Aqueous corrosion performance of nanostructured bainitic steel

In this study, the corrosion performance of nanostructured bainitic steel was compared with martensitic steel in chloride-containing solution using electrochemical techniques. Electrochemical impedance spectroscopy (EIS) results showed that the polarization resistance (R_p) for nanostructured bainitic steel (3400 Ω cm²) was higher than that of martensitic steel (2000 Ω cm²). Potentiodynamic polarization results showed an 85% lower corrosion current density for nanostructured bainitic steel compared to martensitic steel. Galvanostatically polarized martensitic steel revealed high localized corrosion i.e., intergranular corrosion (IGC) as well as localized attack in the grains. However, the nanostructured bainitic steel when polarized galvanostatically exhibited only a marginal selective dissolution of retained austenite. Thus, it can be suggested that nanostructured bainitic steel will perform better than martensitic steel in chloride-containing environments.     

Study on the behaviour of ZnCoCu alloy electroplating

Ternary zinc–cobalt–copper alloys of wide range composition were deposited on to steel substrates from dilute metal sulphate bath. The bath consisted of 1–20 g dm⁻³ CuSO₄·5H₂O, 1–30 g dm⁻³ CoSO₄·7H₂O, 1–50 g dm⁻³ ZnSO₄·7H₂O, 20 g dm⁻³ Na₂SO₄ and 150–200 g dm⁻³ NH₂CH₂COOH. The effect of bath composition, current density and temperature on the cathodic potential, cathodic current efficiency and composition of the deposits were investigated. The codeposition of ZnCoCu alloys from these solutions can be classified as regular. Increasing current density enhances the rate of Zn deposition but suppresses that of Cu deposition. However, increasing the bath temperature favours Cu deposition. Co content in the deposits is hardly affected by changing these variables. Increasing Cu content in the bath or increasing the applied current density greatly improves the cathodic efficiency for the alloy deposition. X-ray diffraction studies showed that the deposits obtained at high current density (Zn-rich alloy) consisted of a cubic CuZn₂ phase, while that obtained at high temperature (Cu-rich alloy) consisted of a face, centred cubic CuCo phase. The structure and morphology of the deposited alloys were characterised by anodic stripping and SEM.     

Effect of cumulative gamma irradiation on microstructure and corrosion behaviour of X65 low carbon steel

X65 low carbon steel was exposed to Co-60 radiation source with 1.25 MeV gamma rays, and cumulatively absorbed gamma irradiation doses (1, 2, and 3 MGy) were obtained after different exposure time (333, 667, and 1000 h). The effect of cumulative gamma irradiation on microstructure and corrosion behaviour of the carbon steel in unirradiated aerobic Beishan groundwater at 25 °C was investigated by using positron annihilation, scanning vibrating electrode, and electrochemical techniques. Cumulative gamma irradiation increases vacancy intensity and decreases open circuit potential (OCP) of carbon steel. They indicate that the irradiated carbon steel is activated. Measured current density distribution above the irradiated carbon steel shows that cumulative gamma irradiation accelerates localized corrosion after 0.5 h of immersion. In contrast, the analysis of electrochemical impedance spectroscopy of the irradiated carbon steel indicates that localized corrosion is transformed into general corrosion after 12 h of immersion, which is also accelerated by cumulative gamma irradiation.     

Microstructural characterisation of vacuum sintered T42 powder metallurgy high-speed steel after heat treatments

High-speed steel powders (T42 grade) have been uniaxially cold-pressed and vacuum sintered to full density. Subsequently, the material was heat treated following an austenitising + quenching + multitempering route or alternatively austenitising + isothermal annealing. The isothermal annealing route was designed in order to attain a hardness value of ～50 Rockwell C (HRC) (adequate for structural applications) while the multitempering parameters were selected to obtain this value and also the maximum hardening of the material (～66 HRC). Microstructural characterisation has been carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microstructure consists of a ferrous (martensitic or ferritic) matrix with a distribution of second phase particles corresponding to nanometric and submicrometric secondary carbides precipitated during heat treatment together with primary carbides. The identification of those secondary precipitates (mainly M₃C, M₆C and M₂₃C₆ carbides) has allowed understanding the microstructural evolution of T42 high-speed steel under different processing conditions.     

Green light-emitting Lu3Al5O12:Ce phosphor powders prepared by spray pyrolysis

Green light-emitting Lu_2.985Al₅O₁₂:Ce_0.015 (LuAG:Ce) phosphor powders are prepared by spray pyrolysis. The only crystallized phase in the precursor powders and post-treated powders at temperatures below 800 °C is Lu₂O₃ and the other components are amorphous. Phase pure cubic garnet LuAG:Ce phosphor powders are obtained by post-treatment at 1000 °C. Phosphor powders post-treated at temperatures below 1400 °C retain the spherical shape of the precursor powders. The mean crystallite sizes of phosphor powders post-treated at 1200, 1400, and 1500 °C are 30, 46, and 54 nm, respectively. The excitation spectra contain two bands: a weak band with the maximum peak at 345 nm and a strong broad band in the spectral range from 400 to 490 nm with the maximum peak at 455 nm. The LuAG:Ce phosphor powders have broad emission spectra between 480 and 600 nm, with the maximum peak intensity located at 507 nm. The photoluminescence intensity of the phosphor powders post-treated at 1400 °C is 84.2% of that of the powders post-treated at 1500 °C.     

Effects of β-alanine on morphology and optical properties of CoAl2O4 nanopowders as a blue pigment

In this paper, we have synthesized cobalt aluminate (CoAl₂O₄), nanopowders as blue pigments by the combustion method, which metal nitrates were used as precursor materials and mixture of urea and glycine as fuel. The effect of β-alanine weight percentage as a novel excess fuel on some physical characteristics (e.g. crystallite size and color) of powders has been investigated. The synthesized powders were characterized by means of X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), Fourier transform infrared (FT-IR) and Ultraviolet–visible (UV–Vis) spectroscopies. XRD patterns and FT-IR spectra confirmed the formation of pure nanocrystalline CoAl₂O₄ powders after calcination of the metal-fuel gel precursors at 600 °C for 2 h. Optical band gap of 2.3 eV observed for the prepared powders. The crystallite sizes were estimated of 20–30 nm by means of TEM images and Williamson–Hall method. UV–Vis spectra of the blue metal oxides were characteristics of Co²⁺ metal ions located in tetrahedral sites. CIE L¹a¹b¹ chromatic coordinates indicated that the bluest color was obtained for β-alanine = 5.5 and 35.6 wt.%.     

Studies on the electrochemical preparation of MgCeCo alloy thin films on Cu substrates in urea–DMSO system

Cyclic voltammetry was used to investigate the electrochemical behaviors of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO (dimethylsulfoxide). The electrode processes of Mg(II), Ce(III) and Co(II) reducing on Pt electrodes were irreversible steps. The transfer coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO system was calculated as 0.07, 0.05 and 0.05 at 298.15 K, respectively. The diffusion coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO system was calculated as 2.27 × 10^− 10, 1.77 × 10^− 10 and 3.16 × 10^− 10 m² s^− 1 at 298.15 K, respectively. The MgCeCo alloy thin films with smooth, uniform and metallic luster were obtained on Cu substrates by cyclic electrodeposition in 0.01 mol L^− 1 Mg(ClO₄)₂–0.01 mol·L^− 1 Ce(CH₃SO₃)₃₋0.01 mol L^− 1 CoCl₂–3.00 mol L^− 1 urea–DMSO system. The potential sweep rate was found to be important with respect to the adhesion of the thin films.     

Effect of tin on the corrosion behavior of sea-water corrosion-resisting steel

This paper investigated the effect of tin on the corrosion resistance of tin-containing steel and tin-free steel using electrochemical measurements in seawater. Results showed that tin-containing steel had lower corrosion current and higher impedance than tin-free steel. Surface analyses of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicated that tin could form SnO₂ and SnO in rust layer, and both of them could improve impedance and corrosion resistance of rust layer. Besides, the coprecipitation process of tin oxides with iron oxides could make the rust layer more uniform and compact, which could make the tin-containing steel have better corrosion resistance than tin-free steel. Secondary ion mass spectrometer (SIMS) showed that there was no obvious segregation of tin on substrate steel when tin addition was 0.038 wt.%, and tin could improve the oxidation resistance of substrate steel evenly by lowering the steel's Fermi energy from − 9.276 eV to − 14.445 eV.     

Formation of high-density scintillation ceramic from LuAG:Ce + Lu2O3 powders obtained by co-precipitation method

The results of formation of the high density effective scintillation ceramics consisting of two compounds of the cubic symmetry, LuAG:Ce and Lu₂O₃ (LuAG:Ce + Lu₂O₃), are described. Powders of a novel material LuAG:Ce + Lu₂O₃ were synthesized by co-precipitation method. The introduction of Lu₂O₃ into LuAG:Ce was shown to increase the density of the ceramics obtained and modify its scintillation properties.     

Co2(OH)3Cl nanoparticles as new-type electrode material with high electrochemical performance for application in supercapacitor

In this work, we report the preparation of Co₂(OH)₃Cl nanoparticles with average size of ～20 nm and well-defined cubic shape at room temperature by an epoxide precipitation route. It was found that the as-prepared Co₂(OH)₃Cl nanoparticles could be used as a promising new electrode material for application in redox supercapacitors due to its high electrochemical performance. It presented superior specific capacitance of 783 F g^?1 at low current density of 2.8 A g^?1, while it had a high value of 604 F g^?1 at high current density of 56.6 A g^?1, proving its excellent high rate performance. Its 75% capacitance retention after 10,000 cycles of charge–discharge demonstrated its long-life span. According to characterization results, the possible mechanism for the electrochemical process that Co₂(OH)₃Cl nanoparticles underwent was proposed as a process of Co₂(OH)₃Cl → β-Co(OH)₂ → CoOOH ? Co₃O₄.     

Effect of Cu-doping on the electrochemical performance of FeS2

FeS₂ reportedly has a high specific capacity of 893 mAh/g; however, its poor cyclic performance limits its commercialization. To circumvent this limitation, strategies such as preparation of high-purity FeS₂ and Ni-doping were adopted to modify the electrochemical properties of FeS₂. Nevertheless, these approaches resulted only in limited improvements in the electrochemical properties. Therefore, in this study, we synthesized Cu-doped FeS₂ via a solvothermal process, aiming at improved electrochemical properties. Systematic studies indicated that Cu doping changed the morphology of FeS₂ from larger irregular particles to smaller spherical ones. The charge–discharge measurements indicated that the Cu-doped FeS₂ exhibited two discharge plateaus, at 1.6 V and 1.4 V. The initial specific discharge capacity of Cu-doped FeS₂ was about 866 mAh/g at a current density of 90 mA/g, which is approximately 11% higher than that of the undoped FeS₂. The initial discharge capacity of the Cu-doped FeS₂ at a current density of 2700 mA/g was 518 mAh/g, and its cyclic discharge capacity exceeded 105 mAh/g at the 20th cycle. Cyclic voltammetry and resistance measurements revealed that Cu-doping reduces both the internal resistance and polarization of Li/FeS₂ batteries.     

Mixture of fuels approach for the solution combustion synthesis of LaAlO3 nanopowders

A modified solution combustion approach was used in the preparation of nanosize LaAlO₃ (～23.6 nm) using mixture of citric acid and oxalic acid as fuels with corresponding metal nitrates. The synthesized and calcined powders were characterized by Fourier transform infra red spectrometry (FTIR), Differential thermal analysis-Thermogravimetry analysis (DTA–TGA), X-ray diffractometry (XRD) and Transmission electron microscopy (TEM). The FTIR spectra show the lower frequency bands at 656 and 442 cm^?1corresponds to metal–oxygen bonds (possible La–O and Al–O stretching frequencies) vibrations for the perovskite structure compound. DTA confirms the formation temperature of LaAlO₃ varies between 830–835 °C. XRD results show that mixture of fuels ratio is influential on the crystallite size of the resultant powders. The average particle size of LaAlO₃-1 as determined from TEM was about 41 nm, whereas for LaAlO₃-2 and LaAlO₃-3 samples, particles are seriously aggregated.     

Role of Co–Cr substitution on the structural,electrical and magnetic properties of nickel nano-ferrites synthesized by the chemical co-precipitation method

Nano-spinel nickel ferrites doped with Co–Cr at iron and nickel sites are synthesized by the chemical co-precipitation method and are characterized by the XRD, DC electrical resistivity and hysteresis loops measurements. The XRD analyses confirm the formation of single spinel phase and the crystallite size calculated by Scherer's formula is found in the range of 17–19 nm. This crystallite size is small enough to obtain the suitable signal to noise ratio in the high density recording media. The values of electrical resistivity (8.28 × 10⁷ to 29.6 × 10⁷ ohm cm), activation energy (0.545–0.884 eV), saturation magnetization (23.67–33.49 emu g^?1) and remanence (12.48–18.67 emu g^?1) are increased up to a doping level of x = 0.2 and then starts to decrease. The increase in electrical resistivity, saturation magnetization and remanence suggest that the material with composition Co_0.2Ni_0.8Fe_1.8O₄ can be used for applications in microwave devices and high density recording media.     

Evaluation of transport parameters for PVC based polyvinyl alcohol Ce(IV) phosphate composite membrane

The aim of this study was to investigate the preparation of novel membrane and the characterization of their properties. A new class of polyvinyl chloride (PVC) based polyvinyl alcohol Ce(IV) phosphate composite membrane was successfully prepared by solution casting method. The structural formation was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and morphological studies. The thermal property was investigated by thermogravimetry analysis (TGA) method. The order of surface charge density for various electrolytes was found to be LiCl < NaCl < KCl.     

The effect of Mg add on morphology and mechanical properties of Al–xMg/10Al2O3 nanocomposite produced by mechanical alloying

Effect of Mg content on microstructure and mechanical properties of Al–xMg/10 wt.%Al₂O₃ (x = 0, 5, 10 and 15 wt.%) powder mixtures during milling was investigated. The results show that for the binary Al–Mg matrix, the predominant phase was an Al–Mg solid solution. With the increment of Mg to 15 wt.% the crystallite sizes of 20 h milled powders diminish from 44 to 26 nm and lattice strains increased from 0.22% to 0.32% caused by Mg atomic penetration into the substitution sites of the Al lattice. With up to 15 wt.% Mg (for 20 h milled composites) microhardness increases from 120 to 230 HV caused by the increment of the Mg concentration and dislocation density as well as the decrease of the crystallite size.     

Protection of reinforcement steel corrosion by phenyl phosphonic acid pre-treatment PART I: Tests in solutions simulating the electrolyte in the pores of fresh concrete

The carbon steel electrodes were first treated by immersion in 0.1 M phenyl phosphonic acid (C₆H₅P(O)(OH)₂, PPA) solution during 24 or 72 h, then they were transferred into the corrosion test solution representing interstice pore electrolyte polluted by seawater: (sat. Ca(OH)₂ + 0.5 M NaCl) to evaluate the protective effectiveness of the pre-treatment. The investigation was performed essentially by polarisation curves and electrochemical impedance measurements with rotating disc electrode. Very high protective effect was observed with steel pre-treated during 72 h with stationary electrode. From polarisation and electrochemical impedance spectroscopy experiments, the protective efficiency was found to be in the 90–99% range for 72 h pre-treatment. This protective property remains effective even one month immersion. EDS analysis showed the presence of the phosphorus on the steel surface, probably due to the presence of iron-PPA complex.     

Study on the microstructure and electrochemical kinetic properties of MmNi4.50−xMnxCo0.45Al0.30 (0.25 ≤ x ≤ 0.45) hydrogen storage alloys

The phase structures, surface morphologies and electrochemical kinetic properties of MmNi_4.50?xMn_xCo_0.45Al_0.30 (Mm is the mischmetal, x = 0.25, 0.30, 0.35, 0.40 and 0.45) hydrogen storage alloys have been investigated in this paper. The X-ray diffraction (XRD) shows that all the alloys mainly consist of LaNi₅ phase with CaCu₅-type structure, which belongs to P6/mmm space group (central symmetry). Scanning electron microscopy (SEM) tests indicate that there are partial element segregations in the alloys. Meanwhile, energy dispersive spectrum (EDS) results display that the elements constituting Mm exist in the matrix phase in relatively larger proportion, while Mn, Al and Co tend to appear in precipitate phase. For the alloy with x = 0.35, the electrochemical performances, including discharge capacity, high-rate dischargeability (HRD) and cycling life, of the alloy electrode are better than that of other alloy electrodes. With the increase of Mn content, the exchange current density (I₀) of the alloy electrodes first increases and then decreases, the hydrogen diffusion coefficient (D) of alloy electrodes gradually decreases. There is a linear correlation between HRD at a discharge current density of 1500 mA/g and I₀.     

Cobalt–carbon derived from zeolitic imidazolate framework on Ni foam as high-performance supercapacitor electrode material

ZIF-67 (Co(MeIM)₂, MeIM = 2-methylimidazole) was selected as a precursor to synthesize the metallic cobalt/carbon composites on Ni foam directly and intimately. The results show that ZIF-67 forms a uniform membrane and densely covers the Ni foam substrate. Besides, the cobalt/carbon composites obtained are composed of cobalt nanoparticles with a diameter up to around 2.6 nm, which are anchored on carbon homogeneously. The specific capacitance of the composites material is up to 512 F g⁻¹ at a current density of 1 A g⁻¹ in 1.0 M KOH electrolyte. Furthermore, the specific capacitance loss is ∼46.4% with increase at the current density from 1 to 20 A g⁻¹. More significantly, the specific capacitance retention rate is 87.5% at a current density of 5 A g⁻¹ after 1000 cycles. These results suggest that the electrochemical performance can be greatly enhanced by the well-controlled size and distribution of the cobalt nanoparticles, which is mainly attributed to the unique structure and composition of ZIF-67.     

Effect of the Ti/Na molar ratio on the acidity and the structure of TiO2 nanostructures: Nanotubes,nanofibers and nanowires

TiO₂ nanotubes were prepared by the hydrothermal treatment of TiO₂ particles with different NaOH concentrations (5, 7, 10 and 12 N) at 140 °C; afterwards, HCl was added until reaching pH 1. Both the crystalline phase and coordination of the TiO₂ nanotubes, composed principally of H₂Ti₃O₇ and H₂Ti₄O₉·2H₂O, were significantly affected by the NaOH rinsing treatment. Likewise, the surface area, pore volume and pore size of the TiO₂ nanotubes changed with the NaOH rinsing treatment. Finally, the NaOH rinsing treatment exerted a notable effect on the generation of Brönsted sites, which is shown by the following sequence: NT7 > NT10 > NT12 > NT5; meanwhile Lewis sites were only present on the NT5 sample.     

Effect of NaHCO3 on synthesis of anatase TiO2 nanopowders by thermal processing of the precursor

Titanium dioxide (TiO₂) nanopowders were successfully prepared by thermal processing of the precursor of titanium hydroxide, urea and sodium acid carbonate (NaHCO₃). The products were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that NaHCO₃ has a certain effect on the average crystallite size and dispersity of TiO₂ nanopowders, at the same time other phases (Na₂SO₄ and Na₂CO₃) will be introduced. However, Na₂SO₄ has distinctive intercalation ability and catalytic activity. TiO₂ (anatase) powders can be prepared at ?600 °C for 2 h with addition of 2–10 wt% NaHCO₃, and the average crystallite size is 20.0–22.3 nm. The surface of the sample mainly consists of Ti, O, C, Na and S five species elements.