Sodium diethyldithiocarbamate as a novel corrosion inhibitor to mitigate corrosion of 2024-T3 aluminum alloy in 3.5 wt% NaCl solution

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Highlights

  • Sodium diethyldithiocarbamate (DDTC) was used as a novel corrosion inhibitor.

  • The corrosion behavior of AA2024-T3 was improved in the presence of DDTC.

  • Corrosion mechanism was studied by electrochemical methods.

  • DDTC acted as the mix-type inhibitor and created a larger passive state.

  • Pitting corrosion was the main degradation mechanism in the presence of DDTC.

Abstract

In this work, sodium diethyldithiocarbamate (DDTC) was used as a novel corrosion inhibitor for AA2024-T3. For this purpose, the inhibition behavior of the DDTC was assessed by employing electrochemical tests and surface analysis. The electrochemical results indicated that DDTC acts as an effective corrosion inhibitor, and precipitation of a thin organic film on the AA2024-T3 surface is the main reason preventing the pitting corrosion of the samples. All of the electrochemical tests were proved by surface study analysis. The results of the SEM-EDS and ATR-FTIR studies showed the thin organic film formation on the aluminum alloy in the presence of DDTC.

Introduction

Due to the high strength to weight ratio and good corrosion behavior of the aluminum and its alloys, these engineering materials have found various applications in recent years [1]. AA2024-T3 is one of the famous grades of heat-treated aluminum alloys, used in aerospace and aeronautic applications [2,3]. The surface thin oxide film is the response of the good corrosion behavior of aluminum [4]. But, this alloy is susceptible to pitting corrosion in corrosive environments. The low oxide film thickness and presence of intermetallic compounds such as Al2MgCu (S-phase) and Al-Cu-Fe-Mn intermetallic phases in its structure are the main reasons for the vulnerability of this alloy to localized corrosion [5,6]. The Fe-containing phases are nobler than the Al matrix and act as cathodic reaction sites. However, S-phase structures are less nobler than the Al matrix and are the main intermetallic phase of the AA2024-T3. Therefore, this phase acts as an anodic site and the corrosion commences by chemical or electrochemical dealloying of this phase from the Mg and Al elements. The dealloying corrosion leads to enrichment of the S-phase structure with Cu. Then, these Cu-riched intermetallic particles act as cathodic sites for the preferential corrosion of the Al matrix [[7], [8], [9]]. In the presence of these intermetallic compounds, the micro-galvanic cells are formed which leads to create the localized corrosion on the AA2024-T3 surface. Therefore, the substrate is locally degraded especially in the presence of Cl anions [10].

Various methods such as conversion coatings, organic coatings, and corrosion inhibitors have been employed to improve the corrosion behavior of the aluminum alloy [[1], [2], [3], [4],6,[10], [11], [12], [13]]. Among the main engineering methods which have been employed for this purpose, organic corrosion inhibitors are the low-cost and most effective method [14,15]. It is well known that copper complexing compounds can prevent the corrosion process of the AA2024-T3 due to the cathodic oxygen reduction [16]. Water-soluble chromium (VI) oxyanions are one example in this case which is the most effective corrosion inhibitor for improving the localized corrosion of precipitated hardening AA2024-T3 [17]. The ability of the chromium (VI) oxyanions to passivate the S-phase intermetallic compounds and prevent anodic dealloying process is the main inhibitive action of this derivate [18]. But, it would be mentioned that these chromate derivates have a carcinogenic effect and they are hazardous for environment [19]. Therefore, the global concern is emerged to replace chromate derivates by environment-friendly compounds.

Various copper complexants which effectively suppress oxygen reduction reaction, as the main cathodic reaction in cathodic sites, were used to prevent the AA2024-T3 corrosion [1,16,20,21]. Also, researches showed that Cu inhibitors can inhibit both general and localized corrosion of the AA2024-T3 against the chloride-containing solutions [1]. In this regard, dithiocarbamate products have found application for corrosion inhibition of the Cu alloy against the corrosive media [22,23]. Sodium diethyldithiocarbamate is the famous derivate which was used for improving the corrosion inhibition of pure copper as a complexing compound [24,25]. Also, it has been shown that DDTC has low acute toxicity LD50 value (1500 mg/kg) [25]. Therefore, it can be promoted as a new green inhibitor [26,27].

It is generally believed that organic compounds containing sulfur, nitrogen, and/or oxygen atoms can effectively act as the corrosion inhibitors [25]. DDTC with a general chemical formula of C5H10NS2Na contains one nitrogen atom and two sulfur atoms. The existence of both sulfur and nitrogen atoms in the DDTC structure provides good inhibition efficiency for this compound. DDTC has been widely used for improving the corrosion behavior of carbon steel and copper alloy [[22], [23], [24], [25],[27], [28], [29]]. But, there is no comprehensive work for evaluating the subsequence effects of DDTC on the corrosion behavior of the AA2024-T3. Therefore, the corrosion behavior of the AA2024-T3 in the existence of the DDTC, as the corrosion inhibitor, is the main subject of this work. For this purpose, electrochemical tests in terms of EIS, ECN, and PD were employed to investigate the corrosion behavior of the AA2024-T3 in the presence of DDTC. Also, SEM and ATR-FTIR studies were performed to study the inhibition mechanism in the presence of the DDTC.

Section snippets

Materials and specimen preparation

The AA2024-T3 plates (0.45% Fe, 0.45% Si, 1.24–1.85% Mg, 0.32–0.94% Mn, 3.88–4.96% Cu, and balanced Al), ethanol, acetone, deionized water, and NaCl were purchased from Mojallali company. DDTC was purchased from Merck. The sample which is used in this study cut in the dimension of 50 × 30 × 2 mm and 10 × 10 × 2 mm for the electrochemical tests and surface analysis, respectively. For preparing the specimens, the aluminum plates were subjected to a preparation procedure as the follows: a)

Potentiodynamic polarization

The PD curves of the 2024-T3 aluminum alloy at different immersion times and DDTC concentrations are illustrated in Fig. 1. Corrosion potential (Ecorr) and breakdown potential (Ebr), as the main parameters for calculating the resistance of the surface against the pitting corrosion [30], were calculated and the obtained outcomes were presented in Table 1.

As can be seen in Fig. 1 and Table 1, all of the specimens in the presence of the DDTC shifted to more negative corrosion potential values. It

Conclusion

In this paper, sodium diethyldithiocarbamate was employed as a novel corrosion inhibitor for the aluminum alloy. For evaluation of the electrochemical behavior of the DDTC as a novel corrosion inhibitor, the EIS, ECN, and PD tests were used. Also, SEM-EDS and ATR-FT-IR analyses were employed to study the structure of the AA2024-T3 surface film in the presence and absence of the DDTC. The results of this work are presented as follows:

  • The PD results indicated that the DDTC acts as the mix-type

CRediT authorship contribution statement

Iman Mohammadi: Investigation, Writing - original draft. Taghi Shahrabi: Conceptualization, Supervision, Writing - review & editing. Mohammad Mahdavian: Conceptualization, Supervision, Writing - review & editing. Mazdak Izadi: Writing - review & editing, Investigation.

Declaration of competing interest

There is no conflict of interest to declare.

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