Corrosion Inhibition of Mild-Steel in 0.5 M HCl using some prepared 1,2,3-Triazoles Derivatives

The Weight loss was employed to investigate the impact of triazole on mild-steel dissolution in 0.5 M HCl solution. The inhibitor’s inhibition efficiency was seen to increase with concentration yielding (81.61%,82.61%,88.29%,91.64%,94.32%) of (T9, T8, T6, T4, T1) at concentration 1×10-4 M HCl, at a temperature of 25°C for 240 min. At a temperature range from 25–45°C, we studied the temperature impact on the corrosion behavior, wherein the results demonstrated decrease in inhibition efficiency with rising in temperature to achieve (61.7%, 52.26%, 63.1%, 72.11%, 75.77 %) of (T9, T8, T6, T4 and T1) at a concentration of 1×10-4 M, at a temperature 45°C for 240 min. A study was also performed regarding the impact of temperature on the corrosion rate in the presence and absence of triazole. The activation energy and Kinetic parameters were calculated and discussed. Polarization curves revealed that the studied inhibitors represent a mixed – type inhibitors. Adsorption of inhibitors was found to obey Langmuir isotherm and was isotherm physisorption type.


Introduction
The corrosion can be defined as a phenomenon that leads to materials deterioration via electrochemical or chemical interaction with the environment. This process could also compromise the equipment's physical and mechanical characteristics, which cast severe environmental and economic effects on all infrastructure sectors, like oil gas pipelines, roads, water and sewage systems and construction, which results in severe damage as well as threats to public safety and health 1 .
Numerous industrial applications employ acid solutions, such as in cleaning, elimination of located deposits, pickling and many other processes of industrial synthesis. Because of their aggressiveness characteristics, corrosion inhibitors are widely employed to limit the attack by metallic materials. The use of corrosion inhibitors needs to be estimated as per the particular parameters about the system, the kind of the acid employed, temperature solution, its concentration, presence of inorganic or dissolved organic substances and particularly the type of metallic materials employed 2 .
Carbon steel is known for its mechanical properties and cost-effectiveness and thus is widely employed in the industry. However, low corrosion resistance is associated with this material, which results in a decrease in performance as well as useful life about the engineering products. Thus, it is crucial to apply methodologies to protect against the corrosion process, for example, corrosion inhibitor application and pre-treatments.
The corrosive process can be delayed or minimized with organic corrosion inhibitors. Their effectiveness can be chiefly associated with the adsorption on the metal surface 3 , which behaves as a barrier layer and decreases access to aggressive species 4 . As per the literature, on the metal surface, they usually get adsorbed by the action of water molecules displacement 5 , while improved bonding efficiency is achieved due to the presence of polar functions in the molecule's S, O or N atoms, π electrons and heterocyclic compounds 6 .
As 1,2,3-triazole can form a protective film on various metallic materials, it is broadly employed as a corrosion inhibitor. Also, the literature has shown that it can effectively impede steel corrosion in different types of media 7 . However, currently, there exist disagreements pertaining to inhibitor's toxicity for humans and the environment 8 . Thus, industries and researchers are now focusing their efforts towards mitigating this issue. Recent research studies in the corrosion field are directed towards the use of natural corrosion inhibitors that have been derived from plants 9 , natural herbs 10 , seeds 11 and medicinal plants 12 . These are regarded as sustainable, biodegradable, cost-effective and easily available substances. Also, these do not include toxic compounds 13 . Numerous reports showing successful use of these substances against corrosion in various metals and acidic media 14 .
The current work aims at evaluating the inhibitive action of triazole, Table 1 (T9, T8, T6, T4, T1) 15 , 16 in corrosion of mild steel in 0.5 M hydrochloric acid by employing weight loss and galvanostatic polarization techniques. Furthermore, the investigation was carried out to determine the impact of temperature on the dissolution carbon mild steel and on the studied compound's inhibition efficiency. Table 1. The structures of Triazoles (T9, T8, T6, T4, and T1).

Experimental method
The mild-steel sample employed with a dimension of 3×1.9×0.4 cm for measurements of weight loss. The study employed a cylinder rod that was embedded in Araldite with 1 cm2 expose e surface area. The corrosive solution was prepared by employing AR grade hydrochloric acid. For weight loss experiments, weighing of the cleaned Mild-steel coupons was done beforehand and post immersion in the 25 ml test solution for 4 hrs. For the experiments, the expression of weight loss was done in grams. 15,16 A general description of the process N-substituted maleimide (1 mmol) was combined with N-((4-azidophenyl) sulfonyl) acetamide (1 mmol) before the mixture was subjected to heating for a period stretching between 6 and 15 hours. The resulting precipitate was then filtered and cleansed through re-crystallization in chloroform and hexane.

Potentiodynamic polarisation
To study the corrosion inhibitors in HCl solution, measurement of potentiodynamic polarisation (Tafel) is considered crucial and is achieved via the conventional three-electrode system, while all potential were referred to SCE in this study. Tafel polarization obtained by changing the electrode potential automatically from (+250 mV to -250 mV) at open circuit potential with a scan rate of 0.5 mV S-1 to study the effect of the inhibitor on mild steel corrosion [17][18][19] . The calculation of corresponding inhibition efficiency (IE %)) was done based on Eq.
(1) 20 . In this equation, Icorr and Icorr(inh) represent the corrosion current density pertaining to QS corrosion in HCl solution in the presence and absence of various concentrations of Inhi-ST. The linear Tafel segment of cathodic and anodic curves was extrapolated to corrosion potential to obtain the corrosion current densities (Icorr).
(1) Table 2 shows the parameters of the polarisation results (Ecorr, Icorr and βc) for both inhibited and uninhibited solutions, after which inhibition efficiency was calculated for the MS corrosion process in the collected hydrochloric solutions.  Table 3 shows comparison between E% for some triazoles (ATM, 3) 21,22 with compound T9 by using electrochemical method. Table 3. E% for some triazoles using electrochemical method at inhibitor con. of 10 -4 M in 0.5M HCl.

84.39
3 76.27 Figure 1 shows a graphical representation of the polarisation curves of MS in an acidic medium, which included 10 -4 M concentrations of (T9, T8, T6, T4, T1) compound at 30°C. Both reactions, i.e. anodic and catholic, were seen to get inhibited along with the tested compounds, which resulted in retardation of the hydrogen evolution reaction as well as metal dissolution when tested compounds inhibitors were added.  Triazole  (T9, T8, T6, T4, T1) at a temperature of 25°C. For the percentage with regards to the inhibition efficiency %IE as well as surface parameter coverage θ, which signifies the part of the surface that was covered by inhibitor molecules, the following equation was employed for the calculation 17 : (2) (3) Here, Wadd and Wfree represented the weight losses of M-Steel in the presence and absence of inhibitors. Figures 2, 3, 4, 5 and 6 demonstrate the variation of the inhibition efficiency %IE that has been considered as a function of time. An increase in inhibition efficiency was observed with a rise in inhibitor concentration. Calculation of the corrosion rate Rcorr was done by employing the following equation 23 : Where ΔW= is the weight losses of metal, S= is the surface area (cm 2 ), T= is the exposed time (min).

1. 2. Effect of Temperature
The temperature effect on the performance of mild-steel∕acid in the presence of Triazole (T1, T4, T6, T8 and T9) at different concentrations was evaluated via weight-loss at a temperature range of 25-45C when immersed for 4 hrs. The variation of inhibition efficiency of Triazole (T1, T4, T6, T8 and T9) along with temperature was seen to reduce with the rise in temperature, which suggests a physical adsorption mechanism that is improved with rising in temperature 24 . Fig 7 shows the variation in inhibition efficiency %IE with regards to the function of the temperature at a concentration of (1 × 10 -4 M). The results of these measurements are depicted in Table 11 (p. 304). The temperature had an impact on the corrosion parameters of mild-steel at a concentration of 0.5 M HCl.
From inspection of Table 5 it is clear that the positive values of ΔH reflect that the process of adsorption of the inhibitors on the Mild-steel surface is an endothermic process. The value of ΔS in the presence and absence of the inhibitors are negative.
This implies that the activation complex is the ratedetermining step representing association rather than dissociation, indicating that a decrease in disorder takes place on going from reactant to the activated complex 27 .
The negative values of ΔG mean that the adsorption of Triazole (T1, T4, T6, T8, T9) on Mild-steel surface is a spontaneous process, and the negative values of ΔG also show the strong interaction of the inhibitor molecules on to the Mild-steel surface 31 .
It was found that ΔG increases negatively with increasing the temperature. This phenomenon once again indicates that the adsorption is favourable with increasing experimental temperature and dominates on the desorption of the inhibitor from the Mild-steel surface 32 .

2. Adsorption Isotherm
Adsorption isotherms are crucial to understanding the inhibition mechanism of corrosion reaction. Some of the most frequently employed adsorption isotherms include Freundlich, Frumkin, Langmuir and Temkin isotherms. The one that is best fitted follows the Langmuir isotherm. Plotting (C/ ) against concentration (C) yields straight lines as presented in Fig.9 On the mild-steel surface, the inhibitor Triazole (T9, T8, T6, T4, T1) gets adsorbs  as per the Langmuir kind isotherm model via the  relation [33][34][35] .
Where K= is the equilibrium constant of the adsorption process.

Conclusions
Can be used of Triazole compounds as inhibitors corrosion of mild steel in 0.5 M HCl. There is an increase in inhibition efficiency with the rise in the concentration of Triazole compounds. The inhibition efficiency of triazole compounds decreases with temperature while there is increased activation of corrosion energy when the inhibitor is present. The inhibition corrosion of Triazole compounds (T1, T4, T6, T8 and T9) was Physisorption on the metal surface. 1,2,3-triazole derivatives obey Langmuir adsorption isotherm, and the inhibition efficiency of these compounds was in order (T1> T4 >T6 > T8>  T8> T9).