Repassivation of Aluminum in the Presence of Phosphate and Nitrate Inhibitors in Corrosive Media

Abstract

We study the efficiency of inhibition of the corrosion of aluminum in the stage of repassivation after the destruction of the surface oxide film. It is shown that the addition of phosphate and nitrate inhibitors to an acid-rain solution decreases the difference between the free corrosion potential of the aluminum surface and its transient potential in the course of formation of passive films. It is discovered and proved that the phosphate-nitrate composition exerts a synergistic anticorrosion effect on the mechanically activated aluminum surface.Aluminum and its alloys are characterized by a quite high corrosion resistance in working media, which explains their extensive application in various branches of industry; in particular, in chemical, automotive, food, and aircraft industries [1]. The oxide films formed on the surfaces of these metals serves as reliable protection against the influence of corrosive media. However, in many cases, these surface films can be mechanically destroyed in the course of operation and, as a result, the corrosion rate of aluminum and its alloys becomes several tens times higher [2][3][4]. At present, the regularities of corrosion inhibition of aluminum and aluminum alloys by different organic and inorganic compounds are thoroughly investigated under the conditions of integrity of their oxide films [5][6][7][8][9]. However, it is also necessary to find corrosion inhibitors that would be efficient in the stage of repassivation of aluminum and its alloys, i.e., in the absence of continuous passive films on their surfaces. As shown in [10], phosphate inhibitors can be promising for the protection of D16 aluminum alloy against tribocorrosion when the oxide film formed on the metal surface is cyclically destroyed. At the same time, it is known that one can enhance the protective action of phosphate by combining it with the other inhibitors and, in particular, with sodium nitrate [11] or nitrite [12]. The anodic oxidation and passivation of the mechanically activated surfaces of aluminum alloys in nitrate solutions was observed in [13]. These facts can be important for the improvement of the protective action of phosphate inhibitors in the case where the oxide film formed on the aluminum alloy is mechanically damaged. Hence, the aim of the present work is to investigate the protective action of compositions based on the phosphate and nitrate corrosion inhibitors in the stage of repassivation of pure aluminum (used in our investigation as a model material). Materials and Methods of InvestigationsWe study the efficiency of corrosion inhibitors in the stage of aluminum repassivation in a special guillotining device according to the procedure described in [14].

A Combined Inhibiting Effect of Sodium Alginate and Sodium Phosphate on the Corrosion of Magnesium Alloy AZ31 in NaCl Solution

“…As such, the inhibition efficiency of SP is not enough for Mg alloys to meet the requirements in practice and further improvements are still needed. [43][44][45] Inhibiting effect of joint addition of SA and SP.-When SA and SP were added jointly into NaCl solution, the inhibiting efficiency was improved noticeably (Tables I-III). As a result, the co-deposited film on the surface of Mg alloy AZ31 contained Mg(OH) 2 , organic alginate and inorganic phosphate, and exhibited a much more compact structure (Figs.…”

Evaluating the Corrosion Resistance of the Novel Al-Aln Metal Matrix Composites Produced Of Hot Direct Extrusion

“…It was also established that AlN particles are prone to hydrolysis and thus cause deterioration of the corrosion resistance of MMK in neutral chloride solution [4]. Therefore, the main of this work was to determine the corrosion resistance of the novel extruded Al-AlN MMCs in a humid environment and an artificial acid rain solution [5].…”