The Influence of Sodium Molybdate on the Rate of Corrosion of Aluminum in Phosphoric(V) Acid

Abstract

Corrosion rates of aluminum in phosphoric (V) acid solutions were determined gravimetrically in a presence of sodium molybdate which acts as an inhibitor. Inhibition efficiencies were calculated. The most effective corrosion inhibition was observed for 0.5 M H3PO4 and 100 mM of Na2MoO4. Since insoluble corrosion products precipitated onto specimens and influenced the determined corrosion rates, an analysis of a morphology of the specimens was performed by using a scanning electron microscope. The corrosion products are composed of Mo, P, Al and O. An Mo/P atomic ratio varied between 0.8 and 1.6 depending on the concentrations of phosphoric (V) acid and sodium molybdate. For three concentrations of H3PO4, the concentration ranges of sodium molybdate, where the gravimetric method may be applied were determined.

The Sealing Step in Aluminum Anodizing: A Focus on Sustainable Strategies for Enhancing Both Energy Efficiency and Corrosion Resistance

“…Its lower oxidizing power increases the chances of its compatibility with post-sealing applied organic coatings. Furthermore, on the basis of reports of the respective inhibitive effects of cerium [251][252][253][254][255][256][257], and molybdates [152,217,220,[258][259][260][261][262][263][264] on corrosion of aluminum alloys, and active corrosion of aluminum by cerium molybdate [265][266][267], we postulate that simultaneous inclusion of both cerium and molybdate species in the sealing bath preferably as their respective sulphates or acetates or as cerium molybdate might be beneficial to the sealing of aluminum and impart some active corrosion protection to sealed materials. The preference for inclusion of these into the sealing baths as sulphates and/or acetate is premised on the known non-deleterious effects of these anions on the sealing process [37].…”

Spectrophotometric study of corrosion inhibition of aluminium in orthophosphoric acid aqueous solutions by using sodium molybdate

“…As the alternative for hexavalent chromium species, organic and inorganic inhibitors can be applied in acidic solutions [3][4][5][6][7][8][9]. So far, only sodium molybdate was demonstrated to be the promising alternative for CrO 3 in the stripping solution for anodic coatings [6].…”

“…Therefore, molybdophosphoric acid initially act as the additional (apart from the H 3 O + species) depolariser. Subsequently, PMB species adsorb onto the surface of aluminium and inhibit the corrosion process [5][6][7]9]. In addition, well adherent corrosion products containing Al, Mo, P and O can be formed onto the surface of aluminium at the certain range of the concentration of Na 2 MoO 4 .…”

“…In addition, well adherent corrosion products containing Al, Mo, P and O can be formed onto the surface of aluminium at the certain range of the concentration of Na 2 MoO 4 . It makes the gravimetric analysis of the corrosion kinetics complicated [6,7,9]. Although the kinetics of corrosion of aluminium in H 3 PO 4 aqueous solutions, in the presence of Na 2 MoO 4 was studied with different methods (gravimetric [5], gravimetric and gasometric [6,7,9] and electrochemical [5,11]), the mechanism of corrosion inhibition is still not fully understood.…”

“…It makes the gravimetric analysis of the corrosion kinetics complicated [6,7,9]. Although the kinetics of corrosion of aluminium in H 3 PO 4 aqueous solutions, in the presence of Na 2 MoO 4 was studied with different methods (gravimetric [5], gravimetric and gasometric [6,7,9] and electrochemical [5,11]), the mechanism of corrosion inhibition is still not fully understood. It was proposed that PMo 12 O 40 7− species are the corrosion inhibitor in the studied system.…”