4648205439410SUMMARYelectrochemical studies of novel corrosion inhibitor for mild steel in 1m hydrochloric acid
Cuwan le Roux: 217539386
00SUMMARYelectrochemical studies of novel corrosion inhibitor for mild steel in 1m hydrochloric acid
Cuwan le Roux: 217539386
An investigation on how a novel corrosion inhibitor acts on mild steel was conducted. The results showed that the inhibitor slowed the rate of corrosion of the steel when placed in an acidic environment, by adding a protective coating onto the steel. It was noted that an increase in the temperature weakened the coating of the inhibitor and became more efficient at high concentrations of the inhibitor.
Various studies proved that organic compound containing nitrogen atoms reduced the attack of corrosion on the steel. This phenomenon is a result of the compound lone pairs and p-electrons forming a covalent coordinate bond with the metal, the electrons are transferred from the compound to the metal. The electron density of the inhibitors electron donating functional group and the polarizability of the group influences the strength of the coordination bond, this leads to the delay of 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. For the protective coating to form onto the metal, the inhibitor needs to adsorb to the metal surface. The molecular structure and the surface charges of the metal and the electrolyte used will determine how well the inhibitor is adsorbed to 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. In industry, inhibitors are used on metals that are exposed very corrosive environments to protect the metal from corrosion and increase its lifespan.
This experiment investigates how the organic inhibitor, 6-(4-hydrophenyl)-3-mercapto-7,8-dihydro-1,2,4 triazolo4,3-b1,2,4,5,tetrazine, HT3 acts as corrosive inhibitor for mild steel in 1M HCl using potentiodynamic polarization.
Materials & methods
Before synthetic procedure of the inhibitor all chemical (reagent grade) were checked impurities using Thin Layer Chromatography. 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 keep track of the reaction as it progressed
The mixture was then chilled and the precipitate was filtered, washed, desiccated and recrystallized
An IR, 1H NMR and 13C NMR was run on the product to verify purity of the synthesized product.
Before experiment was performed, the mild steel (working electrode) was cleaned using the ASTM standard procedure. The specimens were then immersed into 1.0M HCl solution pumped with carbon dioxide gas, the system was left unstirred. Varying amounts of the inhibitor was added to each solution for the analysis on the effects of the inhibitors concentration on the corrosion. 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.
Results and Discussion
After the synthesis of the corrosion inhibitor the molecular weight was determined using Mass Spectroscopy to 248 g/mol. Further tests namely proton-NMR and C13 NMR were conducted on HT3 to verify that synthesis was successful.
The polarization measurements were taken firstly at varying concentrations of the HT3 at a constant temperature and secondly at constant concentration of HT3 increasing the temperature from 30°C to 60°C. Potentiodynamic curves were plotted for each. The effects of varying concentrations of HT3 resulted in change in the redox processes. HT3 was classified as a mixed type inhibitor since the change in corrosion potential (Ecorr) was greater than 85mV (429mV at 30°C). In the study of the effects of temperature on the HT3 efficiency the corrosion density (icorr) increased as the temperature increased. This phenomenon is explained as follows: HT3 is adsorbed to the metal surface and upon increasing the temperature leads to these molecules to desorb, consequently causing more of the metal being exposed to the acid leading to and increase the corrosion rate of the metal making the inhibitor less efficient. From the data collected in the analysis the inhibition efficiency (IE) was determined using the following equation:
IE%=i°corr- icorri°corr ×100Where:
i°corr = corrosion current density in absence of inhibitor
icorr = corrosion current density in presence of inhibitor
The following was noted from the analysis data:
The current density decreases as the concentration of the inhibitor increased.
The current density increased as the temperature of the acid solution increased.
The slopes of the curves all showed differences with increase in the HT3 concentration, this is evidence that HT3 influences the redox reactions.
The current potential values shifted towards the positive side at each increase in the concentration of HT3, proving that the protection from the corrosion for mild steel.
With an increase in solution temperature the current potential decreased significantly, consequently lowering the level of protection of the steel specimens.
The inhibition efficiency calculated increased as the HT3 concentration increased, but decreased at high temperatures.
Lastly when the temperature of both the acid solution and inhibitor is increased it was observed that the efficiency was lowered.
After completion of this experiment it was concluded that the synthesized inhibitor acts in a similar fashion when compared to other organic inhibitors. The inhabitation is due to the presence of the oxygen and nitrogen atoms in the compound. The effects of increasing the concentration and temperature influenced the efficiency of the inhibitor as previously discussed. The inhibitor is an appropriate corrosion inhibitor for mild steels and has a maximum inhibition efficiency of 74%.