Synthesis and Characterization of SmxGdyCe1-x-yO2-δ Nanopowders

SmxGdyCe1-x-yO2-δ (x+y=0.2 and x=0, 0.04, 0.08, 0.12, 0.16, 0.2) nanopowders were prepared by a coprecipitation method. The zeta potential and sedimentation volume of Ce(OH)4 aqueous dispersions at different pH values were measured. The isoelectric point (IEP) of Ce(OH)4 suspensions is 7.0. The maximum potential value of -18.5 mV and maximum sedimentation volume of 19 ml are reached at pH=10. The evolution behaviors of the xSm(OH)3•yGd(OH)3•(1-x-y)Ce(OH)4 dried powders in the heating process was characterized by DTA/TG and XRD. The powders decompose to ceria based solid solution at a temperature below 300℃ and forms cubic fluorite structure ceria at about 650℃. The properties of SmxGdyCe1-x-yO2-δ solid solutions were characterized by XRD, TEM and BET. The lattice parameter of doped CeO2 increases linearly with increasing Sm3+ substitution (or decreasing Gd3+ substitution). The particle size of the doped ceria powders is from 5 nm to 10 nm     

Co-doping Effect on Microstructures and Ionic Conductivity of Aliovalent Cations Modified Ceria

Microstructural features and ionic conductivity of divalent （ Mg2 ＋ ） and trivalent （ Gd^3＋ ） cations co-doped ceria electrolyte system Ce0.8sGd0.2MgxO1. 9-s were investigated by scanning electron microscopy （SEM） and AC impedance analysis. The experimental results exhibit that addition of MgO to GDC reduces the average binding energy of GDC by decreasing the energy barrier of oxygen ion migration in ceria matrix and the ionic conductivity of 2 mol% magnesium doped GDC （0.018 S/cm） is higher than that of GDC matrix at 650℃ （0.0105 S/cm）. Co-doping Mg^2＋ and Gd^3＋ is found to increase the ionic conductivity of ceria and hence decreases the operation temperature as well as the cost of solid oxide fuel cell （SOFC）.     

Study on the Properties of Nanometer CeO2 Doped with Zr4+, La3+, Pr3+

Different nanometer CeO_2-ZrO_2 mixed oxides doped with lanthanum or praseodymium were prepared by coprecipi-tation. The characteristics of all mixed oxides were tested by XRD, SEM, TEM, and XPS. XRD results showed thatall oxides were formed solid solution with CaF_2 structure at low temperature and had good thermal stability. MoreCe~(4+) ions were rich on the surface by XPS, which were beneficial to oxygen storage. The particle mediun sizes (d_(50))of all oxides powders were approximately 10～20 nm by small angle scattering goniometer. When doped Zr~(4+) inCeO_2, the specific surface areas were improved at low or high temperature. The area of Ce_(0.6)Zr_(0.3)La_(0.04)Pr_(0.06)O_2powder had excess 110 m~2/g after calcining at 923 K for 4 h, even calcined at 1273 K for 4 h, the area was up to65 m~2/g.     

Characterization of Gradual Porous Ceramic Structures Obtained by Powder Sedimentation

Asymmetric membranes present better separation and service characteristics than the symmetric ones. In our preliminary studies the possibility of obtaining sintered porous materials with gradual structure by sedimentation of metallic and ceramic powders was demonstrated. Zirconium silicate (ZrSiO4) particles were used for the manufacturing of the porous supports, and mullite powder was deposited by sedimentation in order to achieve the active layer with pores size gradient. The used powders and the obtained structures were characterized by laser scattering particle size analyzer, scanning electron microscopy and mercury porosimetry. The permeability and the filtration fineness of the structures were also determined. By using a thin active layer made of small particles deposited onto a macro-porous support, one can achieve membranes with high flow rates and filtration fineness in the microfiltration area.     

Preparation and Characterisation of Sr2CeO_4:Eu~(3+) Rare Earth Luminescent Material by High Temperature Mechano-Chemical Method

A novel, high-temperature, mechano-chemical(HTMC) method was developed to synthesise singlephase Sr_2CeO_4:Eu~(3+)phosphor. Phosphors were characterised by X-ray diffraction(XRD), scanning electron microscopy(SEM), and luminescence spectra. Compared with phosphors prepared by the traditional hightemperature solid state method and citric acid gel method, single-phase Sr_2CeO_4:Eu~(3+)powders by using the HTMC method, with small average particle sizes of about 5 μm, a narrow size distribution range and uniform dispersion, were prepared at 800 ℃, and reached their maximum luminescent intensity at 900 ℃.Under ultraviolet excitation at 298 nm, the sample showed good luminescence with the strongest red light of 616 nm. However, Sr_2CeO_4:Eu~(3+)was prepared at the higher temperature of 1100 ℃ by solid state method and citric acid gel method. The particle size was too large and uneven with phosphor agglomeration by high-temperature solid state method. The luminescent intensity reached a maximum for Sr_2CeO_4:Eu~(3+)phosphor at a synthesis temperature of 1100 ℃ by using the high-temperature solid state method, and at 1200 ℃ by both citric acid gel and chemical precipitation methods. Furthermore, the advantages of the Sr_2CeO_4:Eu~(3+)powder prepared by HTMC method were discussed compared with that prepared using traditional high-temperature solid state and citric acid gel methods.     

Preparation of Nano-structured LiFe_xMn_(1-x)PO_4(x=0,0.2,0.4) by Reflux Method and Research on the Influences of Fe(Ⅱ) Substitution

Nano structured LiFexMn1-xPO4(x=0,0.2,0.4) materials were successfully prepared by one-step reflux method in a water/PEG400 mixed solvent, and were coated by carbon using glucose as the precursor. The materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The electrochemical properties of the materials were investigated by galvanostatic cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the materials consisted of nanorods with a diameter of 50 nm and a length of 500 nm. Galvanostatic cycling showed that the capacity of LiMnPO 4 could be largely increased by Fe2+ substitution. At a current rate of C/20, the capacity of the three samples (x=0,0.2,0.4) were 47, 107 and 150 mA·h·g-1 , respectively. CV result showed that the Fe2+ substitution could decrease the polarization during charging/discharging, accelerating the electrochemical process. EIS result showed that the Fe2+ substitution could decrease the charge transfer resistance between the electrode and electrolyte,     

A Method to Adjust Dielectric Property of SiC Powder in the GHz Range

The SiC powders by Al or N doping have been synthesized by combustion synthesis, using Al powder and NH4Cl powder as the dopants and polytetra?uoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SiC and the Al and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2-12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure Al or N doping and decrease by the Al and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.     

Sintering of Doped, Nanocrystalline CeO_2 Powders Prepared under Hydrothermal Conditions

Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change slightly with the dopant concentrations. The the of the dopants on the sintering of the compacted powders was investigated during heating at a constant rate of 10℃/min. The elemental composition and the concentration of the dopant has significant efFect on the densification and grain growth. Compared to undoped CeO2, the dopants produce a shift in the densification curve to higher temperatures. For the same dopant concentration and under identical sintering conditions, the Ca doped samples reach nearly full density with the smallest grain size (≈50 nm), however, the Mg doped sample has the lowest density (≈95% of the theoretical) with the largest grain size (≈1 μm)     

Fullerenol-containing Materials Derived by Sol-gel Processing

Water soluble fullerenols were synthesized and incorporated in SiO2, SiO2-TiO2, GPTMS-SiO2, GPTMS-ATPS inorganic and organic-inorganic materials by sol-gel processes. The maximum concentrations of C60(OH)n and C70(OH)n in the obtained SiO2 gels were estimated to be about 0.6% and 1.5% in weight, respectively. The characteristics of the UV/visible spectra of fullerenols in H2O and various gels were measured and compared. The thermal stability of fullerenols in gels was investigated with differential thermal analysis (DTA). The results indicate that the absorption features of fullerenols in solid gels are similar to those in H2O and the fullerenols in SiO2 are stable at 400℃. The optical limiting effect of the fullerenols was investigated preliminarily.     

Cobalt-free Composite Ba_(0.5)Sr_(0.5)Fe_(0.9)Ni_(0.1)O_(3-δ)-Ce_(0.8)Sm_(0.2)O_(2-δ) as Cathode for Intermediate-Temperature Solid Oxide Fuel Cell

New cobalt-free composites consisting of Ba0.5Sr0.5Fe0.9Ni0.1O3-δ(BSFN) and Ce0.8Sm0.2O2-δ(SDC) were investigated as possible cathode materials for intermediate-temperature solid oxide fuel cell (IT-SOFC). BSFN, which was synthesized by auto ignition process, was chemically compatible with SDC up to 1100℃ as indicated by X-ray diffraction analysis. The electrical conductivity of BSFN reached the maximum value of 57 S·cm-1 at 450℃. The thermal expansion coefficient (TEC) value of BSFN was 30.9×10-6K-1 , much higher than that of typical electrolytes. The electrochemical behavior of the composites was analyzed via electrochemical impedance spectroscopy with symmetrical cells BSFN-SDC/SDC/BSFN-SDC. The area specific interfacial polarization resistance (ASR) decreased with increasing SDC content of the composite. The area specific interfacial polarization resistance (ASR) at 700℃ is only 0.49, 0.34 and 0.31 Ω·cm2 when 30, 40, and 50 wt% SDC was cooperated to BSFN, respectively. These results suggest that BSFN-SDC is a possible candidate for IT-SOFC cathode.     

Effect of Sm+ Rare Earth Ion on the Structural,Thermal,Mechanical and Optical Properties of Potassium Hydrogen Phthalate Single Crystals简

Rare earth Sm~+ ion doped potassium hydrogen phthalate(KHP) single crystal was grown by slow evaporation technique.Single crystal and powder X-ray diffraction analyses confirm the crystalline perfection of Sm~+ ion doped KHP crystal.The functional groups of pure and Sm~+ ion doped KHP crystals were identified by Fourier transform infrared spectroscopy(FTIR) spectral studies.Thermogravimetric and differential thermal analyses were carried out to study the thermal behavior of the grown crystals.UV—Vis studies explored the optical transmittance of the grown crystals in the entire visible region.The mechanical strength and etching studies were performed to assess the perfection of the pure and Sm~+ ion doped KHP crystals.The refractive index and birefringence properties of the grown crystal were analyzed.The second harmonic generation efficiency of Sm~+ ion doped KHP crystals was observed by Kurtz—Perry powder test.     

Thermomechanical Analysis of (Cu0.5Tl0.5)-1223 Substituted by Pr and La

The thermomechanical analysis (TMA) of Cu 0.5 Tl 0.5 Ba 2 Ca 2 x R x Cu 3 O 10 δ,where R=Pr and La,with 0.0≤x≤0.15,was carried out in temperature range from 450 to 1145 K.The samples were prepared by singlestep solid state reaction technique.The prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The superconductivity of the prepared samples was investigated by electrical resistivity measurement.The results showed that low substitution content enhanced the (Cu 0.5 Tl 0.5)1223 phase formation,while the higher substitution content degraded this phase.The higher superconducting transition temperatures T c were found to be 114 K and 109 K at x= 0.025 for Pr-and La-substitutions,respectively.The average linear thermal expansion coefficient increased as x increased,while the shrinkage temperature decreased as x increased.Those results were emphasized by porosity and Vickers microhardness calculations.Debye temperature θ D was calculated from the linear thermal expansion coefficient data and correlated to T c to estimate the electron-phonon coupling λ ep.     

Preparation of Core-Shell Structured Cobalt Coated Tungsten Carbide Composite Powders by Intermittent Electrodeposition

Core-shell structured cobalt coated tungsten carbide(WC/Co) composite powders were prepared by intermittent electrodeposition. The influence of process parameters such as current density, single deposition pulse, p H value and surfactants on the formation of WC/Co was investigated and characterized by scanning electron microscopy(SEM), electrochemical station, acidometer and X-ray diffraction(XRD) techniques.The composite powders with 54% cobalt content were fabricated at a current density of 16 A dm-2, with a load of 10 g dm-3WC powders and a stirring speed of 600 r min-1at an operation temperature of 40 ± 2 °C,and 90% current efficiency was obtained with a single deposition pulse of 1.5 min and single stirring pulse of 2 min during 12 min efficient electrodeposition time. The uniformly distributed WC/Co powders could be obtained in the cobalt electrolyte containing 300 mg dm-3PEG-2000. The spherical cobalt grains coated WC particles were prepared in the p H 4-5 electrolyte at the Co deposition rate of 0.58 g min-1. A practical process for high efficient production of WC/Co powders by electrodeposition was developed in the present work.     

Synthesis and Characterization of Tb-incorporated Apatite Nano-scale Powders

Nano-scale Tb-incorporated apatite (nano-Tb-AP) particles with different Tb contents (Tb/(Tb+Ca)) of 0%, 5%, 10% and 20% were synthesized through a simple wet chemical method in this study. The crystal structure, thermal stabilities, chemical groups, crystal morphologies and crystal sizes of the nano-Tb-AP particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM), respectively. It was found that lattice constants, particle sizes, crystalline and thermal stability varied with the doped Tb contents. With the increasing of Tb content, the lattice constants, particle size, length/diameter ratio, crystalline and thermal stability of nano-Tb-AP gradually decrease. Especially, almost all the 20%Tb-AP nano particles had been decomposed at 1200 C while only a few of the decomposed products (β-TCP) were detected in the Tb-free nano apatite powders. This kind of nano-scale Tb-incorporated apatite exhibits an extremely potential clinic application because it integrates both the excellent biological functions of Tb element and apatite in human body.     

Plasma Enhanced Chemical Vapor Deposition Nanocrystalline Tungsten Carbide Thin Film and Its Electro-catalytic Activity

Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition (PECVD) at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS), respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V (vs SCE).     

Acetone Sensors Based on La3+ Doped ZnO Nano-rods Prepared by Solvothermal Method

La3+ doped ZnO nano-rods with different doping concentration were prepared via solvothermal method.The doped ZnO nano-rods were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM),respectively.The effect of La3+ doping on the gas-sensing properties was investigated.The results revealed that the sensor based on 6 mol% La3+ doped ZnO nano-rods exhibited high response to dilute acetone,and the responses to 0.01×10-6 acetone reached 2.4 when operating at 425 ℃.The response time and the recovery time for 0.01×10-6 acetone were only 16 and 3 s,respectively.     

Influence of Lithium Oxide Addition on the Sintering Behavior and Electrical Conductivity of Gadolinia Doped Ceria

Ceria-based electrolytes have been widely researched in intermediate-temperature solid oxide fuel cell (SOFC), which might be operated at 500-600?C. Sintering behavior with lithium oxide as sintering additive and electrical conductivity of gadolinia doped ceria (Gd0.1Ce0.9O2δ, GDC10) electrolyte was studied in this paper by X-ray di?raction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). As the results, the fully dense GDC10 electrolytes are obtained at a low temperature of 800?C with 2.5 mol% Li2O as sintering additive (called 5LiGDC800). During sintering process, lithium oxides adsorbed by around GDC10 surface help to sinter at 800?C and are kept at the grain boundary of GDC10 in the end. The fine grains of 100-400 nm and high electrical conductivity of 0.014 S/cm at 6000C in 5LiGDC800 were achieved, which contributed to the lower sintering temperature and enhanced grain boundary conductivity, respectively. Lithium, staying at grain boundary, reduces the depletion of oxygen vacancies in the space charge layers and increases the oxygen vacancy concentration in the grain boundary, which leads to improve the total electrical conductivity of 5LiGDC800.     

Effect of Sintering Temperature on the Texturing Behavior of NaCo_2O_(4-δ) Synthesized by Urea Auto-Combustion Method

Polycrystalline NaCo2O4-δ materials were prepared using the urea auto-combustion method. The reaction process and crystal growth were investigated through X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), and Fourier transform infrared spectrometry (FTIR). The results indicate that the formation temperature of NaCo2O4-δ is about 620°C, which is lower than that for solid-state reaction. XRD results show that the texturing along c-axis occurred as the powders calcined at 700°C ...     

Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

The MoNbTaTiV refractory high-entropy alloy(RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying(MA) and spark plasma sintering(SPS).The microstructural evolutions,mechanical properties and strengthening mechanisms of the alloys were systematically investigated.The nanocrystalline mechanically alloyed powders with simple bodycentered cubic(BCC) phase were obtained after 40 h MA process.Afterward,the powders were sintered using SPS in the temperature range from 1500 ℃ to 1700 ℃.The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic(FCC) precipitation phases.The bulk alloy sintered at 1600℃ had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm,exhibiting outstanding micro-hardness of 542 HV,compressive yield strength of 2208 MPa,fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature.The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening.It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.     

La Doping Effect on the Dielectric Property of Barium Strontium Titanate Glass – Ceramics

Ferroelectric barium strontium titanate(BST) glasse ceramics doped with different content of La2O3 were prepared via the melt-quenching technique followed by controlled crystallization. The microstructures of crystallized samples were examined by X-ray diffraction and scanning electron microscopy. Dielectric properties were also investigated. The aliovalent substitution of Ba by La induced dispersion of semiconducting BaxSr1-x TiO3 crystallites sealed in a glassy silicate matrix, which increased the εr and loss tangent values of the BST glasse ceramic. The experimental results indicate that aliovalent substitution is an effective method to process glasse ceramics with better dielectric properties.