Study of Inhibition and Adsorption Properties of Mild Steel Corrosion by Expired Pharmaceutical Gentamicin Drug in Hydrochloric Acid Media

Introduction

Simple accessibility, minimal effort of mellow steel has numerous industrial applications. It is broadly utilized as a part of different ventures like sugar, cowhide, sustenance, petrochemical, paper and material businesses. In most mechanical procedures, the acidic arrangements are regularly utilized for the pickling, acid cleaning, de-scaling of acids etc. The decreasing corrosion rate of metals spares the current assets and thusly creates conservative advantages amid the mechanical applications. The lifetime of types of gear can be expanded and viable corrosion restraint will diminish the disintegration of harmful metals from the parts into nature [1-3]. Hydrochloric acid is most the most corrosive with most of the common metals and alloys, difficult of this acid to handle from corrosion and materials of constructions, due to its industrial applications the corrosion inhibitors are became an answer for corrosion attack witch lead to metal damage and also replacement of the metal. Many reviews on consumption inhibitors tell that a large portion of the inhibitors are organic with N, O and S atoms or with polar groups of N-hetero cyclic compounds. They have fundamental properties with high electron thickness, making them the response focuses [4-10].These block the dynamic corrosion locations by adsorption  on the metallic surface and the majority of them are exceedingly dangerous to the people and also the earth. Thus replacement by these eco-friendly inhibitors is necessary. The use of pharmaceutical compounds which are contains hetero atoms in their structure, high solubility and high molecular weight offers interesting possibilities for corrosion inhibition [11-20]. Few drugs like azosulpha and antimalarial have been accounted for that they are great corrosion inhibitors on mild steel [21-23]. In this studies Gentamicin drug (Eye/Ear Drops) that has been expired is chosen for the corrosion inhibition on the mild steel in 1M hydrochloric acid medium on the mild steel by using weight loss, electrochemical spectroscopy strategies. Gentamicin is a non-toxic pharmaceutical medication used to prevent or treat a wide variety of bacterial infections. It belongs to a class of drugs known as amino glycoside antibiotics, it contain N- atom having high electron density to block the active sites of corrosion. The inhibitor is available in the brand name of ‘Gentamicin’ fabricated in India by CIPLA LTD it works as an anticorrosive agent in hydrochloric acid medium on mild steel.

Scheme 1 Click here to View scheme

 

Experimental

Materials

Mild steel strips are cut into segments of dimensions 5 cm x1 cm x 0.2cm, with a hole (2mm) which has a uniform diameter length at one of its end for hooking. The composition of strip is as follows: 0.256 % Mn, 0.034% C, 0.004 % P, 0.023 % Si and the remainder Fe. For studies in electrochemistry, these specimens of the same composition were made by fixing the mild steel of size 1 cm² to a mild steel rod with a diameter 1mm utilizing araldite. Each piece was polished with emery paper, degreased with acetone and was washed with distilled water. After dried they are stored in the desiccators. Weight of these specimens (strips) was given utilizing electronic balance. Analar grade HCL acid and double time distilled water were utilized to make all the solutions. Expired Gentamicin (Eye/Ear Drops) drug obtained from medical shop and used for this study without any further purification.

Results and Discussion

Weight loss Method

Initial weights of the pretreated example’s are noted triplicate was inundated in the 100 ml (1M HCL) solution in nearness and nonappearance of the inhibitors at difference  concentrations (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0%) for the period of 0.5, 2, 4, 6, 8 and 24 hours with the help of glass hooks after the experiment period the final weights were also noted and also studied impact of temperature on mild steel corrosion at five distinct temperatures ranging from 303K to 343K. From this the inhibition efficiency (IE %), rate of corrosion (mils Penetration per year), surface coverage (θ) were estimated by utilizing the following formulae.

Where, W_I and W_U are weight losses in acids with and without inhibitors respectively.

Corrosion parameters obtained from this method are given in Tables 1 & 2. It shows that, the inhibition efficiency incremented with the increase in temperature, concentration and immersion period of inhibitor as it is shown in the Figures 1 & 2. The maximum inhibition efficiency 92.36% was noticed in 6 hours immersion period at room temperature (303 K) with concentration of 0.9% .This outcome shows that the inhibitor could act as effective corrosion inhibitor for mild steel in 1M HCl medium.

Table 1: Influence by the concentration of expired Gentamicin inhibitor in corrosion of 1M HCL at the room temperature (303 K) with various time periods. 

Time	½ hrs		2 hrs		4 hrs		6 hrs		8 hrs		24 hrs
InhibitorConc.(%V/V)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)
Blank	514.52		590.34		633.18		647.62		699.58		714.34
0.1	472.69	40.22	500.21	44.36	506.64	49.28	514.68	55.23	546.24	52.36	564.38	43.26
0.2	408.64	47.65	395.64	53.26	391.12	57.23	386.98	60.21	402.82	58.65	445.67	49.68
0.3	321.76	55.36	314.06	60.25	306.16	64.65	293.19	67.64	308.19	65.23	348.68	58.31
0.4	249.08	63.21	238.18	66.21	229.06	69.36	221.98	72.63	240.68	70.26	279.98	62.35
0.5	187.23	65.23	180.64	68.65	174.33	72.25	166.82	75.34	184.96	73.65	223.14	67.32
0.6	146.72	67.54	138.21	71.26	130.28	74.65	123.04	78.26	142.08	76.31	180.86	69.11
0.7	138.66	69.28	127.82	74.63	124.67	78.56	102.98	83.69	126.82	79.98	139.68	73.01
0.8	124.28	73.02	121.36	77.65	115.29	83.99	98.89	88.69	111.21	85.02	125.68	76.99
0.9	119.66	76.65	112.99	80.36	106.28	86.23	95.29	92.36	107.08	88.55	116.69	80.64
1.0	126.78	74.36	118.87	78.21	116.72	83.26	110.88	87.66	116.66	85.06	146.95	74.66

 

Figure 1: Gentamicin inhibitor Inhibition efficiency with various concentrations and time periods at the room temperature (303 K).  Click here to View figure

Table 2: Temperature effect on mild steel corrosion in the presence of various concentrations of Expired Gentamicin inhibitor in 1M HCL

Temperature	303K		313K		323K		333K		343K
InhibitorConc.(%V/V)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)	CR(mpy)	IE(%)
Blank	514.52		1539.18		3519.25		8109.48		16527.78
0.1	472.69	40.22	1006.36	44.28	2432.69	50.36	5257.26	55.65	11063.23	48.65
0.2	408.64	47.65	821.63	52.64	1802.69	59.82	3806.23	65.63	7706.21	56.32
0.3	321.76	55.36	563.21	60.98	1698.31	65.32	2722.61	69.36	5423.65	63.21
0.4	249.08	63.21	390.23	68.36	1230.65	72.16	1960.23	74.32	3994.25	68.65
0.5	187.23	65.23	269.32	72.98	893.22	76.21	1426.33	78.61	2904.66	73.63
0.6	146.72	67.54	188.78	75.36	647.23	79.45	999.69	82.65	1725.36	77.65
0.7	138.66	69.28	169.08	78.22	499.29	82.01	785.25	85.65	1529.99	80.65
0.8	124.28	73.02	162.55	80.11	466.21	85.75	726.32	87.65	1389.45	82.31
0.9	119.66	76.65	158.36	82.65	438.62	87.06	665.32	89.31	1198.32	84.65
1.0	126.78	74.36	166.32	78.23	528.95	83.22	869.66	86.32	1456.01	80.65

 

Figure 2: Gentamicin inhibitor Inhibition efficiency with various concentrations and temperatures. Click here to View figure

Potentiodynamic Polarization Method

Electrochemical analyzer was used for Potentiodynamic polarization measurements. These estimations were concluding to assess the corrosion potential, corrosion current and Tafel slopes. A conventional three electrode cell assembly which contains working electrode as the mild steel specimen with area 1 cm² which is exposed and rest covered with araldite, as counter electrode rectangular Pt foil was used and the SCE as reference electrodes. To get the steady state open circuit potential for each test, ten to thirty minute’s time interval was given. From the cathode with potential of -450mV (vs. SCE) to an anode with potential of -250mV (vs. SCE) at a sweep rate of 10mV per second polarization measurements were given. Corrosion potential, Tafel slopes and corrosion rates were calculated with polarization curves. The inhibitor efficiency was given by utilizing the following formulas.

Where, I_corr and I_{corr (i)} are the corrosion current in absence of the inhibitor and presence of the inhibitor, similarly R_p and R_{p (i) are} the polarization resistance in the absence and presence of the inhibitor.

Polarization studies observed that when concentration of inhibitor increased from 0.4% to 0.9% the I_corr values decreased 0.996 mA/cm² to 0.249 mA/cm² with inhibition value increase from 64.16% to 75.06% and also (R_p) values increased from 18.92Ωcm² to 73.15Ωcm² with increase of inhibition efficiency from 65.51% to 74.13%. Tafel polarization behaviors of the mild steel 1M HCL shows in the Figure 3.  From the graph we can observe that the inhibitor behaves like mixed type [24-28]. In the Table 3.all the calculated data of Polarization studies was given.

Table 3: Electrochemical polarization (Tafel) parameters for mild steel corrosion in 1M HCL without and with various concentrations of inhibitor at room (303 K) temperature.

conc.(%)	-Ecorr (mV)	I corr(mA/cm2)	Icorr	ba (mV/dec)	bc(mV/dec)	Rp(Ωcm2)	Rp
			IE (%)				IE (%)
blank	346.8	0.996	–	70.0	114	18.92	–
0.4	306.0	0.355	64.16	77.0	107	54.86	65.51
0.7	304.5	0.329	66.90	70.0	110	56.27	66.38
0.9	305.1	0.249	75.06	68.0	109	73.15	74.13

 

Figure 3: Potentiodynamic polarization technique diagram for mild steel in 1M HCl in the absence and presence of different concentrations of the inhibitor. Click here to View figure

 1A=BLANK, 1B=0.4%, 1C=0.7%, 1D=0.9%

 

Electrochemical Impedance Methods

The same cell as utilized which potentiodynamic polarization in the calculations of electrochemical impendence, An AC potential 50 mV was super forced on the consistent open circuit potential. The genuine part (Z’) and the fanciful part (Z”) were measured at different frequencies in the scope of 10 kHz to 10MHz. The genuine and imaginary parts of the impendence were plotted in Nyquist plots. From the plots of Z’ versus Z,” the charge transfer resistance (R_ct) quantities were acquired. The estimation of (R_t + R_s) compares to the point where the plot cuts z’ and at a higher frequency the distinction amongst Rt and Rs gives the charge exchange resistance R_ct values. The double layer capacitance C_dl quantities were acquired from the following condition

Where, C_dl means double layer capacitance

R_ct means charge transfer resistance

f_max means frequency at Z” maximum value .

The inhibition efficiencies were calculated from R_p and R_ct quantities as follows

Where, R_ct and R_{ct (i)}   are charge transfer resistance in the absence of inhibitor  and presence of the inhibitor Nyquist plots shows in the Figure 4 for the measurements of the genuine part (Z’) and imaginary one (Z”). We can conclude the corrosion is mostly controlled by the process of charge transfer from semi-circle curves of the impedance. In Table 4, parameters for impedance of mild steel in 1M HCL in the presence of inhibitor and absence of the inhibitor are shown. The values of R_ct had increased from 3.43 Ωcm² to 15.91 Ωcm² and simultaneously the values of C_dl had decreased 438 μF/Cm² to 88 μF/Cm²  with the increase in inhibitor concentrations.

Table 4: Electrochemical impedance parameters for the mild steel corrosion in 1M HCL without and with various concentrations of inhibitor at room (303 K) temperature.

Conc.(%)	Rct(Ωcm2)	CdlµF/cm2	IE(%)
blank	3.43	438	–
0.4	9.21	132	62.76
0.7	12.95	164	73.51
0.9	15.91	106	78.44

 

Figure 4: Impedance technique for mild steel diagram in 1M HCl in the absence and presence of different concentrations of the inhibitor. Click here to View figure

1A=BLANK, 1B=0.4%, 1C=0.7%, 1D=0.9%

 

Thermodynamic Consideration

From the following Arrhenius equation the   activation energy with different concentrations at various temperatures was calculated.

 

Where, ρ₁ is the corrosion rate at T₁ and ρ₂ is the corrosion rate  at T2 temperature. And ‘R’ is the real gas constant.

The change in the free energy at various temperatures compared to room temperature in various concentrations of the inhibitor was calculated by the following equation

Where, Surface coverage (θ), Concentration (C), Temperature (T) & Equilibrium constant (K).

A change in enthalpy of adsorption (∆H) and a change in entropy of adsorption (∆S) can be calculated by utilizing the following equations.

Values of activation energy (Ea), free energy (∆Gads), the entropy (∆S) and the enthalpy (∆H) for mild steel in 1M HCl acid in the presence and the absence of the inhibitor are calculated and are shown in Table 5.   Value of activation energy (Ea) of blank is 73.83 kJ mol^-1 and 51.66 kJ mol^-1 for 0.9% inhibitor concentration, it’s now clear that the addition of the inhibitor leads to decrease in the obvious activation energy (Ea) with some value that is lesser than the value of the uninhibited solution which is trailed by the dull decline with the rise in the concentration of the inhibitor which points out the action upon mild steel in the 1M HCl acid takes place through via the chemical adsorption. The (-ve) value of the free energy of adsorption (∆Gads) points out adsorption which would be spontaneous. (+ve ) values of enthalpy recommend that high temperatures will favor the complexation activity and same in with a fantastic agreement with the incrementing firmness with temperature. The negative estimations of ΔSact indicated a greater order which is generated during the activation process. This can be accomplished by the creation of initiated complex and it shows the affiliation or fixation with the resulting decrease in the degrees of the freedom of framework in this procedure. This also supports supposition of the chemical adsorption. Figure 5 illustrates the Arrhenius plot for mild steel dissolution in 1M HCl acid in the presence and the absence of the inhibitor at various temperatures.

Table 5: Thermodynamic data for mild steel corrosion in 1M HCL in the presence and absence of Expired Gentamicin inhibitor in 1M HCL for a period of ½ hour.

InhibitorConc.(%V/V)	Ea (KJ/mol)	– ΔG                  (KJ/mol)										-ΔS(KJ/mol)	ΔH(KJ/mol)
Temp		θ	303K	θ	313K	θ	323K	θ	333K	θ	343K	303K	303K
blank	73.83												71.31
0.1	67.97	0.402	14.92	0.442	15.34	0.503	15.95	0.556	16.49	0.486	15.78	0.265	65.45
0.2	63.36	0.476	13.93	0.526	14.44	0.598	15.17	0.656	15.80	0.563	14.81	0.246	60.84
0.3	61.92	0.553	13.69	0.609	14.27	0.653	14.74	0.693	15.21	0.632	14.51	0.241	59.4
0.4	61.33	0.632	13.79	0.683	14.36	0.721	14.82	0.743	15.10	0.686	14.40	0.239	58.81
0.5	61.16	0.652	13.45	0.729	14.36	0.762	14.79	0.786	15.14	0.736	14.45	0.237	58.64
0.6	56.45	0.675	13.25	0.753	14.22	0.794	14.81	0.826	15.33	0.776	14.54	0.221	53.93
0.7	54.09	0.692	13.06	0.782	14.23	0.820	14.84	0.856	15.51	0.806	14.61	0.213	51.57
0.8	54.03	0.730	13.19	0.801	14.19	0.857	15.20	0.876	15.61	0.823	14.55	0.213	51.51
0.9	51.66	0.766	13.38	0.826	14.31	0.870	15.18	0.893	15.73	0.846	14.68	0.206	49.14
1.0	55.91	0.743	12.80	0.782	13.34	0.832	14.15	0.863	14.76	0.806	13.71	0.218	53.39

 

Figure 5: Arrhenius plot for mild steel dissolution in 1M HCL from 303K to 343 K temperature with and without inhibitor. Click here to View figure

 

Adsorption Consideration

Corrosion Inhibition is recognized with inhibitor adsorption molecules on the metal surface. Surface coverage (θ) is equal to IE/100. In order to find out the adsorption isotherm for the present review, a plot C/θ and C ought to be linear. This demonstrates that the adsorption takes place after the Langmuir adsorption isotherm. These isotherms give the best fit with the correlation co efficient almost near to (0.9989) unity. In Figure 6 shows a straight line showing Langmuir adsorption isotherm. Organic molecules contain polar atoms which are adsorbed on the surface of the metal and interact with mutual repulsion or attraction. Because this plot is linear, gradients never unite, Langmuir adsorption isotherm is shown as:

C/θ=1/K + C

Figure 6: Langmuir isotherm plot on mild steel surface in 1 M HCL solution for the adsorption of inhibitor. Click here to View figure

 

Morphology Examination

The pictures of mild steel in the acidic medium containing without and with the inhibitor are shown in Figures 7 & 8. It is shows that the assault of the mild steel within the existence of inhibitor in 1 M HCl is very less compared to the nonappearance of inhibitor, because of the presence of adsorbed layer of inhibitor on the surface which blocks corrosion rate of metal evidently. This is ascribed to the contribution of compounds of the inhibitor in interaction with the active sites on surface of the metal, thus gives enhanced surface coverage of metal so that there is a decrease in contact amongst aggressive medium and the metal.

Figure 7: The SEM photo of mild steel when immersed in 1M HCL without inhibitor. Click here to View figure

 

Figure 8: The SEM photo of mild steel when immersed in 1M HCL containing 0.9% concentration of inhibitor.  Click here to View figure

 

Table 6: The inhibition efficiency competition of inhibitor in 1M HCl for mild steel from weight loss, polarization and impedance techniques for the period of ½ hour studies.

Conc.(%)	Inhibition efficiency (%)
	Weight loss	Polarization		Impedance
		Icorr	Rp
0.4%	63.21	64.16	65.51	62.76
0.7%	69.28	66.90	66.38	73.51
0.9%	76.65	75.06	74.13	78.44

 

Conclusion

The expired Gentamicin (Eye/Ear drops) pharmaceutical drug acts as excellent, efficient and economically benefitted inhibitor for corrosion in the 1M HCl acid medium on mild steel. The efficiency of the inhibitor is increase with period of immersion, temperatures and concentration of inhibitor. The Inhibitor with concentration (0.9%) showed maximum efficiency (92.36%) in 6h immersion period at room temperature (303K) and found sufficient for pickling. The chemical adsorption mechanism of the inhibition process was conformation with the data obtained; Langmuir adsorptions were best fitted into the obtained results. Thermodynamic parameters like activation energy (Ea) values also conformed to a chemical adsorption mechanism. Free energy (Gads) of absorption values are negative which shows spontaneous adsorption of the inhibitor on the surface. The positive Enthalpy values are proposing high temperature favors inhibition efficiency. The corrosion is mainly controlled by phenomena of charge transfer by seeing semi circle curves of impedance.  High performance of the inhibitive effect on the surface of mild steel has confirmed by SEM morphology of protective film. Obtained results in electrochemical and weight loss studies are very much excellent agreement with each other. This experiment promotes eco-friendly and economically benefitted inhibitor and also avoids pollution and recycles the drugs. Inhibition efficiency of inhibitor for mild steel in 1M HCl for three difference methods is given in the Table 6.

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