Iron corrosion inhibition with dihydrobis- and hydrotris-(1-pyrazolyl)borates

Purpose - The objective in the present paper is a better understanding of acidic corrosion inhibition by polypyrazolylborates on iron electrodes. Structural and electronic effects of these compounds are discussed in relation to the inhibiting efficiencies and absorption. Design/methodology/approach - Two polypyrazolylborates, i.e. dihydrobis(1-pyrazolyl) borate (Bp) and hydrotris(l-pyrazolyl)borate (Tp) were investigated as corrosion inhibitors for iron in 1 mol/l HCl and in 0.5 mol/l H2SO4 using Tafel measurements, linear polarization resistance and electrochemical impedance spectroscopy. Theoretical explanation between molecular parameters of these compounds and inhibitor efficiency (IE) was made using the MNDO SCF-MO method. Morphological changes of the reacted surfaces were monitored via SEM. Findings - Results obtained show higher inhibition effect of Bp than Tp. Inhibitors are more efficient in HCl than in H2SO4. Corrosion current and corrosion rate (CR) decrease with inhibitor concentration, while polarization and charge transfer resistance markedly increase from 10(-4) to 10(-2) Mol/l inhibitor concentration range. All impedance data are modeled with an equivalent circuit model. The semicircular shape of Nyquist plots is indicative of a charge transfer process occurring via a parallel resistor and capacitor. Originality/value - This study provides constructive information relative to corrosion inhibitor behavior of polypyrazolylborates in acids. Using the molecular modeling calculations, the compounds were characterized in terms of their structural properties and inhibition activity. It was noticed how exposure to the inhibitor solution changes the film morphology.