Corrosion inhibition of carbon steel in tetra-n-butylammonium bromide aqueous solution by benzotriazole and Na3PO4

The corrosion inhibition behavior of benzotriazole, Na₃PO₄ and their mixture on carbon steel in 20 wt.% (0.628 mol l⁻¹) tetra-n-butylammonium bromide aerated aqueous solution was investigated by weight-loss test, potentiodynamic polarization measurement, electrochemical impedance spectroscopy and scanning electron microscope/energy dispersive X-ray techniques. The inhibition action of BTA or SP or inhibitors mixture on the corrosion of carbon steel is mainly due to the inhibition of anodic process of corrosion. The results revealed that inhibitors mixtures have shown synergistic effects at lower concentration of inhibitors. At 2 g l⁻¹ BTA and 2 g l⁻¹ SP showed optimum enhanced inhibition compared with their individual effects.     

The synergistic effect of Na3PO4 and benzotriazole on the inhibition of copper corrosion in tetra‐n‐butylammonium bromide aerated aqueous solution

The effect of Na₃PO₄ and the mixture of benzotriazole (BTA) and Na₃PO₄ (SP) on the corrosion of copper in 17 wt% (0.534 mol/L) tetra‐n‐butylammonium bromide (TBAB) aerated aqueous solution has been investigated by means of weight‐loss test, potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy/energy dispersive X‐ray techniques. The experimental results showed that a dosage of Na₃PO₄ stimulated the copper corrosion, and the corrosion rate increased with increasing Na₃PO₄ concentration, whereas the mixture of BTA and Na₃PO₄ could protect copper in aqueous TBAB solution. The inhibition action of the mixture of BTA and Na₃PO₄ on the corrosion of copper is mainly due to the inhibition of the anodic process of corrosion. The inhibition efficiency of a mixture consisting of 2 g/L BTA and 1 g/L Na₃PO₄ was about 96%. The mixture of BTA and Na₃PO₄ inhibits the corrosion of copper better than BTA by itself, indicating that Na₃PO₄ has a synergistic role with BTA on the corrosion inhibition of copper in TBAB aqueous solution.     

Self-healing mechanism of a protective film prepared on a Ce(NO3)3-pretreated zinc electrode by modification with Zn(NO3)2 and Na3PO4

Self-healing mechanism of a protective film against corrosion of zinc at scratches in an aerated 0.5 M NaCl solution was investigated by polarization measurements, X-ray photoelectron spectroscopy (XPS) and electron-probe microanalysis (EPMA). The film was prepared on a zinc electrode by treatment in a Ce(NO₃)₃ solution and addition of aqueous solutions containing 9.98 or 19.9 μg/cm² of Zn(NO₃)₂ · 6H₂O and 55.2 μg/cm² of Na₃PO₄ · 12H₂O. After the coated electrode was scratched with a knife-edge crosswise and immersed in the NaCl solution for many hours, polarization measurements, observation of pit formation at the scratches, XPS and EPMA were carried out. This film was remarkably protective and self-healing against zinc corrosion on the scratched electrode. The cathodic and anodic processes of zinc corrosion were markedly suppressed by coverage of the surface except for scratches with a thin Ce₂O₃ layer containing a small amount of Ce⁴⁺ and the surface of scratches with a layer composed of Zn₃(PO₄)₂ · 4H₂O, Zn(OH)₂ and ZnO mostly.     

Synergistic inhibition effect of 6-benzylaminopurine and iodide ion on the corrosion of cold rolled steel in H3PO4 solution

The synergistic inhibition effect of 6-benzylaminopurine (BAP) and iodide ion (I⁻) on the corrosion of cold rolled steel (CRS) in 1.0 M H₃PO₄ solution was studied by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. The results show that BAP has a moderate inhibitive effect. However, incorporation of BAP with I⁻ improves the inhibition performance significantly. The adsorption of BAP in the absence and presence of I⁻ obeys Langmuir adsorption isotherm. BAP and BAP/I⁻ mixture act as mixed-type inhibitors. A probable synergism mechanism is proposed.     

Brass corrosion in tap water distribution systems inhibited by phosphate ions

The effect of sodium orthophosphate on the protective characteristics of the surface layers are studied on brass in contact with moderately hard, highly carbonated and chloride rich simulated drinkable water. The optimal inhibitor concentration is evaluated from the composition, thickness and pitting resistance of the surface film. This layer is mainly composed by zinc(II) oxide–hydroxide and cuprous oxide. By adding PO₄³⁻, the film quality improves, attributed to the incorporation of CuO or Zn(II) compounds. The changes are evident with 5 mg l⁻¹ P, and between 10 and 20 mg l⁻¹ P no significant differences are observed.     

Sodium molybdate as a corrosion inhibitor for aluminium in H3PO4 solution

The inhibition effect of sodium molybdate (Na₂MoO₄) on the corrosion of aluminium in 1.0 M H₃PO₄ solution was studied by weight loss, potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS) methods. The results show that Na₂MoO₄ is a good inhibitor, and the inhibition efficiency obtained by three methods is higher than 84% at 20 mM. The adsorption of Na₂MoO₄ obeys Freundlich isotherm at lower concentrations (1–7 mM), while Langmuir isotherm at higher concentrations (7–20 mM). Polarisation curves indicate that Na₂MoO₄ acts as an anodic inhibitor. EIS spectra exhibit three loops (two capacitive loops and one inductive loop).     

Synergistic inhibition of zinc corrosion in 0.5 M NaCl by combination of cerium(III) chloride and sodium silicate

The synergistic inhibition effects of cerium(III) chloride, CeCl₃ and sodium silicate, Na₂Si₂O₅ (water glass) on corrosion of zinc in an aerated 0.5 M NaCl solution at 30°C were examined by polarization measurements. Equimolar mixtures of these inhibitors were markedly effective, indicating that the inhibition efficiencies of the mixture at 1×10⁻⁴ of each inhibitor were 95.9 and 93.6 after immersion of a zinc electrode in the solution for 3 and 120 h, respectively. X-ray photoelectron spectra revealed that a protective layer composed of hydroxylated or hydrated cerium-rich oxide and small amounts of zinc hydroxide and silicate formed on the zinc surface. A high inhibition efficiency of 1×10⁻³ M Na₂Si₂O₅, 97.7% was obtained for corrosion of a zinc electrode which was previously treated in the NaCl solution of 1×10⁻³ M CeCl₃ at 30°C for 30 min.     

Synergism between red tetrazolium and uracil on the corrosion of cold rolled steel in H2SO4 solution

The synergism between red tetrazolium (RT) and uracil (Ur) on the corrosion of cold rolled steel (CRS) in H₂SO₄ solution is first investigated by weight loss, potentiodynamic polarization, and atomic force microscope (AFM). Effects of inhibitor concentration (25-500 mg l⁻¹), temperature (20-50 °C), and acid concentration (1.0-5.0 M) on synergism are discussed systematically. The results reveal that RT has a moderate inhibitive effect, and its adsorption obeys the Freundlich adsorption isotherm. For Ur, it has a poor effect. However, incorporation of RT with Ur significantly improves the inhibition performance, and produces synergistic inhibition effect.     

Oxidation of green rust suspensions containing different chromium ion species

The oxidation of hydrosulphate green rust (GR2(SO₄²⁻)) suspension containing different chromium ion species was investigated by X-ray diffraction, X-ray absorption spectroscopy and transmission electron microscopy. The pH, oxidation-reduction potential and amount of dissolved oxygen in aqueous solutions were measured during the reactions. The results show that the addition of Cr(III)₂(SO₄)₃ solution suppresses the transformation of GR2(SO₄²⁻) into iron oxyhydroxides and oxides in aqueous solution, while the addition of Na₂Cr(VI)O₄ solution promotes the transformation of GR2(SO₄²⁻) in which Cr(VI) is reduced to Cr(III); α-FeOOH particles were refined by the addition of the chromium ions.     

Effect of ZrO2 on corrosion behaviour of chromium coatings

To study the effect of ZrO₂ particles on corrosion behaviour of Cr coating, steel samples were plated in Cr(VI) baths without and with ZrO₂. The corrosion behaviour of plated samples was studied at different exposure times in a solution containing 0.01 mol l⁻¹ H₂SO₄ + 0.5 mol l⁻¹ Na₂SO₄ using cyclic voltammetry and impedance spectroscopy. The equivalent circuit model R_e(Q_cR_pore)(Q_s[OR_s]) was proposed to fit the corrosion process and the parameters Y₀(Q_c),Y₀(Q_s) and R_pore reflecting corrosion behaviour of samples were evaluated. From the results, it was found that samples plated in bath containing ZrO₂ exhibited improved protective properties as a result of the structural characteristics of the coatings obtained; namely, the size and shape of pores.     

Growth and spectroscopic properties of Nd-doped Na2Gd4(MoO4)7 crystal

This paper reports the growth and spectral properties of Nd³⁺:Na₂Gd₄(MoO₄)₇ crystals. An Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal with dimensions of Ø20 × 25 mm³ has been grown by the Czochralski method. The spectroscopic properties of Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The polarized absorption cross-sections of Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal are 4.25 × 10⁻²⁰ cm² with full width at half maximum (FWHM) of 14.6 nm for the π-polarization and 2.87 × 10⁻²⁰ cm² with FWHM of 16.2 nm for the σ-polarization, respectively. The emission cross-sections are 10.0 × 10⁻²⁰ cm² at 1060 nm for π-polarization and 13.6 × 10⁻²⁰ cm² at 1067 nm for σ-polarization, respectively. The fluorescence quantum efficiency has been estimated to be 90.0%. Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal may be considered as a potential laser gain medium for the diode laser pumping.     

The characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media

The nature of the protective film formed by benzotriazole (BTAH) on the surface of the 90/10 CuNi alloy in deaerated 0.5 mol L⁻¹ H₂SO₄ solution containing Fe(III) ions as oxidant was investigated by weight-loss, calorimetric measurements, and by surface-enhanced Raman spectroscopy (SERS). The SERS measurements show that the protective film is composed by the [Cu(I)BTA]_n polymeric complex and that the BTAH molecules are also adsorbed on the electrode surface. A modification of the BET isotherm for adsorption of gases in solids is proposed to describe the experimental results obtained from weight-loss experiments that suggest an adsorption in multilayers. Electrochemical studies of copper and nickel in 0.5 mol L⁻¹ H₂SO₄ in presence and absence of BTAH have also been made as an aid to interpret the results. The calculated adsorption free energy of the cuprous benzotriazolate on the surface of the alloy is in accordance with the value for pure copper.     

Influence of silica sol particle behavior on the magnesium anodizing process with different anions addition

Combining the processes of colloid chemistry and electrochemistry the anodic films were made in electrolytes with silica sol addition. Two basic electrolytes 1 M NaOH + 10 vol.% silica sol and 1 M Na₂SiO₃ +10 vol.% silica sol were chosen to investigate the silica sol particle behavior during the anodizing process. The anodic films were prepared separately in the two basic electrolytes with various Na₂CO₃ or Na₃PO₄ additions at 2 A/dm², 20 °C for 10 min. The micro-images and element contents of the specimen were characterized by SEM and EDS. The results showed that some cracks appeared on the films by adding PO₄³⁻ in both of the two basic electrolytes. And the films became compact and uniform with the addition of CO₃²⁻ in Na₂SiO₃ basic solution. Moreover, the film average thickness decreased with adding anions. It can be confirmed that the sol particle adsorbing behavior in the solution was influenced by the amount of anions' charges, size and structure.     

Self-healing protective films prepared on zinc by treatments with cerium(III) nitrate and sodium phosphate

Chromate-free, self-healing protective films were prepared on a surface of zinc electrode previously treated in a solution of cerium(III) nitrate Ce(NO₃)₃ by coverage of the surface with a layer of sodium phosphate Na₃PO₄. The self-healing ability of the film was examined by polarization measurements of the electrode after scratching the surface with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution for many hours and by observation of pit formation at the scratches. A thin film containing 0.0552 mg/cm² of Na₃PO₄·12H₂O prepared on the electrode previously treated in 1×10⁻³ M Ce(NO₃)₃ at 30 °C for 30 min and dried at 90 °C for 23 h was highly self-healing and protective against corrosion of zinc in 0.5 M NaCl at the scratches. No pit was detected at the scratches on the electrode coated with this film after immersion for 72 h.     

Improvement in the self-healing ability of a protective film consisting of hydrated cerium(III) oxide and sodium phosphate layers on zinc

A self-healing protective film prepared on a zinc electrode by previous treatment in a Ce(NO₃)₃ solution and coverage with a Na₃PO₄ layer was improved by the addition of Zn(NO₃)₂. The protective and self-healing abilities of the films against corrosion of zinc in an aerated 0.5 M NaCl solution were examined by polarization measurements and observation of pit-like anodic dissolution feature (plf) and pit formation after the electrode was scratched with a knife-edge crosswise and immersed in the solution for many hours. The film prepared on the pretreated electrode coated with 9.98 or 19.9 μg/cm² of Zn(NO₃)₂ · 6H₂O and 55.2 μg/cm² of Na₃PO₄ · 12H₂O was significantly protective and self-healing against zinc corrosion on the scratched electrode. The protective efficiency of the film was more than 96% in the region of the immersion time between 72 and 360 h. No plf was observed at the scratches after immersion for 120 h. Results of Fourier transform infrared reflection and X-ray photoelectron spectroscopies revealed that the film was composed of Na₃PO₄, Zn₃(PO₄)₂ and Ce₂O₃ layers.     

Luminescent properties of Na3Gd1−xEux(PO4)2 and energy transfer in these phosphors

A series of Eu³⁺ activated Na₃Gd_1−xEu_x(PO₄)₂ (0 ≤ x ≤ 1) phosphors were synthesized by solid-state reaction method. The structures and photo-luminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the orthorhombic Na₃Gd(PO₄)₂. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370-410 nm) light. The intensities of magnetic dipole transition ⁵D₀ → ⁷F₁ and forced electric dipole transition ⁵D₀ → ⁷F₂ are comparable, and the energy ratio (⁵D₀ → ⁷F₁/⁵D₀ → ⁷F₂) is 1.1. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x = 0.62, y = 0.38), which is due to the ⁵D₀ → ⁷F_J transitions of Eu³⁺ ions. The correlation between the structure and the photo-luminescent properties of the phosphors was studied. The energy transfer and concentration quenching of the phosphors were discussed. Na₃Gd_1−xEu_x(PO₄)₂ has a potential application for white light-emitting diodes.     

Some aspects of copper corrosion in presence of benzotriazole and chloride ions

This paper deals with the investigation of electrochemical behaviour of copper in a sodium tetraborate (borax) solution in the presence and absence of chloride ions. The influence of benzotriazole (BTA) on the anodic behaviour of copper was also investigated. It was found that Cu₂O and CuO oxides were formed on copper and that peak current moved to the positive side with increased immersion time in a sodium tetraborate solution. After 1 h immersion of the copper electrode in a sodium tetraborate solution containing various chloride ion concentrations (0.001, 0.010, 0.050, and 0.100 mol/dm³ Cl⁻) the activation effect of those ions was found, whereas after 6 h immersion of copper in the above mentioned solutions, chloride ions were found to have not only activation but also passivation effect. The investigation of the effect of benzotriazole led to a conclusion that BTA has an inhibiting effect with increasing immersion times (15 min, 1 h, 4 h, and 48 h) as well as with increasing BTA concentrations (8.4 × 10⁻⁶, 8.4 × 10⁻⁵, 8.4 × 10⁻⁴, and 8.4 × 10⁻³ mol/dm³). In addition, at the lowest investigated BTA concentration (8.4 × 10⁻⁷ mol/dm³) an activation effect of this compound on copper dissolution was observed. Based on the Langmuir adsorption isotherm, the value of the standard free energy adsorption was found to be ΔG⁰ = −35.4 kJ/mol.     

Corrosion behavior of alumina ceramics in aqueous HCl and H2SO4 solutions

The corrosion behavior of cold isostatically pressed (CIP) high purity alumina ceramics in aqueous HCl and H₂SO₄ solutions with various concentrations has been studied simultaneously at room temperature (25 °C). Corrosion tests were also performed with 0.65 mol/l HCl and 0.37 mol/l H₂SO₄ solutions at 40, 55 and 70 °C for 48 h. Chemical stability was monitored by determining the amount of Al³⁺, Mg²⁺, Ca²⁺, Na⁺ Si⁴⁺ and Fe³⁺ ions eluted in different concentrations of HCl and H₂SO₄ solutions by means of atomic absorption spectrometry (AAS). By increasing the concentration from 0.37 to 6.5 mol/l, it was notified that the corrosion susceptibility in HCl and H₂SO₄ solutions for the CIP alumina specimens at room temperature decreases.     

A study of chromium-free pickling process before electroless Ni-P plating on magnesium alloys

A chromium-free pickling process of magnesium alloys in H₃PO₄ + Na₂MoO₄ solution for electroless Ni-P plating was described. The dosage of Na₂MoO₄ was established by detecting adhesion and corrosion resistance of chemical nickel coatings. Electrochemical behaviors of pickling solution of H₃PO₄ + Na₂MoO₄ and NH₄HF₂ activation solution were investigated with the open circuit potential curves and the polarization curves. The results show that the Na₂MoO₄ has strong inhibition ability. Na₂MoO₄ in H₃PO₄ solution can reduce active sites of microcathodic and microanodic zones in the corrosion cells of the substrate surface of magnesium alloys and plays an inhibition role. The activation film with some oxides and fluorides can prevent the substrate magnesium from the fierce displacement and corrosion reaction of electroless plating bath. The chemical Ni-P coating with good adhesion and corrosion resistance was obtained by the pretreatment of 200 cm³ dm⁻³ 85% H₃PO₄ + 5 g dm⁻³ Na₂MoO₄ pickling bath and activation in 200 g dm⁻³ NH₄HF₂ solution. This procedure of surface pretreatment before electroless nickel plating can replace the existing acid pickling containing chromium and HF activation.     

Inhibiting effects of butyl triphenyl phosphonium bromide on corrosion of mild steel in 0.5 M sulphuric acid solution and its adsorption characteristics

Butyl triphenyl phosphonium bromide (BuTPPB) has been evaluated as a corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solutions using galvanostatic polarisation and potentiostatic polarisation measurements. The study was also complemented by infra red (IR) spectroscopy, scanning electron microscopy (SEM) and quantum chemical calculations. Galvanostatic polarisation measurements showed that the presence of BuTPPB in aerated 0.5 M H₂SO₄ solutions decreases corrosion currents to a great extent and the corrosion rate decreases with increasing inhibitor concentration at a constant temperature. At 298K, inhibition efficiency was found to be 94.5% for 10⁻⁷ M BuTPPB which increased to about 99% for the BuTPPB concentration of 10⁻² M. The effect of temperature on the corrosion behaviour of mild steel was studied at five different temperatures ranging from 298 to 338K. The polarisation curves clearly indicate that BuTPPB acts as a mixed type inhibitor. Adsorption of BuTPPB on the mild steel surface follows the Langmuir isotherm.Potentiostatic polarisation measurements showed that passivation was observed only for lower BuTPPB concentrations (10⁻⁵ and 10⁻⁷ mol l⁻¹) for the mild steel in 0.5 M H₂SO₄. IR and SEM investigations also confirmed the adsorption of BuTPPB on the mild steel surface in 0.5 M H₂SO₄ solutions. The molecular parameters obtained using PM3 semi-empirical method, were correlated with the experimentally measured inhibitor efficiencies.