Preparation of one-dimensional polymer films by modification of a hydroxymethylbenzene self-assembled monolayer on iron with alkyltriethoxysilanes for preventing iron corrosion

A self-assembled monolayer (SAM) of p-hydroxymethylbenzene HOCH₂C₆H₄ - (HOMB) moiety adsorbed on iron by the formation of a covalent bond between carbon and iron atoms was prepared by electrochemical derivatization of an iron electrode with p-hydroxymethylbenzenediazonium tetrafluoroborate HOCH₂C₆H₄N₂BF₄. The electrode covered with the HOMB SAM was modified with alkyltriethoxysilanes C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18) to prepare a film of one-dimensional polymer. The protective ability of the polymer film was determined by polarization measurement of the covered electrode in an aerated 0.5 M NaCl solution. The ability was enhanced by modification of the HOMB SAM with C_nTES markedly. The iron surface coated with the one-dimensional polymer film of the HOMB SAM modified with C₈TES was characterized by contact angle measurement and FTIR reflection and X-ray photoelectron spectroscopies. The persistence in the protective ability of the polymer film against iron corrosion in 0.5 M NaCl may be associated with the strong adsorption via the covalent bond, revealed by electron-probe microanalysis.     

Additional modification to two-dimensional polymer films of a hydroxymethylbenzene self-assembled monolayer with alkyltriethoxysilanes for enhancing the protective abilities against iron corrosion

Additional modification of the ultrathin two-dimensional polymer film, a p-hydroxymethylbenzene C₆H₄CH₂OH self-assembled monolayer modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (BTESE) and alkyltriethoxysilane C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18), was attempted to improve the protective ability of the film against iron corrosion. The ability of the film was examined by polarization measurement of an iron electrode coated with the film in an oxygenated 0.5 M NaCl solution after immersion in the solution for 1.5 to 72 h. Marked improvement of the protective efficiency, P was not obtained by additional modification to the polymer film with BTESE. The P values of the two-dimensional polymer films were markedly increased by additional modification with C₈TES. The increases in P were ascribable to improvement of alkyl tail arrangement and additional interconnection in the polymer films. The film on the iron surface was characterized by contact angle measurement, FTIR reflection spectroscopy and X-ray photoelectron spectroscopy. The protective abilities of the two-dimensional polymer films additionally modified with C₈TES were persistent during immersion for 72 h.     

Prevention of passive film breakdown and corrosion of iron in 0.1 M KClO4 with and without Cl by covering with an ultrathin two-dimensional polymer coating and healing treatment in 0.1 M NaNO3

A two-dimensional polymer coating, the self-assembled monolayer of 16-hydroxy hexadecanoate ion HO(CH₂)₁₅ modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃ was prepared on the passivated iron electrode and further, the passive film was healed by additional treatment in 0.1 M NaNO₃. This electrode was immersed in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ to 1 × 10⁻² M of Cl⁻. Protection of passive film against breakdown by covering the electrode with the polymer coating was examined by monitoring the open-circuit potential during immersion in the solutions for many hours to determine the time for passive film breakdown, t_bd. Repeated polarization measurements were carried out during immersion in these solutions for obtaining the protective efficiency, P. The t_bd value of the passivated, polymer-coated and healed electrode in 0.1 M KClO₄ solutions with and without Cl⁻ increased with a decrease in the concentration of Cl⁻. No breakdown occurred on the electrode during immersion in 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ of Cl⁻ for 360 h. The P values were extremely high, more than 99.9% before t_bd, indicating complete protection of iron from corrosion. The effect of healing treatment in 0.1 M NaNO₃ on passive film breakdown was investigated by electron-probe microanalysis.     

Protection of iron against corrosion by coverage with ultrathin two-dimensional polymer films of a hydroxymethylbenzene self-assembled monolayer anchored by the formation of a covalent bond

Ultrathin films of two-dimensional polymers were prepared on an iron electrode by modification of a p-hydroxymethylbenzene p-HOCH₂C₆H₄ (HOMB) self-assembled monolayer (SAM) with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (BTESE) and alkyltriethoxysilanes C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 and 18). The electrode was derivatized by cathodic reduction of p-hydroxymethylbenzenediazonium tetrafluoroborate HOCH₂C₆H₄N₂BF₄ in an electrolytic acetonitrile solution below 10 °C for 1 h to form the SAM via a covalent bond between carbon and iron atoms. The protective ability of the polymer film against iron corrosion was determined by polarization measurement of the coated electrode in an oxygenated 0.5 M NaCl solution. The protective efficiencies of the polymer films prepared by modification with BTESE plus C₈TES and C₁₈TES were 63.9% and 68.5% after immersion in 0.5 M NaCl for 1.5 h, respectively. These values were higher than those of the one-dimensional polymer films prepared with the respective C_nTES. The film of the HOMB SAM modified with BTESE plus C₈TES was characterized by contact angle measurement using a drop of water and X-ray photoelectron and FTIR reflection spectroscopies. The films of the HOMB SAM modified with BTESE plus C₈TES and C₁₈TES were persistent during immersion of the coated electrodes in 0.5 M NaCl for many hours by far as compared with the alkanethiol SAM anchored on iron by the formation of a coordinate bond.     

Electrically conducting nylon 6,6–polyaniline short composite fibres synthesised by the solvent coagulation method

Polyaniline (PANI) was blended with nylon 6,6 in concentrated H₂SO₄ and HCl solutions. The solvent coagulation method was utilised to extract short composite fibres of a centimetre in length. A solution of n-butyl acetate, acetone, toluene, 1 μM HCl and chloroform were used as coagulating bath to extract the fibres. The diameters of the fibres ranged from 200 to 300 nm, while the length measured approximately 1 cm, as determined from Scanning Electron Microscopy (SEM). The electrical conductivity varied from 10⁻⁴ to 10⁻² S/cm for different mass fractions of PANI (x_PANI) in the composite fibres. The percolation threshold was reached at x_PANI values between 0.15 and 0.2, and further addition of PANI resulted in saturation of the conductivity of the composite fibre. To observe the effect of MWCNTs on the electrical conductivity of the nylon–PANI fibres, 0.04 g, 0.08 g, 0.4 g and 0.5 g of MWCNTs (1, 2, 10, 12.5 weight percentage, respectively) were added into the nylon–PANI solution and were extracted as fibres in the aforementioned solvents. The electrical conductivity of the short fibres increased by an order of magnitude (0.372 S/cm at 12.5 wt.%) when they were extracted in the presence of the MWCNTs. PANI doped in concentrated HCl exhibited an electrical conductivity of 4.46 S/cm.     

A study on mechanism of corrosion protection of polyaniline coating and its failure

Polyaniline (PANI) coatings were electrochemically deposited on substrates of stainless steel and platinum in solutions of 0.2 M H₂SO₄ and 0.1 M aniline by cyclic voltammetry. The corrosion protection of the PANI coatings and their failure were investigated in 0.2 M H₂SO₄ solution. It was observed that the corrosion protection ability of the coating to steel substrate was increased with the increase of the coating thickness. The corrosion protection ability was mainly attributed to the passivating effect of PANI due to its oxidizing ability in its emeraldine state. During its operation, the PANI coating in emeraldine state tended to gradually lose its corrosion protection ability. This gradual failure of the PANI coating, but faster than expected, was confirmed to be related to a gradual reduction of the emeraldine PANI and a gradually increased resistance between the PANI coating and the stainless steel substrate. These findings lead to a new mechanism for the corrosion protection of PANI coating and its failure.     

Preparation of a self-assembled monolayer on iron by the formation of a covalent bond between carbon and iron atoms

A self-assembled monolayer (SAM) of toluene moiety CH₃C₆H₄- was prepared on an iron electrode by electrochemical modification in a deaerated acetonitrile (AN) solution of p-toluenediazonium tetrafluoroborate CH₃C₆H₄N₂BF₄ (TDFB). The protection of the modified electrode was examined by polarization measurements in an oxygenated 0.5 M NaCl solution after immersion in the solution for 1.5 and 4.0 h. The average values of protective efficiency, P for the films prepared by modification in the TDFB solution at −1.013 V/Ag/Ag⁺AN for the modification time, t_m more than 5 min were fairly high, 78.1% and 53.6% at 1.5 and 4.0 h of the immersion time, t, respectively. However, X-ray photoelectron spectra of the iron surface modified with TDFB for 10 min revealed that the film thus prepared on iron was a polymer of the toluene moieties. A layer formed by the cathodic modification in the TDFB solution for 1 min seemed to be a monolayer of the toluene moiety, revealed by X-ray photoelectron spectra of the surface coated with the layer. The contact angle on the coated surface using a drop of water supported the formation of toluene SAM. The P values of the layer for iron corrosion in 0.5 M NaCl were 31.8% and 28.9% at 1.5 and 4.0 h of t, respectively, being a little higher than those of the toluenethiol CH₃C₆H₄SH SAM. The higher values may be attributed to the formation of a strong covalent bond between carbon and iron atoms.     

Microwave assisted chemical bath deposited polyaniline films for supercapacitor application

In the present investigation, we are reporting the first time synthesis of polyaniline (PANI) thin films by microwave assisted chemical bath deposition (MW-CBD) method on the stainless steel substrate. The PANI thin films are prepared by the oxidation of aniline in the domestic microwave oven working with frequency 2.45 GHz. The PANI thin films are characterized for their structural, morphological and optical studies by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and UV-vis spectrophotometer. The wettability study is carried out by measuring the contact angle. The supercapacitive behavior of PANI electrode is studied in 0.5 M H₂SO₄ using cyclic voltammetric (CV) measurements. The X-ray diffraction pattern showed the films are amorphous. Morphological study revealed PANI thin film is well covered over the entire substrate surface with less overgrown fine spherical granules. The optical band gap of PANI thin film is found to be 2.5 eV. The hydrophilic nature of the PANI thin films is observed from water contact angle measurement. A maximum specific capacitance is found to be 753 F g⁻¹ at the scan rate of 5 mV s⁻¹.     

Effects of pretreatment on the aluminium etch pit formation

The effect of chemical pretreatments on the electrochemical etching behavior of aluminium was investigated with the topographic studies of surface and the analysis of initial potential transients. Two-step pretreatments with H₃PO₄ and H₂SiF₆ result in a high density of pre-etch pits on aluminium surface by the incorporation of phosphate ion inside the oxide film and the removal of surface layer by aggressive fluorosilicic acid solution. It generates a high density of etch pits during electrochemical etching and results in the capacitance increase of etched Al electrode by expanding the surface area, up to 61.3 μF/cm² with the pretreatment solution of 0.5 M H₃PO₄ at 65 °C and 10 mM H₂SiF₆ at 45 °C.     

In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles

The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO₂) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO₂ composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO₂ composites were quite different from those of pure PANI or TiO₂, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO₂ composite was estimated to be 0.91 × 10⁻¹ S/cm at 25 °C in the range of semiconductor.     

The corrosion behaviour of Fe-15Mn-7Si-9Cr-5Ni shape memory alloy

The corrosion behaviour of Fe-15Mn-7Si-9Cr-5Ni (mass%) shape memory alloy at 25 °C in 0.5 M H₂SO₄ and 3.5% NaCl solutions has been studied using potentiodynamic polarization and electrochemical impedance techniques. Three different microstructures viz., single-phase γ, γ-δ and γ-Fe₅Ni₃Si₂, were produced by heat-treating the alloy in different equilibrium phase fields. The corrosion behaviour in 0.5 M H₂SO₄ solution is almost same for all three microstructures, barring a slight difference in the passivation range. Although, the passivation current in 0.5 M H₂SO₄, is in the same range as that of SS 304, the critical current required for onset of passivation is almost three orders higher and the passivation range is much shorter. In 3.5% NaCl solution the corrosion behaviour of all three microstructures of the Fe-15Mn-7Si-9Cr-5Ni shape memory alloy was that of general dissolution without passivity or localized attack (pitting). The best corrosion resistance in both H₂SO₄ and NaCl solutions is shown by the single-phase γ microstructure.     

Electrochemical fabrication of a porous nanostructured nickel hydroxide film electrode with superior pseudocapacitive performance

A porous nickel film is prepared by selectively anodic dissolution of copper from an electrodeposited Ni-Cu alloy film. A porous nanostructured nickel hydroxide film electrode is further fabricated by the cathodic electrodeposition of Ni(OH)₂ film on the obtained porous nickel film. The specific capacitances of the as-prepared porous nanostructured Ni(OH)₂ film electrode at current densities of 2, 5 and 10 A/g are 1634, 1563 and 1512 F/g, respectively. The nanoporous Ni substrate significantly improves the electrochemically cyclic stability of the electrodeposited nickel hydroxide film in 1.0 M KOH solution. The superior pseudocapacitive properties such as large specific capacitance, excellent rate capability and improved electrochemically cyclic stability of the as-prepared nickel hydroxide electrode suggest its potential application in electrochemical capacitors.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

The effects of niobium and nickel on the corrosion resistance of the zinc phosphate layers

In this investigation the viability of nickel substitution by niobium in zinc phosphate (PZn) baths has been studied. Samples of carbon steel (SAE 1010) were phosphated in two baths, one containing nickel (PZn + Ni) and the other with niobium substituting nickel (PZn + Nb). Potentiodynamic polarization curves (anodic and cathodic, separately) and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion resistance of the phosphated carbon steels in a 0.5 mol L^− 1 NaCl electrolyte. The phosphate layers obtained were analysed by X-ray diffraction and it was found that they are composed of Zn₃(PO₄)₂.4H₂O (hopeite) and Zn₂Fe(PO₄)₂.4H₂O (phosphophylite). Surface observation by scanning electron microscopy (SEM) showed that the PZn + Ni layer is deposited as needle-like crystals, whereas the PZn + Nb layer shows a granular morphology. The electrochemical results showed that the PZn + Nb coating was more effective in the corrosion protection of the carbon steel substrate than the PZn + Ni layer. The results also suggested that nickel can be replaced by niobium in zinc phosphate baths with advantageous corrosion properties of the layer formed.     

Synergistic effect of halide ions on improving corrosion inhibition behaviour of benzisothiozole-3-piperizine hydrochloride on mild steel in 0.5 M H2SO4 medium

The synergistic effect of iodide ions and benzisothiozole-3-piperizine hydrochloride (BITP) on corrosion inhibition of mild steel in 0.5 M H₂SO₄ solution has been studied by both chemical and electrochemical methods. The corrosion performance of BITP in 1.0 M HCl and 0.5 M H₂SO₄ media was examined and compared. The adsorption of BITP and its combination with iodide ions on mild steel surface followed Langmuir adsorption isotherm via chemisorption mechanism. The calculated values of synergism parameter (S_θ) were found to be greater than unity. This result clearly showed the existence of synergism between iodide ions and BITP molecules.     

An ultrathin polymer coating of carboxylate self-assembled monolayer adsorbed on passivated iron to prevent iron corrosion in 0.1 M Na2SO4

For preparing an ultrathin two-dimensional polymer coating adsorbed on passivated iron, a 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer (SAM) was modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Protection of passivated iron against passive film breakdown and corrosion of iron was investigated by monitoring of the open-circuit potential and repeated polarization measurements in an aerated 0.1 M Na₂SO₄ solution during immersion for many hours. The time required for passive film breakdown of the polymer-coated electrode was markedly higher in this solution than that of the passivated one, indicating protection of the passive film from breakdown by coverage with the polymer coating. The protective efficiencies of the passive film covered with the coating were extremely high, more than 99.9% in 0.1 M Na₂SO₄ before the passive film was broken down, showing prominent cooperative suppression of iron corrosion in the solution by coverage with the passive film and polymer coating. The polymer-coated surface was characterized by contact angle measurement and electron-probe microanalysis (EPMA). Prevention of passive film breakdown and iron corrosion for the polymer-coated electrode healed in 0.1 M NaNO₃ was also examined in 0.1 M Na₂SO₄.     

Effect of underpotential deposition of lead on polarization behavior of nickel in acidic perchlorate solutions at room temperature

The effect of Pb²⁺ on polarization behavior of nickel has been investigated in 0.1 M NaClO₄ + 10⁻² M HClO₄ + x M PbO solutions (x = 0, 10⁻⁵, 10⁻⁴, 10⁻³) at room temperature. The cyclic voltammogram has suggested that Pb²⁺ degrades the stability of the passive film on Ni. The corrosion potential of Ni shifted to the more noble direction and the anodic current peak of Ni dissolution decreased with increasing Pb²⁺ concentration in solution, indicating that Pb²⁺ suppresses significantly the anodic dissolution. The underpotential deposition (UPD) of lead on Ni in the potential range more noble than −0.215 V (SHE) corresponding to the equilibrium potential of the Pb²⁺ (10⁻³ M)/Pb electrode was confirmed by XPS and GDOES analyses. The anodic Tafel slope, b⁺, of Ni dissolution changed from b⁺ = 40 mV decade⁻¹ in the absence of Pb²⁺ to b⁺ = 17 mV decade⁻¹ in the presence of 10⁻⁴ or 10⁻³ M Pb²⁺, which was ascribed to the increase in active sites of Ni surface emerged as a result of electrodesorption of Pb adatoms. The roles of Pb adatoms in active dissolution and active/passive transition of Ni were discussed from the above results.     

Corrosion prevention of passivated iron in 0.1 M NaCl by coverage with an ultrathin polymer coating and healing treatment in 0.1 M NaNO3

An ultrathin, ordered and two-dimensional polymer coating was prepared on a passivated iron electrode by modification of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Subsequently, the electrode was healed in 0.1 M NaNO₃. Protection of passivated iron against passive film breakdown and corrosion of iron was examined by monitoring of the open-circuit potential and repeated polarization measurements of the polymer-coated and healed electrode in an aerated 0.1 M NaCl solution during immersion for many hours. Localized corrosion was markedly prevented by coverage with the polymer coating and the healing treatment in 0.1 M NaNO₃. Prominent protection of iron from corrosion in 0.1 M NaCl was observed before the breakdown occurred. The electrode surface covered with the healed passive film and polymer coating was analyzed by contact angle measurement, X-ray photoelectron spectroscopy and electron-probe microanalysis.     

Preparation of ultrathin polymer coatings adsorbed on iron via a covalent bond by multistep modification of a hydroxymethylbenzene SAM with ethoxysilanes and alkanediol for preventing iron corrosion in 0.5 M NaCl

The film thickness, d of a p-hydroxymethylbenzene - C₆H₄CH₂OH (HOMB) self-assembled monolayer (SAM) adsorbed on iron via a covalent bond was increased by multistep modification with tetraethoxysilane (C₂H₅O)₄Si (TES) and 1,8-octanediol HO(CH₂)₈OH (C₈DO) and subsequently with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (BTESE) and akyltriethoxysilane C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18). The protective ability of the film against iron corrosion was examined by polarization measurement of the iron electrode coated with the film in an oxygenated 0.5 M NaCl after immersion in the solution for many hours. The values of protective efficiency, P for the films, the HOMB SAM modified with TES and C₈DO twice and subsequently with BTESE and C_nTES were high, more than 81% at n = 8 and 85% at n = 18 in the range of the immersion time, t up to 240 h, respectively. The maximal P values of the respective films were 88.0% and 92.2%, of which approximate d values were 4.6 and 5.8 nm. The high protection of iron against corrosion was attributed to increases in the film thickness and interconnection between the adsorbed molecules with Si-O polymer linkages. The protective ability of the film was remarkably persistent during immersion in the solution for many hours. A slight enhancement of P was observed by additional modification of the modified HOMB SAM with C₈TES due to increases in interconnection and close packed arrangement. The formation of strong adsorption bonds, σ-covalent bond and back-donating π-bond, between the carbon atom of HOMB moiety and iron atom was discussed.     

Changes in mass and stress during anodic oxidation and cathodic reduction of the Cu/Cu2O multilayer film

The anodic oxidation and cathodic reduction processes of the Cu/Cu₂O multilayer film and pure Cu film in pH 8.4 borate buffer solution were analyzed by electrochemical quartz crystal microbalance (EQCM) for gravimetry and bending beam method (BBM) for stress measurement. The mass loss of the multilayer film during anodic oxidation at 0.8 V (SHE) in the passive region was less than that of the pure Cu film. The comparison between current transients and mass changes during anodic oxidation has succeeded in separating the anodic current density into two partial current densities of oxide film growth, i_O^2-, and of Cu²⁺ dissolution through the passive film, i_Cu²⁺. As a result, in the case of the pure Cu film, the anodic current density was mainly due to i_Cu²⁺, while in the case of the multilayer film, i_Cu²⁺ was almost equal to i_O^2-. The compressive stress for the multilayer film was generated during anodic oxidation, while the tensile stress for the pure Cu film was generated.The mass loss of the multilayer film during cathodic reduction at a constant current density (i_c = −20 μA cm⁻²) was significantly less than that estimated from coulometry, suggesting that H₂O produced by cathodic reduction remained in the multilayer film. The compressive stress was generated during cathodic reduction of the multilayer film, which was ascribed to H₂O remained in the multilayer film.