Corrosion of Titanium: Part 1: Aggressive Environments and Main Forms of Degradation

Abstract

expanded to other applications, such as power plants, the foodindustry,petrochemicalplants,refineries,heatexchangers,marinestructuresandmedicalprostheses(4,5). Commercially available titanium is classified depending on its purity and elemental composition. The main classification for titanium is provided by the American Society forTestingandMaterials(ASTM).Thefirst4ASTMgradesof titanium are referred to as "commercially pure" and are not alloyed but only present differences in terms of contents of impurities, especially oxygen (6): grade 1 contains a maxi-mumof0.18% oxygen whilegrade4hasamaximumof0.40%.

Enhancement of pure titanium localized corrosion resistance by anodic oxidation

“…After surface polishing, anodization treatments were conducted in two different regimes: fixed current density, for samples anodized up to 120 V, and constant voltage ramp, for samples anodized from 120 to 200 V. In the first case the current was supplied by an AimTTi PLH120 DC power supply, able to operate up to 120 V and 0.75 A; in the second case a custom pre‐industrial implant with three rectifiers of 150 V each and a current limit of 10 A was used. All the anodization treatments were conducted in 0.5 M sulfuric acid electrolyte at ambient temperature because of previous knowledge on the behavior of this electrolyte . However, the possibility to carry out anodization treatment in similar but less aggressive electrolytes, such as sodium sulfate, was already demonstrated by past work …”

“…All the anodization treatments were conducted in 0.5 M sulfuric acid electrolyte at ambient temperature because of previous knowledge on the behavior of this electrolyte . However, the possibility to carry out anodization treatment in similar but less aggressive electrolytes, such as sodium sulfate, was already demonstrated by past work …”

Evaluation of oral microbial corrosion on the surface degradation of dental implant materials

“…In particular, Ti and other metallic substrates are hypothesized to undergo accelerated corrosion due to an acidic, crevice‐like environment generated by biofilm formation and bacterial cell metabolism on the implant surface . The combination of an acidic environment and crevice reduces the passivity of the oxide layer while restricting the flow of oxygen necessary to re‐passivate the surface . As a result, Ti 4+ ions are generated which can accumulate into the surrounding soft and bone tissues, thereby exacerbating the inflammatory response .…”

Corrosion resistance enhancement of chemically oxidized titanium through NaOH and H2O2 exposure

“…Titanium and its alloys are widely appreciated for their high corrosion resistance in environments that are critical even for high‐end stainless steel (duplex UNS S31803 and UNS S32750), such as concentrated chlorides . This resistance is due to a thin (1.5–10 nm) but compact oxide layer that is naturally formed when the metal is exposed to the air. For this property, together with high strength, high fracture toughness and low density, titanium is used where other metals would fail, such as offshore, acid environment, aerospace, automotive, high temperature, chemical & food industry, marine hydrometallurgical application, and nuclear fuel wastes containment …”

“…Hydrogen embrittlement happens on alpha and alpha plus beta titanium due to their low hydrogen solubility in α‐Ti, stress corrosion cracking can also happen in very specific environments, for example, nitrogen tetroxide (N 2 O 4 ), red‐fuming nitric acid or solid cadmium . However, the most critical forms of corrosion of titanium are due to localized breaking of passive layer and this is favored by the presence of concentrated halides, such as hot salty water (above 200 °C) or bromide containing species …”