Aqueous Corrosion of Aluminum

Abstract

Aluminum alloy 1100 corrodes uniformly in nearly pure water at rates which increase with temperature. The reaction is characterized by an initial period of relatively rapid corrosion, followed by a constant lower rate of corrosion. The slope of the linear part of the curve or the “corrosion rate” changes from about 0.02 to 2.5 mg/dm2-day (.01 to 1.3 mil/yr) from 50 to 200 C. Above 200 C intergranular attack occurs, with resultant more rapid penetration and deterioration of the metal. The corrosion rate can be reduced by the addition of an acid to the water. The solution pH of minimum corrosive attack on aluminum goes down with increasing temperature. It is of the order of 6.5 at 50 C and 3 at 300 C. Corrosion in slightly alkaline solutions (pH 8.5) is more rapid than in neutral water at all temperatures. At 100 C the difference shown in stagnant tests is very slight, but increases considerably if the temperature is increased to the order of 200 C. Presumably the effect of solution flow rate would be greater in the case of alkaline water than in neutral water. At 200 C the addition of dichromate ion increased the rate of corrosion. A small concentration of sodium silicate resulted in a higher corrosion rate at pH 9.4, while at pH 3.5 it reduced the rate significantly. Chloride ion (5 ppm) caused some pitting and increased the corrosion rate slightly. Electrical coupling to more cathodic materials, such as graphite, zirconium or stainless steel produced no undesirable effects in distilled water at 200 C. At 315 C, the corrosion life of samples was extended by such coupling. 6.4.2

The Behavior of the Metal-Oxide Interface During the Early Stages of the High-Temperature Corrosion of Aluminum

“…The effects of decreased oxide resistance by this mechanism, in causing the hydrogen discharge to occur at the oxide water interface, have been discussed by Brown (8) as one alternate explanation to Draley's original hypothesis that the iron and nickel alloying elements function as cathodes for the discharge of hydrogen (1)(2)(3).…”

“…This paper was prepared for delivery before the Detroit Meeting, Oct [1][2][3][4][5]. 1961.Any discussion of this paper will appear in a Discussion Section to be published in the June 1963 JOURNAL.…”

“…The time at which this reversal occurs varies with temperature, and after it occurs the aluminum matrix surface recedes past the second phase particles leaving them isolated and not further corroded. The method of preparing the sample for examination is described briefly.Draley et al (1)(2)(3) have shown that aluminum can be made very much more resistant to corrosion in high-temperature water by alloying with cathodic metals, such as iron and nickel. Krenz and Biefer (4, 5) have reported considerable testing of two such alloys (alloy 10155 and alloy 10157) developed at Atomic Energy of Canada Ltd., and have correlated the enhanced properties of these alloys with presence of second phase particles in the metal and their size and distribution.…”

Steam assisted oxide growth on aluminium alloys using oxidative chemistries: Part I Microstructural investigation

“…13(a) shows the stability regions at room temperature and shift in boundaries due to increased temperature to 125 • C. Increase in temperature shows similar regions of stability except for the shift in boundaries for Al 3+ , AlO(OH), and AlO 2 − equilibrium to lower pH values. The shift of these boundaries results due to high corrosion rate of aluminium at elevated temperatures under aqueous environment [23]. However, the Pourbaix diagram at 125 • C showed the possibility of formation and stability of AlO(OH) at lower pH values on the acidic side compared to that at room temperature.…”

Corrosion of Aluminum Alloys by Flowing High-Temperature Water.

“…Such cathode sites serve as active sites for the liberation 18 of hydrogen. In some instances, the cathodic intermetallic compounds are imbedded (unoxidized) in the oxide, decreasing the difficulty of transport of electrons through the film.…”