Preparation and performance of Pr-doped Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) cathode for IT-SOFCs

(Ba0.5Sr0.5)1-xPrxCo0.8Fe0.2O3-δ(BSPCFx;x=0.00-0.30) oxides were synthesized by a sol-gel thermolysis process using combination of PVA and urea,and were also investigated as cathode material for intermediate temperature solid oxide fuel cells(IT-SOFCs).X-ray diffraction(XRD) results showed that all the samples formed a single phase cubic pervoskite-type structure after being calcined at 950 oC for 5 h and the lattice constant decreased with the Pr content increasing.The electrical conductivity of Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) was greatly enhanced by Pr-doping.The thermal expansion coefficient(TEC) of BSPCFx was increased with the content of Pr increasing,and all the thermal expansion curves had an inflection at about 250-400 oC due to the thermal-induced lattice oxygen loss and the reaction of Co and Fe ion.Ac impedance analysis indicated that BSPCFx possessed better electrochemical performance.The polarization resistance of the sample with x=0.2 was only ～0.948 Ω cm2 at 500 oC,significantly lower than that of BSCF(～2.488 Ω cm2).     

Synthesis and characterization of calcium and manganese-doped rare earth oxide La_(1-x)Ca_xFe_(0.9)Mn_(0.1)O_(3-δ) for cathode material in IT-SOFC

In order to develop novel cathode materials with high performance for intermediate temperature SOFC(IT-SOFC),Ca and Mn doped rare earth oxides La1-xCaxFe0.9Mn0.1O3-δ(x=0.1,0.3 and 0.5,denoted as LCFM9191,LCFM7391 and LCFM5591) were synthesized by solid state reaction(SSR) method.The formation process,phase structure and microstructure of the synthesized samples were characterized using thermogravimetry/differential scanning calorimetry(TG/DSC),X-ray diffraction(XRD) and scanning electron microscopy(SEM).The thermal expansion coefficients(TEC) of the samples were analyzed at 100-900 oC by thermal dilatometry.The electrical conductivities of the samples were measured with direct current(DC) four-terminal method from 300 to 850 oC.The results indicated that the samples(x=0.1 and 0.3) exhibited a single phase with orthorhombic and cubic perovskite structure,respectively after being sintered at 1200 oC for 3 h.The electrical conductivity of the samples increased with temperature up to a maximum value,and then decreased.The small polaron hopping was regarded as the conducting mechanism for synthesized samples at T≤600 oC.The negative temperature dependence occurring at higher temperature was due to the creation of oxygen vacancies for charge balance.LCFM7391 had higher mixed conductivity(>100 S/cm) at intermediate temperature and could meet the demand of cathode material for IT-SOFC.In addition,the average TECs of LCFM9191 and LCFM7391 were 11.9×10-6 and 13.1×10-6 K-1,respectively,which had good thermal match to the common electrolytes.     

Serration Behavior in Zr-Cu-Al Glass-forming Systems

The metallic glass matrix composites(MGMCs)and bulk metallic glasses(BMGs)were studied by statistical analysis during plastic deformation at the strain rates of 2×10~(-2),2×10~(-3),and 2×10~(-4) s~(-1),respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10~(-2) s~(-1).When deformed at the strain rate of 2×10~(-3) s~(-1),the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.     

Transition of dominant diffusion process during superplastic deformation in AZ61 magnesium alloys

The superplastic behavior of the AZ61 magnesium alloy sheet, processed by one-step hot extrusion and possessing medium grain sizes of ∼12 μm, has been investigated over the temperature range of 523 to 673 K. The highest superplastic elongation of 920 pct was obtained at 623 K and a deformation rate of 1×10⁻⁴ s⁻¹. In the lower and higher strain rate regimes, with apparent m values of ∼0.45 and ∼0.25, respectively, grain-boundary sliding (GBS) and dislocation creep appeared to dominate the deformation, consistent with the scanning electron microscopy (SEM) examination. The SEM examination also revealed that individual GBS started to operate from the very initial deformation stage in the strain rate range with m∼0.45, which was attributed to the relatively high fraction (88 pct) of high-angle boundaries. The analyses of the superplastic data over 523 to 673 K and 5×10⁻⁵ to 1×10⁻³ s⁻¹ revealed a true stress exponent of ∼2, and the activation energy was close to that for grain-boundary and lattice diffusion of magnesium at 523 to 573 K and 573 to 673 K, respectively. The transition temperature of activation energy is ∼573 K, which is attributed to the change in the dominant diffusion process from grain-boundary diffusion to lattice diffusion. It is demonstrated that the effective diffusion coefficient is a valid parameter to characterize the superplastic behavior and the dominant diffusion process.     

Genesis of nanocrystalline Ho2O3 via thermal decomposition of holmium acetate: Structure evolution and electrical conductivity properties

This study focuses on the preparation of nanostructured holmium oxide via the decomposition of holmium acetate precursor utilizing the non-isothermal strategy. Thermogravimetric analysis(TGA) was used to follow up the various thermal events involved in the decomposition process. Dehydration completes approximately at 150℃, which is followed by the decomposition of the anhydrous acetate leading to the formation of holmium oxide. Based on the TGA results the acetate precursor was heated non-isothermally at the temperature range of 150 e700℃. The obtained solids were characterized using powder X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR), field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). It is found that nanocrystalline Ho_2 O_3 starts to form at 500℃ and presents the only phase detected at the 500 e700℃ range. The electrical conductivity of the solids that form at the temperature range of 300 e700℃ was investigated. The obtained values were correlated with the observed structural modifications accompanying the heat treatment. The electrical conductivity of the Ho_2 O_3 samples prepared at 500, 600 and 700℃ reaches the values of 1.92 × 10~(-7), 1.61 × 10~(-7) and 8.33 × 10~(-8) Ω~(-1)cm~(-1) at a measuring temperature of 500℃, respectively. These values are potentially advantageous for high-resistivity devices.     

Study on Properties of LSGM Electrolyte Made by Tape Casting Method and Applications in SOFC

Solid oxide fuel cell is attracting more attention in recent years for its lower pollution emission and high energy convert efficiency. La0.9Sr0.1Ga0.8Mg0.2O3-δ is a new kind of electrolyte for intermediate temperature SOFC. In this paper, La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) was prepared by solid state reaction method and formed by tape casting process to make a planar electrolyte. The appropriate amount of the dispersive was obtained by viscosity test. The densities of sintered samples increase with the increasing sintering temperature. It was found that the relative density of electrolyte can approach the value of 95% by the isostatic pressing treatment of the green tape. The average thermal expansion coefficient of the LSGM is 11.4×10-6/℃ at temperature range (200～1200 ℃). Measurements of the current-voltage and power-current characteristics of the H2-Air cell show that the open-circuit voltage is 1.067 V at 800 ℃, peak current density is 0.56 A·cm-2 and the maximum power output is 0.147 W·cm-2.     

Sensitivity of a solid Eu(Ⅲ) complex towards acetonitrile vapor:Structural and spectroscopic characterization

The Eu(Ⅲ) nitrate complex of the meso-N,N'-bis(2-pyridylmethylene)-1,2-(R,S)-cyclohexanediamine ligand was synthesized and characterized by single crystal and powder X-ray diffraction.The crystal lattice of the complex is capable of absorbing and desorbing selectively acetonitrile molecules,at 293 K upon an acetonitrile vapor pressure of ～0.1 × 10~5 Pa.This process,which is partially reversible,can be easily followed by both powder X-ray diffraction(P-XRD) and Eu(III) luminescence spectroscopy.The acetonitrile molecule,located in the outer coordination sphere of the metal ion,does not affect the radiative transition probability of ~5 D_0 level of Eu(Ⅲ) and also it does not activate further non-radiative channels from this level.On the other hand,this molecule is capable of affecting the energy position and intensities of the crystal field components of the 5 D_0 →~7 F_2 transition.The complex in solid form can be considered a promising material for the optical sensing of acetonitrile vapors.     

VOLTAMMETRIC STUDY ON THE REDUCTION OF RARE EARTHS IN ACETONE

The voltammetric and polarographic behaviours of 14 rare earth elements were investigated in anhydrousacetone.The influence of residual oxygen on their waves was examined.At a concentration lower than 6×10~(-4)mol/L,Eu~(3 ),Yb~(3 )and Sm~(3 ) produce two waves and other rare earth ions exhibit only one wave.When the concentration is greater than 8×10~(-4)mol/L,two waves could be observed on the reductionof Yb~(2 ),Sm~(2 )and other RE~(3 )ions except for Eu~(3 ).By adding 0.6% H_2O(or 1×10~(-4)mol/L NH_4ClO_4)one well-defined wave appears instead of two.The phenomenon is explained that a thin deposit film may beformed at electrode surface owing to the interaction of RE~(3 ) with O_2~-,which is the reduction product of traceoxygen in aprotic solvent.In the presence of a proton donor such as H_2O or NH_4~ ,oxygen reduces directly toH_2O_2 and eliminates the appearance of two waves.     

Solid state reaction synthesis and total electrical conductivity of La_(0.7)Sr_(0.3)Cr_yMn_zCo_(1-y-z)O_(3-δ)

The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The single orthorhombic phase La0.7Sr0.3CryMnzCo(1-y-z)O3-δ perovskite oxides were obtained when sintered at l350 °C for 10 h.The oxygen nonstoichiometry of the materials varied inversely with the total electronic conductivity.The sample with composition of La0.7Sr0.3Cr0.5Mn0.35 Co0.15O3-δ had the maximal total electronic conductivity and the lowest oxygen nonstoichiometry which were 22.4 S/cm and 0.040 at 850 °C,respectively.The low total electronic conductivity is related to the low relatively density of the samples directly.The activation energy of conduction changed at 550 °C,and the activation energy of conduction at high temperature(T550 °C) was higher than that at low temperature range(T550 °C).     

Hydrogen Absorption and Release Behavior in Hydrogen Decrepitation Process of Nd-Fe-B Alloys

The behavior of hydrogen absorption and release in hydrogen decrepitation (HD) process of Nd-Fe-B alloys were investigated. The results reveal that the reactivity and the amount of hydrogen absorption in HD process are related to the surface activity of the alloy so that the fresh and active surface has a higher efficiency. The presence of Nd-rich phase at the grain boundary is an essential factor of the HD activity of the alloy at room temperature. On degassing, hydrogen is released from the HD powder continuously with increasing temperature. And the residual hydrogen is as low as 0.0015% at 1073K, which shows that the hydrogen is almost exhaused. It is feasible to remove the hydrogen from the HD powder by heating treatment at the temperature of 523-723K for 1h prior to the magnetic field forming in order to decrease the harmful effect of hydrogen on the easy axis alignment of HD magnet.     

Effect of Pressure on Intermediate Valence States in Cerium Kondo Compounds

Electrical resistance, thermal expansion, lattice constants of the intermediate valence materials, α-Ce and CeBe13, were measured at high pressure. It is found that the Grttneisen parameters of Kondo temperature TK are 13 and 42 for α-Ce and CeBe13, respectively, and it decreases with increasing pressure. The magnetoresistance of α-Ce shows H^2 dependence and its coefficient increases with pressure below 1 GPa, but becomes nearly constant above 1 GPa. The results indicate that the intermediate valence states are enhanced at high pressure indicating the enhancement of hybridization between the 4f electron and conduction band.     

Effects of Cobalt Content and Preparation on Electrochemical Capacity of AB5-Type Hydrogen Storage Alloys at Different Temperature

The effects of Co as a substituent for Ni on microstructure and electrochemical capacity of hydrogen storage alloys MI(NiCoMnAl)5.4 at -30～ 80 ℃, in which the content of Co was 0, 1.31%, 2.63%, 3.94%, 5.25%, and 6.56% (mass fraction), respectively, were reported. All of the alloys were prepared by vacuum induction melting followed by melt-spinning. It is found that the electrochemical capacity of alloys at different temperature depends upon the compositions and preparation methods. The electrochemical capacity of alloys increases at higher temperature (40 ～ 80 ℃ )and decreases at lower temperature ( - 30 ～ 0 ℃ ) with an increasing cobalt content. With an increasing temperature,melt-spinning is more favorable for improved capacity of the alloys than casting. Analyses of the charging/discharging potential curves illustrate that higher cobalt content and melt-spinning techniques are more effective to increase the capacity at higher temperature because of the higher hydrogen evolution potential. On the contrary, the capacity of alloys at lower temperature can be increased by decreasing cobalt content and casting, which is ascribed to higher hydrogen evolution potential and delayed hydrogen evolution reaction, as well as reduced potential drop in the charging/discharging process.XRD patterns confirm that all of the specimens present a single hexagonal CaCu5-type structure and an increased lattice parameters with increasing Co content. The FWHM of the main peak of melt-spun ribbons reduces because of more homogeneous composition and less lattice strain defects.     

Investigation on pumping oxygen characteristics of (Bi2O3)0.73(Y2O3)0.27 solid electrolyte

(Bi2O3)0.73(Y2O3)0.27 fine powders prepared by wet chemical precipitation method were cold isostatically pressed to form solid electrolyte tubes, and sintered at 900 ℃ for 10 h in the air. Their pumping oxygen characteristics in non-dehydrated Ar gas were investigated, where a ZrO2 (Y2O3 stabilized) oxygen sensor was used to measure the oxygen partial pressure Po2. The results showed that the Po2 value reached magnitudes of 1×10-20-1×10-10 Pa at the applied pumping oxygen voltage of 0.5 V, 1×10-37-1×10-27 Pa at 1.0 V and 1×10-53-1×10-47 Pa at 2.0 V within the temperature range from 550 to 650 ℃. Moreover, no cracks were found in the tested solid electrolyte tubes. Thus, the Bi2O3-Y2O3 system might be used in solid electrolyte oxygen pump for purifying gases.     

Growth and spectral characteristics of a new promising stoichiometric laser crystal: Ca9Yb（VO4）7

A Ca9Yb(VO4)7 crystal with dimensions of Φ23 mm×35 mm was grown successfully by Czochralski method. Its thermal conductivity was 1.06 W/(m?K) at room temperature. The absorption cross-sections at 980 nm were 1.80×10–20 cm2 and 1.28×10–20 cm2 for π- and σ- polarizations, respectively, with a full-width at half-maximum of 34 nm. The crystal had a broad emission at around 1025 nm with a full-width at half-maximum of 67 nm for π- polarization and 70 nm for σ- polarization. The emission cross-sections of the crystal were calculated by using reciprocity method and Füchtbauer-Ladenburg formula. The emission cross-sections at 1025 nm were 3.57×10–20 cm–2 and 1.91×10–20 cm–2 for π- and σ- polarization, respectively. The fluorescence lifetime was 332 μs. The results indicated that the crystal is a promising femtosecond and tunable laser material.     

Upconversion Luminescence of YLiF4 :Er3+ Synthesized by Hydrothermal Method

YLiF4: Er3 was synthesized by hydrothermal method. Concentration of Er3 is changed from 0 to 5 %. The absorption of Er3 in all samples from 200 to 1200 nm was measured at room temperature. The J-O parameters calculated from absorption spectrum areΩ 2 = 1.05 × 10- 20 cm2, Ω4 = 1.25 × 10- 20 cm2 andΩ6 = 1.35 × 10- 20 cm2. Infrared-to-visible upconversion emission of YLiF4: Er3 was observed when excited by 980 nm. The results show that the Er3 content is less than 1.5 %, excite-state absorption is the main mechanism of upconversion emission. When Er3 content is larger than 1.5 %, both of the excite-state absorption and energy transfer lead to the upconversion luminescence. The upconversion intensity was enhanced with the increasing of Er3 concentration. At room temperature, the lifetime of 2H11/2 and 4S3/2is 205μs while that of 4F9/2 is 188μs for sample Er-2. The transition rates and quantum efficiency were also calculated.The quantum efficiencies of 4S3/2 and 4F9/2 are 27.9% and 10.7%, respectively.     

Effect of calcination temperature and reaction conditions on methane partial oxidation using lanthanum-based perovskite as oxygen donor

We investigated the effect of calcination temperature, reaction temperature, and different amounts of replenished lattice oxygen on the partial oxidation of methane （POM） to synthesis gas using perovskite-type LaFeO3 oxide as oxygen donor instead of gaseous oxygen, which was prepared by the sol-gel method, and the oxides were characterized by XRD, TG/DTA, and BET. The results indicated that the particle size increased with the calcination temperature increasing, while BET and CH4 conversion declined with the calcination temperature increasing using LaFeO3 oxide as oxygen donor in the absence of gaseous oxygen. CO selectivity remained at a high level such as above 92%, and increased slightly as the calcination temperature increased. Exposure of LaFeO3 oxides to methane atmosphere enhanced the oxygen migration of in the bulk with time online owing to the loss of lattice oxygen and reduction of the oxidative stated Fe ion simultaneously, The high reaction temperature was favorable to the migration of oxygen species from the bulk toward the surface for the synthesis gas production with high CO selectivity. The product distribution and evolution for POM by sequential redox reaction was determined by amounts of replenished lattice oxygen with gaseous oxygen. The optimal process should decline the total oxidation of methane, and increase the selectivity of partial oxidation of methane.     

CeO2 nanoscale particles: Synthesis,characterization and photocatalytic activity under UVA light irradiation

CeO_2 nanoparticles(NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 ℃/24 h(assigned as CeO_2-80) and 500 ℃/2 h(assigned as CeO_2-500). The as-prepared materials and the commercial ceria(assigned as CeO_2-com) were characterized using TGA-MS, XRD, SEM-EDX, UV-vis DRS and IEP techniques. The photocatalytic performances of all obtained photocatalysts were assessed by the degradation of Congo red azo-dye(CR) under UVAlight irradiation at various environmental key factors(e.g., reaction time and calcination temperature).Results reveal that CeO_2 compounds crystalize with cubic phase, CeO_2-500 exhibits smaller crystallite size(9 nm vs 117 nm) than that of bare CeO_2-com. SEM analysis shows that the materials are sphericallike in shape NPs with strong assembly of CeO_2 NPs observed in the CeO_2-500 NPs. EDX analysis confirms the stoichiometry of CeO_2 NPs. UV-vis DRS measurement reveals that, CeO_2-500 NPs exhibits a red-shift of absorption band and a more narrow bandgap(2.6 eV vs 3.20 eV) than that of bare CeO_2-com. On the contrary, Urbach energy of Eu is found to be increased from 0.12 eV(CeO_2-com) to 0.17 eV(CeO_2-500),highlighting an increase of crystalline size and internal microstrain in the CeO_2-500 NPs sample. Zeta potential(IEP) of CeO_2-500 NPs is found to be 7.2. UVA-light-responsive photocatalytic activity is observed with CeO_2-500 NPs at a rate constant of 10×10~(-3) min~(-1), which is four times higher than that of CeO_2-com(K_(app)=2.4×10~(-3) min~(-1)) for the degradation of CR. Pseudo-first-order kinetic model gives the best fit. On the basis of the energy band diagram positions, the enhanced photocatalytic performance of CeO_2-500 nano-catalyst can be ascribed to O_2~-, 'OH and R'~+ as the primary oxidative species involved in the degradation of RC under UVA-light irradiation.     

Source and Control of Nitrogen for X70 Pipeline Steel

The effects of some key factors on nitrogen absorption during the smelting process of X70 pipeline steel were studied,and the source of nitrogen pick-up was analyzed to find the bottleneck for nitrogen control.A series of measures were put forward to decrease the nitrogen pick-up.The results indicated that an exponential relationship existed between the nitrogen absorption index and the free oxygen in molten steel.Nitrogen absorption index could decrease below 0.3when free oxygen in molten steel was above 100×10~(-6) after tapping.For low sulfur killed steel,the nitrogen absorption ratio and sulfur content satisfied a linear relationship with a slope of-0.007.Low free-oxygen and sulfur were beneficial to the deep desulfurization during vacuum treatment.The contradiction of high desulfurization ratio and low nitrogen pick-up during LF process could be resolved by skimming oxidizing slag after tapping and making new high basicity top slag.After optimization,the average content of nitrogen in final product decreased from 46×10(-6)to 35×10(-6).     

Oxidation resistance,thermal expansion and area specific resistance of Fe-Cr alloy interconnector for solid oxide fuel cell

It is promising for metal especially ferritic stainless steel(FSS)to be used as interconnector when the solid oxide fuel cell(SOFC)is operated at temperature lower than 800°C.However,there are many challenges for FSS such as anti-oxidant,poisoning to cathode and high area specific resistance(ASR)when using as SOFC interconnector.The effect of Cr content(12-30 mass%)in Fe-Cr alloys on thermal expansion coefficient(TEC),oxidation resistance,microstructure of oxidation scale and ASR was investigated by thermo-gravimetry,scanning electron microscopy,energy dispersive spectroscopy and four-probe DC technique.The TEC of Fe-Cr alloys is(11-13)×10~(-6) K~(-1),which excellently matches with other SOFC components.Alloys have excellent oxidation resistance when Cr content exceeds 22mass% because of the formation of chromium on the surface of alloy.The oxidation rate constants kdand ksdecrease rapidly with increasing the Cr content and then increase slowly when the Cr content is higher than 22mass%.The kinetic results indicate that Cr evaporation must be considered at high temperature for Fe-Cr alloys.After the alloys were oxidized in air at 800°C for500 h,log(ASR/T)(Tis the absolute temperature)presents linear relationship with 1/T and the conduct activation energy is 0.6-0.8eV(Cr16-30).Optimal Cr content is 22-26mass%considering the oxidation resistance and ASR.     

Heat Transfer and Energy Analysis of a Pusher Type Reheating Furnace Using Oxygen Enhanced Air for Combustion

 Oxy-fuel firing is more energy efficient and environmental friendly than conventional air-fuel firing and its application for reheating furnaces has begun since 90s. In this study, a computational methodology is presented to predict the steady heat transfer to the billets and temperature distribution in a continuous Pusher type reheating furnace which combustion air is enhanced by oxygen. The furnace is modeled as 2D radiating medium and Weighted Sum of Gray Gases model is used for absorption coefficient. The billets are moved in constant speed through zones of furnace. Radiative heat flux calculated from the radiative heat exchange within the furnace is modeled using the FVM considering the effects of furnace walls and billets. Energy consumption per ton of steel, production rate and thermal efficiency of furnace, and trend of NOx emission in various levels of oxygen enrichment is investigated by comparison with baseline furnace (21% O2 in air).