Aluminum pure, corrosion rate

Fig. 2-11 Relation between corrosion rate of pure aluminum at 25°C 1 M Na SO after [39] A 1.5 g L NaCl o tapwater (about 0.002 mol L Na" ) ...

Figure 21.4. Corrosion rates of commercially pure aluminum (1100) in nitric acid, room temperature [23], (Copyright NACE International 1961.)...

Corrosion rates tend to decrease as the electrol3rte becomes spent and saturated with aluminum ions. Consequently, a greater amount of corrosion can be expected for conditions that prevent this, such as high flow rates, and a low ratio of area of metal surface to volume of solution. Contamination of a pure solution can increase, or decrease, the corrosion rate. Therefore, predictions of the corrosion performance should be obtained from Refs 8-10 or by experimentation. 

Magnesium and its alloys are definitely anodic to the A1 alloys and, thus, contact with aluminum increases the corrosion rate of magnesium. For example, in sodium chloride solutions (3-6%), the potential of Mg alloys is -1.67 V/SHE while that of Al-12%Si and pure aluminum are -0.83 to -0.85, respectively. However, such contact is also likely to be harmful to aluminum, since magnesium may send sufficient current to the aluminum to cause cathodic corrosion in alkaline medium. Aluminum oxide is amphoteric and so it is soluble in acid as well as in alkaline solutions. The standard reduction potentials of these two half-reduction reactions are (-1.66 V/SHE) and (-2.35 V/SHE), respectively. Alkaline reaction of the possible existence of aluminum phase in sacrificial Mg anodes is ... 

For more than a century, a number of different aluminum alloys have been commonly used in the aircraft industry These substrates mainly contain several alloying elements, such as copper, chromium, iron, nickel, cobalt, magnesium, manganese, silicon, titanium and zinc. It is known that these metals and alloys can be dissolved as oxides or other compounds in an aqueous medium due to the chemical or electrochemical reactions between their metal surfaces and the environment (solution). The rate of the dissolution from anode to cathode phases at the metal surfaces can be influenced by the electrical conductivity of electrolytic solutions. Thus, anodic and cathodic electron transfer reactions readily exist with bulk electrolytes in water and, hence, produce corrosive products and ions. It is known that pure water has poor electrical conductivity, which in turn lowers the corrosion rate of materials however, natural environmental solutions (e g. sea water, acid rains, emissions or pollutants, chemical products and industrial waste) are highly corrosive and the environment s temperature, humidity, UV light and pressure continuously vary depending on time and the type of process involved. ... 

The use of aluminum in acids is very limited. Pure aluminum shows the highest corrosion resistance and could be used at room temperature in up to 25% sulfuric acid, in which the dissolution rate is between 0.18 and 0.3 mm yr . With increasing content of alloying components, the corrosion resistance decreases as can be seen in Fig. 26. 

ABSTRACT The corrosion protection capabilities of sol-gel-based polysiloxane coatings applied to surfaces of pure aluminum and of aluminum alloy AA7075 prepared from different starting molecules have been evaluated with electrochemical methods. A rating of the studied polymer coatings could be deduced and correlated with the hydro-phobicity of these coatings. 

HALOGENATED HYDROCARBONS. Aluminum alloys are usually resistant to pure halogenated hydrocarbons and other organic chemicals containing halogens under most conditbns particularly at room temperature or lower. Under certain conditions some of these hydrocarbons may produce a rapid rate of corrosion of aluminum or a violent reaction. Hence, the service conditions to insure safety should be rec-c ized or established before aluminum all< are used with any halogenated hydrocarbon. 

In practice. Mg alloys are much more popular than pure Mg in industrial applications. One of the well-known uses of Mg alloys is for cathodic protection, and some Mg alloys are used as sacrificial anodes due to their negative potential. Although their rapid rate of corrosion is a disadvantage. Mg alloys are superior to aluminum and zinc anodes in some environments such as in soil and water. The most important application of Mg alloys is for aerospace and military purposes, and some high-strength and creep-resistant... 

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