Introduction

In developed and developing countries, billions of dollars every year are spent on capital replacement and control methods for corrosion infrastructure [1,2]. In recent years, owing to the growing interest and attention of the world towards the protection of the environment and the hazardous effects of using chemicals on the ecological balance, the use of eco-friendly inhibitors to replace the older, which is more toxic and harmful to the environment are been intensified [3-5].

Research has shown that for an inhibitor to be an effective protector against metal corrosion, it should be readily adsorbed on the metal surface through either physisorption or chemisorption processes [6-11]. Either of these adsorption processes depends primarily on the physicochemical properties of the inhibitor group such as functional groups, electronic density at the donor atom, molecular structure, etc. For instance, organic molecules, which have had a wide applicability and that have been extensively studied and used as corrosion inhibitors, often contain the hetroatoms nitrogen, oxygen, and sulfur atoms, as well as multiple bonds in their molecules. Several researches have been carried out on the use of drugs as corrosion inhibitors for several metals in various media. For example, Fouda et al., studied the corrosion inhibition characteristics of floxacillin, cloxacillin, dicloxacillin, cefadroxil and cephalexin on aluminum in 0.5 M H₃PO₄ using weight loss and galvanostatic polarization techniques

Results obtained revealed that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface.

Other drugs that have been found to be good corrosion inhibitors include norfloxacin, Streptomycin, Cefatrexyl, and Cefazolin [13-15]. The choice of some of the drugs used as corrosion inhibitors may be due to the fact that they have a large number of functional adsorption centers, are biodegradable, can be easily produced and purified. 

In the present investigation, the corrosion inhibiting behavior of Cefuroxime axetil [Chemical name: 1-Acetoxyethyl (6R,7R)-3-{(aminocarbonyl)oxy]methyl}-7-{[(2Z)-2-(2-furyl)-2-(methoxyimino) acetyl]amino}-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate] was investigated on aluminum in hydrochloric acid at 303 and 333 K using weight loss, thermometric gasometric and scanning electron microscope techniques.

Cefuroxime is a broad-spectrum, β-lactamase-stable second generation cephalosporin antibiotic drug with well-defined pharmacokinetics after injection [16]. It is commercially available for parenteral (intramuscular and intravenous) administration as a sodium salt and for oral administration as cefuroxime axetil, the 1-(acetoxy)ethyl ester of the drug [17]. In humans, gastrointestinal absorption of cefuroxime is negligible, whereas cefuroxime axetil shows a bioavailability of 30 to 40% when taken on fasting and 50 to 60% when taken after food [18-23]. In fact like the other cephalosporins, the parenteral cefuroxime, is not orally absorbed due to the presence of a highly polar carboxyl group that is ionized at intestinal pH, making transport across intestinal mucosa unlikely [24,25]. Cefuroxime axetil is a prodrug of cefuroxime and has little, if any, antibacterial activity until hydrolyzed in vivo to cefuroxime. The cefuroxime axetil esterase can hydrolyze cefuroxime axetil to the non-absorbable cefuroxime in the gut lumen [26]. Esterase hydrolysis leads to ethanoic acid and an unstable hydroxyethyl ester, which dissociates rapidly to ethanol and the parent cefuroxime [27]. Figure 1 shows the chemical structures of both cefuroxime and cefuroxime axetil.

The selection of cefuroxime axetil as a corrosion inhibitor is based on the following facts: 

1.     It contains three kinds of heteroatoms (four nitrogen, ten oxygen and one sulphur atom) as reactive center through which they can adsorb readily on the metal surface.

2.     The compound is readily soluble in medium.

3.     It does not cause any health hazards, but also find its diverse applications in various biological and pharmacological activities; hence the use of Cefuroxime axetil as corrosion inhibitors is safe.

Materials and Methods

Weight loss method

A previously weighed metal (aluminum sheet) was completely immersed in 250 ml of the test solution in an open beaker. The beaker was inserted into a water bath maintained at a temperature of 30 °C. Similar experiments were repeated at 60°C. In each case, the weight of the sample before immersion was measured using Scaltec high precision balance (Model SPB31) After every 24

Figure 1: Chemical structures of Cefuroxime and Cefuroxime axetil.

hours, each sample was removed from the test solution, washed in a solution of NaOH containing zinc dust and dried in acetone before re-weighing. The difference in weight for a period of 168 hours was taken as total weight loss. The inhibition efficiency (% I) for each inhibitor was calculated using equation (1) [28]

Where, W₁ and W₂ are the weight losses (g/dm³) for mild steel in the presence and absence of inhibitor in HCl solution respectively. The degree of surface coverage θ is given by the equation (2) [29]:

The corrosion rates for mild steel corrosion in different concentrations of the acid was determined for 168 h immersion period from weight loss using equation (3) [6]

 Where, W = weight loss (mg); D = density of specimen (g/ cm3), A = area of specimen (square inches) and T = period of immersion (hour).

 Gasometry method

The method used for hydrogen evolution measurement is as described elsewhere [30]. The test solution (different concentrations of acid, inhibitor or their mixtures) was poured into the reaction vessel (gasometer). Upon the introduction of mild steel, the flask was quickly corked and the rise in volume of the paraffin due to hydrogen evolution was noted after every minute until a steady volume was observed. From the results obtained, the corrosion inhibition efficiency was calculated using the following equation,

Where, V_b is the volume of hydrogen gas evolved by the blank and V_t is the volume of hydrogen gas evolved in the presence of the inhibitor, after time, t.

Thermometric method

This was also carried out as reported elsewhere [31]. The reaction number (RN) of each system was calculated by dividing the difference between the highest and lowest temperature attained by the time interval. From the reaction number, the inhibition efficiency (% I) of the inhibitor was calculated using equation (5)Where, RN_aq is the reaction number in the absence of inhibitors (blank solution) and RN_wi is the reaction number of 2 M HCl containing the studied inhibitor.

 Scanning electron microscopy

The scanning electron microscope (SEM) Model No JSM-5600 LV was used to study the morphology of corroded in the presence and absence of inhibitor. The photographs were taken from that portion of the specimen where better information was expected.

Results and Discussions

Effect of cefuroxime axetil

The corrosion rate (CR) and reaction number (RN) of aluminum in HCl containing various concentrations of Cefuroxime axetil determined for 168h immersion period from gravimetric, gasometric and thermometric are presented in Table 1. The results obtained indicates that the aluminum corrosion is reduced by the presence of Cefuroxime axetil in HCL at all concentrations used in this study, since there is a general decrease in the rate of corrosion of the aluminum with increase in concentration of the inhibitor. This may be ascribed to the adsorption of this compound on the aluminum, producing a barrier, which isolates the surface from the corrosion environment.

Table 2. presents inhibition efficiencies of various concentrations of Cefuroxime axetil in HCL. The inhibition efficiency was estimated to be 73.40 % even at extremely low inhibition concentration (0.1 M) and reaches 89.87 % at a concentration of 0.5 M. Such remarkable performances may be due to, the high molecular weight of CA, the presence of C=N, O-H, C=O, etc. which are electron donation groups and the presence of aryl groups. The inhibition efficiency was found to increases with increase in the concentration of the inhibitor but decreases with increase in temperature indicating that the mechanism of physical adsorption favours the adsorption of Cefuroxime axetil on aluminum surface. For a physical adsorption mechanism, the inhibition efficiency is expected to decrease with increase in temperature but for a chemical adsorption mechanism, the reverse is expected [31].

Also, the inhibition efficiency of CA obtained from the two methods were found correlate strongly (R2 = 0.8798 and 0.9644 for gasometric and thermometric respectively) with those obtained from gravimetric method. However, values of inhibition efficiency obtained from the weight loss were higher than the values obtained from thermometric and gasometric methods indicating that the average inhibition efficiency of CA is better than its instantaneous inhibition efficiency.

Table 1: Corrosion rate (CR) and reaction number (RN) of aluminum in HCl containing various concentrations of Cefuroxime axetil.

Table 2: Inhibition efficiencies of Cefuroxime axetil for the corrosion of aluminum in HCL

The stability of the inhibitive properties of the studied inhibitor over 168 hours of immersion was studied by plotting values of inhibition efficiencies gotten from weight loss studies against time as shown in Figure 2. From the plots, it is also evident that the inhibition efficiency first decreased with time until a critical value was attained after which it started increasing. This trend suggests that at first, there was competition between the forces of adsorption and desorption and that after the critical zone, adsorption facilitated the formation of a protective layer and thus protected the metal against further corrosion attack.

Effect of temperature

According to Eddy [32], temperature affects the rate of any chemical reaction such that an increase in temperature leads to a corresponding increase in the rate of the reaction. Hence the effect of temperature on the corrosion of aluminum in HCl (in the absence and presence of CA) was studied using the Arrhenius Equation (equation 6) where the apparent activation energies (E_a) for the corrosion process in absence and presence of inhibitor were evaluated [6,33].

Figure 2: Variation of inhibition efficiency from weight loss technique of Cefuroxime axetil with time.

Figure 3: Langmuir isotherm for the adsorption of Cefuroxime axetil on the surface of aluminum.

Table 3: Activation energy and heat of adsorption of Cefuroxime axetil on the surface of aluminum

Table 4: Langmuir parameters for the adsorption of Cefuroxime axetil on the surface of aluminum.

Figure 4: SEM of Aluminum exposed to 0.1 M hydrochloric acid in the absence of 0.5 g / L Cefuroxime axetil.

Figure 5: SEM of Aluminum exposed to to 0.1 M hydrochloric acid in the presence of 0.5 g / L Cefuroxime axetil.

Where, CR₁ and CR₂ are the corrosion rates of aluminum in solution of HCl at the temperatures, T₁(303 K) and T₂ (333 K) respectively, E_a is the activation energy for the adsorption of CA on Al surface and R is the gas constant. Calculated values of the E_a are shown in Table 3. It can be seen from the table that the activation energies are lower than the value of 80 kJmol-1 required for a chemical adsorption mechanism supporting the earlier claims the adsorption of CA on aluminum proceeds by physical adsorption mechanism.

Conclusions

From the study, the following conclusions can be drawn. CA efficiently inhibits the corrosion of mild steel in 0.1M HCl medium. Adsorption of CA on the surface of aluminum from 1M HCl obeys Langumur adsorption isotherm. The inhibition efficiency of CA increases with increasing the inhibitor concentration and on increasing the temperature, the corrosion rate increases. The calculated values of E_a, Q_ads, ∆G_ads indicates that the adsorption of inhibitor on the metal surface

Acknowledgment

The authors are grateful to TEFUND for sponsoring the research and Mrs Janet Onoja Ameh for typesetting the manuscript.

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