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Eco Friendly Green Inhibitor Tinosporacordifolia (Linn.) For The Corrosion Control of Aluminum in Sulfuric Acid Medium

Pushpanjali1, Suma A Rao2, Padmalatha Rao3
  1. Assistant Professor, Department of Chemistry, M. I. T, Manipal University, Manipal-Karnataka, India
  2. Associate Professor, Department of Chemistry, M. I. T, Manipal University, Manipal-Karnataka, India
  3. Professor, Department of Chemistry, M. I. T, Manipal University, Manipal-Karnataka, India
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Abstract

Aqueous extract of stems of Tinosporacordiofolia was studied as a corrosion inhibitor for aluminum in sulfuric acid (pH = 3) by using potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) technique in the temperature range of 30 °C to 50 °C. The concentrations of inhibitor used were in the range of 50- 400ppm. Inhibition efficiency was found to increase with increase in inhibitor concentrations and decrease with increase in temperature. Tinosporacordiofolia stems extract (TCSE) acted as an anodic type inhibitor and underwent physical adsorption process on the surface of the metal and followed Langmuir adsorption isotherm.

Keywords
Aluminum, potentiodynamic polarisation, Tinosporacordiofolia, Sulfuric acid, EIS.

INTRODUCTION
Aluminum is one of the most common metals used for industrial and domestic purposes due to its excellent electrical conductivity, good forming properties, low cost and other relatively noble properties [1]. The applications of aluminum and its alloys are often possible because of the natural tendency of aluminum to form a passivating oxide layer. However in aggressive media, the passivating layer can be destroyed and corrosive attack can take place. The protection of aluminum and its oxide films against the corrosive action of sulfate ions have been extensively studied. Sulfuric acid in the pH range of 2-4.5 is mainly used for pickling, chemical and electrochemical etching of aluminum and its alloys. A useful method to protect metals and alloys deployed in service in aggressive environments against corrosion is the addition of inhibitors. A number of organic compounds are known to be applicable as corrosion inhibitors for aluminum and its alloys in acidic environments[2]. Such compounds mainly contain nitrogen, oxygen sulfur or π bonds throughwhich adsorption of the molecules on the metal surface can take place. This creates a barrier between the metal and corrosive and brings down the rate of corrosion.

LITERATURE SURVEY
Despite of broad spectrum of organic compounds, the choice of appropriate inhibitor for a particular application is restricted by several factors. These include increased environmental awareness and the need to promote environment friendly processes. There exists a need to develop a new class of corrosion inhibitors with low toxicity and good efficiency. The exploration of natural products of plant origin as non-expensive eco-friendly inhibitor is an essential field study [3]. These plant products are not only eco- friendly, but also readily available, cost effective renewable source of materials and contain organic compounds such as amino acids, tannins and alkaloids which have inhibitive effect. Till date lots of works have been reported for using natural product as corrosion inhibitors [4] for aluminum in acidic media. Investigation of natural inhibitors is particularly interesting because they are non-expensive, ecologically acceptable and possess no threat to the environment.As a part of our research work with natural inhibitors for the corrosion control of aluminum and its alloys [5], we report herein, the results of utility of Tinosporacordiofolia stems extracts (TCSE) for the corrosion control of aluminum in sulfuric acid medium of pH=3.0

MARTIALS AND METHOD
3.1. Materials: The composition of aluminum is: Si: 0.467%, Fe: 0.163%, Mg: 0.530% and aluminum: Balance. Cylindrical test coupons of 10 mm diameter and approximately 20 mm height were machined from the rods of aluminum and metallographically mounted up to 10mm height using cold setting resin. The exposed flat surface of the mounted part was polished as per standard metallographic practice - belt grinding followed by polishing on emery papers (in the range of 600-2000) and finally disc polished using levigated alumina abrasive.The stock solution of 2 M sulfuric acid was prepared by using analar grade sulfuric acid and double distilled water. Standardization was done by volumetric method. From the standard solution, sulfuric acid solution of required concentration was prepared as and when required. Experiments were carried out at different temperatures using a calibrated thermostat under unstirred conditions.
Tinosporacordiofolia stems extracts (CLE) was prepared by literature method [6]. The stems of Tinosporacordiofolia were cut into pieces. These were completely air-dried at room temperature for 4 weeks. The dried stems were pulverized into fine powder using a domestic mixer grinder. 40 g of the powder was boiled in 500 mL of distilled water for 5 h. It was filtered using a piece of clean white cotton gauze. The filtrate was evaporated to complete dryness at 40 ℃, producing a fine sweet smelling and chocolate color solid residue. The extraction process was repeated 4 times and the solid residue weighed after extraction was pooled together in an air and water-proof container and kept in a refrigerator at 4 ℃. It was characterised by FTIR spectrum. Aqueous solution of the inhibitor of required concentration was prepared freshly as and when required.
Method
Electrochemical studies were carried out using a potentiostat (CH600D-series, U.S.model with CH Instruments beta software). Studies were done by using conventional three electrode Pyrex glass cell with platinum as counter electrode and SCE as reference electrode. Working electrode was aluminum.Finely polished aluminum specimen was exposed to sulfuric acid(pH=3)at different temperatures (30 ℃ to 50 ℃) and allowed to establish a steady state open circuit potential by immersing the electrodes in corrosive medium for 30 minutes. Potentiodynamic polarisation method and electrochemical impedance spectroscopy studies were carried out as reported earlier [7].
Result
Fourier transform infrared (FTIR) spectroscopy of TCSE
Absorption at 3425 cm-1 can be assigned to both O-H (overlapped by the strong stretching mode of N-H) and N-H. The 1643 cm-1 band is assigned to the N-H bending. The peak at 1149 cm-1 can be assigned to stretching mode of C-N group of aromatic amines. The band at 1404 cm-1 is attributed to C-C in aromatic ring. The adsorption band at 1026cm- 1 is assigned to the C-N stretch of aliphatic amines.
3.3.2Potentiodynamic polarization (PDP) measurements
Figure 1 shows the potentiodynamic polarization plot for the corrosion of aluminum in sulfuric acid (pH=3) containing different concentrations of TCSE at 30 °C.
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CONCLUSIONS
TCSE is a green inhibitor, which is readily available and cost effective for the corrosion control of aluminum.
The inhibition efficiency increased with increase in inhibitor concentration and decreased with increase in temperature. It acted as an anodic inhibitor.
TCSE adsorbed on the aluminum surface via both physisorption process and followed Langmuir’s adsorption.

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