Effect of Implanted Cl and Deposited Oxides on the Pitting Behavior of Aluminum

Abstract

Insight into the influence of Cl on the pitting behavior of aluminum has been gained using a combination of ion implantation and oxide deposition. High-purity Al thin-film samples were implanted with 35 keV Cl + followed by plasma deposition of an aluminum oxide ͑Al 2 O 3 ͒. The pitting potential of unimplanted areas in 50 mM NaCl increased with increasing deposited oxide thickness ͑0, 80, 140 Å͒. For implanted areas, polarization in 50 mM NaCl resulted in pitting that was insensitive to oxide thickness and implant fluence above a critical level. By comparison, polarization in 50 mM K 2 SO 4 resulted in pitting which exhibited a dependence on both deposited oxide thickness and implant fluence. Finally, the effect of the Cl source ͑solution, implantation, or both͒ on the pitting behavior of Al with a deposited oxide was examined. These results are used to support the hypothesis that both a critical chlorine distribution and oxide modification are contributing factors to pit nucleation. Pitting corrosion can be described in terms of four distinct and consecutive stages: ͑i͒ interactions at the oxide/solution interface, ͑ii͒ interactions within the passive film, ͑iii͒ metastable pitting, and ͑iv͒ stable pit growth. 1 The first two stages have been the subject of intense research efforts yet remain the least understood. The inherent difficulties in studying pit nucleation arise due to the localized nature of the attack and the short time scale associated with nucleation. Furthermore, while there are many proposed theories which seek to explain the breakdown of passive films, 2-10 the role of chloride in the oxide destabilization and pit nucleation process remains unclear. The prominent mechanisms describing the interaction of aggressive anions with the passive film include but are not limited to the following: Cl − penetration of the oxide resulting in film breakdown at the metal/oxide interface 2 ; competitive anion ͑O 2− vs. Cl − ͒ adsorption 3,4 ; complex ion formation leading to localized film dissolution or thinning 5 ; and according to the point defect model ͑PDM͒, increased cation diffusion resulting in void formation at the metal/oxide interface. 6 The first step in the penetration of chloride into the oxide film is adsorption of ions followed by absorption and migration. Several authors have studied the distribution of chloride at the oxide/solution interface 11,12 and within the oxide 12,13 under electrochemical conditions relevant to pit nucleation ͑i.e., below and at the pitting potential͒. Measurements of average chloride levels in the oxide, however, may not be representative of the local distribution associated with pit nucleation in the metal.Recently, ion implantation techniques have been used to study the pitting behavior of aluminum. 14,15 For clarity, in this paper the aqueous species is referred to as chloride, Cl − , and the implanted species is chlorine, Cl. The use of ion implantation provides a different approach to the problem, allowing the Cl concentration and distribution to be specified t...

The corrosive influence of chloride ions preference adsorption on α-Al2O3 (0 0 0 1) surface

“…For instance, using anodic polarization method, Serna et al found the pitting potential of Al 2 O 3 surface has relationship with the oxide film thickness, both a critical Cl − distribution and oxide modification are contributing factors to pit nucleation [11]. Voltammetric anodic growth curves were performed by Boxley et al to report the dissolution rate of the Al 2 O 3 film in 0-150 mM NaCl solution.…”

Effect of shot blasting on Aerial Aluminum Conductor corrosion behavior

“…After atmospheric corrosion, ACSR conductor mechanical properties and electrical properties are reduced, and may lead to line broken stocks, bolt, or even a power outage accidents. Himself at home and abroad such as aluminium and its alloy and zinc on corrosion behavior under different atmospheric corrosion medium to carry out the more basic research [1][2][3], but due to the complexity of ACSR conductor composition and structure, the composition of the corrosion behavior and corrosion products, structure more complicated [4].For the first time under laboratory conditions, such as through a cyclical wet/dry salt spray environment under the accelerated corrosion test to study the corrosion behavior of aluminum, steel and galvanized steel, based on the mass loss of the wire to evaluate degree of atmospheric corrosion of the wire, start the transmission wire corrosion behavior of laboratory research by Wang, etc [5]. Zhengyao [6] has been adopting NaHSO3 + NaCI to zinc ion in aqueous solution and aluminum alloy atmospheric corrosion process of research, the main research results and field exposure experiment results are identical with each other [7][8][9].…”

The Role of Chloride in Al Oxide Surface Transformations and Pitting -an AFM Study

“…Implantation of chlorine into the Al oxide and the oxide/metal interface was introduced as one alternative way to validate importance of the chloride incorporation mechanism [20][21][22] . It was shown that in a chloride-free environment pitting takes place on Cl + -implanted Al samples only for a chlorine distribution above some critical value [20][21][22] . The average pitting potential as a measure of the pitting susceptibility decreases with an increase of the chlorine incorporated in the oxide 22 .…”

“…Recently, the ion implantation technique has been introduced in studies of pitting corrosion 19 . Implantation of chlorine into the Al oxide and the oxide/metal interface was introduced as one alternative way to validate importance of the chloride incorporation mechanism [20][21][22] . It was shown that in a chloride-free environment pitting takes place on Cl + -implanted Al samples only for a chlorine distribution above some critical value [20][21][22] .…”