1 Introduction

The most suitable materials for many industrial applications are copper and its alloys because of their outstanding workability, potent electrical and thermal conductivities, and satisfactory corrosion resistance. They are utilized in many heating and cooling systems [1, 2]. Copper and its alloys are widely used in marine environments because of their good corrosion resistance, high electrical and thermal conductivities, mechanical workability, and biofouling resistance. They can be used in various marine engineering constructions, including marine ship power systems, marine ship power generation systems, seawater desalination, and reverse irrigation generators [3, 4]. Most of the studied organic inhibitors are heterocyclic molecules with S, P, O, and N atoms, which improve the corrosion inhibitors’ efficiency [5]. An inhibitor's adsorption protects the metal surface [6,7,8,9,10]. Consequently, a corrosion-preventing adsorption film can be created on the metal's surface using covalent bonding (chemisorption) and/or electrostatic contact (physisorption) [11,12,13]. Organic inhibitors work well to protect because the polar group acts as an adsorption active center on metal surfaces [14, 15]. Atoms that can donate electrons establish coordination bonds with copper atoms due to unoccupied d-orbitals [16].

Some work was done to inhibit the corrosion of copper and its alloys by utilizing organic compounds that adsorb onto the surface of the sample and provide a protective film owing to the survival of heteroatoms N, S, and O, electrons in conjugate bonds, and electronegative functional groups [17,18,19]. Derivatives of azole are thought to be the best organic inhibitors used for corrosion control. Benzotriazole (BTA) is frequently used in various corrosive conditions for copper alloys. Cu(I)-BTA and Cu(II)-BTA films can develop on copper surfaces in most aqueous corrosive environments, influencing both anodic and cathodic processes [20, 21].

To find out how some pyrimidinone derivatives prevent copper corrosion, A. S. Fouda et al. ran weight loss (WL), potentiodynamic polarisation (PP), and electrochemical impedance spectroscopy (EIS) studies. As the inhibitor’s concentration and temperature increase, so does its inhibition efficiency. Polarization curves demonstrated how these compounds served as mixed-type compounds. Because of their adsorption on the copper surface, they formed a protecting thin film that shielded them from corrosive environments, according to Langmuir’s adsorption isotherm. Energy-dispersive X-rays and a scanning electron microscope (SEM) were used to investigate the copper samples’ surface morphology [22]. Diniconazole and triadimefon were studied by Lichao Hu et al. as copper corrosion inhibitors in a 3.5% NaCl solution. According to polarization curves, they functioned as mixed-type inhibitors. The EIS results show that the inhibitor forms a protective covering by adhering to the copper surface. Their respective inhibitory efficacy reached 99.2% and 97.3% at 100 mg/L. They examined Langmuir's adsorption isotherm and chemically adsorbed on the copper surface, according to thermodynamic predictions [23]. Haijun Huang and colleagues looked at the synthesis of PBTB, a potent water-soluble corrosion inhibitor with a single benzotriazole part, and PDBTB, which contains two benzotriazole parts for copper in a 3.5% NaCl solution. Impedance spectroscopy, polarization curves, and scanning electron microscopy demonstrate that PDTB suppresses copper corrosion more potently than PBTB [24]. Matjaž Finšgar et al. have proven the great efficiency of 4-methyl-2-phenylimidazole (MePhI), a good way to keep brass from corrosion in a 3% NaCl solution. An orgno-metallic complex was detected during surface characterization using XPS and ToF–SIMS [25]. Adenine (A), guanine (G), and hypoxanthine (I), three purine-derivative inhibitors, were employed to investigate how they stop corrosion and how copper binds to them in alkaline saltwater. The investigation showed that the inhibitors under test reduced corrosion on the copper surface by creating a protective film [26]. Nordin Ben Seddik et al. studied the protection mechanism of brass in a 3% NaCl solution using organic inhibitors containing heteroatoms such as amino acids. The corrosion protection of brass resulted in the lowest corrosion current density (10.36 μA/cm2) and reaching a maximum inhibition efficiency of about 86% [27].

This study compares the corrosion inhibition of 5-Mercapto-1-methyltetrazole (MTAH) and 5-Aminotetrazole (ATAH) on copper and brass utilizing surface characterization, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Additionally investigated is the influence of the structures and functions of organic inhibitors on the inhibition of corrosion. The novelty of this research is based on the consideration that tetrazole derivatives are economically viable and simple to synthesize, in addition to demonstrating high inhibition efficiency. A literature search indicates that few systematic studies have been published on using tetrazole derivatives to control the corrosion of copper alloys in simulated seawater.

2 Experimental

2.1 Materials

The corrosion prevention effect of 5-Mercapto-1-methyltetrazole and 5-Aminotetrazole from Sigma Aldrich on commercial brass (61.76 wt.% Cu, 36.28 wt.% Zn, 1.13 wt.% Al, 0.4 wt.% Fe, and 0.43 wt.% Ni) and electrolytic copper (99.99 wt.%) was studied. The chemical structures are shown in Fig. 1. Both inhibitors were dissolved in a salt solution at different concentrations (0.001, 0.0025, 0.005, and 0.01 M). Disc specimens with a diameter of 1.5 cm2 were made from electrolytic copper and commercial brass. Using SiC papers to continuously polish specimens up to 2400 grits to obtain a mirror-like quality. Following a thorough cleaning with distilled water, specimens were air-dried. After the polished specimens were secured in the corrosion cell, a 0.785 cm2 area was exposed to the testing fluid.

Fig. 1
figure 1

Molecular structure of inhibitors

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2.2 Electrochemical measurements

The working electrode’s open circuit potential (OCP) was measured with and without corrosion inhibitors using a standard three-electrode cell. Reference and auxiliary electrodes are saturated calomel electrodes (SCEs) and Pt sheets, respectively. Corrosion of copper and brass samples was assessed using the EIS with and without corrosion inhibitors. The investigations, which included a frequency ranging from 0.01 Hz to 65 kHz, were conducted at room temperature. The amplitude of the sinusoidal voltage signal is 10 mV. An automated potentiostat was used to modify the potentials (Auto Lab PG STAT 30). At a scan rate of 1 mVs−1, the potentials were scanned from − 0.3 V below the Ecorr to 1 V above the Ecorr. Before the polarization curves were measured, the electrodes were dipped in the testing solution for 30 min.

2.3 Surface measurements

Copper and brass specimens were submerged for 60 min in simulated seawater with and with inhibitors at room temperature, then rinsed and dried. A field emission scanning electron microscope (Fe-SEM) model JOEL, JSM-6700F, examined the sample morphologies.

3 Results and discussion

3.1 Potentiodynamic measurements

Three separate runs were conducted for each one to ensure reproducibility. Every run was operated with a different, freshly prepared sample. Under each experimental setting, the statistical analysis produced the mean corrosion potential values (Ē) and standard deviation (σ). Figure 2 displays three independent brass potentiodynamic curve measurements in a 3.5% NaCl solution, and the standard corrosion potential analysis is represented in Table 1 [28].

$${\overline{\text{E}}}_{{{\text{corr}}}} = \frac{{\left( {{\text{E}}_{{{\text{corr}}1}} + {\text{E}}_{{{\text{corr}}2}} + {\text{E}}_{{{\text{corr}}3}} { }} \right){ }}}{3}$$
(1)
$$\sqrt {\frac{{({\overline{\text{E}}}_{corr} - E_{corr1} )^{2} + ({\overline{\text{E}}}_{corr} - E_{corr2} )^{2} + ({\overline{\text{E}}}_{corr} - E_{corr1} )^{2} }}{2}}$$
(2)
Fig. 2
figure 2

Brass’s potentiodynamic curves in 3.5% NaCl solution

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Table 1 The standard corrosion potential analysis from brass potentiodynamic curves in 3.5% NaCl solution
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Table 1 shows the standard corrosion potential analysis from brass potentiodynamic curves in 3.5% NaCl solution for three runs as evidence of reproducibility.

According to Fig. 3a, in a 3.5% NaCl solution, copper is anodized with ATAH, which results in a significantly decreased anodic current density. It reaches 1.09 × 10–7 A cm−2 at the most significant concentration compared to 6.322 × 10–6 A cm−2 in the inhibitor-free solution (see Table 2). As the inhibitor concentration increases, the current density falls much more noticeably. The intensity of the decrease in current density increases with increasing inhibitor concentration. The anodic current decreased similarly for brass in Fig. 4a as the ATAH concentration was raised to as low as 7.480 × 10−7A cm−2, comparable to the current density obtained for brass without the inhibitor, is 5.305 × 10–6 A cm−2. Similar to this, as shown in Figs. 3b and 4b, the polarization of copper and brass in a 3.5% NaCl solution in the presence of MTAH exhibits a similar drop in current density with an increase in inhibitor. The initial contact of copper alloy with 3.5% NaCl solution proposed the anodic dissolution of copper:

$${\text{Cu}} \to {\text{Cu}}^{ + } + {\text{ e}}^{ - }$$
(3)
Fig. 3
figure 3

Copper’s potentiodynamic polarization curves in 3.5% NaCl at varying ATAH (a) and MTAH (b) concentrations

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Table 2 Copper and brass electrochemical characteristics in 3.5% NaCl solution at 25 °C with and without various concentrations of ATAH and MTAH
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Fig. 4
figure 4

Brass’s potentiodynamic polarization curves in 3.5% NaCl at varying ATAH (a) and MTAH (b) concentrations

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The cathodic reaction implicates the reduction of oxygen:

$${\text{O}}_{{2}} + {\text{ 2H}}_{{2}} {\text{O }} + {\text{ 4e}}^{ - } \to {\text{OH}}^{ - }$$
(4)

Consistent with the following equations, the creation of a protective coating on copper and brass surfaces is what causes the anodic current to decrease [20, 29, 30]:

$${\text{Cu}}^{ + } + {\text{ ATAH}} \to {\text{Cu}}^{ + } \left[ {{\text{ATA}}} \right]_{{{\text{ads}}}}^{ - } + {\text{ H}}^{ + }$$
(5)
$${\text{Cu}}^{ + } + {\text{ MTAH}} \to {\text{Cu}}^{ + } \left[ {{\text{MTA}}} \right]_{{{\text{ads}}}}^{ - } + {\text{ H}}^{ + }$$
(6)

The following expression can be used to determine the inhibitor's efficiency at various concentrations [31,32,33]:

$${\text{I}}.\mathrm{E\% }=\frac{Icorr\left(b\right)-Icorr(inh)}{Icorr(b)}\mathrm{X }100$$
(7)

where Icorr(b) and Icorr(inh) stand for corrosion current densities without and with inhibitors, respectively. Based on polarization curves, Table 2 shows the inhibitory efficiency for various inhibitor doses.

3.2 Adsorption mechanism analysis

3.2.1 Langmuir adsorption isotherm

Organic inhibitors are well known for their ability to adsorb onto metal surfaces and create protective layers that shield the metal from aggressive attack. Utilizing the following expression, one may determine the surface coverage at different ATAH and MTAH concentrations:

$$\uptheta =\frac{Icorr\left(b\right)-Icorr(inh)}{Icorr(b)}$$
(8)

where Icorr(inh) and Icorr(b) are the corrosion current densities with and without inhibitors, respectively. The surface coverage (θ) for various inhibitor doses, as determined by polarization curves, is shown in Table 2. After fitting surface coverage (θ) values in several adsorption isotherm models, the correlation coefficient (R2) was utilized to determine the best isotherm. The Langmuir isotherm was the most effective tool for describing how ATAH and MTAH interacted with copper and brass surfaces. The computation of this isotherm is done using the given equation [34, 35]:

$$\frac{\theta }{1 - \theta } = AC\,exp\left( {\frac{{ - E^{\# } }}{RT }} \right) = {\text{KC}}$$
(9)

where C is concentration in mol L−1, θ is surface coverage, and K is the adsorption process constant. \({E}^{\#}\) is the activation energy. The equation above can be simplified as [36,37,38].

$$\frac{C}{\theta }=\frac{1}{K}+{\text{C}}$$
(10)

The relationship between the adsorption constant K and the adsorption standard free energy, ΔG0, is demonstrated by [39]:

$${\text{K}}=\left(\frac{1}{55.55}\right){\text{exp}}\left(\frac{-\Delta {G}^{0}}{RT}\right)$$
(11)

where R is the universal gas constant, and T is the absolute temperature. The relationship between C/θ and C for copper and brass is depicted in Fig. 5, with an intercept of 1/K. The estimated values of K and ΔG0 for the inhibitors are recorded in Table 3. Copper in ATAH and MTAH has an adsorption standard free energy (ΔG0) of − 31.252 kJ mol−1 and − 28.968 kJ mol−1, respectively, whereas brass has a standard free energy of − 28.047 kJ mol−1 in ATAH and a standard free energy of − 28.149 kJ mol−1 in MTAH. The measurement of (ΔG0) shows that the adsorption reaction of both inhibitors on copper and brass was spontaneous. The adsorption method that both inhibitors and samples employ is called physicochemical adsorption. Because of the protonation of nitrogen atoms, the physical adsorption may be caused by electrostatic interaction. Coordination bonds, which enable charge transfer from the inhibitor molecules to the specimen’s surface, cause the chemical adsorption of both inhibitors on both samples [28].

Fig. 5
figure 5

Copper and brass Langmuir isotherm plots in the presence of ATAH and MTAH

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Table 3 The parameters of the Langmuir adsorption isotherm used to determine Δ \({G}^{0}\) for ATAH and MTAH in both brass and copper
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Potentiodynamic tests were conducted on copper and brass at varying temperatures (30–80 °C) with and without 0.01 M ATAH in a 3.5% NaCl solution. The potentiodynamic curves were analyzed to determine the corrosion currents, which were then used to calculate activation energies (Ea) of both samples with and without inhibitors by using the Arrhenius equation as follows [40]:

$${\text{I}}_{{{\text{corr}}}} = {\text{k exp }}\left( { - {\text{E}}_{{\text{a}}} } \right)/{\text{RT}}$$
(12)

The Arrhenius plot was utilized to compute the activation energies without and with ATAH, as displayed in Fig. 6. Table 4 shows that for copper, the activation energy was determined to be 5.241 kJ without an inhibitor. In addition, it was 64.758 kJ in the existence of ATAH. Also, the brass activation energy was 18.082 kJ without an inhibitor, whereas it was 42.102 kJ in the presence of ATAH. A significant increase in activation energy was seen in these studies when ATAH was present because of the development of a protective metal-inhibitor complex layer on the sample surface. This complex slows down the corrosion process on both copper and brass. The higher Ea values when ATAH exists demonstrate how tetrazole derivatives limit copper and brass corrosion by creating an energy barrier to the corrosion process [41].

Fig. 6
figure 6

Copper (a) and brass (b) Arrhenius plots without and with 0.01M ATAH

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Table 4 The intercepts and slopes derived from Arrhenius plots
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3.3 EIS measurements

Utilizing the EIS technique, the Bode plots of copper and brass electrodes in 3.5% NaCl in the existence and absence of inhibitors at various concentrations are shown in Fig. 7a–d. The impedance investigation verifies the prior polarization-based results. The impedance curves were fitted using the Auto Lab software. The EIS behavior can be simulated utilizing a simple equivalent circuit as shown in Fig. 7e, where Rs signifies the solution resistance, CPE is a constant phase element corresponding to the electrode surface's capacitance, and Rp refers to the polarization resistance. The Rp increases with the copper and brass inhibitor concentrations, maximizing the efficiency at 0.01 M for the two inhibitors. The Rp values accurately indicate the inhibitor's protectivity [42]. While evaluating surface heterogeneity, like the adsorption of the inhibitor on the sample surface, a CPE is determined by its impedance value and is used to replace the ideal capacitance.

$${\text{Z}}_{{{\text{CPE}}}} = \, \left[ {{\text{C }}\left( {{\text{j}}\omega } \right) \, \alpha } \right]^{{ - {1}}}$$
(13)

where the frequency in Hz is f = S−1, ω = 2πf is the angular frequency in rad/s, j is an imaginary integer (j = (− 1)1/2), and α is the surface heterogeneity exponent.

Fig. 7
figure 7

Bode graphs in simulated seawater in presence and absence of ATAH and MTAH (a, b) copper and (c, d) brass. The equivalent circuit is (e)

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The parameters obtained from equivalent circuit fitting analysis with and without inhibitors in simulated seawater are given in Table 5. When the concentration of the inhibitors increases at a concentration of 0.01 M, it provides significant protection.

Table 5 EIS parameters for both copper and brass in absence and resence of ATAH and MTAH
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Figure 8 demonstrates the following order of both samples (copper and brass) resistances in the presence of the two inhibitors: MTAH < ATAH. As a result of the existence of tetrazole ring in both inhibitors, the impact of substituents on both compounds’ varying inhibitory performances could be detected. Based on the two inhibitors’ chemical structures and inhibition levels, adding an amino group to ATAH improves its inhibition efficiency more than adding a mercapto group to MTAH.

Fig. 8
figure 8

Polarization resistance in various concentrations of ATAH and MTAH (a, b) copper and (c, d) brass

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3.4 Surface investigation

Figure 9 shows the copper sample tested in 3.5% NaCl without and with 0.01M ATAH. The surface has deteriorated in the absence of ATAH, as seen by the weak blistering and increased surface roughness. In the presence of 0.01M ATAH, the copper surface remains almost unaffected, indicating the protectiveness of the inhibitor.

Fig. 9
figure 9

SEM pictures of copper after being tested in 3.5% NaCl without (a) and with (b) 0.01 M ATAH

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Figure 10 shows micrographs of brass tested in 3.5% NaCl without and with 0.01 M ATAH. In the absence of ATAH Fig. 10a, the surface is perforated so that two levels are visualized. The upper one represents an uncorroded surface, while the lower one represents a corroded surface. The corroded surface shows granulated morphology. In the presence of 0.01 M ATAH Fig. 10b, the surface shows better morphology appearing in uncorroded surfaces except for a few areas (almost round) that suffer from shallow corrosion attacks.

Fig. 10
figure 10

SEM pictures of brass after being tested in 3.5% NaCl without (a) and with (b) 0.01 M ATAH

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Figure 11a, b shows the EDS analysis of brass after being tested in 3.5% NaCl with ATAH corrosion inhibitor. EDS in the uncorroded surface show about 58% copper, 39% Zn, and about 3% oxygen. This EDS analysis reveals the presence of CuO on the surface. The CuO layer protects brass from corrosion. However, the zinc content drops to 31% in the corroded surface in a few spots where the corrosive media affects the brass surface, causing the zinc to dissolve. Dezincification of brass can be classified as a plug time mechanism in which the dissolution occurs perpendicular to the surface. The zinc dissolution is likely to occur at inhibitor film imperfections. Figure 11c shows the EDS analysis of copper in the presence of ATAH; the copper percentage was approximately 97% and oxygen content 2.74%, which indicates the formation of CuO and the inhibitor could minimize the dissolution of copper. These agree with the inhibition efficiency and corrosion rate determined by electrochemical techniques.

Fig. 11
figure 11

The EDS spectra of brass after being tested in 3.5% NaCl with ATAH corrosion inhibitor on a section of the sample that was not corroded (a), with ATAH corrosion inhibitor on a section of the sample that was corroded (b), and on copper in the presence of ATAH (c)

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The comparison of the corrosion inhibition performance of various inhibitors for copper and brass in the literature is given in Table 6. Our inhibitors in this work provide the highest inhibition efficiency value compared to others, as seen in Table 6, reaching 98.28% and 85.89% with ATAH for copper and brass, respectively.

Table 6 Comparison of the inhibition efficiencies of different inhibitors for copper and brass
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Finally, based on the obtained outcomes, it confirms that tetrazole derivatives show good promise to improve the inhibition efficiency of copper and brass in the simulated seawater medium.

4 Conclusions

The outcomes of this study may prompt the following remarks:

  • Copper and brass corrosion resistance improved with the addition of ATAH and MTAH to the simulated saltwater solution; however, ATAH exhibits better inhibitory efficiency than MTAH.

  • Results from EIS and potentiodynamic tests indicated that when inhibitor concentrations increased, the effectiveness of their ability to inhibit corrosion increased. At 0.01 M ATAH, the maximum level of inhibitory effectiveness was attained.

  • Both inhibitors follow the Langmuir adsorption model, and copper and brass have physicochemical adsorption processes.

  • The SEM results suggest that the examined inhibitors’ capacity to inhibit may be correlated with their adsorption on the sample surface.

  • The reason ATAH performs better than MTAH is because of its amino group, which has the best inhibitory effect and exhibits better adsorption performance.