Study Of The Corrosion Inhibition Of Mild Steel In Acid Media By N-heterocyclic Organic Ccompounds

Heterocyclic compounds have been widely used in corrosion protection of metals due totheir specific physical and chemical properties. As organic inhibitors, they are well absorbedon the fresh metal surface and form a dense and ordered layer which can provide greatpossibility to protect metal substrate from corrosion.In this thesis, organic compounds of Imidazolium Chloride and Cephalosporin arechosen as inhibitors for pure iron corrosion in sulfuric acid solution. The protective ability ofthe inhibitors in corrosive solutions are investigated by potentiodynamic polarization curves（Tafel curves） and electrochemical impedance spectroscopy （EIS） methods, and theelectrochemical kinetics parameters are analyzed with the software of Zenniumelectrochemical workstation. The surface analytical methods, Fourier transform infraredspectroscopy （FT-IR） was used to confirm the action of adsorption by detecting the group inthe organic molecules adsorbedon the metal surface. Phenomenon of chemical adsorption isproposed from the trend of inhibition efficiency with temperature and values G0adsobtained.The main contents of this paper are as the following:1. The inhibitive effect of Imidazolium Chloride compounds for the corrosion of carbonsteel in0.2M sulfuric acidThe present work is the study of the corrosion inhibition efficiency of ImidazoliumChloride organic inhibitors toward Q235steel in0.2M H₂SO₄. The work strategy includes theconventional weight loss method, electrochemical impedance spectroscopy （EIS）, adsorptionstudies and quantum chemical calculations. Polarization curves for Q235steel in acid mediumwith and without Imidazolium Chloride organic inhibitors were also used to measure theinhibitive efficiency. And when the Q235steel electrode is covered with ImidazoliumChloride, both the cathodic current density and the anodic current density reduce markedly,which indicates the inhibition of both the anodic and the cathodic electrochemical processes.Results of electrochemical measurements show that Imidazolium Chloride compounds haveprotected Q235steel electrode against corrosion to some extent. In order to explain theexperimental results, Scanning electron microscopy was applied to confirm the adsorptionfilm of Imidazolium Chloride formed on the carbon steel surface. Adsorption of inhibitormolecules on the carbon steel surface showed Langmuir isotherm model in both acid media.The optimized structure of Imidazolium Chloride and other parameters were calculated bycomputational quantum chemical methods.2. The inhibitive effect of Cephalosporin compounds for the corrosion of iron in0.1M sulfuric acidThe inhibitive effect of Cephalosporin compounds for corrosion of iron in0.1M H₂SO₄has been investigated using electrochemical impedance spectroscopy （EIS）, potentiodynamicpolarization, weight loss and SEM. Impedance spectra demonstrated that the values ofcharge-transfer resistance increased when adding these inhibitors into0.1M H₂SO₄.Potentiodynamic polarization results showed that these compounds decreased both cathodicand anodic corrosion current densities of iron in0.1M H₂SO₄. Results of weight lossmeasurement showed these compounds caused the decrease of corrosion rate of iron in0.1MH₂SO₄. Generally speaking, inhibition efficiency depends on the concentration and the type ofthe compound. The inhibition efficiency of the investigated compounds increased withincreasing concentration of these compounds. Among the investigated compounds,ceftriaxone sodium was the best inhibitor for the corrosion of iron. Thermodynamicparameters indicated the adsorption of the investigated compounds on the carbon steel surfacefollowed Langmuir isotherm model. SEM analysis confirmed that the corrosion of carbonsteel surface had been inhibited by these inhibitors.The groups of Cephalosporin moleculeswere detected by Fourier transform infrared （FT-IR） spectroscopy. Results show that thecharacterization peaks corresponding to the groups in the compounds were all detected andthis confirms the appearance of Cephalosporin on the iron surface.