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1.
Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa2Ti3O10 (BLT) was produced by solid-state reaction of BaCO3, TiO2 and La2O3 at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10− 5–12.5 × 10− 6 K− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications. 相似文献
2.
SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba3Si4C2. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba3Si4C2 has the Ba3Ge4C2 type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO3), and contains isolated anion groups of slightly compressed [Si4]4− tetrahedra and [C2]2− dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10−2–7 × 10−3 S cm−1 in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K−1. 相似文献
3.
New pyrophosphate Sn0.9Sc0.1(P2O7)1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn0.9Sc0.1(P2O7)1−δ have been investigated. XRD analysis indicates that Sn0.9Sc0.1(P2O7)1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn0.9Sc0.1(P2O7)1−δ in open air is 2.35 × 10−6 and 2.82 × 10−9 S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10−7 S/cm at 400 °C) than in open air indicating some proton conduction. SnP2O7 and Sn0.92In0.08(P2O7)1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP2O7-based materials might be related to the synthetic history. The possible conduction mechanism of SnP2O7-based materials has been discussed in detail. 相似文献
4.
The microwave dielectric properties and the microstructures of ZnO-doped La(Co1/2Ti1/2)O3 ceramics prepared by conventional solid-state route have been studied. Doped with ZnO (up to 0.75 wt%) can effectively promote the densification of La(Co1/2Ti1/2)O3 ceramics with low sintering temperature. At 1320 °C, La(Co1/2Ti1/2)O3 ceramics with 0.75 wt% ZnO addition possesses a dielectric constant (r) of 30.2, a Q × f value of 73,000 GHz (at 8 GHz) and a temperature coefficient of resonant frequency (τf) of −35 ppm/°C. 相似文献
5.
The thermal expansion of U2Fe13.6Si3.4 and Lu2Fe13.6Si3.4 has been measured by X-ray powder diffraction. Both compounds exhibit a large spontaneous magnetostriction. In the ground state, the volume effect 11.2 × 10−3 in U2Fe13.6Si3.4 consists of almost equal contributions from the Fe–Fe and U–Fe exchange interactions (6 × 10−3 and 5 × 10−3, respectively). In Lu2Fe13.6Si3.4, the volume effect is 8.9 × 10−3. 相似文献
6.
Spherical Li3V2(PO4)3 was synthesized by using N2H4 as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li3V2(PO4)3 has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li3V2(PO4)3 were 123 mAh g−1 in the voltage range of 3.0–4.3 V and 132 mAh g−1 in the voltage range of 3.0–4.8 V. 相似文献
7.
Wen Wu Ying Wang Xianyou Wang Quanqi Chen Xin Wang Shunyi Yang Xiuming Liu Jia Guo Zhenhua Yang 《Journal of Alloys and Compounds》2009,486(1-2):93-96
Orthorhombic structure FeF3 was synthesized by a liquid-phase method using FeCl3, NaOH and HF solution as starting materials, and the FeF3/V2O5 composites were prepared by milling the mixture of as-prepared FeF3 and the conductive V2O5 powder. The properties of FeF3/V2O5 composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge and cyclic voltammetry measurements. Results showed that the FeF3/V2O5 composites can be used as cathode material for lithium-ion battery. Electrochemical measurements in a voltage range of 2.0–4.5 V reveal that the addition of conductive V2O5 improves significantly the electrochemical performance of FeF3, and the FeF3/V2O5 composite prepared by milling for 3 h exhibits high discharge capacity and good cycle performance, and its discharge capacity maintains about 209 mAh g−1 at 0.1 C (23.7 mA g−1) after 30 cycles. 相似文献
8.
Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation for Ge22.5Te77.5 glass. The kinetic parameters of glassy Ge22.5Te77.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (1–50 K/min). A strong heating rate dependence of the activation energy of crystallization was observed. The analysis of the present data shows that the activation energy of crystallization is not constant but varies with the degree of crystallization and hence with temperature. The crystallization mechanisms examined using the local Avrami exponents indicate that one mechanism (two-dimensional growth) is responsible for the crystallization process for heating rates 1–30 K/min and two mechanisms (one- and two-dimensional growth) are working simultaneously during the amorphous–crystalline transformation of the Ge22.5Te77.5 glass for a heating rate 50 K/min. The reaction model that may describe crystallization process of the Ge22.5Te77.5 glass is Avrami–Erofeev model (g(α) = [−ln(1 − α)]1/n) with n = 2 for the heating range 1–30 K/min and n = 1.5 at a heating rate 50 K/min for the whole range of conversion crystallization fraction (α = 0.05–0.95). A good agreement between the experimental and the reconstructed (α − T) curves has been achieved. The transformation from amorphous to crystalline phase in glassy Ge22.5Te77.5 demonstrates complex multi-step involving several processes. 相似文献
9.
Yih-Chien Chen Shi-Li Yao Ren-Jie Tsai Kuei-Chien Chen 《Journal of Alloys and Compounds》2009,486(1-2):410-414
In this paper, the dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics at microwave frequency have been studied. The diffraction peaks of Ca(1−x)MgxLa4Ti5O17 ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca0.99Mg0.01La4Ti5O17 ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm3 can be obtained for Ca0.99Mg0.01La4Ti5O17 ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (r) and quality factor (Q × f) of Ca0.99Mg0.01La4Ti5O17 ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τf) of −9.6 ppm/°C can be obtained for Ca0.99Mg0.01La4Ti5O17 ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved. 相似文献
10.
Xuean Chen Ming Li Xinan Chang Hegui Zang Weiqiang Xiao 《Journal of Alloys and Compounds》2008,464(1-2):332-336
A new calcium borate, CaB6O10, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB6O10 crystallizes in the monoclinic space group P21/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B3O7]5− triborate groups are bridged by one oxygen atom to form a [B6O13]8− group that is further condensed into a 3D network, with the shorthand notation 6: ∞3[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca2+ cations reside. The IR spectrum further confirms the presence of both BO3 and BO4 groups. 相似文献
11.
R.V. Vovk M.A. Obolenskii A.V. Bondarenko I.L. Goulatis A.V. Samoilov A. Chroneos V.M. Pinto Simoes 《Journal of Alloys and Compounds》2008,464(1-2):58-66
The temperature dependence of the transport anisotropy of ReBa2Cu3O7−δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δc increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa2Cu3O7−δ, the temperature dependence of the anisotropy of the resistivity ρc/ρab(T) for the HoBa2Cu3O7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity. 相似文献
12.
The material characteristics of W2N layer and electrical properties of W/W2N/SiO2/Si metal–oxide–semiconductor (MOS) capacitors with different W2N thickness upon annealing in N2 + H2 ambient at 500 °C for 20 min are investigated. The nitrogen concentration of W2N for the W/W2N stack with thin W2N layer (≤10 nm) is lower than that for the W/W2N stack with thick W2N layer (≥15 nm). In addition, the crystallinity of W2N in the W/W2N (15 nm) stack is better than that in the W/W2N (10 nm) stack. For all capacitors, the oxide charges decrease significantly after annealing and the amount of oxide charges is independent of the W2N thickness. However, the work function (Φm) of the W/W2N (≤10 nm) stack (4.6 eV) is smaller than that of W/W2N (15 nm) stack (5.0 eV). The Φm of W/W2N (15 nm) stack is close to that of W2N single layer. After annealing, the Φm of W/W2N (15 nm) stack and W2N single layer decrease, especially for the W2N single layer. But for the W/W2N (≤10 nm) stack, the Φm increases after annealing. 相似文献
13.
V.I. Dybkov V.G. Khoruzha V.R. Sidorko K.A. Meleshevich A.V. Samelyuk D.C. Berry K. Barmak 《Journal of Alloys and Compounds》2008,460(1-2):337-352
The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type cs = 4.94 × 102 exp(−39500/RT)% for the former alloy and cs = 4.19 × 102 exp(−40200/RT)% for the latter, where R is in J mol−1 K−1 (8.314 J mol−1 K−1) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10−5 m s−1 at disc rotational speeds of 6.45–82.4 rad s−1. Appropriate diffusion coefficients vary from 0.16 × 10−9 to 2.02 × 10−9 m2 s−1. With both alloys, the Ni3Sn4 intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni3Sn4 layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%. 相似文献
14.
C.F. Shih K.T. Hung C.Y. Hsiao S.C. Shu W.M. Li 《Journal of Alloys and Compounds》2009,480(2):541-546
This work elucidates the properties of Al/HfO2/GaN metal-oxide-semiconductor capacitors using reactively sputtered HfO2 as a gate dielectric. The influence of GaN surface treatments and the post-annealing of HfO2 films on the leakage current, flat-band voltage, interface trap densities, dielectric constants, and effective oxide charges of the GaN MOS capacitors are presented. The Ga oxynitride on the surface of GaN was effectively removed by chemical solutions that also slightly reduced the dielectric constant, slightly increased the flat-band voltage, eliminated the hysteresis of the capacitance–voltage measurement, and yielded a similar leakage to that without surface treatment. A highest dielectric constant of HfO2 (17) was obtained when the sample was annealed at 600 °C for 20 min, while the lowest interface trap density (5.3 × 1011 cm−2) was obtained when the sample was annealed at 800 °C for 40 min. The leakage mechanism was well fitted by the Schottky emission and Frenkel–Poole emission models at a lower and higher electric field. 相似文献
15.
Sichun Zhang Haiping Xia Jinhao Wang Yuepin Zhang 《Journal of Alloys and Compounds》2008,463(1-2):446-452
The near-stoichiometric LiNbO3 (SLN) single crystals doped Mn2+, Co2+ and Ni2+ in 0.5 mol% concentration in the raw compositions were grown by the Bridgman method under the conditions of taking K2O as flux, a high temperature gradient (90–100 °C/cm) for solid–liquid interface. The XRD, absorption spectra, excitation spectra and emission spectra have been carried out. From the absorption edges of Mn2+, Co2+ and Ni2+-doped SLN crystals, the molar ratio of [Li+]/[Nb5+] are estimated to be about 0.977. The absorption spectra of Mn2+:SLN have shown a broad absorption band centered at 571 nm (6A1g(6S) → 4T1g(4G)), three absorption peaks at 520, 549 and 612 nm (overlapping of the 4T1(F)–4A2(F), 4T1(F)–4T1(P)), and a wide absorption band at 1400 nm (4T1(F) → 4T2(F)) of Co2+:SLN, Ni2+:SLN, and five absorption peaks at 381 nm (3A2g(F) → 3T1g(P)), 733 nm (3A2g(F) → 3T1g(F)), 1280 nm (3A2g(F) → 3T2g(F)), 430 nm (3A2g(F) → 1T2g(D)), and 840 nm (3A2g(F) → 1E(D)) of Ni2+:SLN were observed. A red emission at 612 nm (4T1g(4G) → 6A1g(6S)) for Mn2+:SLN, a red emission at 775 nm (4T1(P) → 4T1(F)) for Co2+:SLN, and a green emission at 577 nm (1T2g(D) → 3A2g(F)) and a red emission at 820 nm (1T2g(D) → 3T2g(F)) for Ni2+:SLN were observed under excited by 416, 520 and 550 nm lights, respectively. The concentration distribution of Mn2+, Co2+and Ni2+ ion in SLN crystals was investigated primarily from the absorption and emission spectra for various parts. The effective distribution coefficient for Mn2+ was less than 1. While, for Co2+ and Ni2+ were more than 1. 相似文献
16.
T. Satyanarayana I.V. Kityk K. Ozga M. Piasecki P. Bragiel M.G. Brik V. Ravi Kumar A.H. Reshak N. Veeraiah 《Journal of Alloys and Compounds》2009,482(1-2):283-297
PbO–Sb2O3–B2O3 glasses mixed with different concentrations of TiO2 (ranging from 0 to 1.5 mol.%) were synthesized. The samples are characterized by X-ray diffraction, scanning electron microscopy and DSC techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra, magnetic susceptibility, photo-induced birefringence (PIB) and dielectric properties (constant ′, loss tan δ, a.c. conductivity σac over a wide range of frequency and temperature) of these glass–ceramics have been explored. The analysis of these results indicated that Ti ion surrounding ligands play principal role in the observed PIB and the sample crystallized with 0.8 mol.% of TiO2 is the most suitable for the applications in non-linear optical devices. 相似文献
17.
Wei Li Limei Zhou Yali Li Jun Jiang Gaojie Xu 《Journal of Alloys and Compounds》2009,486(1-2):335-337
A series of samples have been fabricated through vacuum melting method followed by hot-pressing for Zn4Sb3−xTex (x = 0.02–0.08), XRD patterns indicated that all the samples were single-phased β-Zn4Sb3. Electrical conductivity and Seebeck coefficient were evaluated in the temperature range of 300–700 K, showing p-type conduction. The thermoelectric figure of merit (ZT) was increased with the increase of Te content. ZT values of 0.8 and 1.0 were obtained at 673 K for Zn4.08Sb3 and Zn4Sb2.92Te0.08, respectively. 相似文献
18.
Chia-Che Chuang Hsing-I Hsiang Jenn Shyong Hwang Tai Shen Wang 《Journal of Alloys and Compounds》2009,470(1-2):387-392
Al2O3-Ce0.5Zr0.5O2 catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al3+ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce0.5Zr0.5O2 powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al2O3 formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m2/g) was larger than that of ACZ-M (62.1 m2/g) and Ce0.5Zr0.5O2 (17.1 m2/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al2O3, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al2O3. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce0.5Zr0.5O2 powders. 相似文献
19.
M.D. Dramianin B. Viana
. Andri V. Djokovi A.S. Luyt 《Journal of Alloys and Compounds》2008,464(1-2):357-360
In this paper, a novel route for the synthesis of Y2SiO5 (YSO) nanoparticles doped with Eu3+ ions, based on the use of a hydrothermally prepared silica sol as a chemical precursor and nanostructuring template, is presented. X-ray powder diffraction revealed crystallization of nanoparticles in an X1 monoclinic structural type (P21/c) with well pronounced diffraction peaks and without any sign of additional phases. Transmission electron microscopy showed that the particle diameter was around 40 nm and that the particles formed loose aggregates. The synthesized materials exhibited characteristic luminescence emission of the trivalent europium ion, with the strongest emission (5D0 → 7F2 transition) at 611.5 nm and a corresponding lifetime of 1.8 ms. Two site occupancy, as expected, were demonstrated. 相似文献
20.
Surface resolidification experiments using a high power CO2-laser have been performed on an Al2O3ZrO2 containing 36.8 at.% ZrO2 eutectic alloy at beam velocities between 0.3 and 8 mm·s−1. The local growth rate has been measured by observation of the orientation of the microstructure using scanning electron microscopy. In the whole range of velocities, the structure is essentially a regular lamellar eutectic and the value of the growth productλ2V was found to be ≈ 9.6·10−17 m3·s−1. The measured eutectic spacings were compared with Jackson and Hunt model. Using thermophysical properties from the literature, the measured spacings were more than four times larger than the calculated ones. Assuming all parameters of the growth relationship except the diffusion coefficient to be of the right order of magnitude or to have a negligible influence, agreement is found when using a larger liquid diffusion coefficient,DL≈5·10−10m2·s−1. 相似文献