2003 F.N. Speller Award Lecture:Platinum Group Metal Additions to Titanium: A Highly Effective Strategy for Enhancing Corrosion Resistance

Abstract

Although recognized for their exceptional corrosion resistance in a wide range of chemical environments, titanium and its alloys can be susceptible to corrosion in reducing acid media, crevice attack in hot chlorides and other halide solutions, and/or stress corrosion in certain higher-strength alloys. These serious limitations may be practically and costeffectively overcome to a great extent by the addition of very minor (<0.25 wt%) amounts of platinum group metals (PGMs) to titanium and its alloys; while imparting little or no effect on alloy mechanical/physical properties or metallurgy. Through the catalytic facilitation of cathodic reduction reactions (primarily the hydrogen evolution reaction [HER]) in acidic aqueous media, these PGM alloy additions shift titanium toward noble (positive) potentials where the protective titanium oxide surface film is stable. This radically decreases alloy corrosion rates in dilute inorganic and organic acids with no detrimental influence in oxidizing media or to hydrogen absorption resistance; and dramatically elevates alloy crevice and stress corrosion temperature threshold limits in aqueous chloride (halide) environments. Although any PGM may be effective, titanium alloys based on minimal Pd and/or Ru alloying additions have been commercialized and proven to be most cost-effective to date. This paper presents an overview of the commercial PGM-enhanced titanium alloys available today, their historical evolution and metallurgy, insight into corrosion-resistance enhancement mechanisms, the scope of expanded alloy corrosion performance limits achieved, relative cost impact, and relevant current and candidate applications.

Modeling the hydrogen-induced cracking of titanium alloys in nuclear waste repository environments

“…17] On the other hand, alloying elements capable of catalyzing proton reduction may also catalyze hydrogen absorption into the alloys.…”

Materials Degradation Issues in the U.S. High-Level Nuclear Waste Repository

“…Alloying elements in a Ti alloys are generally added to enhance corrosion resistance in reducing acid conditions [61,62]. This is particularly so for the platinum group metals (PGMs).…”

Anodic Polarization Behavior of Titanium Grade 7 in Dust Deliquescence Salt Environments

“…Under reducing conditions the corrosion rate of Ti is higher than under oxidizing conditions [5]. Halide and sulfate containing solutions may induce crevice corrosion in Ti at temperatures higher than 70°C [5]. Anodic polarizations of Ti Gr 7 in 1 molar (M) chloride and fluoride containing solutions at 95°C have shown that the presence of fluoride produces significantly higher current densities at potentials above the corrosion potential [6][7][8].…”

“…It has been suggested that the susceptibility to crevice corrosion is due to the formation of low pH reducing solution under occluded conditions. Under reducing conditions the corrosion rate of Ti is higher than under oxidizing conditions [5]. Halide and sulfate containing solutions may induce crevice corrosion in Ti at temperatures higher than 70°C [5].…”

“…Also, the addition of small amounts of platinum group metals (PGM) such as Pd, Ru, etc. reduces considerably the general corrosion rate of Ti in reducing acids [3][4][5]. Some Ti alloys may be susceptible to crevice corrosion under certain conditions; however, Ti alloys are practically immune to pitting corrosion in chloride solutions under most practical applications.…”