3.1 Open Circuit Potential plots of Copper in NaCl/Chickenbone medium
The open circuit potential (OCP) graph of copper in chicken bone inhibited solution of NaCl is shown in Fig. 1 at a measured temperature of 30°C. The plot shows that the sample without the inhibitor had the highest potential over the entire 120-second period. This sample had the greatest shift towards the positive region, indicating a higher potential. In contrast, the subsequent inhibitor-treated samples had lower potentials and moved towards the negative potential range. The sample with 0.2g of Chicken bone inhibition had the lowest potential, slightly less than − 0.25V. The shift of the curve towards the negative area indicates that the cathodic reaction is more pronounced than the anodic reaction. Moving on, Fig. 2 shows a more positive shift in the copper samples' OCP with an increase in Chicken bone inhibition at 60°C.The result leads to the conclusion that as the temperature rises, inhibitions become more potent. There is a clear relationship between the effectiveness of inhibition and temperature, suggesting that higher temperatures contribute to improved inhibition performance [11]–[14].
3.2 Analysis of Copper's Potentio-dynamic Polarization in a NaCl/Chickenbone Medium
Table 1 shows the electrochemical parameters of copper corrosion in NaCl with different concentrations of chickenbone inhibition, including ECORR (V), JCORR (A/cm2), corrosion rate (mm/year), and polarization resistance (Ω). The results in the table show that as the concentration of chickenbone inhibition increases, the corrosion rate decreases. This finding is supported further by Figs. 3 and 4, which show a decrease in both the cathodic and anodic reactions of copper corrosion. Chicken bone's inhibitive properties are responsible for the corrosion reduction at 30°C and 60°C. Notably, the data in Table 1 and Figs. 3 and 4 show a consistent shift of ECORR towards the Negative (Cathodic) region across a wide range of samples and temperature variations. Also, the ECORR deviation across some sample temperatures is less than 0.085V. Based on these findings, it is possible to conclude that the chicken bone inhibitor has cathodic-type inhibition behavior [15]–[17].
Table 1
Potentiodynamic polarization data for copper in Chickenbone Inhibited NaCl medium
Temp. of medium (ᵒC) | Conc. of inhibitor (g) | ECORR (V) | JCORR (A/cm2) | Corrosion rate (mm/year) | Polarization resistance (Ω) |
30 | Control | -0.304294 | 1.69E-05 | 195.963 | 54.513 |
0.2 | -0.770591 | 4.76E-05 | 55.331 | 35.722 |
0.4 | -0.395099 | 1.14E-04 | 43.786 | 21.879 |
0.6 | 0.987073 | 1.45E-04 | 23.004 | 23.247 |
0.8 | 1.311970 | 3.23E-04 | 17.988 | 16.112 |
40 | Control | -1.33383 | 1.54E-05 | 179.316 | 168.858 |
0.2 | -0.603871 | 3.48E-04 | 43.189 | 48.212 |
0.4 | -0.919682 | 4.81E-04 | 30.977 | 34.433 |
0.6 | -1.11331 | 6.18E-04 | 25.584 | 34.225 |
0.8 | -1.18011 | 8.73E-04 | 14.153 | 24.213 |
50 | Control | -0.936825 | 1.88E-05 | 218.959 | 38.285 |
0.2 | -0.584499 | 1.46E-04 | 47.005 | 26.056 |
0.4 | -0.420661 | 1.77E-04 | 33.614 | 22.239 |
0.6 | -0.350539 | 1.95E-04 | 27.563 | 19.658 |
0.8 | -1.2227 | 2.82E-04 | 21.176 | 14.286 |
60 | Control | -0.663104 | 9.66E-05 | 112.247 | 69.751 |
0.2 | -0.457108 | 1.43E-04 | 42.567 | 54.238 |
0.4 | -0.473323 | 2.65E-04 | 30.849 | 38.146 |
0.6 | -1.14401 | 5.16E-04 | 29.9873 | 35.047 |
0.8 | -0.37213 | 7.54E-04 | 17.914 | 16.901 |
3.3 Inhibitor Efficiency of Chicken bone
Figure 5 depicts the copper inhibition efficiency of chicken bone. At 50°C, the inhibitor performs admirably, with efficient inhibition observed across all concentration gradients. Notably, the inhibitor is of the anodic type. The trends in inhibitor performance observed with varying concentrations are especially favorable at lower temperatures. [18].
3.4 Adsorption Isotherms and Adsorption Parameters
The adhesion of the investigated inhibitor to the metal surface plays a crucial role in the process of corrosion prevention. Various adsorption isotherms, including Temkin, Langmuir, Frumkin, and Freundlich, are commonly used to describe the mechanism of inhibitor adsorption. In this study, the Temkin adsorption isotherm, represented by Eq. (2), was identified as the most suitable model for fitting the data obtained from electrochemical impedance and potentiodynamic polarization measurements. This finding emphasizes the significance of the Temkin adsorption isotherm in comprehending the behavior of inhibitor adsorption and its impact on corrosion inhibition [19].
ϴ = BKads + BlnCinh (2)
The heat of adsorption constant is denoted by the constant B. This isotherm takes into account the interactions between adsorbent and adsorbate. If the minimal and maximum concentration values are ignored, the models determine that the heat of adsorption of all layer molecules decreases linearly rather than logarithmically with coverage, as shown in Fig. 6. Table 2 summarizes the Kads(mol-1), Gads (KJmol-1) and R2 values obtained from the Temkin adsorption model. Kads is the force that holds adsorbate and adsorbent together. Larger Kads values indicate greater adsorption and thus better inhibition performance. According to Table 2, the values of Kads decreased with increasing temperature, indicating that the adsorption of Chicken bone ashes on the surface of copper was not favourable, with the exception of 50oC, which had the highest and optimal Kads value.[20], [21], [22].
Table 2
Adsorption Parameters determined from Temkin isotherm.
Temperature (ᵒC) | Kads(mol− 1) | ΔGads (KJmol− 1) | R2 | ln(Kads) | 1/T | ΔGads/T | B = Slope |
30 | 656.9611 | -26.4659 | 0.9446 | 6.4876 | 0.0033 | -0.0873 | 0.1448 |
40 | 359.3698 | -25.7691 | 0.9990 | 5.8844 | 0.0032 | -0.0823 | 0.1747 |
50 | 913.2658 | -29.0975 | 0.9707 | 6.8170 | 0.0031 | -0.0901 | 0.1530 |
60 | 66.5888 | -22.7476 | 0.9461 | 4.1985 | 0.0030 | -0.0683 | 0.2418 |
The results show that the negative value of the Gibbs free energy of adsorption, G°ads, confirms the adsorption process's spontaneity and the stability of the adsorbed coating on the copper surface. Furthermore, the adsorbed layer's stability improves with increasing temperature, as evidenced by higher absolute values of G°ads at higher temperatures. This implies that higher temperatures favor the adsorption mechanism, possibly due to increased attraction to the adsorbent and increased movement of ions and molecules in the solution. The calculated values of G°ads range from − 22.7476 to -29.0975 kJ/mol, indicating that physisorption rather than chemisorption drives the adsorption process. G°ads values below or around − 20 kJ/mol are associated with physisorption, while values above − 40 kJ/mol are typically associated with chemisorption. [23].
3.5 Activation Parameter on the Inhibition Mechanism
The Inhibition mechanism of the corrosion process can easily be understood by temperature variations. The temperature change causes a change in the intensity for all electrochemical system causing changes in the kinetics and the adsorption parameters of a system. The effect oof temperature variation on the corrosion process of copper in a chicken bone inhibited Nacl medium between 30ᵒC to 60ᵒC could be analysed using activation energies. Figure 7 show the relationship between the logarithmic of corrosion density (log JCORR) and temperature reciprocal (1/T), which follows the model of Arrhenius plot for measuring activation energy. Eq. 3 and Table 3 shows the formulation for this plot and the values of each parameter respectively.
$$Log{ J}_{CORR}=Log \lambda -\frac{Ea}{2.30RT}$$
3
where, Ea is the activation energy, R molar gas constant and λ the Arrhenius pre-exponential factor.
Figure 7 depicts a linear relationship with a regression coefficient close to unity between the logarithm of corrosion current density obtained from electrochemical measurements and the reciprocal of temperature (1/T). The activation energy (Ea) and pre-exponential factor (λ) values were calculated from the slope and intercept, respectively, and are shown in Table 3. According to the table, the activation energy decreases with increasing inhibitor concentrations, implying that the chicken bone ash impedes the corrosion process on copper. The observed Ea values are less than the chemisorption threshold of 80 KJ/mol, indicating that the adsorption is physical in nature. This change in Ea causes a decrease in the ash adsorption on copper with increasing temperature, increasing the risk of corrosion in a more aggressive environment[24], [25].
Table 3
Activation parameters of Chicken bone inhibitor in NaCl
Inhibitor Concentration (g) | Ea (KJ/mol) | λ (mgcm− 2) | ΔHo (KJ/mol) | ΔSo (KJ/molK) | ΔGo (KJ/mol) |
30ᵒC | 40ᵒC | 50ᵒC | 60ᵒC |
Control | 12.1009 | 1.51E-07 | -14.7406 | -0.3270 | 84.3282 | 87.5978 | 90.8674 | 94.1370 |
0.2 | 21.4673 | 4.62E-01 | 18.8276 | -0.2028 | 80.2672 | 82.2949 | 84.3226 | 86.3503 |
0.4 | 32.4026 | 3.60E-02 | 10.7629 | -0.2240 | 78.6324 | 80.8723 | 83.122 | 85.3522 |
0.6 | 41.5348 | 1.56E + 00 | 19.8951 | -0.1926 | 78.2623 | 80.1886 | 82.1149 | 84.0412 |
0.8 | 50.8768 | 4.44E-02 | 9.2371 | -0.2222 | 76.5787 | 78.8012 | 81.0237 | 83.2462 |