Standardization of Plant Extract as Corrosion Inhibitor for Mild Steel in Acid Media

 

Saratha R.*, Anandhi D., Meenakshi H. N. and Saritha T.

Department of Chemistry, Avinashilingam Deemed University for Women, Coimbatore-641043, Tamilnadu. India

*Corresponding Author E-mail: Saratha63@gmail.com

ABSTRACT:

Any product that has been developed should undergo various tests for standardization before it is put into use by the customers. Numerous plants have been evaluated/investigated as corrosion inhibitors for mild steel in acid medium. In the present study the corrosion inhibitive nature of the acid extract of Tectona Grandis for mild steel in 1M HCl and 0.5M H₂SO₄ media for standardization of the plant extract was evaluated through gasometric method. The stability and storage condition of the extract was tested using weight loss method. Gasometric method shows decrease in hydrogen gas evaluation with increase in extract concentration showing the inhibitive nature of the extract. The extract in the base HCl was found to be up to 45 days of storage period in room temperature. There is no significant difference in inhibition efficiency exhibited by plant extract stored in room temperature and in refrigerated condition. The mode of inhibition has been explained from the physiochemical constituents present in the extract and FTIR results.

 

 

 

INTRODUCTION:

Corrosion inhibitors are widely used in industry to reduce the corrosion rate of metals and alloys in contact with aggressive environments. Many chemical compounds have been evaluated as corrosion inhibitors^1-5. Most of the corrosion inhibitors are synthetic chemicals, expensive and very hazardous to environments. Therefore, it is desirable to source for environmentally safe inhibitors. Review of literature reveals several reports on many plant products as corrosion inhibitors for the metals^6-11. There are reports on the inhibition effects of non-toxic compounds on the corrosion of metals^12-19. Tectona Grandis as a cheap and non-toxic material on mild steel corrosion in 1M HCl and 0.5M H₂SO₄ has been evaluated and found to be a good inhibitor²⁰. It is essential that any product should be standardized before it is used for industrial process. Numerous plants have been evaluated as corrosion inhibitor for various metals in different media, but now no plant material has been used as inhibitors in the industries. The present study aims at standardizing an inhibitor of plant origin.

 

Standardization involves:

1.      The stability of the inhibitor

2.      Storage condition

3.      pH monitoring to find out how long the pickling bath can be used effectively in presence of the inhibitor

4.      To measure the hydrogen gas evaluation this will also provide information about the inhibiting efficiency of the inhibitor.

5.      Mechanism of inhibition is necessary to check the quality of the material after subjected to pickling process.

 

EXPERIMENTAL:

Preparation of mild steel:

Mild steel (C=0.176%, Mn=0.431%, Si=0.00, S=0.029%, P=0.03% Cr=0.006%, Mo=0.023%, Ni=0.011% and Fe=99.3%) of area 5× 1 cm² were used. The specimens were degreased, cleaned with fine quality emery sheet, washed with distilled water and stored in desiccator before use.

 

Mass loss method:

Mild steel specimens were accurately weighed and fully immersed in 100ml of 1M HCl and 0.5M H₂SO₄ for different concentrations of the inhibitor. Test specimens were removed after 3 hours of immersion and dipped in sodium bicarbonate solution for neutralisation of remaining acid in the specimen. They were washed with distilled water, dried and reweighed. The loss in weight was determined in triplicate and results averaged. The inhibition efficiency was calculated using the formula given in earlier paper¹⁶.

 

Gasometric Technique:

A flask with a side tube was connected to a delivery tube to a graduated gas collector, a reservoir of water. 100ml of the test solution were then introduced into the flask and the initial volume of the air in the graduated gas collector was set to zero. Thereafter one mild steel coupon was dropped into the test solution and the reaction vessel immediately closed. The volume of the hydrogen gas evolved by the corrosion reaction was estimated from the change in volume of the water in the reservoir. The progress of the reaction was monitored by careful measurement of the evolved hydrogen gas at fixed time intervals. The experiment was conducted at room temperature.

                    V (b) – V (inh)

I.E (%) =                                X 100

                            V (b)

Where,

V (inh) is the volume of hydrogen evolved at time‘t’ for inhibited solution.

V (b) is the volume of hydrogen evolved at time‘t’ for uninhibited solution

 

FT-IR:

The mild steel specimen was immersed in 100ml of 1M HCl and 0.5M H₂SO₄ in the presence and absence of the inhibitor (Concentration of the inhibitor 1,3,5,7,9,11,13% v/v) at 24 hours. They are taken out and immersed in saturated sodium bi carbonate solution to remove residual acid and washed thoroughly with distilled water and dipped in acetone then dried, scratched the specimen and collected the powder. The powder was analyzed by using SHIMADZU FT-IR spectrometer.

 

RESULTS AND DISCUSSION:

The leaves of Tectona Grandis (TGL) has been evaluated as acid corrosion inhibitors for mild steel by gasometric method. By varying the concentration of the extract at different storage period of the extracts (7,14,21,28,45 and 60 days) study were carried out at room temperature(RT) and refrigerated condition (RC) and the results are discussed in this chapter.

 

Gasometric Techinque:

The volume of hydrogen gas evolved, during the corrosion reaction of mild steel in 1M HCl and 0.5M H₂SO₄ in the absence and presence of different concentrations of TGL extract at room temperature were measured as a function of the reaction time, and the data are given in table 1 and the same are represented in Figure 1 and 2 respectively. The volume of hydrogen evolved at different concentrations of acid extract of TGL is lower than volumes evolved for the blank solution (1M HCl and 0.5M H₂SO₄) indicating that different concentrations of these extracts retard the corrosion of mild steel.

 

Figure-1 Variation of the volume of hydrogen gas evolved with time during the inhibition of the corrosion of mild steel 1 M HCl by various concentrations of the extract

 

Figure-2 Variation of the volume of hydrogen gas evolved with time during the inhibition of the corrosion of mild steel in 0.5 M H₂SO₄ by various concentrations of the extract

 

From Table (1), it is clear that the volume of hydrogen gas evolved decreases as the concentration of extract increases, confirming that the inhibition efficiency increases with concentration of the additives.

 

Table -1 Inhibition Efficiency of Extract (TGL) for the corrosion of Mild Steel in Acid Medium (Gasometric Method)

Conc. of the extract %(V/V)	TGL
	HCl		H2SO4
	Vol. of Gas	I.E	Vol. of Gas	I.E
Blank 1 7 13	64 40 32 16	- 38 50 75	68 52 32 26	- 23.5 52.9 61.7

 

Durability test:

The weight loss measurement was adopted to evaluate the durability of the extracts under room temperature. The inhibition efficiency for mild steel in 1 M HCl and 0.5 M H₂SO₄ in the absence and presence of various concentrations of the TGL and extract stored for a prolonged period are determined. The results of the study are given in Tables (2,3) .The inhibition efficiency at 13% (v/v) concentration of the TGL in 0.5 M H₂SO₄ and 1 M HCl was 87.1% and 88.6 % respectively during 28 days, 86.6% and 85.4% respectively during 45 days, 75.7 % and 78.5% respectively during 60 days.

 

 

Table-2 IE of TGL extract on the corrosion of mild steel in 1M HCl at room temperature during various storage period of the extract

Conc % (V/V)	1 day	7 day	14 day	21day	28 day	45 day		60 day
	I.E	I.E	I.E	I.E	I.E		I.E	I.E
Blank 1 3 5 7 9 11 13	- 43.1 58.1 58.9 82.2 83.6 90.4 95.8	- 30.4 52.4 56.3 78.3 80.8 86.4 91.4	- 27.6 46.3 51.3 77.4 80.3 81.0 90.5	- 25.0 35.6 48.8 74.6 78.5 81.0 89.7	- 25.4 34.4 47.3 61.7 68.0 79.7 88.6		- 24.7 34.0 45.6 59.7 68.7 78.4 85.4	- - - - - 52.1 63.1 78.5

 

Table-3 IE of TGL extract on the corrosion of mild steel in 0.5M H₂SO₄ at room temperature during various storage period of the extract

Conc % (V/V)	1 day	7 day	14 day	21day	28 day	45 day		60 day
	I.E	I.E	I.E	I.E	I.E		I.E	I.E
Blank 1 3 5 7 9 11 13	- 54.1 56.6 57.4 80.4 84.0 90.3 95.8	- 36.8 44.1 58.3 74.2 79.5 85.7 89.0	- 34.6 41.6 55.9 74.0 79.4 82.0 88.5	- 35.0 64.9 72.2 82.0 83.0 87.7 95.0	- 25.0 35.8 47.9 58.6 73.0 82.0 87.1		- 22.7 34.9 46.4 57.8 70.9 80.3 86.6	- - - - - 52.1 63.2 75.7

 

 

Figures 3 and 4 represent variation in IE with storage period. The inhibition efficiencies are found to increase with increasing extract concentration at all storage periods. From the values of IE, it is clear that the corrosion inhibition may be due to increase in the adsorption of pytochemical constituent of extract on the metal surface. The decrease in IE with storage period may be due to the desorption of the adsorbed photochemical constituents from the surface of the metal surface. Even though the decrease in inhibition efficiency was noticed at 21 days of storage period, the extract was efficient up to 28 days in 0.5 M H₂SO₄ and 45 days in 1M HCl. This decrease in inhibition efficiency can be explained on the basis of physical observation made during the study, ie. some sedimentation was noticed at the bottom of the standard flask showing that some of the phytoconstituents might have been settled down during prolonged storage period.

 

Figure-3: Change in % IE with storage period of the extract in 1 M HCL at room temperature

 

Figure-4 Change in % IE with storage period of the extract in 0.5M H₂SO₄at room temperature

 

Stability Test:

The development of any product depends on various factors. Storage condition of the product, i.e whether it should be kept under refrigerated condition or on the table is very important. Storage at room temperature will reduce the storage cost (cost of electricity). The results of weight loss measurements using TGL extracts in 0.5 M H₂SO₄ and 1 M HCl stored in refrigerator and on table condition are given in Tables (4,5).

 

The comparison of  %I.E of TGL  under RT and RC in 1 M HCl and 0.5 M H₂SO₄ shows that there is no significant change in the inhibition efficiency of the extract stored at room temperature and in refrigerator condition.

Table -4 IE of TGL on mild steel in 0.5m H₂SO₄ at room temperature and refrigerated condition

Conc  % (V/V)

Inhibition efficiency (%)

Storage period of the extract (Days)

7 days

14 days

21 days

28 days

45 days

60 days

RT

RC

RT

RC

RT

RC

RT

RC

RT

RC

RT

RC

1 3 5 7 9 11 13

36.8 44.1 58.3 74.2 79.5 85.7 89.0

24.4 40.1 54.6 73.7 78.2 85.0 89.2

34.6 41.6 55.9 74.0 79.4 82.0 88.5

23.7 39.0 50.4 68.5 73.8 83.0 88.6

35.0 64.9 72.2 82.0 83.0 87.7 95.0

21.6 39.0 57.5 69.7 80.8 83.9 93.0

25.0 35.8 47.9 58.6 73.0 82.0 87.1

23.5 36.3 47.5 58.5 69.7 82.5 88.0

22.7 34.9 46.4 57.8 70.9 80.3 86.6

22.6 36.4 47.3 54.7 68.6 81.1 87.3

- - - - 52.1 63.2 75.7

- - - - 48.6 54.0 72.5

 

 

Table -5 IE of TGL on mild steel in 1M HCl at room temperature and refrigerated condition

Conc % (V/V)

Inhibition efficiency (%)

Storage period of the extract (Days)

7 days

14 days

21 days

28 days

45 days

60 days

RT

RC

RT

RC

RT

RC

RT

RC

RT

RC

RT

RC

1 3 5 7 9 11 13

30.4 52.4 56.3 78.3 80.8 86.4 91.4

30.6 42.3 61.6 74.6 78.8 86.9 90.0

27.6 46.3 51.3 77.4 80.3 81.0 90.5

24.1 42.7 54.2 74.2 77.7 86.0 89.9

25.0 35.6 48.8 74.6 78.5 81.0 89.7

24.0 41.6 52.6 66.4 76.5 84.1 89.2

25.4 34.4 47.3 61.7 68.0 79.7 88.6

24.1 35.9 48.5 61.7 74.5 82.7 87.7

24.7 34.0 45.6 59.7 68.7 78.4 85.4

22.5 34.6 47.6 60.4 71.4 82.0 86.2

- - - - 52.1 63.1 78.5

- - - - 43.6 57.8 67.2

 

 

FT-IR Technique:

The qualitative aspect of IR spectroscopy is one of the most powerful attributes of the diverse and versatile analytical techniques. The respective FT-IR peaks of the powder form of TGL,  mild steel immersed in blank, mild steel sample immersed in 1 M HCl and 0.5 M H₂SO₄ containing 13% (v/v) of TGL are given in Table (6) and the corresponding spectra are shown in Figures (5-7).From the Table it is clear that there is shift in IR peak from powdered form of the plants and mild steel immersed in acid medium containing plant extracts which shows there is formation of metal-plant extract complex. The peaks at 3566, 2920, 2850 cm^-1 can be assigned to the presence of superfacial adsorbed water, stretching mode of an O-H and/or N-H and aromatic C-H groups (from plant extract).  The peaks at 1734, 1618 cm^-1corresponds to C=O, R₂-C=N, C=C, this shows that the plant extracts contains mixtures of compounds. Almost all peaks observed for plant extract is also noticed for mild steel immersed in 1 M HCl and 0.5 M H₂SO₄ containing 13%(v/v) volume of plant extracts. However, the spectra shows the reduced intensity of the broad peak around  3356 (TGL) designates the reduction of the free O-H groups, since it is proximity of hydroxyl groups on the aromatic rings which enables the compound to form iron-plant extract complex.

 

Table-6 Frequencies and peaks of adsorption of IR by Acid Extract

TGL powder	Mild steel in		Possible groups
	TGL extract in HCl	TGL extract in H2SO4
3356 2850 1612 1244 1037 -	3385 - 1610 1273 1020 650	3385 2856 1618 - 1026 -	O-H/N-H Aromatic C-H C=C, esters, C=O,Phenols,20alcohols C-OH,C-H,10 alcohols Fe2O3

 

Figure-5 IR spectra of TGL

 

Figure-6 IR spectra of TGL in 1 M HCl

 

Figure-7 IR spectra of TGL in 0.5 M H₂SO₄

 

Mechanism of Inhibition:

The acid extracts investigated in the study are organic in nature and found to contain the following compounds (www.corrosion doctors.com).

 

                                          Salicylic acid                Anthraquinone

 

The mechanism of corrosion inhibition of mild steel in acidic solution can be explained on the basis of one or more of these compounds on the metal surface. The inhibitor possesses electroactive nitrogen, oxygen atoms and aromatic rings which favor the adsorption on metal surface. In the presence of inhibitor, a thin greenish black film has always been observed on the surface of the specimens. This shows that the inhibition is due to the formation of some complex film formed between plant extract and the metal ions, which is confirmed from the spectral studies.

 

CONCLUSION:

§      The inhibitor act as potent inhibitors for corrosion of mild steel in acid medium was confirmed by Gasometric method.

§      Corrosion inhibition increases with increase in the concentration of the extract.

§      The extract could be stored at room temperature (no need to store under refrigerated condition) and effective up to 28 days in 0.5 M H2SO4 and 45 days in 1 M HCl of the storage period.

§      FT-IR study shows that inhibitor prevent corrosion by the adsorption of phytoconstituents on the metal surface.

 

ACKNOWLEDGMENT:

The authors sincerely thank the authorities of Avinashilingam Deemed University for Women, Coimbatore, Tamilnadu, India for providing the facilities to carry out the study.

 

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Received on 12.04.2011        Modified on 22.06.2011

Accepted on 04.07.2011        © AJRC All right reserved