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1.
Ca
x
Ba 1−x
TiO 3 (CBT) fine particles doped with red luminescence center of Pr 3+ ions (Pr: CBT) were successfully synthesized by salt assisted spray pyrolysis (SASP) process. Scanning electronic microscope
(SEM) and laser scattering analysis demonstrate that salt can be removed from the surface of particles by washing with Milli-Q
water and the particles can be further separated by ball-milling to get well-dispersed Pr 3+ ions doped CBT fine particles. The luminescence properties, such as photoluminescence (PL) and mechanoluminescence (ML),
of as-synthesized Pr: CBT particles were investigated. For Pr: CBT fine particles with different Ca molar ratios, all the
samples show one emission at 612 nm, with increasing Ca molar ratio, PL intensity of Pr: CBT fine particles become stronger
and stronger. When pressure was loaded on the Pr: CBT pellet, mechanoluminescence(ML) emission was measured. The results show
that the ML intensity is proportional to the applied pressure. 相似文献
2.
SMnxZn1-xFe2O4 (x=1,0.9,0.8,0.7,0.6,0.5,0.25,0) nanoparticles were prepared by ball-milling hydrothermal and investigated by X-ray diffraction, DTG and TEM. Nanocrystallite grain size was determined by X-ray linewidth to be from 63 A to 274 A. The thermal properties indicate absorbed water still remain at low temperature, crystalline wate will be decomposed from 230 ℃ to 260 ℃, partial Mn^2+ will be oxidized near 730 ℃. TEM shows the ferrite particles pocess a spherical morphology and uniform nanosize. 相似文献
3.
以铁氧体、铁粉作为吸收剂制备多种电磁吸波涂料,测试与分析所得电磁吸波涂料的电导率、电磁参数及吸波性能。结果表明随着铁粉掺量的增加,所得电磁吸波涂料的电导率增加,在中高频区介电损耗和磁损耗均有所提高;铁粉与铁氧体的质量比为2:8时吸波涂层的吸波性能最好;反射率损耗〈-10.0 dB时的有效吸收频段在中低频区,有效带宽达4.5 GHz,最大吸收率为-16.63 dB。 相似文献
4.
Ca 3Co 4O 9 ceramics were prepared using the sol-gel process with ordinary pressing sintering and their thermoelectric properties were
measured from room temperature to 673 K. The experimental results show that single phase Ca 3Co 4O 9 can be fabricated at 750–900 °C in different citrate acid molar proportions for 0.2–1.0. For all the oxides, both the Seebeck
coefficients S and the electrical conductivities κ increase with the increasing temperature. The Seebeck coefficients S are all positive. The thermal conductivities k increase with the increasing temperature also and the lattice thermal conductivity
κ
l plays an important role to the thermal conductivity κ. The citrate acid molar proportions have a large influence on the particle sizes, which influences the thermoelectric properties
of the ceramics. The figure of merit increases with the increasing temperature and reaches 4.5×10 −5 K −1 at 573 K for the sample in the citrate acid molar proportion of 0.46. 相似文献
5.
Aiming at developing novel microwave-transparent ceramics with low dielectric loss,high thermal conductivity and high strength,Si3N4-AlN(30%,mass fraction) composite ceramics with La2O3 as sintering additive were prepared by hot-pressing at 1 800 °C and subsequently annealed at 1 450 °C and 1 850 °C for 2 h and 4 h,respectively.The materials were characterized by XRD and SEM.The effect of annealing process on the phase composition,sintering performance,microstructure,bending strength,dielectric loss and the... 相似文献
6.
Based on the structural characteristic of metal drill collar for induction logging while drilling, we have given the analytical
formulae of lengthways fields E
z
and H
z
when the tool is located in a fan-ring shaped slot of drill collar by the boundary conditions of electromagnetic field, and
derived the other components of electromagnetic field in and out the fan-ring slot from E
z
and H
z
. In the other intervals of formation, where the drill collar is a solid cylinder, the analytical formulae of field are educed
through the method of variable coefficient. The total analytical solutions of field in whole space have been obtained. With
the help of the analytical formulae, we have also given numerical examples and analyzed the distributive characteristic of
electromagnetic field. From the computational results we find that the secondary scattering field H
z
is in a linear relation with the conductivity of stratum. The characteristic of field is very useful for induction logging
while drilling, which can be used to measure and analyze the logging responses of the stratum conductivity. This paper sets
up a theoretical foundation for us to study the distrbutions of field and to direct the design of logging instruments.
Supported by the National Natural Science Foundation of China (Grant No. 10705049), the Beijing Natural Science Foundation
(Grant No.1083011) and Funding Project for Academic Human Resources Development in Institutions of Higher Learning [PHR(IHLB)] 相似文献
7.
By using inorganic Fe 3O 4 nanoparticles of different content as nucleation sites, PAn-Fe 3O 4 nanorods were successfully synthesized through a simple, conventional, and inexpensive one-step in-situ polymerization method. The TEM images revealed the size and morphology of the resultant nanocomposite. The EDS pattern confirmed
the existence of Fe 3O 4 in the composite. The FT-IR spectral analysis confirmed the formation of PAn encapsulated Fe 3O 4 nanocomposite. With the content of Fe 3O 4 increasing, the conductivity of the nanocomposites gradually decreases, meanwhile, the saturation magnetization increases
and reveals a super paramagnetic behavior. With controllable electrical, magnetic, and electromagnetic properties, the well-prepared
nanocomposites may have the potential applications in chemical sensors, catalysis, microwave absorbing, and electro-magneto-rheological
fluids, etc. 相似文献
8.
1 Introduction Microwave absorbing materials (MAM) refer to a kind of materials that can be used to absorb the emitted electromagnetic (EM) energy and to minimize the wave reflected in the direction of an energy radar receiver. When the EM wave incidents into MAM, it is readily absorbed, attenuated, and changed into heat or other energy. MAM are functional materials that possess special performance for absorbing EM wave. Along with the advancement in radar and microwave technologies, MA… 相似文献
9.
A theoretical model of describing the electromagnetic and thermal dynamics of high-Tc superconducting bulks in a high-Tc superconducting Maglev system is built up. The model contains the effects of hysteresis-type loss, flux flow, flux creep, and thermal diffusion on the superconducting bulks in the Maglev system. As the first stage of this study, the behavior of magnetic and electric fields, as well as the distribution energy flow density in the superconducting bulk is studied. The results show that the flux flow and thermal diffusion affect the behaviors of the electromagnetic field in the high-Tc superconducting bulks in different ways; however, both of them contribute significantly to the energy dissipation of the superconducting bulks when they are used in the Maglev train. 相似文献
10.
(PEO)8LiClO4-SiO2 composite polymer electrolytes(CPEs) were prepared by in-situ reaction, in which ethyl-orthosilicate (TEOS) was catalyzed by HCl and NH3·H2O, respectively. The ionic conductivity, the contact angle and the morphology of inorganic particles in the CPEs were investigated by AC impedance spectra, contact angle method and TEM. The conductivities of acid-catalyzed CPE and alkali-catalyzed CPE are 2.2×10^-5 and 1.1×10^-5 S/cm respectively at 30 ℃. The results imply that the catalyst plays an important role in the structure of in-situ preparation of SiO2, and influences the surface energy and conductivity of CPE films directly. Meanwhile, the ionic conductivity is related to the surface energy. 相似文献
11.
Cerium-substituted yttrium iron garnet( CexY3-xFe5O12, Ce : YIG ) was prepared via coprecipitation. The structure, morphology, valence state and constituent of Ce ions were investigated respectively. X-ray powder diffraction( XRD ) analysis shows that Ce : YIG was of single cubic YIG phase. The result of X-ray photoelectron spectroscopy( XPS ) indicates the Ce ions in Ce : YIG were in the state of trivalence. Scanning electron microscope ( SEM ) demonstrates the conglobatian of Ce : YIG particles about 0.2μm scale. The magnetic properties were studied by a vibrating sample magnetometer (VSM) and the result exhibits that substitution of Ce 3 changes the magnetic parameters of YIG. The effects of doping content of Ce ions and synthesis temperature on valence control were discussed in detail. 相似文献
12.
Surface roughness of quartz particles was determined by measuring the specific surface area of particles. The wettability
characteristics of particles were determined by measuring the flotation rate using a laboratory flotation cell. Experimental
results show that the rod mill product has higher roughness than the ball mill product. For the particles with larger surface
roughness, the flotation kinetics constant is also higher. Finally, empirical relationships between surface roughness ( r) and the flotation kinetics constant ( k) of quartz particles as k= A+ Br+ Cr
0.5ln r+ D/ln r+ E/r and k= A+ Br are presented, in which A, B, C, D and E are constants related to experimental conditions and mineralogical properties of mineral. 相似文献
13.
1 IntroductionSynthetichydroxyapatite (HAP) ,whichisthemajorconstitutionofnaturalboneandteeth ,iswell knownasbiocompatibleandbioactivematerialthathasbeenwidelyusedinmanyclinicalapplications[1 3] .Forexample ,po roushydroxyapatitehasbeenusedinbone ingrow… 相似文献
14.
Magnetohydrodynamic flow around the nonmetallic inclusions in aluminum melt and the force exerted on the inclusions were explored by dimensional analysis and numerical calcula-tions. Dimensional analysis shows that the invariant characterizes the force exertedon the inclusions and the flow intensity of the melt. The physical significance of A is represented as a modified particle Reynolds number that reflects the effects of electromagnetic force. The fluid flow around the particle becomes unstable when A>2×103. It is shown that the neglect of the in-ertial terms has little effect on the force exerted on the inclusions in the range of A≤1×106. However, the analytical solution of the maximum velocity inside the melt does not apply due to the appearance of turbulent flow in the case of A>2?103. 相似文献
15.
A series of nanometer TiO2 photocatalysts co-doped respectively with rare earth Er3+-Ce3+ and La3+-Fe3+ were prepared by sol-gel method,and the photocatalytic activity under ultra-violet light was evaluated by photocatalytic degradation of methyl blue.The crystallographic forms,particles size,and morphology were characterized by XRD and TEM.The results showed that the optimum heat temperature of co-doped TiO2 was 550 ℃,and the co-doped TiO2 kept anatase.The anatase crystal had the average size of 20 nm.The ... 相似文献
16.
A series of SiO 2/ β-Zn 4Sb 3 core-shell composite particles with 3, 6, 9, and 12 nm of SiO 2 shell in thickness were prepared by coating β-Zn 4Sb 3 microparticles with SiO 2 nanoparticles formed by hydrolyzing the tetraethoxysilane in alcohol-alkali-water solution. SiO 2/ β-Zn 4Sb 3 nanocomposite thermoelectric materials were fabricated with these core-shell composite particles by spark plasma sintering
(SPS) method. Microstructure, phase composition, and thermoelectric properties of SiO 2/ β-Zn 4Sb 3 nanocomposite thermoelectric materials were systemically investigated. The results show that β-Zn 4Sb 3 microparticles are uniformly coated by SiO 2 nanoparticles, and no any phase transformation reaction takes place during SPS process. The electrical and thermal conductivity
gradually decreases, and the Seebeck coefficient increases compared to that of β-Zn 4Sb 3 bulk material, but the increment of Seebeck coefficient in high temperature range remarkably increases. The thermal conductivity
of SiO 2/ β-Zn 4Sb 3 nanocomposite material with 12 nm of SiO 2 shell is the lowest and only 0.56 W·m −1·K −1 at 460 K. As a result, the ZT value of the SiO 2/ β-Zn 4Sb 3 nanocomposite material reaches 0.87 at 700 K and increases by 30%. 相似文献
17.
SMnZn1-xFe2O4 (x=1,0.9,0.8,0.7,0.6,0.5,0.25,0) nanoparticles were prepared by ball-milling hydrothermal and investigated by X-ray diffraction, DTG and TEM, Nanocrystallite grain size was determined by X-ray linewidth to be from 63 (A) to 274 (A). The thermal properties indicate absorbed water still remain at low temperature, crystalline ware will be decomposed from 230 ℃ to 260 ℃, partial Mn2 will be oxidized near 730 ℃. TEM shows the ferrite particles pocess a spherical morphology and uniform nanosize. 相似文献
18.
This study is an attempt to establish a suitable speed–density functional relationship for heterogeneous traffic on urban arterials. The model must reproduce the traffic behaviour on traffic stream and satisfy all static and dynamic properties of speed–flow–density relationships. As a first attempt for Indian traffic condition, two behavioural parameters, namely the kinematic wave speed at jam (Cj) and a proposed saturation flow (λ), are estimated using empirical observations. The parameter Cj is estimated by developing a relationship between driver reaction time and vehicle position in the queue at the signalised intersection. Functional parameters are estimated using Levenberg–Marquardt algorithm implemented in the R statistical software. Numerical measures such as root mean squared error, average relative error and cumulative residual plots are used for assessing models fitness. We set out several static and dynamic properties of the flow–speed–density relationships to evaluate the models, and these properties equally hold good for both homogenous and heterogeneous traffic states. From the numerical analysis, it is found that very few models replicate empirical speed–density data traffic behaviour. However, none of the existing functional forms satisfy all the properties. To overcome the shortcomings, we proposed two new speed–density functional forms. The uniqueness of these models is that they satisfy both numerical accuracy and the properties of fundamental diagram. These new forms would certainly improve the modelling accuracy, especially in dynamic traffic studies when coupling with dynamic speed equations. 相似文献
19.
PEO-LiClO4-TiO2 composite polymer electrolyte films were prepared. TiO2 was formed directly in matrix by hydrolysis and condensation reaction of tetrabutyl titanate. The crystallinity, morphology and ionic conductivity of composite polymer electrolyte films were examined by differential scanning calorimetry, scanning electron microscopy, atom force microscopy and alternating current impedance spectroscopy, respectively. The glass transition temperature and the crystallinity of composite polymer electrolytes are decreased compared with those of PEO-LiClO4 polymer electrolyte film. The results show that TiO2 particles are uniformly dispersed in PEO-LiClO4-5%TiO2 composite polymer electrolyte film. The maximal conductivity of 5.5×10^-5 S/cm at 20℃ of PEO-LiClO4-TiO2 film is obtained at 5% mass fraction of TiO2. 相似文献
20.
Lithium metal anodes (LMAs) are considered as the promising alternatives for next-generation high energy density batteries, but are still hampered by the severe growth of uncontrollable lithium dendrites. The growth of lithium dendrites induces poor cycling lifespan and serious safety concerns, dragging lithium metal batteries out of practical applications. We designed a bilayer carbon-based structure covered with Co/C nanosheets and vertical graphene sheets (VGS). The enormous specific surface area and uniformly distributed Co nanoparticles of the CC@Co/C-VGS host are derived from its unique design, which can reduce local current density and nucleation overpotential, resulting in a dendrite-free morphology and exceptional cycling stability. Symmetric cells exhibit over 400 cycles (800 h) at a high current density/capacity of 10 mA cm?2/10 mA h cm?2. Full cells using LiFePO4 as the cathode have an enhanced rate capability and a prolonged lifespan, reaching 90 mA h g?1 after 1000 cycles at 2 C with 73.5% capacity retention. This unique design sheds light on developing high-performance LMAs. 相似文献
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