Radiotracer study of embedding of SO4 and Cl ions into the surface film formed on Mn corroding in perchlorate solution

The adsorption of radiolabelled Cl⁻ and SO₄⁻ ions from aqueous perchlorate solutions onto powdered Mn metal was studied. It was found that the extent of the adsorption is determined by the continuous increase of the thickness of the surface oxide/hydroxide layer formed as a consequence of the slow corrosion of the metal in neutral or quasi-neutral media. At low pH values (pH < 6) the extent of the adsorption decrease significantly owing to the dissolution of the surface layer. At high pH values (pH > 10) the adsorption decreases presumably owing to the competitive adsorption of OH⁻ ions or the modification of the adsorption centres by some kind of deprotonation.     

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.     

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.     

On the reduction of ClO4 ions in the course of metal dissolution in HClO4 solutions

The problem of the application of perchloric acid and/or perchlorate supporting electrolyte in electrochemical and corrosion studies is discussed. It is demonstrated that in contrast to the general view in the literature the reduction of perchlorate ions could be an important step in the overall process occurring in the course of spontaneous dissolution of some metals in acid perchlorate medium. It is shown that especially in the case of the dissolution of iron the reduction of ClO₄⁻ leading to the formation of Cl⁻ plays a substantial role. Consequently, all interpretations concerning the dissolution of iron in the presence of ClO₄⁻ ions should be revisited taking into consideration the possibility of the reduction process.     

The electrochemical behaviour of leaded brass in neutral CL and SO4 media

The electrochemical behaviour of lead brass with different leaded content in neutral chloride and sulphate solutions was investigated using the EIS technique. For comparison, the behaviour of the pure components of the alloy was investigated under the same conditions. The corrosion process was found to proceed via oxygen reduction following a diffusion controlled mechanism. The Cu electrode showed a higher polarization resistance due to film formation during oxygen reduction. Zn and Pb showed markedly lower impedance values due to continuous dissolution. The two investigated brass alloys (1.8% and 3.5% Pb, respectively) showed higher impedance values indicating the passivation of the surface in the Cl⁻ or SO₄⁻ media. Brass II was found to be more stable against corrosion indicating the beneficial effect of the lead content in the alloy.At cathodic potentials, the only process is the oxygen reduction. Anodic polarization leads to selective dissolution of Zn. At more positive potentials simultaneous dissolution of the alloy components with the deposition of Cu(I) salt takes place leading to the passivation of the alloy surface. At higher potentials, film breakdown occurs producing Cu(II) compounds whose diffusion control the corrosion process. At potentials higher than − 0.1 V, pitting corrosion was observed and a transmission line type in the impedance spectra was recorded.     

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.     

Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

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.     

Color-tunable and white-light emitting lanthanide complexes based on (CexEuyTb1−x−y)2(BDC)3(H2O)4

Ce³⁺, Eu³⁺ and Tb³⁺ complexes were synthesized through facile and mild approaches with terephthalic acid (H₂BDC) as the ligand. Their chemical compositions were determined as (Ce_xEu_yTb_1−x−y)₂(BDC)₃(H₂O)₄ by elemental analysis (EA), Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) measurements. Fluorescent properties of the as-synthesized complexes were investigated by changing the molar ratio of Ce³⁺, Tb³⁺ and Eu³⁺ ions, and the optimized ratio of 3.0:2.0:0.15 for Ce³⁺:Tb³⁺:Eu³⁺ in the complex was determined for white-light emission. Tuning on the emitting color was realized by adjusting the ratio among lanthanide ions, indicating the energy transfer process inside the complex. It was found that Tb³⁺ could sensitize the fluorescence of Eu³⁺ while its own fluorescence was quenched by the latter ion, and concentration quenching of Ce³⁺ was also observed. Fairly good thermal stability and oxidation resistance of the as-synthesized complexes were also demonstrated.     

Novel application of radiotracer techniques for corrosion studies of zinc and aluminium in acidic medium

The adsorption of sulphate ions on Zn and Al was studied in 0.5 M NaClO₄ supporting electrolyte at various pH values in the range of pH=2-7 by radiotracer techniques. It was found in both cases that the adsorption of sulphate passes over maximum in the pH range studied.The phenomena observed are interpreted by the assumption that the main component of the overall process is anion adsorption on the protonated oxides/hydroxides formed as a result of corrosion. At low pH values the steady state coverage with respect to these products should be very low owing to their dissolution; consequently the extent of anion adsorption induced must also be very low. At higher pH values where no protonation occurs the adsorption of anions decreases significantly.     

Corrosion inhibition of zinc in tetra-n-butylammonium bromide aerated aqueous solution by benzotriazole and Na3PO4

The effect of benzotriazole (BTA), Na₃PO₄ and their mixture on the corrosion of zinc in 17 wt.% (0.534 mol l⁻¹) 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 SEM/EDX techniques. The experimental results showed that BTA or Na₃PO₄ or inhibitor mixture could protect zinc in aqueous TBAB solution. The inhibitor combinations led to higher efficiencies compared to those obtained when added individually. An inhibition efficiency of an inhibitor mixture consisting of 0.5 g l⁻¹ BTA and 1 g l⁻¹ Na₃PO₄ was more than 97%.     

Synthesis,characterization, morphology control of poly (p-phenylenediamine)-Fe3O4 magnetic micro-composite and their application for the removal of Cr2O7 from water

In this paper, poly (p-phenylenediamine)-Fe₃O₄ (PpPD-Fe₃O₄) magnetic micro-composite was synthesized via chemical oxidation polymerization of p-phenylenediamine (pPD) monomers with (NH₄)₂S₂O₈ (APS) and Fe(NO₃)₃ at room temperature. The results demonstrated that the morphologies of this magnetic micro-composite were varied by tuning the consistence of Fe(NO₃)₃ in solution. The structures, morphologies and properties of the composites were characterized with IR, Raman spectroscopy, XRD, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and flame atomic absorption spectrometry (FAAS). This magnetic composite showed excellent ability on absorption of Cr₂O₇²⁻. This magnetic composite is low cost, easy to operate and separate from solution. The mechanism research shows that the chemical adsorption and physical adsorption exist at the same time in adsorption process.     

Synthesis and conductivity of GdPO4 nanorods: Impacts of particle size and Ca doping

A series of Gd_1−xCa_xPO₄·nH₂O nanorods were prepared using a simple hydrothermal reaction which was optimized by tuning the pH values of the precursor. The resulted nanorods were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, and alternative current impedance technique. It is demonstrated that all Gd_1−xCa_xPO₄·nH₂O nanorods crystallized in a pure hexagonal structure. For x = 0, the particle dimension decreased with increasing the pH value. For x > 0, the solid solution limit of Ca²⁺ in GdPO₄·nH₂O nanorods was about 3 mol%, below which the lattice volume increased with increasing the doping level of Ca²⁺. The conductivities of nanorods were highly dependent on both the particle size and Ca²⁺ concentration, as indicated by the increased conductivity as particle size reduces or Ca²⁺ doping level increases. These observations were understood in terms of the dehydration and the introduction of HPO₄²⁻ defects by Ca²⁺ doping.     

Preparation of Ni0.5Zn0.5Fe2O4/SiO2 nanocomposites and their adsorption of bovine serum albumin

The magnetic nanocomposites of (1 − x)Ni_0.5Zn_0.5Fe₂O₄/xSiO₂ (x = 0-0.2) were synthesized by the citrate-gel process and their absorption behavior of bovine serum albumin (BSA) was investigated by UV spectroscopy at room temperature. The gel precursor and resultant nanocomposites were characterized by FTIR, XRD, TEM and BET techniques. The results show that the single ferrite phase of Ni_0.5Zn_0.5Fe₂O₄ is formed at 400 °C, with high saturation magnetization and small coercivity. A porous, amorphous silica layer is located at the ferrite nanograin boundaries, with the silica content increasing from 0 to 0.20, the average grain size of Ni_0.5Zn_0.5Fe₂O₄ calcined at 400 °C reduced from about 18-8 nm. Consequently, the specific surface area of the nanocomposites ascends clearly with the increase of silica content, which is largely contributed by the increase in the thickness of the porous silica layer. The Ni_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites demonstrate a better adsorption capability than the bare Ni_0.5Zn_0.5Fe₂O₄ nanoparticles for BSA. With the increase of the silica content from 0 to 0.05 and the specific surface area from about 49-57 m²/g, the BSA adsorption capability of the Ni_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites calcined at 400 °C improve dramatically from 22 to 49 mg/g. However, with a further increase of the silica content from 0.05 to 0.2, the specific surface area increase from about 57-120 m²/g, the BSA adsorption for the nanocomposites remains around 49 mg/g, owing to the pores in the porous silica layer which are too small to let the BSA protein molecules in.     

Role of ClO4 in breakdown of tin passivity in NaOH solutions

The anodic behaviour of a tin electrode in NaOH solutions containing different concentrations of NaClO₄ was studied by employing potentiodynamic, potential transient under constant current density methods and complemented with scanning electron microscopy (SEM). In perchlorate-free NaOH solutions, the E/i response exhibits active/passive transition. The active region involves two anodic peaks corresponding to the formation of Sn(II) and Sn(IV) species respectively. The permanent passive layer is duplex and consists of SnO and SnO₂. Additions of NaClO₄ to the alkali solution, accelerates the active dissolution of tin and tends to breakdown the duplex passive layer at a certain breakdown potential. SEM examination confirms the occurrence of film breakdown. The breakdown potential decreases with an increase in ClO₄⁻ concentration, but increases with increasing both OH⁻ concentration and scan rate. The potential-time transients display that the incubation time for pit initiation decreases with increasing both ClO₄⁻ concentration and anodic current density.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Environmental factors affecting the corrosion behavior of reinforcing steel II. Role of some anions in the initiation and inhibition of pitting corrosion of steel in Ca(OH)2 solutions

Potential-time curves are constructed for the steel electrode in naturally aerated Ca(OH)₂ solutions simulating the corrosion behavior in concrete. Cl⁻ and SO₄²⁻ ions cause the destruction of passivity and initiation of pitting corrosion. The rate of oxide film growth by Ca(OH)₂ and oxide film destruction by Cl⁻ and SO₄²⁻ ions follows a direct logarithmic law as evident from the linear relationships between the open-circuit potential and the logarithm of immersion time. Chromate, phosphate, nitrite, tungstate and molybdate ions inhibit the pitting corrosion of steel. The rate of oxide film healing and thickening increases with their concentrations. In presence of constant inhibitor concentration, the efficiency of pitting inhibition increases in the order: (weak) CrO₄²⁻ < HPO₄²⁻ < NO₂⁻ < WO₄²⁻ < MoO₄²⁻ (strong).     

Environmental factors affecting the corrosion behavior of reinforcing steel III. Measurement of pitting corrosion currents of steel in Ca(OH)2 solutions under natural corrosion conditions

Using a simple electrolytic cell, the pitting corrosion current of reinforcing steel is measured in Ca(OH)₂ solutions in presence of chloride and sulfate as aggressive ions. Pitting corrosion current starts to flow after an induction period which depends on the concentration of both the aggressive and the passivating anions. The pitting corrosion current densities reach steady-state values which depend also on the type and concentration of the corrosive and passivating anions. The corrosive action of the aggressive species decreased in the order: SO₄²⁻ > Cl⁻. Corrosion of the steel is found to be governed by a single electron transfer reaction. Raising the temperature decreases the induction period associated with pit initiation and increases the corrosion current associated with pit propagation. From Arrhenius plots, the activation energies for both pit initiation and pit propagation in presence of chloride and sulfate ions are calculated.     

Polarized spectral analysis of Er ions in Er:LiGd(MoO4)2 crystal

The Er³⁺:LiGd(MoO₄)₂ crystal with Ø21 × 33 mm³ was grown by the Czochralski technique, and the absorption spectra, the fluorescence spectra and the fluorescence decay curves were measured at room temperature. Some spectroscopic parameters, such as the parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the emission cross-sections were estimated based on Judd-Ofelt theory and Füchtbauer-Ladenburg method. The infrared emission at 1450-1650 nm, due to ⁴I_13/2 → ⁴I_15/2 transition and the visible emission at 520-569 nm corresponding to ²H_11/2,⁴S_3/2 → ⁴I_15/2 transition were observed in Er³⁺:LiGd(MoO₄)₂ crystals under 979 nm excitation at room temperature. The emission cross-sections are 4.37 × 10⁻²⁰ cm² at 553 nm and 0.584 × 10⁻²⁰ cm² at 1561 nm for π-polarization, and the following measured lifetimes are 4.57 ms and 10.74 μs. The upconversion emissions were attributed to energy transfer between Er³⁺ ions and the excited state absorption.     

One-pot synthesis of polyaniline/Fe3O4 nanocomposites with magnetic and conductive behaviour. Catalytic effect of Fe3O4 nanoparticles

Polyaniline/Fe₃O₄ nanocomposites were prepared by a one-pot synthesis using N-(4-aminophenyl)aniline as the reagent, molecular oxygen or hydrogen peroxide as the oxidizing agents in the presence of Fe₃O₄ nanoparticles (NPs) in powder and ferrofluid form. Both magnetic NPs in powder and ferrofluid form showed similar catalytic behaviour. The catalytic effect is particularly evident when molecular oxygen was used as the oxidizing agent. However, concerning the morphological aspects, only the composites prepared in the presence of ferrofluid-type Fe₃O₄ NPs showed a preferential morphology of nanorods (between 30 and 110 nm in diameter). All the composites are superparamagnetic at room temperature but at low temperature they are in a blocked state. Inter-particle interactions significantly affect the magnetic properties of the composites. The electrical conductivity of the composites is about 10⁻² S cm⁻¹, in agreement with the values obtained for polyaniline prepared by chemical route. A mechanism of the nanorods formation is proposed.