Schiff bases of increasing complexity as mild steel corrosion inhibitors in 2 M HCl

The effect of three Schiff base compounds with increasing number of coordination sites, namely, 2-{(E)-[(2-hydroxyethyl)imino]methyl} phenol (I), 2-[(E)-({2-[(2-hydroxyethyl)amino]ethyl}imino)methyl]phenol (II) and 2,2′-{iminobis[ethane-2,1-diylnitrilo(E)methylylidene]}diphenol (III) have been investigated at 298 K by weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The inhibition efficiencies obtained from all methods employed are in good agreement. Results show compound III to be the best inhibitor with a mean efficiency of 93% at 10⁻² M additive concentration. Studies showed all three compounds to act as mixed type inhibitors.     

Two-dimensional X-shaped organic dyes bearing two anchoring groups to TiO2 photoanode for efficient dye-sensitized solar cells

Novel two-dimensional X-shaped donor–π–acceptor (D–π–A)-type dyes were designed and successfully synthesized for use in a dye-sensitized solar cell (DSSC). Two triphenylamine units in these dyes act as electron donor units, while two cyanoacrylic acid groups act as electron acceptor units and anchoring groups to the TiO₂ photoanode. The photovoltaic properties of the newly synthesized dye-containing DSSCs were investigated to identify the effects of conjugation length between the electron donors and acceptors, and the molecular energy levels of the dyes. Among the three dyes we synthesized, (2E,2′E)-3,3′-(5′,5″-(4,5-bis(4-(bis(4-tert-butylphenyl)amino)styryl)-1,2-phenylene)bis(2,2′-bithiophene-5′,5-diyl))bis(2-cyanoacrylic acid) (11) showed the highest power conversion efficiency of 3.14% (η_max = 4.06% with TiCl₄ treatment) under AM 1.5G illumination (100 mW cm⁻²) in a photoactive area of 0.418 cm² with short circuit current density of 7.27 mA cm⁻², open circuit photovoltage of 612 mV, and a fill factor of 70.6%.     

Synthesis and nonlinear optical characterization of new poly{2,2′-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]}

A new donor–acceptor type poly{2,2′-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]} (P) was synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. The polymerization was carried out using chemical polymerization technique. The optical and charge-transporting property of the copolymer was investigated by UV–vis, fluorescence emission spectroscopic and cyclic voltammetric studies. The copolymer shows UV absorption maxima at 375 nm and displays bluish-green fluorescence in DMF solution. Its electrochemical band gap was determined to be 2.07 eV. The nonlinear optical (NLO) properties of the copolymer was investigated at 532 nm using single beam Z-scan and degenerate four-wave mixing (DFWM) techniques with nanosecond laser pulses. The copolymer exhibits strong optical limiting behavior due to effective three-photon absorption (3PA). Values of the effective 3PA coefficient (γ), third-order nonlinear susceptibility (χ⁽³⁾) and figure of merit (F) have been calculated.     

Action of chelators on solid iron in phosphate-containing aqueous solutions

To study the effect of strong iron-ligands on steel corrosion, mild steel electrodes were immersed in solutions containing 20 mM phosphate buffer (pH=7.2) and between 0.01 mM and 1 M of either the iron(II)-chelators 2,2^′-bipyridine or FerroZine, or the iron(III)-chelators citrate or acetylacetonate. Resulting surface reactions were investigated by quantifying the electrochemical potential (E), the electrochemical polarization resistance (R_p), the corrosion current (I_corr) and the release of iron into solution. The surface was further analyzed by scanning electron microscopy (SEM/SEM-EDAX) and atomic force microscopy. Concentrations of 0.1 mM of any of the chelators led to slight, temporary changes in E, I_corr and R_p. Concentrations of 10 mM resulted in characteristic changes of E, which were the same for all chelators and in the precipitation of FePO₄ in the case of citrate and acetylacetonate, or vivianite [Fe₃(PO₄)₂ · 8H₂O] in the case of bipyridine and FerroZine. Concentrations of 1 mM of both iron(III)-chelators led to a temporary drop of E similar to that found with 0.1 mM chelator. With iron(II)-chelators, E dropped to about −500 mV before oscillating for several days. The amplitudes of the oscillations were up to 200 mV with periods of 30 and 20-25 min for bipyridine and FerroZine, respectively.     

Novel cationic gemini surfactants as corrosion inhibitors for carbon steel pipelines

In the present investigation novel cationic gemini surfactants namely: bis(p-(N,N,N-octyldimethylammonium bromide)benzylidene)benzene-1,4-diamine (I), bis(p-(N,N,N-decyldimethylammonium bromide)benzylidene)benzene-1,4-diamine (II), and bis(p-(N,N,N-dodecyldimethylammonium bromide)benzylidene)benzene-1,4-diamine (III) were synthesized, characterized, and tested as corrosion inhibitors for carbon steel in 1 M HCl solution. The corrosion inhibition efficiency was measured by using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and weight loss methods. The obtained results showed that, the synthesized inhibitors are excellent inhibitors for carbon steel in 1 M HCl solution. The inhibition efficiency decreased in the temperature range 30-40 °C and then increased in the temperature range 40-60 °C. The prepared inhibitors act as mixed inhibitors. Thermodynamic and activation parameters were discussed. Adsorption of the synthesized inhibitors was found to follow the Langmuir’s adsorption isotherm. Mixed physical and chemical adsorption mechanism is proposed. The morphology of carbon steel samples was investigated by scanning electron microscopy (SEM).     

High color rendering white organic light-emitting diodes fabricated using a broad-bandwidth red phosphorescent emitter for lighting applications

High color rendering white organic light-emitting devices (WOLEDs) were developed using a broad-bandwidth red phosphorescent iridium complex, bis[2-(1-naphthyl)benzothiazolato-N,C²′]iridium(III) acetylacetonate [Ir(absn)₂(acac)]. The red phosphorescent emitter Ir(absn)₂(acac) was used to fabricate blue–red and blue–green–red WOLEDs by combining blue-emitting bis[2-(4,6-difluorophenyl)pyridinato-N,C²′]iridium(III) picolinate (FIrpic) and green-emitting tris-fac-(2-cyclohexenylpyridine) iridium (III) [Ir(chpy)₃] in multiple-emissive layers. Mixed host emissive layers were employed using a hole-transport-type host 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) and an electron-transport-type host 2,6-bis[3-(carbazol-9-yl)phenyl]pyridine (DCzPPy) for efficient charge carrier injection. Di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) and 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB) were used as the hole and electron transporting layers, respectively. The effects of the emissive layer thickness and the doping ratios of different color dopants on WOLED performances were investigated. The WOLED based on ITO/TAPC/TCTA:FIrpic (10%):Ir(absn)₂(acac) (4%)/TCTA:Ir(chpy)₃ (9%, 6 nm)/DCzPPy:FIrpic (13%):Ir(absn)₂(acac) (4%)/BmPyPB/LiF/Al exhibited an external quantum efficiency of 10.7%, a power efficiency of 23.0 lm/W, a very high color rendering index (CRI) of 88.1, and a correlated color temperature (CCT) of 2629 K at 1000 cd/m².     

The inhibition of mild steel corrosion in acidic solutions by 2,5-bis(4-pyridyl)-1,3,4-thiadiazole: Structure-activity correlation

The effect of 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (4-PTH) on the corrosion of mild steel in acidic media (1 M HCl, 0.5 M H₂SO₄, 1 M HClO₄) has been investigated using weight loss measurements, electrochemical impedance spectroscopy and potentiodynamic polarisation. These studies have shown that 2,5-bis(4-pyridyl)-1,3,4-thiadiazole is good inhibitor for mild steel in 1 M HCl, 0.5 M H₂SO₄ and 1 M HClO₄ solutions, the better performances are seen in the case of 1 M HCl solutions. But in 1 M HClO₄, the 4-PTH stimulates corrosion at low concentrations. Polarisation curves indicate that the 4-PTH is a mixed-type inhibitor in all acidic media and E (%) is temperature-dependent. Adsorption on the mild steel surface follows the Langmuir isotherm model in all acidic media. The electronic properties obtained using the Hartree-Fock AB initio 3-21G quantum chemical approach, were correlated with the experimental efficiencies.     

Impedance and modulus analysis of the (Na0.6Ag0.4)2PbP2O7 compound

The electrical properties of the (Na_0.6Ag_0.4)₂PbP₂O₇ compound were studied using the complex impedance spectroscopy in the temperature range (502-667 K). Grain interior, grain boundary and electrode-material interface contributions to the electrical response are identified by the analysis of complex plan diagrams. The imaginary part of the modulus at several temperatures shows a double relaxation peaks, furthermore suggesting the presence of grains and grain boundaries in the sample. An analysis of the dielectric constants ?′, ?″ and loss tangent tan(δ) with frequency shows a distribution of relaxation times. The dc conductivity of the material is thermally activated with an activation energy about 0.8 eV which is in the vicinity of the that obtained from tan(δ) (E = 0.7 eV) and modulus (E_m = 0.68 eV) studies.     

Dielectric investigation of MM(PO4)2 double orthophosphates (M = Ca, Sr, Ba, Pb; M = Ti, Zr, Hf, Ge, Sn)

M^IIM^IV(PO₄)₂ (M^II = Ca, Sr, Ba, Pb; M^IV = Ti, Zr, Hf, Ge, Sn) ceramics were prepared by solid state reaction method and consolidated by spark plasma sintering in order to study their electrical properties. The dielectric study performed at room temperature was aimed to determine the basic electrical properties of these compounds. Maxwell-Wagner polarization contributions, which are active at low frequencies cause a strong extrinsic increase of both real and imaginary part of permittivity as well of the dc-conductivity for BaZr(PO₄)₂, BaTi(PO₄)₂, BaHf(PO₄)₂, and SrGe(PO₄)₂ double orthophosphates. Moderate real (ε^′r=20-150) and imaginary low-frequency permittivity (ε^′r=7-300) and typical Debye relaxation with relaxation time in the range of ms is typical for: PbHf(PO₄)₂, PbZn(PO₄)₂, and CaGe(PO₄)₂. At high-frequency (f = 10⁹ Hz), the ceramics have permittivities of 2.29÷8.02 and tangent loss of 0.003÷0.153. The compounds SrGe(PO₄)₂, BaGe(PO₄)₂, BaZr(PO₄)₂ and BaSn(PO₄)₂ have excellent high-frequency dielectric characteristics, with losses of 3÷6% and permittivity slightly above 2 and are possible candidate as microwave ceramics.     

The effects of substituting oxygen for terminal nitrogen in aniline oligomers 2: A DFT comparison of diamino,dihydroxyl, and monoamino/monohydroxyl terminated aniline trimers

The variant aniline trimers, N,N′-bis (3′,4′-diaminophenyl)-1,4-quinonediimine; N,N′-bis (3′-hydroxy-,4′-aminophenyl)-1,4-quinonediimine; and N,N′-bis (3′,4′-dihydroxyphenyl)-1,4-quinonediimine were synthesized, and the properties of the compounds compared to the results of density functional theory (DFT) calculations using the B3LYP functional. The calculations are complicated by the large number (five) of isomeric forms of each compound. Each compound energetically preferred the syn-, syn- (outer) isomer. The computed vertical ionization energies for the same isomer of each compound are 75.0, 76.10, and 83.1 kcal mol⁻¹, respectively. The trimer with two oxygen atoms on each outer ring thus holds electrons more tightly than the trimers with either one or zero oxygen atoms on the outer rings. The electronic spectra computed by the ΔSCF method are in excellent agreement with experimental values, though inclusion of solvent effects does not improve the predictions. A red-shift upon change to more polar solvents confirms that the principal absorption band for each trimer is π → π*, in agreement with electronic structure calculations.     

Novel efficient blue materials with 4H-cyclopenta[def]phenanthrene for OLEDs

Novel blue emitters, 2-[10-(4,4-dioctyl-4H-cyclopenta[def]phenanthrene-2-yl)-9-anthryl]-4,4-dioctyl-4H-cyclopenta[def]phenanthrene (OCPA) and 4,4,4′,4′,4″,4″-hexaoctyl-2,6′:2′,6″-tercyclopenta[def]phenanthrene (TerCPP) have been synthesized and characterized. The introduction of cyclopenta[def]phenanthrene units into the structure of OCPA and TerCPP leads LEDs with high efficiency and pure blue emission. Thermal analysis of OCPA and TerCPP reveals their high thermal stability. Their decomposition temperatures are around 410 °C for OCPA and 425 °C for TerCPP. The high-quality amorphous films of OCPA and TerCPP were prepared by vapor deposition. UV–visible absorption spectra of the thin films of these compounds appear at about 303–400 nm, and their maximum PL emission appeared at about 434 and 401 nm, respectively. The multi-layered OLEDs with the configuration of ITO/with or without PEDOT:PSS/NPD/OCPA or TerCPP/BAlq or BCP/Alq₃/LiF/Al were fabricated to investigate the electroluminescent properties and the current–voltage–luminescence characteristics of the compounds. Multi-layer organic EL devices with OCPA and TerCPP as an emitting layer produced bright blue (434 nm) and sky blue emissions (440 nm), respectively. The device of OCPA with the configuration of ITO/NPD/OCPA/BAlq/Alq₃/LiF/Al showed the turn-on voltage of about 5.6 V, the maximum brightness of 2500 cd/m² (at 11 V), the maximum luminescence efficiency of 1.2 cd/A, and CIE coordinates of 0.16 and 0.12 which are quite close to that of the National Television System Committee (NTSC) standard blue (0.14, 0.08).     

Selective dissolution of the γ phase in a binary Ni(γ)/Ni3Al(γ′) two-phase alloy

Selective dissolution of Ni(γ) in a binary Ni(γ)/Ni₃Al(γ′) two-phase alloy was performed in an aqueous electrolyte including 1 wt.% (NH₄)₂SO₄ and 1 wt.% citric acid to obtain a rough, γ′-terminated surface. The electrochemical potential for the selective dissolution was determined from the polarization curves of the γ and γ′ single-phase alloys. The selective dissolution tests proved that γ was precisely removed above 1.7 V_SCE, resulting in the formation of a rough, γ′-terminated surface. Surface analyses revealed that a passive AlO_x, which retarded the dissolution, was preferentially formed on γ′, resulting in a successful selective dissolution.     

Nanocrystals of a new complex perovskite dielectric Ba2TmSbO6

Nanocrystals of a new complex perovskites ceramic oxide, barium thulium antimony oxide - Ba₂TmSbO₆, were synthesized using a single step auto-ignition combustion process. The combustion product was single phase and composed of aggregates of nanocrystals of sizes in the range 20-50 nm. Ba₂TmSbO₆ crystallized in cubic perovskite structure with lattice parameter, a = 8.4101 Å. The polycrystalline fluffy combustion product was sintered to high density (∼97%) at ∼1450 °C for 4 h. Resistivity of the sintered specimen was ∼5 MΩ/cm. The Ba₂TmSbO₆ has dielectric constant (?′) and dielectric loss (tan δ) of 17 and ∼10⁻⁴ at 5 MHz; the new material would probably be developed as a low-loss dielectric material.     

Morphology influence of the oxidation kinetics of carbon nanofibers

This paper reports the stability and oxidation rate of five types of carbon nanofiber (CNF) with distinctly different orientation of their graphite sheets based on conversion to CO₂ when heated in the presence of oxygen. A non-isothermal technique was used to determine the oxidation kinetic parameters including the activation energy (E_a). Graphite shows a similar activation energy (E_a = 158 kJ/mol⁻¹) to CNF with longitudinal alignment (E_a = 156 kJ/mol⁻¹). CNF type herringbone (E_a = 126 kJ/mol⁻¹) and platelet (E_a = 145 kJ/mol⁻¹) show the lowest oxidation resistance which improved dramatically after a heat treatment at 3023 K of the herringbone (E_a = 216 kJ/mol⁻¹) and platelet (E_a = 174 kJ/mol⁻¹) structures.     

The isoxazolidines: the effects of steric factor and hydrophobic chain length on the corrosion inhibition of mild steel in acidic medium

Several new isoxazolidines having varying degree of steric environment and hydrophobic chain length, prepared efficiently using single-step nitrone cycloaddition reactions, are tested for corrosion inhibition of mild steel in 1 M and 5 M HCl at 50-70 °C range by gravimetric and electrochemical methods. All compounds have shown very good corrosion inhibition efficiency (IE%) in acidic solution. Steric crowding around the nitrogen centres and hydrophobic chain lengths as well as increase in temperature (in the presence of the inhibitor in the higher concentration range 100-400 ppm) are found to increase the inhibition efficiency of the isoxazolidines. Thermodynamic parameters (ΔG°_ads, ΔH°_ads, ΔS°_ads) for the adsorption process and kinetic parameters for the metal dissolution (or hydrogen evolution) reaction in the presence of one of the isoxazolidines were determined. Experimental results agree with the Temkin adsorption isotherm. The inhibition of corrosion in 1 M HCl, influenced by both physi- and chemi-sorption, was found to be under mixed control, but predominantly under cathodic control.     

Formation of ‘ferric green rust’ and/or ferrihydrite by fast oxidation of iron(II-III) hydroxychloride green rust

Fast oxidation processes of iron(II-III) hydroxychloride green rust GR(Cl⁻), Fe^II₃Fe^III(OH)₈Cl · 2H₂O, were simulated by two different methods. The first one consisted in using a strong oxidiser, namely H₂O₂. The main end product, analysed by X-ray diffraction and Mössbauer spectroscopy, is an iron(III) compound, designated as “ferric GR(Cl⁻)”, characterised by a layered structure identical to that of normal GR(Cl⁻). The second method consisted in decreasing the initial concentrations of reactants, thus increasing the proportion of dissolved O₂. Suspensions of GR(Cl⁻), obtained by mixing 4 × 10⁻³ M NaOH with FeCl₂ solutions for various R^′=[Cl⁻]/[OH⁻] values, oxidised rapidly into ferrihydrite-like compounds.     

Enhanced magnetoelectric properties in Bi0.95Ho0.05FeO3 polycrystalline ceramics

Polycrystalline samples of Ho doped BiFeO₃ were prepared by solid state reaction method and effect of partial substitution of Ho on dielectric, magnetic and ferroelectric properties was studied. High temperature dielectric results show two dielectric anomalies both in ? and tan δ, out of which, anomaly at higher temperature (∼400 °C) could be ascribed to antiferromagnetic Néel temperature which, is a signature of magnetoelectric coupling. The magnetic moment is greatly improved and the maximum magnetization was found to be 0.736 emu/g. Saturated ferroelectric hysteresis loops were observed for Bi_0.95Ho_0.05FeO₃ with remnant polarization (P_r) = 1.59 μC/cm², maximum polarization (P_max) = 2.56 μC/cm² and coercivity (E_c) = 5.45 kV/cm. We have conducted comprehensive magnetoelectric and magnetodielectric properties at room temperature. Magnetic field induced ferroelectric hysteresis loop observed in Bi_0.95Ho_0.05FeO₃ is of prime importance.     

Preparation and fluorescent properties of europium (III) complexes with β-diketone ligand and 2,2-dipyridine or 1,10-phenanthroline

The β-diketone ligand, 1-(4-methoxyphenyl)-3-phenylpropane-1,3-dione (MPPD), and its binary Eu(III) complexes Eu(MPPD)₃, ternary complexes Eu(MPPD)₃·Bipy with 2,2-dipyridine (Bipy) and Eu(MPPD)₃·Phen with 1,10-phenanthroline (Phen) were prepared. The complexes were characterized with by elemental analysis, FT-IR, ¹H NMR, UV–vis absorption, thermogravimetric analysis (TGA), ESI-MS and fluorescence spectroscopic techniques. TGA results showed that these complexes have good thermal stability. The emission spectra for complexes 2–4 exhibited the characteristic emission bands that arise from the ⁵D₀ → ⁷F_J (J = 0–4) transitions of the europium ion in solid state and chloroform solution. Based on the emission spectra in solid state, the Eu(III) ion could be sensitized efficiently by the ligands to some extent, in particular, in the ternary system, the secondary ligands Bipy and Phen acting as a light-harvesting center was involved in the highly efficient energy transfer process. In addition, the experimental intensity parameters, Ω₂ and Ω₄ were calculated from the fluorescence emission spectra. The radiative decay rate A_rad, the nonradiative rates A_nrad, the lifetime (τ) and the luminescent quantum yield (η) were determined and analyzed.     

The influence of the conditions of the ZrO2 passive film formation on its properties in 1 M NaOH

In this paper, results of the potentiodynamic-potentiostatic formation of a homogeneous, passive films of ZrO₂ onto a Zr electrode in 1 M NaOH solution at different potentials (2.0, 4.0, 6.0 and 8.0 V vs. SCE) are presented. The properties of such films were investigated by EIS measurements at different potentials. After fitting the EIS spectra by an appropriate equivalent circuit, the capacitance (C_pf) and resistance (R_pf) of these films were determined. All films were found to become insulators at the potentials equal and/or more positive than 2.0 V, with their thicknesses increasing linearly with the potential from about 7 nm at 2.0 V to about 20 nm at 8.0 V. In the potential range 0.8 V < E < 2.0 V a transition from a semiconducting to insulating behaviour has been recorded for all films (except for the one formed at 2.0 V). The donor densities (N_sc) for all films, as well as their flat band potentials (E_fb) and their thicknesses of the space charge layer (d_sc), were determined from the corresponding Mott-Schottky plots (MS) recorded in the potential range (0.0 V < E < 0.8 V), where all films behaved as n-type semiconductors.     

Theoretical study of benzimidazole and its derivatives and their potential activity as corrosion inhibitors

A theoretical study of benzimidazole (BI) and two of its derivatives namely 2-methylbenzimidazole (2-CH₃BI) and 2-mercaptobenzimidazole (2-SHBI) recently used as corrosion inhibitors for mild steel in 1 M HCl was undertaken by considering Density Functional Theory (DFT) at the B3LYP/6-311G++(d,p) level. The properties most relevant to their potential action as corrosion inhibitors has been calculated in the neutral and protonated form: E_HOMO, E_LUMO, energy gap (ΔE), dipole moment (μ), electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). The theoretical results are in agreement with the experimental data.