Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X   Vol. 2(2), 18-27, Feb. (2012) Res.J.Chem.Sci. International Science Congress Association        
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Corrosion Inhibitory Effects of Some Substituted Thiourea on Mild Steel  in Acid Media Tripathi R., Chaturvedi A.* and Upadhayay R.K. Department of Chemistry, Government College, Ajmer – 305001, INDIAAvailable online at: 
www.isca.in
(Received 17th September 2011, revised 6th January 2012, accepted 7th January 2012)Abstract Mass loss and thermometric methods have been used to study the inhibition of mild steel corrosion in HCl and HSO solution by the pyridyl substituted thiourea compound 1-(2,6-diazene)–3–benzyl thiourea (ST), 1–(3’-pyridyl) – 3 – benzyl thiourea (ST), 1 – (3’- pyridyl) – 1 –phenyl thiourea (ST), 1–(2’- pyridyl)–3–phenyl thiourea (ST). Values of inhibition efficiency obtained from the two methods are in good agreement with each other and are dependent upon the concentration of inhibitor and acid. The difference in the inhibition behaviour of the compounds have been explained in terms of the solubility of the substituted thiourea compounds and strength of the inhibitor-metal bond. Inhibition efficiency of all inhibitors increas with increasing concentration of inhibitor. Inhibition efficiency is more in case of HSO rather than in HCl. Inhibition efficiency was found maximum upto 99.26% for mild steel in HSO solution. Inhibition efficiencies of synthesised substituted thiourea have been found much more than their parent thiourea. Keywords: Corrosion inhibition, weight loss method, thermometric method,  surface coverage, corrosion rate etc. IntroductionMild steel finds a variety of applications industrially, for mechanical and structural purposes, like bridge work, building, boiler plates, steam engine parts and automobiles. It finds various uses in most of the chemical industries due to its low cost and easy availability for fabrication of various reaction vessels, tanks, pipes etc. Since it suffers from severe corrosion in aggressive environment, it has to be protected acids like HCl and HSO have been used for drilling operations, pickling baths and in decaling processes. Corrosion of mild steel and its alloys in different acid media have been extensively studied1-4. It has been reported5-6 that addition of certain organic compounds bearing hetero atoms, retards the corrosion of mild steel in acidic environments. Recently considerable interest has been generated in the use of nitrogen, oxygen and sulphur containing organic compounds as corrosion inhibitor for mild steel in different acids7-8. Organic compounds having hetero atoms atoms like O, N, S and in some cases Se, are found to have higher basicity and electron density. Thus to help corrosion inhibition, O, N and S are the active centres for the process of adsorption on the metal surface10-15. The electric charge, orientation, shape and size of the molecule play an important role on the effectiveness of inhibition. Efficiency of their inhibitory effect depends upon the basicity of these atoms16-18. Among these, thiourea and its derivatives have been investigated extensively. These are polar molecules in which S atom having permanent –ve charge and N atom have +ve charge. As the molecule approaches the electrode surface the electric field of double layer increases the polarization of molecule and induces additional charges on S and N atoms, a condition that  enhance the adsorption of molecule.In the present study an attempt has been made to study the influence of varying concentration of substituted thiourea viz. (ST, ST, ST, ST) on corrosion of mild steel in different concentration of hydrochloric acid, sulphuric acid  employing mass loss and thermometric method. Material and MethodsMild steel specimens of composition 99.3% Fe,  0.2% C, 0.3% Mg, 0.14% Si and 0.04 % S of size 2.00 cm Χ 2.00 cm Χ 0.03 cm were used for the complete immersion test. All the specimens were polished by buffing and rubbing with emery paper to obtain mirror like finishing. The solution of HCl were prepared by using double distilled water. All chemicals used were of AR grade.  Each specimen was suspended by a V-shaped glass hook made by capillary tubes and immersed in a glass beaker containing 50 mL of the test solution at room temperature, after the test specimen was cleaned with benzene and then dried with hot air dryer. The percentage efficiency was calculated as19 % = 100 
uiuWWWD
D
-
D
)( 
Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X  Vol. 2(2), 18-27, Feb. (2012)   Res.J.Chem.SciInternational Science Congress Association 
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where  and  are the weight loss of the metal in uninhibited and inhibited solution, respectively. Inhibition efficiency were also calculated using a thermometric method. This involve the immersion of single specimen of measurement 2.00 Χ 2.00 Χ 0.03 cm in a reaction insulating chamber having 50 mL of solution at an initial room temperature. Temperature changes were measured at regular intervals using a thermometer with a precision of 0.1ΊC. The increase in temperature was initially slow then rapid and attained a maximum value and then decreased. The maximum temperature was noted. Percentage inhibition efficiency was calculated as20% = 
RNRNRN100
-
where RN and RN are the reaction number in the free solution and in presence of inhibitor. RN is defined as RN = 
tTTim)(
-
where Tm and Ti are maximum and initial temperature, respectively and t is the time in minutes required to attain maximum temperature. The corrosion rate (CR) in mm/yr can be obtained by the following equation21Corrosion rate (mm / yr) = 
d
T
A
W΄΄
΄
D
6.87where,  is weight loss in mg, A is area of specimen in cm, T is time of exposure in hours, d is density of metal in gm/cm3 ) can be calculated as22 = 
uiuWWWD
D
-
D
where  and  are the weight loss of the metal in uninhibited and in inhibited solution, respectively. Results and Discussion Weight Loss Method: Weight loss, percentage inhibition efficiencies, corrosion rate and surface coverage for different concentration of HCl and inhibitor are given in table-1 and for different concentration of HSO and inhibitors are given in table-2. It can be seen from the both the tables that inhibition efficiency of inhibitor increases with increasing concentration of inhibitor. Inhibition efficiency also increases with increasing concentration of acid and all the inhibitors show maximum inhibition efficiency at the highest concentration of acids used i.e. 2.5 N HCl and 2.5 NHSO. The maximum inhibition efficiency was obtained for (ST) at an inhibitor concentration of 0.8% in 2.5 N HCl and 2.5 N SO i.e. 98.48% and 99.26%, respectively. These results show that  substituted thiourea show more inhibition efficiency in HSO than in HCl. The variation of percentage inhibition efficiency with inhibitor concentration are depicted graphically in figure 1 for HCl and in figure 2 for HSO. Figures show a linear curve of percentage inhibition efficiency with the concentration of inhibitor, indicating that the inhibition efficiency increases with increasing inhibitor concentration. Thermometric Method:  Inhibition efficiency values were also determined by the thermometric method. Temperature changes for mild steel in 2N, 3N and 4N sulphuric acid and hydrochloric acid solution were recorded with various inhibitor concentration. However no significant temperature changes were measured in the acid concentration of 1N HCl and HSO4 solution. Results obtained are dipicted in table 3 for HCl and table - 4 for HSO. The results obtained are in good agreement with those from weight loss experiments. Inhibition efficiency increases with increasing acid  concentration. The variation of reaction number with inhibitor concentration, presented graphically in figure 3 for HCl and in figure 4 for HSO4 shows linear behaviour with positive slope, indicating that the reaction number increase with increasing acid concentration it decreases with increasing inhibitor concentration. Generally, the Inhibitor having oxygen, nitrogen and sulphur atoms responsible for the adsorption on metallic surface. This process may block active sides, hence may decrease the corrosion rate. Adsorption plays an important role in the inhibition of metallic corrosion by organic inhibitors. Many investigators have used the Langmuir adsorption isotherm to study inhibitor characteristics. Assuming that the inhibitors adsorbed on the metal surface decrease the surface are available for cathodic and anodic reactions to take place, Hoar and Holliday have shown that the Langmuir isotherm  log [ / (1 ) = log A + log C  ( / 2.3 RT)] should give a straight line of unit gradient for the plot of log[ / (1 )] versus log C, where surface coverage  is calculated as (RN - RN)/RN. A is a temperature independent constant, and C is the bulk concentration of the inhibitor (mol L-1) The corresponding plots, shown in figure 5 and 6 are linear, but the gradients are not equal to unity as would be expected for the ideal Langmuir adsorption isothem equation.It has also been observed that the efficiency is higher in higher concentration of HCl and HSO. This may be because of the fact that the inhibitor ionize more readily under more acid strength and is absorbed more easily on the surface of metal. Acids which have more dissociation constant i.e. higher values of Ka or lower values of pK like HCl and HSO4 enhance the ionization of thiourea thus causes more adsorption of substituted thiourea on metal surface. Therefore they act as better inhibitor at higher concentrations. Adsorption plays an important role in the inhibition of metallic corrosion by organic inhibitors. The efficiencies of inhibitors expressed as the relative reduction in corrosion rate can be quantitatively related to the amount of adsorbed inhibitors on the metal surface. It is assumed, that the corrosion reaction are prevented from occuring over the active sites of the metal surface covered by adsorbed inhibitors species, whereas the corrosion reaction occurs normally on the surface at inhibitors free area. 
Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X  Vol. 2(2), 18-27, Feb. (2012)   Res.J.Chem.SciInternational Science Congress Association 
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TABLE – 1 Weight loss and percentage inhibition efficiency (hh %) for mild steel in HCl solution with given inhibitor additions Inhibitor Addition 1.0 N HCl (24 hr) 1.5 N HCl (24 hr) 
DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) 
Uninhibited – – – – – – – – 
ST0.2% 0.4% 0.6% 0.8% 68 62 52 48 89.95 90.84 92.31 92.90 5.39 4.91 4.12 3.80 0.8995 0.9084 0.9231 0.9290 49 48 41 35 92.57 92.72 93.78 94.69 3.88 3.80 3.25 2.77 0.9257 0.9272 0.9378 0.9469 
ST0.2% 0.4% 0.6% 0.8% 72 68 55 52 89.36 89.95 91.87 92.31 5.70 5.39 4.36 4.12 0.8936 0.8995 0.9187 0.9231 50 49 45 40 92.42 92.57 93.18 93.93 3.96 3.87 3.56 3.17 0.9242 0.9257 0.9318 0.9393 
ST0.2% 0.4% 0.6% 0.8% 75 70 60 59 88.92 89.66 91.13 91.28 5.94 5.55 4.75 4.67 0.8892 0.8966 0.9113 0.9128 55 50 48 45 91.66 92.42 92.72 93.18 4.36 3.96 3.80 3.56 0.9166 0.9242 0.9272 0.9318 
ST0.2% 0.4% 0.6% 0.8% 80 78 70 70 24.91 59.96 66.94 76.07 6.34 6.18 5.56 5.55 0.2491 0.5996 0.6694 0.7607 55 51 50 45 54.66 75.42 85.90 90.50 4.36 4.04 3.96 3.56 0.5466 0.7542 0.8590 0.9050 
Inhibitor Addition 2N HCl (3 hr.) 2.5 N HCl (3 hr.) 
DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) 
Uninhibited – – – – – – – – 
ST0.2% 0.4% 0.6% 0.8% 40 39 30 15 93.30 93.62 95.09 97.54 25.36 24.72 19.02 09.51 0.9330 0.9362 0.9509 0.9754 35 30 16 9 94.10 94.94 97.47 98.48 22.19 19.02 10.14 5.706 0.9410 0.9494 0.9747 0.9848 
ST0.2% 0.4% 0.6% 0.8% 41 40 32 19 93.30 93.46 94.77 96.89 25.99 25.36 20.28 12.04 0.9330 0.9346 0.9477 0.9689 40 39 25 11 93.26 93.43 95.79 98.14 25.36 24.72 15.85 6.974 0.9326 0.9343 0.9579 0.9814 
ST0.2% 0.4% 0.6% 0.8% 50 34 28 20 91.83 94.44 95.42 96.73 31.70 21.55 17.75 12.68 0.9183 0.9444 0.9542 0.9673 45 44 28 11 92.42 92.59 95.28 98.14 28.53 26.13 17.75 6.974 0.9242 0.9449 0.9528 0.9814 
ST0.2% 0.4% 0.6% 0.8% 56 30 26 23 90.84 93.62 95.75 96.24 35.28 19.02 16.48 14.58 0.9084 0.9362 0.9575 0.9624 52 50 32 16 91.24 91.58 94.61 97.97 32.96 31.70 19.00 10.14 0.9175 0.9461 0.9730 0.9797 
 
Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X  Vol. 2(2), 18-27, Feb. (2012)   Res.J.Chem.SciInternational Science Congress Association 
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TABLE – 2 Weight loss and percentage inhibition efficiency (hh %) for mild steel in HSOsolution with given inhibitor additions Inhibitor Addition 1.0 N HSO (24 hr.) 1.5 N HSO (24 hr.) 
DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) 
Uninhibited – – – – – – – – 
ST0.2% 0.4% 0.6% 0.8% 43 38 28 15 93.59 94.33 95.82 97.76 3.40 3.01 2.22 1.18 0.9359 0.9433 0.9582 0.9776 40 24 20 9 94.10 96.46 97.05 98.67 3.17 1.90 1.58 0.71 0.9410 0.9646 0.9705 0.9867 
ST0.2% 0.4% 0.6% 0.8% 45 40 29 19 93.29 94.03 95.67 97.16 3.56 3.17 2.29 1.50 0.9329 0.9403 0.9567 0.9716 43 27 22 11 93.65 96.01 96.75 98.37 3.40 2.14 1.74 0.87 0.9365 0.9601 0.9675 0.9837 
ST0.2% 0.4% 0.6% 0.8% 45 41 30 21 93.29 95.38 95.52 97.61 3.56 3.25 2.37 1.66 0.9329 0.9538 0.9552 0.9761 45 30 25 14 93.36 95.57 96.31 97.93 3.56 2.37 1.98 1.11 0.9336 0.9557 0.9631 0.9793 
ST0.2% 0.4% 0.6% 0.8% 48 35 33 26 92.84 94.78 95.08 96.56 3.80 2.77 2.61 2.06 0.9284 0.9478 0.9508 0.9656 47 32 29 15 93.06 94.83 95.72 97.78 3.72 2.53 2.29 1.18 0.9306 0.9483 0.9572 0.9778 
Inhibitor Addition 2.0 N HSO (3 hr.) 2.5 N HSO (3 hr.) 
DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) DDM (mg) I.E. hh%) Corrosion rate(mmpy) Surface Coverage (qq) 
Uninhibited – – – – – – – – 
ST0.2% 0.4% 0.6% 0.8% 27 22 15 8 96.02 96.75 97.79 98.96 17.11 13.94 9.51 5.07 0.9602 0.9675 0.9779 0.9896 25 14 10 5 96.32 97.94 98.52 99.26 15.85 8.87 6.34 3.17 0.9632 0.9794 0.9852 0.9926 
ST0.2% 0.4% 0.6% 0.8% 29 25 19 8 95.72 96.31 97.20 98.96 18.38 15.85 12.04 5.07 0.9572 0.9631 0.9720 0.9896 79 19 14 8 95.73 97.20 97.94 98.82 15.85 12.04 8.87 5.07 0.9573 0.9720 0.9794 0.9882 
ST0.2% 0.4% 0.6% 0.8% 30 30 20 9 95.58 95.58 97.05 98.67 19.02 19.02 12.68 5.70 0.9558 0.9558 0.9705 0.9867 30 19 15 8 95.58 97.20 97.79 98.82 19.02 12.04 9.51 5.07 0.9558 0.9720 0.9779 0.9882 
ST0.2% 0.4% 0.6% 0.8% 35 32 22 10 94.84 95.28 96.17 98.52 22.19 20.28 13.94 6.34 0.9484 0.9528 0.9617 0.9852 33 20 20 9 95.14 97.05 97.05 98.67 20.92 12.68 12.68 5.70 0.9514 0.9705 0.9705 0.9867 
 
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TABLE – 3 Reaction Number (RN) and percentage inhibition (hh %) for Mild Steel in HCl solution with given inhibitor additions Inhibitor Addition 2N HCl 3N HCl 4N HCl 
RN (kmin-1) I.E. (hh%) RN (kmin-1) I.E. (hh%) RN (kmin-1) I.E. (hh%) 
Uninhibited 0.0277 – 0.0666 – 0.1500 – 
ST0.2% 0.4% 0.6% 0.8% 0.0077 0.0072 0.0061 0.0050 72.20 74.00 77.97 81.94 0.0170 0.0160 0.0138 0.0110 74.47 75.97 79.27 83.48 0.0383 0.0366 0.0300 0.0250 74.46 75.60 80.00 83.33 
ST0.2% 0.4% 0.6% 0.8% 0.0100 0.0088 0.0083 0.0061 63.89 68.23 70.03 77.97 0.0238 0.0216 0.0194 0.0150 64.26 67.56 70.87 77.47 0.0508 0.0475 0.0441 0.0400 66.13 68.33 70.60 73.33 
ST0.2% 0.4% 0.6% 0.8% 0.0111 0.0105 0.0090 0.0080 59.92 62.09 67.50 71.11 0.0250 0.0244 0.0211 0.0200 63.03 63.36 68.31 69.96 0.0541 0.0491 0.0466 0.0450 63.93 67.26 68.93 70.00 
ST0.2% 0.4% 0.6% 0.8% 0.0122 0.0116 0.0100 0.0070 55.95 58.12 63.89 74.72 0.0277 0.0266 0.0222 0.0216 58.40 60.06 66.66 67.56 0.0566 0.0525 0.0500 0.0483 62.26 65.00 66.66 67.80 
TABLE – 4 Reaction Number (RN) and percentage inhibition (hh %) for Mild Steel in HSO solution with given inhibitor additions Inhibitor Addition 2N H
2
SO
4
 3N H
2
SO
4
 4N H
2
SO
4
 
RN (kmin-1) I.E. (hh%) RN (kmin-1) I.E. (hh%) RN (kmin-1) I.E. (hh%) 
Uninhibited 0.1388 – 0.1666 – 0.2833 – 
ST0.2% 0.4% 0.6% 0.8% 0.0388 0.0377 0.0361 0.0350 72.04 72.83 73.99 74.78 0.0455 0.0444 0.0416 0.0405 72.68 73.34 75.03 75.69 0.0725 0.0708 0.0691 0.0666 74.40 75.00 75.60 76.49 
ST0.2% 0.4% 0.6% 0.8% 0.0416 0.0405 0.0380 0.0372 70.02 70.82 72.62 73.19 0.0477 0.0455 0.0438 0.0422 71.36 72.68 73.70 74.66 0.0741 0.0716 0.0700 0.0675 73.84 74.72 75.29 76.17 
ST0.2% 0.4% 0.6% 0.8% 0.0438 0.0422 0.0388 0.0377 68.44 69.59 72.04 72.83 0.0483 0.0461 0.0444 0.0427 71.00 72.32 73.34 74.36 0.0766 0.0750 0.0733 0.0725 72.96 73.52 74.12 74.40 
ST0.2% 0.4% 0.6% 0.8% 0.0444 0.0433 0.0400 0.0388 68.01 68.80 71.18 72.04 0.0500 0.0488 0.0466 0.0450 69.98 70.70 72.02 72.98 0.0858 0.0833 0.0791 0.0758 69.71 70.59 72.07 73.24 
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Figure-1 Variation of inhibition efficiency (hh%) with inihibitor concentration (C) for aluminium in 2.5 N HCl Figure-2 Variation of inhibition efficiency (hh%) with inihibitor  concentration (C) for aluminium in 2.5 N HSOST:1 – (2, 6-diazene) – 3 –benzyl thiourea, ST : 1 – (3’-pyridyl) – 3 – benzyl thiourea, ST : 1 – (3’- pyridyl) – 1 –phenyl thiourea, ST : 1 – (2’- pyridyl) – 3 –phenyl thiourea 
91.0091.5092.0092.5093.0093.5094.0094.5095.0095.5096.0096.5097.0097.5098.0098.500.20.40.60.8C%
ST1
ST2
ST3
ST4
95.0095.5096.0096.5097.0097.5098.0098.5099.0099.500.20.40.60.8C%
ST1
ST2
ST3
ST4
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Figure-3 Variation of Reaction Number (RN) with inhibitor concentration (C) for aluminium in 4 N HCl Figure-4 Variation of Reaction Number (RN) with inhibitor concentration (C) for aluminium in 4 N HSOST : 1 – (2, 6-diazene) – 3 –benzyl thiourea, ST : 1 – (3’-pyridyl) – 3 – benzyl thiourea, T : 1 – (3’ - pyridyl) – 1 –phenyl thiourea, T : 1 – (2’ - pyridyl) – 3 –phenyl thiourea 
0.0200.0250.0300.0350.0400.0450.0500.0550.0600.20.40.60.8RN(kmin-1C%
ST1
ST2
ST3
ST4
0.0650.0700.0750.0800.0850.0900.20.40.60.8RN(kmin-1C%
ST1
ST2
ST3
ST4
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Figure-5 Langmuir adsorption isotherms for mild steel in 2.5N HCl with inhibitor addition Figure-6 Langmuir adsorption isotherms for mild steel in 2.5N HSO with inhibitor additions ST : 1-(2, 6-diazene) – 3 –benzyl thiourea, ST : 1 - (3’ pyridyl) – 3 – benzyl thiourea, ST : 1 – (3’ - pyridyl) – 1 –phenyl thiourea, ST : 1 – (2’ - pyridyl) – 3 –phenyl thiourea 
1.011.091.171.251.331.411.491.571.651.731.81-0.69-0.39-0.22-0.09Log (1-qlog C
ST1
ST2
ST3
ST4
1.251.331.411.491.571.651.731.811.891.972.052.13-0.69-0.39-0.22-0.09Log (1-qlog C
ST1
ST2
ST3
ST4
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NNNN
N
||||||||(ST)(ST)(ST)(ST)NHCNHCH--NHCNHCH
-
2
--
NHCNH--NHCNH--
The results revealed that thiourea compounds effectively reduce the corrosion rates of mild steel in acid solution. The following order of inhibition efficiency has been observed for the four substituted thiourea for Mild Steel ST  ST  ST  ST. Organic compounds absorb on the metal surface forming a barrier between the metal and the corrosive environment. Some structural features of the organic compounds help them to do so. The lone pair electrons of the mentioned atoms facilitate the adsorption process. ST is most effective inhibitor since lone pair of electron present on nitrogen atoms of pyrimidine ring and thiourea moiety is maximum. ST has pyridyl ring having less electron density in comparision to ST hence it is less basic than ST. In case STand ST lone pair present on nitrogen atom attached to benzene take part in the resonance. Hence they are less available for bonding with metal surface. The substituted thiourea possess N and S as hetero atom and thereby offering a electron rich reaction centre. It has been reported that inhibitors are adsorbed on corroding metal surface through electron rich N and S atom thus forming a chemisorbed monolayer of the inhibitor which act as physical barrier between the metal and corrosive solution. The higher ionization of substituted thiourea in HSO than in HCl may be the reason of these compound exhibiting higher inhibition efficiencies in HSO4 as compared in HCl since increased ionisation of inhibitor molecule will facilitate the adsorption of inhibitor on the Mild Steel surface. The inhibition efficiency is thus, directly proportional to the fraction of the surface covered with adsorbed inhibitors. Conclusion A study of pyridyl substituted thiourea compounds (ST, ST, ST, ST) are efficient inhibitors of corrosion of mild steel in sulphuric acid and hydrochloric acid. Both mass loss and thermometric methods has shown that the inhibition efficiency of four inhibitors increases with increasing in concentration of inhibitor and increases as increasing the concentration of HCl and HSO. The highest inhibitor efficiency upto 98.48% in 2.5 N HCl and 99.26% in 2.5 N SO. The corrosion rate of mild steel is maximum in HCl. The corrosion rate is governed by number of complex reactions taking place and also the nature of the protective film. Finally it may be concluded from the results that the newly synthesised pyridyl substituted thiourea are efficient corrosion inhibitor for mild steel in HSO and HCl. The inhibition of the compound is governed by chemisorption mechanism in both the acid media. As the molecule approaches the electrode surface the electric field of double layer increase the polarization of molecules and induces additional charges on S and N atom and thus enhances the adsorption of molecules. Acknowledgement One of the authors (Tripathi Richa) is thankful to Department of Chemistry Govt. College, Ajmer for providing research facilities in the department. References 1. Quarishi M.A., Rawat J. and Ajmal M., Corros., its control, Proc. Int Conf. Corros., 2, 634, (1997)2. Laskawiec J., Sozanska B.,  Trzcionka J.,  Koroz Sukurczynska, 38, 249 (1995)3. Shibad P.R. and Adhe K.N., Electrochem J. Sec. (India), 30, 103 (1981)4. Shibad P.R., Electrochem J. Soc. (India), 27, 55, (1987)5. Yadav P.N. and Wadhwani R., Trans. SAEST, 25, 134, (1993)6. Edwards B.C., Corros. Sci., 9, 395 (1969)7. Abdennabi A.M.S. and Addulhadi A.I. Abu-orabis,  Anti Corrros. Meth. and Mat.,  45, 103 (1998)
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8. Suetaka W., Bull. Chem. Soc., 37, 112 (1964)9. Sputnik E. and Ademovic Z., Proceedings of the 8th  European Symposium on Corrosion Inhibitors (8 SEIC) Ann. Univ. Ferrara, N.S. Sez V, Suppl., 257 (1995)10. Clubby B.G., Chemical Inhibitors for Corrosion Control, Royal Soc. Chem., Cambridge, 141, (1990)11. Gojic M. and Kosec L., ISIJ Int.,37(7), 685 (1997)12. Metikos-Hukovic M., Babic R., Grubac Z. and Brinic S., J. Appl. Electrochem., 24, 325 (1994)13. Kobatiatis L., Pebere N., Koutsookos P.G., Corros. Sci., 41, 941 (1999)14. Guillamuin V. and Mankowski G., Corros. Sci., 41, 421 (1999)15. Quafsaoui W., Blanc C.h., Bebere N., Srhiri A. andMankowski G., J. Appl. Electrochem.,30, 959 (2000)16. Blanc C., Gastaud S. and Mankowski G., J. Electrochem. Soc. 150, 396, (2003)17. Mozalev A., Poznyok A., Mazaleva and Hassel A.W., Electrochem. Comm.,, 299 (2001)18. Ebenso E.E., Okafor P.C. and Eppe U.J., Anti Corros. Meth. and Mat.,50(6), 414 (2003)19. Talati J.D. and Gandhi D.K., Indian.J. Technol., 29,277 (1991)20. Mylius F. and Metalik Z., 14, 239 (1992)21. Jones D.A., Principles and Prevention of Corros. London, Prentice – Hall International (U.K.) Limited, nd ed. 34 (1996)22. Dubey R.S., Uppadhyaye S.N., J. Electrochem. Soc. (India), 74, 143 (1944)  
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