bearing Ti alloys, such as Ti Grade 7(1) (UNS R52400)(2) and Ti Grade 16(3) (no UNS designation). Ti-Pd alloys are Ti alloys that have mechanical properties similar to commercial-purity (CP) Ti but exhibit considerably better corrosion resistance than CP Ti in many aqueous environments.2 Ti alloys are known to exhibit excellent corrosion resistance under many conditions as a result of the spontaneous formation of a protective Ti oxide passive film. Under undisturbed repository conditions, precipitation of salts from minerals and constituents found in the prevailing groundwater at YM may occur when incoming water contacts the heated DS surface, and this may, in turn, lead to enhanced corrosion. Studies have shown that the concentration of aggressive species such as chloride (Cl­)3 and fluoride (F­)4 can reach concentrations as high as 5 M and 0.2 M, respectively, when simulated groundwater chemistries are subjected to evaporative concentration processes. Additional studies have also shown that liquid water containing entrained solids can penetrate a boiling isotherm;5 thus, the possibility