Magnetic properties of (Fe)1−x–(Al2O3)x and (Fe50Ni50)1−x–(Al2O3)x nanocomposite magnetic media synthesized using gel like Al2O3 matrix

Composites with ferromagnetic nanoparticles, Fe and Fe₅₀Ni₅₀, dispersed in Al₂O₃ have been synthesized by a solution phase technique. The structure and magnetic properties of these composites with varying fractions of Al₂O₃ have been investigated. Both Fe and Fe₅₀Ni₅₀ nanoparticles are amorphous in the as-prepared state and become crystalline on heat treating with near equilibrium lattice parameters of 0.287 nm and 0.358 nm respectively. The interparticle distance increases with increasing Al₂O₃ from 0 wt.% to 20 wt.%. The size of Fe nanoparticles is 40 nm while the Fe₅₀Ni₅₀ nanoparticles are 20 nm in size. The Fe and Fe₅₀Ni₅₀ nanoparticles dispersed composites are found to be ferromagnetic at room temperature both in the as-prepared and heat treated conditions with clear coercive fields of 5.5–35 × 10³ A m⁻¹. The saturation magnetization increases by orders of magnitude on heat treatment, for e.g. from <1.0 emu g⁻¹ to 143.4 emu g⁻¹ for Fe–15 wt.% Al₂O₃ and 95.6 emu g⁻¹ for Fe₅₀Ni₅₀–15 wt.% Al₂O₃. The Fe-composites exhibit a Curie transition at 1000 K while the Fe₅₀Ni₅₀ composites exhibit a transition at 880 K, both temperatures close to bulk values.     

Structure and electrochemical performance of FeF3/V2O5 composite cathode material for lithium-ion battery

Orthorhombic structure FeF₃ was synthesized by a liquid-phase method using FeCl₃, NaOH and HF solution as starting materials, and the FeF₃/V₂O₅ composites were prepared by milling the mixture of as-prepared FeF₃ and the conductive V₂O₅ powder. The properties of FeF₃/V₂O₅ composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge and cyclic voltammetry measurements. Results showed that the FeF₃/V₂O₅ composites can be used as cathode material for lithium-ion battery. Electrochemical measurements in a voltage range of 2.0–4.5 V reveal that the addition of conductive V₂O₅ improves significantly the electrochemical performance of FeF₃, and the FeF₃/V₂O₅ composite prepared by milling for 3 h exhibits high discharge capacity and good cycle performance, and its discharge capacity maintains about 209 mAh g⁻¹ at 0.1 C (23.7 mA g⁻¹) after 30 cycles.     

Crystal structure of Nax(MoO)5(P2O7)4 studied by synchrotron X-ray diffraction

The crystal structure of sodium pentamolybdyl tetradiphosphate Na_x(MoO)₅(P₂O₇)₄ has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) Å, γ = 90.641(9)° and a = 22.898(3), b = 23.056(2), c = 4.8551(2) Å, γ = 90.82(1)°, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90° rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo_1.3OP₂O₇ [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81–84]. Comparison of the two structures led us to conclude that the Mo₂ and Mo₃ clusters were erroneously identified in Mo_1.3OP₂O₇. A revised structure of Mo_1.3OP₂O₇ contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)₅(P₂O₇)₄. In both structures, the (MoO)₅(P₂O₇)₄ framework strongly resembles the one in the earlier reported Ag(MoO)₅(P₂O₇)₄, while the location of Na and Ag atoms differ.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1 − x) La_0.8Sr_0.2MnO₃/x YSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1 -x)La_0.8Sr_0.2MnO₃/x YSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm²) was the highest and that of the monolayer cathode (0.13 A/cm²) was the lowest. The polarization resistance (R_p) of the triple-layer graded composite cathode was only 0.182 ω·cm² and that of the monolayer composite cathode was 0.323 ω·cm². The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

Synthesis of Er2Ti2O7 nanocrystals and its electrochemical hydrogen storage behavior

Ultrafine Er₂Ti₂O₇ was synthesized at 700 °C within 2 h by a soft-chemistry route named citric acid sol–gel method (CAM). The obtained Er₂Ti₂O₇ with high dispersibility was square-like and the average size was about 70 nm. The prepared Er₂Ti₂O₇ nanocrystals in 6 M KOH aqueous solutions were investigated as a hydrogen storage material. It was found that the Er₂Ti₂O₇ powders would function as electrochemical hydrogen storage, showed fair electrochemical reversibility, and considerably high charge–discharge capacity. The reversible discharge capacity of the Er₂Ti₂O₇ electrode was found to exceed 320 mAh/g and adsorption capability of hydrogen is up to 1.27% at a current rate of 100 mA/g. In addition, the cycling ability and high rate capability of the Er₂Ti₂O₇ electrode are fairly good with only 4% capacity decay after 25 cycles. Cyclic voltammograms (CVs) were carried out to further examine the electrochemical hydrogen storage mechanism of Er₂Ti₂O₇.     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries

In this paper we report a novel Mn₃O₄ electrode doped with nano-NaBiO₃. It is demonstrated that doping with nano-NaBiO₃ alters the electrochemical inertia of Mn₃O₄, converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn₃O₄ electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn₃O₄ electrode doped with nano-NaBiO₃ can reach and become stable at 372 mAh g⁻¹ under 60 mA g⁻¹. The doped cathode can also maintain a cycling capacity of 261 mAh g⁻¹ while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g⁻¹. Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn₃O₄ cathode could possibly shorten to as little as 30 min.     

Synthesis of crystalline γ-Al2O3 with high purity

Crystalline γ-AlO(OH) was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And then γ-AlO(OH) was successfully transferred to γ-Al₂O₃ after subsequent high temperature heat treatment. The effects of reaction conditions on formation of γ-AlO(OH) and γ-Al₂O₃ were further investigated in detail. The XRD analysis shows that the complete formation of crystalline γ-Al₂O₃ is at pH 8–9, reaction temperature of 93–96 °C and calcination temperature of higher than 400 °C. The product of γ-Al₂O₃ contains impurity, including iron, calcium and silicon ion with a low content of about 0.01% and has large specific surface area and high pore volume of 269.9 m²/g and 0.57 mL/g, which can be applied in catalysts and catalyst supports.     

Synthesis, characterization and magnetic properties of complex oxides Ln2Mn2/3Re4/3O7 (Ln = Er, Y) and Y2Zn2/3Re4/3O7

Complex oxides Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) and Y₂Zn_2/3Re_4/3O₇ with a zirkelite structure and hexagonal unit cells (space group P3₁21, z = 6) have been obtained. Static and dynamic magnetic susceptibility measurements show that these oxides possess spin-glass behavior at low temperatures. Valence combinations of d-metals in the oxides are Mn²⁺(Zn²⁺)–Re⁵⁺. It is supposed that the examined specimens Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) contain the second magnetic phase of an unknown composition.     

Synthesis of K0.3WO3 tungsten bronze with gaseous permeation of K3PW12O40 by Sm and electrical properties of K0.3WO3 tungsten bronze

The permeation of the rare earth element Sm to the heteropoly compound K₃PW₁₂O₄₀ using the rare earth gas phase-heated diffused permeation method at 550 °C is reported for the first time. The studies of infrared spectroscopy (IR) and X-ray diffraction (XRD) indicate that the Keggin structure of the compound is destroyed. The bond of W–O–W is broken and tungsten bronze K_0.3WO₃ is produced after permeation. Inductively coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS) were used to determine the percentage composition of the Sm in a permeated sample. The result shows that there is Sm in a permeated sample and Sm interacts with the other component of the compound. Conductivity of compounds before and after permeation was investigated by four-electrode method. It reveals that the conductivity of the permeated sample is 4.18 × 10⁻⁴ S cm⁻¹, which is 1000 times higher than that of the original sample.     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

MoS2 coated with Al2O3 for Ni-MoS2/Al2O3 composite coatings by pulse electrodeposition

The MoS₂ powders were coated with Al₂O₃ (5 wt.%) through controlling hydrolysis of Al (NO₃)₃·9H₂O. MoS₂ powder coated with Al₂O₃ was written as MoS₂/Al₂O₃ hereinafter. MoS₂/Al₂O₃ powders were put into Ni plating electrolyte bath. Cetyltrimethylammonium bromide (CTAB) — the surfactant was also put into the bath. The experiment proves that MoS₂/Al₂O₃ particles were absorbed onto the Ni plate. The amount of MoS₂/Al₂O₃ deposited on Ni plate rises with the increasing concentration of MoS₂/Al₂O₃ in the bath. The microhardness, micro-surface, phase and the tribological property of the MoS₂/Al₂O₃ multi-plating coating were measured and analyzed. The performances of microhardness and wear resistance of the Ni-MoS₂/Al₂O₃ composite are better than those of Ni-MoS₂ composite.     

On the wide range of mechanical properties of ZTA and ATZ based dental ceramic composites by varying the Al2O3 and ZrO2 content

In this work the influence of pressureless sintering on the Vickers hardness and fracture toughness of ZrO₂ reinforced with Al₂O₃ particles (ATZ) and Al₂O₃ reinforced with ZrO₂ particles (ZTA) has been investigated. The ceramic composites were produced by means of uniaxial compacting at 50 MPa and the green compacts were heated to 1250 °C using a heating rate of 10 °C min⁻¹, then to 1500 °C at 6 °C min⁻¹ and maintained at this temperature during 2 h. After sintering, relative density over 94%, hardness values between 9.5 and 21.9 GPa, and fracture toughness as high as 3.6 MPa m^1/2 were obtained. The presence of TZ-3Y particles on the grain boundaries suggests that they inhibit notably the alumina grain growth. The grain sizes of pure Al₂O₃ and TZ-3Y as well as Al₂O₃ and TZ-3Y in the 20 wt% Al₂O₃+80 wt% TZ-3Y composite were 1.27 ± 0.51 μm, 0.57 ± 0.12 μm, 0.65 ± 0.19 μm and 0.41 ± 0.14 μm, respectively. The 20 wt% Al₂O₃ + 80 wt% ZrO₂ + 3 mol% Y₂O₃ (TZ-3Y) composite showed a hardness of 16.05 GPa and the maximum fracture toughness (7.44 MPa m^1/2) with an average grain size of 0.53 ± 0.17 μm. On the other side, the submicron grain size and residual porosity seem to be responsible for the high hardness and fracture toughness obtained. The reported values were higher than those obtained by other authors and are in concordance with international standards that could be suitable for dental applications.     

Residual stress measurement of an EB-PVD Y2O3-ZrO2 thermal barrier coating by micro-Raman spectroscopy

Residual stress distribution in an EB-PVD 4 mol% Y₂O₃-ZrO₂ thermal barrier coating (TBC) layer coated on a superalloy substrate has been measured by micro-Raman spectroscopy. Piezo-spectroscopic coefficient was independently calibrated on a freestanding TBC layer. The coefficient for uniaxial stress is Π_uni = 5.43 cm^− 1GPa^− 1. The stress measurement through the TBC thickness shows compressive stress distribution from small to an almost large constant value. Such a distribution agrees with theoretical consideration since the small stress correctly reflects the free edge effect and the large constant stress is closely related to TBC bulk stresses.     

Dielectric dispersion in Li2O–MoO3–B2O3 glass system doped with V2O5

Li₂O–MoO₃–B₂O₃ glasses containing different amounts of V₂O₅, ranging from 0 to 1.5 mol%, were prepared. The dielectric properties (viz., constant ′, loss tan δ, AC conductivity σ_ac over a wide range of frequency and temperature) have been studied as a function of the concentration of vanadium ions. The variation of AC conductivity with the concentration of V₂O₅ passes through a maximum at 0.8 mol% V₂O₅. In the high-temperature region, the AC conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The dielectric relaxation effects exhibited by these glasses have been analyzed quantitatively by pseudo Cole–Cole plot method and the spreading of relaxation times has been established. Further analysis of these results has been carried out with the aid of the data on ESR, IR and optical absorption spectra.     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Structural and electrochemical properties of LiV3O8 prepared by combustion synthesis

LiV₃O₈ powders were prepared by combustion synthesis, using metallic nitrates as the oxidant and metal sources and urea as fuel. The effect of (Li + V)/CO(NH₂)₂ ratio and heat-treatment temperature on the structure and electrochemical properties were discussed. The electrochemical behavior of the product showed that sample B₁ synthesized at 300 °C with 1:0.5 ratio of (Li + V)/CO(NH₂)₂ showed the highest initial discharge capacity of 317.3 mAh g⁻¹ and the best cycle ability with 238.9 mAh g⁻¹ after 30 cycles.     

Effect of (NaPO3)6 concentrations on corrosion resistance of plasma electrolytic oxidation coatings formed on AZ91D magnesium alloy

Different plasma electrolytic oxidation (PEO) coatings were prepared on AZ91D magnesium alloy in electrolytes containing various concentrations of (NaPO₃)₆. The morphologies, chemical compositions and corrosion resistance of the PEO coatings were characterized by environmental scanning electron microscopy (ESEM), X-ray diffractometer (XRD), energy dispersive analysis of X-rays (EDAX), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) test. The results showed that the PEO coatings were mainly composed of MgO, Mg₂SiO₄, MgAl₂O₄ and amorphous compounds. As the (NaPO₃)₆ concentrations increased from 0 to 10 g/l, the thickness and surface roughness of the coatings approximately linearly increased; the MgO and Mg₂SiO₄ phase increased within the concentration range of 0–3 and 0–5 g/l, and then decreased within the range of 3–10 and 5–10 g/l, respectively, while the MgAl₂O₄ phase gradually decreased. Moreover, the corrosion resistance of the coatings increased within the range of 0–5 g/l and then decreased within the range of 5–10 g/l. The best corrosion resistance coating was obtained in electrolyte containing 5 g/l (NaPO₃)₆, it had the most compact microstructure. Besides, a reasonable equivalent circuit was established, and the fitting results were consistent with the results of the EIS test.     

Preparation and photocatalytic activity of nano-sized nickel molybdate (NiMoO4) doped bismuth titanate (Bi2Ti4O11) (NMBT) composite

Various compositions of nano-sized (NiMoO₄)_x-doped Bi₂Ti₄O₁₁ (x = 0.01, 0.05, 0.1) composites have been prepared by chemical solution decomposition (CSD) method using triethanolamine (TEA) as complexing agent. Ni(II) is one of reactive species on the catalyst surface and Mo(VI) ion helps to compensate the charge of the lattice. The photocatalysts based on the above compositions have been tested for photobleaching of methyl orange (MO) solution under Hg-lamp. The prepared nanopowders are characterized by XRD, EDAX, UV–vis spectra, specific surface area (BET), zeta potential, ESR and HRTEM analyses. The average particle size of nickel molybdate-doped bismuth titanate lies around 30 ± 2 nm measured from TEM. Result shows nickel molybdate-doped bismuth titanate (NiMoO₄)_x(Bi₂Ti₄O₁₁)_1−x (NM_xBT_1−x; x = 0.01) composite is found to be more photoactive compared all the compositions studied except degussa P25 titania.