The inhibitive characteristics of Gmelina leaf extract on corrosion of mild steel in dilute 1 and 2 mol HNO3 solution was investigated using weight loss method and the electrochemical techniques. The SPECTRO analytical Instrument was used to determine the chemical compositions of the mild steel which gave the carbon content as 0.17% and other elemental compositions. The extract was subjected to some phytochemical analysis and some elements were determined as follows: alkaloid (0.08), Flavonoid (0.06) saponins (0.023), tannins (0.009) and phenol (0.023). A pH meter was also used to determine the pH level of all the chemical used. The concentrations of the leaf extract were varied from 10 to 60ml. The experimental duration for the weight measurement as observed from 168 hours to 1176 hours.  The values and data obtained were used to determine the corrosion rate (mm/yr) and the inhibition efficiency (%IE).  All the behaviour of the inhibitors gave the desired weight-loss time curves. It is evident that the weight loss of a mild steel electrode in the presence of inhibitors varies linearly over time, and the data shows that the corrosion rate was highest in 2mol HNO3, then 1 mol HNO3. A compact and coherent inhibition over film was formed on the mild steel, which lessens chemical attacks on the metal. Following the data generated, the corrosion rate decreased as the inhibition efficiency increases with respect to the addition of the leaf extract which was progressively from the control as follows: 10 ml, 20 ml, 30 ml, 40 ml, 50 ml, and 60 ml. The finding was also accomplished using Open Circuit Time Potential (OCPT), Tafel polarization; Inhibition was found to increase with increase in the inhibitor concentration.  The study revealed that the experimented extract serves as good inhibitors in preventing the materials from corroding. The leaf extracts is very much affordable especially in this part of the world.

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