Factors affecting the corrosion behaviour of aluminium in acid solutions. II. Inorganic additives as corrosion inhibitors for Al in HCl solutions

CrO₄²⁻, WO₄²⁻ and HPO₄²⁻ ions affect on the corrosion behaviour of Al in 2 M HCl. The inhibition efficiencies of the additives depend on their type and increase with increasing concentration. Oxide film destruction and/or repair follow a direct logarithmic law. The inhibitive action of these anions is discussed in terms of competitive adsorption with Cl⁻ ions on the electrode surface followed by a reduction mechanism to form metal oxides. The calculated values of ΔG°_ads of the inhibition process reveal a physical adsorption of the inhibitors. The inhibition efficiency is found to decrease in the order: CrO₄²⁻ > WO₄²⁻ > HPO₄²⁻.     

Passivity of Sanicro28 (UNS N-08028) stainless steel in polluted phosphoric acid at different temperatures studied by electrochemical impedance spectroscopy and Mott–Schottky analysis

Corrosion resistance of a highly alloyed austenitic stainless steel (Sanicro28) in 50 wt.% H₃PO₄ industrial medium containing impurities at temperatures from 20 °C to 80 °C was evaluated after different immersion times. Electrochemical measurements (polarization curves, OCP, EIS and Mott–Schottky) demonstrated that Sanicro28 passivates spontaneously. From impedance results, film thicknesses of about 1.6–4.5 nm were obtained. At low temperature, the resistance to corrosion increases with immersion time due to the formation of iron phosphate and/or chromium phosphate. At higher temperature, phosphate formed a porous polyphosphate film identified by μ-Raman. No pits are initiated on surface whatever the temperature.     

XPS study on the surface films of a newly designed Ni-free Ti-based bulk metallic glass

The electrochemical and corrosion behavior of a newly designed Ni-free Ti-based bulk metallic glass (BMG) was investigated. The Ti₄₅Zr₁₀Pd₁₀Cu₃₁Sn₄ BMG exhibits excellent corrosion resistance after immersion in 3 mass% NaCl, 1 N H₂SO₄ and 1 N H₂SO₄ + 0.01 N NaCl solutions. X-ray photoelectron spectroscopy measurements were used to analyze the changes of the elements on the alloy surface before and after immersion in various solutions. The formation of Ti- and Zr-enriched highly protective thin surface films is responsible for the high corrosion resistance of this alloy in corrosive solutions.     

Influence of anions on the formation of artificial steel rust particles prepared from acidic aqueous Fe(III) solution

For simulation of atmospheric corrosion of steels, artificial steel rust particles were prepared in acidic aqueous solutions containing FeCl₃, Fe(NO₃)₃ and Fe₂(SO₄)₃. A single phase α-FeOOH was formed in only Fe(NO₃)₃ system. The β-FeOOH was formed by added Cl⁻ in FeCl₃–Fe(NO₃)₃ system. Adding SO₄²⁻ in Fe(NO₃)₃, FeCl₃ and a mixture of FeCl₃–Fe(NO₃)₃ solutions turned the products following as α- or β-FeOOH → Schwertmannite (Fe₈O₈(OH)₆(SO₄)·nH₂O). Further, increasing the added SO₄²⁻ suppressed the formation of steel rust particles. Accordingly, the influence of anions on the formation of steel rust particles was to be suggested in order of SO₄²⁻ ≫ Cl⁻ > NO₃⁻.     

Microstructural characteristics and microwave dielectric properties of Ba[Mg1/3(Nbx/4Ta(4−x)/4)2/3]O3 ceramics

Sintering behaviors and microstructural characteristics in solid solutions of Ba[Mg_1/3(Nb_x/4Ta_(4−x)/4)_2/3]O₃ (BMN_xT_4−x, x = 0, 1, 2, 3 and 4) were investigated by X-ray diffraction, SEM and TEM. Microwave dielectric properties, such as the relative permittivity (ɛ_r), quality factor (Q) value and temperature coefficient of resonator frequency (τ_f), were also measured. The excellent microwave dielectric property of Ba(Mg_1/3Ta_2/3)O₃ (BMT) sample imply the necessity to sinter at higher temperature (1650 °C) and to use longer soaking times (9 h), but not for Ba(Mg_1/3Ta_2/3)O₃ (BMN). The 1:2 B-site ordering was maintained at all Nb substitution contents and the 1:2 B-site ordering existed in the grains with antiphase domain boundaries (APBs). The Ba[Mg_1/3(Nb_1/4Ta_3/4)_2/3]O₃ specimen exhibited excellent microwave dielectric properties, ɛ_r = 25.534, Qf = 140 666 GHz, and τ_f = 4.8 (ppm/°C). The excellent microwave dielectric property is due to the improvement of sintering property by appropriate Nb atoms substitution in the BMT matrix and the maintaining of 1:2 ordering in the BMN_xT_4−x series.     

Growth kinetics of oxide films at the polyaniline/mild steel interface

The growth rate of oxide film formed at the polyaniline/mild steel interface was investigated by open circuit potential (OCP) measurements. The OCP of polyaniline base (EB) coated electrode displayed three feature changes during immersion: t₁ ? t₂, t₂ ? t₃ and >t₃, and the oxide film grew mainly in t₂ ? t₃ time range. The oxide film growth followed a direct logarithm law, the growth rate decreased with increasing NaCl concentration and temperature. With increasing pH, the growth rate decreased first and then increased. The apparent activation energy of oxide film growth was calculated as ?39.8 kJ/mol, indicates that oxide film growth was under diffusion control.     

Corrosion properties of glassy Mg70Al15Ga15 in 0.1 M NaCl solution

The corrosion behavior of glassy Mg₇₀Al₁₅Ga₁₅ was investigated in 0.1 M NaCl solutions of various pH values. Potentiodynamic polarization measurements confirm a pronounced passivity for 4 ≤ pH ≤ 12. Corrosion currents in neutral solutions are found to be as low as 10^?6 A/cm². Optical microscopy and Auger electron spectroscopy were performed on samples immersed under open-circuit conditions in neutral, acidic and alkaline 0.1 M NaCl solutions to observe their time-dependent passive film formation. A significant incorporation of aluminum in the surface layers was found. The alloys show an unusual stability against dissolution in chloride-containing solutions, raising expectations of a highly corrosion-resistant Mg-based alloy. The time-dependent limitations of this stability are discussed in context with the surface films observed.     

Effects of CF4 plasma treatment on the moisture uptake,diffusion, and WVTR of poly(ethylene terephthalate) flexible films

We studied the effects of CF₄ plasma surface treatment on moisture uptake, diffusion, and the water-vapor-transmission-rate (WVTR) of poly(ethylene terephthalate) (PET) films using a CF₄ plasma generated by a radio-frequency (13.56 MHz) reactive ion etcher at 60 W. After CF₄ plasma treatment, moisture uptake in PET film was reduced with increasing treatment time due to (1) lower adsorption of water molecules onto the hydrophobic surface, as confirmed by contact angle measurement and XPS analysis, and (2) reduced diffusion coefficient through the denser fluorinated top-layer as detected by XRR. In addition, the WVTR of untreated PET is found to be 2.7 g/m²/day, while a significant reduction (84%) of WVTR to 0.43 g/m²/day, is achieved for CF₄ plasma-treated PET film (60 W, 15 min), which alters the surface hydrophobicity (~ 107°) and simultaneously builds a denser, fluorinated top-layer (47 nm). The surface fluorinated layer has a diffusivity of to 8.7 × 10^?12 m²/s and a WVTR of ~ 1.0 × 10^?4 g/m²/day based on a series resistance model.     

High hydrogen permeability in the Nb-rich Nb–Ti–Ni alloy

The microstructure and the hydrogen permeability of the Nb-rich Nb–Ti–Ni alloy, i.e., the Nb₅₆Ti₂₃Ni₂₁ alloy were investigated and compared with those of the Nb₄₀Ti₃₀Ni₃₀ alloy. The Nb₅₆Ti₂₃Ni₂₁ alloy consisted of a combination of the primary phase bcc- (Nb, Ti) solid solution with the eutectic phase {bcc- (Nb, Ti) + B2-TiNi}. The volume fraction of the former and the latter phases were 62 and 38 vol.%, respectively. The Nb₅₆Ti₂₃Ni₂₁ alloy showed the higher Φ value of 3.47 × 10⁻⁸ (mol H₂ m⁻¹ s⁻¹ Pa^−0.5) at 673 K, which is 1.8 times higher than that of the Nb₄₀Ti₃₀Ni₃₀ alloy, which has been reported to be highest in the Nb–Ti–Ni system. The present work demonstrated that the Nb-rich Nb–Ti–Ni alloys consisting of only the primary phase bcc- (Nb, Ti) and the eutectic phase {bcc- (Nb, Ti) + B2-TiNi} are promising for the hydrogen permeation membrane.     

Effect of additives on the properties of plasma electrolytic oxidation coatings formed on AM50 magnesium alloy in electrolytes containing K2ZrF6

A plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was obtained in a K₂ZrF₆–NH₄H₂PO₄–KF–C₆H₅O₇Na₃ electrolyte solution. The influence of the electrolytes on the properties of the PEO coating had been investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), roughness determination and electrochemical measurements. The experimental results show that 10 g L^? 1 K₂ZrF₆ and the presence of 8 g L^? 1 NH₄H₂PO₄ are beneficial for the passivation effect of the solution on AM50 Mg alloy as well as the compactness of the PEO coating. Many pores with large dimension on the surface of the coating are filled with coating compounds (mainly MgF₂), and the characteristics of these pores are influenced by the concentration of KF. The addition of KF and C₆H₅O₇Na₃ enhances the growth rate of the coating. The coating shows high corrosion resistance in the presence of 10 g L^? 1 K₂ZrF₆ combined with 8 g L^? 1 NH₄H₂PO₄, 3 g L^? 1 KF and 5 g L^? 1 C₆H₅O₇Na₃.     

The migration of ions through poly(3-octylthiophene)

Molecular dynamics (MD) simulations are used to investigate the abilities of several anions (Cl⁻, BF₄⁻, ClO₄⁻, SO₄²⁻ and PO₄³⁻) to migrate in a matrix of oxidised poly(3-octylthiophene) formed by doping the polymer. The transport of the ions is considered when it is induced both by thermal effects and by an electric field. When a degree of disorder is introduced into the lattice, the Coulomb association of the polymer and anion subsystems retains persistent lattice domains in which the ions are intercalated between the thiophene rings of the polymer backbone forming channel sites for the ions. This order seems to be a consequence of the alkyl side chains, as it is not found in unsubstituted polythiophene. Transport of the singly-charged ions occurs readily along the channels’ encountering low barriers (4 kJ mol⁻¹), but the motions of the SO₄²⁻ and PO₄³⁻ ions are precluded, presumably due to coulombic effects. Application of electric fields along the channel directions induces the motion of the SO₄²⁻ and PO₄³⁻ ions also, but applying fields perpendicular to the channel destroys the lattice order. The transport of BF₄⁻ ions in a molecular channel is simulated by twisting the poly(3-octylthiophene) into a helix and examining the migration of the ions both inside and outside the helix channel.     

Synthesis,characterization, thermal stability,conductivity and band gap of oligo-4-[(2-hydroxybenzylidene)amino]benzoic acid

In this study, the oxidative polycondensation reaction conditions of 4-[(2-hydroxybenzylidene)amino]benzoic acid (4-HBAB) by using oxidants such as air O₂, H₂O₂ and NaOCl were studied in an aqueous alkaline medium between 40 and 90 °C. The structures of the synthesized monomer and oligomer were confirmed by FT-IR, UV–vis, NMR and elemental analysis. The characterization was made by TG-DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of oligo-4-[(2-hydroxybenzylidene)amino]benzoic acid (O-4-HBAB) was found to be 68% (for air O₂ oxidant), 70% (for air H₂O₂ oxidant) 53% (for NaOCl oxidant). According to the SEC analysis, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of O-4-HBAB were found to be 932, 1469 g mol⁻¹ and 1.576, using H₂O₂, and 1895, 2560 g mol⁻¹ and 1.354, using air O₂ and 2320, 3015 g mol⁻¹ and 1.300, using NaOCl, respectively. According to TG analysis, the weight losses of 4-HBAB and O-4-HBAB were found to be 96.86% and 73.10% at 1000 °C, respectively. O-4-HBAB was shown higher stability against thermal decomposition. Also, electrical conductivity of the O-4-HBAB was measured, showing that the polymer is a typical semiconductor. Electrochemical HOMO, LUMO and energy gaps (E_g) of 4-HBAB and O-4-HBAB were found to be −6.28, −6.36; −2.39, −2.64; 3.89 and 3.72 eV, respectively. According to UV–vis measurements, optical band gap (E_g) of 4-HBAB and O-4-HBAB were found to be 3.23 and 3.09 eV, respectively.     

Neutron structural and vibrational studies of dipotassium selenate tellurate

At room temperature the potassium selenate tellurate K₂SeO₄·Te(OH)₆ (KSeTe) was prepared from water solution of H₆TeO₆ and K₂SeO₄. Its structure has been determined from single crystal using neutron diffraction data. KSeTe is monoclinic with C2/c space group. The unit cell parameters are: a = 11.572(9) Å, b = 6.437(7) Å, c = 13.938(1) Å, β = 106.07(7)°, V = 997.7(1) Å³ and Z = 4. The main feature of this structure is the presence of two different and independent anions (TeO₆⁶⁻ and SeO₄²⁻) in the same unit cell. The structure is built by layers of TeO₆ octahedra altering with planes of SeO₄ tetrahedra linked by a network of hydrogen bonds performed by protons belonging to the OH hydroxide groups. DSC measurements indicate that the crystals of K₂SeO₄·Te(OH)₆ undergo three endothermal peaks at 433, 480 and 495 K.Raman scattering measurements on KSeTe material taken between 300 and 620 K are reported in this paper. The spectra indicate clearly these phase transitions.     

Barium- and strontium-enriched (Ba0.5Sr0.5)1+xCo0.8Fe0.2O3−δ oxides as high-performance cathodes for intermediate-temperature solid-oxide fuel cells

(Ba_0.5Sr_0.5)_1+xCo_0.8Fe_0.2O_3−δ, or BSCF(1 + x), (0 ⩽ x ⩽ 0.3) oxides were synthesized and investigated as cathodes for intermediate-temperature solid-oxide fuel cells. The A-site cation excess in BSCF(1 + x) resulted in a lattice expansion and the creation of more active sites for oxygen reduction reaction due to the lowered valence states of the B-site ions and the increased oxygen vacancy concentration, which improved the oxygen adsorption process. On the other hand, the A-site excess could also result in higher resistances for oxygen adsorption (due to the formation of BaO and/or SrO impurities), and oxygen-ion transfer (by facilitating the solid-phase reaction between the cathode and the electrolyte). By taking all these factors into account, we found BSCF1.03 to be the optimal composition, which lead to a peak power density of 1026.2 ± 12.7 mW cm⁻² at 650 °C for a single cell.     

Synthesis of macroscopic SiC nanowires at the gram level and their electrochemical activity with Pt loadings

Macroscopic SiC nanowires (SiCNWs) were successfully synthesized at the gram level (2–4 g h^?1) by using a simple solid–vapor reaction of silicon powders and carbon oxides, assisted by ZnS. This results in a promising material for a wide range of applications. The obtained products possess a small size of 10–30 nm and a good single-crystal structure. In addition, a specific surface area of 1.6 m² g^?1 was achieved. A high electrochemical activity to H₂ adsorption/desorption and methanol oxidation was observed from cyclic voltammograms in H₂SO₄ and H₂SO₄/CH₃OH solutions after loading with 50 wt.% Pt. Furthermore, a high catalytic performance for oxygen reduction at ～0.57 V and good chemical stability were displayed. The novel SiCNW-supported catalyst shows potential for fuel cells with long lifetimes.     

Preparation of self-organized porous anodic niobium oxide microcones and their surface wettability

Porous anodic niobium oxide with a pore size of ～10 nm was formed at 10 V in glycerol electrolyte containing 0.6 mol dm^?3 K₂HPO₄ and 0.2 mol dm^?3 K₃PO₄ at 433 K. After prolonged anodizing for 5.4 ks, niobium oxide microcones develop on the surface. X-ray diffraction patterns of the anodized specimens revealed that the initially formed anodic oxide is amorphous, but an amorphous-to-crystalline transition occurs during anodizing. As a consequence of the preferential chemical dissolution of the initially formed amorphous oxide, due to different solubility of the amorphous and crystalline oxides, crystalline oxide microcones appear on the film surface after prolonged anodizing. The surface is superhydrophilic. After coating with fluorinated alkylsilane, the surface becomes superhydrophobic with a contact angle of 158° for water. The surface is also oil repellent, with a contact angle as high as 140° for salad oil.     

Preparation and characterization of a polypyrrole hybrid film with [Ni(dmit)2]2−, bis(1,3-dithiole-2-thione-4,5-dithiolate)nickellate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Ni(dmit)₂] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in acetonitrile solution is reported. The material was characterized by cyclic voltammetry, UV–vis and infrared spectroscopies, scanning electron microscopy (SEM), atomic force microscopy (AFM) and thermal gravimetric analysis (TGA). The FTIR spectroscopy showed that the [Ni(dmit)₂]²⁻ anion has been inserted in the polypyrrole framework and was not destroyed or modified during the polymerization process. The voltammetric analysis indicated that the material has electroactivity and undergoes redox processes associated with the conducting polymer and the counteranion. The cyclic voltammetry results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Ni(dmit)₂]²⁻ exhibits good thermal stability and a intrinsic conductivity value in the range of semiconductors (10⁻³ S cm⁻¹).     

Polypyrrole nanowire modified graphite (PPy/G) electrode used in capacitive deionization

With high specific capacitance and good conductivity, polypyrrole nanowire modified graphite (PPy/G) electrode has great promising applications in capacitive deionization (CDI). Preparation parameters of modified electrode such as concentration of supporting electrolyte solution (LiClO₄), concentration of monomer (pyrrole, Py), pH of polymerization medium, polymerization potential and time have significant effects on the electrode adsorption capacity of NaCl. The experimental results indicate that the optimal preparation condition of the PPy/G electrode used for CDI is 0.10 M LiClO₄, 0.19 M Py and pH 5.91 which was controlled by phosphates buffer solution (PBS, 0.10 M), polymerized at 0.85 V vs saturated calomel electrode (SCE) with polymerization time of 150 s. The obtained electrode has an area specific capacitance of 0.188 F/cm² determined by cyclic voltammetry (CV) method in 1.0 M HClO₄ at a scanning rate of 0.05 V/s. In addition, the desalination experiments of the electrode were carried out in 500 ppm NaCl solution at a working voltage of 1.4 V. The experimental results indicate that the NaCl can be removed from the feed solution by electroadsorbing of the electrode with good desalination stability and the electrode can be regenerated efficiently by its electrodesorbing.