COMPARISON OF CORROSION PROTECTION EFFICIENCY OF TWO KIND OF POLYSACCHARIDES EXTRACTED BY DIFFRENT LEGUMINOSAE PLANT

The green inhibitors are friendly with the environment. For this reason they are a good choice for corrosion protection. As green inhibitors, were used some kind of polysaccharides (galactomannan), extracted by leguminosae plant as green coffee beans, chickpeas and endosperms of carob tree (Ceratonia siliqua). Galactomannans are polysaccharides consisting of a mannose backbone with galactose side groups (more specifically, a (1-4)-linked beta-D-mannopyranose backbone with branchpoints from their 6-positions linked to alpha-D-galactose, i.e. 1-6-linked alpha-D-galactopyranose.). They have shown good inhibitor properties in protection of low allow carbon steel against the corrosion in acidic media (especially H2SO4) (1, 2). The aim of this study is to compare corrosion protection efficiency of these extracts, based on their solubility that depends by their mannose/galactose ratio. Material under investigation is low alloy carbon steel marked as: Steel 39, Steel 44, and iron B-500 (usually applied to concrete as reinforcing bars). The corrosion media is: 1M H2SO4 + 10-3mol/L Cl- (in form of NaCl). A Tafel polarization technique was used for investigation of corrosion inhibitor efficiency, accompanying with microscopic surface investigation of working electrode. Extract taken by green coffee beans is more soluble than that, taken by endosperms of carob tree. Use of them in the same concentration 0.5 g/L (better solubility for extract taken by endosperms of carob tree), referring the corrosion protection of steel 39 (the best case in the respect of corrosion sustainability), presents protection efficiency respectively 83.41% and 80.89%.