Aluminum Alloy Corrosion Inhibition by Vanadates

Abstract

The inhibition of Al alloy corrosion by vanadates was studied in this work. Vanadium speciation is very complicated and vital to the inhibition efficacy. Critical conditions for decavanadate polymerization from clear metavanadate solutions were investigated. Decavanadate only formed when metavanadate was added to solutions of pH 3 or less. It was not possible to change the pH of a metavanadate solution without forming decavanadates, creating an orange-colored solution. According to 51 V nuclear magnetic resonance, monovanadates were present only in clear metavanadate solutions; orange solutions always contained decavanadates and never contained monovanadates. Orange decavanadate solutions containing 0.5 M NaCl at pH 8.71 exhibited no significant inhibition of the oxygen reduction reaction and increasing decavanadate concentration was detrimental. In contrast, clear metavanadate solutions containing monovanadate exhibited strong inhibition of the oxygen reduction reaction, to a level similar to chromate. At a fixed pH, increased NaVO 3 concentration in clear metavanadate solutions increased inhibition efficiency.High-strength aluminum alloys are used widely in structural aircraft applications because of the combination of good mechanical properties and light weight.

A study of the mechanisms of corrosion inhibition of AA2024-T3 by vanadates using the split cell technique

“…Previous findings showed that orange decavanadate solutions did not have a significant effect on the kinetics of the ORR [39]. The effects of injecting orange decavanadate solutions to the AA2024/Cu split cell are shown in Fig.…”

“…Previous results indicated that the rate of the ORR in orange solutions containing decavanadates was only slightly lower than in the base solution with no vanadate [39]. Thus, when testing decavanadates by the split cell, a smaller reduction in galvanic current was to be expected.…”

“…A pitting potential (E P ) of -748 mV SCE was observed. In solutions containing 0.5 M NaCl + 5 mM clear metavanadate (approximately 1.6 mM monovanadate [39]), no significant changes were observed. The OCP was on average 50 mV lower than in the absence of the inhibitor.…”

“…Orange solutions containing decavanadates were prepared by acidification of the clear solutions to pH 4, and subsequent re-adjustment to pH 8.71. Prepared in this fashion, monovanadates (V 1 ) are present only in clear solutions and decavanadates (V 10 ) are present only in orange electrolytes [39]. For simplicity, these solutions will be referred to as orange decavanadate and clear metavanadate solutions, respectively, even though the former solutions also contain some metavanadates.…”

Vanadate post-treatments of anodised aluminium and AA 2024 T3 alloy for corrosion protection

“…10 Work has revealed that crevice corrosion of aluminium can be inhibited in a sodium chloride solution. 11 Metavanadates have been shown to inhibit oxygen reduction on AA 2024-T3 alloy, 12,13 although no effect was found with decavanadate. 13 It has been reported that inhibition does not involve reduction of vanadate.…”