Ca- and Al-doped ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles as possible anode materials

Spinel ferrites are an amazing class of materials that can find application in different fields, from sensors and lithium-ion batteries to the intriguing biomedical field. For the use as anode in lithium-ion batteries, ZnFe₂O₄ is rather competitive due to low price, abundance, environmental benignity, working voltage of ~1.5 V, and, most importantly, a high theoretical specific capacity (~1072 mA h g^?1). For its practical application, however, some issues must be overcome, in particular its fast capacity fading and poor rate capability resulting from an inherent low electronic conductivity. Possible strategies are represented by ferrite carbon coating/embedding, peculiar synthesis routes, and doping. In this frame, we synthesized Ca- and Al-doped ZnFe₂O₄ nanoparticles by using microwave-assisted combustion synthesis, followed by a classical carbon coating (determined as about 5 wt% by thermogravimetry). A good solubility of Ca and Al up to 25 atom% on both Zn and Fe sites was obtained. Cyclic voltammetries evidenced redox reactions involving Zn and Fe ions, but also the Al intervention could be supposed. Galvanostatic charge–discharge cycles proved that particularly Al ions were useful to improve the anode structural stability at high C rate (up to 3C), thanks to the stronger Al–O bonds with respect to Fe–O ones. A further improvement of capacities comes from the use of sodium alginate as binder to substitute polyvinylidene fluoride in the anode preparation.     

Nano-Architecture of Facetted NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/(Ni,Fe)O Particles Produced by Induction Plasma

Facetted nickel ferrite (NiFe₂O₄) and bunsenite [(Ni,Fe)O] nanocrystals were grown from the decomposition of iron and nickel nitrate precursors using an inductively coupled plasma reactor. The full range of the two-phase region of the Fe₂O₃–NiO pseudo-equilibrium phase diagram was investigated by producing nanopowders with bulk Ni/(Ni + Fe) ratios of 0.33, 0.4, 0.5, 0.75 and 1.0. A Ni-poor [Ni/(Ni + Fe) ≤ 0.5] precursor solution produced truncated octahedron nanocrystals, whereas nanocubes were obtained at higher ratios [Ni/(Ni + Fe) ≈ 1]. In both cases, it is shown that the nanocrystals adopt a morphology close to the Wulff shape of the crystalline system (spinel and NaCl, respectively). As the bulk Ni/(Ni + Fe) ratio increases from 0.33 (the stoechiometric composition of nickel ferrite), bunsenite is epitaxially segregated on the {110} and {111} facets of nickel ferrite, while leaving the NiFe₂O₄ {100} facets exposed. A precursor solution at a Ni/(Ni + Fe) ratio of 0.75 gave an (Ni,Fe)O-rich nanopowder with a random and irregular interconnected morphology. The structure of these nanocrystals can be understood in terms of their thermal history in the plasma reactor. These results highlights the possibility of producing organized multi-phased nanomaterials of binary systems having two phases stable at high temperatures, using a method known to be easily scalable.     

Synthesis of MgFe<Subscript>1.6</Subscript>Ga<Subscript>0.4</Subscript>O<Subscript>4</Subscript> by Gel Combustion Using Glycine and Hexamethylenetetramine

A powderlike material of composition MgFe_1.6Ga_0.4O₄ was synthesized by gel combustion using a glycine–hexamethylenetetramine mixture. The gel produced by the synthesis was studied by thermal analysis (TGA/DSC) and IR spectroscopy. This mixture was shown to be efficient for obtaining homogeneous nanosized MgFe_1.6Ga_0.4O₄. The morphology of the powders was characterized by scanning electron microscopy and X-ray powder diffraction analysis.     

Effect of CuO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on low temperature sintered MnZn-ferrite by sol–gel auto-combustion method

A sol–gel auto-combustion method was investigated to incorporate small amounts of additives of Cu and Bi uniformly into soft magnetic MnZn-ferrite nanoparticles, which were prepared by Fe(NO₃)₃·9H₂O, Mn(NO₃)₂ and Zn(NO₃)₂·6H₂O dissolved in water and citric acid. The powder was characterized by the X-ray diffraction analysis and transmission electron microscope method. The effects of nano-particle sized powders in microstructure development and adding CuO–Bi₂O₃ into MnZn-ferrite on phase formation, densification process as well as magnetic properties were studied by scanning electron microscope and vibrating sample magnetometer techniques. The sample without additive can be sintered well at 930 °C, while the samples with a small amount of the additive can be sintered at less than 900 °C. Obviously, the micron-sized powders exhibited high sintering activity. It was also found that CuO–Bi₂O₃ additive promoted the growth of grains and improved magnetic properties. The permeability and the saturation magnetization were improved substantially by adding CuO–Bi₂O₃ into MnZn-ferrite and the sintering temperature was lowered to 875 °C, which may be associated with the redistribution of cations on the tetrahedral (A) sites and octahedral (B) sites within the spinel lattice.     

Conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-NiO composites

The conductivity and transport number of oxygen ions of Bi₂O₃-(10, 30, 50) vol % NiO composites are measured using the four-probe and coulomb-volumetric methods at various temperatures. It is shown that the Bi₂O₃-50 vol % NiO composite exhibits a high mixed ionic-electronic conductivity in the temperature range from 730 to 800°C.     

Preparation of CuCr<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders using two different chromium sources

CuCr₂O₄ spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr₂O₃) and (ii) ammonium dichromate ((NH₄)₂Cr₂O₇). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO₃)₂·3H₂O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr₂O₃, Cu(NO₃)₂·3H₂O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr₂O₃). In the second case (ii), (NH₄)₂Cr₂O₇, Cu(NO₃)₂·3H₂O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH₄)₂Cr₂O₇ took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr₂O_3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr₂O₄) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr₂O₄ was highlighted by XRD and FTIR analyses.     

Sol–gel process of ZnO and ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> coated aluminum borate whiskers

Zinc nitrate and citric acid were used to prepare ZnO sol. ZnO and ZnAl₂O₄ coated aluminum borate whiskers were separately prepared by a sol–gel process. The results show that ZnO forms when ZnO xerogel is calcined at 500 °C and it does not undergo any phase transformation in the range of 500 and 1000 °C during calcinations. In ZnO xerogel coated aluminum borate whiskers system, a large amount of heat, gas and pores are produced during the heating process. When ZnO xerogel coated aluminum borate whiskers are calcined at 500 °C, ZnO can be uniformly coated on the surface of the whikers and the coated whiskers can be easily dispersed in distilled water through an ultrasonic vibration apparatus. During the calcination of ZnO coated whiskers at 1000 °C, ZnO reacts with the whiskers and ZnAl₂O₄ forms on the surface of aluminum borate whiskers.     

Kinetics of Li-ion transfer reaction at LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>, LiCoO<Subscript>2</Subscript>, and LiFePO<Subscript>4</Subscript> cathodes

Kinetics of LiFePO₄, LiMn₂O₄, and LiCoO₂ cathodes operating in 1 M LIPF₆ solution in a mixture of ethylene carbonate and dimethyl carbonate was deduced from impedance spectra taken at different temperatures. The most striking difference of electrochemical impedance spectroscopy (EIS) curves is the impedance magnitude: tens of ohms in the case of LiFePO₄, hundreds of ohms for LiMn₂O₄, and thousands of ohms for LiCoO₂. Charge transfer resistances (R _ct) for lithiation/delitiation processes estimated from the deconvolution procedure were 6.0 Ω (LiFePO₄), 55.4 Ω (LiCoO₂), and 88.5 Ω (LiMn₂O₄), respectively. Exchange current density for all the three tested cathodes was found to be comparable (0.55–1·10^?2 mAcm^?2, T = 298 K). Corresponding activation energies for the charge transfer process, \( {E}_{ct}^{\#} \), differed considerably: 66.3, 48.9, and 17.0 kJmol^?1 for LiMn₂O₄, LiCoO₂, and LiFePO₄, respectively. Consequently, temperature variation may have a substantial influence on exchange current densities (j _o) in the case of LiMn₂O₄ and LiCoO₂ cathodes.     

Molten salt synthesis and characterization of fast ion conductor Li<Subscript>6.75</Subscript>La<Subscript>3</Subscript>Zr<Subscript>1.75</Subscript>Ta<Subscript>0.25</Subscript>O<Subscript>12</Subscript>

The limited electrochemical stability and the flammability of the liquid electrolytes presently used in Li-ion batteries stimulates the search for alternatives including ceramic solid electrolytes. Moreover, solid electrolytes also fulfil crucial functions in various large-scale energy storage systems, e.g. as anode-protecting membranes in aqueous Li-air batteries. Here, the processing of the solid electrolytes Li₇La₃Zr₂O₁₂ is studied for applications in Li-air batteries. Molten salt method (MSM) was adopted previously on synthesis of simple oxides; to the best of our knowledge, we report for the first time the adaptation of the MSM to prepare this class of solid electrolytes. As a model compound, we prepared the garnet-related Li_6.75La₃Zr_1.75Ta_0.25O₁₂. It has been prepared by using stoichiometric amounts of La₂O₃, ZrCl₄, and Ta₂O₅ in excess 0.88 M LiNO₃:0.12 M LiCl molten salt. Subsequently, samples were heated to various temperatures in the range 600–900 °C for 6 h in air in a recrystallized alumina crucible and finally washed with distilled water to remove excess salts. The obtained Li_6.75La₃Zr_1.75Ta_0.25O₁₂ electrolyte powder was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman, and impedance spectroscopy as well as surface area measurements. The cubic single phase was obtained for samples prepared at temperatures ≥700 °C. The effects of washing with water or aqueous LiOH solution on the structure and conductivity of the phases will be discussed.     

Thermal analysis on C<Subscript>6</Subscript>H<Subscript>10</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>-doped MgB<Subscript>2</Subscript>

Additives to MgB₂ can improve the superconducting functional characteristics, such as critical current density (J _c) and irreversibility field (H _irr). Recently, we have shown that repagermanium (C₆H₁₀Ge₂O₇) is an effective additive, enhancing both J _c and H _irr. To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s^?1, in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric—differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB₂ and 3 mol% C₆H₁₀Ge₂O₇. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB₂ is not observed. Above this temperature, partial decomposition of MgB₂ occurs. Crystalline Ge and MgO are detected before formation of Mg₂Ge and MgB₄, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB₂ is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.     

BaTi<Subscript>1–x</Subscript>Zr<Subscript>x</Subscript>O<Subscript>3</Subscript> nanopowders prepared by the modified Pechini method

The results reported here based on a study of BaTi_1–xZr_xO₃ (x=0, 0.2 and 1) nanometric powders prepared by the modified Pechini method. The powder samples annealed from 600 to 1000°C/2 h were characterized by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The decomposition reactions of resins were studied using thermal analysis measurements. The barium titanate zirconate system presented just one orthorhombic phase. Furthermore, this study produced BaTiO₃ powders with a tetragonal structure using shorter heat treatments and less expensive precursor materials than those required by the traditional methods.     

Coordination mechanism,characterization, and photoluminescence properties of spinel ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles prepared by a modified polyacrylamide gel route

Single-phase ZnAl₂O₄ nanoparticles with the spinel structure were successfully synthesized using a modified polyacrylamide gel method according to the atomic ratio of Zn to Al = 1: 1.8. The as-prepared samples were characterized by means of X-ray powder diffraction (XRD), thermogravimetric analysis (TG), differential scanning calorimetry analysis (DSC), field-emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) spectra. XRD patterns show that the pure phase of ZnAl₂O₄ is obtained after heating the xerogel at 900°C for 5 h in air. The SEM images reveal that the ZnAl₂O₄ nanoparticles have a narrow particle size distribution and the average particle size is around 45 nm. Photoluminescence (PL) spectra demonstrate the single phase ZnAl₂O₄ nanoparticles have an emission peak located at 469 nm when excited by 350 nm light. The phase structure, coordination mechanism, and luminescence properties have been discussed on the basis of the experimental results.     

Effect of nitrile butadiene rubber/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/YSZ fillers for PMMA denture base on the thermal and mechanical properties

This study is to investigate the effect of nitrile butadiene rubber (NBR as impact modifier) together with Al₂O₃/YSZ (toughening) as filler loading in PMMA denture base on the thermal and mechanical properties. PMMA matrix without fillers was mixed between PMMA powder and 0.5 mass% of BPO, and it is used as the control group. The liquid components consist of 90% of methyl methacrylate (MMA) and 10% as the cross-linking agent of ethylene glycol dimethacrylate. The denture base composites were fabricated by incorporating PMMA powder and BPO and fixed at 7.5 mass% NBR particles and filler loading (1, 3, 5, 7 and 10 mass%) of Al₂O₃/YSZ mixture filler by (1:1 ratio) as the powder components. The ceramic fillers were treated with silane (γ-MPS) and the powder/liquid ratio (P/L) according to dental laboratory practice. The TGA data obtained show that the PMMA composites have better thermal stability compared to unreinforced PMMA, while DSC curves show slightly similar Tg values. DSC results also indicated the presence of unreacted monomer content for both reinforced and unreinforced PMMA composites. The fracture toughness, Vickers hardness and flexural modulus values were statistically increased compared to the unreinforced PMMA matrix (P?<?0.05).     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Ni functionally graded materials (FGM) obtained by centrifugal-slip casting method

The paper deals with the study of latent heats of melting of three real steels (one low-alloyed steel and two chromium steels) and temperatures of liquidus, peritectic transformation and solidus of these steels. All quantities were obtained using the differential scanning calorimetry method (DSC). The Setaram MHTC (multi-high-temperature calorimeter) Line 96 device equipped with 3D DSC sensor was used for all experiments. Measurements were done in alumina crucibles under inert atmosphere of pure argon. Controlled heating and cooling of steel samples was conducted at the rate of 5 K min^?1. All investigated quantities were also calculated using the Thermo-Calc software package with the use of the Thermo-Calc Fe-based alloys (TCFE) database. Comparison and discussion of experimental and calculated data was performed, and very good agreement was observed. The largest difference between measured and calculated values was 18 J g^?1 for latent heat of melting and up to 2 °C for all investigated temperatures of phase transformation, except for one temperature of peritectic transformation.     

Synthesis and characterization of Eu<Superscript>3+</Superscript> doped Lu<Subscript>2</Subscript>O<Subscript>3</Subscript> nanophosphor using a solution-combustion method

Fine Eu³⁺-doped lutetium oxide (Lu₂O₃:Eu³⁺) nanophosphor were synthesized using a low-temperature solution-combustion method in a methyl-alcohol solution. The characteristics of the nanophosphors synthesized at various sintering temperatures with different Eu³⁺ concentrations were analyzed to determine the optimum synthesis conditions. Thermogravimetry/differential thermal analysis showed that Lu₂O₃:Eu³⁺ crystallizes completely when the dry powder is sintered at 500 °C. The Lu₂O₃:Eu³⁺ crystals had a cubic structure and monoclinic phase. The peak position of the luminescence spectrum did not differ with the concentration of Eu or the sintering temperature or atmosphere, whereas the luminescence intensity was strongly dependent on the concentration and sintering conditions.     

High-temperature X-ray study of the formation and delamination of manganese-alumina spinel Mn<Subscript>1.5</Subscript>Al<Subscript>1.5</Subscript>O<Subscript>4</Subscript>

The behavior of the manganese-alumina system with Mn:Al = 1:1 on heating in air and vacuum was studied. The starting samples were mixtures of β-Mn₃O₄, α-Mn₂O₃, and γ-Al₂O₃. On heating to 950°C in air, the samples were partially oxidized into α-Mn₂O₃, and corundum α-Al₂O₃ formed along with mixed manganese-alumina cubic spinel, whose composition was close to Mn₂AlO₄. In vacuum at 1200°C, the starting sample with a ratio of Mn:Al = 1:1 transformed into the manganese-alumina spinel Mn_1.5Al_1.5O₄, which retained its cubic structure after slow cooling in vacuum. When cooled in air, this solid solution delaminated, and a nanocrystalline Mn_2.8Al_0.2O₄ phase formed, whose structure was β-Mn₃O₄ type tetragonal spinel.     

Heat capacity measurements on BaTa<Subscript>2</Subscript>O<Subscript>6</Subscript> and derivation of its thermodynamic functions

Heat capacity measurements of barium tantalate (BaTa₂O₆) were carried out by using a differential scanning calorimeter at temperatures between 323 and 1323 K. From the heat capacity values of BaTa₂O₆, other thermodynamic functions (enthalpy and entropy increments) were derived between 298.15 and 1323 K. The C _p,m (298.15) value of BaTa₂O₆ was computed as 184.857 J mol^?1 K^?1. Moreover, fitted heat capacities exhibited good agreement with Neumann–Kopp rule at the temperatures between 298.15 and 1300 K.     

Phase equilibria in the Ce<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Ce₂O₃-K₂O-P₂O₅ ternary system has been investigated by thermoanalytical methods (DTA, DSC), powder X-ray diffraction, XPS and IR spectroscopy. The existence of three double potassium-cerium(III) phosphates has been confirmed and a new binary phosphate K₄Ce₂P₄O₁₅ has been found. Phase diagram and isothermal section at room temperature of the system Ce₂O₃-K₂O-P₂O₅ have been presented.     

Synthesis of Mg(Fe<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> by Gel Combustion Using Glycine and Starch

A powdery material Mg(Fe_0.8Ga_0.2)₂O₄ has been prepared by combusting a gel containing magnesium(II), iron(III), and gallium(III) nitrates and a glycine–starch mixture. The gel produced during the synthesis has been studied by thermal analysis (TGA/DSC) and IR spectroscopy. This mixture has been shown to be efficient to produce a homogeneous nanosized powderlike material Mg(Fe_0.8Ga_0.2)₂O₄. The morphology and properties of ceramic samples are characterized by scanning electron microscopy, X-ray powder diffraction, neutron diffraction, and vibrational magnetometry.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)