Comparison of corrosion behaviour of zinc in NaCl and in NaOH solutions. Part I: Corrosion layer characterization

The corrosion layer formed on zinc sample in 0.6 M NaCl and 0.5 M NaOH solution under ambient conditions has been investigated. The corrosion layer morphology was analyzed using scanning electron microscopy (SEM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the corrosion products of zinc. The thickness evolution of the corrosion layer was investigated by glow discharge optical emission spectroscopy (GDEOS). The corrosion layer formed in 0.5 M NaOH solution appeared more compact than that formed in 0.6 M NaCl solution. Zinc hydroxide chloride (Zn₅(OH)₈Cl₂·2H₂O) and zinc hydroxide carbonate (Zn₅(CO₃)₂(OH)₆) were formed on zinc surface in 0.6 M NaCl solution while in 0.5 M NaOH solution, zinc oxide (ZnO), zinc hydroxide (Zn(OH)₂) and zinc hydroxide carbonate (Zn₅(OH)₆(CO₃)₂·H₂O) were detected. Probable mechanisms of zinc corrosion products formation are presented.     

Synthesis of Ni3Al intermetallic powder in eutectic molten salts

The powders of Ni₃Al intermetallic compounds were simply and economically synthesized by the chemical reaction in the various molten salts systems. In the relatively low temperature ranges, we studied to synthesize Ni₃Al intermetallic powders from Al and NiCl₂ in five kinds of eutectic molten salts by varying the reaction time and mole ratio of reactants. Ni₃Al intermetallic powders could be synthesized in AlCl₃–NaCl (63:37 in mol%), AlCl₃–NaCl–KCl (66:20:14 mol%), NaCl–KCl (50:50 mol%) and MgCl₂–NaCl–KCl (50:30:20 mol%) systems. However, it was impossible to separate the Ni₃Al powders from MgCl₂–NaCl–KCl (50:30:20 mol%) system. The Ni₃Al powders could not be synthesized in AlCl₃–NaCl (50:50 mol%) molten salt. The obtained powders were uniformly sub-micrometer sized. The reaction temperature at 500 °C, the reaction time for 3 h and the mole ratio of NiCl₂/Al=1.3 were the optimum conditions for synthesis of Ni₃Al intermetallic powders in AlCl₃–NaCl (63:37 mol%) molten salt.     

Mechanochemical preparation and investigation of properties of magnesium,calcium and lithium–magnesium alanates

Ball milling of MgCl₂ and CaCl₂ with NaAlH₄ or LiAlH₄ can be used for the preparation of magnesium, calcium and lithium–magnesium alanates in mixture with NaCl or LiCl. Using wet chemical separation methods, it was possible to obtain these alanates in nearly pure state. The alanates were characterized by X-ray diffractometry, solid-state ²⁷Al NMR and IR spectroscopy and thermovolumetric (TV) and differential scanning calorimetry (DSC) measurements. Mg(AlH₄)₂ dissociates thermally in one step to MgH₂, Al and hydrogen; at a higher temperature, MgH₂ and Al transform to Mg–Al alloy and hydrogen. Thermal dissociations of Ca(AlH₄)₂ and of LiMg(AlH₄)₃ (in mixture with NaCl or LiCl) proceeds in several steps, of which the first two can be assigned to the formation of CaH₂ and of a MgH₂/LiH mixture, respectively, in addition to Al and H₂. Possible intermediates of these two steps are CaAlH₅ and LiMgAlH₆. Higher temperature dissociations include formation of MgH₂ (LiH) and Ca–Al alloys from CaH₂, CaH₂ and Al, respectively. Upon ball milling of MgCl₂ or CaCl₂ with NaAlH₄ or LiAlH₄ in the presence of Ti catalysts, only the thermal dissociation products of the expected alanates are obtained. This indicates that dehydrogenation discharge of earth alkali metal alanates can be catalyzed by Ti. According to DSC measurements, the thermodynamic stability of Mg(AlH₄)₂ (ΔH = 1.7 kJ/mol) is too low for the purpose of reversible hydrogen storage. Determination of ΔH values for the second, endothermal step of calcium and lithium–magnesium alanate dissociations gave values of around 31.6 and 13.1 kJ/mol, respectively.     

Effect of H2/CO2 mixture gas treatment temperature on the activity of LaNiO3 catalyst for hydrogen production from formaldehyde aqueous solution under visible light

H₂/CO₂ mixture gas treatment at moderate temperature is found to be effective in improving the activity of LaNiO₃ catalyst for hydrogen production from formaldehyde aqueous solution under visible light. The LaNiO₃, as a precursor, was treated at various temperatures (573–973 K) for 4 h under continuous flow mixture gas with a molar ratio of H₂/CO₂ = 4:1. Among all the resultant photocatalyst, the LaNiO₃ treated at 773 K (Ni/LaNiO_3?δ–La₂O₂CO₃), exhibited highest photocatalytic activity when exposed to visible-light irradiation and was further characterized by XRD, SEM, TEM, UV-diffuse reflectance spectroscopy. The results indicated that Ni/LaNiO_3?δ–La₂O₂CO₃ photocatalyst had narrow bandgap and can efficiently transfer photogenerated electrons on the surface and thus reduce H⁺ to hydrogen.     

The effect of Ti-addition on plastic deformation and fracture behavior of directionally solidified NiAl/Cr(Mo) eutectic alloys

To improve the high-temperature strength of NiAl/Cr(Mo) eutectic alloys, the effect of Ti-addition on microstructure and mechanical properties was examined. Three directionally solidified (DS) alloys with the composition of Ni–(33 − x)Al–31Cr–3Mo–xTi (x = 0, 3 and 5 at.%, respectively), denoted 0Ti-, 3Ti- and 5Ti-alloys hereafter, were prepared. Temperature dependence of the yield stress and the room temperature fracture toughness of these DS alloys was examined. The aligned lamellae with B2-NiAl and A2-Cr(Mo) were formed in 0Ti-alloy, but the formation of lamellar structure was hindered by the Ti-addition. Cellular microstructures containing short plate shapes of Cr(Mo) phases were obtained in 3Ti- and 5Ti-alloys. In 5Ti-alloy, the precipitation of the L2₁-Ni₂AlTi was confirmed in NiAl matrix phase after the DS treatment. The Ti-addition induced a significant increase in high-temperature strength accompanied by a large deterioration of room temperature fracture toughness. The fracture toughness of 5Ti-alloy showed the low value of about 4 MPa m^1/2 because of the disturbance of microstructure.     

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.     

Studies on the leaching of tungsten from composite barite–scheelite concentrate

Studies on the recovery of tungsten from a composite barite–scheelite concentrate ore were conducted utilizing a soda–silicon roast-Na₂CO₃ solution leach technique. Scheelite and barite mainly compose this ore with a slight trace of other impure components. A high tungsten recovery ratio is not achievable by physical separation by beneficiation or caustic autoclaving procedures as a significant amount of scheelite and barite occur in an interspersed state. Soda–silicon roast-Na₂CO₃ solution leach is then proposed to extract tungsten from this special ore with effects of the roasting and leaching process tested under variables such as roasting time, temperature, Na₂CO₃ amount and leaching conditions. Approximately 95.93% of W was dissolved into the solution under optimum roasting conditions of temperature 850 °C, reactive time 2 h, molar ratio of Na₂CO₃/W 3 and 10% SiO₂ dosage of feed mass with leaching conditions of temperature 60 °C, stirrer speed 300 rpm, leaching time 1 h, liquid/solid ratio 4 and in 10 g/l Na₂CO₃ solution.     

Morphology-dependent crystallization and luminescence behavior of (Y, Eu)2O3 red phosphors

(Y_0.95Eu_0.05)₂O₃ red phosphor particles with three distinctive morphologies of submicron spheres (up to 180 nm), microflowers (up to 10 μm) and microplates (up to 50 × 10 μm) have been converted from their respective precursors autoclaved (100–180 °C, 12 h) from mixed solutions of the component nitrates and hexamethylenetetramine [(CH₂)₆N₄]. The three types of precursors were found to have the approximate compositions M(OH)CO₃·H₂O for the sphere (M = Y and Eu), M₄O(OH)₉NO₃ for the flower and M₂(CO₃)₃·3H₂O for the plate, and their formation domains were defined. Both X-ray diffraction and photoluminescence analysis indicated that a calcination temperature of ?800 °C is needed to attain a homogeneous (Y_0.95Eu_0.05)₂O₃ solid solution and thus improved luminescence. Morphology-confined crystal growth of (Y_0.95Eu_0.05)₂O₃ was observed from the microplates, yielding a significantly higher exposure of the (4 0 0) facets at elevated temperature. The three types of phosphors exhibited a substantial morphology-dependent photoluminescence (PL)/photoluminescence excitation (PLE) behavior, but did not differ much in the positions of the PLE/PL bands or in the asymmetry factor [I(⁵D₀ → ⁷F₂)/I(⁵D₀ → ⁷F₁)] of the luminescence. Upon UV excitation into the charge transfer band at ～240 nm the microplates showed the strongest red emission at ～613 nm (the ⁵D₀ → ⁷F₂ transition of Eu³⁺) at a calcination temperature of 1000 °C, whose intensity was ～2.49 and 1.57 times those of the flowers and spheres, respectively. Fluorescence decay analysis yielded similar lifetimes of ～1.5 ± 0.1 ms for the 613 nm emission of the three morphologies, suggesting that the differing luminescence was largely morphology-dependent, rather than defect-dependent.     

Study of pitting corrosion on mild steel during wet–dry cycles by electrochemical noise analysis based on chaos theory

Electrochemical noise (EN) was used to investigate the corrosion behaviour of mild steel (Q235) in 0.1 M Na₂SO₄ and 0.1 M NaCl aqueous solutions during wet–dry cycles. The positive fraction and value of the Largest Lyapunov Exponent (LLE) of electrochemical current noise (ECN) were found out to represent the number and isolation degree of the pits formed in two electrolyte conditions. The calculated results indicate that metastable pits are more plentiful and uniformly distributed in wet cycles and in Na₂SO₄ solution than those in dry cycles and in NaCl solution respectively.     

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.     

Protonation-induced rearrangements in Langmuir films and redox properties of Langmuir–Blodgett films of 2-(n-alkyl)fulleropyrrolidines

The effect of protonation of the pyrrolidine ring nitrogen of 2-(n-alkyl)fulleropyrrolidines, C₆₀pyr–C_m (m=4, 6, 8, 10 and 12), on the properties of the Langmuir and Langmuir–Blodgett (LB) films was investigated. The isotherms of both surface pressure (π) and surface potential change (ΔV) versus area per molecule (A) for the Langmuir films of C₆₀pyr–C_m were determined simultaneously. It was found that the longer the alkyl chain of the fulleropyrrolidine the larger is the film compressibility, κ, i.e., κ(C₆₀pyr–C₄)=(2.1±0.4)×10⁻² m mN⁻¹, κ(C₆₀pyr–C₈)=(3.5±0.4)×10⁻² m mN⁻¹ and κ(C₆₀pyr–C₁₂)=(4.1±0.5)×10⁻² m mN⁻¹, as expected for the liquid surface films. The values of surface area at zero surface pressure (A₁) differ in the range 0.6 nm² molecule⁻¹ (for m=4–8) to 1.4 nm² molecule⁻¹ (for m=10–12), indicating that all 2-(n-alkyl)fulleropyrrolidines form multilayer or aggregated films on neutral water subphase. However, acidification of the water subphase increases the A₁ values for all investigated fulleropyrrolidines up to ca. 1.9 nm² molecule⁻¹, i.e., the value corresponding to maximum area occupied by a fulleropyrrolidine at horizontal orientation in a monolayer film. Apparently, 2-(n-alkyl)fulleropyrrolidinium cations formed at low pH are markedly de-aggregated in the films and their orientation is changed due to protonation of the pyrrolidine nitrogen. Similarly, however, less pronounced effects are observed if ionic strength of the subphase solution, I, is increased in the range 0≤I≤1.0 mol dm⁻³ NaCl. The Langmuir films formed on a water subphase were the most stable with respect to the LB transfer onto 5 MHz Au–quartz crystal vibrators. Simultaneous cyclic voltammetry and piezoelectric microgravimetry at an electrochemical quartz crystal microbalance of these films showed at least two electroreductions where the fulleropyrrolidine mono anions were stable with respect to dissolution.     

Precipitation evolution in Al–0.1Sc,Al–0.1Zr and Al–0.1Sc–0.1Zr (at.%) alloys during isochronal aging

Precipitation strengthening is investigated in binary Al–0.1Sc, Al–0.1Zr and ternary Al–0.1Sc–0.1Zr (at.%) alloys aged isochronally between 200 and 600 °C. Precipitation of Al₃Sc (L1₂) commences between 200 and 250 °C in Al–0.1Sc, reaching a 670 MPa peak microhardness at 325 °C. For Al–0.1Zr, precipitation of Al₃Zr (L1₂) initiates between 350 and 375 °C, resulting in a 420 MPa peak microhardness at 425–450 °C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 °C, Zr additions provide a secondary strength increase from the precipitation of Zr-enriched outer shells onto the Al₃Sc precipitates, leading to a peak microhardness of 780 MPa at 400 °C for Al–0.1Sc–0.1Zr. Compositions, radii, volume fractions and number densities of the Al₃(Sc_1?xZr_x) precipitates are measured directly using atom-probe tomography. This information is used to quantify the observed strengthening increments, attributed to dislocation shearing of the Al₃(Sc_1?xZr_x) precipitates.     

Synthesis,crystal structure and two-photon absorption of a cadmium complex constructed by DMIT ligand

The cadmium complex [(CH₃)₄N][Cd(C₃S₅)₂]·H₂O constructed by 1,3-dithiole-2-thione-4,5-dithiolato (DMIT) ligand has been synthesized and its structure has been determined by means of X-ray single crystal diffraction. Its two-photon absorption (TPA) has been studied in acetonitrile solution using open-aperture Z-scan technique with 20 picosecond (ps) pulses at wavelength 1064 nm. Its TPA coefficient β was determined to be 4.475 × 10^?10 m/W, corresponding the TPA cross-section σ₂ is 3.95 × 10^?53 (m⁴ s/photon molecule).     

Two-step hot pressing of bimodal micron/nano-ZrB2 ceramic with improved mechanical properties and thermal shock resistance

The densification and grain growth behaviors for micron- and nano-sized ZrB₂ particles were investigated. The densification on-set temperature (T_d-micron) and grain growth on-set temperature (T_g-micron) for micron-sized ZrB₂ particles were about 1500 °C and 1800 °C, respectively. And the densification on-set temperature (T_d-nano) and grain growth on-set temperature (T_g-nano) for nano-sized ZrB₂ particles were about 1300 °C and 1500 °C, respectively. A bimodal micron/nano-ZrB₂ ceramic was therefore prepared using a novel two-step hot pressing. A high relative density of 99.2%, an improved flexural strength of 580.2 ± 35.8 MPa and an improved fracture toughness of 7.2 ± 0.4 MPa·m^1/2 were obtained. The measured critical thermal shock temperature difference (ΔT_c) for this bimodal micron/nano-ZrB₂ ceramic was as high as 433 °C.     

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⁻.     

2-Butyne-1,4-diol as a novel corrosion inhibitor for API X65 steel pipeline in carbonate/bicarbonate solution

The inhibition effects of 2-butyne-1,4-diol on the corrosion susceptibility of grade API 5L X65 steel pipeline in 2 M Na₂CO₃/1 M NaHCO₃ solution were studied by electrochemical techniques and weight loss measurements. The results indicated that this inhibitor was a mixed-type inhibitor, with a maximum percentage inhibition efficiency of approximately 92% in the presence of 5 mM inhibitor. Atomic force microscopy revealed that a protective film was formed on the surface of the inhibited sample. The adsorption of the inhibitor was found to conform to the Langmuir isotherm with the standard adsorption free energy of ?21.08 kJ mol^?1.     

Effects of grain size on the corrosion resistance of wrought magnesium alloys containing neodymium

A range of grain size from 70 μm to 0.7 μm was studied for corrosion resistance of Mg–Y–RE magnesium alloy using electrochemical and constant immersion testing in 3.5 wt.% NaCl solution. The linear polarization resistance (R_p) showed a clear trend of increasing R_p value with grain refinement. The ultrafine grained sample showed the most positive pitting potential as compared to coarse grained samples. One order of magnitude decrease in corrosion rate was observed between coarsest and ultrafine grained microstructure.     

Texture and orientation characteristics of α-Al2O3 films prepared by laser chemical vapor deposition using Nd:YAG laser

α-Al₂O₃ films were prepared by laser chemical vapor deposition (LCVD) and the effects of precursor vaporization temperature (T_vap), total chamber pressure (P_tot), laser power (P_L) and deposition temperature (T_dep) on the phase, orientation and texture of Al₂O₃ film were investigated. At P_tot = 0.93 kPa, α-Al₂O₃ films were obtained in the region of T_vap > 423 K and T_dep > 1100 K. The orientation of α-Al₂O₃ film changed from (1 1 0) to (0 1 2) to (1 0 4) to (0 0 6) with increasing P_tot. Porous α-Al₂O₃ films were formed at high T_vap (443 K) and low P_tot (0.47 kPa). At T_vap = 413 K, α-Al₂O₃ film had hexagonal and rectangular plate-like grains with finely faceted edges. With increasing P_tot = 0.93–1.4 kPa, (0 0 6)-oriented α-Al₂O₃ film with a hexagonal terrace texture was obtained.     

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.     

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.