共查询到20条相似文献,搜索用时 31 毫秒
1.
TERRENCE B. LINDEMER ALFRED L. SUTTON Jr. 《Journal of the American Ceramic Society》1988,71(7):553-561
The extensive nonstoichiometry in the 〈U1– z Gd z O2± x 〉 † phase was investigated experimentally and the data are represented by a chemical thermodynamic method. The experimental ranges of temperature, oxygen potential, and z were 1273 to 1773 K, 0 to −600 kJ/mol, and 0.1 to 0.8, respectively. For hypostoichiometry, ideal-solution thermodynamics for the equilibrium 3Gd4/3 O2 + 4UO2 + (O2 ) = 6U2/3 Gd2/3 O8/3 were used to represent the experimental data, while for hyperstoichiometry a nonideal solution was used for the equilibrium 4UO2 + (O2 ) = 2U2 O5 . The wide ranges in x and z led to an improvement of the previous analysis of literature data and led to partial molal Gibbs free energy values that are useful for any thermodynamic calculation involving the phase. 相似文献
2.
Terrence B. Lindemer John F. Hunley Jacques E. Gates Alfred L. Sutton Jr. Jorulf Brynestad Camden R. Hubbard Patrick K. Gallagher 《Journal of the American Ceramic Society》1989,72(10):1775-1788
The dependence of the nonstoichiometry of 〈YBa2 Cu3 O7−x 〉 (solid) has been studied over 5 orders of magnitude in oxygen pressure and from 573 to 1173 K. Hydrogen-reduction methods for determining the absolute oxygen to-metal ratio were developed. The resulting data were used to derive a chemical thermodynamic representation of the experimental variables. The data were used to derive a chemical thermodynamic representaltion of the experimental variables. The data were also compared with several other investigations to indentify the selfconsistent sets of data. The present data and thermodynamic data from the literature were correlated on an Ellingham diagram. 相似文献
3.
Single crystals of Al2 O3 containing 0.5 wt% Fe were exposed to low p o2 atmospheres at 1500°C to produce precipitate phases. Analytical TEM identified the precipitate phases as spinel (hercynite) and iron, with the following orientation relationships: 〈001〉Fe ‖〈2 2 01〉s with {1 1 0}Fe ‖{11 2 0}s , 〈111〉Fe ‖〈10 1 0〉s with {0 1 1}Fe ‖ (0001)s , and 〈1 1 0〉H ‖〈01 1 0〉s with {111}H ‖ (0001)s . The three phase fields observed — (Fe, Al)2 O3 , spinel +α-Al2 O3 , and iron +αAl2 O3 — are in accordance with phase stability diagrams. Precipitation kinetics indicate that oxygen is mobile in the reduced region of the crystal. 相似文献
4.
Michael Rozumek Peter Majewski Heike Schluckwerder Fritz Aldinger Klaus Künstler Gerhard Tomandl 《Journal of the American Ceramic Society》2004,87(9):1795-1798
Ceramics of the melilite-type compound La1+ x Sr1− x Ga3 O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x =−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four-point direct-current conductivity measurements and electromotive force measurements. La1+ x Sr1− x Ga3 O7−δ samples exhibited a p -type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C. 相似文献
5.
Michael Rozumek Peter Majewski Linda Sauter Fritz Aldinger 《Journal of the American Ceramic Society》2004,87(4):662-669
Ceramic samples of the melilite-type La1+ x Sr1– x Ga3 O7–δ ( x =−0.15 to 0.60) compound were prepared by conventional ceramic processing. Sintering characteristics and microstructural evolution were studied. A phase diagram study was performed to establish the solid solubility limits as a function of the La:Sr ratio. Structural investigations of the Dalton composition as well as strontium- and lanthanum-rich samples entailed X-ray, neutron, and electron diffraction techniques at ambient and elevated temperatures. The homogeneity region was remarkably broad ( x =−0.15 to 0.60) with no changes in space group observed. A small shrinkage of the unit cell was found with increased lanthanum content. Phase transitions at ambient and intermediate temperatures did not occur. 相似文献
6.
Oxygen potentials for U0.85 Zr0.15 O2+x solid solutions with the fluorite structure (prepared at 1500°C) were measured at 1500°C by a thermogravimetric technique. The oxygen potentials were 12 to 20 kJ/mol lower than those of pure UO2+x at a given oxygen-to-metal ratio; they cannot be represented as a function of mean uranium valence . 相似文献
7.
The cermet fuel (U3 O8 dispersed in Al) being considered for use in the Savannah River Site Reactors is thermodynamically unstable because of the potential for an exothermic metallothermic reduction reaction. This paper describes work performed to quantify the extent of reaction during powder metallurgy (P/M) processing of the U3 O8 —Al cermet fuel, and to determine the effect of partial reduction to U4 O9 on the metallothermic reduction reaction. During the fabrication of the U3 O8 —Al cermet fuel by the P/M technique, a significant portion of the U3 O8 is reduced to U4 O9 . The reaction between U4 O9 and Al is also exothermic; however, the maximum heat released by the reaction is substantially less than that released for the U3 O8 —Al reaction, approximately 335 J (80 cal) per gram of oxide reacted compared to 940 J (225 cal). Metallothermic reduction reactions for U3 O8 /U4 O9 /Al mixtures do not occur at the normal reactor operating temperature, ∼ 370 K (∼ 100°C) or at temperatures below the melting point of aluminum, 930 K (660°C). 相似文献
8.
The thermodynamic data for the Y2 O3 –BaO–Cu2 O–CuO quaternary system were optimized from measured thermodynamic data. A two-sublattice model for ionic solution was used to express the Gibbs free energy of the liquid phase, and a two-sublattice regular solution model was used for the nonstoichiometric YBa2 Cu3 O6+δ superconducting compound. The optimized thermodynamic data were used to calculate the phase diagrams of the Cu2 O–CuO binary system and the CuO x –Y2 Cu2 O5 and CuO x –BaCuO2 quasi-binary systems. The results were in good agreement with reported measured data. The liquidus projection and isothermal and vertical sections of the Y2 O3 –BaO-CuO x quasi-ternary system were calculated. The effect of oxygen pressure on some reaction temperatures was predicted by calculating them at various oxygen pressures, and the oxygen contents (6 +δ) in YBa2 Cu3 O6+δ were calculated at various temperatures and oxygen pressures. The results were compared with experimental data. 相似文献
9.
Tomoya Sato Yusuke Yoshida Toshio Kimura 《Journal of the American Ceramic Society》2007,90(9):3005-3008
Dense, highly 〈110〉-textured BaTiO3 ceramics were prepared by the reactive-templated grain growth method. Needlelike TiO2 (rutile) particles with their needle axis parallel to 〈001〉 were used as reactive template particles. Slurry containing an equimolar mixture of TiO2 and BaCO3 was tape cast to form a green compact, in which TiO2 particles were aligned with their needle axis parallel to the casting direction. Calcination of the green compact changed TiO2 particles into BaTiO3 grains with their 〈110〉 direction parallel to the casting direction, for which the topotaxial relation of was responsible. Sintering yielded a dense, highly textured BaTiO3 compact. 相似文献
10.
Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba 6−3 x Sm8+2 x Ti18 O54 solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τf ) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba6−3 x Sm8+2 x (Ti1− z Snz )18 O54 -based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm2 O4 and Sm2 (Sn,Ti)2 O7 appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τf . Excellent microwave dielectric properties were achieved in Ba6−3 x (Sm1− y Nd y )8+2 x (Ti1− z Sn z )18 O54 ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τf =+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value. 相似文献
11.
Girish Harshé Dinesh Agrawal Santosh Limaye 《Journal of the American Ceramic Society》1994,77(7):1965-1968
The NaZr2 P3 O12 (NZP) family of materials is attracting increasing attention due to its low-thermal-expansion behavior. The system Ba1+x Zr4 P6–2x Si2x O24 (0 ≤ x ≤ 1), belonging to the NZP family, shows ultralow thermal expansion over a wide temperature range. It also shows anisotropy in its lattice thermal expansion. This causes microcracking as the sintered specimens are cooled, which results in degradation of the mechanical properties. In this work, the chemical stability, strength, and Young's modulus of Ba1+x Zr4 P6–2x O24 ( X = 0.25 and 0.5) ceramics at high temperatures have been determined. An attempt has been made to correlate the mechanical properties to the thermal expansion anisotropy. 相似文献
12.
Hiroaki Takeda Masataka Ohgaki Takashi Kizuki Kazuaki Hashimoto Yoshitomo Toda Shigekazu Udagawa Kimihiro Yamashita 《Journal of the American Ceramic Society》2000,83(11):2884-2886
The formation process of Ba2 La8 (SiO4 )6 O2 was clarified using thermogravimetry–differential thermal analysis (TG-DTA) and a high-temperature powder X-ray diffraction (HT-XRD) method. Phase changes identified from the HT-XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG-DTA curves. Raw material with the composition Ba2 La8 (SiO4 )6 O2 was completely reacted at 1400°C and produced only an apatite-type compound without a secondary phase. Moreover, the synthesis of Ba2+ x La8− x (SiO4 )6 O2−δ crystals with x = 0–2 was attempted using a solid-state reaction. 相似文献
13.
The compositional range for glass formation below 1600°C in the Sm2 O3 ─Al2 O3 ─SiO2 system is (9–25)Sm2 O3 ─(10–35)Al2 O3 ─(40–75)SiO2 (mol%). Selected properties of the Sm2 O3 ─Al2 O3 ─SiO2 (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm2 O3 content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm2 O3 content and with increasing temperature to 70°C. The transformation temperature ( T g ) and dilatometric softening temperature ( T d ) of the SmAS glasses exceeded 800° and 850°C, respectively. 相似文献
14.
Microhardness anisotropy profiles for the (100) and (111) planes of single-crystal stoichiometric MgAl2 O., spinel were determined at room temperaturé. The (100) microhardness profile has ahardness maximum in tiie [001] and a minimum in the [O11], which supports the previous suggestion that the primary slip system is the {111}〈11¯0〉. The microhardness of the (111) plane is independent of indenter orientation, also consistent, with a {111}〈11¯0〉 primary slip system. It is concluded that these microhardness profiles are in accord with other experimental observations that the {111}〈11¯0〉 is the primary slip system in stoichiometric MgAl2 O4 spinel. 相似文献
15.
Ni Qin Marjeta Maek Krmanc Danilo Suvorov 《Journal of the American Ceramic Society》2008,91(8):2593-2600
K x Ba1− x Ga2− x Ge2+ x O8 (0.6≤ x ≤1) polycrystalline ceramics are potential materials for glass-free low-temperature cofired ceramics (LTCC) substrates. We have made a comprehensive study of the kinetics of the monoclinic-to-monoclinic P 21 / a ⇔ C 2/ m phase transition. The low-temperature-stable P 21 / a phase with a high Q × f value was synthesized using a subsolidus method and was well sintered at the LTCC temperature with a H3 BO3 additive. A good combination of low sintering temperature (910°–920°C), high Q × f values (96 700–104 500 GHz), low permittivities (5.6–6.0), and a small temperature coefficient of resonant frequency (∼−20 ppm/°C) was obtained for ceramics with x =0.67 and 0.9 and with 0.1 wt% of H3 BO3 . 相似文献
16.
A. DOMINGUEZ-RODRIGUEZ V. LANTERI A. H. HEUER 《Journal of the American Ceramic Society》1986,69(3):285-287
Precipitation hardening was observed in two-phase (cubic plus tetragonal) Y2 O3 -partia1ly-stabilized ZrO2 single crystals deformed at 1400°C. Slip was activated on (001) 〈110〉, primarily in Luders bands. 相似文献
17.
Yi Li Xiang Ming Chen † Ni Qin YaoWu Zeng 《Journal of the American Ceramic Society》2005,88(2):481-484
Tin (Sn) substitution for titanium (Ti) was investigated in Ba6−3 x Nd8+2 x Ti18 O54 ( x =1/2, 2/3, and 3/4) ceramics. A small amount ( z <0.1) of Sn substitution resulted in Ba6−3 x Nd8+2 x (Ti1− z Sn z )18 O54 solid solutions, and some secondary phases were observed with increasing Sn content. A small amount of Sn substitution improved the Q f value significantly, while, due to the formation of secondary phases, the Q f value degraded sharply for larger Sn content. The relative dielectric constant (ɛr ) decreased with increasing Sn-content, while the temperature coefficient of resonant frequency (τf ) generally decreased, although an obvious fluctuation was observed for x =3/4. 相似文献
18.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
19.
Alessandro Martucci Sabrina Sartori Alessandro Muffato Lidia Armelao Elisabetta Di Bartolomeo Enrico Traversa Massimo Guglielmi 《Journal of the American Ceramic Society》2003,86(11):1965-1968
Na2 O· x Al2 O3 ( x = 9, 11)films have been obtained by sol–gel method. Crystallization processes during heat treatments have been investigated by X–ray diffraction analysis. A metastable phase with the mullite structure, λ–Na2 O· x Al2 O3 , has been observed starting from 800°C. Films remained stable after a heat treatment at 1000°C for 250 h. Impedance spectroscopy measurements showed that the films of λ-Na2 O· x Al2 O3 possess a large three–dimensional ionic conductivity at 400°C. 相似文献
20.
The interface structures of calcium–alumino–silicate (CAS) glassy intergranular films (IGFs) formed between the combined basal and prism orientations of α-Al2 O3 crystals were studied using molecular dynamics simulations. Preferential adsorption of specific ions from the IGFs to the contacting surfaces of the alumina crystals was observed. This segregation of specific ions to the interface enables formation of localized, ordered structures between the IGF and the crystal. However, the segregation behavior of the ions is anisotropic, depending on the orientation of the α-Al2 O3 crystals. The results show that the enrichment of Ca atoms at the basal interface inhibits growth in the 〈0001〉 direction. However, at the (11 2 0) prism plane, Ca ions have little effect on the epitaxial adsorption of Al and O ions from the IGF onto the (11 2 0) surface. Increasing alumina concentration in the glassy IGF enhances adsorption of Al ions onto the prism surface, with little effect on the basal surface, indicating the tendency of growth in the 〈11 2 0〉 direction on the prism plane, but limited growth on the basal plane. These results are consistent with the experimental data regarding anisotropic grain growth in alumina sintered in the presence of CAS IGFs. 相似文献