The Unexpected Role of Benzotriazole in Mitigating Magnesium Alloy Corrosion: A Nucleating Agent for Crystalline Nanostructured Magnesium Hydroxide Film

Abstract

Benzotriazole (BTA), an effective corrosion inhibitor for Cu or Cu-containing Al alloys, was added to 0.1 M NaCl to study its potential role in suppressing corrosion of the commercial Mg alloy, AMlite. In particular, the impact of pH and BTA concentration was investigated, indicating that BTA was effective at restricting corrosion of AMlite in weakly alkaline NaCl solution, i.e. pH 10.0. The degree of the protection afforded was a function of BTA concentration. The best corrosion inhibition was found in the NaCl containing 15 g/L BTA, however, the mechanism of inhibition was not a classical function, nor related to the inhibition mechanism of BTA for Cu-bearing alloys. Instead it is posited that BTA − anions act as a nucleating agent to stimulate the formation of a dense and highly crystalline Mg(OH) 2 surface film with a uniform nano-structure capable of passivating the Mg-alloy, in contrast to say, the insoluble Cu-BTA complex via Cu-N coordination bonds for Cu-alloys. The magnitude of this effect of BTA on Mg corrosion was not anticipated, but effective, with beneficial implications to utilization of Mg alloys as anode materials, where in such cases, when dissolution occurs, the anode can passivate with little change in its potential.

Self-healing plasma electrolytic oxidation coatings doped with benzotriazole loaded halloysite nanotubes on AM50 magnesium alloy

“…As a result, corrosion sites and the solution in the pores of the PEO coating will be alkalised. According to Wang et al [53], protection for the Mg alloy because of the loose structure ( Fig. 17(a,b)), which can be identified by the significant decrease in impedance after 4 h of immersion in NaCl solution ( Fig.…”

Effect of the pH in the growth of benzotriazole model layers at realistic environmental conditions

“…Although copper does not react with hydrochloric acid, because the reduction potential of copper is higher than that of hydrogen, copper specimens immersed in 0.5 M HCl solution [66,67,68] BTAH has a pKa of 8.4 at 25 °C in water [5,27,69,71,72], which means that at pH values lower than pKa the prevalent species is BTAH in its neutral form; at pH < 1 is in the protonated form, BTAH2 + ; above 8.4 is in the anionic form, BTA -, instead. Therefore at our experimental conditions BTAH is prevalent as a solvated neutral species.…”

Influence of commercial corrosion‐inhibiting compounds on the atmospheric corrosion of the magnesium alloys EV31A, WE43B, ZE41A and pure magnesium

“…Benzotriazole (BTA), included in Ardrox 3961, has been studied as an inhibitor for Cu, Al, Mg and steels. [30][31][32][33][34][35][36][37][38] For example, Abu-Baker et al [38] reported that BTA was an effective corrosion inhibitor for Cu and 5% tin bronze in 0.5 M NaCl + 0.1 M CuCl 2 solution, while Žerjav and Milošev [31] found that (a) BTA accelerated Cu corrosion in simulated urban rain and (b) inhibited corrosion when combined with stearic acid. BTA was found to inhibit Cu corrosion by the formation of BTA-Cu and BTA-Cu(O) complexes.…”

“…[37,39] Guo et al [40] found that BTA was effective for anodised AZ91B. Wang et al [35] found that BTA was effective by the formation of a dense, highly crystalline Mg(OH) 2 film. In contrast, Lamaka et al [34] found that BTA accelerated the corrosion of pure Mg and the Mg alloys WE43, ZE41 and EV31.…”