For verification of this paper, please visit on http://www.socialresearchfoundation.com/innovation.php#8

Aluminium is applied broadly as a metal or alloy in numerous industrial applications. Acid solutions are applied in various industrial processes namely acid descaling and acid cleaning etc. Corrosion inhibitors are the substances added to the corrosive medium to reduce the rate of its attack on the metal or alloy [1] and these may be organic or inorganic compounds [2 - 4]. Numerous industries exploitation equipment made from metals under diverse circumstances ranging from mild to stiff chemical environments, making their surfaces susceptible to corrosion [5-6]. Investigation have shown that corrosion cannot be perfectly removed from metal surfaces due to the different environments in which metals are applied [7]. Corrosion is the disintegration of metal and its alloy by the chemical (wet or dry reaction) when the metals in contact with the moisture or environment. Corrosion of aluminium in nitric acid media is usual phenomena. Commonly the creation of metals is from ores or the compounds which occur naturally with greatly high energy of huge magnitude of energy [8]. Corrosion inhibitors are the classic choice to protect metal by the electrochemical attack. To inhibit the corrosion the corrosion different synthetic corrosion inhibitors came into the existence but these are toxic and hazardous in nature [9]. Plant extracts are applied usually now a days as potential corrosion inhibitor. Naturally plant extracts are readily available, nontoxic in nature, cheap and eco-friendly. These plant extracts involves organic constituents or polar atoms such as N, O, S and P [10]. A protective oxide film is produced when these ( N, O, S and P) polar atoms works as a bridge among extract of plant and surface of metal [11]. Owing to organic constituents, plant extracts interact with the corroded metal by their electrons [12]. In view of which protective oxide layer is generated and the corrosion is controlled. A numerous researchers studies have been dedicated to the corrosion of aluminium and use of natural products as a potential corrosion inhibitor Azadirachta indica [11], Justicia gendarussa [13], Ipomoea triloba [14] in order to aluminium in acidic media. Acacia nilotica extract endows a benign protection to aluminium against corrosion. The no toxicity of this organic plant constituents, its antimicrobial characteristics and sustainable sources of production present as having a large scope of applications as green potential corrosion inhibitors. Alcoholic extract of Acacia nilotica pod contains alkaloids, Tannins, Glycosides, Terpenoids, Gallic acid, catechin and galloylated flavan-3,4-diol ( leucocyanidin) has been from pods [15- 18]. In the present work, the inhibitory efficacy of Acacia nilotica extract for 1.5M HNO3 nitric acid corrosion of aluminium has been analysed at 12 hrs immersion period.

Preparation of Test Coupons: Sheet of aluminium achieved locally and of 0.20 cm thickness was mechanically cut into coupons of 2.54 × 1.52 cm2 size containing a hole of about 0.12 mm diameter near the upper edge in order to the purpose of hanging in the test solution. Different strips were polished to mirror finish by applying different grades emery paper. Test solutions & Experimentation : The electrolytic solutions of 1.5M HNO3 were prepared by using bi-distilled water. All chemicals applied were of Analar grade. Ethanolic extraction of Acacia nilotica extract was obtained by refluxing the dried fruits in soxhlet extractor [19]. Each coupons was suspended by the glass hook plunge into a beaker containing100 ml of the test solution and different concentration of the Acacia nilotica inhibitor. The investigation has been carried out at 303 K temperature. Since fixed intervals of immersion time period, test coupons were washed with distilled water and dried thereafter hanging the washed strips in desiccators in order to appropriate time period [19].

Weight Loss Studies

The value of inhibition efficiency (η%), Fractional surface coverage (θ ),  Corrosion rate (ρcorr), Adsorption equilibrium constant (K_ads) obtained from experimental data (Table.1) at varying concentration of the Acacia nilotica inhibitor in 1.5M nitric acid solution in order to an immersion period of 12 hrs .

From the mass loss value (ΔM), the inhibition efficiency (η%)  was calculated using the following equation [20].

η%    =  [ ( ΔM_u  -  ΔM_i )  /  ΔM_u ]  ×  100

Where ΔM_u is mass loss without inhibitor and ΔM_i  is weight loss with inhibitor.

The corrosion rate (ρcorr) in millimetre penetration per year (mmpy) can be determined by following equation

ρcorr     =   ( ΔM  × 87.6  )  /   area ×   time  ×   metal density

Where ΔM weight loss expressed in mg, area expressed in cm² of metal surface exposed, time expressed in hours of exposure and metal density expressed in g / cm³.

Table 1 - Kinetic parameters on corrosion of aluminium in 1.5M HNO₃ with and without ethanolic extract of varying concentration of fruit, stem bark and root bark of Acacia nilotica at 303  0.1 K.

 Effective area of Specimen : 7.72 cm² Immersion period : 12 hrs.

Inhibitor Concentration ( % )	Mass Loss ΔM  (mg)	Corrosion Rate (mmy-1)	Fractional Surface Coverage  (θ)	Inhibition   Efficiency    (η % )	log (θ/1-θ)
Uninhibited	273.4	95.75	-	-	-
Fruit Extract
0.09	156.8	54.91	0.4264	42.64	-0.1288
0.18	135.0	47.27	0.5062	50.62	0.0107
0.27	119.6	41.88	0.5625	56.25	0.1091
0.36	99.8	34.95	0.6349	63.49	0.2402
0.45	79.5	27.84	0.7092	70.92	0.3871
Stem bark extract
0.09	169.5	59.36	0.3800	38.00	-0.2126
0.18	147.3	51.58	0.4612	46.12	-0.0675
0.27	132.4	46.37	0.5157	51.57	0.0272
0.36	114.6	40.13	0.5808	58.08	0.1415
0.45	85.7	30.01	0.6865	68.65	0.3403
Root bark extract
0.09	173.4	60.72	0.3657	36.57	-0.2392
0.18	153.0	53.58	0.4403	44.03	-0.1042
0.27	140.6	49.24	0.4857	48.57	-0.0248
0.36	124.5	43.60	0.5446	54.46	0.0776
0.45	98.3	34.42	0.6404	64.04	0.2506

                 
 
Fig. 1 Variation of inhibition efficiency with concentration of fruit, stem bark and root bark extract of Acacia nilotica for aluminium in 1.5M HNO₃ at 12hrs immersion period.
 

Fig. 2. Langmuir adsorption isotherm curve for aluminium in 1.5M HNO₃ with fruit, stem bark and root bark extract of Acacia nilotica at 12 hrs immersion period.

Outcomes obtained from the table revealed that the addition of inhibitor to the acid had diminished the corrosion rate (ρcorr). The inhibition efficiency (η%) increased with increase in concentration of inhibitors in 1.5M HNO₃  nitric acid solution.    

Adsorption Isotherm

Langmuir adsorption isotherm graph was plotted between log (θ / 1- θ) and log C.                                                                    

 log (θ / 1- θ)   =   log K_ads  +  log C

Where Kads is adsorption equilibrium constant, the Kads value can be calculated from the intercept line on the log (θ / 1 –θ ) axis and is related to standard free energy of adsorption.

The values of ΔG0ads at all studied temperature can be evaluated from the equation as follows

ΔG⁰ads  =  - 2.303 RT log (55.5 K_ads )

Where R = 0.008314 KJ / mol is the universal gas constant, 55.5 indicate the molar concentration of water in the solution whereas T is the absolute temperature in Kelvin.

SEM Analysis

SEM observations were performed to endorse the creation of a protective oxide film of the Acacia nilotica extract on the aluminium metal surface. The SEM images obviously indicates in Figures 3 and 4,  the aluminium coupons exposed for 12 hours to 1.5 M HNO₃ solution in the presence and absence of 0.45 % of the fruit extract.

Fig. 3   SEM image of aluminium in 1.5M HNO₃ acid medium at 12 hrs.

Fig.4 SEM image of aluminium in 1.5M HNO₃ with 0.45 % of the inhibitor concentration at 12hrs.

[1]. Shastri, V.S. (1998). “ Corrosion inhibitors : Principles and Applicationsˮ. John Wiley & Sons : England. [2]. Iannuzzi, M. and Frankel, G.S. (2007). “ Mechanism of Corrosion Inhibitor of AA2024-T3 by Vanadates. Corrosion Scienceˮ. Vol. 49, pp. 2371-2391. [3]. Yasakau, K.A., Zheludkevich, M.L., Ferreira, M.G.S. (2008). “ Lanthanide salts as corrosion inhibitors for AA5083 Mechanism and Efficiency of corrosion inhibitionˮ. J. Electrochem. Society, Vol. 155(5), pp. 169-177. [4]. Yurt, A. Ulutas, H. and Dal, H. (2006). “ Electrochemical and Theoretical Investigation on the corrosion of Aluminium in acidic solution containing some Schiff basesˮ. Appl. Surf. Sci., Vol. 253(2), pp. 919-925. [5]. Caines, S., Khan, F., Shirokff, J. & Qiu, W. (2015). “Demonstration of increased corrosion activity for insulated pipe systems using a simplified electrochemical potential noise method ˮ. Journal of Loss Prevention in the Process Industries, Vol. 33, pp 39-51. [6]. Ali, A. & Mahrous, Y. (2017). “ Corrosion inhibition of C-steel in acidic media from fruiting bodies of Melia azedarach L extract and a synergistic Ni2+ additive ˮ. RSC Advances, Vol. 7(38), pp. 23687- 23698. [7]. Landolt, D. (2007). “Corrosion and Surface Chemistry of Metals ˮ, Ist Ed.,Taylor and Francis Group, New York, pp 400. [8]. Bhawsar, J., Jain, P.K. Jain. and Jagwani, D. (2012) “ Eco friendly corrosion inhibitors from natural plant extract ˮ. A review, Proceeding National Seminar on Recent Trends in Chemical and Biological Sciences. [9]. Bhawsar, J., Jain, P. K. and Jain. P. (2015). Alexendria Engg J. Vol. 54(3), pp. 769-775. [10]. Eddy, N.O. and Mamza, P.A.P. (2009). Portugaliae Electrochimica Acta. Vol. 27, pp. 443-456. [11]. Popoola, A.P.I., Abdulwahab, M. and Fayomi, O.S.I. (2012). International Journal of Electrochemical Science. Vol. 7, pp. 5805-5816. [12]. Leelavathi, S. and Rajalakshmi, R. (2013). Journal of Material Environmental Science,Vol. 4(5), pp. 625-638. [13]. Amitha Rani B.E. and Basu, J. (2012). International Journal of Corrosion, Vol. 15. [14]. Popoola, A.P.I., Abdulwahab, M and Fayomi, O.S.I.(2012). International Journal of Electrochemical Science. Vol. 7, pp.5805-5816. [15]. Malviya S., Rawat, S., Verma, M. and Kharia, A. (2011). “ Preliminary Phytochemical investigation of Acacia nilotica Linn Plant, ˮ Current Pharma Research, Vol. 1(2), pp. 91-100. [16]. Chaubal, R. and Tambe, A. (2006). Isolation of new straight chain compound from Acacia nilotica, Int. J. Chem., 45(B), pp. 1231-1233. [17]. Maviya, S., Rawat, S., Kharia, A. and Verma, M. (2011). “Medicinal attributes of Acacia nilotica Linn. – A comprehensive review on ethnopharmacological claims, ˮ Int. J. PHARMACY & LIFE SCIENCES, Vol. 2(6). [18]. Verma, V., Singh, U.K., Sharma, A.K., Singh, B. and Singh, R. (2012). “ A review on Acacia nilotica Linn. And its ethnobotany, phytochemical and pharmacological profile ˮ Int. J. of pharmaceutical research and development. Vol. 4(3), pp. 251-256. [19]. Meena, A.K. and Bairwa, B.S. (2021). “ Inhibitory efficacy of Capparis decidua extract on the corrosion of Al in various acidic media ˮ. Journal of Advanced Scientific Research, Vol. 12(1) Suppl 2. [20]. Meena, A.K. and Bairwa, B.S. (2019). “ Use of Tamarindus indica extract as potential corrosion inhibitor for Al in acidic medium ˮ. Remarking an analisation. Vol. 3•, Issue 12• (Part-1 ).