Received: 26/09/2012; Revised: 02/02/2013; Accepted: 17/02/2013
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Turmeric extract, Langmur’s and Temkin’s isotherm.
H2SO4 acid is a major chemical which has manu use in industries and cleaning product, especially in the cloth and removel of scale from boiler. Generally 11N and 36N acid destroys the metal and alloys which used in tank and boiler, the data has been published about the resistance of these materials to corrosion by the HCl solution [1,2,3,4]. The most of studies were focused on the inhibition of Al in H2SO4 acid using organic compounds containing nitrogen, sulphur, and oxygen atoms as corrosion inhibitors [5,6], the inhibitors and synthetic inhibitors are toxic in nature and harmful for the environment therefore it necessary to develop rnviromentally acceptable and low cost inhibitors in this term turmeric is best inhibion product against the corrosion of metal because turmeric have tannins and terpins and other phytochemicals which is known for the mediclinical properties like antiseptic, antibacterial, antioxidant and most likely corrosion inhibition.
So, in this present study and investigation, the corrosion of Al in 0.1N H2SO4 solution in presence and absence of turmeric extract at different temperature has been studied by electrochemical and spectral technique.
Al specimens were cut to size of 4.5 x1.5cm x 0.2cm were prepared by polishing with 600 grit silicon carbide paper, rinsed with distilled water and finally dried in a stream of air.
Preparation of Plant Extract
The extract of turmeric is prepared by the root of Turmeric which dried in air and grained. The 50 gm powder subjected to the soxhlet extraction using 80% methanol, the solvent can be removed by boiled at constent temperature at 55 °C in vacuume evaporator, all the solution is prepared with AR grade chemicals in double distilled water.
Technique of AC Impedance Method
Corrosive media used were 0.1M KCl and NaF. The pH of solution was adjusted to different range values from pH 2, pH 4 to pH 9.5 by adding dilute HCl and NaOH solutions. The N2 gas was constantly purged to maintain deaerated condition. Metal electrode was than immersed in the sealed cell containing the test solution. A saturated calomel electrode and platinum electrode were used as reference and counter electrodes, respectively. AC measurement was carried out after 1 hour, when a constant potential was attained. The slope, ΔE/ΔI, at the corrosion potential, is defined as polarization resistance, Rp if we defined the constant B as:
B= babc /2.3(ba+bc) Rp
Were ba and bc are the Tafel slopes determined from E Vs log10 I plot.
The corrosion current density is given by
The electrochemical impedance measurements were performed under the response analyzer, Solartron 1250 and 1287electrochemical interface using small amplitude sine wave signals, 10mV, over the 1 kHz frequency range of 1 kHz to 1 MHz with 5 points per decade. This tourniquet is based on the theories that describe the response of a circuit to an alternating current or voltage as a function of frequency.
The electrochemical potentiostatic polarization measurements were performed under the response analyzer, Solartron 1250 and interface using small amplitude sine wave signals, 10mV, over the 1 kHz frequency range of 1 kHz to 1 MHz with 5 points per decade. This tourniquet is based on the theories that describe the response of a circuit to an alternating current or voltage as a function of frequency at different tempearature.
Voltammograms were obtained using a PAR Model 273 Potentiostat fitted with current interrupt and positive feedback iR compensation. The cell, consisted of a cell body (containing approximately 200 mLof electrolyte) fitted with a lid. The working electrode was acement-coated iron wire Four platinum wirecounter-electrodes were held in fritted glass compartments,which were placed in an equidistant configuration around thecentrally located working electrode to provide uniform radial current distribution along the length of the working electrode.Electrical contact with the saturated calomel referenceelectrode was maintained via a luggin capillary shield. Thecell was maintained at 25.0 6 0.28C using a recirculatingwater bath.
Chloride determinations were carried out using static mercury drop polarography. Loss on ignition was determined using either a muffle furnace or a thermogravimetric analyzer.
Figure 1.1.1 shows the Nyquist and Bode plots of the metals in deaerated 0.1M KCl at 40 °C. In this plot the imaginary component (Z) is taken against the real-component at each frequency. Here, frequency is increased in counter clockwise direction. At high frequencies, impedance was almost entirely created by the solution resistance, Rs, while at low frequencies; the impedance was almost entirely created by the combined polarization resistance and solution Rs, Rp. The [Z] Vs f plot also gave a value of Rs and Rp. The value of [Z] is the high limiting value; Rp is the difference between low frequency limit and high frequency limit.
There was no variation and effect of Rs when the speed of rotation increased; this behavior indicates that the corrosion rate of reaction is strongly controlled by diffusion through a fluid boundary layer of inhibitor. Fig.2 shows the Nyquist and Bode plots of metal in deaerated 0.1M KCl solution at 40 °C and pH 9.5.These results also reveled. The comparison in AC spectrum between pH 4 and pH 9.5 are correlated by Fig.3 .The analysis of impedance plot, through fitting results, is indicative that the equivalent circuit at pH 9.5 gave a better fitting of two circuits.
A parallel combination of capacitance and resistance as a series to the circuit of cathodic branch as a charge transfer resistance, with parallel charge transfer resistance-diffusion impedance for the anodic branch, the circuit after solution resistance is attributed to the passive film, which is found by the inhibitor on the metallic surface. This the entire conclusion summarized in the Table-1.1.1, and Table-2, the impedance diagram obtained for the Al in 0.1 N H2SO4 in the presence of the Bixin inhibitor are depicted in the Figure 1.1.1 to 1.1.4. They are perfect semicircles and this was attributed to charge transfer reaction. Impedance parameters derived from the Nyquist plots are tabulated in the Table 1.1.1 to 1.1.2. It can be seen that as the concentration of inhibitor increases, Cdl value also decreases in the value of Cdl, result of molecules function by adsorption at the metal- solution interface.
The Nyquist representation of the impedance behavior of Al in 0.1N H2SO4 and solution with and without the turmeric extract shown in Figure-1.1.1 to 1.1.4. The existence of a single semicircle shows the presence of single charge transfer process during corrosion which was unaffected by the presence of inhibitor molecule.
All the analysis earliar reported by the El-Etre A Y, JColloidInterface Sci., (2007),Chetouani A, Hammouti B and Benkaddour M, Pigment & Resin Technology, (2004)Pandian Bothi Raja and Mathur Gopalakrishnan Sethuraman(2008)and Ferreria E.S.,Giacomelli C.,Giacomelli F.C.,and Spinelli A., (2004).
The slightly depressed nature of the semicircle, which has the center below the x-axes, is the characteristics for the solid electrodes and such frequency dispersion has been attributed to roughness and other electrode. The charge transfer resistance (Rct) and the interfacial double layer capacitance values were derived using the equivalent shown in Figure 1.1.1 to 1.1.4. The value of Rct is increased from 32.8 to 458.6 Ω cm2. With the decrease in CPE value from 7.78 x 10-5 to 2.1x 10 -5 μFcm2 for the Bixin and similarly for the other inhibitors, variation in these values is similarly shown in the Tables 1 and 2. All the data show that the inhibition of Al corrosion made by using plant extract inhibitors show good results and percent efficiency order of inhibitors can be given as such [7,8].
Polarization measurements were carried out in a conventional three electrode cell. Al strip coated with the lacquer except for an exposed area of 1.2cm2 were used as the working electrode. The saturated calomel electrode and Pt electrode were used as reference and counter electrode respectively. The BAS-300 instrument is used for the potential analysis at different temperature.The potential of the electrode measured with respect to SCE; Pt electrode was used as auxiliary electrode.
The potentiometry analysis of corrosion is recent method, in this analysis cureent density is analysed with the variation of potential for the Turmeric it found that the current density vary between 106 to 107 mA/cm2 and potential -58 and -78 mV respectively.
The Cyclic voltametry measurement of corrosion inhibition determine by the ANOVA modal of instrument and during the analysis it found that the potential change with the Ag/AgCl electrode between the -90mV to -125mV which reveald the inhibitor adsorbs over the metal surface given a tendancy of inhibition.
• The corrosion rate of Al in 0.1N sulphuric acid decreased with the increasing of concentration of inhibitor.
• The inhibition efficiency increased with respect to the concentration of inhibitor and decreased with rise in tempareture.
• LCR and CR circuit which using for the AC impedance technique reveled that the turmeric shows 98.5% inhibition efficiency.
• The Potentiometry and polarization measurement shows that the Turmeric is very good corrosion inhibition efficiency.
I am thanks to Dr. S.K.Jain, Director of Pharmacy, SIRTP College Bhopal, for his kind encouragement in pursuing this work.