Preparation of Fe2B boride coating on low-carbon steel surfaces and its evaluation of hardness and corrosion resistance

Fe₂B coating was prepared on low-carbon steel by surface alloying. A series of experiments were carried out to examine some surface properties of boride coating. The surface heat treatment of coated low-carbon steel was performed at 700 °C, 800 °C and 900 °C for 2 h, 4 h, 6 h and 8 h under hydrogen atmosphere. The boride coating was revealed by XRD analysis and the microstructure of the boride coating was analyzed by scanning electron microscopy (SEM). Depending on the temperature and time of the process, the hardness of the borided low-carbon steel ranged from 99 to 1100 HV. The hardness showed a maximum (about 1100 HV) at 900 °C for 8 h. The corrosion resistance of the borided samples was evaluated by the Tafel polarization and electrochemical impedance spectroscopy (EIS). Shift in the corrosion potential (E_corr) towards the noble direction was observed, together with decrease in the corrosion current density (I_corr), increase in the charge transfer resistance (R_ct) and decrease in the capacitance (C_c), which indicated an improvement in corrosion resistance with increasing temperature and time of the treatment.     

Synthesis and characterization of polyaniline–Fe3O4 nanocomposite: Electrical conductivity,magnetic, electrochemical studies

Fe₃O₄ nanoparticles were prepared by hydrolysis reaction of urea in ethylene glycol as solvent at 160 °C. The prepared Fe₃O₄ nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline:Fe₃O₄ (19:1, 16:1, 12:1, 9:1) using (NH₄)₂S₂O₈ as oxidant in aqueous solution of sodium dodecylbenzene sulphonic acid under N₂ atmosphere. Room temperature conductivities of the synthesized PANI, PANI/Fe₃O₄ (19:1) and PANI/Fe₃O₄ (9:1) are 3.2 × 10^?4, 1.8 × 10^?5 and 1.0 × 10^?5 S/cm, respectively, indicating decrease of conductivity with increase of Fe₃O₄ in PANI. Saturation magnetizations of Fe₃O₄, PANI/Fe₃O₄ (19:1), and PANI/Fe₃O₄ (9:1) are 27.5, 5.5 and 6.3 emu/g, respectively, indicating an increase of ferromagnetic interaction with more incorporation of Fe₃O₄ in PANI matrix, whereas PANI is diamagnetic. Electrochemical studies shows that Zn-PANI/Fe₃O₄ (9:1) battery had delivered maximum discharge capacity (78.6 mAh/g) as compared to Zn-PANI battery (50.1 mAh/g) at constant current of 0.5 mA cm^?2. At constant resistance of 1000 Ω, discharge capacities of Zn-PANI/Fe₃O₄ and Zn-PANI battery are 73.37 and 50.8 mAh/g, respectively.     

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⁻.     

Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu

Fe–Pd–Cu thin films are of great interest for applications in magnetic shape memory microsystems due to their increased martensitic transformation temperature. Here we analyse the consequences of Cu addition to Fe–Pd on the binding energy and magnetic properties by a combination of thin film experiments and first-principles calculations. Strained epitaxial growth of Fe₇₀Pd_30-xCu_x with x = 0, 3, 7 is used to freeze intermediate stages during the martensitic transformation. This makes a large range of tetragonal distortion susceptible for analysis, ranging from body-centred cubic to beyond face-centred cubic (1.07 < c/a_bct < 1.57). We find that Cu enhances the quality of epitaxial growth, while spontaneous polarization and Curie temperature are reduced only moderately, in agreement with our calculations. Beyond c/a_bct > 1.41 the samples undergo structural relaxations through adaptive nanotwinning. Cu enhances the magnetocrystalline anisotropy constant K₁ at room temperature, which reaches a maximum of ?2.4 × 10⁵ J m^?3 around c/a_bct = 1.33. This value exceeds those of binary Fe₇₀Pd₃₀ and the prototype Ni–Mn–Ga magnetic shape memory system. Since K₁ represents the maximum driving energy for variant reorientation in magnetic shape memory systems, we conclude that Fe–Pd–Cu alloys offer a promising route towards microactuator applications with significantly improved work output.     

Microstructure,dielectric response and electrical properties of polypyrrole modified (poly N-vinyl carbazole–Fe3O4) nanocomposites

N-vinyl carbazole (NVC) was polymerized in the presence of nanodimensional Fe₃O₄ in solid state at ～65 °C and a nanocomposite of poly N-vinyl carbazole with Fe₃O₄ (PNVC–Fe₃O₄) was isolated. This composite was further modified by encapsulation with polypyrrole (PPY) via oxidative polymerization of pyrrole in an aqueous dispersion of the PNVC–Fe₃O₄ composite in the presence of potassium persulfate (KPS). The presence of PNVC and of PPY in the PPY–PNVC–Fe₃O₄ composite was confirmed by FTIR spectroscopic analyses. TGA and DTA analyses showed the overall thermal stability trend as: Fe₃O₄ > PNVC–Fe₃O₄ > PPY–(PNVC–Fe₃O₄) > PNVC. HRTEM images revealed that the PPY–(PNVC–Fe₃O₄) nanocomposites have an average grain size of ≈37 nm in good agreement with the values estimated from XRD data. SEM analysis indicated the preponderance of spherical particles embedded in the matrix. The dielectric constants of PNVC–Fe₃O₄ and the PPY–Fe₃O₄ systems were low (110–400) whereas the PPY encapsulated PNVC–Fe₃O₄ nanocomposites showed significantly higher values of dielectric constant (>1000), suggested that the interfaces between grain and grain boundary of the composite play a dominant role for enhancing dielectric properties of the system. Relaxation behaviors for the nanocomposite system were explained considering Maxwell–Wagner two-layered dielectric models. The ac conductivity was found to be independent on frequency in the range 10²–10³ Hz for all the nanocomposites implying contribution of free charges and rise thereafter appreciably in the frequency range of 1–25 kHz due to trapped charges in the grain boundary.     

Oxidation of Fe–Si,Fe–Al and Fe–Si–Al alloys in CO2–H2O gas at 800 °C

Binary Fe–(1, 2, 3)Si and Fe–(2, 4, 6)Al, and ternary Fe–(2, 3)Si–(4, 6)Al alloys (all in wt%) were oxidised in Ar–20% CO₂, with and without H₂O, at 800 °C. All binary alloys except Fe–6Al, in all gases, formed a thin outer layer of Fe₃O₄, an intermediate Fe₃O₄ + FeO layer, an inner FeO + Fe₂SiO₄ (or FeAl₂O₄) layer and internally precipitated SiO₂ (or FeAl₂O₄). Ternary alloys and Fe–6Al developed a protective Al₂O₃ layer beneath Fe₂O₃ in Ar–20% CO₂. Water vapour affected ternary alloy oxidation only slightly, but Fe–6Al oxidized internally in high H₂O-content gas, and its scale was non-protective.     

Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

Glass coatings on stainless steels for high-temperature oxidation protection: Mechanisms

The oxidation behavior of a martensitic stainless steel with or without glass coating was investigated at 600–800 °C. The glass coating provided effective protection for the stainless steel against high-temperature oxidation. However, it follows different protection mechanisms depending on oxidation temperature. At 800 °C, glass coating acts as a barrier for oxygen diffusion, and oxidation of the glass coated steel follows linear law. At 700 or 600 °C, glass coating induces the formation of a (Cr, Fe)₂O₃/glass composite interlayer, through which the diffusion of Cr³⁺ or Fe³⁺ is dramatically limited. Oxidation follows parabolic law.     

Cr effects on magnetic and corrosion properties of Fe–Co–Si–B–Nb–Cr bulk glassy alloys with high glass-forming ability

Effects of the Cr addition on glass formation, magnetic and corrosion properties of {[(Fe_0.6Co_0.4)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_100−xCr_x (x = 1, 2, 3, 4 at.%) alloys have been investigated. It was found that the addition of Cr element slightly decreases the glass-forming ability (GFA), but is very effective in increasing corrosion resistance and improving soft magnetic properties for this Fe–Co–B–Si–Nb bulk glassy alloy within the composition range examined. The Fe–Co–B–Si–Nb–Cr alloys exhibit high GFA. Full glassy rods with diameters up to 4 mm can be synthesized by copper mold casting. The Fe-based bulk glassy alloys (BGAs) exhibit a high saturation magnetization of 0.81–0.98 T as well as excellent soft magnetic properties, i.e., extremely low coercive force of 0.6–1.6 A/m and super-high initial permeability of 26,400–34,100. Furthermore, corrosion measurements show that corrosion rate and corrosion current density of these Fe-based BGAs in 0.5 M NaCl solution decrease from 7.0 × 10⁻¹ to 1.6 × 10⁻³ mm/year and 3.9 × 10⁻⁶ to 8.7 × 10⁻⁷ A/cm², respectively, with increasing Cr content from 0 to 4 at.%. The success of synthesizing the new Fe-based BGAs exhibiting simultaneously high GFA as well as excellent good soft magnetic properties combined with high saturation magnetization and enhanced corrosion resistance allows us to expect future progress as a new type of soft magnetic materials.     

Fe–B–C composites produced using spark plasma sintering

Fe–B–C composites were produced using iron and boron carbide powders. The powders were mixed to produce various compositions, ranging from 1 vol.% Fe to 80.1 vol.% Fe. Spark plasma sintering (SPS) was used to densify the composite powder green compacts. The sintering temperatures used ranged from 900 °C for the composites with a high iron content to 2000 °C for those with a high boron carbide content. It was evident that during the sintering process the iron reacted with the boron carbide. XRD analysis showed the presence of FeB, Fe₂B, Fe₃C, Fe₃(B_0.6C_0.4), Fe₂₃(B,C)₆ and residual carbon as reaction products. The composites were found to have hardness values between 9.8 and 33.1 GPa with the higher hardness being associated with the higher boron carbide contents. The fracture toughness values determined were in the range of 2.8–5.3 MPa m^0.5. With increasing iron content from 1 to 5 vol.%, it is evident that the FeB formed begins to embrittle the material rather than increase the fracture toughness as a result of the high residual stresses between the B₄C and FeB phases.     

Effect of Fe2O3 on Sm-doped ceria system solid electrolyte for IT-SOFCs

The effect of Fe₂O₃ addition (0–2.5 mol%) on the densification, crystal structure, ionic conductivity, and aging behavior of Ce_0.8Sm_0.2O_1.9 (SDC) was studied. The addition of Fe₂O₃ promotes densification, reducing sintering temperature by ～100–150 °C. X-ray diffraction showed that these materials exhibit a fluorite structure; a second phase of Fe₂O₃ is identified when Fe₂O₃ content was ≥1.5 mol%. Impedance spectroscopy measurements indicated that SDC with 0.25 mol% Fe₂O₃ has the highest conductivity, about 10% higher than that of SDC at 700 °C. Conversely, a reduction in conductivity is observed in all samples after aging in air at 800 °C for 120 h. Because of the harmful effect of aging, conductivity rapidly decreases as Fe₂O₃ content in the samples exceeded 0.25 mol%. However, SDC with 0.25 mol% Fe₂O₃ shows the same magnitude of decrease in conductivity compared with that of SDC after aging. This indicates that SDC with 0.25 mol% Fe₂O₃ continues to present the best conductivity even after high-temperature aging.     

Synthesis and characterization of organically modified silicate/NiZn ferrite hybrid coatings

Hybrid coatings based on organically modified silicate (Ormosil)/Ni_0.5Zn_0.5Fe₂O₄ (10–30 wt.%) were synthesized through a sol–gel technique. Tetraethylenepentamine, 3-glycidoxypropyltrimethoxysilane, tetraethoxysilane and Ni_0.5Zn_0.5Fe₂O₄ were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy in order to improve the corrosion protection and to act as infrared stealth coatings. The effects induced by the NiZn ferrite content on the chain dynamic, ferromagnetic behavior, infrared stealth and corrosion performances of the coated samples were investigated. The rotating-frame spin–lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked, dense and adhered to the aluminum alloy substrates. The magnetic properties of the resulting hybrids showed super-paramagnetic behavior, such as zero coercive force (coercivity = 0 G) and a low blocking temperature (∼75 K). The thermal extinction of the hybrid coatings increased with the increase in the NiZn ferrite content. Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.     

The enhanced passivation of 316L stainless steel in a simulated fuel cell environment by surface plating with palladium

A thin layer of Pd deposition on the surface significantly improves the corrosion resistance of 316L stainless steel in 0.5 mol L⁻¹ H₂SO₄ + 2 ppm F⁻ solution at 80 °C. Compared with the air-formed passive film, the passive film formed in the stainless steel/Pd couple contains more Cr, Cr(OH)₃ and Fe₃O₄ and less point defects, which provides better protection to the stainless steel substrate. The interfacial contact resistance of the stainless steel surface is also decreased. The Pd plated stainless steel is a potential material for bipolar plates in proton exchange membrane (PEM) fuel cells.     

Fabrication of LiMn2O4 thin film cathode from chitosan-containing solution

Thin film of spinel LiMn₂O₄ was obtained by spin coating the chitosan-containing precursor solution on a platinumized Si substrate, followed by a two-step annealing procedure at 300 and 700 °C, respectively. It was demonstrated that the addition of the appropriate amount of chitosan to the precursor solution enhanced the deposition of LiMn₂O₄ films. The thickness of the deposited film from chitosan-containing precursor solution is about 5.2 μm after five-time spin coating under a spinning speed of 2500 rpm. Without the addition of chitosan in precursor solution, the deposited film was as thin as 0.16 μm under the same processing parameters. Furthermore, the electrochemical behavior for the deposited LiMn₂O₄ film calcined at 700 °C for 1 h was characterized by the charge–discharge test. The result shows that the 1st discharge capacity is 56.31 μAh cm⁻² μm⁻¹ at a discharge rate of C/2 and the fading rate of the discharge capacity is only 0.19% cycle⁻¹ after 50 cycles.     

Effect of molybdenum on high-temperature corrosion of Fe–Al intermetallics

Fe41Al4Mo and Fe32Al19Mo (at.%) intermetallics were prepared by self-propagating high-temperature synthesis (SHS) combined with arc melting (AM) and vacuum annealing. Corrosion resistance was evaluated on the basis of sulphidation and oxidation tests. Sulphidation experiments were carried out in the flowing H₂/H₂S mixtures mainly at a temperature of 1273 K and at sulphur pressures 10⁻³–0.3 Pa. Reaction progress was followed thermogravimetrically. The extent of corrosion attack increased with sulphur pressure, temperature and molybdenum concentration. Oxidation tests were carried out in air in isothermal (at 1073 and 1273 K) and thermal cycling conditions (24-h cycles at 1223 K). The results of kinetic studies, metallographic observations as well as phase and chemical analysis of corrosion products indicated limited resistance of the investigated FeAlMo alloys to sulphidation or oxidation at elevated temperatures.     

Effect of boron doped fullerene C60 film coating on the electrochemical characteristics of silicon thin film anodes for lithium secondary batteries

In this work, boron doped fullerene (B:C₆₀) films were prepared by the radio frequency plasma assisted thermal evaporation technique for use as a coating material for the silicon thin film anode in lithium secondary batteries. Raman and XPS analyses revealed that the boron atoms were well inserted into the fullerene film lattices. The effect of the B:C₆₀ film on the electrochemical characteristics of the silicon thin film was studied by charge–discharge tests, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The B:C₆₀ coated silicon film exhibited a high reversible capacity of more than 1200 mAh g^?1 when cycled 50 times between 0 and 2 V at a current density of 1200 μA cm^?2 (1.5 C). The film also showed good rate capacity at different current densities and a more improved coulombic efficiency of 87.7% in the first cycle in comparison with that of the C₆₀ coated film electrode.     

Electrochemical corrosion behaviour of Incoloy 800 in sulphate solutions containing hydrogen peroxide

The aim of this study is to evaluate the electrochemical corrosion behaviour of Incoloy 800 in sulphate solutions containing H₂O₂ in the temperature range of 25–80 °C. The open circuit potential measurements, cathodic and anodic polarization and electrochemical impedance spectroscopy (EIS) were used to characterize the corrosion behaviour. The results provide kinetic data for reduction of hydrogen peroxide on Pt surface. The anodic polarization curves for Incoloy at different pH, temperature and H₂O₂ concentration are presented. EIS data generally confirm the polarization interpretations about the effects of various parameters. An equivalent circuit was used to fit all the acquired data.     

First-principles assessment of hydrogen absorption into FeAl and Fe3Si: Towards prevention of steel embrittlement

We characterize the ability of two potential surface alloys, FeAl and Fe₃Si, to prevent H incorporation into steel, with a view toward inhibiting steel embrittlement. Periodic density functional theory calculations within the generalized gradient approximation are used to evaluate H dissolution energetics and the kinetics of H diffusion into and through FeAl and Fe₃Si. We predict increased dissolution endothermicities and diffusion barriers in both alloys compared to bulk Fe. Fe₃Si is predicted to be the most effective at inhibiting H incorporation, with a 1.91 eV [0.97 eV] surface-to-subsurface diffusion barrier on the (1 1 0) surface [(1 0 0 surface)] and a 0.79 eV endothermicity to bulk dissolution, compared to a 1.02 eV [0.38 eV] barrier and 0.20 eV dissolution energy in pure Fe [37]. We therefore propose that a thin layer of Fe₃Si may provide protection against H embrittlement of the underlying steel.     

The oxidation behavior of an Fe61B15Zr8Mo7Co5Y2Cr2 bulk metallic glass at 650 °C in various oxygen-containing environments

The oxidation behavior of an Fe₆₁B₁₅Zr₈Mo₇Co₅Y₂Cr₂ bulk metallic glass (Fe7-BMG) was investigated in three oxygen-containing atmospheres over the oxygen partial pressure range of 10³–10⁵ Pa at 650 °C. The oxidation kinetics of the Fe7-BMG followed the parabolic rate law in all cases, indicating that solid-state diffusion is the rate-controlling step during oxidation. The oxidation rate constants (k_p values) increased with increasing oxygen partial pressure, implying a typical scaling behavior with a p-type semiconductivity. Duplex scales formed on the Fe7-BMG consisted of an outer layer of mostly iron oxides (Fe₂O₃/Fe₃O₄) and minor amounts of B₂O₃, and a heterophasic inner layer of mostly tetragonal-ZrO₂ (t-ZrO₂) intermixed with non-oxidized intermetallic phases.     

Correlation between the corrosion resistance and the semiconducting properties of the oxide film formed on AZ91D alloy after solution treatment

The corrosion resistance and semiconducting properties of the oxide film formed on the AZ91D alloy were evaluated. The alloy was tested in the as-cast condition and after a solution annealing treatment. Electrochemical impedance spectroscopy measurements and potentiodynamic polarization curves were obtained in a H₃BO₃ (0.05 M) + Na₂B₄O₇⋅10H₂O (0.075 M) solution with pH = 9.2 at room temperature. The semiconducting properties of the oxide film were evaluated using Mott–Schottky plots. The corrosion resistance of the AZ91D was reduced after the solution treatment while the semiconducting properties of the passive films were little affected.