The inhibition effect of
The corrosion of metals remains a worldwide scientific problem as it affects the metallurgical, chemical and oil industries. The increasing interest in the manufacture of hydrochloric acid has created the need for obtaining information on the corrosion resistance of mild steel to hydrochloric acid attack [
In the present work, electrochemical and nonelectrochemical techniques were used to investigate the inhibition of mild steel corrosion by 5′-phenyl-2′,4′-dihydrospiro[indole-3,3′-pyrazol]-2(1
Molecular structure of 5′-phenyl-2′,4′-dihydrospiro[indole-3,3′-pyrazol]-2(1
Mild steel specimen of the size (3.5 × 1.5) − 0.5 was used for measurement of weight loss study. The strips were mechanically polished using 1/0, 2/0, 3/0, and 4/0 emery papers and finally degreased with the organic solvent trichloroethylene and dried before use. 1 M HC1 and 0.5 M H2SO4 solutions were prepared by the dilution of analytical grade HC1 and H2SO4 with double-distilled water, respectively. The concentration range of inhibitor used was (1 ppm, 3 ppm, 5 ppm, 7 ppm, and 9 ppm) in both the acids. The compound has been synthesized in 3 steps. The structural formula of the investigated compound is given below.
Weight loss measurements were carried out by weighing the specimens in triplicate before and after immersion in 100 mL acid solution for 3 hours in the absence and presence of inhibitor for various concentrations.
Electrochemical measurements were carried out in a glass cell with a capacity of 100 mL. A platinum electrode and a saturated calomel electrode were used as a counter electrode and reference electrode, respectively. The mild steel electrode was then placed in the test solution (uninhibited and inhibited solutions) for 10–15 minutes before electrochemical measurements. Electrochemical impedance spectroscopy (EIS) and Tafel polarization were conducted in an electrochemical measurement unit (model 1280 B Solartron, UK). The EIS measurement was made at corrosion potentials over a frequency range of 10 KHz to 0.01 Hz with signal amplitude of 10 mV. The Tafel polarization measurements were made after EIS for a potential range of −200 mV to +200 mV with respect to open circuit potential at a scan rate of 1 mV/sec.
The specimen used for surface morphological examination was immersed in acid (1 M HCl) containing higher concentration (9 ppm) for the inhibitor and blank for 3 hours. Then removed, rinsed quickly with distilled water, and dried. The analysis was performed on HITACHI model S-3000 H SEM. The IR spectra of the inhibitors were recorded on a Bruker Optik GmbH model no-Tensor 27 Spectrophotometer in the range 4000–400 cm−1 using KBr disc technique.
The inhibition efficiency with different concentration of the inhibitor (SPAH) on mild steel has been evaluated by weight loss measurements and the results are given in Table
Inhibition efficiencies of SPAH for the corrosion of mild steel obtained by weight loss measurements.
Name of the inhibitor | Inhibitor concentration (ppm) | Weight loss (g) | Corrosion rate (mpy) | Inhibition efficiency (%) | Surface coverage ( |
---|---|---|---|---|---|
1 M HCl | Blank | 0.0863 | 1227 | ||
1 | 0.0549 | 780 | 36.4 | 0.3638 | |
3 | 0.0447 | 635 | 48.4 | 0.4840 | |
5 | 0.0361 | 513 | 58.2 | 0.5816 | |
7 | 0.035 | 497 | 64.7 | 0.6465 | |
9 | 0.0261 | 371 | 69.8 | 0.6975 | |
| |||||
0.5 M H2SO4 | Blank | 0.1611 | 2290 | ||
1 | 0.0938 | 1333 | 41.8 | 0.4177 | |
3 | 0.0623 | 885 | 61.3 | 0.6132 | |
5 | 0.0424 | 603 | 73.7 | 0.7368 | |
7 | 0.0385 | 547 | 76.1 | 0.7610 | |
9 | 0.0342 | 486 | 78.8 | 0.7877 |
The effect of temperature on the performance of the SPAH (Table
Inhibition efficiencies of inhibitor for the corrosion of mild steel obtained by weight loss measurements at various temperatures.
Concentration of the inhibitor (ppm) | Temperature (K) | 1 M HCl | 0.5 M H2SO4 | ||
---|---|---|---|---|---|
Corrosion rate (mpy) | Inhibition efficiency (%) | Corrosion rate (mpy) | Inhibition efficiency (%) | ||
303 | 930 | 32.7 | 887 | 43.5 | |
313 | 1927 | 29.4 | 1151 | 37.2 | |
1 | 323 | 2294 | 27.1 | 5756 | 28.6 |
333 | 5211 | 16.0 | 9858 | 20.3 | |
343 | 10353 | 12.2 | 18019 | 15.0 | |
| |||||
303 | 759 | 54.1 | 733 | 53.3 | |
313 | 1595 | 41.6 | 785 | 50.0 | |
3 | 323 | 1902 | 39.6 | 3795 | 48.9 |
333 | 4375 | 28.8 | 7411 | 40.1 | |
343 | 9611 | 18.5 | 14975 | 29.4 | |
| |||||
303 | 623 | 54.9 | 452 | 71.2 | |
313 | 1296 | 52.5 | 631 | 65.6 | |
5 | 323 | 1535 | 51.2 | 3087 | 58.4 |
333 | 3411 | 45.0 | 5876 | 52.5 | |
343 | 8613 | 27.0 | 13380 | 36.9 | |
| |||||
303 | 529 | 61.7 | 409 | 73.9 | |
313 | 1117 | 59.1 | 588 | 67.9 | |
7 | 323 | 1441 | 54.2 | 2695 | 63.7 |
333 | 2857 | 50.5 | 5475 | 55.7 | |
343 | 7334 | 37.8 | 12502 | 41.1 | |
| |||||
303 | 461 | 66.7 | 341 | 78.3 | |
313 | 1015 | 62.8 | 452 | 75.3 | |
9 | 323 | 1237 | 60.7 | 2072 | 72.1 |
333 | 2499 | 59.7 | 4827 | 61.0 | |
343 | 5543 | 53.0 | 10114 | 52.3 |
The activation energies were calculated from the slopes of Arrhenius plots (Figure
Activation energies (
−Δ |
||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Name of the inhibitor |
|
1 M HCl | 0.5 M H2SO4 | |||||||||
HCl | H2SO4 | 303 K | 313 K | 323 K | 333 K | 343 K | 303 K | 313 K | 323 K | 333 K | 343 K | |
Blank | 26.07 | 58.97 | — | — | — | — | — | — | — | — | — | — |
SPAH | 48.84 | 76.02 | 6.32 | 6.09 | 6.05 | 6.12 | 5.52 | 7.80 | 7.64 | 7.43 | 6.27 | 5.45 |
Arrhenius plot for the corrosion of mild steel.
The thermodynamic functions such as the free energy of adsorption (
The negative values [
Some thermodynamic parameters Δ
Name of the inhibitor | Δ |
−Δ |
||
---|---|---|---|---|
1 M HCl | 0.5 M H2SO4 | 1 M HCl | 0.5 M H2SO4 | |
SPAH | 15.7 | 46.17 | 60.7 | 26.52 |
Free energy of adsorption of SPAH in in 1 M HCl and 0.5 M H2SO4 in the presence of SPAH 1 M HCl and 0.5 M H2SO4.
Figure (
Langmuir adsorption isotherm for inhibitor in 1 M HCl and 0.5 M H2SO4.
Temkin adsorption isotherm for inhibitor in 1 M HCl and 0.5 M H2SO4.
The electrochemical parameters such as corrosion potential
Potentiodynamic polarization parameters for the corrosion of mild steel in 1 M HCl and 0.5 M H2SO4 with and without inhibitor.
Name of the inhibitor | Inhibitor concentration (ppm) |
|
|
|
|
Inhibition efficiency (%) |
---|---|---|---|---|---|---|
1 M HCl | Blank | 1.6759 | −555.68 | 149.91 | 89.961 | |
1 | 1.3797 | −543.91 | 157.94 | 92.412 | 17.67 | |
SPAH | 5 | 1.1145 | −550.84 | 130.20 | 83.362 | 33.49 |
9 | 9.5813 | −544.70 | 150.50 | 90.651 | 42.82 | |
| ||||||
0.5 M H2SO4 | Blank | 16.99 | −444.62 | 113.48 | 231.18 | |
1 | 9.1947 | −536.55 | 273.62 | 123.04 | 45.88 | |
SPAH | 5 | 6.2370 | −534.52 | 249.93 | 101.00 | 63.29 |
9 | 5.6636 | −534.78 | 229.22 | 97.09 | 66.66 |
Polarisation curves of SPAH for mild steel in (a) 1 M HCl and (b) 0.5 M H2SO4.
The corrosion kinetic parameters such as charge transfer resistance
Impedance parameters for the corrosion of mild steel in 1 M HCl and 0.5 M H2SO4 with and without inhibitor.
Name of the inhibitor | Inhibitor concentration (ppm) | 1 M HCl | 0.5 M H2SO4 | ||||
---|---|---|---|---|---|---|---|
|
|
Inhibition efficiency (%) |
|
|
Inhibition efficiency (%) | ||
Blank | 136.53 | 1.1717 | 11.32 | 6.2030 | |||
1 | 154.83 | 2.1938 | 11.8 | 37.49 | 2.8020 | 69.8 | |
SPAH | 5 | 168.33 | 2.7641 | 18.9 | 55.50 | 2.3966 | 79.6 |
9 | 227.45 | 1.6896 | 40.0 | 60.94 | 2.4798 | 81.4 |
Nyquist plots of SPAH for mild steel in (a) 1 M HCl and (b) 0.5 M H2SO4.
The results obtained from impedance show a similar trend for the tested compound as those obtained from potentiodynamic polarization and weight loss measurement but yield different value of IE due to different experimental conditions.
SEM photograph of the metal sample in the presence and absence of inhibitor are shown in Figures
(a) SEM micrographs of 1 M HCl, (b) 1 M HCl + SPAH.
The calculated values of the quantum chemical parameters obtained using the Hartree-fock- Density functional theory (HF-DFT) by Becke 3 Lee, Yang, and Parr (B3LYP) method with 6–31G* basis set of Spartan′06 V112 program are presented in Table
Quantum chemical parameters obtained by Spartan’06.
Quantum chemical parameters | SPAH |
---|---|
Molecular formula | C16H13N3O |
Total energy (a.u) | −856.984 |
|
−5.32 |
|
−0.92 |
Δ |
4.4 |
Dipole moment ( |
4.68 |
Molecular weight (amu) | 263.300 |
Polarizability | 62.02 |
Cosmo area (Å2) | 281.24 |
Cosmo volume (Å3) | 267.31 |
Global hardness ( |
2.20 |
Global softness ( |
0.45 |
Electronegativity ( |
3.12 |
The negative sign of the
(a–d) Optimised Geometry, Mulliken charges, HOMO and LUMO density distribution of SPAH.
The main conclusions drawn from this study are SPAH efficiently inhibits the corrosion of mild steel in 1 M HCl and 0.5 M H2SO4 media. SPAH behaves as mixed type inhibitor. Adsorption of SPAH on the surface of mild steel from 1 M HCl and 0.5 M H2SO4 obey’s Langmuir and Temkin’s adsorption isotherm. Reduction in the values of
The authors thank the Director of ICP centre, CECRI, Karaikudi, for providing the facilities of electrochemical studies and SEM facilities and Dr. Jeyakanthan, Head of the Department of Bioinformatics, Alagappa University, Karaikudi, for providing the Spartan software facilities, and Management and Principal, PSGR Krishnammal college for Women, Coimbatore for providing necessary facilities and encouragement.