1 Introduction

Hydrochloric acid stimulated acidizing solution is mainly used in the oil and gas industries during acid treatment to improve the productivity of oil wells. Acidizing have been in existence for over 100 years and predates every other technique of well stimulation including hydraulic fracturing. However, lack of efficient acid corrosion inhibitors to ensure the protection of pipeline steels in the wells limited the use of acidizing up until the early 1930′s.[1]. Having developed effective inhibitors for acid corrosion, acidizing of oil wells proliferated, leading to establishment of the well stimulation service industry. It is widely known today, that acidizing also known as acid treatment is one of the most effective means for improving stimulation (productivity) of wells in the oil and gas industry [2].

Several researches have been carried out on the application of various inorganic and organic compounds as corrosion inhibitors for metals in acidic medium. Most of the effective inhibitors have been those containing heteroatoms and multiple bonds in their molecular structure by which they get adsorbed on the metallic surface to prevent the dissolution of metals in the corrosive medium [3,4,5,6]. Though most synthesized compounds possesses good anti-corrosive potentials, majority of them are not safe in the environment and to human beings. Some of the known eco-friendly corrosion inhibitors include plant-based natural products [7, 8] and some nontoxic synthesized compounds such as, Schiff bases [9, 10], medicines [11, 12] and dyes [13, 14], which have been classified as green inhibitors. There has been increased interest on the use of natural substances as inhibitors of metal corrosion because apart from being ecologically friendly, they are readily available and cheap. Moreover, they are organic in nature with constituents including alkaloids, pigments, organic and amino acids and tannins which are known to exhibit inhibitive properties. Recent reports have shown that gum exudates from different plant such as Moringa Oleifera [15], Acacia Senegal [16], Acacia drepanolobium [16], Gum Arabic [17] Azadirachta indica [18], Raphia hookeri [19] Albizia ferruginea [20], Khaya senegalensis [20], Dorema ammoniacum [21] Ferula asafoetida [21], Guar Gum [22] etc. are efficient corrosion inhibitors being eco-friendly, green and less toxic.

The present work aims to contribute to the search for eco-friendly and affordable corrosion inhibitors as a replacement for the toxic and expensive inorganic and some organic inhibitors. This study on the corrosion inhibition of N80 carbon steel in 1 M HCl stimulated acidizing solution using gum exudate from Terminalia Mentaly, which has not been previously investigated, was carried out using different techniques like Electrochemical ımpedance spectroscopy (EIS), gravimetric and potentiodynamic polarization (PDP). Scanning Electron Microscopy (SEM) measurements were used to study the surface morphologies.

2 Experimental

2.1 Material preparation

The N80 steel plates utilized for all tests were sourced from an oil field in Nigeria. The plates with thickness 2 mm and composition as described previously [23] were cut into coupons of dimensions 30 × 20 mm for gravimetric and surface morphological studies, and 25 × 10 mm for electrochemical tests. Prior to the measurements, the N80 steel samples were polished using various grades (# 400–1000) of silicon carbide paper, washed with double distilled water, rinsed and degreased in ethyl alcohol and acetone respectively then finally air-dried and stored in a desiccator. The N80 steel samples used for electrochemical studies were encapsulated in epoxy resin with an exposed surface area of 1 cm2. 1 M HCl solution prepared with AR grade 37% HCl in double distilled water was used as the corrosive medium.

The Terminalia Mentaly (TM) gum exudate was collected from its parent tree at the University of Port Harcourt Nigeria and authenticated by Plant Science Department of same University. Weighed amount of the dry gum was thoroughly washed with distilled water to remove dust and sand impurities, and soaked for two days in 100 mL of 1 M HCl solution. The GETM which was soluble in the acid solution (solubility = 53% v/v) was used for the corrosion studies after preparation at concentration range from 0.1 g/L to 2.0 g/L.

2.2 Electrochemical measurements

The EIS and PDP tests were performed by employing a CHI model of electrochemical workstation (CHI-760) utilizing electrochemical cell assembly consisting of three electrodes. In the cell, N80 steel was the working electrode, the reference electrode was saturated calomel electrode (SCE) and Platinum foil was the counter electrode. Gamry E-Chem software was used to analyze the data. The electrochemical measurements were conducted in aerated, non-stirred 1 M HCl solutions containing different concentrations of GETM. Each experiment was run in triplicate to check reproducibility and average values of the electrochemical data recorded. All tests were performed in a solution temperature of 303 K. Before performing each test, the N80 steel was submerged in the corrosive medium for 30 min to attain steady open circuit potential (OCP). EIS measurements employed an AC signal with 10 mV peak to peak amplitude within the frequency range 100–0.01 Hz. PDP curves were obtained at a scan rate of 1 mV/s, at − 250 to + 250 mV against SCE with respect to EOCP.

2.3 Gravimetric measurement

The N80 steel samples previously weighed and recorded were immersed in 250 mL of 1 M HCl without and with various concentrations of GETM at 303 K. Each specimen was removed from the various test solution after an exposure period of 5 h, scrubbed with bristle brush under running water, rinsed in acetone, dried and reweighed [24]. The difference in weight of the N80 steel before and after immersion in the test solutions was recorded as the weight loss. The same test as described above which was carried out three times was also performed at 313, 323 and 333 K. The weight loss data measured in mg was utilized to evaluate the corrosion rate (CR), deploying the following equation:

$$C_{R} \left( {{\text{mg h}}^{ - 1} {\text{cm}}^{ - 2} } \right) = \frac{W}{tA}$$
(1)

where W is weight loss in mg, A is the area of N80 steel specimen in cm2 and t is exposure time in h. The surface coverage (θ) and inhibition efficiency (IWL %) of GETM were determined using the corrosion rate values as follows:

$${\uptheta } = { }\frac{{C_{R}^{o} - C_{R}^{i} }}{{C_{R}^{o} }}$$
(2)
$$I_{WL} \% = \left( {1 - \frac{{C_{R}^{i} }}{{C_{R}^{o} }}} \right) \times 100$$
(3)

where \(C_{R}^{o}\) and \(C_{R}^{i}\) are corrosion rates in blank and inhibited acid solutions.

2.4 SEM analyses

The surface morphologies of the N80 steel without and with 2.0 g L−1 GETM was assessed utilizing a JEOL 5300 model of scanning electron microscope while applying a voltage of about 15 kV and 1000 × magnification. The pre-treated steel specimens were immersed in the various test solutions for 4 h and thereafter retrieved at the expiration of the stipulated time, cleaned and subsequently scanned.

3 Results and discussion

3.1 Electrochemical impedance spectroscopy (EIS)

EIS spectra help in the proof of protective film formation on metal surfaces. Figure 1 presents the Nyquist plots obtained at OCP for N80 steel without and with GETM inhibitor in 1 M HCl solution at 303 K. The Nyquist plots have a single depressed semi-circular loop over the entire frequency range, which indicates that N80 steel electrode dissolution in the aggressive acid is controlled by charge-transfer process which functions on the magnitude of change of the double layer capacitance [4, 25, 26]. The size of the semicircle increases with increase in GETM concentration. However, the impedance spectra are not perfect semicircles, which could be attributed to frequency dispersion effect resulting from inhomogeneity of the electrode surface [27, 28]. The impedance data were analyzed by utilizing the equivalent circuit shown in Fig. 2. The circuit consists of the electrolyte or solution resistance \((R_{s} )\), charge transfer resistance \((R_{ct} )\) in parallel combination with constant phase element (CPE) standing in for the capacitor. The validity of the equivalent circuit was ascertained from the χ2 values presented in Table 1. The magnitude of CPE \(\mathop Y\limits^{\prime }_{o}\) is related to the impedance (ZCPE) by the equation:

$$Z_{CPE} = {\mathop Y\limits^{\prime }}_{0}^{ - 1} \times \frac{1}{{\left( {j\omega } \right)^{n} }}$$
(4)
Fig. 1
figure 1

Nyquist plots for N80 steel in 1 M HCl solution at 303 K without and with various concentrations of GETM

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Fig. 2
figure 2

Equivalent circuit model used to fit the EIS data

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Table 1 Impedance parameters for N80 steel in 1 M HCl solution without and with various concentrations of GETM at 303 K
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where ω is the angular frequency \((\omega=2\pi {f_{max}})\), at which the imaginary part of the impedance \(( - Z_{im} )\) is maximum, \(f_{max}\) is maximum AC frequency, \(j^{2} = \sqrt {( - 1)}\) is the imaginary unit and n is the exponent (phase shift), associated with the heterogeneity or roughness of the metal surface [29]. With \(n = - 1, 0\) or close to 1, the CPE represents an inductance, a resistance or a capacitor respectively. Still, for a Warburg impedance, n = 0.5. In this study, the values of n are close to 1 for both uninhibited and inhibited environment suggesting that the CPE represents a capacitor [30, 31]. These values of n indicate that the molecules of GETM adsorbed as pseudo-capacitive protective films on the N80 steel surface [3]. Double layer capacitance \(\left( {C_{dl} } \right)\) values were evaluated utilizing the following equation [32]:

$$C_{dl} = \sqrt[n]{{{\mathop Y\limits^{\prime }}_{o} R_{ct}^{1 - n} }}$$
(5)

The inhibition efficiency (IEIS %) calculated from Rct values is expressed by the relation [33]:

$$I_{EIS} \% = \frac{{R_{ct}^{i} - R_{ct}^{o} }}{{R_{ct}^{i} }} \times 100\,$$
(6)

where, \(R_{ct}^{i}\) and \(R_{ct}^{o}\) stand for charge transfer resistance with and without inhibitors. The derived and calculated EIS parameters are presented in Table 1.

The obtained results showed increased \(R_{ct}\) values and a decrease in \(C_{dl}\) values for N80 steel in 1 M HCl solution with GETM compared to the bare electrolyte (1 M HCl) without GETM. The \(R_{ct}\) and \(C_{dl}\) continually increased and decreases respectively as the inhibitor concentration increases, which eventually leads to an increase in IEIS %. The observed increase in \(R_{ct}\) values with inhibitor addition indicates protective thin layer formation on the N80 steel surface as a result of adsorption of GETM molecules. Again, decrease in the values of \(C_{dl}\) could be due the lowering of the local dielectric constant, or maybe increased electrical double layer thickness, indicating that GETM molecules function by adsorption at the metal/solution interface [34, 35].

3.2 Potentiodynamic polarization

The kinetics of the reactions taking place at the cathodic and anodic sites of the corrosion cell is understood by carrying out polarization experiments. Figure 3 presents the Tafel polarization curves for N80 steel in 1 M HCl solution with and without various concentrations of GETM at 303 K. The current–potential curves in Fig. 3 show that the anodic and cathodic segments were shifted towards lower region of the corrosion current density upon adding GETM inhibitor as compared to the bare 1 M HCl. The kinetic parameters derived from the curves by extrapolation of the Tafel lines, including corrosion current density \(i_{corr}\), cathodic and anodic Tafel slops (βc, βa), corrosion potential \(E_{corr}\) and inhibition efficiency (IPDP %) are listed in Table 2. The IPDP % values were calculated using Eq. 6 [33]:

$$I_{PDP} \% = \left\langle {1 - \frac{{i_{corr} }}{{i_{corr}^{o} }}} \right\rangle \times 100$$
(7)
Fig. 3
figure 3

Tafel polarization curves for N80 steel in 1 M HCl without and with various GETM concentrations at 303

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Table 2 Polarization parameters for N80 steel corrosion in 1 M HCl in the presence and absence of different concentration of GETM
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where, \(i_{corr}\) and \(i^{o}_{corr}\) refers to the corrosion current density with and without inhibitors.

It is seen from Fig. 3 that the introduction of GETM affected both the anodic and cathodic arms of the Tafel plot suggesting that it acted as a mixed type inhibitor. However the anodic partial reaction is more affected than the cathodic as also observed from the higher values of βa compared to βc, indicating that GETM slightly acted more like an anodic inhibitor. The \(i_{corr}\) values are observed to have decreased with increase in the inhibitor concentration with the least value obtained at the optimum concentration (2.0 g L−1), because of protective film formation on the N80 steel surface by adsorption [36]. Table 2 also reveals that the \(E_{corr}\) shifted to a more noble positive value upon addition of GETM compared to the blank. Nevertheless, the maximum shift in \(E_{corr}\) value between the uninhibited and inhibited system is less than 85 mV, supporting that GETM acted as a mixed-type inhibitor [37, 38]. The IPDP % values increased with increase in GETM concentration in agreement with EIS result.

3.3 Gravimetric measurement

Figure 4a-b shows the variation of corrosion rate (CR) and corrosion inhibition efficiency (IWL %) of GETM with its concentrations. Figure 4a shows that the introduction of GETM diminished the corrosion rate at different temperatures and the CR continually decreased as the inhibitor concentration increases. The IWL % on the other hand, increased with increase in inhibitor concentration (Fig. 4b), indicating that the adsorption and surface protective ability of GETM is strengthened with its concentration thus separating the N80 steel surface from the aggressive solution by thin layer formation on the metal surface [39, 40]. In addition, the corrosion inhibition performance of GETM has been compared with those of gum exudates from different plants reported in literature as shown in Table 3.

Fig. 4
figure 4

(a) CR against GETM concentration for N80 steel in 1 M HCl at different temperatures, (b) IWL % against GETM concentration of for N80 steel in 1 M HCl at different temperatures

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Table 3 Comparison between the inhibition efficiency of GETM and some other reported gum inhibitor on steel in acidic medium
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3.4 Adsorption studies

The mechanism of interaction between the N80 steel (adsorbent) and the adsorbate (GETM inhibitor) can be better explained using the adsorption isotherms. Surface coverage (\(\theta\)) values at various GETM concentrations in 1 M HCl in the temperature range (303–333 K) was fitted with different adsorption isotherms such as, Temkin, Langmuir, Freundlich, El-Awady, Frumkin and Flory–Huggins [41]. The Langmuir adsorption isotherm was the best fit, expressed as:

$$\frac{{C_{inh} }}{\theta } = \frac{1}{{K_{ads} }} + C_{inh}$$
(8)

where \(C_{inh}\) represent inhibitor concentration and \({K}_{ads}\) the equilibrium constant of adsorption–desorption process. Figure 5 presents linear plots of \(C_{inh} /{\uptheta }\) against \(C_{inh}\) at all studied temperatures, by which the \(K_{ads}\) values were deduced from the intercept of the plots. The obtained results reveal that all the linear regression coefficients (R2) and the slope are close to unity (Table 4), indicating that GETM adsorption on N80 steel surface follows Langmuir adsorption isotherm [42]. The slope values as seen in Table 4 show that the deviation from ideal Langmuir isotherm is not very pronounced. The slope of an ideal Langmuir isotherm should be equal to unity, which means absence of interaction between the adsorbed species. When the slope values are less or greater than unity, it indicates that there is interaction among the adsorbed species on the surface of the metal [43]. Temkin isotherm was therefore considered because the model considers lateral interaction. The Temkin model can be expressed as follows:

$$\theta = \frac{ - 2.303}{{2a}}\log K_{ads} - \frac{2.303}{{2a}}\log C_{inh}$$
(9)
Fig. 5
figure 5

Langmuir plots for GETM adsorption on N80 steel in 1 M HCl at different temperatures

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Table 4 Langmuir and Temkin isotherms parameters for GETM adsorption on N80 steel in 1 M HCl at different temperatures
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Figure 6 presents linear plots of \({\uptheta }\) against \(\log C_{inh}\) with slope equal to \(- 2.303/2{\text{a}}\) and intercept equal to \(\left( { - \frac{2.303}{{2{\text{a}}}}} \right)\log K_{ads}\). The Temkin adsorption parameters are also presented in Table 4. The observed relatively high linear regression coefficients (R2) confirm the applicability of the Temkin model to the adsorption of GETM on N80 carbon steel surface. The negative values of the interaction parameter (a) indicate that repulsion exists in the adsorption layer [44]. The fit of the experimental data to the Langmuir and Temkin isotherms indicates that GETM inhibit N80 steel corrosion by adsorption on the metal surface. The additives could be adsorbed by the interaction between the free electron of the heteroatoms on the GETM moiety and steel surface (chemisorption). The adsorption standard Gibb’s free energy \(\Delta G_{ads}^{o}\) was deduced from its relationship with \(K_{ads}\) expressed as [45]:

$$K_{ads} = \frac{1}{{1 \times 10^{3} }} exp\left( {\frac{{ - \Delta G_{ads}^{o} }}{RT}} \right)$$
(10)

where \(1 \times {10}^{3}\) is the concentration of water molecules expressed in g L−1, R and T represents gas constant and absolute temperature, respectively. It is well known that high \(K_{ads}\) value and a low \(\Delta G_{ads}^{o}\) value automatically results to a high metal-inhibitor interaction. \(K_{ads}\) values as presented in Table 4 are fairly high enough which is the reason for a strong interactions between the inhibitor and the N80 steel [46]. The values of \(\Delta G_{ads}^{o}\) listed in Table 4 are seen to be negative in all the cases, indicating the spontaneity of GETM adsorption on the steel surface and the stability of the protective layer on the N80 steel. The free energy of adsorption \(\left( {\Delta G_{ads}^{o} } \right)\) values obtained using the Langmuir isotherm ranged from − 21.87 to − 22.84 kJ/mol and for Temkin isotherm, from − 35.10 to − 36.03 kJ/mol. These values of \(\neg \Delta G_{ads}^{o}\) indicate complex mode of interactions, which involve both chemisorption and physisorption mechanisms between N80 steel and the gum exudate [47].

Fig. 6
figure 6

Temkin isotherm for GETM adsorption on N80 steel in 1 M HCl at different temperatures

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3.5 Effect of temperature

The influence of temperature on the stability of protective film of GETM on N80 steel surface likewise temperature effect on the CR and IWL % was evaluated by gravimetric measurements at temperature range 303–333 K without and with various concentrations of GETM in 1 M HCl. Figure 4a and b clearly show that increase in temperature augments the CR but diminished the inhibition efficiency [48]. The values of CR were used to deduce the apparent activation energy \({E}_{a}\) according to the Arrhenius equation [31]:

$$\log C_{R} = \frac{{ - E_{a} }}{2.303RT} + \log {\AA}$$
(11)

where Å, T and R represent the pre-exponential factor, absolute temperature and gas constant, respectively. Figure 7a presents linear regression between log CR and 1/T, through which \({E}_{a}\) was calculated from the slope \(( - E_{a} /2.303R)\) of the graph and listed in Table 5. Other thermodynamic parameters such as enthalpy of activation (ΔH*) and entropy of activation (ΔS*) were evaluated by utilizing the transition state equation given as:

$$C_{R} = \frac{RT}{{Nh}} {\exp}\left( {\frac{{\Delta S^{ * } }}{R}} \right){\exp}\left( {\frac{{ - \Delta H^{ * } }}{RT}} \right)$$
(12)
Table 5 Activation parameters for N80 steel corrosion in 1 M HCl without and with different concentrations of GETM
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where N and h are Avogadro's number and Planck constant, respectively. Linear plots of log (CR/T) vs. 1/T obtained is depicted in Fig. 7b, through which ΔH* values were calculated from the slope \(( - \Delta H^{*} /2.303R)\) and ΔS* from the intercept \([{\log}(R/Nh) + \Delta S^{*} /2.303R]\) and also presented in Table 5. The result in Table 5 shows that \(E_{a}\) values for the solution with GETM are higher than that without the inhibitor, which suggests that more energy barrier is needed for the corrosion reaction to take place [49]. Generally, values of \(E_{a}\) between 20 and 40 kJ mol−1 suggest physisorption mechanism while \({E}_{a}\) values between 80–240 kJ mol−1 suggest chemisorption. In this study, the value ranges between 48.29 and 64.54 kJ mol−1 which suggests that the adsorption of GETM involves both physical and chemical adsorption. The positive values of ΔH* in both systems, show the endothermic nature of N80 steel dissolution. The negative high values of ΔS* suggests that the activated complex in the rate ascertaining step representing dissociation with a more ordered platform on going from reactants to the activated complex [50].

3.6 SEM studies

SEM micrographs of N80 steel prior and after immersion in 1 M HCl without and with optimum concentration (2.0 g L−1) of GETM at 303 K for 4 h are shown in Fig. 8 (a-c). The SEM micrograph before immersion in corrosive solution (Fig. 7a) displays a clear and sleek surface of N80 steel due to corrosion free surface. Figure 8b depicts the SEM micrograph of N80 steel surface without the inhibitor, which is clearly seen to be badly damaged with cracks due to the metal dissolution in the acidic corrosive medium. However, in presence of GETM (Fig. 8c), the surface damage diminished and it looks smoother than without GETM. These observations suggest the adsorption of GETM molecules unto the N80 steel surface which in turn forms a deterrent film that inhibits the corrosion process.

Fig. 7
figure 7

a Arrhenius plots of log CR vs. 1/T and b Transition state plots of log (CR/T) vs. 1/T

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3.7 Mechanism of inhibition

It is necessary to know the chemical composition of GETM to better explain its inhibition mechanism. Tizhe and co-workers [51] reported that GETM have a variety of phytochemicals like alkaloids, saponins, flavonoids, tannins and terpenes among others. These compounds are rich in conjugated aromatic structures and contain heteroatoms with free electron pairs that are available to form bonds with the metal surface [52]. It is therefore, pertinent to say that the adsorption of these compounds onto mild steel surface is responsible for the corrosion inhibition effect. Similar to most organic corrosion inhibitors, GETM also inhibit the corrosion of metals by blocking both anodic and cathodic reaction sites. Based on the results of the present study and several literature reports, anodic and cathodic reactions mechanism and their inhibition can be shown as follows [53,54,55]:

Anodic reactions:

$${\text{Fe}} + { }n{\text{H}}_{2} {\text{O }} \to {\text{ Fe}}({\text{H}}_{2} {\text{O}})_{n}$$
(13)
$${\text{Fe}}({\text{H}}_{2} {\text{O}})_{n} + { }2{\text{Cl}}^{ - } { } \to { }\left[ {{\text{Fe}}({\text{H}}_{2} {\text{O}})_{n} 2{\text{Cl}}^{ - } } \right]$$
(14)
$$\left[ {{\text{Fe}}({\text{H}}_{2} {\text{O}})_{n} 2{\text{Cl}}^{ - } } \right] + \left[ {{\text{GETM}}} \right]^{ + } \to \left[ {{\text{Fe}}({\text{H}}_{2} {\text{O}})_{n} 2{\text{Cl}}^{ - } } \right]\left[ {{\text{GETM}}} \right]^{ + }$$
(15)
$$\left[ {{\text{Fe}}({\text{H}}_{2} {\text{O}})_{n} 2{\text{Cl}}^{ - } } \right]\left[ {{\text{GETM}}} \right]^{ + } + { }e^{ - } { } \to { }[{\text{Fe}}({\text{H}}_{2} {\text{O}})_{n} 2{\text{Cl}}^{ - } {\text{GETM}}]^{ - }$$
(16)

The anodic dissolution of N80 steel proceeds according to the Eqs. (10) and (11). Nevertheless, with GETM, the anodic dissolution reactions rate slows down due to protective film formation by [GTEM] as represented in Eqs. (12) and (13) which separate the aggressive acidic solution from the metal surface.

Cathodic reactions:

$$2{\text{H}}^{ + } + { }e^{ - } { } \to {\text{ H}}_{2}$$
(17)
$${\text{Fe}} + [{\text{GETM}}]^{ + } { } \to \left( {{\text{Fe}}\left[ {{\text{GETM}}} \right]} \right)^{ + }$$
(18)
$$({\text{Fe}}\left[ {{\text{GETM}}} \right])^{ + } + { }e^{ - } { } \to {\text{ Fe}}\left[ {{\text{GETM}}} \right]$$
(19)

Cathodic reactions majorly involve hydrogen gas evolution according to Eq. (14). Nevertheless, in the presence of GETM, the positively charged GETM moiety gets adsorbed at the cathodic site and inhibits cathodic reactions as shown in Eqs. (15) and (16). Generally, steel surfaces are known to carry positive charge in acidic medium, which attracts the electrolyte’s (e.g. HCl) negative ion. The adsorbed layer then assumes a negative charge and attracts the cations of the inhibitor. This means that the anion is seen as a junction between the two positive dipoles (GETM and steel) that forms a protective film of the molecules of GETM and prevents higher amount of corrosive solution passing to the steel surface.

Fig. 8
figure 8

SEM micrograph of N80 steel surface: a polished free sample, b in 1 M HCl without inhibitor c in 1 M HCl + 2.0 g L−1 GETM at 1000 × magnification

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4 Conclusion

The investigation of the surface protective ability of Terminalia Mentaly gum exudate for carbon steel corrosion in HCl stimulated acidizing solution carried out utilizing electrochemical ımpedance spectroscopy (EIS), gravimetric, potentiodynamic polarization (PDP) and scanning electron microscopy (SEM) measurements draw the following conclusions:

  1. 1.

    The gum exudate from Terminalia Mentaly (GETM) has shown to be an effective inhibitor for N80 steel corrosion 1 M HCl and its protective ability enhances with increment in the inhibitor concentration.

  2. 2.

    Results from PDP measurements show that GETM behave as a mixed inhibitor for N80 steel dissolution in 1 M HCl and to an extent retarded both anodic and cathodic corrosion with greater anodic effect.

  3. 3.

    The mode of GETM adsorption on the steel surface obeyed Langmuir adsorption isotherm and proceeds by physical adsorption.

  4. 4.

    EIS measurements show that GETM adsorb on N80 steel surface with diminishing the double-layer capacitance and increasing charge transfer resistance.

  5. 5.

    The SEM results confirmed that the corrosion inhibition mechanism proceeds through adsorption process.

  6. 6.

    The inhibition efficiencies obtained utilizing different techniques had fantabulous agreement.