Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(9), 50-55, Sept. (2012) Res.J.Chem.Sci. International Science Congress Association 50 Study the Performance of Volatile Corrosion Inhibitors in Protection of Mild Steel in Cl Gas Environments Kannan P., Lavanya K.2 and Natesan M.St. Joseph’s College, Trichy -620002, Tamil Nadu, INDIA selvamm Arts and Science College, namakkal-637003, Tamil Nadu, INDIA Central Electro Chemical Research Institute, Karaikudi 630006, Tamil Nadu, INDIAAvailable online at: www.isca.in Received 9th June 2012, revised 22nd June 2012, accepted 27th June 2012Abstract Apprehend the corrosion of the mild steel (MS) in various environment has been studied. Amide like octylpalmamide (OTP), octylstearamide (OTS), octylcaprilamide (OTC) and dicyclohexylaminebenzotriazole (DCHA.BTZ) compounds exploited as VCI in this paper and tentative its corrosion rate and its inhibition power in corrosive Cl gas medium. Weight loss mode used to calculate the former parameter. Surface characterization had been analyzed SEM and FTIR. Electro chemical studies of EIS and Tafel polarization and its parameter were computed by characterization. And find OTS was best VCI in Cl medium via the above characterizations. The thermodynamic property adsorption isotherm has been calculated. Keywords: Mild steel, volatile corrosion inhibitor, inhibition efficiency, corrosion rate, environment. Introduction Corrosion is universal process which can’t apprehend but can control. Day by day, the new chemical compounds were synthesized and being discover for the treatment of corrosion. Among them volatile corrosion inhibitor (VCI) which, could easily vaporized and give a best passive film on the mild steel. There are various investigation has been done on volatile corrosion inhibitor, by using aliphatic amine and salicylic acid and their salts. In this work, reveal the behavior of OTP, OTS, OTC and DCHA.BTZ in Cl medium. The choice of the VCI is depends on its vaporization power and deposit on the surface of metal. There are numerous investigations on corrosion inhibition studies by aliphatic amines, salicylic acid and their salts as vapor phase corrosion inhibitors for various industrial metals and alloys2-5. Benzoic hydride and its salt derivatives has been used VCI in at relative humidity atmosphere. Inhibition effect depends on the inhibitor due some specialization fact like, chain length, size of the molecule and strength of bonding to the metal. Cyclohexylamine has high thermal stability in power plant and have VCI characteristic too, in pipeline. Aromatic compound such as, naphthalene has been a VCI at 250-350C in the HCl environment. Bayer synthesized cylcohexylamine and dicylcohexylamine as volatile corrosion inhibitor on iron. Varity of aliphatic and alicyclic amine used as VCI. Cyclohexylamine and dicycloheylamine used in an SO2 environment as VCI. Dicyclohexylamine also exhibit its volatile nature for an inhibitor for steel, copper and zinc10. The use of several VCI as an effective inhibitor has reported for carbon steel11. Many of amine carboxylate derivatives as VCI has discovered for different environmental condition12. From the literature survey, not much more article on corrosion behavior of mild steel in Cl gas medium by using Amide as a volatile corrosion inhibitor (VCI). This article described the corrosion behavior of mild steel in a forth mentioned medium using SEM, FTIR, EIS and Tafel technique. Material and MethodsPreparation of Specimens and Inhibitors: The specimen carbon steel’s were made with following chemical composition of Carbon-0.07%, sulphur- nil, phosphorous-0.008%, silicon – nil, manganese -0.34%, Fe – balance. The synthesis of OTP, OTS, OTC and were prepared by the equimolar mixture of octylamine (Aldrich) with corresponding acids such as palmetic, stearic, caprylic acid(Merck) by stirring them at room temperature. And DCHA.BTZ was synthesised by incorporate dicyclohexylamine and benzotriazole (Aldrich). Finally, the synthesized inhibitors were characterized by FTIR. The molecular structure and weight of the amide inhibitor were shown below table-1. Weight loss method: The metal specimen preparation and initial weighing procedure has been followed as before mentioned15. Cl gas was passed though the chamber separately to create two different environments. The specimens were held by hooks in the desiccators over desiccators which consist of Clgas. This setup was kept in a thermostat water bath maintained at 50ºC. This arrangement produced a continuous under saturation of water vapors. One cycle included 5 hours exposure in the thermostat. The experiments were carried out in the absence and in the presence of inhibitor. The observations were made at the end of the test period. Specimens were then cleaned using pickling solution. Washed, dried and reweighed. Mass loss was then found to determine the corrosion rate. The specimens were weighed prior and after the tests. The corrosion rate and inhibition efficiency (IE) was calculated as mentioned14. Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(9), 50-55, Sept. (2012) Res.J.Chem.SciInternational Science Congress Association 51 Table-1 Structures of VCI’s S.No Structure Molecular formula & weight Vapour pressure (mmHg) Name of VCI 1 16 H33 NO and 255.4393 2.5653×10 - 3 OTC 2 C 2449 NO and 367.652 1.9667×10 - 3 OTP 3 26 H53 NO and 395.7051 1.2740×10 - 3 OTS 4 18 H29 N4 and 301.4498 1.253×10 - 3 DCHA.BTZ Potentiodynamic Measurement: The polarization measurement has been taken with help of three electrode system working. The potentio dynamic measurements were started by changing step wise 60mV/m on a PGP20IP potentiostat/galvanostatic. The anode potential could find at the steady potential. Tafel polarization drawn via interchanges the potential (E) and log I, the parameter b and bc were evaluated. Electrochemical Impedance Spectroscopy: The cell configuration of EIS was done by the electrochemical measurement unit solartron 1280b. Rct and Cdl value obtain from the difference between the values of real axis. They employed amplitude of ±20mV, frequency ranging 0.5Hz to 100 KHz. Fourier Transformation Infrared Spectroscopic Studies (FTIR): Surface analyses of adsorbed film, on the mild steel during the gravimetric tests in the presence of inhibitor were obtained by FTIR (Model No - TENSOR 27 Software - OPUS version 6.5) spectrum. SEM: For SEM image, 1cm specimen sample were taken, HITACHI S-3000H was used for scan the samples. Results and DiscussionWeight loss method: The inhibition effect of volatile corrosion inhibitor, on the carbon steel after 5Hrs exposure in Cl was discussed by weight loss method. And calculate the corrosion rate and inhibition efficiency of the VCIs which is shown in the table-2. In all environments OTS shows that it is high and best inhibition on iron in the corresponding environments. Table-2 Effect of VCI’s on MS in Cl gas environment S. No Inhibitor Weight loss (g) Inhibition efficiency (%) Corrosion Rate (µm/y) 1 Blank 8 Nil 0.7132 2 DCHA.BTZ 2.4 70 0.2139 3 OTP 2.1 74 0.1872 4 OTC 0.8 90 0.0772 5 OTS 0.1 98 0.0133 EIS Technique: The nyquist plot of the carbon steel with this five inhibitor were drawn which is exposed about 5hrs in the Clgas environment is shown in the figure-1. It shows that the corrosion behavior of mild steel in the sense of resistance to the corrosive medium in the presence and absence of inhibitor. The VCI’s doesn’t amend the mechanism dissolution of metal. Hence, it’s purely depends on the charge transfer process. All experimental plots approximately have a semi-circular shape. The impedance measurement shows that the inhibition of the VCIs is characterized by increasing diameter of the arc which is acting the resistance. The Cdl and Rct values are shown in the Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(9), 50-55, Sept. (2012) Res.J.Chem.SciInternational Science Congress Association 52 table-3, which has highest inhibition efficiency in weight loss method for Cl gas. And shows that OTS having highest value of Rct and Cdl value of 14571ohm cm, 3.508 x10µF/ cm and than the other (which doesn’t shown). The impedance spectrum shown figure-1, 2 Inhibition efficiency can also be calculated with this. Inhibition efficiency has been computed by equation-3. Table-3 Electrochemical Impedance Studies in Cl2 gas medium Inhibitor used ct Ohm cmdl µF/cmInhibition Efficiency (%) Blank 2389 3.005x10 - 5 Nil OTS14571 3.508x10 - 7 83 Tafel polarization Technique: Tafel Polarization monitoring is an effective electrochemical method of measuring corrosion. Monitoring the relationship between electrochemical potential and current generated between electrically charged electrodes in environment allows the calculation of the corrosion rate. In our studies the current produced by the blank is in the increasing order increase with increase in volt apply. But it is totally inversely related, the current produced by the best inhibitor is very low. With this account, which shows the best inhibition in measurement is OTS in Cl gas environments. Retained inhibitors shows that less inhibition than the others (which doesn’t show). Tafel graph took only for which represented highest inhibition in weight loss in the given below figure-3 the parameter values are given in below table-6. Table-4 Polarization parameters for MS in presence of VCI after 5 hrs exposure at Cl gas medium Inhibitors icor (µA/cm) Tafel slope (mV/Decade) p K Ohm.cInhibition Efficiency (%) -B Blank 1.5 112 133 12.6 Nil OTS 0.0399 218 187 82 85 Adsorption Isotherm: As mentioned weight % of VCI took for the demonstrations13. And it was obeyed the adsorption isotherm. Adsorption Isotherms of VCI on MS in both Cl gas medium had shown in the figure-5. And it implied the maximum adsorption occurred 1.2%, at which maximum inhibition efficiency observed. Hence, we made the former Wt % for the all VCI to determine the inhibition efficiency in both Cl and steam medium. The adsorption isotherm adhere the Langmuir adsorption isotherm. SEM Spectral Details: SEM image reveals that the specimens are containing the corroded iron and unaffected specimen in their surface after exposure in Cl gas environment. The amount of surface defects decreases by the inhibitor of OTS on the MS. The best coordinate bond layer distribution was observed on specimen containing inhibitor which shows in the figure-5 (magnification 1X). On comparing these two images, which is not having the inhibitor shows highly corroded particle on the MS surface. When compare with the first image there is no that much amount of corroded particle. Form the SEM analysis shows that OTS inhibitor is shows high inhibition efficiency among the others (which doesn’t shown). Table-5 Polarization parameters for MS in presence of 1.2wt % of VCI in Cl gas mediumInhibitors cor (µA/cm) Tafel slope (mV/Decade) Rp (KOhm.cm) Inhibition Efficiency (%) Ba -Bc Blank 1.5 112 133 12.6 Nil DCHA.BTZ 0.2636 197.7 155.3 45 72 OTP 0.16 137 170 58 78 OTC 0.05 219 66.8 63 80 OTS 0.0399 218 187 82 85 Table-6 Absorption frequencies of FTIR spectra recorded for OTS and in Cl gas medium Inhibitor Bond Frequency range cm-1Measured bond Inhibitor cm-1MS Surface film cm OTS N-H 3650-3200 3426 3604 C=O 1800-1600 1635 1646 C-N 1360-1080 1103 931 FT-IR Spectrum Analysisfor OTS: The mechanism for inhibition of corrosion on mild steel by the VCI compounds is clear from the spectral data obtained in the below table-6. FTIR spectrums and tables are portrait for the best inhibitor, which has best inhibition in Cl gas medium. It is seen from FTIR spectral data of VCI film formed on the metal surface in the Clmedium, which the C-N stretching frequency of OTS has shifted from 1103 to 931cm-1. It suggests that nitrogen atoms present in inhibitor are coordinated to MS resulting in the formation of inhibitor– Fe complex on metal surface. Similarly N-H, C=O absorption frequencies 3426, 1635cmshifted to , 3604, 1646cm-1, respectively in environment A. The shift in the value is due to the donation of lone pair of electrons of N atoms present in the VCI compound to Fe resulting in the formation of inhibitor-Fe complex. From the FTIR spectral analysis it is clear that inhibitor – Fe complex is formed on the metal surface. The higher inhibition efficiency of OTS may be due the presence of 2 nitrogen atoms when compared to other inhibitors. The lone pair electrons and then strong C-N sigma bond is present in the OTS formed thick non- visible complex on the metal surface to reduce the corrosion rate of metal in comparison with other VCIs. Research Journal of Chemical Sciences ______ Vol. 2(9), 50-55, Sept. (2012) International Science Congress Association Impedance diagram for the blank and OTS in Tafel Polarization curve of Blank with OTS in Cl 0.4 0.6 1012141618 /(q-1 DCHABTZ OTP OTC OTS Adsorption isotherms in Cl   \n \n \n\r \n ______ _________________________________ ______________ International Science Congress Association Figure-1 Impedance diagram for the blank and OTS in Cl gas medium. Figure-2 Polarization curve of Blank with OTS in Cl gas medium 0.6 0.81.01.21.4 Con (%) DCHABTZ OTP OTC OTS Figure-3 Adsorption isotherms in Cl gas medium Figure-4 Rp and IE of inhibitors in Cl medium   ! ______________ _____ ISSN 2231-606X Res.J.Chem.Sci 53 gas medium. 1.6