Abstract
The inhibitive action of stem extracts of <i>Tetrapleura tetraptera</i> on mild steel corrosion in 1.0M & 5.0M H<sub>2</sub>SO<sub>4</sub> solutions was studied. The stem were dried under room temperature and mechanically ground into powder form. 100g of the stem powder were extracted with a mixture of methanol/water in the ratio of 4:1 using a Soxhlet extractor for 24 hours. The extracts were distilled at 60°C in a water bath until almost the entire methanol evaporated. 4.0g of the methanol extracts were digested in 1000ml of 1M H<sub>2</sub>SO<sub>4</sub> and 5M H<sub>2</sub>SO<sub>4</sub> and left to cool for 24 hours and the resulting solution was filtered and stored in a 1.0L volumetric flask. The stem extracts test solutions were prepared from the stock solution by dissolving 0.5g/L, 1.0g/L, 2.0g/L and 4.0g/L of the extracts in 1L solution of 1M H<sub>2</sub>SO<sub>4</sub> and 5M H<sub>2</sub>SO<sub>4</sub>. Phytochemical analysis was carried out and the result showed the presence of some secondary metabolites such as alkoliods, flavonoids, steroids, saponins and tannins. Weight loss (gravimetric) and gasometric techniques were used to determine the inhibition action of the stem of <i>Terapleaura tetraptera</i>. The results showed that stem of <i>Tetrapleura tetraptera</i> can function as good corrosion inhibitor in acid medium. Inhibition efficiencies (%I) of the stem of <i>Tetrapleura tetraptera</i> extracts was found to reach 73.69% & 50.39% for 1.0M H<sub>2</sub>SO<sub>4</sub> while for 5.0M was 83.31% & 79.54% for gravimetric and gasometric analyses respectively. The corrosion inhibition efficiency increased with increase in the concentration of the extracts and decreased with the increase in time and temperature. The corrosion inhibition efficiency exhibited by the <i>Tetrapleura tetraptera</i> stem extracts is attributed to the stronger adsorption of the phytochemicals present in the plant extracts unto the mild steel. The mechanism of adsorption proposed for the <i>Tetrapleura tetraptera</i> stem extracts is physical adsorption. The corrosion inhibition of the stem of <i>Tetrapleura tetraptera</i> extracts followed Langmuir, Tempkin and Freundlich adsorption isotherm for both 1.0M & 5.0M H<sub>2</sub>SO<sub>4</sub>.
Highlights
Corrosion control of metals and alloys is an expensive process and industries spend huge amount to control this problem
As a contribution to the current interest on environmentally friendly, green, corrosion inhibitors which are readily available and renewable, the present study investigates the use of extracts from the stems of Tetrapleura tetraptera as corrosion inhibitor for mild steel in H2SO4 medium using weight loss and gasometric techniques which has not been reported anywhere in literature to the best of our knowledge
The results indicated that the values of ∆:°ads are negative and this implied that the adsorption of methanol extracts of the stem of Tetratpleura tetraptera plant in 1.0M H2SO4 and 5.0M H2SO4 was spontaneous suggesting a physical adsorption mechanism [17]
Summary
Corrosion control of metals and alloys is an expensive process and industries spend huge amount to control this problem. The challenge is that it has low corrosion resistance especially in acidic environments [2]. Industrial processes such acid cleaning, pickling, descaling and drilling operations in oil and gas exploration use acidic solutions extensively and as such iron and steel vessels or surfaces used in these environments are prone to corrosion [3]. Synthetic organic inhibitors have been extensively applied but their use is being marred by their toxicity and high cost of manufacturing. This has prompted researchers to explore other areas to produce eco-friendly, cheap and biodegradable
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