Xanthione: A new and effective corrosion inhibitor for mild steel in sulphuric acid solution

The adsorption and inhibition effect of xanthione (XION) on mild steel in 0.5 M H₂SO₄ at 303–333 K were studied using gravimetric and UV–visible spectrophotometric methods. The results obtained show that XION acts as an effective corrosion inhibitor for mild steel in sulphuric acid and inhibition efficiency reaches 98.0% at a very low inhibitor concentration of 10 μM. Inhibition efficiency was found to increase with increase in XION concentration but decreased with temperature suggesting physical adsorption mechanism. Arrhenius law and its transition equation lead to estimate the activation parameters of the corrosion process. XION inhibits the corrosion of mild steel effectively at moderate temperature and adsorbs according to the Langmuir isotherm. Thermodynamic parameters governing the adsorption process have been calculated and discussed. The UV–visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a XEN–Fe complex. Attempt to correlate the molecular structure to quantum chemical indices was made using density functional theory (DFT).     

Synthesis,characterization and corrosion inhibition efficiency of 2-(6-methylpyridin-2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline on mild steel in sulphuric acid

Phenanthroline derivative, 2-(6-methylpyridin-2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline (MIP) was synthesized and characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR, and single crystal X-ray diffraction study. MIP was evaluated as corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solution using gravimetric and UV–Visible spectrophotometric methods at 303–333 K. Results obtained show that MIP acts as inhibitor for mild steel in H₂SO₄ solution. The inhibition efficiency was found to increase with increase in MIP concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process using statistical physics were calculated and discussed. The UV–Visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a MIP-Fe complex.     

Inhibitive action of ethanol extracts from Nauclea latifolia on the corrosion of mild steel in H2SO4 solutions and their adsorption characteristics

The inhibitive action of ethanol extracts from leaves (LV), bark (BK) and roots (RT) of Nauclea latifolia on mild steel corrosion in H₂SO₄ solutions at 30–60 °C was studied using weight loss and gasometric techniques. The extracts were found to inhibit the corrosion of mild steel in H₂SO₄ solutions and the inhibition efficiencies of the extracts follow the trend: RT > LV > BK. The inhibition efficiency increased with the extracts concentration but decreased with temperature rise. Physical adsorption of the phytochemical components of the plant on the metal surface is proposed as the mechanism of inhibition. The adsorption characteristics of the inhibitor were approximated by the thermodynamic-kinetic model of El-Awady et al.     

Essential oil of Salvia aucheri mesatlantica as a green inhibitor for the corrosion of steel in 0.5 M H2SO4

Essential oil of aerial parts of Salvia aucheri Boiss. var. mesatlantica was obtained by hydrodistillation and analyzed by GC and GC/MS. The oil was predominated by camphor (49.59%). The inhibitory effect of this essential oil was estimated on the corrosion of steel in 0.5 M H₂SO₄ using electrochemical polarization and weight loss measurements. The corrosion rate of steel is decreased in the presence of natural oil. The inhibition efficiency was found to increase with oil content to attain 86.12% at 2 g/L. Polarization curves revealed that the oil of S. aucheri mesatlantica acts as mixed type inhibitor with a strong predominance of anodic character. The temperature effect on the corrosion behavior of steel in 0.5 M H₂SO₄ without and with the inhibitor at 2 g/L was studied in the temperature range from 303 to 343 K, the associated activation energy have been determined. The adsorption of oil on the steel surface was found to obey Langmuir’s adsorption isotherm.     

Inhibition effect of hexadecyl pyridinium bromide on the corrosion behavior of some austenitic stainless steels in H2SO4 solutions

The inhibition effect of hexadecyl pyridinium bromide (HDPB) as a cationic surfactant on the corrosion behavior of some Egyptian austenitic stainless steel SS 304L, SS 316H and SS 304H in 0.5 M H₂SO₄ solutions was investigated by using potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results indicate that HDPB is a good inhibitor for the samples under investigation in 0.5 M H₂SO₄ solutions. In addition, the inhibition efficiency η% increases with the inhibitor concentration while decreases with the increasing temperature referring to physical adsorption. The adsorption of the inhibitor obeys a Temkin adsorption isotherm. Polarization curves show that HDPB is a mixed inhibitor in H₂SO₄ solutions. The results obtained from polarization and impedance measurements are in good agreement. Activation-free energies, enthalpies, and entropies for the inhibition process of HDPB were determined.     

Inhibition of cold rolled steel corrosion in sulphuric acid solution by 2-mercapto-1-methylimidazole: Time and temperature effects treatments

2-Mercapto-1-methylimidazole (MMI) has been evaluated as a corrosion inhibitor for cold rolled steel in aerated 2 M H₂SO₄ by gravimetric method. The effect of MMI on the corrosion rate was determined at various immersions time and concentrations. The effect of the temperature on the corrosion behaviour with addition of different concentrations of MMI was studied in the temperature range 30–60 °C. The MMI acts as an effective corrosion inhibitor for cold rolled in sulphuric acid medium. The inhibition process is attributed to the formation of an adsorbed film of MMI on the metal surface which protects the metal against corrosion. The protection efficiency increased with increase in inhibitor concentration at various immersions time and decreased with increase in temperature. Adsorption of MMI on the cold rolled steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined.     

Spirulina platensis – A novel green inhibitor for acid corrosion of mild steel

The inhibition of the corrosion of mild steel in 1 M HCl and 1 M H₂SO₄ by Spirulina platensis has been studied at different temperatures viz., 303 K, 313 K and 323 K by weight loss method, potentiodynamic polarization method, electrochemical impedance spectroscopy measurements and SEM analysis. The inhibition efficiency increased with increasing concentration of the inhibitor in both HCl and H₂SO₄ media. The results of weight loss studies correlated well with those of impedance and polarization studies. From the results of weight loss studies at various temperatures, the mode of adsorption is confirmed to be physisorption. Further the adsorption has been found to follow Temkin isotherm. From this isotherm, the free energy of adsorption (ΔG) and entropy (ΔS) are calculated. The study reveals the corrosion inhibition potential of S. platensis in both the acid media, thus bringing to light another facet of this microalga as it has so far been used only to produce antioxidant principles, finding extensive use in medicine especially as neutraceutical.     

Ternary non-noble metal chalcogenide (W–Co–Se) as electrocatalyst for oxygen reduction reaction

In this study, a catalyst based on a novel ternary non-noble metal chalcogenide, W–Co–Se, was synthesized for the oxygen reduction reaction (ORR) in acidic medium. The non-noble metal chalcogenide catalyst was electrochemically stable in the potential range of 0.05–0.8 V versus NHE in 0.5 M H₂SO₄ aqueous solution. This catalyst demonstrated significant catalytic activity towards the ORR, showing the ORR onset potential at 0.755 V versus NHE in 0.5 M H₂SO₄ at 25 °C. Such high activity might be attributed to the electronic structure of non-noble metals modified by chalcogen.     

The irreversible characteristic analysis of thiourea on copper electrodes in aqueous 0.5 mol/L sulphuric acid

The reaction behaviors of various concentrations thiourea (TU) on copper electrode in 0.5 mol/L H₂SO₄ solution were investigated by electrochemical impedance spectroscopy (EIS) and single crystallogram. The loop at low frequency shifts negatively with the concentration of TU increasing to 0.25 mol/L in the research. It reveals the adsorption of TU converts the acidic corrosion of copper electrode to the final irreversible complexation of copper and TU. Furthermore, the dependence of irreversiblility on Cu(I)–TU complex surface coverage (θ) was discussed by an EIS mathematical model. The three-dimensional supermolecular network structure of [Cu₂(NH₂CSNH₂)₆]SO₄ · H₂O enhances the stability of the complex, and leads to the final irreversibility of whole reaction.     

Synergistic inhibition effects between leaves and stem extracts of Sida acuta and iodide ion for mild steel corrosion in 1 M H2SO4 solutions

The synergistic action caused by iodide ions on the corrosion inhibition of mild steel in 1 M H₂SO₄ by leaves and stem extracts of Sida acuta was studied using weight loss and hydrogen evolution methods at 30–60 °C. It was found that the leaves and stem extracts of S. acuta inhibited the acid induced corrosion of mild steel. Addition of iodide ions enhances the inhibition efficiency to a considerable extent. The inhibition efficiency increases with increase in the iodide ion concentration but decreases with rise in temperature. Adsorption of the extracts alone and in combination of iodide ion was found to obey Freundlich adsorption isotherm at all temperatures studied. Inhibition mechanism is deduced from the temperature dependence of the inhibition efficiency as well as from assessment of kinetic and activation parameters that govern the processes. The synergism parameter (S₁) is defined and evaluated from the inhibition efficiency values. This parameter for the different concentrations of iodide ions from the two techniques employed is found to be greater than unity indicating that the enhanced inhibition efficiency of the extracts caused by the addition of iodide ions is due to synergism.     

Inhibition of aluminium and mild steel corrosion in acidic medium using Gum Arabic

The corrosion behaviour of mild steel and aluminium exposed to H₂SO₄ solution and their inhibition in H₂SO₄ containing 0.1–0.5 g/L Gum Arabic (GA) used as inhibitor was studied at temperature range of 30–60 °C using weight loss and thermometric techniques. Corrosion rate increased both in the absence and presence of inhibitor with increase in temperature. Corrosion rate was also found to decrease in the presence of inhibitor compared to the free acid solution. Inhibition efficiency increases with increase in concentration of the inhibitor reaching a maximum of 37.88% at 60 °C for mild steel and 79.69% at 30 °C for aluminium at 0.5 g/L concentration of GA. The inhibitor, GA was found to obey Temkin and El-Awady et al. thermodynamic kinetic adsorption isotherm for mild steel and aluminium respectively from the fit of the experimental data at all concentrations and temperatures studied. The phenomenon of chemical adsorption is proposed for mild steel corrosion, while physical adsorption mechanism is proposed for aluminium corrosion. Results obtained for the kinetic/thermodynamic studies indicate that the adsorption of GA onto the metals surface was spontaneous. GA is a better corrosion inhibitor for aluminium than for mild steel.     

Interaction parameters and (solid + liquid) equilibria calculation for KCl–H2O–HCl–C2H5OH,K2SO4–H2O–H2SO4 and K2SO4–H2O–C2H5OH mixed solvent-electrolyte systems

This work deals with the prediction and experimental measurements of the (solid + liquid) equilibrium (SLE) in acid medium for industrial purposes. Specific systems including KCl–ethanol–water–HCl and K₂SO₄–water–H₂SO₄ were analyzed. At first, a critical discussion of SLE calculations was given, based on the well-known UNIQUAC extended and LIQUAC models. Two new proposals were derived, considering the explicit necessity of a new reference state for SLE calculations for the studied (solvents + acid) mixtures. The solubility of KCl in water–ethanol–HCl mixed solvents was measured in the temperature range of 300.15 to 315.15 K using an analytical gravimetric method. These results combined with some other experimental data reported in the open literature let us to propose a set of parameters for the new models. They included the interaction parameters between ethanol and the H⁺ ion. The prediction capability of the new models, for calculations in acid medium, was illustrated. Experimentally, it was observed that the (K₂SO₄ + water + H₂SO₄) system presented the unusual behavior of increasing K₂SO₄ solubility with an increase in the sulfuric acid concentration. This was accurately predicted by the newly proposed models.     

Visible light photocatalysis by a Titania–Rhodium(III) complex

Titania hybrid photocatalysts containing 0.5, 1.0, 2.0, and 5.0 wt% of rhodium(III) were prepared by chemisorption of RhCl₃ × 3H₂O onto anatase hydrate powder (TH). Analytical data suggest that a titania–trichlororhodate complex is produced containing a [TiO₂]–O–Rh bond.Similar results are found in the case of modification by RhBr₃ × 3H₂O. Diffuse reflectance spectra exhibit an absorption shoulder throughout the visible region down to 700 nm. Photoelectrochemical measurements indicate that the quasi-Fermi level of electrons is gradually shifted to more anodic potentials with increasing rhodium loading reaching a value of ?0.34 V at pH 7 (vs. NHE) in the case of 5.0%RhCl₃/TH. This is more anodic by 210 mV as compared to unmodified TH. Upon visible light irradiation this photocatalyst induces a fast mineralization of 4-chlorophenol whereas cyanuric acid, which is known to be mineralized in the presence of the analogous Pt(IV) modified titania, is not degraded.     

Electrochemical and XPS studies of a Nb-containing Ti-based glass-forming alloy system in H2SO4 solution

The corrosion behaviors of Ti₄₀Zr₂₅Ni_12 -xNb_xCu₃Be₂₀ (x = 0, 4, 8, and 12 at.%) alloys in 0.5 mol/L H₂SO₄ solution were studied, aiming to establish the relationship between Nb content and corrosion resistance. The addition of Nb element gives rise to a clear microstructural evolution, from a completely amorphous structure for the alloys without Nb and with 4% Nb alloys to an amorphous/crystalline composite structure for the alloys with 8% and 12% Nb. The alloy with higher Nb content exhibits better corrosion resistance, which can be attributed to the formation of Ti^4 +-, Zr^4 +-, and Nb^5 +-enriched highly protective surface film in corrosive solutions.     

Spatial determination of diffusible hydrogen concentrations proximate to pits in a Fe–Cr–Ni–Mo steel using the Scanning Kelvin Probe

The diffusible hydrogen concentration (C_H,diff) was mapped spatially, proximate to acidic corrosion pits formed in MgCl₂ droplets, on an ultra-high strength stainless steel using a Scanning Kelvin Probe (SKP). A secondary hardened martensitic stainless steel (Fe–11Ni–12Cr–1Mo–0.005C–0.02Mn wt%) was evaluated. Predetermined, uniform C_H,diff levels quantified by electrochemical extraction after homogeneous cathodic charging, were calibrated versus the SKP potential at 57% RH (0.16 kPa H₂O, 20.26 kPa O₂, 79.03 kPa N_2, and 0.55 kPa residual gas species) [1]. Calibration enabled estimation of C_H,diff near pitted surfaces. Cross-sections of corrosion damage sites after pitting were also examined to determine the distribution of the C_H,diff perpendicular to the exposure surface.     

An acidic cellulose–chitin hybrid gel as novel electrolyte for an electric double layer capacitor

A novel acidic cellulose–chitin hybrid gel electrolyte including binary ionic liquids (ILs) with an aqueous H₂SO₄ solution was prepared for an electric double layer capacitor (EDLC). Its electrochemical characteristics were investigated by galvanostatic charge–discharge measurements. The test cell with a hybrid gel electrolyte shows a specific capacitance of 162 F g^?1 at room temperature, which is higher than that for a cell with an H₂SO₄ electrolyte, 155 F g^?1. This hybrid gel electrolyte exhibits excellent high-rate discharge capability in a wide range of current densities as well as an aqueous H₂SO₄ solution. The discharge capacitance of the test cell can retain over 80% of its initial value in 100,000 cycles even at a high current density of 5000 mA g^?1.     

Thermodynamic aspects of solubility,solvation and partitioning processes of some sulfonamides

The thermodynamic aspects of sublimation processes of three sulfonamides with the general structures C₆H₅–SO₂NH–C₆H₄–R (R = 4-NO₂) and 4-NH₂–C₆H₄–SO₂NH–C₆H₄–R (R = 4-NO₂; 4-CN) were studied by investigating the temperature dependence of vapor pressure using the transpiration method. These data together with those obtained earlier for C₆H₅–SO₂NH–C₆H₄–R (R = 4-Cl) and 4-NH₂–C₆H₄–SO₂NH–C₆H₄–R (R = 4-Cl; 4-OMe; 4-C₂H₅) were analyzed and compared. A correlation was derived between sublimation Gibbs free energies and the sum of H-bond acceptor factors of the molecules. Solubility processes of the compounds in water, phosphate buffer with pH 7.4 and n-octanol (as phases modeling various drug delivery pathways) were investigated and corresponding thermodynamic functions were calculated as well. Thermodynamic characteristics of the sulfonamides solvation were evaluated. Also in this case a correlation between solubility/solvation Gibbs free energy values and the sum of H-bond acceptor factors was observed. For the sulfonamides with various substituents at para-position the processes of transfer from one solvent (water or buffer) to n-octanol were studied by a diagram method combined with analysis of enthalpic and entropic terms. Distinguishing between enthalpy and entropy, as is possible through the present approach, leads to the insight that the contribution of these terms is different for different molecules (entropy- or enthalpy-determined). Thus, in contrast to the interpretation of only the Gibbs free energy of transfer (extensively used for pharmaceuticals in the form of the partition coefficient, log P), the analysis of thermodynamic functions of the transfer process provides additional mechanistic information. This may be important for further evaluation of the physiological distribution of drug molecules and may provide a better understanding of biopharmaceutical properties of drugs.     

V2O5·0.6H2O nanoribbons as cathode material for asymmetric supercapacitor in K2SO4 solution

V₂O₅·0.6H₂O nanoribbons were prepared and their electrochemical behaviors in K₂SO₄ aqueous solution were investigated. Results show for the first time that K⁺ ions could intercalate/deintercalate reversibly in the V₂O₅·0.6H₂O lattice. An asymmetric supercapacitor activated carbon/0.5 mol/l K₂SO₄/V₂O₅·0.6H₂O was successfully assembled, which could be cycled reversibly in the voltage region of 0–1.8 V. This supercapacitor presents an energy density of 29.0 Wh/kg based on the total mass of the active electrode materials, a very good rate behavior with energy density of 20.3 Wh/kg at power density of 2 kW/kg, and also a rather good cycling performance.     

Characterisation of salt films on dissolving metal surfaces in artificial corrosion pits via in situ synchrotron X-ray diffraction

The salt films formed on metal surfaces dissolving inside artificial corrosion pits formed in 1 M HCl have been probed with synchrotron X-ray diffraction. NiCl₂ · 6H₂O is the main phase in the salt film on nickel, whereas salt films on both iron and 316 L stainless steel are predominantly FeCl₂ · 4H₂O. However, the salt film on iron has a very fine homogeneous crystallite size whereas that on stainless steel is much coarser. The potential-dependence of the film formed on iron has been determined.     

Gas phase dissociation of H2SO4: A computational study

The decomposition of gaseous sulfuric acid has been investigated computationally. In particular the role of the hydrated gaseous coordination adducts of SO₃(g) and H₂SO₄(g) in the (dissociation + decomposition) process has been evaluated. A first principles study of the gaseous coordination complexes SO₃(H₂O)_n (n = 1 to 3) and H₂SO₄(H₂O)_m (m = 1 to 2) has been carried out deriving equilibrium ground state structures, vibrational frequencies and energetic stabilities by the Moller–Plesset perturbation approximation. These results have been used to derive the enthalpy of formation at 0 K and the Gibbs energy functions of these molecules. A new thermodynamic modeling of the decomposition of H₂SO₄(g) has been therefore performed considering the effect of temperature, pressure and initial composition of the gas (hydration conditions).