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1.
(1 − x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 (CSLNT) ceramic powder was prepared by a liquid mixing method using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. TG, DTA, XRD and TEM characterized the precursors and derived oxide powders. When x = 0.3, perovskite CSLNT was synthesized at 1000 °C for 3 h in air. The CSLNT (x = 0.3) ceramics sintered at 1200 °C for 3 h show excellent microwave dielectric properties of ?r = 99, Qf = 6200 GHz and τf = 9 × 10−6 °C−1. 相似文献
2.
Helena Nilsson Sylvain Galland Per Tomas Larsson E. Kristofer Gamstedt Takashi Nishino Lars A. Berglund Tommy Iversen 《Composites Science and Technology》2010
All-cellulose composites are commonly prepared using cellulose solvents. In this study, moldable all-cellulose I wood fiber materials of high cellulose purity (97%) were successfully compression molded. Water is the only processing aid. The material is interesting as a “green” biocomposite for industrial applications. Dissolving wood fiber pulps (Eucalyptus hardwood and conifer softwood) are used and the influence of pulp origin, beating and pressing temperature (20–180 °C) on supramolecular cellulose nanostructure is studied by solid state CP/MAS 13C NMR. Average molar mass is determined by SEC to assess process degradation effects. Mechanical properties are determined in tensile tests. High-density composites were obtained with a Young’s modulus of up to 13 GPa. In addition, nanoscale cellulose fibril aggregation was confirmed due to processing, and resulted in a less moisture sensitive material. 相似文献
3.
The Cox–Krenchel micromechanical model was applied to give predictions for the tensile moduli of isotropic and oriented wood polymer composites (WPC). The oriented WPC were produced by the Leeds die-drawing process using polypropylene filled with softwood and hardwood powders. The wood particles were extracted from the composites to determine their density and aspect ratio by dissolving in hot decalin. To measure particle shape and size, image analysis was employed. These experimental parameters were then introduced to the Cox–Krenchel model which was found to give prediction of tensile modulus in very good agreement with the experimental values. 相似文献
4.
Toshihiro Isobe Takuya Umezome Yoshikazu Kameshima Akira Nakajima Kiyoshi Okada 《Materials Research Bulletin》2009,44(11):2045-3464
Using solid-state reaction method, Zr2WP2O12 powder was synthesized for this study. The optimum heating condition was 1200 °C for 4 h. The obtained powder was compacted and sintered. The relative density of the Zr2WP2O12 ceramics with no sintering additive was 60%. That of samples sintered with more than 0.5 mass% MgO was about 97%. The average grain size (D50), as estimated from the polished surface of a sample sintered at 1200 °C for 4 h was about 1 μm. The obtained ceramics showed a negative thermal expansion coefficient of about −3.4 × 10−6 °C−1. Young's modulus, Poisson's ratio, three-point bending strength, Vickers microhardness, and fracture toughness of the obtained ceramics were, respectively, 74 GPa, 0.25, 113 ± 13 MPa, 4.4 GPa and 2.3 MPa m1/2. 相似文献
5.
Low temperature co-fired ceramic (LTCC) is prepared by sintering a glass selected from CaO-SiO2-B2O3 system, and its sintered bodies are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the optimal sintering temperature for this glass-ceramic is 820 °C for 15 min, and the major phases of this material are CaSiO3, CaB2O4 and SiO2. The glass-ceramic possesses excellent dielectric properties: ?r = 6.5, tan δ < 2 × 10−3 at 10 MHz, temperature coefficient of dielectric constant about −51 × 10−6 °C−1 and coefficient of thermal expansion about 8 × 10−6 °C−1 at 20-400 °C. Thus, this material is supposed to be suitable for the tape casting process and be compatible with Ag electrode, which could be used as the LTCC materials for the application in wireless communications. 相似文献
6.
Claire Bonhomme Sophie Beaudet-Savignat Caroline Pirovano 《Materials Research Bulletin》2010,45(4):491-1712
In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cell (SOFC) down to about 700 °C. In this respect, materials with a high ionic conduction at intermediate temperature have to be found and the processes to elaborate fuel cells, using these new materials, have to be developed.Apatite materials (La10−xSrx(SiO4)6O2±δ) are attractive candidates for solid electrolyte working at intermediate temperature. The ceramic powder was produced by solid state reaction and was tape cast to obtain green sheets.Concerning the cathode, a perovskite oxide (La1−xSrxMn1−yCoyO3−δ) has been chosen. The perovskite powder was also shaped by tape casting with the introduction of a pore forming agent (corn-starch) to obtain the required porosity in the sintered cathode.The co-firing of the electrolyte/cathode half-cell in air at 1400 °C-2 h gives a flat sample with a dense apatite (98.2%), a 42.7% porous cathode and neither delamination nor chemical reactivity between electrolyte and cathode materials.The dimensional behaviour of the electrolyte material is stable for an oxygen partial pressure ranging from 10−10 to 0.21 atmosphere, from room temperature to 700 °C. The thermal expansion coefficients of the electrolyte and cathode materials are rather close (Δα = 2.8 × 10−6 K−1) under air. 相似文献
7.
Md. Saiful Islam Sinin Hamdan Zainal Abidin Talib Abu Saleh Ahmed Md. Rezaur Rahman 《Composites Science and Technology》2012
In this study, wood polymer nanocomposites (WPNCS) were manufactured from five Malaysian tropical wood species by vacuum-impregnation attended by in situ polymerization using phenol–formaldehyde resin and montmorillomite nanoclay. Percentage weight gain and density of wood polymer nanocomposites depended on wood species. Thermo-mechanical properties of wood samples were investigated by the dynamic mechanical thermal analysis (DMTA) over the temperature range of −100 °C to 200 °C. The intrinsic properties of the components, morphology of the system and the nature of interface between the phases were also determined through DMTA test. Storage modulus (E′) of WPNC samples exhibited significant improvement over the temperature range, in both glassy region and rubbery plateau in relation to their corresponding raw wood samples and wood polymer composites (WPCs). Furthermore, damping (loss tan δ) peaks of all wood species were lowered by PF-Nanoclay system treatment, an indication of improved surface interphase of wood. Dynamic Young’s modulus (Ed) of wood was also calculated using free–free vibration testing. A significant increment was obtained for the PF-Nanoclay impregnated WPNC samples. 相似文献
8.
The thermal expansion of ZnSe was measured by Fabry-Perot interferometry from 17 to 1080 °C during the heat-up of a seeded crystal growth experiment of ZnSe. The measured thermal expansion follows the two-step heating schedule very well. A single linear interpolation between the measured thermal expansion at 17 and 1080 °C gives a value for the thermal expansion coefficient, a as 4.95 × 10− 6 °C− 1. The estimated errors associated with a give its range of 4.60 to 4.99 × 10− 6 °C− 1. 相似文献
9.
Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO2-xAg2O-xWO3 (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO4], [TeO3]/[TeO3+1], [WO4] units. Thermal properties such as the glass transition (Tg), onset crystallization (To), thermal stability (ΔT), glass transition width (ΔTg), heat capacities in the glassy and liquid state (Cpg and Cpl), heat capacity change (ΔCp) and ratios Cpl/Cpg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO2-22.5Ag2O-22.5WO3 glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27-260 °C, the activation energy (Eact) values varied from 1.393 to 0.272 eV and for the temperature interval 170-260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10−9 to 1.47 × 10−6 S cm−1. 相似文献
10.
M.K. Suresh H. Sreemoolanadhan Annamma John P.R.S. Wariar 《Materials Research Bulletin》2010,45(7):761-3095
Nanocrystalline magnesium titanate was synthesized through an auto-ignited combustion method. The phase purity of the powder was examined using X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and Raman spectroscopy. The transmission electron microscopy study showed that the particle size of the as-prepared powder was in between 20 and 40 nm. The nanopowder could be sintered to 98% of the theoretical density at 1200 °C for 3 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant (?r) of 16.7 and loss factor (tan δ) of the order of 10−4 were obtained at 5 MHz when measured using LCR meter. The quality factor (Qu × f) 73,700 and temperature coefficient of resonant frequency (τf) −44.3 ppm/°C, at 6.5 GHz are the best reported values for sintered pellets obtained from phase pure nanocrystalline MgTiO3 powder. 相似文献
11.
S. Heitsch G. Wagner A. Rahm G. Benndorf M. Schubert M. Grundmann 《Thin solid films》2006,496(2):234-239
C-axis oriented ZnO thin films were grown on silicon (100) and (111) substrates by pulsed laser deposition. Low temperature photoluminescence spectra show besides the peaks of free excitons, of defect bound excitons, and of a donor-acceptor pair transition a new doublet at 3.328/3.332 eV. The doublet seems to originate from the columnar textured ZnO film structure. A corresponding structural dependence of the broadening parameter of the infrared dielectric functions was derived from spectroscopic ellipsometry in the spectral range from 380 to 1200 cm− 1. The wave numbers of the E1 transverse optical and A1 longitudinal optical phonon modes of the ZnO films on silicon are determined to be 406 and 573 cm− 1, respectively. These values are slightly smaller than those of single-crystalline ZnO thin films on sapphire. 相似文献
12.
Liang Fang Hui Zhang T.H Huang Richard Dronskowski 《Materials Research Bulletin》2004,39(11):1649-1654
Two new cation-deficient hexagonal perovskites Ba4LaMNb3O15 (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba4LaTiNb3O15 has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (τf) +93 ppm °C−1 at room temperature; Ba4LaSnNb3O15 has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and τf −29 ppm °C−1. 相似文献
13.
Huizhong Li Haijun WangMin Zeng Xiaopeng LiangHongting Liu 《Composites Science and Technology》2011,71(6):925-930
Compression tests of 6061/B4CP composite have been performed in the compression temperature range from 300 °C to 500 °C and the strain rate range from 0.001 s−1 to 1 s−1. The flow behavior and processing map have been investigated using the corrected data to elimination of effect of friction. The processing maps exhibited two deterministic domains, one was situated at the temperature between 300 °C and 400 °C with strain rate between 0.003 s−1 and 0.18 s−1 and the other was situated at the temperature between 425 °C and 500 °C with strain rate between 0.003 s−1 and 0.18 s−1.The estimated apparent activation energies of these two domains, were 129 kJ/mol and 149 kJ/mol, which suggested that the deformation mechanisms were controlled by cross-slip and lattice self-diffusion respectively. The optimum parameters of hot working for the experimental composite were 350 °C - 0.01 s−1 and 500 °C - 0.01 s−1. In order to exactly predict dangerous damaging mechanism under different deformation conditions exactly, Gegel’s criterion was applied to obtain processing map in the paper. The result showed that the processing map used Gegel’s criterion can be effectively to predict the material behavior of the experimental composite. 相似文献
14.
The system CoIn2S4xSe4(1−x) has been investigated by X-ray powder methods on samples quenched at 700 °C. The spinel type phase has a phase width of 1≥x>0.9. A new layered compound is formed for 0.9>x>0.45 which crystallizes with the α-FeGa2S4-type with a=392.6 pm and c=1270.3 pm (x=0.5) for the hexagonal cell. Platelike crystals of the layered phase are obtained by transport reactions with iodine in a temperature gradient 750→700 °C. The band gaps of these crystals measured by optical absorption vary from 1.2 to 1.4 eV. The electrical conductivities of the crystals are found in the order of 10−5 Ω−1 cm−1. 相似文献
15.
Rigoberto López Federico González M.E. Villafuerte-Castrejon 《Materials Research Bulletin》2011,46(1):70-5072
Potassium-sodium niobate was synthesized at 800 °C for 1 h using dried precursors in a powder form obtained by the spray drying method. Different samples were sintered from 1060 to 1120 °C for 2 h reaching a relative density as high as 96% of the theoretical value. Piezoelectric and ferroelectric properties were studied for these samples and some of the most prominent results are: kp, d31, 2Pr, and 2EC of 0.36, 39 pC/N, 29 μC/cm2 and 16.5 kV/cm, respectively, for the sample sintered at 1080 °C. The methodology presented in this study can be used to synthesize submicrometer powders. 相似文献
16.
The three-dimensional hybrid compound Ni3(C4H4N2)3(V8O23) has been synthesized by mild hydrothermal methods under autogenous pressure at 170 °C. The structure of the phase is stable until 380 °C. The removal of the pyrazine molecules from the structure induces its collapse. The IR spectrum shows the vibration modes of the pyrazine molecule and those of the [VO4]3− groups. A UV-visible spectrum shows the characteristic bands of the Ni(II) d8-high-spin cation in a slightly distorted octahedral coordination. Magnetic measurements indicate the existence of antiferromagnetic interactions that can be fitted with a chain model to give g = 2.31, J/k = −5.3, and zJ′/k = −5.5. 相似文献
17.
Chemical preparation, crystal structure, calorimetric and spectroscopic investigations (IR and RMN) are given for a new non-centrosymmetric organic-cation dihydrogen phosphate-arsenate [H2(C4H10N2)][H2(As, P)O4]2. This compound is triclinic P1 with the following unit-cell parameters: a = 7.082(2) Å, b = 7.796(1) Å, c = 12.05(3) Å, α = 95.37(2)°, β = 98.38(3)°, γ = 62.98(1)°, Z = 2, V = 586.2(1) Å3 and Dx = 1.836 g cm−3. The crystal structure has been solved and refined to R = 0.03 using 2328 independent reflections. The structure can be described as infinite (H2XO)n chains spreading parallel to the b direction. These chains are themselves interconnected by a set of NH?O hydrogen bonds generated by the organic entities, alternating with the chains. Solid-state 13C, 15N and 31P MAS NMR spectroscopies are in agreement with the X-ray structure. 相似文献
18.
Zhiwen Zhu 《Materials Research Bulletin》2010,45(11):1771-1774
SmBaCuCoO5+δ, a double-perovskite oxide, was synthesized by the modified Pechini method and developed as cathode material for proton-conducting solid oxide fuel cells. The SmBaCuCoO5+δ powders calcined at 800 °C, show the double-perovskite structure in powder XRD pattern. SmBaCuCoO5+δ has a more suitable thermal expansion coefficient than SmBaCo2O5+δ for BaCe0.7Zr0.1Y0.2O3−δ electrolyte-based solid oxide fuel cells. The single cell was tested with humidified hydrogen (∼3% H2O) as the fuel and static air as the oxidant. The performance of the cell was characterized by DC Electronic Load and AC impedance spectroscopy. The peak power densities reached 355-86 mW cm−2 in the range of 700-550 °C and the interfacial polarization resistance decreased with increasing operation temperature, from 3.1 Ω cm2 at 550 °C to 0.22 Ω cm2 at 700 °C. The high power density and low polarization demonstrate that SmBaCuCoO5+δ is a potential candidate for proton-conducting solid oxide fuel cells. 相似文献
19.
Archana Gupta 《Materials Research Bulletin》2005,40(1):67-77
Composite solid electrolytes in the system [(BaCl2)1−x:(KCl)x]1−y:(ZrO2)y were prepared following the conventional ceramic powder processing route. In the mixed matrix system prepared by melt quench technique, a nominal increase in conductivity (σ) was found in (BaCl2)0.9:(KCl)0.1. On ZrO2 particle dispersion in this mixed matrix, the maximum conductivity (∼90 times that of base matrix value) was found to occur with 50 m/o of ZrO2. Conductivity increases monotonically over the temperature range from 100 to 300 °C studied and attains the value of 10 × 10−6 S cm−1 at 300 °C. The mobility (μ) of the charge carriers at room temperature was found to be 18.5 × 10−2 cm2 V−1 s−1 and the increase in μ with temperature was not very significant. The transference ionic number determination showed that the electrical conductivity of the electrolyte is predominantly due to ions. This study indicates that the conductivity is governed by mobile ion concentration. 相似文献
20.
A.V. Shlyakhtina A.V. Levchenko V.Yu. Bychkov V.A. Rassulov O.K. Karyagina 《Materials Research Bulletin》2007,42(4):742-752
The Er2+xTi2−xO7−δ (x = 0.096; 35.5 mol% Er2O3) solid solution and the stoichiometric pyrochlore-structured compound Er2Ti2O7 (x = 0; 33.3 mol% Er2O3) are characterized by X-ray diffraction (phase analysis and Rietveld method), thermal analysis and optical spectroscopy. Both oxides were synthesized by thermal sintering of co-precipitated powders. The synthesis study was performed in the temperature range 650-1690 °C. The amorphous phase exists below 700 °C. The crystallization of the ordered pyrochlore phase (P) in the range 800-1000 °C is accompanied by oxygen release. The ordered pyrochlore phase (P) exists in the range 1000−1200 °C. Heat-treatment at T ≥ 1600 °C leads to the formation of an oxide ion-conducting phase with a distorted pyrochlore structure (P2) and an ionic conductivity of about 10−3 S/cm at 740 °C. Complex impedance spectra are used to separately assess the bulk and grain-boundary conductivity of the samples. At 700 °C and oxygen pressures above 10−10 Pa, the Er2+xTi2−xO7−δ (x = 0, 0.096) samples are purely ionic conductors. 相似文献