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Inhibition of the corrosion of mild steel in acidic medium by penicillin V potassium.

Introduction

Most corrosion inhibitors protect the corrosion of metals when they are adsorbed on the surface of the metal (Abdallah, 2004a,b, 2002; Agrawal et al., 2003; Eddy and Odoemelam, 2008a,b,c; Eddy and Ekop, 2008a; Eddy et al., 2008a,b). The adsorption and inhibitive properties of some corrosion inhibitors containing hetero atoms in their long carbon chain/aromatic structure have also been studied (Abiola et a., 2007,2004; Ashassi-Sorkhabi et al., 2006). Studies have also been conducted on the adsorptive and inhibitive properties of some natural products (Ashassi_Sorkhabi and Ghalebsaz-Jeddi, 2005). In most of these studies, these properties are found to be strongly influenced by the chemical structure of the compound, the corrosive medium, temperature, concentration of the inhibitor, period of contact, etc.(Arora et al., 2007; Babi-Samordzia et al., 2005). Adsorption characteristics of an inhibitor can be studied by the used of adsorption isotherms and the application of the theory of thermodynamics (Eddy and Odoemelam, 2008a).

Recently, studies on the use of drugs as corrosion inhibitors have been intensified (Awad, 2006; Bendahou et al., 2006; Bouyanzer and Hammouti, 2004). According to Eddy and Odoemelam (2008[o']), the used of drugs for the inhibition of the corrosion of metals has some advantages over the use of some organic/inorganic inhibitors because of their eco-environmental nature. Therefore, the present study is aimed at investigating inhibitive and adsorptive properties of penicillin V potassium for the corrosion of mild steel in acidic medium. Penicillin V potassium is an antibiotic that is used for the treatment of some infection. This compound can be synthesized from plant and it does not contain heavy metals or other toxic substance.

Experimental

Materials used for the study were mild steel sheets of composition (wt %) Mn (0.6), P(0.36), C(0.15) and Si(0.03) and dimension, Sx4x0.1 lcm. Each coupon was degreased by washing in ethanol, dried in acetone and preserved in a desiccator. The inhibitor was supplied by VERBATA pharmaceutical store, Ikot Ekpene, Nigeria.

All reagents used for the study were anclar grade. Double distilled water was used for the preparation of all solutions. Concentrations of [H.sub.2]S[O.sub.4] used for the study were 1.0, 1.5, 2.0 and 2.SM while the concentrations of the inhibitor were 3 x [10.sup-4], 6 x [10.sup.-4], 9 x [10.sup.-4], 12 x [10.sup.-4] and 15 x [10.sup.-4] M. These were respectively dissolved in 2.5M [H.sub.2]S[O.sub.4].

Gasometric method

Hydrogen evolution measurements were carried out at 303 and 333K as described in literature (Eddy and Ebenso, 2008; Eddy and Ekop, 2008). From the volume of hydrogen evolved per minutes, inhibition efficiency (h), and degree of surface coverage (q) were calculated using Equation 1 and 2 respectively.

%I = {1 - [V'.sub.Ht]/[V.sup.0.sub.Ht]} x 100 (1)

[theta] = %I/100 (2)

where [V'.sub.Ht] is the volume of hydrogen evolved at time t for inhibited solution and V[degree]rr- is the volume of hydrogen evolved at time t for unhibited solution.

Thermometric method

This was also carried out as reported elsewhere (Eddy and Ebenso, 2008). From the rise in temperature of the system per minutes, the reaction number (RN) and inhibition efficiency were calculated using equation 3 and 4 respectively:

RN ([degree]C minutes) = [T.sub.m] - [T.sub.i] (3)

%I = [RN.sub.b] - [RN.sub.w] / [RN.sub.b] x 100 (4)

Results and discussion

Fig. 1 shows the variation of the volume of hydrogen gas evolved with time during the corrosion of mild steel in various concentrations of HzS04. The Figure revealed that the rate of evolution of hydrogen increases as the concentration of the acid increases indicating that the rate of corrosion of mild steel increases with increase in the concentration of HzS04. Values of corrosion rate of mild steel in various concentrations of [H.sub.2]S[O.sub.4] are recorded in Table 1. The results obtained also indicate that the rate of corrosion of mild steel increases with increase in the concentration of [H.sub.2]S[O.sub.4].

Figs. 2 and 3 show the variation of the volume of hydrogen gas evolved with time for the corrosion of mild steel in 2.SM HZS04 containing various concentrations of penicillin V potassium at 303 and 333K respectively. These Figures revealed that the rate of corrosion of mild steel increase as the temperature increases but decreases as the concentration of penicillin V potassium increases indicating that penicillin G inhibited the corrosion of mild steel in [H.sub.2]S[O.sub.4].

Table 1 shows values of corrosion rate of mild steel in [H.sub.2]S[O.sub.4] containing various concentrations of penicillin V potassium. Values of inhibition efficiency of penicillin V potassium are also recorded in the Table. From the results, it was seen that the rate of corrosion of mild steel in [H.sub.2]S[O.sub.4] decreases as the concentration of penicillin V potassium increases but increases with increase in temperature. These findings confirmed that penicillin V potassium inhibited the corrosion of mild steel and that the inhibition efficiency of penicillin V potassium for mild steel corrosion decreases as the concentration of penicillin V potassium increases but decreases as the temperature increases. Fig. 4 shows the variation of inhibition efficiency of penicillin V potassium with concentration at 303 and 333K. The Figure clearly shown that the inhibition efficiency of penicillin V potassium for mild steel corrosion decreases with increase in temperature but increases as the concentration of penicillin V potassium increases supporting the mechanism of physical adsorption. For a physical adsorption mechanism, the inhibition efficiency of the inhibitor is expected to decrease with increase in temperature as observed in this work (Ebenso, 2004, 2003; Ebenso et al., 2005).

The Arrhenius equation (Equation 5) was used to investigate the effect of temperature (T) on the rate of corrosion (CR) of mild steel in the presence and absence of penicillin V potassium (Emregul et al., 2004a,b; 2005a,b).

CR = Aexp(-[E.sub.a]/RT) (5)

where [E.sub.a] is the activation energy and R is the gas constant. Taking the logarithm of both sides of Equation 5, Equation 6 is obtained,

logCR = logA-[E.sub.a]/2.303RT] (6)

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Assuming that the corrosion rates of mild steel at 303K ([T.sub.1]) and 333K ([T.sub.2] are [CR.sub.1] and [CR.sub.2], then Equation 6 is transformed to Equation 7,

Log([CR.sub.2]/[CR.sub.1])= [E.sub.a]/2.303r(1/[T.sub.1] - 1/[T.sub.2]) (7)

Values of [E.sub.a] calculated from Equation 7 were recorded in Table 3. These values ranged from 60.8445 to 75.0473KJ/mol. The values are greater than the value (-55.667J/mol) obtained fro the blank indicating that the penicillin V potassium retarded the corrosion of mild steel in [H.sub.2]S[O.sub.4]. The values are also consistent with data expected for the mechanism of physical adsorption ([E.sub.a] < 80KJ/mol).

Values of the heat of adsorption of penicillin V potassium on mild steel surface were calculated using Equation 8 (Eddy and Ebenso, 2008).

[Q.sub.ads] = 2.303R[log([[theta].sub.2]/1-[[theta].sub.2]) - log([[theta].sub.1]/[[theta].sub.1]) x ([T.sub.2][T.sub.1])/([T.sub.2] - ([T.sub.2] - [T.sub.1]) (8)

where R is the gas constant, [q.sub.1], and [q.sub.2] are the degree of surface coverage at temperatures, [T.sub.1], and [T.sub.2] respectively. Values of [Q.sub.ads] calculated from Equation 8 ranged from - 15.6509 to -31.5849KJ/mol indicating that the adsorption of penicillin V potassium on mild steel surface is exothermic.

Data obtained for degree of surface coverage were used to fit curves for different adsorption isotherms including Langmuir, Frumkin, Freundlich, Bockris-Swinkel, Temkin and Florry--Huggins adsorption isotherms. The results revealed that the isotherms that best described the adsorption characteristics of penicillin V potassium on mild steel surface are Langmuir and Frumkin adsorption isotherms.

Starting from Langmuir adsorption isotherm, the degree of surface coverage ([theta]) and the concentration of the inhibitor in the bulk electrolyte are related according to Equation 9 (Eddy and Odoemelam, 2008a,[o']; Oguzie, 2007,2006a,b).

C/[theta] = 1/k+C (9)

where k is the equilibrium constant of adsorption of penicillin V potassium on mild steel surface. Taking the logarithm of both sides of Equation 9, Equation 10 is obtained (Sheatty et al., 2006; Shockry et al., 2006; Rajendran et al., 2005)

log(C/[theta]) = logC - logK (10)

From Equation 10, a plot of log(C/[theta]) is expected to produce a straight line provided the assumptions of Langmuir isotherm are valid. Fig. 5 shows Langmuir isotherm for the adsorption of penicillin V potassium on the surface of mild steel.

[FIGURE 4 OMITTED]

The expression for Frumkin isotherm is as given by Equation 11(Eddy and Ebenso, 2008),

[theta]1-[theta] = B.C.[e.sup.2aq] (11)

From the logarithm of Equation 11, Equation 12 is obtained:

log[([theta])/(1-[theta])]*[C]=logK+2a [theta] (12)

where q is the of surface coverage, C is the concentration of the adsorbate, K is the adsorption-desorption equilibrium constant and a is an interaction parameter. From Equation 12, a plot of log[([theta]/(1-[theta])]*[C] versus q should produce a straight line if Frumkin isotherm is applicable. Fig. 6 shows Frumkin isotherm for the adsorption of penicillin V potassium on the surface of mild steel. Values of Frumkin adsorption parameters are recorded in Table 4. From the results, it was seen that values of the adsorption parameters were positive indicating the attractive behaviour of the inhibitor (Eddy and Ebenso, 2008).

The free energy of adsorption of penicillin V potassium is related to the equilibrium constant of adsorption according of Equation 13 (Okafor et al., 2008,2007a,b;Rajappa and Vekateshal, 2002).

[DELTA][G.sub.ads] = -2.303RTlog(55.5K) (13)

where R is the gas constant and T is the temperature. Values of K obtained from Langmuir and Frumkin adsorption isotherms were used to calculate values of DGaas according to Equation 13. These values are recorded in Table 4. The results indicated that the adsorption of penicillin V potassium is spontaneous ([DG.sub.ads] is negative) and suggest the applicability of the mechanism of physical adsorption ([DG.sub.ads] < 40KJ/mol) (Eddy and Odeoemalm, 2008a,b; Eddy and Ekop, 2008).

The chemical structure of penicillin V potassium is as shown by Fig. 7. From the structure, it can be stated that the inhibition ability of this compound is largely contributed by the presence of nitrogen and sulphur in their aromatic/cyclic structure. These atoms tend to enhance the electron donation ability of the inhibitor. The compound also contained amino and carbonyl functional groups. We therefore proposed that the mechanism of adsorption of penicillin V potassium (hence its inhibition efficiency) is due to the donation of electron by the molecule of penicillin V potassium to a vacant d-orbital of Fe in mild steel (Fig. 8). The formation of Fe-penicillin V potassium complex thereby stabilized the mild steel and prevent it against further corrosion attack.

[FIGURE 5 OMITTED]

Conclusion

From the results and findings of the study, the following conclusions were drawn,

* Penicillin V potassium is a good inhibitor for the corrosion of mild steel in [H.sub.2]S[O.sub.4].

* The adsorption of the inhibitor on mild steel surface is exothermic, spontaneous and is consistent with the mechanism of physical adsorption. Langmuir and Frumkin isotherms best described the adsorption characteristics of the inhibitor.

Acknowledgement

The authors are grateful to Mrs. Edikan Nnabuk Eddy, Ndifreke Nde and Esther Edim for supporting this research.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

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Corresponding Author: N. O. Eddy, Department of Chemistry, Ahmadu Bello University, Zaria Kaduna State. E-mail: nabukeddy@yahoo.com

Department of Chemistry, Ahmadu Bello University, Zaria Kaduna State. Department of Chemistry, Michael Okpara University Of Agriculture, Umudike, Abia State.

N.O. Eddy and S.A. Odoemelam: Inhibition of the Corrosion of Mild Steel in Acidic Medium by Penicillin V Potassium: Adv. in Nat. Appl. Sci., 2(3): 225-232, 2008
Table 1: Values of corrosion rate ([cm.sup.3]/minute) and reaction
number ([degrees]C/minute) for the corrosion of mild steel in
[H.sub.2]S[O.sub.4]

Con. of
[H.sub.2]S[O.sub.4] (M) CR(303K) RN(303K)

1.0 0.175 0.0167
1.5 0.180 0.0200
2.0 0.220 0.0267
2.5 0.380 0.0500

Table 2: Values of corrosion rate (CR) and reaction number (RN) for
the corrosion of mild steel in [H.SUB.2]S[O.sub.4] containing various
concentrations of penicillin V potassium

Con. of penicillin CR CR RN
V potassium(M) (333K) (303K) (303K)

3 x [10.sup.-4] 0.2625 2.3063 0.0370
6 x [10.sup.-4] 0.2000 2.3063 0.0313
9 x [10.sup.-4] 0.1813 2.2250 0.0255
12 x [10.sup.-4] 0.1750 2.0875 0.0255
15 x [10.sup.-4] 0.1375 2.0063 0.0238

 Gasometric Thermometric
Con. of penicillin
V potassium(M) %I(303K) %I(333K) %I (303K)

3 x [10.sup.-4] 30.00 16.89 26.00
6 x [10.sup.-4] 46.67 16.89 37.32
9 x [10.sup.-4] 51.67 19.82 49.08
12 x [10.sup.-4] 53.33 24.70 49.08
15 x [10.sup.-4] 63.33 27.70 52.33

Table 3: Some thermodynamic parameters for the adsorption of
penicillin V potassium on mild steel surface

Concentration. of
penicillin V [E.sub.a] [Q.sub.ada]
potassium (M) (KJ/mol) (KJ/mol)

3 x [10.sup.-4] 60.8445 -15.6509
6 x [10.sup.-4] 68.4582 -30.6254
9 x [10.sup.-4] 70.2095 -30.7169
12 x [10.sup.-4] 69.4060 -26.1792
15 x [10.sup.-4] 75.0473 -31.5849

Table 4: Values of Langmuir, Frumkin and Freundlich adsorption
parameters

 Temperature (K) Slope logK

Langmuir 303 0.5748 0.9978
 333 0.7477 0.8810

 Temperature (K) Slope logK

Frumkin 303 2.0121 3.7917
 333 2.2984 0.9869

 [DELTA][G.sub.ada]
 Temperature (K) [R.sup.2] (KJ/mol)

Langmuir 303 0.9554 -15.91
 333 0.9557 -16.74

 [DELTA][G.sub.ada]
 Temperature (K) [R.sup.2] (KJ/mol)

Frumkin 303 2.2141 -22.97
 333 0.8818 -25.78
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Title Annotation:Original Article
Author:Eddy, N.O.; Odoemelam, S.A.
Publication:Advances in Natural and Applied Sciences
Article Type:Report
Geographic Code:6NIGR
Date:Sep 1, 2008
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