Estimation of residual corrosion rates of steel under cathodic protection in soils via voltammetry

Steel coupons were buried in soil for 2 months under cathodic protection. Their residual corrosion rates were deduced from voltammetry and weight loss measurements. In aerated soils, the current density due to O₂ reduction, j_K,O2, was modelled with a mixed activation–diffusion controlled kinetic. The anodic part j_A of the current density j, computed as j_A = j − j_K,O2, obeyed Tafel law. Its extrapolation to the protection potential gave a corrosion rate (∼7 μm yr⁻¹) consistent with that obtained from weight loss measurements. With a deficient protection, corrosion rates remained at ∼80 μm yr⁻¹, a value given by both methods.     

The temporal evolution of the negative ion density in a low duty cycle pulsed reactive magnetron discharge

Time-resolved O^? density measurements have been made in the bulk plasma of a unipolar pulsed-DC magnetron using laser photodetachment. The magnetron was operated with a titanium target at a total pressure of 1.3 Pa and a fixed oxygen-to-argon partial pressure ratio of 10%. The duty cycle was maintained at 5% but the peak on-time discharge power was varied from 120 to 720 W.For all discharge powers, both the electron (n_e) and negative ion (n_?) densities increase during the plasma on-time, with the electron density reaching a maximum at the end of this phase. In the off-time, the electron density initially decreases at a rapid rate (characteristic decay time ~ 25 μs) for the first 50 μs, followed by a slower rate (~ 150 μs) for the remainder of the off-time, however, the negative ion density continues to increase in this phase, reaching a maximum at about ~ 150 μs after the termination of the discharge power. Both the electron and negative ion densities increase with discharge power. The maximum negative ion density was 2.5 × 10¹⁶ m^?3 for a peak power of 720 W, corresponding to a negative ion-to-electron density ratio n_?/n_e (α) of about 3. In the long afterglow, this ratio reaches a maximum value of 12 as the electron density decreases faster than the negative ion density. This shows that in the afterglow the plasma is highly electronegative.     

Structural dependence of the piezoelectric properties of KNbO3 nanowires synthesized by the hydrothermal method

Because of the presence of OH^? and H₂O in the KN unit cell, tetragonal KNbO₃ (KN) nanowires were formed when the synthesis was carried out at 120 °C for 48 h. However, when the fabrication was conducted at high temperatures (?150 °C) or at 120 °C for a long period of time (?72 h), orthorhombic KN nanowires were formed. Moreover, the KN nanowires synthesized at 120 °C for 60 h showed a morphotropic phase boundary (MPB) structure in which both tetragonal and orthorhombic structures coexisted. Tetragonal, orthorhombic and MPB KN nanowires were also grown on the Nb⁵⁺-doped SrTiO₃ substrate, and their d₃₃ values were measured for the first time. A tetragonal KN nanowire exhibited a d₃₃ value of 23.5 pm V^?1, which is larger than that of the orthorhombic KN nanowire (11.6 pm V^?1), probably because of the softening effect of the metal vacancies. The MPB KN nanowires exhibited a larger d₃₃ value of 40.0 pm V^?1. The d₃₃ values of KN nanowires increased to 104.5, 137.1 and 146.0 pm V^?1 for the orthorhombic, tetragonal and MPB KN nanowires, respectively, after the KN nanowires were poled along the [1 0 0] direction by application of a DC voltage of 10 V.     

Improving hardness and tribological characteristics of nanocrystalline Cr–C films obtained from Cr(III) plating bath using pulsed electrodeposition

Effect of pulsed electrodepostion on the nanocrystal size, composition, hardness, coefficient of friction and wear resistance was investigated for the Cr–C electrodeposits obtained from a trivalent chromium bath. The electrodeposits were shown to contain about 9% of carbon. Pulsed electrodeposition does not virtually affect the carbon content. At the same time, an increase in the off time duration leads to a decrease in the nanocrystals size. The hardness and wear parameters of the electrodeposits may be sufficiently improved when using pulsed current. For instance, at t_on = t_off = 1 s, the hardness reaches the values of ~ 1200 ÷ 1300 HV (meanwhile, it is close to 850 ÷ 950 HV at a steady-state electrolysis).     

Mechanical properties and oxidation resistance of CrAlN/BN nanocomposite coatings prepared by reactive dc and rf cosputtering

CrAlN/BN nanocomposite coatings were deposited through reactive cosputtering, i.e., pulsed dc and rf sputtering, of CrAl and h-BN targets, respectively. X-ray diffraction (XRD) and selected area electron-diffraction (SAED) analysis indicated that the CrAlN/BN coating consists of very fine grains of B1 structured CrAlN phase. With an increasing BN volume fraction of over 8 vol.%, the nanocrystalline nature of the grains is revealed through a dispersion of fine grains in the CrAlN/BN coating. A cross-sectional observation using a transmission electron microscope (TEM) clarified that the coating demonstrating the highest level of hardness has a fiber-like structure consisting of grains that are ~ 20 nm in width and ~ 50 nm in length. X-ray photoelectron spectroscopy (XPS) analysis revealed that the coating consists mainly of CrAlN and h-BN phase. The indentation hardness (H_IT) and effective Young's modulus (E*) of the coatings increased with the BN phase ratio, reaching a maximum value of ~ 46 and ~ 440 GPa at ~ 7 vol.% of BN phase; it then decreased moderately to ~ 40 and ~ 350 GPa at 18 vol.% of BN, respectively. Furthermore, CrAlN/BN coatings showed superior oxidation resistance compared with CrAlN coatings. After annealing at 800 °C in air for 1 h, the indentation hardness of CrAlN coatings decreased to 50% of the as-deposited hardness; in contrast, the hardness of CrAlN/BN nanocomposite coatings either stayed the same or increased, attaining a value of about 46 GPa. After annealing at 900 °C for 1 h, the hardness of all the coatings decreased to about 40%.     

Effects of stress ratio on fatigue crack propagation properties of submicron-thick free-standing copper films

The dominant mechanics and mechanisms of fatigue crack propagation in ca. 500 nm thick free-standing copper films were evaluated at the submicron level using fatigue crack propagation experiments at three stress ratios, R = 0.1, 0.5 and 0.8. Fatigue cracking initiated at the notch root and propagated stably under cyclic loading. The fatigue crack propagation rate (da/dN) vs. stress intensity factor range (ΔK) relation was dependent on the stress ratio R;da/dN, increases with increasing R. Plots of da/dN vs. the maximum stress intensity factor (K_max) exhibited coincident features in the high-K_max region (K_max ? 4.5 MPa m^1/2) irrespective of R, indicating that K_max is the dominant factor in fatigue crack propagation. In this region, the fatigue crack propagated in tensile fracture mode irrespective of the R value. The region ahead of the fatigue crack tip is plastically stretched by tensile deformation, causing necking deformation in the thickness direction and consequent chisel-point fracture. In contrast, in the low-K_max region (K_max < 4.5 MPa m^1/2), the da/dN vs. K_max function assumes higher values with decreasing R; in this region, the fracture mechanism depends on R. At the higher R value (R = 0.8), the fatigue crack propagates in the tensile fracture mode similar to that in the high-K_max region. On the other hand, at the lower R values (R = 0.1 and 0.5), a characteristic mechanism of fatigue crack propagation appears: within several grains, intrusions/extrusions form ahead of the crack tip along the Σ3 twin boundaries, and the fatigue crack propagates preferentially through the intrusions/extrusions.     

Structure–conductivity relationships in chemical polypyrroles of low,medium and high conductivity

Chemically synthesized polypyrroles of low (σ < 75 S/cm), medium (75 < σ < 200 S/cm) and high (σ > 200 S/cm) electrical conductivity (σ) with the same dopant and degree of doping have been investigated by means of Wide Angle X-ray Scattering (WAXS), ¹³C Cross Polarized Magic Angle Spinning Nuclear Magnetic Resonance (¹³C CP/MAS NMR) spectroscopy and Fourier Transform Infrared (FTIR) Spectroscopy to establish structure–conductivity relationships useful for industrial applications. A similar amorphous structure was found by WAXS even for the higher conducting PPy (σ = 288 S/cm). WAXS spectra for polypyrroles of medium and high conductivity showed a weak peak at 2θ = 10–11° due to improved order of the counterions in these materials. The effect of the counterion size in the asymmetry of the PPy main WAXS peak was elucidated by performing ion exchange of the Cl⁻ dopant with counterions of larger size such as BF₄⁻ and ClO₄⁻. From ¹³C CP/MAS NMR measurements predominantly α–α′ bonding was found in these materials. The main ¹³C CP/MAS NMR resonance peak of PPy located at 126–128 ppm was broadened upon increasing conductivity. Interestingly, a linear relationship was observed between the half-width at half-height (HWHH) of the ¹³C CP/MAS NMR peak and conductivity where a doubling of the polypyrrole conductivity leads to an increase of HWHH by 6–7 ppm. FTIR data of these materials were analysed in the framework of the Baughman–Shacklette theory describing the dependence of conductivity on conjugation length. By comparison of model predictions and experimental results, the PPy samples were found to be in the regime of long conjugation lengths, L ≫ K₂/k_BT, where K₂ is a parameter related to the energy change on going from j − 1 to j charges on a conjugated segment of conjugation length L, k_B the Boltzman constant and T is the absolute temperature.     

Sintering behavior and mechanical properties of spark plasma sintered β–SiAlON/TiN nanocomposites

In this study, fully dense β-SiAlON/TiN composites were produced by Spark Plasma Sintering (SPS) method. Si₃N₄, Al₂O₃, AlN and TiO₂ powders were used as precursors. Starting powders were mixed with high energy ball milling and then were sintered by SPS method (at 1750 °C under pressure of 30 MPa for 12 min.). The milled powders had an average particle size of below ~ 155 nm. The XRD patterns of SPS-ed composites showed that the entire β-SiAlON phase constituent was in the form of Si₄Al₂O₂N₆ phase and cubic TiN phase can be formed by the phase transformation of TiO2 in relation with other precursors. FESEM micrographs confirmed that TiN particles were distributed homogeneously throughout β-SiAlON matrix. Mechanical properties evaluation revealed that by adding micro sized TiO₂, optimal mechanical properties with a hardness ~ 14.6 GPa and a fracture toughness ~ 6.3 MPa m^1/2 were obtained. The improvement in the fracture toughness was attributed to the presence of the crack deflection as the dominant toughening mechanism in the SPS-ed β–SiAlON/TiN composites.     

Effect of graphene platelets on tribological properties of boron carbide ceramic composites

The friction and wear behaviour of hot pressed boron carbide/graphene platelets (GPLs) composites have been investigated using the ball-on-flat technique with SiC ball under dry sliding conditions at room temperature. The hardness and fracture toughness of the investigated materials varied from 18.21 GPa to 30.35 GPa and from 3.81 MPa·m^1/2 to 4.60 MPa·m^1/2, respectively. The coefficient of friction for composites were similar, however the wear rate significantly decreased ~ 77% in the case of B₄C + 6 wt.% GPLs when compared to reference material at a load of 5 N, and ~ 60% at a load of 50 N. Wear resistance increased with increasing GPLs content in regards to the present graphene platelets, which during the wear test pulled-out from the matrix, exfoliated and created a wear protecting graphene-silicon based tribofilm.     

Synthesis and luminescence of red,fluorinated iridium (III) complexes containing alkenyl benzothiazole ligand

Two novel iridium(III) complexes (2-FSBT)₂Ir(acac) and (4-FSBT)₂Ir(acac) (2-FSBT, (E)-2-(2-fluorostyryl)benzo[d]thiazole; 4-FSBT, (E)-2-(4-fluorostyryl)benzo[d]thiazole; acac, acetylacetone) were synthesized and characterized by ¹H NMR and mass spectrometry. The organic light emitting diodes based on these complexes with the structure of ITO/m-MTDATA(10 nm)/NPB(20 nm)/CBP:Ir-complex(X %, 30 nm)/BCP(10 nm)/Alq₃(30 nm)/LiF(1 nm)/Al(100 nm) were fabricated. The device based on (2-FSBT)₂Ir(acac) exhibited a maximum efficiency of 9.32 cd/A, a luminance of 8800 cd/cm²; and the device based on (4-FSBT)₂Ir(acac) showed a maximum efficiency of 8.5 cd/A, a luminance of 6986 cd/cm². The Commission International de L’Eclairage (CIE) coordinates (1931) of these complexes were (0.619, 0.381) and (0.621, 0.378), respectively.     

Structural phase transformation and electrical properties of (0.90 – x)Pb(Mg1/3Nb2/3)O3–xPbTiO3–0.10Pb(Fe1/2Nb1/2)O3 ferroelectric ceramics near the morphotropic phase boundary

Novel solid solutions of (0.90 – x)Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃–0.10Pb(Fe_1/2Nb_1/2)O₃, where x = 0.29, 0.31, 0.33 and 0.35, were investigated from the viewpoint of structural phase transformation, dielectric, ferroelectric and piezoelectric properties. X-ray diffraction and Raman scattering measurements demonstrated that their phase structures experienced a gradual transition process from rhombohedral to tetragonal phase near the morphotropic phase boundary (MPB) region with increasing PbTiO₃ content (x). Corresponding to the structural phase transition near the MPB, large dielectric constants (ε_r) were obtained at the compositions of x = 0.31 (ε_r = 3094 at 1 kHz) and x = 0.33 (ε_r = 2927 at 1 kHz). The maximum remnant polarization (P_r = 26.5 μC cm⁻²) was obtained at the composition x = 0.31, and the electromechanical factor (k_p = 0.59) and piezoelectric coefficient (d₃₃ = 545 pC N⁻¹) were also maximized at this composition, which indicated the enhanced electrical properties near the MPB.     

Effects of annealing atmosphere on the structural and electrical properties of (Na0.5K0.5)NbO3 thin films grown by RF magnetron sputtering

Amorphous (Na_0.5K_0.5)NbO₃ (NKN) thin films were grown at 300 °C and subsequently annealed at 800 °C under Na₂O, K₂O and NKN atmospheres. When the annealing time was less than 50 min, K₆Nb_10.88O₃₀ and Na₂Nb₄O₁₁ secondary phases were formed in all the films. Moreover, they were also found in films annealed at 750 °C for 180 min under NKN atmosphere, indicating that they were transient phases formed when the sintering time and temperature were not sufficient. For the film annealed for 50 min under Na₂O atmosphere, an Na-excess (Na_1?xK_x)NbO₃ (N_1?xK_xN) phase was formed, whereas a K-excess N_1?xK_xN phase was developed in the film annealed under K₂O atmosphere. On the other hand, a homogeneous NKN phase was developed in the film annealed under NKN atmosphere and this was maintained after a long period (100 min) of annealing at 800 °C. A high leakage current density and a small dielectric constant (ε_r) were observed for films annealed under Na₂O and K₂O atmospheres due to the evaporation of K₂O and Na₂O, respectively. Moreover, they exhibited a small remnant polarization (P_r) and a small coercive electric field (E_c). On the other hand, the film annealed under NKN atmosphere exhibited a very low leakage current density of 2.6 × 10^?9 A cm^?2 at 0.2 MV cm^?1 and had good ferroelectric and piezoelectric properties of ε_r = 620, P_r = 11.7 μC cm^?2, E_c = 133.8 kV cm^?1 and d₃₃ = 74 pm V^?2 at 50 kV cm^?1.     

Growth behavior of superconducting DyBa2Cu3O7–x thin films deposited by inclined substrate deposition for coated conductors

Superconducting DyBa₂Cu₃O_7–x (DyBCO) films were grown on biaxially textured MgO buffer layers deposited by inclined substrate deposition (ISD) on Hastelloy substrates. Despite the large lattice mismatch (8.5%) between DyBCO and MgO, the DyBCO grew epitaxially on the MgO buffer layer and the biaxial texture of the MgO was well transferred to the DyBCO. Typical critical current densities, j_c, of the DyBCO film were 2.1 MA cm^?2 at 77 K in a self-field. Biaxial texturing is the key for reaching the high critical current densities and was investigated by transmission electron microscopy. DyBCO grains were found to be ～130–500 nm in size, with faceted grain boundaries. The c-axis of the DyBCO grains was tilted away from the substrate normal by 29° such that it was perpendicular to the MgO (0 0 2) facets. A high dislocation density of ～7.4 × 10¹¹ cm^?2 and stacking faults along the ab-planes were observed in the DyBCO film. Interface, grain boundary and volume energies of the DyBCO film were calculated and a growth model for the DyBCO film is discussed. ISD offers the potential for high-quality, biaxially textured MgO buffer layers suitable for long-length superconducting coated conductors.     

The influence of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture

We examine the effects of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-additive concentration, molecular weight, and specimen elongation on the temperature-dependent electronic transport properties of polyaniline films prepared with AMPSA in the presence of a great excess of a formic and dichloroacetic acid (DCAA) solvent mixture. The AMPSA-additive dependent resistivity and thermopower are reported for free-standing PANI:AMPSA_x (M_w=200,000 g mol⁻¹) films (x=0.1–0.5) in the temperature range from 2 to 325 K. The low-temperature data indicate that these samples are just on the insulating side of a disorder-induced metal–insulator (M–I) transition (dρ/dT<0), and that thermal motion at elevated temperatures is sufficient to produce a metallic state (dρ/dT>0) at room temperature. Transport occurs via variable-range hopping (VRH) for temperatures below 200 K, with hopping parameters that are a strong function of x; increased AMPSA concentration decreases the resistivity and moves the samples towards the M–I phase boundary. There is a minimum in the resistivity for all samples at a temperature T_min that is also doping dependent. Stretch orientation of PANI:AMPSA_0.5 films, prepared with higher molecular weight PANI (M_w=300,000 g mol⁻¹), along the resistivity measurement direction decreases the room-temperature resistivity at the expense of a more insulating low-temperature state. The T_min values of both stretched and unstretched PANI:AMPSA_0.5 films are pushed below 200 K, which reflects reduced disorder in film processed with higher molecular weight polyaniline. These results reflect an evolution in the underlying inhomogeneous mesoscopic disorder present in doped conducting polymers.     

Crystal structure and physical properties of EPCo4.7Ge9 (EP = Sr,Ba, Eu)

BaCo_4.7Ge₉ (BaCo_5?xGe₉, x = 0.29) is a novel ternary compound which forms incongruently from the melt and crystallizes in a unique structure type (space group Pnma; a = 1.39910(2), b = 0.40218(2), c = 1.69882(2) nm, Z = 4). Isotypic compounds were found with SrCo_4.7Ge₉ (a = 1.39389(8), b = 0.39665(1), c = 1.67860(9) nm) and EuCo_4.7Ge₉ (a = 1.3910(1), b = 0.39425(2), c = 1.6741(2) nm). Physical properties (electrical resistivity, specific heat, magnetic susceptibility) were studied for BaCo_4.7Ge₉ and EuCo_4.7Ge₉. BaCo_4.7Ge₉ shows metallic behaviour but neither a superconducting nor a magnetic phase transition was observed for temperatures as low as T = 2 K. Magnetic susceptibility and specific heat data of EuCo_4.7Ge₉, evidence the onset of antiferromagnetic order at 18.5 K. Both magnetic ordering and the effective magnetic moment derived verify the Eu²⁺ state with a total angular momentum j = 7/2.     

Synthesis and characterization of dithienothiophene vinylene based co-polymer for bulk heterojunction photovoltaic cells

An electron-donor–acceptor type co-polymer, PDTTBBO, composed of 3,5-dihexyldithieno [3,2-b:2′3′-d] dithiophene as donor and 2,6-dimethyl benzo[1,2-d; 5,4-d′] bisoxazole as an acceptor unit was synthesized by Horner–Wadsworth–Emmons (HWE) olefination reaction via multi-step procedure. The UV–vis absorption and photoluminescence emission peaks of the co-polymer in chlorobenzene were observed in a range from UV to near 700 nm. The lowest unoccupied molecular orbital (LUMO) and highest unoccupied molecular orbital (HOMO) levels of the co-polymer were estimated at ?5.71 eV and ?3.46 eV, respectively, corresponding to a band-gap of 2.25 eV. Bulk heterojunction photovoltaic cells were fabricated using a blend of PDTTBBO and PCBM with a ratio of 1:1. The short-circuit current density (J_sc), open-circuit voltage (V_oc) and fill factor (FF) of the device were estimated to be 1.306 mA/cm², 0.628 and 0.37, respectively, corresponding to power conversion efficiency (PCE) of 0.31% under AM 1.5 illumination.     

Microstructure study of the hardening mechanism of Cr–Ni alloy deposits after flame heating for a few seconds

Cr–Ni alloy deposits with different chemical compositions could be obtained from a bath with trivalent Cr and divalent Ni ions. With a plating current density above 20 A dm^? 2, amorphous Cr-rich alloy deposits were obtained, and crystalline Ni-rich deposits were achieved with an electroplating current density lower than 15 A dm^? 2. The hardness of the Ni-rich deposit decreased gradually with increasing flame-heating time. On the contrary, the hardness of Cr-rich alloy deposit could be significantly increased from 550 Hv to 1450 Hv after flame heating for 3 s. The results of a microstructure study show that the precipitation of nano-sized carbon-related particles, possibly diamond-like particles, could be the main hardening mechanism of flame-heated Cr-rich alloy deposit. These particles have particularly high hardness values, and they distort the nearby Cr-rich lattice, which leads to obvious strain fields in the flame-hardened Cr-rich alloy deposits.     

Top-seeded solution growth and characterization of rhombohedral PMN–30PT piezoelectric single crystals

Piezoelectric single crystals from 70Pb(Mg_1/3Nb_2/3)O₃–30PbTiO₃ solid solution were grown by a top-seeded solution growth method that prevented phase segregation and promoted (0 0 1) growth. Rhombohedral symmetry was confirmed by polarized light microscopy and the dielectric, piezo- and ferro-electric properties were characterized. A dispersive maximum of dielectric permittivity appears around T_C = 125 °C, which slightly shifts towards higher temperatures with increasing frequency, indicating weak relaxor behaviour. Rhombohedral–tetragonal phase transition was detected at 105 °C. This temperature is higher than the depoling temperature of the morphotropic phase boundary compositions (50–80 °C), thus extending the upper limit of the application temperature for electromechanical transducers. The piezoelectric coefficient (d₃₃) was found to be 1240 pC N⁻¹, with a strain level reaching 0.12% at an electric field of 12 kV cm⁻¹. The longitudinal electromechanical coupling factor k₃₃ reaches 85%, which persists upon heating up to 100 °C.     

Hardness of hexagonal AlB2-like diborides of s,p and d metals from semi-empirical estimations

The high-level ab initio calculations of elastic moduli of materials now become a routine procedure, and the renewed attention is paid to the semi-empirical macroscopic models, providing the correlations between the Vickers hardness H_V and some elastic moduli. Such correlations, building up a bridge between Vickers hardness and elastic parameters, seem a helpful way to semi-quantitative estimations of hardness and to theoretical search of novel hard materials, based on the calculations of their elastic properties. Here, using the results of our calculations of elastic parameters of 14 hexagonal AlB₂-like diborides of s, p and d metals MB₂ (where M = Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W), we have probed six recently proposed correlations between H_V and bulk (B), shear (G), Young's moduli (E), as well as Poisson's ratio (ν), and the parameter k (the G/B ratio), and we compare the obtained results with the available experimental data. Our analysis reveals that for this family of related materials the correlations H_V ~ G, and H_V ~ E will be the most suitable approximations which enable us to roughly evaluate the Vickers hardness of diborides numerically.     

Crystal structure and properties of the new ternary compound Mg21Ga5Hg3

The crystal structure of a new ternary compound Mg₂₁Ga₅Hg₃ has been studied using X-ray powder diffraction data by Rietveld method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for sample composition examination. The compound crystallizes in the Ge₈Pd₂₁ structure type (space group I4₁/a, a = 1.45391(5) nm, c = 1.15955(4) nm, Z = 4). All interatomic distances indicate metallic type bonding. The average thermal expansion coefficients α_a, α_c and α_V of Mg₂₁Ga₅Hg₃ are 2.60 × 10^?5 K^?1, 2.02 × 10^?5 K^?1, and 7.25 × 10^?5 K^?1, respectively. Electrical resistivity of Mg₂₁Ga₅Hg₃ was measured between 5 and 300 K.