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1.
Nanocrystalline and amorphous LaMg_(12)-type LaMg_(11)Ni + x wt% Ni(x = 100, 200) alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter(DSC) connected with a H_2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability(HRD) and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.  相似文献   

2.
The La-Mg-Ni-Mn-based AB2-type La1-xCexMgNi3.5Mn0.5 (x = 0, 0.1, 0.2, 0.3, and 0.4) alloys were fabricated by melt spinning technology. The effects of Ce content on the structures and electrochemical hydrogen storage performances of the alloys were studied systematically. The XRD and SEM analyses proved that the experimental alloys consist of a major phase LaMgNi4 and a secondary phase LaNi5. The variation of Ce content causes an obvious change in the phase abundance of the alloys without changing the phase composition. Namely, with the increase of Ce content, the LaMgNi4 phase augments and the LaNi5 phase declines. The lattice constants and cell volumes of the alloys clearly shrink with increasing Ce content. Moreover, the Ce substitution for La results in the grains of the alloys clearly refined. The electrochemical tests showed that the substitution of Ce for La obviously improves the cycle stability of the as-spun alloys. The analyses on the capacity degradation mechanism demonstrate that the improvement can be attributed to the ameliorated anti-corrosion and anti-oxidation ability originating from substituting partial La with Ce. The as-spun alloys exhibit excellent activation capability, reaching the maximum discharge capacities just at the first cycling without any activation treatment. The substitution of Ce for La evidently improves the discharge potential characteristics of the as-spun alloys. The discharge capacity of the alloys first increases and then decreases with growing Ce content. Furthermore, a similar trend also exists in the electrochemical kinetics of the alloys, including the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (IL) and charge transfer rate.  相似文献   

3.
The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1?x Co x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by melt quenching technology. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The alloy electrodes were charged and discharged with a constant current density in order to investigate the electrochemical hydrogen storage kinetics of the alloys. The results demonstrate that the substitution of Co for Ni results in the formation of secondary phases MgCo2 and Mg instead of altering the major phase Mg2Ni. No amorphous phase is detected in the as-quenched Cofree alloy, however, a certain amount of amorphous phase is clearly found in the as-quenched alloys substituted by Co. Furthermore, both the rapid quenching and the Co substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys, for which the notable increase of the hydrogen diffusion coefficient (D) along with the limiting current density (I L ) and the obvious decline of the electrochemical impedance generated by both the Co substitution and the rapid quenching are basically responsible.  相似文献   

4.
CuO-doped (Ag0.75Li0.1Na0.1K0.05)NbO3 (ALNKN-xCuO, x = 0–2mol%) lead-free piezoelectric ceramics were prepared by the solid-state reaction method in air atmosphere. The effects of CuO addition on the phase structure, microstructure, and piezoelectric properties of the ceramics were investigated. The experimental results show that the ALNKN ceramics without doping CuO possess rhombohedral phase along with K2Nb6O16-type phase and metallic silver phase. For all of the CuO-doped ALNKN ceramics, a pure perovskite structure with the orthorhombic phase was obtained by enclosing the samples in a corundum tube. A homogeneous microstructure with the grain size of about 1 μm was formed for the ceramics with 0.5mol% CuO. The grain size increases with increasing amount of CuO. The temperature dependence of dielectric properties indicates that the ferroelectric phase of the ALNKN-xCuO ceramics becomes less stable with the addition of CuO. The ceramics with x = 1mol% exhibit relatively good electrical properties along with a high Curie temperature. These results will provide a helpful guidance to preparing other AN-based ceramics by solid-state reaction method in air atmosphere.  相似文献   

5.
(Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramics doped with x wt%CaZrO3 (x= 0-10) were synthesized by solid-state reaction method. The effects of CaZrO3 amount on the dielectric properties and structure of (Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramics were investigated. X-ray diffraction results indicated a pure cubic perovskite structure for all samples and that the lattice parameter increased till x=5 and then slightly decreased. A homogenous microstructure was observed with the addition of CaZrO3. Dielectric measurements revealed a relaxor-like characteristic for all samples and that the diffusivity γ reached the maximum value of 1.78 at x=5. With the addition of CaZrO3, the dielectric constant dependence on electric field was weakened, insulation resistivity enhanced and dielectric breakdown strength improved obviously and reached 19.9 kV/mm at x=7.5. In virtue of low dielectric loss (tan δ<0.001 5), moderate dielectric constant (εr >1 500) and high breakdown strength (Eb >17.5 kV/mm), the CaZrO3 doped (Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramic is a potential candidate material for high power electric applications.  相似文献   

6.
TiC x /Cu composites were fabricated by combustion synthesis and hot press technology. Using XRD, SEM, EDS, FESEM analysis methods, the effects of various carbon sources and different Cu contents on the microstructures of TiC x /Cu composites and the size of TiC x particles were investigated. Results showed that TiC x reinforcing particles size increases with decreasing Cu content in Cu-Ti-C reaction system. With carbon nanotubes (carbon black) serving as carbon source, the generated TiC x particles size transits from nanometer to submicron when Cu content corresponding to the reaction system is reduced to 60 vol% (70 vol%); while graphite serves as carbon source, there is no clear limiting concentration. C particles with smaller size, larger specific surface area and better distribution result in finer TiC x particles, which is more beneficial to generating nano-sized TiC x /Cu composites.  相似文献   

7.
The Cu x Si1-x thin films have been grown by pulsed laser deposition (PLD) with in situ annealing on Si (001) and Si (111), respectively. The transformation of phase was detected by X-ray diffraction (XRD). The results showed that the as-deposited films were composed of Cu on both Si (001) and Si (111). The annealed thin films consisted of Cu + η”-Cu3Si on Si (001) while Cu + η’-Cu3Si on Si (111), respectively, at annealed temperature (T a) = 300-600 °C. With the further increasing of T a, at T a= 700 °C, there was only one main phase, η”-Cu3Si on Si (001) while η’-Cu3Si on Si (111), respectively. The annealed thin films transformed from continuous dense structure to scattered-grain morphology with increasing T a detected by field emission scanning electron microscope (FESEM). It was also showed that the grain size would enlarge with increasing annealing time (t a).  相似文献   

8.
This paper reports the effects of variations in the fuel composition of H2/CO/CH4 syngas on the characteristics of NO x and CO emissions in a partially-premixed gas turbine combustor. Combustion tests were conducted on a full range of fuel compositions by varying each component gas from 0% to 100% at heat inputs of 40 and 50 kWth. Flame temperature, combustor liner temperature, ignition delay time, and flame structure were investigated computationally and experimentally to judge whether they are significant indicators of NO x and CO formation. The characteristics of and reasons for NO x and CO emissions were investigated by analyzing the emission mechanisms and relationships among fuel property, equivalence ratio, flame temperature, liner temperature, flame shape. The flame structures were investigated using the following flame visualization methods: (1) time-averaged OH* chemiluminescence and its Abel-deconvolution; (2) direct photography; and (3) instantaneous OH-PLIF. The flame structures were greatly changed by the fuel composition and heat input, and they were subjected to key affecting parameters of the temperatures of the flames and the liners. NO x and CO emissions also largely varied according to fuel composition and heat input, showing neither linearly nor exponentially clear proportional trends toward the syngas compositions because of the singular conditions. For example, only the 100% CO flame at low load emitted lots of CO, whereas complete combustion was observed in other cases. However, the qualitative observations showed that the root causes of NO x emission behaviors were flame temperature and flame structure, which were directly related to the residence time in the flame. Various sets of practical test results were obtained, and these results could contribute to the optimal selection of the fuel-feeding condition when fuel is changed from natural gas to syngas in order to minimize NO x and CO emissions with stable combustion.  相似文献   

9.
The crystal structure, band structure, density of states, Mulliken charge, bond population and optical properties for LiBi1-xMxO3 (M=V, Nb, and Ta) were investigated using hybrid density functional theory. It was found that LiBiO3 doped with V, Nb, and Ta presented distinctly stronger covalent interactions in M-O (M=V, Nb, and Ta) than Bi-O, thus resulting in mild distortion of the structure and facilitating the separation of photogenerated carriers. Furthermore, the hybridizations of Bi-6s, M-d (M=V, Nb, and Ta) and O-2p widened the valence and conduction bands, which promoted transmission of photogenerated carriers in the band edge and thus caused better photocatalytic performance.  相似文献   

10.
ZnMn2O4 films for resistance random access memory (RRAM) were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn2O4 films were investigated. The ZnMn2O4 films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching (BRS) behavior dominated by the space-charge-limited conduction (SCLC) mechanism in the high resistance state (HRS) and the filament conduction mechanism in the low resistance state (LRS), but the ZnMn2O4 films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel (P-F) conduction mechanism in both HRS and LRS. Ag/ZnMn2O4/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 106 seconds. However, the highest R HRS/R LRS ratio of 104 and the lowest V ON and V OFF of 3.0 V have been observed in Ag/ZnMn2O4/Pt device. Though the Ag/ZnMn2O4/n-Si device also possesses the highest R HRS/R LRS ratio of 104, but the highest values of V ON,V OFF, R HRS and R LRS, as well as the poor endurance and retention characteristics.  相似文献   

11.
We put forward a first-principles density-functional theory about the impact of pressure on the structural and elastic properties of bulk CaN2, SrN2 and BaN2. The ground state properties of three alkaline earth diazenides were obtained, and these were in good agreement with previous experimental and theoretical data. By using the quasi-harmonic Debye model, the thermodynamic properties including the debye temperature Θ D, thermal expansion coefficient α, and grüneisen parameter γ are successfully obtained in the temperature range from 0 to 100 K and pressure range from 0 to 100 GPa, respectively. The optical properties including dielectric function ε(?), absorption coefficient α(?), reflectivity coefficient R(?), and refractive index n(?) are also calculated and analyzed.  相似文献   

12.
Polycrystalline Bi4Ti3O12 thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt(111)/Ti/SiO2/Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi4Ti3O12 thin films. The films with high fractions of a-axis and random orientations, i e, f (a-sxis) = 28.3% and f (random) = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm2, respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization (2Pr = 35.5 μC/cm2) was obtained for the Bi4Ti3O12 thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi4Ti3O12 films.  相似文献   

13.
In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys, Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1−x Co x (x=0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied with an X-ray diffractometer (XRD) and a high resolution transmission electronic microscope (HRTEM). An investigation on the thermal stability of the as-spun alloys was carried out with a differential scanning calorimeter (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results demonstrate that the substitution of Co for Ni does not alter the major phase of Mg2Ni but results in the formation of secondary phase MgCo2. No amorphous phase is detected in the as-spun Co-free alloy, but a certain amount of amorphous phase is clearly found in the as-spun Co-containing alloys. The substitution of Co for Ni exerts a slight influence on the hydriding kinetics of the as-spun alloy. However, it dramatically enhances the dehydriding kinetics of the as-cast and spun alloys. As Co content (x) increases from 0 to 0.4, the hydrogen desorption capacity increases from 0.19% to 1.39% (mass fraction) in 20 min for the as-cast alloy, and from 0.89% to 2.18% (mass fraction) for the as-spun alloy (30 m/s).  相似文献   

14.
Ferroelectric and leakage properties are important for ferroelectric applications. Pure and Nd-doped (x=0.05-0.20) BiFeO3 thin films were fabricated by sol-gel method on FTO substrates. The phase structure, surface morphology, leakage current, ferroelectric properties, and optical properties of BiFeO3- based thin films were investigated. The substitution of Nd3+ ions for the Bi3+ site converts the structure from rhombohedral to coexisting tetragonal and orthorhombic. Nd doping improves the crystallinity of BiFeO3 thin films. The leakage current of Nd-doped BiFeO3 decreases by two to three orders of magnitude compared with that of pure BiFeO3. Among the samples, 15% Nd-doped BiFeO3 exhibits the strongest ferroelectric polarization of 17.96 μC/cm2. Furthermore, the absorption edges of Bi1-xNd x FeO3 thin films show a slight red-shift after Nd doping.  相似文献   

15.
The effect of Ga2O3 on the structure and properties of calcium aluminate glasses fabricated by vacuum melting process was investigated by Raman spectrum, differential scanning calorimeter (DSC), and infrared spectrum methods. The results show that calcium aluminate glass network only consists of [AlO4] tetrahedral units. With the gradual addition of Ga2O3, the quantity of [GaO4] tetrahedral units increases. Substitution of Ga2O3 for Al2O3 results in a decrease in T g T x, and T p, and an increase in the thermal stable index ΔT. Similarly, the absorption band around 3.0 μm obviously reduces and the transparency in 4.0-6.0 μm rapidly increases with increasing Ga2O3 content. However, the chemical stability of calcium aluminate glasses decreases if Ga2O3 is introduced due to the increasing of [GaO4] units in the glass network.  相似文献   

16.
In this paper, the effects of Si and Ce on the microstructure and hydrogen storage property of Ti26.5Cr20V45Fe8.5Ce0.5 alloy were studied, respectively. First of all, effects of Si on the microstructure and hydrogen storage properties of Ti26.5Cr20(V45Fe8.5)1−x Si x Ce0.5 (x = 0, 0.5, 1.0, 1.5 and 2.0 at%) alloys were studied by X-ray diffraction, scanning electron microscopy and P-C isotherm measurements. As the Si addition increases, the hydrogen absorption capacities of alloys decrease but the equilibrium pressure increases, due to the formation of Laves phase. Secondly, the effect of Ce on Ti26.5Cr20 (V45Fe8.5)0.98Si2 alloy was studied. It was found that Ce addition is an effective way to eliminate the effect of Si on the hydrogen storage properties of the alloy. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA05Z144)  相似文献   

17.
BiB3O6 (BIBO) single crystals with size of 46×23×10 mm3 and weight of 26.0 g have been successfully grown by top-seeded method. Problems encountered in the growth process of this crystal have been discussed in detail, and the methods of growing high-quality large crystals have been put forward. The relationship between their structure and properties is studied. The space group of monoclinic BiB3O6 is C2 and the cell parameters are a=7.1203(7) Å, b=4.9948(7) Å, c=6.5077(7) Å, β=105.586(8)″, and V=222.93(5) Å3. The density of BIBO is 4.8965 g/cm3. The Mohs’s scale of hardness is 5.5–6. There is no cleavage face in the crystal. The transmittance of BIBO is about 80 percent in the range from visible coherent light to near-infrared light. The ultraviolet cutoff wavelength is at 276 nm. BiB3O6 is a biaxial crystal and has two sets of axes, and the relative orientation of (X, Y, Z) with regard to (a, b, c) is: X//b, (Y, c)=47.2°, (Z, a)=31.6°, determined by X-ray analysis combined with polarized microscopy. Second-harmonic-generation (SHG) experiments were carried out for the first time. In type I phase-matching (PM) directions (11.1°, 90°) and (168.9°, 90°), SHG conversion efficiencies of two directions for 1.064 μm light are up to 67.7% and 58%, respectively. We have also obtained the third-harmonic-generation (THG) of 1.064 μm. The comparative experiments between BIBO and KTP were carried out on conversion efficiency, transmittance and hardness. All the above results indicate that BiB3O6 is a kind of excellent nonlinear optical (NLO) crystal.  相似文献   

18.
The spontaneous magnetic transitions and corresponding magnetoelastic properties of intermetallic compounds RMn2Ge2 (R=Gd, Tb and Dy) were investigated by using the X-ray diffraction method and magnetic measurement. The results showed that the compounds experience two magnetic transitions, namely the second-order paramagnetic to antiferromagnetic transition at temperature TN (TN=368, 423 and 443 K for GdMn2Ge2, TbMn2Ge2 and DyMn2Ge2, respectively) and the first-order antiferromagnetic - ferrimagnetic transition at temperature Tt (Tt=96, 80 and 40 K for GdMn2Ge2, TbMn2Ge2 and DyMn2Ge2, respectively) as the temperature decreases. The temperature dependence of the lattice constant a(T) displays a negative magnetoelastic anomaly at the second-order transition point TN and, at the first-order transition Tt, a increases abruptly for GdMn2Ge2 and TbMn2Ge2, Δa/a about 10-3. Nevertheless, the lattice constant c almost does not change at these transition points indicating that such magnetoelastic anomalies are mainly contributed by the Mn-sublattice. The transitions of the magnetoelastic properties are also evidenced on the temperature dependence of magnetic susceptibility χ. The first-order transition behavior at Tt is explained by the Kittel mode of exchange inversion.  相似文献   

19.
Amorphous La0.7Zn0.3MnO3 (LZMO) films were deposited on p+-Si substrates by sol-gel method at low temperature of 450 °C. The Ag/LZMO/p+-Si device exhibits invertible bipolar resistive switching and the R HRS/R LRS was about 104-106 at room temperature which can be kept over 103 switching cycles. Better endurance characteristics were observed in the Ag/LZMO/p+-Si device, the V Set and the V Reset almost remained after 103 endurance switching cycles. According to electrical analyses, the conductor mechanism was in low resistor state (LRS) governed by the filament conductor and in the high state (HRS) dominated by the traps-controlled space-charge-limited current (SCLC) conductor.  相似文献   

20.
Preparation and thermoelectric properties of nanostructured n-type Mg2Si bulk materials were reported. Nanosized Mg2Si powder was obtained by mechanical milling of the microsized Mg2Si powder prepared by solid-state reaction. The bulk materials with 30 nm and 5 µm were prepared by spark plasma sintering of the nanosized and microsized Mg2Si powder, respectively. Both the samples show n-type conduction and the Seebeck coefficient of the sintered samples increase determinately with the grain size decrease from 5 µm to 30 nm. On the other hand, the electrical and thermal conductivity decrease with the decrease of grain size. Accordingly, decreasing their grain size increases their thermoelectric-figure-of-merit. A maximum thermoelectric figure of merit of 0.36 has been obtained for the nanostuctured Mg2Si sample at 823 K, which is 38% higher than that of microsized Mg2Si bulk materials and higher than results of other literatures. It could be expected that the properties of the nanocomposites could be further improved by doping optimization.  相似文献   

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