Corrosion, aluminium

Arora, G. P., Isasi, J. A. and Metzger, M., Protective Films and Structure Dependent Corrosion in Aluminium , Corrosion, 25, 445 (1969)... 

Cr, Br , I, which cause pitting attack, and anions which form soluble complexes with aluminium , e.g. citrate and tartrate, which cause general attack. Competitive effects , similar to those observed on iron, are observed in the action of mixtures of inhibitive anions and chloride ions on aluminium. The inhibition of aluminium corrosion by anions exhibits both an upper and a lower pH limit. The pH range for inhibition depends upon the nature of the anion . 

Copper Aluminium Corrosion to copper sulphate (green) Corrosion to aluminium sulphate (white)... 

It appeared to us that if we could add aluminium corrosion inhibitors to the encapsulating resin it was possible that diffusing moisture would transport the inhibitor to the chip surface so that the aluminium conductors would experience an inhibited electrolyte rather than an agressive electrolyte and corrosion would thereby be reduced. It should be noted that this mechanism does not operate in the absence of diffusing moisture but that it is not needed in those circumstances because corrosion would not normally occur. For this approach to be successful the following conditions must be met ... 

To establish if these conditions could be met, the literature of aluminium corrosion inhibitors was searched, suitable inhibitors were chosen for evaluation, and a programme of measurements and testing Initiated. 

E. Oguzie, B.N. Okolue, C.E. Ogukwe, A.I. Onuchukwu, C. Unaegbu (2004), Studies on the inhibitive action of methylene blue dye on aluminium corrosion in KOH solution. Journal of Corrosion Science and Technology 1.1, p. 89. 

B. Garcia, M. Armand, J. Power Sources 2004, 132, 206-208. Aluminium corrosion in room temperature molten salt. 

Some understanding of the corrosion of aluminium alloys used as cladding on research and test reactor fuel has been obtained from the CRP. Aluminium corrosion is extremely complex and the variables affecting localized corrosion (pitting and crevice corrosion) act both independently and synergistically. Additional information about the effects of deposited particle composition on the corrosion behaviour of aluminium alloys is needed. Surface finish affects the corrosion of aluminium alloys, and more information is required with respect to this parameter. Additional data on the effects of certain impurity ions in basin water on localized corrosion behaviour are necessary to better identify the ions that cause corrosion. A goal would be to develop an equation for pitting as a function of water chemistry parameters. 

From an engineering standpoint, the kinetics or rate of corrosion of a system is usually of primary importance. Corroding systems are not in equilibrium and therefore thermodynamic calculations cannot be applied. For metal corrosion to occur, an oxidation reaction (generally metal dissolution or oxide formation) and a cathodic reduction reaction (such as oxygen reduction) proceed simultaneously. In most normal water environments, the overall reaction for aluminium corrosion is reaction with water to form aluminium hydroxide and hydrogen. The aluminium hydroxide has very low solubility in water and precipitates as bayerite or boehmite, depending on the temperature of the water [2.8]. 

The major factors believed to influence the pitting of aluminium alloys are conductivity, pH, and bicarbonate, chloride, sulphate and oxygen content [2.6]. Because of the interrelationship of the composition and service factors, it is difficult to predict the influence of water on aluminium corrosion from a table of water composition alone. A number of studies have been conducted of synthetic waters containing several metal and salt ions alone and in combination [2.15-2.17]. They found that the corrosion of aluminium was accelerated when salts of copper, chlorides and bicarbonates were present together, compared with cases where only a single impurity was present. In some cases where two of the three constituents were present, there was little corrosion, but with the three species present together, nodular corrosion occurred. 

The factors promoting corrosion of aluminium alloys are complex and interrelated. They often operate synergistically, making prediction of corrosion difficult. In wet storage of aluminium clad spent fuel, there are a number of corrosion mechanisms involved. The most important mechanisms as related to spent nuclear fuel are briefly discussed here. Other details and definitions related to aluminium corrosion can be found in the normative publications and ISO standards provided therein. 

C. Brett, The application of electrochemical impedance techniques to aluminium corrosion in acidic chloride solution, Journal of Applied Electrochemistry, vol. 20, no. 6, pp. 1000-1003, 1990. 

P. Cabot, F. Centellas, J. Garrido, E. Perez, and H. Vidal, Electrochemical study of aluminium corrosion in acid chloride solutions, Electrochimica acta, vol. 36, no. 1, pp. 179-187, 1991. 

S. Doulami, K. Beligiannis, T. Dimogerontakis, V. Ninni, and I. Tsangaraki-Kaplanoglou, The influence of some triphenylmethane compounds on the corrosion inhibition of aluminium, Corrosion science, vol. 46, no. 7, pp. 1765-1776, 2004. 

Davenport, A.J., Isaacs, H.S., Kendig, M.W. (1991). XANES investigation of the role of cerium compoimds as corrosion inhibitors for aluminium. Corrosion Science, Vol. 32, No.5-6, pp. 653-663, ISSN 0010-938X. 

A number of corrosion inhibitors have been developed to mitigate aluminium corrosion for the last two decades. A variety of inhibitors have been tested such as chromates, dichromates, molybdates, nitrate, nitrite and sulfate. Their high efficiency/cost ratio has made them standard corrosion inhibitors for a wide range of metals and alloys (Benthencourt et al, 1997). 

Anodic and cathodic processes of aluminium corrosion in seawater are dissolution of aluminium and reduction of dissolved oxygen, respectively, as... 

The first passivation layers were pure silicon dioxide, produced by a chemical vapour deposition (CVD) process. Later phosphorus was added, in uncontrolled amounts, to relieve strain in the layer and thus prevent cracking and loss of adhesion. By 1974 it had been established that, in order to minimise aluminium corrosion in a moist environment, the optimum amount of phosphorus in a silicon dioxide layer is about 2% by weight. The relationship between phosphorus content and time to failure is shown by the typical set of results presented in Fig. 6.7. Below the 2% level, the time to failure is an increasing function of the amount of phosphorus, because the latter reduces cracking and improves adhesion. Above the 2% level, the time to failure decreases... 

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