In this experiment the electrochemical performance of a novel corrosion inhibitor on mild steel was investigated using potentiodynamic curves. The results indicate that inhibitor slows down the corrosion process on the mild steel with 1M hydrochloric acid solution by adding a protective coating on the steel. This coating is weakened as the temperature increases. The efficiency of this coating also increased as concentrations of the inhibitor increased.
Studies have shown that organic compounds that contain atoms such as nitrogen have reduced the attack of corrosion on steel. This is due to the lone pairs and p-electrons from the inhibitor forming a coordinate covalent bond with the metal, with electrons being transferred from the inhibitor to the metal. The strength of this bond is dependent on the electron density of the inhibitors functional group donating electrons and the polorizability of the functional group. At the point where the inhibitor is attached to the metal its electron density changes, which in turn delays/slows down the reactions that result in corrosion. The adsorption rates and covering capabilities of the organic inhibitor onto the metal surface influences how effective the inhibitor will be. The molecular structure and the surface changes of the metal and the type of electrolyte used will determine how well the inhibitor is adsorbed by the metal. When the metal is immersed in an aqueous phase the inhibitor will replace the water molecules that were initially adsorbed onto the metal. Other factors that can influence adsorption of the inhibitor include the surface charge of the metal, type of electrolyte and the inhibitors chemical structure. The efficiency of the inhibitor is dependent on the environment it is in, nature on the metal and the electrochemical potential at its interface. In industry where acid is commonly used, inhibitors are used to reduce the aggressive corrosive abilities of acids.
This experiment investigates how the organic inhibitor, 6-(4-hydrophenyl)-3-mercapto-7,8-dihydro-1,2,4triazolo4,3-b1,2,4,5,tetrazine, HT3 acts as corrosive inhibitor for mild steel in 1M HCl using potentiodynamic polarization.
Materials & methods
The reagent grade chemicals used for the synthesis were checked for impurities using Thin Layer Chromatography using silica gel as the stationary phase and a mixture of benzene, ethyl acetate and methanol or a toluene and acetone mixture as the mobile phase. Using a UV light (at 254 and 365nm) the spots were visualized. Other techniques used to test for purity of reagents include FT-IR and NMR.
The corrosion inhibitor was synthesized using the following procedure:
– 1.22g of 4-formylphenol and 1.46g 4-amino-5-hydrazinyl-3mecapto-1,2,4-trazole was mixed with 5.0g of ferric ammonium sulphate in 50ml of water
– The mixture was then refluxed to allow the reaction to occur
– After 6 hours, 10g ferric ammonium sulphate in 50ml of water was added to the reaction mixture
– It was then allowed to react for another 4 hours.
– TLC was used to track the reaction progress
– The mixture was then cooled and the precipitate was filtered, washed, dried and recrystallized
– An IR, 1H NMR and 13C NMR was run on the product to verify purity of the synthesized product.
Before analysis was conducted, the mild steel (working electrode) was cleaned using the ASTM standard procedure. The steel was then immersed into 1.0M HCl solution pumped with carbon dioxide gas, which was left unstirred. Each solution contained varying amounts of the inhibitor. The measurements were taken at a steady corrosion potential. The results were only taken 30 minutes after the steel was inserted to establish a stable steady state potential. the experiment was repeated 5 times and the average values reported.