Comparative study of Levofloxacin and its amide derivative as efficient water soluble inhibitors for mild steel corrosion in hydrochloric acid solution

The influence of 8-fluoro-3-methyl-9-(4-methyl-piperazin-1-yl)-6-oxo-2,3-dihydro-6H-1-oxa-3a-aza-phenalene-5-carboxylic acid or levofloxacin (P1) and newly synthesized 8-fluoro-3-methyl-9-(4-methyl-piperazin-1-yl)-6-oxo-2,3-dihydro-6H-1-oxa-3a-aza-phenalene-5-carboxylic acid-(5-methyl-pyridin-2-yl)-amide (P2) on corrosion inhibition of mild steel in 0.5 M hydrochloric acid solution was studied using weight loss and electrochemical techniques. Inhibition efficiency of P1 and P2 increased with concentration and decreased with temperature in the concentration range 0.14--0.35 mM in the temperature range 303--333 K. Thermodynamic parameters for dissolution and adsorption process were studied. Increase in energy of activation after the addition of inhibitors indicated formation of barrier film which prevents charge and mass transfer. Free energy of adsorption showed that the type of adsorption was neither physical nor chemical but comprehensive. The adsorption of the P1 and P2 on the mild steel surface was found to obey the Langmuir isotherm. Impedance measurement showed that there is increase in the polarization resistance and decrease in double layer capacitance after the addition of inhibitors. From polarization study as the shift in corrosion potential is more than 85 mV, both P1 and P2 are anodic type of inhibitors. Scanning electron microscope images confirm the formation of inhibitory film on mild steel surface. Quantum chemical calculation results well correlated with experimental results. Lower values of energy gap, ionization potential and hardness, higher value of softness make P2 better inhibitor compared to P1

Experimental and theoretical studies on the corrosion inhibition performance of molecules containing tert-butyl benzyl group on mild steel in acid media

The inhibition by (4-tert-butyl-phenyl)-acetic acid hydrazide (TPAH), 5-(4-tert-butyl-benzyl)-[1,3,4] oxadiazole-2-thiol (TBOT) and 5-(4-tert-butyl-benzyl)-4H-[1,2,4] triazole-3-thiol (TBTT) of mild steel corrosion in 0.5 M HCl was investigated using gravimetric and electrochemical techniques. These inhibitors acted more effectively at higher concentration and at lower temperature; among these TBTT being the most efficient inhibitor, which showed highest efficiency of 92.6% at 303 K and 4.8 mM concentration. Adsorption of TPAH followed Freundlich isotherm, whereas TBOT and TBTT followed Langmuir isotherm. Energy of activation for corrosion increased after the addition of inhibitors. Free energy of adsorption showed that all the three inhibitors get adsorbed to the mild steel surface by both physical and chemical processes. EIS studies confirmed that all the inhibitors offered higher charge transfer resistance to the corrosion current and this led to decreased double-layer capacitance. Polarization studies showed that all inhibitors emerged as mixed type. Surface studies confirmed that the pits caused by corrosion were decreased by protective film of inhibitors. Corelation of experimental data with quantum chemical parameters like ELUMO, energy gap, dipole moment, hardness and softness confirmed the superior performance of TBTT as compared to TPAH and TBOT

Adsorption and inhibition effect of 2,4-diamino-6-hydroxypyrimidine for mild steel corrosion in HCl medium: experimental and theoretical investigation, Ionics

2,4-Diamino-6-hydroxypyrimidine (2D6H) was examined as corrosion inhibitor of mild steel (MS) in 0.1 M HCl using potentiodynamic measurements, linear polarization resistance (LPR), scanning electron microscopy, electrochemical experiments, and quantum chemical calculations. All measurements show that the corrosion inhibition effectiveness is forthright compared to the concentration of 2D6H ranging from 0.5 to 10.0 mM. Adsorption of 2D6H on the MS surface in the presence of HCl is determined to obey Langmuir adsorption isotherm. The electronic features elucidated by quantum chemical calculations were associated with the experimental inhibition productivities. The mechanism of inhibition was revealed by Epzc measurements