Aluminum nitric acid, corrosion rates

Aluminum is resistant to nitric acid at concentrations above 80%. At 50% nitric acid concentration at room temperature, corrosion rates are as high as 0.08 in. (0.20 cm) per year. 

Figure 8.1 Effect of pH on corrosion of 1100-H14 alloy (aluminum) by various chemical solutions. Observe the minimal corrosion in the pH range of 4-9. The low corrosion rates in acetic acid, nitric acid, and ammonium hydroxide demonstrate that the nature of the individual ions in solution is more important than the degree of acidity or alkalinity. (Courtesy of Alcoa Laboratories from Aluminum Properties and Physical Metallurgy, ed. John E. Hatch, American Society for Metals, Metals Park, Ohio, 1984, Figure 19, page 295.)...

Aluminum and stainless steel are used almost interchangeably for any strength of nitric acid. Figure 3.7 compares the rate of attack of cold nitric acid on stainless steel and aluminum. Figure 3.7 shows that higher rates of aluminum corrosion occur up to about 80% nitric acid (HNO3), but aluminum is still to be preferred over stainless steel for any concentration above 80%. 

Elevated speeds have a marked effect on wear, and this is more pronounced if the solution contains some solid particles in suspension. Aluminum forms films of aluminum nitrate or oxide in fuming nitric acid. At low flow rates there is no attack whereas for speeds greater than 1.22 m s the protective layer is removed and erosion-corrosion occurs more readily.16... 

Morphological studies explain the mechanisms of E-glass corrosion. According to these studies, acid corrosion of E-glass is caused by calcium and aluminum depletion which varies depending on the acid type, fiber type, and acid concentration. Oxalic and sulfuric acids are more corrosive than nitric and hydrochloric acids. This difference is due to the fact that, in oxalic acid, precipitated products are formed which decrease the concentration of leachates in solution. In addition to the loss of mineral content, fibers develop axial and spiral cracks. Crack formation depends on the rate of material depletion. 

Nearly all acids attack aluminum, but concentrated nitric acid does not. In Fig. 27, the corrosion rate of aluminum in nitric acid of different concentrations... 

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

An oxide layer is readily formed on many metals when they are made anodic in aqueous solutions. In the case of aluminum, this process is called anodization. It is also referred to as a passive film which reduces the corrosion rate. Such passive films can be thin, from 0.01 pm, and fragile and easily broken. Thus, when steel is immersed in nitric acid or chromic acid and then washed, the steel does not immediately tarnish nor will it displace copper from aqueous CUSO4. The steel has become passive due to the formation of an adhering oxide film which can be readily destroyed by HCl which forms the strong acid FeCU-. 

MERCURY. Hg. The action of metallic mercury on aluminum is unique. It tends to amalgamate with aluminum to produce a surface that corrodes at an extraordinary rate in the presence of moisture with the production of voluminous columnar corrosion products. When that reaction is started, the rate of corrosion is dependent upon relative humidity. When dry. metallic mercury reacts only with difficulty because of the oxide film on the aluminum surface. Traces of acidity or halides on the surface give rise to rapid attack. Solutions containing mercury ions tend to cause rapid pitting of aluminum alloys because of plating out of mercury in localized areas. Mercury can be removed from aluminum surfaces by treatment w ith 70% nitric acid. Mercury can be distilled away from an aluminum surface by treatment with steam or hot air. See also Ref (Dp- 136. (2) p. 446. (3) p. 80. 

The research on corrosion, started in this institute in the 1950s, continued successfully further. The intergranular corrosion of steels was measured by an electrochemical potentiodynamic reactivation method [310-312]. Since the 1960s, the passivity of brass was further studied, the rates of corrosion were measured by polarization resistance, the effect of deformation on anodic dissolution of steels was followed, and the surface roughness of metals was measured other subjects of research were, e.g., the behavior of passive films on steel, the effect of compositirai and motion of electrolyte on corrosion of passivated aluminum, the cathodic protection of passive metals against corrosion, the anodes for cathodic protection of steels, etc.[313-316]. Measurements of polarization resistance in the system iron—concentrated sulfuric acid or boiling nitric acid, of corrosion and matter... 

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