Kunitsugu Aramaki

Treatment of zinc surface with cerium(III) nitrate to prevent zinc corrosion in aerated 0.5 M NaCl

It has been reported that CeCl3 is an effective inhibitor for corrosion of zinc in an aerated 0.5 M NaCl solution by the formation of a thick film composed of cerium-rich oxide and hydroxide. In this study, a protective film was prepared by treatment of a zinc electrode in an aqueous solution of 1×10−3 M Ce(NO3)3 at 30°C for 30 min and examined in an aerated 0.5 M NaCl solution at 30°C by polarization measurements after immersion of the electrode in the NaCl solution for 4–240 h. The film comprised oxides and hydroxides of Ce(III) and Ce(IV) ions mostly. The protective efficiency of the film against zinc corrosion was maintained remarkably high, more than 91% during immersion in 0.5 M NaCl for 240 h. Little pitting corrosion was observed on the electrode surface. However, this film could not heal the scratched surface of zinc electrode in the NaCl solution.

Self-assembled layers of alkanethiols on copper for protection against corrosion

Self-assembled monolayers of alkanethiols C[sub n]H[sub 2n+1]SH(n = 6 [approximately] 18) adsorbed on the surface of a polycrystalline bulk cu were constructed and characterized by x-ray photoelectron (XPS) and surface-enhanced Raman scattering (SERS) spectroscopy and contact angle and impedance measurements. The protection ability of the alkanethiol monolayers against Cu corrosion in an aerated 0.5 M Na[sub 2]SO[sub 4] solution was examined by impedance and polarization techniques. Results of XPS, SERS, and contact angle measurements showed that alkanethiols were chemisorbed on the Cu surface by the formation of strong bonds between Cu and S atoms following cleavage of a S-H bond and formed densely packed, water-repellent monolayers on the surface. The advancing contact angle of these monolayer films was comparable to that of alkanethiolate monolayers adsorbed at a vapor-deposited Cu on a Si wafer. However, sufficiently high protection abilities of the films against Cu corrosion were not obtained in 0.5 M Na[sub 2]SO[sub 4]. A preliminary experiment demonstrated the formation of a promising protective film which was prepared on the Cu surface by modification of self-assembled 11-mercapto-1undecanol monolayer with octyltrichlorosilane to form cross-linkages between the thiol molecules with siloxane bonds.

The inhibition effects of chromate-free, anion inhibitors on corrosion of zinc in aerated 0.5 M NaCl

Abstract The inhibition effects of chromate-free, environmentally acceptable anion inhibitors were examined on corrosion of zinc in an aerated 0.5 M NaCl solution by polarization measurements. Sodium silicate Na 2 Si 2 O 5 and phosphate Na 3 PO 4 were remarkably effective on zinc corrosion, exhibiting high inhibition efficiencies around 90%. Pitting corrosion was not observed on the zinc electrode inhibited with these anions. The zinc surfaces treated with these anions in the solution were analyzed by X-ray photoelectron spectroscopy and electron-probe microanalysis. The inhibition efficiencies of molybdate MoO 4 2− and tetraborate ions B 4 O 7 2− were not markedly high and phosphonates were less effective inhibitors.

The inhibition effects of cation inhibitors on corrosion of zinc in aerated 0.5 M NaCl

Abstract This investigation deals with inhibition of zinc corrosion in an aerated 0.5 M NaCl solution by environmentally acceptable cation inhibitors, Al 3+ , La 3+ , Ce 3+ and Ce 4+ . The inhibition efficiencies of these cations were determined by polarization measurements of a zinc electrode in the solution. The efficiencies of Ce 3+ and La 3+ were high, more than 90% but those of other cations were negative, indicating stimulation of zinc corrosion. X-ray photoelectron spectra for the zinc surface treated in the solution containing Ce 3+ revealed that a thick protective layer composed of Ce(OH) 3 , Ce 2 O 3 and small amounts of Zn(OH) 2 and ZnO formed on the surface and there was no chloride ion within the layer. Processes of the layer formation on the surface were discussed based on these results.

A SERS study on inhibition mechanisms of benzotriazole and its derivatives for copper corrosion in sulphate solutions

Corrosion inhibition mechanisms of benzotriazole and its derivatives, 1- and 4-hydroxybenzotriazole for copper in aqueous solutions containing sulphate ions were investigated by SERS spectra and electrochemical polarization method. Inhibition effects became larger in the order of 1-hydroxybenzotriazole < benzotriazole < 4-hydroxybenzotriazole in the neutral solutions. SERS study strongly suggested that 4-hydroxybenzotriazole formed a polymeric surface complex, [Cu(C6H3(OH)N3)]n, of which chemical properties suggested a formation of two- or three-dimensional structure on the surface by means of hydrogen bonding with each other or with water molecules. SERS spectra of chemically adsorbed molecules were obtained in the acid solutions of benzotriazole and 4-hydroxybenzotriazole at the potentials more negative than ca −300 mV(SCE).

Self-healing mechanism of an organosiloxane polymer film containing sodium silicate and cerium(III) nitrate for corrosion of scratched zinc surface in 0.5 M NaCl

A highly protective and self-healing film of 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 polymer containing sodium silicate (water glass) Na2Si2O5 and cerium(III) nitrate Ce(NO3)3 was prepared on a zinc electrode previously treated in a Ce(NO3)3 solution. The film was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution after the electrode was scratched and immersed in the solution for 4–72 h. Self-healing mechanism of the film was investigated by X-ray photoelectron spectroscopy and electron-probe microanalysis for the coated electrode surface after scratched and immersed in the NaCl solution. A passive film composed of Zn(OH)2, ZnSi2O5 and Ce3+–Si2O52− salt or complex was formed on the scratched surface and preferential deposition of Si2O52− compounds occurred at a defect of the passive film where Cl− accumulated, resulting in suppression of pitting corrosion at the scratch.

Sers and impedance study of the equilibrium between complex formation and adsorption of benzotriazole and 4-hydroxybenzotriazole on a copper electrode in sulphate solutions

Abstract The corrosion inhibition mechanism of benzotriazole and 4-hydroxybenzotriazole for copper in sulphate solutions was investigated by SERS spectroscopy and impedance measurements. These inhibitors form complex polymers on the copper surface at high pH of the solution, positive potential of the electrode, and high concentration of the inhibitors. At low solution pH, negative electrode potential and low inhibitor concentration, single molecules of the inhibitors are adsorbed chemically on copper. Equilibrium between the complex formation and the adsorption relates strongly with the corrosion inhibition effect. 4-Hydroxybenzotriazole shows a higher inhibition efficiency at the high solution pH than benzotriazole, at low pH values this order is reversed.

One- and two-dimensional polymer films ofmodified alkanethiol monolayers for preventing iron fromcorrosion

Abstract A monolayer of 11–mercapto–1–undecanol HO(CH2)11SH(MUO) adsorbed on the electrolytically reduced iron surface was modified withtetraethoxysilane (C2H5O)4Si(TES), octyltriethoxysilane 8H17Si(OC2H5)3 and⧹oroctadecyltriethoxysilane C18H37Si(OC2H53(C18TES) for preparing one- and two-dimensional polymer films. The filmsthus prepared were characterized by polarization, impedance and contact angle measurementsand X-ray photoelectron and Fourier transform infrared reflection spectroscopies. A two-dimensional polymer film of the MUO monolayer modified twice with TES and subsequentlywith C18TES on the iron surface protected iron from corrosion in aerated 0.5 M NaCland on exposure to room air.

Effects of organic inhibitors on corrosion of zinc in an aerated 0.5 M NaCl solution

Abstract The effects of organic inhibitors on corrosion of zinc in an aerated 0.5 M NaCl solution were investigated by polarization measurements. The inhibitors were sodium benzoate (NaBz), sodium N -dodecanoylsarcosinate (NaDS), sodium S -octyl-3-thiopropionate (NaOTP), 8-quinolinol (8-QOH) and 1,2,3-benzotriazole (BTAH). These inhibitors formed precipitate films of Zn(II) salts or complexes on the zinc surface together with zinc hydroxide and oxide to prevent corrosion in the solution. High inhibition efficiencies of NaOTP were acquired at concentrations c =1×10 −6 –3×10 −5 M, BTAH at c =1×10 −4 –1×10 −3 M, 8-QOH at c =1×10 −3 –3×10 −3 M and NaBz at c =3×10 −3 –1×10 −2 M. Films formed on the zinc surface were analyzed by X-ray photoelectron and Fourier transform infrared reflection spectroscopies.

The synergistic effect of anions and the ammonium cation on the inhibition of iron corrosion in acid solution

Abstract The synergistic effect of various anions and the tetra- n -butylammonium cation on the inhibition of iron corrosion in 1 M HClO 4 and their joint adsorption on iron were studied by using an impedance and a polarization technique. Surface coverage obtained from double layer capacitance showed joint adsorption of the anion and cation on the iron surface. Assuming competitive adsorption of these ions at the interface, the synergism of corrosion inhibition and joint adsorption were estimated using a parameter calculated from the inhibition efficiencies and the surface coverages of the anion and/or cation. The synergistic effect was shown for all of the anions and cation examined.