•Novel benzimidazole derivatives inhibitors have been studied.•Efficiency increases with increasing the number of benzimidazole segments.•Inhibition efficiency depends on the temperature and concentration of HCl medium.•The inhibitors adsorb on mild steel surface both physically and chemically.Three novel benzimidazole derivatives, 2-aminomethyl benzimidazole (ABI), bis (2-benzimidazolylmethyl) amine (BBIA) and tri (2-benzimidazolylmethyl) amine (TBIA), have been studied as inhibitors for mild steel in 1.0 M HCl. The three compounds prevent mild steel from corrosion by adsorption on the steel surface and forming insoluble complex with ferrous species. Inhibition efficiency increases with the increase in the number of benzimidazole segments in the molecules (TBIA > BBIA > ABI). Protection efficiency of the inhibitors depends on concentration of inhibitor, temperature and concentration of hydrochloric acid.

Inhibition performance of 2-(4-pyridyl)-benzimidazole (PBI) against corrosion of mild steel in 1.0 M HCl was investigated by weight loss and electrochemical measurements. The inhibition efficiency increased with increasing inhibitor’s concentration, but decreased with the increase in temperature and concentration of the acid. The theoretical results from DFT and MD simulations reveal that adsorption of PBI depends on the formation of coordinative bonds between PBI molecule and iron surface, and the binding energy between PBI molecule and iron surface is the highest among the three studied compounds.Highlights► Excellent inhibition efficiency of 2-(4-pyridinyl)-benzimidazole (PBI). ► Effects of temperature and concentration of acidic media. ► Active sites and capability of adsorption. ► Nearby flat orientation of PBI on iron surface and highest interaction energy.

The effects of sulfate and BHTPMP (Bis (hexamethylene) triaminepentakis (methylene phosphonic acid)) on the crystallization rate, phase composition and morphology of calcium carbonate have been studied. It was observed that sulfate reduces the nucleation rate and favors the formation of aragonite form in the calcium carbonate precipitate. Moreover, in the presence of sulfate the rhombohedral morphology of the calcite crystals is modified, and during the formation of calcite, the development of {1 0 4} faces are more significantly prohibited than {1 1 0} faces. In the presence of sulfate together with BHTPMP, the crystallization process is inhibited and the modified morphology and the dominant calcite form are observed in the solid. The results from molecular dynamics simulations show the more strong combination of sulfate with calcite surface, in particular the {1 0 4} face, in comparison with the aragonite surface. The strong interaction of BHTPMP with sulfate and the aragonite surface favors the formation of the dominant calcite phase in the precipitate.Graphical abstractHighlights► Reduction in the crystallization rate of CaCO3 by sulfate ions. ► Modifying effects of sulfate on the morphologies, phases and crystal faces. ► Interactions between crystal faces and additives such as sulfate and BHTPMP.

Molecular dynamics (MD) simulations have been used to study the adsorption of dodecylamine (DDA) on iron surfaces in aqueous solution in this paper. In strong acidic solution the protonated form of DDA, DDAH, can adsorb on the iron surface preferentially, while in weak acidic solution containing chloride ions the adsorption of DDA and DDAH forms can occur simultaneously. Different results were obtained when different simulation factors were considered. In order to obtain the correct results, a model close to the realistic inhibition system was fabricated.Research highlights► MD simulations results of the adsorption of DDA on iron surfaces are strongly related to the simulation conditions. ► DDAH is main adsorption form in strong acidic solution. ► Chloride ions play an important role on the adsorption of DDA in weak acidic solution.

The corrosion inhibition of mild steel in 0.5 M H2SO4 and 1.0 M HCl by 2-amino-5-phenyl-1,3,4-thiadiazole (APT) has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the inhibition efficiency increases with the increase of APT concentration in both acids, and the higher inhibition efficiency is obtained in 0.5 M H2SO4. The adsorption of APT molecules on the steel surface obeys Langmuir adsorption isotherm in both acids, and occurs spontaneously. The molecular dynamics method has also been used to simulate the adsorption of ATP molecule and solvent ions on the iron surface. The results show that with the adsorption of sulfate ions the Fe + anion + APT system has the higher negative interaction energy comparing to the case of the adsorption of chloride ions.

The efficiency, as steel corrosion inhibitors in 0.5 M H2SO4, of two thiadiazole derivatives, 2-amino-5-(3-pyridyl)-1,3,4-thiadiazole (3-APTD) and 2-amino-5-(4-pyridyl)-1,3,4-thiadiazole (4-APTD), was investigated by polarization and electrochemical impedance spectroscopy. The protection efficiency increases with increasing inhibitors concentration, but the temperature has hardly effect on the inhibition efficiency of APTD. The adsorption of APTD on iron surface obeys the Langmuir isotherm. The experimental results show that the inhibition efficiency of 4-APTD is higher than that of 3-APTD, and the molecular dynamics (MD) simulations show that the adsorption of 4-APTD on iron surface has the higher binding energy than that of 3-APTD.

Synthesis of layered tetratitanate-n-C12H25NH2 intercalation compounds under microwave radiation was reported in this paper. Under microwave radiation, conversion of K2Ti4O9 to H2Ti4O9 in 1 M HCl solution needs only 1 h with 0.88 nm of interlayer distance, and the intercalation of n-C12H25NH2 could be achieved in 3 h. The formations of the layered hydrogen tetratitanate and the intercalation compounds were confirmed by X-ray diffraction, elemental, thermal gravimetric and differential scanning calorimetric analyses. The interlayer distance of the composite material could expand to 3.92 nm after the intercalation. High power of microwave is favorable during the intercalation of n-C12H25NH2 into the layered hydrogen tetratitanate.

Three thiadiazole derivatives, namely 5-phenyl-2-amino-1,3,4-thiadiazloe (APT), 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazloe (AMPT) and 5-(4-nitrophenyl)-2-amino-1,3,4-thiadiazloe (ANPT), have been synthesized as new inhibitors for the copper corrosion in 0.5 M H2SO4. The inhibition properties of the inhibitors were studied by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the order of inhibition efficiency is AMPT > APT > ANPT. The values of free energies of adsorption, as calculated from the Langmuir adsorption isotherm, indicate that the thiadiazole compounds adsorb on copper by a physisorption mechanism in 0.5 M H2SO4. The correlation between inhibition efficiency and quantum chemical parameters has been investigated by PM3 quantum chemical calculation.