Evaluation of Vitellaria Paradoxa Bark as Corrosion Inhibitor on Mild Steel

ABSTRACT

In this work, the potentials of Vitellaria Paradoxa (African shea tree) bark extract as corrosion inhibitor on mild steel was investigated in 1M HCL. Corrosion in industries and all other ways of life must be avoided as its consequential effects cost heavy loss to economy and lives. There are several conventional methods of converting corrosion such as coating but with limitations of challenges especially to health and high cost of application. Recent researches have focus on using natural organic materials such as vegetable seeds as inhibitors for preventing corrosion especially in food processing industries. Extraction was carried out using Maceration (Cold water) extraction method. The weight loss method was employed to determine corrosion rate by varying the concentration of the extract (0.0,0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 g/dm3). The effect of temperature on the corrosion behavior of mild steel was studied in the temperature range 313-343 k. Other thermodynamic parameters of interest to corrosion study evaluated at elevated temperatures were activation energy, Gibb’s energy, heat of adsorption and equilibrium constant. Corrosion rates for all concentration of Vitellaria Paradoxa bark extract decreased steadily with increasing exposure time. The inhibitive efficiency of Vitellaria Paradoxa Leaves extract was 91.5% at room temperature, over immersion period of 24 hours at extract concentration 1.0g/dm3. While at elevated temperature, the corrosion rate increases with temperature. Results of activation energy, Gibb’s energy, heat of adsorption and equilibrium constant ranged from 35.1024 to 49.5337 KJ/mol, -13.3580 to -14.5944 KJ/mol, -14.8872 to -26.3697 KJ/mol and 4.73 to 1.95 respectively. The values of activation energy are lower than the threshold value of 80KJ/mol, required for Chemical adsorption, hence the adsorption is physical adsorption or physisorption. Gibb’s energy values are negative and less than the threshold value of -20KJ/mol required for Chemical Absorption, which confirms the thermodynamic mechanism to be physical adsorption. Heat of adsorption values were negative which means exothermic in nature, hence physical adsorption took place. Equilibrium constant value reduced from 4.73 to 1.95. This implies that the extracts lose its adsorption strength on the metal surfaces as temperature increases, hence decrease in inhibition efficiency. The presence of Vitellaria Paradoxa still reduces the corrosion rate across all tested temperatures. The least Corrosion rate of 25.83×10^(-2)mm/yr with higher inhibitor efficiency of 79.42% was obtained at a temperature of 303K. This suggests that the inhibitor remains effective even at elevated temperatures, although its efficiency might decrease slightly as temperature increases. Based on the results, it can be concluded that Vitellaria Paradoxa can conveniently be used as inhibitor for mild steel.