IONIC RADII OF HALIDE IONS AND ITS CORROSION INHIBITORY ENHANCEMENT ON SIDA ACUTA.

Abstract

Corrosion Inhibitory efficiencies of Sida acuta leaf extracts in combination with halide ions (F-, Cl-, Br- and I-) as an enhancement on aluminum corrosion in H2SO4 was studied at room temperature (25oC) under varying acid concentrations of 0.05M, 0.1M and 0.5M using weight loss method. From the results obtained, Sida acuta acts as a good inhibitor for aluminum corrosion in acidic environment and it's inhibitory efficiencies increases with time of exposure. Based on the experimental results, the corrosion rate increases rapidly in the blank with a weight loss accelerating from 0.009g to 0.038g but with the introduction of plant extract, weight loss got reduced from 0.007g to 0.027g as well as having inhibition efficiency of 36% to 12% as the concentration of the acid was increased from 0.05M to 0.5M over the time series of 24 h to 96 h.. However, the inhibitory efficiency of Sida acuta in H2SO4 medium was further improved when halide ions were introduced. The weight loss of NaI moved from 0.002g to 0.011g and hence had the highest inhibition efficiency among the halide ions from 78% to 50% , NaBr showed a weight loss ranging from from 0.003g to 0.022g as well as having inhibition efficiency of 67% to 42% while NaCl showed a weight loss of 0.005g to 0.023g as well as having inhibition efficiency of 55% to 32% as the acid concentration was increased from 0.005M to 0.5M over the time exposure of 24 h to 96 h.. Nevertheless, the weight loss of NaF increases rapidly from 0.020g to 0.050g even more than the blank under the same reaction conditions and hence does not show inhibition efficiency. Therefore, the increase in inhibition efficiency (%I) and surface coverage (?) in the presence of the halides was found to be in a special sequence. . This synergistic effect increased according to the following pattern Cl- < Br -< I- suggesting a possible role by ionic radii in the corrosion inhibitory process which also increase in the order, F/F – ( 0.072/0.133nm), Cl/ Cl- (0.099/0.181nm) < Br/ Br - ( 0.114/ 0.195nm) < I/ I- ( 0.133/0.216 nm) . Fluoride ion does not show any inhibitory enhancement on Sida acuta owing to its least ionic radius..