Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 4(6), 45-53, June (2014) Res. J. Chem. Sci. International Science Congress Association 45 N, N, N, N-Tetramethylethylenediamine (TMEDA) and 1, 3-Diaminopropane (DAP) as Vapour Phase Corrosion Inhibitor (VPCI) for mild steel under Atmospheric conditionsSaini V.1* and Kumar H.Material Sci. & Electrochemistry Lab., Dept of Chem., Ch. Devi Lal University, Sirsa, Haryana – 125055, INDIA Material Sci. & Electrochemistry Lab., Dept. of Chem., Janta Girls College, Ellenabad, Haryana– 125102, INDIA Available online at: www.isca.in, www.isca.me Received 9th April 2014, revised 18th May 2014, accepted 16th June 2014Abstract Industrialization and modernization in now a days has made a strong demand of steel and their maintenance for a strong infrastructure for every country in the race of survival, stabilization, growth and competition. Atmospheric corrosion can aggressively accelerate the rate of degradation of steel during their manufacturing, processing, storage and transportation. In these cases, traditional methods to prevent corrosion are not suitable which provide scope of Vapour Phase Corrosion Inhibitors (VPCI) in industries, defense and daily life. N, N, N, N-Tetramethylethylenediamine (TMEDA) and 1, 3-Diaminopropane (DAP)were investigated as VPCI for mild steel under aggressive corrodents of atmosphere by Weight loss test, Eschke test, Salt spray test, Sulphur dioxide (SO) test at 50C and results of these tests were supported by Metallurgical research microscopy technique and SEM technique. Keywords: Mild steel, weight loss test, Eschke test, salt spray test, metallurgical research microscopy, SEM, Vapour phase corrosion inhibitors. IntroductionAtmospheric components such as moisture, air pollutants (SO, S, Ny, CO and Cl) and temperature have been reported as corrodents for metal corrosion. Corvo and Moricelli et al.studied the relationship between chloride concentrations with the corrosion rate in the atmospheric conditions.Ericssonshowed that NaCl can cause corrosion at very low because it can induce corrosion by SO on a carbon steel surface. NaCl can enhance 14 times rate of corrosion by SO at 9% relative humidity. In an another report ofBlucher et al., they have investigated adverse effect of CO on corrosion of Al. Vuorinen et al. and a list of authors have worked on the organic compounds as VPCIs. Due to presence of long chain hydrophobic part and the presence of atom having high electron density, organic compounds are the best selection for the compounds used as VPCIs. Organic substances have been studied as VPCI for mild steel were morpholine derivatives and diaminohexane derivatives, fatty acid thiosemicarbazides, cyclohexylamine and dicyclohexylamine7-8, amine carboxylates, ammonium caprylate10, benzoic hydrazide derivatives11-12, polyamines13, bis-piperidiniummethyl-urea and –amino alcoholic compounds14. Apart from organic substances, natural compounds like wood bark oil15 and thyme16-17 have also been used as VPCIs. Cano et al.18recently have proposed mechanism of inhibition of dicyclohexamineisonitrite and dicyclohexaminenitrite against corrosion due to vapours of acetic acid and formic acid on carbon steel. Zubielewicz et al19studied the electrochemical behaviour of mixed anodic inhibitors. Batis et al.20evaluated the performance the two primers, first natural rust converter and other on organic primer coating containing VPCI against atmospheric corrosion for reinforcing steel.Lyublinski21 studied synergistic corrosion management systems by use of corrosion inhibitors. In continuation to our earlier study22-27, in the present study, the inhibiting properties of N, N, N, N-Tetramethylethylenediamine (TMEDA) and 1, 3-Diaminopropane (DAP) were investigated on mild steel at 85 % relative humidity and 50 °C by Weight loss test, Salt spray test in a solution of 3.0 % NaCl, Eschke test, SO test, Metallurgical research microscopy and Scanning electron microscopy. Material and Methods Many research papers, articles and reviews have been reported to the study of the techniques used to determine the effectiveness of VPCI against the metallic corrosion such as Adsorption isotherm technique28, Weight loss technique29, Potentiodynamic polarization measurements30, Electrodynamical impedance meseaurment31, Audioradiography32 and Capacitance measurments33. Tormoen et al.34 reported three new techniques namely Surface-enhanced Raman spectroscopy, Scanning Kelvin probe microscopy and Contact angle analysis to monitor the adsorption of VPCI on the metallic surface in real time. These techniques can be used to evaluate the ability of two VPCI to diffuse and adsorb on the surface of metal simultaneously. Materials, equipments and methods used to investigate the amine as VPCI for mild steel at 50C in my present study are explained as below: Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(6), 45-53, June (2014) Res. J. Chem. Sci. International Science Congress Association 46 Chemicals: N, N, N, N-Tetramethylethylenediamine (TMEDA): Minimum assay 99.0 %, Grade A.R., Source Spectrochem. Pvt. Ltd., Mumbai. 1, 3-Diaminopropane (DAP): Minimum assay 99.0 %, Grade A.R., Source Qualigens Fine Chemicals, Mumbai. Mild Steel: ASTM-283, coupons of dimensions 3.5 cm × 1.5 cm × 0.025 cm and of percentage chemical composition: C – 0.17, Si – 0.35, Mn – 0.42, S – 0.05, P – 0.20, Ni – 0.01, Cu – 0.01, Cr – 0.01 and Fe - balance (w/w). Along with them triply distilled water (conductivity 1 x 10-6ohm-1cm-1) and sulphuric acid were also used. Equipments: Weighing Balance: Single Pan Analytical Balance, Precision 0.01mg, Model AB 135-S/FACT, Source Mettler Toledo, Japan. Humidity Chamber: Thermotech TIC-4000N Temperature Controller, Humidity controller with course and fine adjustments, AC Frequeny 50-60Hz, Max. Voltage 300V, Source Make-Associated Scientific Tech., New Delhi.Salt Spray Chamber: Thermotech TIC-4000N Temperature Controller, Pumping system Pt-100, AC Frequeny 50-60Hz, Max. Voltage 300V, Source Make-Associated Scientific Tech., New Delhi. Air Thermostat: Nine adjustable Chambered, Electrically controlled, Accuracy ± 0.1C. Metallurgical Research Microscope: CXR II from Laomed, Mumbai, India. Scanning Electron Microscope: JEOL 5900LV scanning electron microscope. Methods: Vapour Pressure Determination Test: A definite amount of exactly weighed VPCI was placed in a single neck round bottom flask fitted with a rubber cork in the neck having a glass capillary of 1.0 mm diameter in the center of rubber cork. Then the flask was kept in electrically controlled air thermostat maintained at the constant temperature of 50C for 10 days. Change in weight of VPCIs was observed by analytical balance and vapour pressure of investigated VPCI was determined by weight loss of VPCI for time of exposure by equation 1. ˝ P = W 2 R T (1) At M Where, P = vapour pressure of the VPCI (mmHg), A = area of the orifice (m), t = time of exposure (sec.), W = weight loss of VPCI (kg), T = temperature (K), M = molecular mass of the inhibitor (kg) and R = gas constant (8.314 JK-1mol-1). Weight Loss Test: Mild steel coupons were mechanically polished successively with the help of emery papers grading 100, 200, 300, 400 and 600 and then thoroughly cleaned with plenty of triple distilled water, ethanol and acetone. Then coupons were dried with hot air blower and stored in desiccators over silica gel. Weight loss tests were carried out in an electronically controlled air thermostat maintained at a constant temperature of 50C. After recording the initial weights of mild steel coupons, they were kept in different isolated chambers of air thermostat having fixed amount of VPCI at a constant temperature of 50C for 24 hours of exposure time. A uniform thin film of VPCI was adsorbed onto the metal coupon after 24 hours of exposure. Then these coupons were transferred to a digitally controlled humidity chamber maintained at 85% humidity at a constant temperature of 50C for 10 days. Blank coupons untreated with VPCI were also kept in the humidity chamber for the same duration in the same corrosive environment. After exposing the coupons for 10 days, coupons were taken out from the humidity chamber and washed initially under the running tap water. Loosely adhering corrosion products were removed with the help of rubber cork and coupon was again washed thoroughly with triple distilled water and dried with hot air blower and then weighed again. Corrosion rate in mils per year (mpy) and percentage corrosion inhibition efficiency (PCIE) were calculated by using the equations 2 and 3 respectively. Corrosion Rate (mpy) = DAT 534 (2) Where, W = weight loss (in mg), D = density of mild steel (in g/cm), A = area of coupon (in sq. inch), T = exposure time (in hour). Percentage Inhibition Efficiency = 100 CRo CRCRo - (3)Where, CRo = corrosion rate in absence of inhibitor and CR = corrosion rate in presence of inhibitor. Salt Spray Test: After exposing the pre weighed mild steel coupons to VPCI in air thermostat for 24 hours, they were transferred to salt spray chamber having 3.0 % NaCl solution maintained at 50C for duration of 10 days along with blank coupons. After exposing coupons for 10 days, coupons were treated in same manner as treated in weight loss test to remove corrosion products and then CR and PCIE were calculated. Eschke Test: Kraft papers of suitable size were dipped in the VPCI for 30 seconds and then dried to adsorb uniform layer of inhibitor on Kraft papers. Mild steel coupons were wrapped in VPCI impregnated Kraft papers and then taken in humidity chamber maintained at 85 % relative humidity maintained at 50C for first 12 hours and 25C for next 12 hours alternately for 10 days. This temperature cycle was maintained in two sets because of formation and condensation of vapours of VPCI on mild steel surface regularly. After exposing coupons for 10 days, coupons were treated in same manner as treated in weight loss test to Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(6), 45-53, June (2014) Res. J. Chem. Sci. International Science Congress Association 47 remove corrosion products and then CR and PCIE were calculated. Sulphurdioxide Test: SO test was carried out on the mild steel coupons as in weight loss test. SO gas was prepared by dissolving 0.04 g of sodium thiosulphate in 30mL aqueous solution of 1.0 % NHCl and 1.0 % NaSO solution and 0.5 mL of 1.0N HSO was added to the flask. Initially pre-weighed and mechanically polished mild steel coupons were placed in air thermostat maintained at 50C for duration of 10 days. Definite weight of VPCIs in a petridis and the flask, which is the source of SO, were placed in the isolated chambers of air thermostat containing mild steel coupons. After exposing coupons for 10 days, coupons were treated in same manner as treated in weight loss test to remove corrosion products and then CR and PCIE were calculated. Metallurgical Research Microscopy: This test was employed to know about nature and type of corrosion using metallurgical research microscope. To investigate the corrosion inhibition efficiency of investigated VPCIs, micrographs of the corroded coupons treated with investigated VPCI were subjected to porosity study and morphology of surface. By the obtained results a comparative study of that porosity and surface morphology was carried which provided the information about the number of pores, size of pores, percentage porosity and area covered by the pores on the surface of coupon after the four different corrosion experiments. Percentage porosity (PP) and total objects (TO) shows the roughness of surface. On the other hand maximum perimeter and maximum area object ratio (A/O) provide the information about the size and depth of the pores on the surface of mild steel. Micrographs of blank corroded coupons were taken after exposure of different aggressive environments for 10 days are shown in table-1 and results of metallurgical research microscopy of blank mild steel coupon after different corrosion tests are reported in table-2 from which it is clear that in weight loss test 9774 pores cover 8886066.4820 µ area due to uniform corrosion in humid environment by which 68.90% surface become porous. In this test, numbers of pores are very high but A/O ratio is not very high as compared to that of salt spray test. In salt spray test, percentage porosity (69.94%) is almost equal to that of weight loss test but the numbers of pores (13,380) and the porous area (10960879.5014 µ) on the mild steel surface are high due to corrosive action of direct exposure of chloride ions on the surface of mild steel coupon. In this test, perimeter of pore (52323.4375 µ) and A/O ratio are high due to large size and high depth of pores respectively. In SO test, although the numbers of pores (3387) are very low as compared to other corrosion experiments yet the percentage porosity (86.52%) are highest in this test. In this test the size of pores (78541.5913 µ) and A/O ratio are very high due to high depth of the pores by the acidic action of SO environment which provide evidence in favour of mechanism of pits formation on the surface of coupon by the acidic action of SO. In Eschke test, depth of pores is very low due to small size of pore of perimeter (20138.1682 µ) but total objects (6448) are high due to roughness of surface by the action of corrodents of environment. Table-1 Micrographs of blank mild steel coupon in different corrosion tests Micrograph of blank mild steel coupon in Weight loss test Micrograph of blank mild steel coupon in Salt spray test Micrograph of blank mild steel coupon in SO 2 test Micrograph of blank mild steel coupon in Eschke test Research Journal of Chemical Sciences ____ _ Vol. 4(6), 45-53, June (2014) International Science Congress Association Metallurgical research microscopy results of blank mild steel coupon in different corrosion tests TO Weight Loss Test 9774 Salt Spray Test 13380 SO 2 Test 3783 Eschke Test 6448 Scanning Electron Microscopy: This technique gives the morphology study of mild steel coupons after treatment of different corrosion tests which provide the evidences in the support of inhibition data of investigated VPCIs, type of corrosion and for the mechanism of inhibition. In this studied at different resolutions on the different spots on the mild steel coupons for complete information about the inhibition mechanism after treating with different tests. SEM of blank mild steel coupons were also taken for the compa rative study of metal specimens which are given in figure- 1. Micrographs of the blank coupons clearly provide the evidence of the pitting and crevice corrosion in corroding environments. Figure-1 Scanning electron micrographs of blank mild steel Results and Discussion Vapour Pressure Determination Test: Results of vapour pressure determination test for investigated VPCIs are given in table- 3. Due to presence of sufficient vapour pressure, vapours investigated VPCIs can easily adsorbed on the surface of mild steel coupon and form a barrier film for water vapours and corrosive aggressive contents of atmosphere around the coupons _ _____________________________________________ _ International Science Congress Association Table-2 Metallurgical research microscopy results of blank mild steel coupon in different corrosion tests TO PP MP(µ) 9774 68.9 55805.5407 13380 69.94 52323.4375 3783 86.62 78541.5913 6448 69.11 20138.1682 This technique gives the morphology study of mild steel coupons after treatment of different corrosion tests which provide the evidences in the support of inhibition data of investigated VPCIs, type of corrosion test, samples were studied at different resolutions on the different spots on the mild steel coupons for complete information about the inhibition mechanism after treating with different tests. SEM of blank mild rative study of metal 1. Micrographs of the blank coupons clearly provide the evidence of the pitting and crevice Scanning electron micrographs of blank mild steel coupon Results of vapour pressure determination test for investigated VPCIs are given in 3. Due to presence of sufficient vapour pressure, vapours of investigated VPCIs can easily adsorbed on the surface of mild steel coupon and form a barrier film for water vapours and corrosive aggressive contents of atmosphere around the coupons and protect coupons from corrosion by the formation of protective layer. Table- 3 Vapour pressure of investigated VPCIs at 50 S. No. Inhibitors 1. TMEDA 2. DAP Weight Loss Test: Results of CR and PCIE for investigated VPCIs obtained by weight loss test at 50 table- 4. CR of mild steel treated with investigated VPCIs are given in figure- 2 form which it is clear that the CR is very low on mild steel coupon which were treated with TMEDA and DAP. PCIE of investigated VPCIs are given in figure clear that both investigated inhibitors work well against corrosion on the mild steel under atmospheric conditions at high temperature. Table- 4 Weight loss test parameters obtained for VPCIs at 50 85% relative humidity for 10 days S.No. VPCI Weight Loss(mg) 1. Blank 14.8 2. TMEDA 4.1 3. DAP 3.4 Figure - Corrosion rate of mild steel coupon treated with VPCI with respect to blank coupons obtained from Weight loss test Salt Spray Test: Results of weight loss and CR of mild steel after 10 days exposure of NaCl at 50 clear from figure- 4 that in salt spray test, direct contact of chloride ions on mild steel coupons accelerate the rate of corrosion. From PCIE of VPCIs in figure- 5, it is shown that both investigated TMEDADAP _ ________ ISSN 2231-606X Res. J. Chem. Sci. 48 Metallurgical research microscopy results of blank mild steel coupon in different corrosion tests MA (µ 2 ) 8886066.4820 1096879.5014 9770443.2133 4461322.7147 and protect coupons from corrosion by the formation of 3 Vapour pressure of investigated VPCIs at 50 C Vapour Pressure (mmHg) 169.91 X 10 - 2 178.92 X 10 - 2 Results of CR and PCIE for investigated VPCIs obtained by weight loss test at 50 C are summarized in 4. CR of mild steel treated with investigated VPCIs are 2 form which it is clear that the CR is very low on mild steel coupon which were treated with TMEDA and DAP. PCIE of investigated VPCIs are given in figure -3 from which it is clear that both investigated inhibitors work well against corrosion on the mild steel under atmospheric conditions at high 4 Weight loss test parameters obtained for VPCIs at 50 C and 85% relative humidity for 10 days Weight Loss(mg) CR (mpy) PCIE 5.12 - 1.41 72.35 1.17 77.05 - 2 Corrosion rate of mild steel coupon treated with VPCI with respect to blank coupons obtained from Weight loss test Results of weight loss and CR of mild steel after 10 days exposure of NaCl at 50 C are shown in figure-4. It is 4 that in salt spray test, direct contact of chloride ions on mild steel coupons accelerate the rate of corrosion. From 5, it is shown that both investigated BLANK VPCI Research Journal of Chemical Sciences ____ _ Vol. 4(6), 45-53, June (2014) International Science Congress Association VPCIs were worked very well against the salt spray at high temperature. Figure-3 Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from Weight loss test Figure-4 Weight loss and corrosion rate of mild steel coupon treated with VPCIs obtained from Salt spray test Figure-5 Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from Salt spray test Eschke Test: Weight loss of the mild steel coupons, CR and PCIE of VPCIs were calculated at 50 C for duration of 10 days in Eschke test and the data obtained are shown in figure figure-7. It is clear from the figure- 6 that both VPCIs perform very significant role against the corrosion at high temperature. Visual observations of mild steel coupons are also given in table 70.00%72.00%74.00%76.00%78.00% TMEDADAP72.35% 77.05% 1012 Wt. loss CR BLANK10.23.51 TMEDA2.91 DAP3.21.1 71.50%67.00%68.00%69.00%70.00%71.00%72.00%TMEDA DAP _ _____________________________________________ _ International Science Congress Association VPCIs were worked very well against the salt spray at high Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from Weight loss test and corrosion rate of mild steel coupon treated with VPCIs obtained from Salt spray test Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from Salt spray test Weight loss of the mild steel coupons, CR and C for duration of 10 days in Eschke test and the data obtained are shown in figure -6 and 6 that both VPCIs perform very significant role against the corrosion at high temperature. observations of mild steel coupons are also given in table -5. Figure - Weight loss and corrosion rate of mild steel coupon treated with VPCIs obtained from Eschke test Figure - Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from E SO Test: Results obtained for different corrosion determination parameters by SO test are given in seen that value of CR of mild steel coupons treated with VPCIs is high in this test for the same duration as compa Eschke test due to the acidic environment of SO is shown that both investigated VPCIs play significant role to prevent the mild steel from the corrosion in acidic environment of SO which is part of atmospheric gases near the industries. Figure - Weight loss and corrosion rate of mild steel coupon treated with VPCIs obtained from SO 77.05% 68.66% DAP 0123456789 Wt. loss BLANK8.3 TMEDA1.5 DAP1.8 81.81%76.00%77.00%78.00%79.00%80.00%81.00%82.00%83.00%TMEDA 10121416 Wt. loss BLANK15.2 TMEDA4.8 DAP4.3 _ ________ ISSN 2231-606X Res. J. Chem. Sci. 49 - 6 Weight loss and corrosion rate of mild steel coupon treated with VPCIs obtained from Eschke test - 7 Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from E schke test Results obtained for different corrosion determination test are given in figure-8 and figure-9. It is seen that value of CR of mild steel coupons treated with VPCIs is high in this test for the same duration as compa red with CR in Eschke test due to the acidic environment of SO . From figure-9 it is shown that both investigated VPCIs play significant role to prevent the mild steel from the corrosion in acidic environment of which is part of atmospheric gases near the industries. - 8 Weight loss and corrosion rate of mild steel coupon treated with VPCIs obtained from SO test. CR 2.86 0.52 0.62 78.32%DAP CR 5.2 1.66 1.48 Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(6), 45-53, June (2014) Res. J. Chem. Sci. International Science Congress Association 50 Figure-9 Percentage corrosion inhibition efficiency of TMEDA and DAP obtained from SO test Metallurgical Research Microscopy: Metallurgical Research Microscopy of TMEDA: Results of metallurgical research microscopy and micrographs of mild steel coupons treated with TMEDA after corrosion tests are reported in table-6 and table-7 respectively. By comparison of the data obtained by different corrosion tests, it is clear that percentage porosity (PP) is significantly low in all tests due to good inhibition action of TMEDA against the atmospheric corrosion. It is shown that PP is almost negligible in Eschke test (3.14%) due to direct contact of TMEDA with surface of mild steel coupon. In weight loss test, 2119 pores cover 5346.2604 µ area due to uniform corrosion in humid environment by which 8.29% surface become porous. In salt spray test, PP (9.95%) is not very high but the numbers of pores (4645) are very high due to more roughness by direct exposure of NaCl along with water vapours on the surface of mild steel coupon. Small porous area of mild steel coupon in salt sprat test is due to inhibition action of TMEDA against pitting and crevice formation. In this test, perimeter of pore (4399.6332 µ) and A/O ratio are very high due to large size and high depth of pores respectively. In SOtest, although numbers of pores (1625) are not very high yet its A/O ratio is very high due to very large pores having high depth. In Eschke test, depth of pores are negligible due to small size of pore of perimeter 513.0056 µ but total objects (1739) are higher than pores in SO2 test due to roughness on surface of mild steel by the action of corrodents of environment. Micrographs of all tests show that almost smooth surface of mild steel coupon without any corrosion products are obtained after the treatment of coupon with TMEDA. Metallurgical Research Microscopy of DAP: Results of metallurgical research microscopy and micrographs of mild steel coupon treated with DAP after four different corrosion tests are reported in table-8 and table-9 respectively. In weight loss test, 3613 pores cover 9612.1884 µ area due to uniform corrosion in humid environment by which 7.38% surface become porous. In salt spray test, PP (10.68%) and numbers of pores (6215) are some high due to direct spray of salt on surface of coupon. In this test, perimeter of pore (8598.8847 µ) are little bit high but A/O ratio are significantly low due to corrosion inhibition action of DAP which prevent the formation of pits on the surface of mild steel coupon by the action of chloride ion. In SO test, although numbers of pores (1941) are low as compare to weight loss test and salt spray test yet its A/O ratio is high due to pores having high depth because the perimeters of pores (6825.0334 µ) are also low than that of salt spray test . In Eschke test, depth of pores is comparatively low due to small size of pore of low perimeter (1958.7325 µ) but total objects (3787) are high due to roughness of surface by the action of corrodents of environment. Micrographs of all tests show that very smooth surface of mild steel coupon without any corrosion products are obtained after the treatment of coupon with DAP. Scanning Electron Microscopy: By comparison of SEM images of coupons treated with TMEDA and DAP as shown in table-10, it is clear that both VPCIs show very excellent corrosion inhibition properties against the aggressive environments. SEM image of TMEDA have no any corrosion product and no pits even at very high resolution of 15000. Clearness of SEM image of coupon treated with DAP provide the evidence in favor of very good PCIE of DAP. Table-5 Visual observations of mild steel coupons surface after performed various tests VPCI Salt Spray Test Eschke Test SO Test BlankClear pits and crevices were visibleUniform corrosionPitting corrosion TMEDA Clean surface No corrosion product Clean surface No corrosion product Clean surface No corrosion product DAP Slightly tarnishing No any pits and crevice No corrosion product Clear clean surface No corrosion product Slightly tarnishing No any pits and crevice No corrosion product 68.72%71.75%67.00%67.50%68.00%68.50%69.00%69.50%70.00%70.50%71.00%71.50%72.00%TMEDADAP Research Journal of Chemical Sciences ____ _ Vol. 4(6), 45-53, June (2014) International Science Congress Association Micrographs of mild steel coupons treated with TMEDA in different corrosion tests Micrograph of Wt. Loss Test Micrograph of SO 2 Test Total objects (TO), percentage porosity (PP), maximum perimeter (MP) of pore and maximum area (MA) covered by pore on mild steel coupon after treated with TMEDA after different corrosion tests Weight Loss Test 2119 Salt Spray Test 4645 SO 2 Test 1652 Eschke Test 1739 Micrographs of mild steel coupons treated with DAP in different corrosion tests Micrograph of Wt. Loss Test Micrograph of SO 2 Test Total objects (TO), percentage porosity (PP), maximum perimeter (MP) of pore and maximum area (MA) covered by pore on mild steel coupon after treated with DAP TO Weight Loss Test 3613 Salt Spray Test 6215 SO 2 Test 1941 Eschke Test 3787 _ _____________________________________________ _ International Science Congress Association Table- 6 Micrographs of mild steel coupons treated with TMEDA in different corrosion tests Micrograph of Wt. Loss Test Micrograph of Salt Spray Test Micrograph of Eschke Test Table-7 objects (TO), percentage porosity (PP), maximum perimeter (MP) of pore and maximum area (MA) covered by pore on mild steel coupon after treated with TMEDA after different corrosion tests TO PP MP(µ) 2119 8.29 3604.6711 4645 9.95 4399.6332 1652 10.86 5889.6992 1739 3.14 513.0056 Table-8 Micrographs of mild steel coupons treated with DAP in different corrosion tests Micrograph of Wt. Loss Test Micrograph of Salt Spray Test Micrograph of Eschke Test Table-9 Total objects (TO), percentage porosity (PP), maximum perimeter (MP) of pore and maximum area (MA) covered by pore on mild steel coupon after treated with DAP after different corrosion tests TO PP MP(µ) 3613 7.38 2855.8658 6215 10.68 8598.8847 1941 8.5 6825.0334 3787 6.44 1058.7325 _ ________ ISSN 2231-606X Res. J. Chem. Sci. 51 Micrographs of mild steel coupons treated with TMEDA in different corrosion tests Micrograph of Salt Spray Test Micrograph of Eschke Test objects (TO), percentage porosity (PP), maximum perimeter (MP) of pore and maximum area (MA) covered by pore on mild steel coupon after treated with TMEDA after different corrosion tests MA (µ 2 ) 15346.2604 24806.0942 25318.5596 1066.4820 Micrographs of mild steel coupons treated with DAP in different corrosion tests Micrograph of Salt Spray Test Micrograph of Eschke Test Total objects (TO), percentage porosity (PP), maximum perimeter (MP) of pore and maximum area (MA) covered by pore after different corrosion tests MA (µ 2 ) 9612.1884 18664.8199 14325.8476 6908.5873 Research Journal of Chemical Sciences ____ _ Vol. 4(6), 45-53, June (2014) International Science Congress Association SEM image of mild steel coupons treated with TMEDA and DAP after corrosion test SEM of coupon treated with TMEDA Mechanism of Inhibition: A deep analysis of the results reveals that the probable mechanism of inhib investigated VPCIs contains the following features: of lone pair donar N atoms in the molecule of TMEDA and DAP provide them specific active functional groups by which it can be easily adhere on the surface of mild steel due to base nature of steel and VPCI respectively. vapour pressure it saturates the environment around the mild steel and excludes the corrosive contents. iii. methyl groups directly attached with the lone pair donar atom in TMEDA enhance the basic strength of TMEDA molecule due to inductive effect by which it can easily neutralized the acidic environment around the mild steel. Conclusion As a result of experimental work carried out on the performance of investigated vapour phase corrosion inhibitors, a deep analysis of corrosion parameters obtained by corrosion testing experiments, morphology of mild steel coupon show that both investigated VPCIs (TMEDA and DAP) perform excellent corrosion inhibition properties against the environments of SO and NaCl at high relative humidity and high temperature. Due to basic nature and high vapour pressure, their vapours neutralize the acidity of atmospheric environment around mild steel and provide barrier for corrosive conten Eschke test and Salt spray test, the order of PCIE of TMEDA in comparison of DAP is exactly reversed in Weight loss test and SO test due to high basic properties and surface area of TMEDA molecule. Metallurgical research microscopy and Scanning ele ctron microscopy give an idea of the uniform type, crevice type and pitting type of corrosion on mild steel in humid environment, NaCl environment and in SO respectively. Acknowledgment We are very thankful to University Grant Commission, New Delhi for provide us financial support and Ch. Devi Lal University and Janta Girls College for laboratory and equipments facility for this research work. _ _____________________________________________ _ International Science Congress Association Table-10 mild steel coupons treated with TMEDA and DAP after corrosion test SEM of coupon treated with TMEDA SEM of coupon treated with DAP A deep analysis of the results reveals that the probable mechanism of inhib ition action of investigated VPCIs contains the following features: i. presence of lone pair donar N atoms in the molecule of TMEDA and DAP provide them specific active functional groups by which it can be easily adhere on the surface of mild steel due to acid- base nature of steel and VPCI respectively. ii. due to high vapour pressure it saturates the environment around the mild iii. presence of four methyl groups directly attached with the lone pair donar atom in TMEDA enhance the basic strength of TMEDA molecule due to inductive effect by which it can easily neutralized the acidic As a result of experimental work carried out on the performance phase corrosion inhibitors, a deep analysis of corrosion parameters obtained by corrosion testing experiments, morphology of mild steel coupon show that both investigated VPCIs (TMEDA and DAP) perform excellent corrosion inhibition properties against the aggressive and NaCl at high relative humidity and high temperature. Due to basic nature and high vapour pressure, their vapours neutralize the acidity of atmospheric environment around mild steel and provide barrier for corrosive conten ts. In Eschke test and Salt spray test, the order of PCIE of TMEDA in comparison of DAP is exactly reversed in Weight loss test and test due to high basic properties and surface area of TMEDA molecule. Metallurgical research microscopy and ctron microscopy give an idea of the uniform type, crevice type and pitting type of corrosion on mild steel in humid environment, NaCl environment and in SO environment We are very thankful to University Grant Commission, New Delhi for provide us financial support and Ch. Devi Lal University and Janta Girls College for laboratory and References 1.Corvo F., Atmospheric Corrosion of Steel in Humid Tropical climates: Humidity, Temperatu Sun Radiation, Corros, 40, 4 (1984) 2. 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