Abstract:
Corrosion is a destructive process or decreases of metal quality because of the reaction with corrosive environment. One of the methods that able to decrease corrosion rate is by the addition of an inhibitors into corrosive media. Tannin is a component that can be extracted from natural material to be used as an inhibitor. Gambier leaves is one of natural materials which contains of tannin. The purpose of this research is to get the best concentration of inhibitor and inhibition efficiency from extracted gambier leaves by varying the contact time and pH of corrosive media in decreasing corrosion rate. This research was done by extracting tannin from gambier leaves with soxhletation method by using ethanol-water solvent with comparison 1:4 and then evaporated to get the condensed extract of gambir leaves. The research parameters is concentrations of inhibitor(1000, 3000, and 5000) ppm, contact time variation (5, 10, 15, 20) days, and pH (3,6,9) of sea water. Examination is conducted with gravimetric method to calculate weight loss of metal. The result of this research : the best concentration of inhibitor is 5000 ppm, contact time is 20 days and the lowest corrosion rate is 0,000507 gr/cm2 per day with inhibition efficiency is 60,345% and pH inhibitor variation from extracted gambier leaves is effective in decreasing corrosion rate at pH ±9 of sea water and contact time 20 days with the lowest corrosion rate are 0,000853 gr/cm² per day at concentration 1000 ppm, 0,000590 gr/cm².day at concentration 3000 ppm, and 0,000372 gr/cm².day at concentration 5000 ppm.
