Inhibition of Mild Steel Corrosion in Acidic Medium by Aqueous Extract of Tridax procumbens L .

The inhibition efficiency (IE) of an aqueous extract of Tridax procumbens L. in controlling corrosion of mild steel has been investigated by weight loss method in the absence and presence of corrosion inhibitor at different time interval at room temperature. The result showed that the corrosion inhibition efficiency of these compounds was found to vary with different time interval and different acid concentration. Also, it was found that the corrosion inhibition behavior of Tridax procumbens L. is greater in sulphuric acid than hydrochloric acid medium. So Tridax procumbens L. can be used as a good inhibitor for preventing mild steel material.


Introduction
Mild Steel (MS) has been extensively used under different condition in chemical and allied industries in handling alkaline, acid and salt solution.Chloride, sulphate and nitrate ions in aqueous media are particularly aggressive and accelerate corrosion.One way of protecting MS from corrosion is to use corrosion inhibitors [1][2][3][4][5] .The known hazardous effects of most synthetic corrosion inhibitors are the motivation for the use of some natural products.Most of the natural products are non-toxic, biodegradable and readily available in plenty [6][7][8][9][10][11][12] .Therefore, in this investigation, the corrosion inhibition of mild steel in 1 N hydrochloric acid and 1 N H 2 SO 4 solution was studied in the absence and presence of Tridax procumbens L.

Experimental
According to ASTM method as reported already 13 , cold rolled mild steel strips were cut into pieces of 5 ×1 cm having the following composition (Table 2).They were pickled in pickling solution (5% H 2 SO 4 ) for 3 minutes and washed with distilled water followed by polished with various grades of emery papers and degreased using trichloroethylene.The weight of specimen were noted and then immersed in test solution containing various concentrations of inhibitors at room temperature.After the duration of one hour in hydrochloric acid and sulphuric acid, the specimens were removed from test solutions and pickled in pickling (5% sulphuric acid) solution, dried and finally weighed.The differences in weights were noted and the corrosion rates were calculated.

Selection of inhibitor
Use of inhibitors is an important task in the protection of metals from corrosion.Till now the majority of metal corrosion inhibitors used is toxic for human beings and environment.Therefore the inhibitor is to be selected on the following consideration.

Preparation of flower extract
The plant leaf was collected, shaded dried and powdered.The material was dried in shade to enrich the active principle in them, by reducing its moisture content.An aqueous extract of Tridax procumbens L. leaf was prepared by boiling 20 g of dried leafs, with distilled water, and making up to 100 mL, after filtering the suspending impurities.

Weight loss method
The corrosion behaviour of mild steel in hydrochloric acid and sulphuric acid with Tridax procumbens L. was given in Figure 1, which was studied by weight loss method at one hour at room temperatures.From the graph, it was observed that the weight loss of mild steel in the acid decreases with increasing concentration of additives establishing that the additives are corrosion inhibitor for mild steel in 1 N hydrochloric acid and 1 N sulphuric acid.From the data of weight loss method, the corrosion rate (CR) was calculated using the equation: CR= (87.6 x W) / (D x A x T) Where W, D, A and T are weight lose (in mg), density of mild steel (7.86 g/cc), area of the specimen in cm square and exposure time in hours respectively.Similarly, inhibition efficiency was calculated using the equation,  2.
From Table 2, it is clear that the corrosion rate is decreased with increasing concentration of inhibitor and inhibition efficiency increased with increasing the concentration of the inhibitor.In addition, the maximum corrosion inhibition efficiency of Tridax procumbens L. was 40.00% at 1 N hydrochloric acid and 56.85% at 1 N H 2 SO 4 respectively at 0.10% solution of inhibitor in one hour at room temperature.And also, it is concluded that the inhibitor was best inhibitor in mild steel corrosion in hydrochloric acid and H 2 SO 4. But when comparing with acids the inhibitor efficiency was best in sulphuric acid than hydrochloric acid.

Conclusion
The Tridax procumbens L. showed good performance as corrosion inhibitor in hydrochloric acid and H 2 SO 4 solution medium.The inhibition efficiency increased with increase in concentration of inhibitors for 0.2% to 0.10% in one hour at room temperature.The maximum inhibition efficiency of Tridax procumbens L. were 40.00% in 1 N hydrochloric acid and 56.85% in 1 N H 2 SO 4 respectively in room temperature [0.10%] for 1 h of immersion time.From the comparative studies, it was concluded that the inhibitor efficiency is better in H 2 SO 4 than hydrochloric acid because sulphuric acid is a dibasic acid, so it stimulated the corrosion rate of mild steel.

Figure 1
Figure 1 (a).Variation of corrosion rate (CR) with concentration of Tridax procumbens L. (in %) in hydrochloric acid solution in one hour at room temperature; (b) Variation of inhibition efficiency (IE) with concentration of Tridax procumbens L. (in %) in hydrochloric acid solution in one hour at room temperature; (c) Variation of corrosion rate (CR) with concentration of Tridax procumbens L. (in %) in H 2 SO 4 solution in one hour at room temperature; (d) Variation of inhibition efficiency (IE) with concentration of Tridax procumbens L. (in %) in H 2 SO 4 solution in one hour at room temperature Where W o and W i are the values of the weight loss (in g) of mild steel in the absence and presence of inhibitor respectively.The values of corrosion rate and inhibition efficiency in absence and presence of difference concentration of inhibitor used in 1 N hydrochloric acid and 1 N H 2 SO 4 solution at room temperature for one hour were given in Table2.From Table2, it is clear that the corrosion rate is decreased with increasing concentration of inhibitor and inhibition efficiency increased with increasing the concentration of the inhibitor.In addition, the maximum corrosion inhibition efficiency of Tridax procumbens L. was 40.00% at 1 N hydrochloric acid and 56.85% at 1 N H 2 SO 4 respectively at 0.10% solution of inhibitor in one hour at room temperature.And also, it is concluded that the inhibitor was best inhibitor in mild steel corrosion in hydrochloric acid and H 2 SO 4. But when comparing with acids the inhibitor efficiency was best in sulphuric acid than hydrochloric acid.

Figure 2 (
Figure 2(a).Comparison of corrosion rate (CR) with concentration of Tridax procumbens L. (in %) in hydrochloric acid and H 2 SO 4 solution in one hour at room temperature; (b) Comparison of inhibition efficiency (IE) with concentration of Tridax procumbens L. (in %) in hydrochloric acid and H 2 SO 4 solution in one hour at room temperature

Table 1 .
Chemical composition of mild steel

Table 2 .
Corrosion inhibition behaviour of mild steel in 1 N hydrochloric acid and 1N sulphuric acid solution in absence and presence of Tridax procumbens L. is studied by weight loss measurementComparison of corrosion inhibitory behaviour of Tridax procumbens L.Tridax procumbens L. is a natural product but it has been used a best inhibitor in the field of corrosion.Hence, Tridax procumbens L. in both hydrochloric acid and H 2 SO 4 shows goods inhibitory character.So, inhibition behaviour of Tridax procumbens L. increases tremendously in H 2 SO 4 when compared to hydrochloric acid in one hour at room temperature.