Utilizing Rhizophora apiculata bark - water extract for protecting steel bar corrosion in aggressively mixed hydrochloric and sulfuric acids

The use of natural products as the corrosion inhibitors is a great attention owning to their high efficiency, abundance, availability, easy reproduction, and cost-saving. Herein, water extract derived from Rhizophora apiculata bark has been investigated for its potential inhibitor for steel bar in various acidic environments. Qualitative and quantitative analyses conducted to assess the content of some compounds in Rhizophora apiculata bark-water extract (RABWE), at the same time combining with ATR-FTIR and GC-MS, revealed the presence of potential components featuring electrostatic functional groups and heteroatoms in polyphenol, flavonoid, tannin, saponin compounds, etc. Surface analysis indicated that entire steel bar surfaces were demolished in the investigated solutions, resulting in the appearance of the wide and deep pits. Fortunately, the inhibited steel bar surface showed a denser protective layer formed on the steel bar surface in 1.0 M HCl solution. While less dense protective layer was observed on the inhibited steel bar surface in a mixture of 1.0 M HCl and 0.5 M H 2 SO 4 and the stretch steel bar surface was observed when it was exposed to H 2 SO 4 solution. The detecting component results also confirmed that protective layers were formed by an interaction of inhibitor species with iron oxides/hydroxides which were uniformly distributed in all inhibited steel bar surfaces. Electrochemical results showed that the corrosion rate of the steel bar agreed with surface analysis results as ranking in order of 1.0 M HCl < mixture of 1.0 M HCl and 0.5 M H 2 SO 4 < 0.5 M H 2 SO 4. Whereas inhibition performance was observed with the highest value (88.24 ± 0.66 %) belonged to higher protective film and polarization resistances for steel bars operated in 1.0 M HCl solution and lower inhibition performances were observed when steel bars were operated in an acidic mixture (83.39 ± 1.27 %) and 0.5 M H 2 SO 4 (76.00 ± 1.62 %), respectively.