Thermal expansion behavior of a β-LiAlSiO<Subscript>4</Subscript>/Cu composite

A copper matrix composite reinforced by β-LiAlSiO₄ with negative thermal expansion coefficient was fabricated using vacuum hot-pressed sintering technique. The thermal expansion behavior of the composite was investigated, and the average residual stress in the matrix was analyzed by a simple model. The results indicate that the residual stress in the matrix affects the thermal expansion properties. After heat treatment, the coefficient of thermal expansion (CTE) of the composite decreases greatly. The CTE of the composite after thermal cycling between 50–350°C is the lowest.     

Effect of the atmosphere of low-temperature annealing on the structure and electrophysical properties of nonstoichiometric YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript> ceramics

The fine structure and electrophysical properties of nonstoichiometric YBa₂Cu₃O_{7 − δ} ceramics and the effect of low-temperature annealing (t ⩾ 200°C) in various atmospheres on these parameters have been studied. It has been shown that, during annealing in a vacuum, the decomposition is quite sluggish; structures typical of initial stages of decomposition are observed. The decomposition in an inert-gas atmosphere occurs more actively, and structures typical of stages of deep decomposition are realized. It has been found that, during low-temperature annealing, the structure and properties are affected by two factors; these are the decomposition into phases differing in the oxygen content, and water absorption, leading to the transformation with the formation of a pseudo-cubic lattice. The annealing atmosphere substantially affects the kinetics of both processes.     

Embrittlement and conditions of the optimization of magnetic properties in the amorphous alloy Co<Subscript>69</Subscript>Fe<Subscript>3.7</Subscript>Cr<Subscript>3.8</Subscript>Si<Subscript>12.5</Subscript>B<Subscript>11</Subscript> in the absence of a viscous–brittle transition

The influence of the holding time upon annealing on the temperature of the viscous–brittle transition (temperature of embrittlement) T_f in a cobalt-based amorphous alloy of the composition Co₆₉Fe_3.7Cr_3.8Si_12.5B₁₁ with a very low saturation magnetostriction λ_s (<10^–7) has been studied. It has been established that the dependence of the embrittlement temperature T_f on the of time of holding t_a can be described by an Arrhenius equation and that the embrittlement at the annealing temperatures above and below 300°C is described by different kinetic parameters. In the alloy under study, irrespective of the holding time, embrittlement occurs in a very narrow range of annealing temperatures, which does not exceed 5 K. Based on the experimental data on the evolution of the hysteresis magnetic properties upon the isochronous annealings and upon the isothermal holding, the regime of heat treatment that ensures a very high (about 50000) magnitude of the permeability µ₅ (H = 5 mOe, f = 1 kHz) without the transition of the alloy into a brittle state has been determined.     

Effect of the decomposition of the supersaturated β solid solution in melt-quenched Ni<Subscript>65</Subscript>Al<Subscript>35</Subscript> and Ni<Subscript>56</Subscript>Al<Subscript>34</Subscript>Co<Subscript>10</Subscript> alloys on the reversibility of the martensitic transformation

Melt-quenched Ni₆₅Al₃₅ and Ni₅₆Co₁₀Al₃₄ (at %) alloys are studied by electrical resistance measurement and electron microscopy. The effects of the isothermal holding time in the supersaturated β solid solution field and the heating rate during thermal cycling on the restoration of the reversibility of the martensitic transformation are investigated. After short-term aging in the B2 austenite field followed by long-term aging in the L1₀ martensite field, the melt-quenched Ni₆₅Al₃₅ and Ni₅₆Co₁₀Al₃₄ alloys retain their high thermal stability of the reversibility of the martensitic transformation.     

The Effect of Pre-oxidation Treatment on Corrosion Behavior of Ni–Cu–Fe–Al Anode in Molten CaCl<Subscript>2</Subscript> Salt

This article presents Ni–Cu–Fe–Al alloy as a novel inert anode used in FFC process (the Fray Farthing Chen) in molten calcium chloride salts for producing titanium. The alloy was prepared by vacuum induction melting; then utilized as anode material in molten CaCl₂ for 16 h at 900 °C. Morphology and the corrosion behavior of the samples were analyzed using scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The product on the cathode was analyzed using X-ray diffraction (XRD). After 16 h electrolysis of anodes, EDS and SEM analysis of the samples showed that the corrosion depth of the non-oxidized sample was shorter. Corrosion attacks more severe for the pre-oxidized sample than the non-oxidized sample, which indicated that the corrosion resistance of outer layer is higher on the non-oxidized sample. The XRD results show that the TiO₂ pellets were successfully reduced to the lower oxides using the Ni–Cu–Fe–Al inert anode.     

Effect of tensile stresses on the Δ<Emphasis Type="Italic">E</Emphasis> effect in ferromagnetic Fe<Subscript>64</Subscript>Co<Subscript>21</Subscript>B<Subscript>15</Subscript> ribbons

Effect of elastic tensile stresses on the Δ E -effect magnitude in ferromagnetic Fe₆₄Co₂₁B₁₅ amorphous ribbons subjected to magnetic annealing and dc treatment was studied. In the case of relatively low tensile stresses, the maximum magnitude of the negative Δ E effect in the ribbons under study is shown to increase whatever their treatment. The subsequent increase in elastic tensile stresses leads to a decrease in the maximum value of the negative ΔE effect. The maximum sensitivity of the ΔE effect to the applied elastic tensile stresses is characteristic of samples subjected to magnetic annealing. The results obtained are explained using a conception of the effect of magnetic domain structure and mechanisms of its transformation induced by magnetic field and elastic tensile stresses on the ΔE effect in amorphous ferromagnetic ribbons.     

Investigations on Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Ti<Subscript>3</Subscript>O<Subscript>5</Subscript> Composite as an Anode Material for Lithium–Ion Batteries

The Ti₃O₅ powder with uniform morphology has been successfully obtained and used to synthesize Li₄Ti₅O₁₂/Ti₃O₅ composite material by ball milling for modifying Li₄Ti₅O₁₂-based, lithium–ion battery anodes. Moreover, according to the relative performance investigations, the synthesized Li₄Ti₅O₁₂/Ti₃O₅ composite shows better electrochemical properties than that of the Li₄Ti₅O₁₂. At a high rate (10 C), the capacity of the Li₄Ti₅O₁₂/Ti₃O₅ composite electrode is 139.8 mAhg^?1, whereas the value of Li₄Ti₅O₁₂ is 121.6 mAhg^?1, showing a capacity enhanced about 14.97%. After 100 cycles at 0.2 C, the discharge capacity of Li₄Ti₅O₁₂/Ti₃O₅ remains at 160 mAhg^?1 with a capacity loss of 2.6%. The results indicate that the Li₄Ti₅O₁₂/Ti₃O₅ composite electrode can be used as anode material with a relatively higher rate capability and excellent cycle performance in lithium–ion batteries.     

Effect of SO<Subscript>4</Subscript> <Superscript>2-</Superscript>, Cl<Superscript>–</Superscript> and NO<Subscript>3</Subscript> <Superscript>-</Superscript> anions on the formation of iron oxide nanoparticles via microwave synthesis

In the present work iron oxide nanoparticles have been prepared by microwave assisted synthesis with the influence of different precursor salts and synthesis of magnetite, hematite, Iron oxide hydroxide and maghemite nanoparticles. Synthesized iron oxide nanoparticles were characterized with Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and Energy-dispersive X-ray Spectroscopy (EDX). XRD measurements show that the peaks of diffractogram are in agreement with the theoretical data of magnetite, hematite, FeO(OH) (Iron oxide hydroxide) and maghemite. Crystallite size of the particles was found to be 33, 45, 36 and 43.5 nm for Fe₃O₄, α-Fe₂O₃, FeO(OH) and γ-Fe₂O₃. FESEM studies indicated that size of the particles is observed in the range of about 19.4 to 46.7 nm (Fig. 2a, average 32 nm), 29.1 to 67.6 nm (Fig. 2b average 45 nm), 29.1 to 40.8 (Fig. 2c average 36.6 nm), 29.1 to 80 nm (Fig. 2d average 43.5) for Fe₃O₄, α-Fe₂O₃, FeO(OH) and γ-Fe₂O₃ respectively. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR graphs indicated absorption bands due to O–H stretching, C–O bending, C–H stretching and Fe–O stretching vibrations.     

The effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles on tribological and corrosion behavior of electroless Ni–B–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite coating

In this study, the Ni–B–Al₂O₃ composite was successfully coated on the surface of Ck45 steel by elecroless method. X-Ray diffraction analysis (XRD) and scanning electron microscopy (SEM) were utilized in order to investigate and identify the coating properties. Wear behavior of the coating was studied by the pinon- disk test. Corrosion behavior of the Ni–B and Ni–B–Al₂O₃ coatings was investigated by using Tafel polarization diagrams in the 3.5% NaCl solution at room temperature. The obtained data demonstrate that the addition of Al₂O₃ nanoparticles to the coating has resulted in improving the tribological behavior of the coating due to the presence of the composite nanoparticles. Also, the results of electrochemical testing show that corrosion resistance of the electroless Ni–B coating with Al₂O₃ nanoparticles has dramatically increased.     

Synthesis and electrochemical performance of LiMn<Subscript>x</Subscript>Fe<Subscript>x−1</Subscript>PO<Subscript>4</Subscript>/C cathode material for lithium secondary batteries

Carbon-coated LiMn_0.8Fe_0.2PO₄/C (C = 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%) cathode material is synthesized using a solid-state method. No impurity is found within the synthesized active material, which is confirmed to have an olivine structure with particle sizes in the range of 100 nm to 200 nm. The LiMn_0.8Fe_0.2PO₄/C (C = 10 wt.%) active material shows an outstanding discharge capacity of 121.7 mAh·g⁻¹, along with a high capacity maintenance rate of 87.9 % at 2 C against the 0.2 C rate. In addition, this sample shows the most outstanding discharge capacity and coulombic efficiency in the cycling performance tests.     

Thermomagnetic and Mössbauer studies of structural transformations caused in the amorphous Nd<Subscript>9</Subscript>Fe<Subscript>85</Subscript>B<Subscript>5</Subscript> alloy by severe plastic deformation and annealing

Thermomagnetic analysis and Mössbauer spectroscopy were used to study the effect of severe plastic deformation (SPD) by high-pressure torsion (HPT) and subsequent annealing on structural transformations and formation of magnetic properties of rapidly quenched Nd₉Fe₈₅B₆ alloy. The HPT of the Nd₉Fe₈₅B₆ amorphous alloy was found to result in the precipitation of α-Fe nanocrystals and in changes in the structural state of the residual amorphous phase A′. In the annealed samples, there was revealed a great amount of nonequilibrium phases with different magnetizations. The total content of nonequilibrium phases depends on the annealing temperature and affects the exchange interaction between magnetically soft α-Fe nanocrystals and Nd₂Fe₁₄B nanocrystalline grains. The results obtained in this study can explain the differences between the high level of hysteresis properties of nanocrystalline materials, which was predicted theoretically, and low magnitudes realized in practice.     

Effect of doping and substitution on the low-temperature decomposition of oxygen-nonstoichiometric Ba<Subscript>2</Subscript>YCu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript>

Effects of doping (with Ce and Pr) and substitution of Sr, Nd, Eu, and Ni for Ba and Cu on the lowtemperature (T = 200–300°C) decomposition of oxygen-nonstoichiometric Ba₂YCu₃O_{7 ? δ} have been studied. Both the doping and partial substitution for any of the principal components was found to increase the stability of the 123 compounds with respect to the decomposition into oxygen-depleted and oxygen-rich phases. Both doping and substitution to a level of ～2% lead to a narrowing of the immisibility dome and a decrease in the critical temperature. In the first place, the decomposition is suppressed in the bulk of grains. To increase the stability of near-boundary regions of grains, a high degree (～20 at %) of substitution is necessary.     

Synthesis of LiFePO<Subscript>4</Subscript> using FeSO<Subscript>4</Subscript>·7H<Subscript>2</Subscript>O byproduct from TiO<Subscript>2</Subscript> production as raw material

As the byproduct of TiO₂ industrial production, impure FeSO₄·7H₂O was used for the synthesis of LiFePO₄. With the purified solution of FeSO₄·7H₂O, FePO₄·xH₂O was prepared by a normal titration method and a controlled crystallization method, respectively. Then LiFePO₄ materials were synthesized by calcining the mixture of FePO₄·xH₂O, Li₂CO₃, and glucose at 700°C for 10 h in flowing Ar. The results indicate that the elimination of FeSO₄·7H₂O impurities reached over 95%, and using FePO₄·xH₂O prepared by the controlled crystallization method, the obtained LiFePO₄ material has fine and sphere-like particles. The material delivers a higher initial discharge specific capacity of 149 mAh·g⁻¹ at a current density of 0.1C rate (1C = 170 mA·g⁻¹); the discharge specific capacity also maintains above 120 mAh·g⁻¹ after 100 cycles even at 2C rate. Thus, the employed processing is promising for easy control, low cost of raw material, and high electrochemical performance of the prepared material.     

Metastable-Stable Phase Transformation Behavior of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Scale Formed on Fe–Ni–Al Alloys

The oxidation behavior of Ni–Fe–41.5at.%Al alloys with different Fe/Ni ratios was investigated in air at 1000 °C in order to clarify the effect of Fe on the phase transformation of Al₂O₃ scale, using in-situ high-temperature X-ray diffraction by means of synchrotron radiation. The oxidation mass gain of alloys after 25 h of oxidation generally decreased with increasing Fe content; however, the initial oxidation mass gain was significantly decreased by increasing alloy Fe content. In-situ X-ray diffraction analysis indicated that higher alloy Fe contents promoted rapid formation of the stable α-Al₂O₃, while lower Fe in the alloy maintained the metastable Al₂O₃ for longer time oxidation. The effect of Fe on promoting α-Al₂O₃ formation can be explained by the initial formation of α-Fe₂O₃, whose structure is isomorphous with α-Al₂O₃. The additional effect of Fe on the growth rate of α-Al₂O₃ is also discussed.     

Effect of Ni–P and Phosphate Intermediate Layers on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating Developed by Sol-Gel Method

Sol–gel method was used for applying of alumina coating on carbon steel substrate. Alumina sol was prepared with Al-isopropoxide as a precursor material. Specimens were coated with prepared alumina sol by dip coating technique. Either a film of Ni–P or phosphated intermediate layer has been pre-deposited on the carbon steel substrate by electroless plating to improve the adherence of alumina coating. The corrosion resistance of coatings in the presence of intermediate layers was evaluated by electrochemical measurement in 3.5% NaCl solution by open-circuit potential measurement at room temperature. The abrasive wear behavior of sol–gel coated specimens was measured in high stress conditions. The results indicate that, after applying an intermediate layer of phosphate or Ni–P by electroless plating technique, the wear and corrosion resistance of alumina coating have been improved. Moreover, the phosphate intermediate layer has been associated with a higher corrosion resistance, while the intermediate layer of Ni–P is more effective to improve the hardness and wear resistance of alumina coating.     

Impact of supporting electrolytes on the stability of TiO<Subscript>2</Subscript>–Ti counter electrode during H<Subscript>2</Subscript>O<Subscript>2</Subscript> electrogeneration

This work focuses on the role of common supporting electrolytes (SEs) in the electro-chemical inertness of Ti-based materials employed for the anodic (direct) oxidation coupled with H₂O₂ electro-generation at the graphite cathode for the concurrent decomposition of organic contaminants. SEs are added to boost up the ionic conductivity of solution but a question always remains on the effect of SEs on the stability of anode materials. The use of ClO ₄ ^? is encouraged in the electro-Fenton process as it does not form complexes with Fe²⁺/Fe³⁺; however, it is found that ClO ₄ ^? corroded the TiO₂ coated Ti (TiO₂–Ti) anode very fast (>60 min) and, Ti⁴⁺ ions formed a yellow color complex (λ_max = 380 nm) with H₂O₂. The influence of Cl^–, NO ₃ ^? and SO ₄ ^2? was insignificant on the stability of TiO₂–Ti. The cell current efficiency of H₂O₂ formation dropped sharply with in the case of TiO₂–Ti anode. The TiO₂–Ti corrosion also reduced the mass transfer co-efficient of DO transport from bulk to the cathode surface because of Ti⁴⁺ adsorption on graphite.     

Accelerated Hot Corrosion Studies of D-Gun-Sprayed Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>–50% Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating on Boiler Steel and Fe-Based Superalloy

In the current investigation, Cr₂O₃–50% Al₂O₃ coating was deposited on ASTM-SA213-T-22 boiler steel and Fe-based superalloy Superfer 800H by D-gun spray process. The high-temperature corrosion performance of the coated as well as bare alloys was evaluated in Na₂SO₄–60%V₂O₅ molten salt, an aggressive environment at 900 °C under cyclic conditions. The kinetics of the corrosion were analyzed by the change in weight measurements which were taken after each cycle (i.e., 1-h heating in a tube furnace followed by 20-min cooling in ambient air) for a total period of 50 cycles. The X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray analysis techniques were used for the analysis of corrosion products. During investigations, it was found that both the selected bare alloys have suffered intensive spallation in the form of removal of their oxide scales, which may be attributed to the formation of non-protective Fe₂O₃-dominated oxide scales, whereas the coated alloys have shown lesser weight gains along with better adhesiveness of the oxide scales with the substrate till the end of the experiment. The oxides of chromium and aluminum were the main phases revealed in the oxide scales of the coated specimens, which are reported to be protective against the hot corrosion.     

The Effect of Synthesis Conditions on the Phase Composition and Structure of EuBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> Samples

The composition and the structure of ceramic EuBa₂Cu₃O_{6 + δ} (Eu-123) oxide samples annealed in steps with varying processing conditions (in air or oxygen and argon atmosphere at a temperature of 940–960°С for 1–70 h with or without homogenization) were studied by the X-ray phase and chemical analysis, electron diffraction pattern analysis, elemental analysis, and high-resolution transmission electron microscopy. Regardless of the processing conditions, Eu-123 nanostructured oxide with a tetragonal or orthorhombic structure and domains 1–20 nm in size was obtained as a result of annealing. Nanostructuring of the samples, which was revealed by high-resolution electron microscopy, is attributed to their chemical nature: the presence of identical structural elements in members of the homologous Eu _n Ba _m Cu_{m + n}O _y series of oxides allows them to intergrow coherently and create an illusion of a single crystal. Just like any other member of the Eu _n Ba _m Cu_{m + n}O _y series, oxide Eu-123 is disproportionate depending on the annealing conditions to form other members of this series located on either side of the dominant oxide. Temperature T_c of the superconducting transition of each member of the series depends on the average oxidation state of copper \(\overline {Cu} \). At \(\overline {Cu} \) < 2, all members of the series have a tetragonal structure and do not exhibit superconducting properties. At \(\overline {Cu} \) = 2.28, five members of the Eu _n Ba _m Cu_{m + n}O _y series with matrices (Ba : Cu) 5 : 8, 3 : 5, 2 : 3, 5 : 7, and 3 : 4 exhibit superconducting properties with T_c = 82–90 K.