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1.
T. D. CHIKALLA 《Journal of the American Ceramic Society》1963,46(7):323-328
The melting points of UO2 and PuO2 in a helium atmosphere were found to be 2730°× 30° C and 2280°× 30° C, respectively. With the exception of a melting maximum at the composition 90 UO2 –10 wt% PuO2 , the liquidus exhibits good continuity and agrees well with that calculated from thermodynamic data. X-ray diffraction data on melted PuO2 and UO2 -PuO2 solid solutions indicate that oxygen is evolved during melting but that no reduction to a second-phase plutonium suboxide occurs. The oxygen-plutonium atomic ratio of melted PuO2 is 1.62, so that the 2280° C temperature reported here is the result of a dissociation reaction and is considered to be a pseudo melting point. Lattice parameters of melted UO2 –PuO2 samples vary linearly with composition but are approximately 0.2% greater than anticipated because of an oxygen deficiency. 相似文献
2.
THEODORE M. BESMANN TERRENCE B. LINDEMER 《Journal of the American Ceramic Society》1983,66(11):782-785
Thermodynamic values for PUO1.5 were assessed using an improved method for estimating fef ° 1.5 and new data for S°298 1.5 . Based on the assessment, a value of ΔH°298 , 1.5 =–828 kJ/mol is recommended. Measurements of (CO) pressure over the nominal equilibrium 1.5 + 1.5 + C were performed between 1348 and 1923 K, yielding pressures between 0.644 and 11600 Pa. Second- and third-law analyses were used to obtain a value for ΔH°298 1.5 =–93.3°3.3 kJ/mol. 相似文献
3.
David H. Chmielewski Kenneth H. Sandhage 《Journal of the American Ceramic Society》1995,78(9):2504-2512
Bi2 Sr2 Ca2 Cu2 O8±δ -type compound thick films were exposed to oxygen-argon-gas mixtures (1% to 20% oxygen gas) at elevated pressures (up to 207 MPa) and temperatures (500° to 940°C) for times ranging from 5 to 96 h. At a sufficiently high oxygen fugacity and temperature, Bi2 Sr2 Ca1 Cu2 O8±δ decomposed via a solid-state reaction. Room-temperature X-ray diffractometry and electron probe microanalysis of decomposed films revealed the presence of Bi2 (Sr,Ca)2 -Cu1 O6±θ ro-type compound, Bi2 Sr2 ,Ca1 O8±δ -type compound, and CuO. Bi2 Sr2 Ca1 Cu2 O8±δ decomposition was accompanied by a modest weight gain, which was consistent with an oxidation reaction. The solid-state decomposition reaction could be reversed by heat treatment of decomposed films at 860°C in pure, flowing oxygen at ambient pressure. 相似文献
4.
DONALD R. MESSIER 《Journal of the American Ceramic Society》1968,51(12):710-713
Total vapor pressures of PuO2-x , compositions were measured gravimetrically with tungsten Knudsen cells from 2070° to 2380°K. The vapor pressure equation for the composition approximating the congruent one, PuO1.82 , is
where Pc , is the pressure if the vapor is assumed to be entirely PuO2 (g). The evaporation of PuO1.562 was univari-ant, indicating the presence of two condensed phases, and that of PuO1.62 was bivariant from 2240° to 2380°K; this result confirms that the phase boundary of the PuO2-x , phase remains at Pu1.61 at temperatures close to the liquidus. 相似文献
where P
5.
Konstantin Efimov Mirko Arnold Julia Martynczuk Armin Feldhoff 《Journal of the American Ceramic Society》2009,92(4):876-880
X-ray diffraction and transmission electron microscopy were applied to investigate a sol–gel synthetic process for the mixed oxygen ion and electron conductor La2 NiO4+δ with a K2 NiF4 structure type. The development of the La2 NiO4+δ is elucidated considering the influence of calcination temperatures and dwell times. Following the thermal decomposition of nitrate and organic precursors in an intermediate step, the lanthanum nickel oxide is obtained after a short dwell time above 750°C. This occurs by the transformation of an ultrafinely dispersed powder consisting of lanthanum oxycarbonate, lanthanum oxide, and nickel oxide. The pure La2 NiO4+δ phase was obtained by similar solid-state reactions between nanocrystalline powder particles at just 950°C. 相似文献
6.
The phase relations in the systems MgO-Y2 O3 -ZrO2 and CaO-MgO-ZrO2 were established at 1220° and 1420°C. The system MgO-Y2 O3 -ZrO2 possesses a much-larger cubic ZrO2 solid solution phase field than the system CaO-MgO-ZrO2 at both temperatures. The ordered δ phase (Zr3 Y4 O12 ) was found to be stable in the system ZrO2 -Y2 O3 at 1220°C. Two ordered phases φ1 (CaZr4 O9 ) and φ2 (Ca6 Zr19 O44 ) were stable at 1220°C in the system ZrO2 -CaO. At 1420°C no ordered phase appears in either system, in agreement with the previously determined temperature limits of the stability for the δ, φ1 , and φ2 phases. The existence of the compound Mg3 Yz O6 could not be confirmed. 相似文献
7.
Sumesh George Prabhakaran Sreekumari Anjana Vasudevan Nair Deepu Pezholil Mohanan Mailadil Thomas Sebastian 《Journal of the American Ceramic Society》2009,92(6):1244-1249
Development of a low-temperature sintered dielectric material derived from Li2 MgSiO4 (LMS) for low-temperature cofired ceramic (LTCC) application is discussed in this paper. The LMS ceramics were prepared by the solid-state ceramic route. The calcination and sintering temperatures of LMS were optimized at 850°C/4 h and 1250°C/2 h, respectively, for the best density and dielectric properties. The crystal structure and microstructure of the ceramic were studied by the X-ray diffraction and scanning electron microscopic methods. The microwave dielectric properties of the ceramic were measured by the cavity perturbation method. The LMS sintered at 1250°C/2 h had ɛr =5.1 and tan δ=5.2 × 10−4 at 8 GHz. The sintering temperature of LMS is lowered from 1250°C/2 h to 850°C/2 h by the addition of both lithium borosilicate (LBS) and lithium magnesium zinc borosilicate (LMZBS) glasses. LMS mixed with 1 wt% LBS sintered at 925°C/2 h had ɛr =5.5 and tan δ=7 × 10−5 at 8 GHz. Two weight percent LMZBS mixed with LMS sintered at 875°C/2 h had ɛr =5.9 and tan δ=6.7 × 10−5 at 8 GHz. 相似文献
8.
The effect of oxygen partial pressure, ranging from 0.001 to 1.0 atm, and temperature, in the range of 930°–955°C, on the solid-state sintering kinetics of the superconducting ceramic YBa2 Cu3 O7-δ has been studied. Isothermal compaction rates between 930° and 955°C reached a maximum at some critical PO2 (PO2 CRIT ), with decreasing rates both above and below this oxygen partial pressure. This behavior was not observed for YBa2 Cu3 O7-δ sintered at 960°C, when a liquid phase is present. The activation energy for sintering above PO2 CRIT has been estimated to be ∼190 kJ/mol, whereas below PO2 CRIT it was found to be ∼130 kJ/mol. The oxygen ion diffusion was considered to be the rate-determining step above PO2 CRIT , while it is hypothesized that lattice strain caused by the formation of oxygen ion vacancies below PO2 CRIT affected the rate of sintering. 相似文献
9.
Our analysis of the microwave dielectric properties of the δ-Bi2 O3 –Nb2 O5 solid solution (δ-BNss ) showed a continuous increase in permittivity and dielectric losses with an increasing concentration of Nb2 O5 . The only discontinuity was found for the temperature coefficient of resonant frequency, which is negative throughout the entire homogeneity range but reaches a minimum value for the sample with 20 mol% Nb2 O5 . At the same composition there is a discontinuity in the grain size of the δ-BNss ceramics. For the sample containing 25 mol% Nb2 O5 two structural modifications were observed. A single-phase tetragonal Bi3 NbO7 , in the literature referred to as a Type-III phase, is formed in a very narrow temperature range from 850° to 880°C. A synthesis performed below or above this temperature range resulted in the formation of the end member of the δ-BNss homogeneity range. Compared with the δ-BNss the Bi3 NbO7 ceramics exhibit lower microwave dielectric losses, an increased conductivity, and a positive temperature coefficient of resonant frequency. 相似文献
10.
The influence of Nd2 O3 doping on the reaction process and sintering behavior of BaCeO3 is investigated. Formation of BaCeO3 is initiated at 800°C and completed at 1000°C. When Nd2 O3 is added to the starting materials, the formation of BaCe1–x Ndx O3–δ is delayed and the temperature for complete reaction is increased to 1100°C. Only a BaCe1-x Ndx O3–δ solid solution with an orthorhombic crystal structure is present in the specimens for x ≤ 0.1. A secondary phase rich in Ce and Nd is formed within grains and at grain boundaries, when the Nd2 O3 content is greater than the solubility limit (x ≥ 0.2). Pure BaCeO3 is difficult to sinter, even at 1500°C, and only a porous microstructure could be obtained. However, doping BaCeO3 with Nd2 O3 markedly enhances its sinterability. The enhancement of the sinterability of Nd2 O3 -doped specimens at x ≤ 0.1 is attributed to the increase in the concentration of oxygen ion vacancies, which increases the diffusion rate. At x ≥ 0.2, the grain size is abnormally coarsened, which is caused by the formation of a liquid phase. While this liquid phase accelerates sintering, its beneficial effect on densification is counteracted by the segregation of the secondary grain-boundary phase which inhibits sintering. 相似文献
11.
Hilde Lea Lein Kjell Wiik Mari-ann Einarsrud Tor Grande Edgar Lara-curzio 《Journal of the American Ceramic Society》2006,89(9):2895-2898
Steady-state compressive creep rate of La0.5 Sr0.5 Fe0.5 Co0.5 O3−δ (LSFC) and La0.5 Sr0.5 CoO3−δ (LSC) is reported in the temperature region 900°–1050°C and stress range 5–28 MPa. The stress exponents for the two materials were 1.71±0.18 and 1.24±0.15, respectively. The activation energy for creep was considerably higher for LSC (619±56 kJ/mol) than for LSFC (392±28 kJ/mol). The grain size exponent for LSC was 1.28±0.14. Considerably higher creep rates were observed for both materials in N2 compared with air. Relaxation by creep of chemical-induced stresses in oxygen-permeable membranes is addressed, especially at low partial pressure of oxygen. 相似文献
12.
Yaping Li Evan R. Maxey James W. Richardson Jr. Beihai Ma Tae H. Lee Sun-Ju Song 《Journal of the American Ceramic Society》2007,90(4):1208-1214
A dense tubular solid electrolyte with the composition Ce0.8 Y0.2 O1.9−δ (CY20) was prepared. In situ time-of-flight neutron powder diffraction (TOF-ND) was performed at 900°C in the oxygen partial pressure p O2 range from 10−1 –10−18 atm, and TOF-ND data were analyzed by the Rietveld method. Diffraction data showed that the lattice parameter moderately increased with decreasing p O2 in the range of p O2 >10−14 atm, while a dramatic expansion (∼0.6%) of the fluorite structure occurred at a p O2 of 10−18 atm. By refining all reasonable structural parameters, an approximately linear relationship between lattice parameter and oxygen vacancy δ was observed, resulting in ɛc /δ=0.08 and corresponding to δ=0.10 at a p O2 of 10−18 atm, all in agreement with the data published in the literature. The relative change in lattice parameter Δ a / a followed a −1/4 power relation with p O2 in a low- p O2 regime. As several (often strongly correlated) structural parameters can affect the intensities in ND profiles, care was taken to select refinement variables. It was found that O atom thermal factors for CY20 increased as the oxygen vacancy concentration and lattice expansion increased. 相似文献
13.
Benjamin P. McCarthy Larry R. Pederson Harlan U. Anderson Xiao-Dong Zhou Prabhakar Singh Gregory W. Coffey Edwin C. Thomsen 《Journal of the American Ceramic Society》2007,90(10):3255-3262
Exposure of (La0.90 Sr0.10 )0.98 MnO3+δ (LSM-10) to repeated oxygen partial pressure cycles (air/10 ppm O2 ) resulted in enhanced densification rates, similar to behavior shown previously due to thermal cycling. Shrinkage rates in the temperature range 700°–1000°C were orders of magnitude higher than Makipirtti–Meng model estimations based on stepwise isothermal dilatometry results at a high temperature. A maximum in enhanced shrinkage due to oxygen partial pressure cycling occurred at 900°C. Shrinkage was the greatest when LSM-10 bars that were first equilibrated in air were exposed to gas flows of lower oxygen fugacity than in the reverse direction. The former creates transient cation and oxygen vacancies well above the equilibrium concentration, resulting in enhanced mobility. These vacancies annihilate as Schottky equilibria are reestablished, whereas the latter condition does not lead to excess vacancy concentrations. 相似文献
14.
C. Greskovich 《Journal of the American Ceramic Society》1984,67(6):111-C
The deviation from stoichiometry, δ, in Cr2 −δO3 was measured by a tensivolumetric method in the high pO2 range of ≊104 to 104 Pa at 1100°C. The value of δ, or chromium vacancy concentration, was≊9×10−5 mol/mol Cr2 O3 in air for Cr2 O3 with 99.999% purity. The chemical diffusion coefficient, DT, determined from equilibration data was ≊4.6× cm2 ·s−1 at 1100°C for pO2 = 2.2 ×101 Pa. The self-diffusion coefficient of Cr ions was calculated from and δ and found to be≊1.6×10-17 cm2 -s−1 , in good agreement with recently measured values. 相似文献
15.
The electrical properties of Sr0.5 Ba0.3 TiO3 in the presence of Nb2 O5 as a donor, 3Li2 O · 2SiO2 as a sintering agent, and Bi2 O3 as a dopant have been studied. When the compositions of the ceramics were 1 mol Sr0.7 Ba0.3 TiO3 + 0.5 mol% Nb2 O5 + 2 mol% 3Li2 O · 2SiO2 + 0.2 mol% Bi2 O3 , the ceramics were sintered at 1100°C and exhibited the following characteristics: apparent dielectric constant ɛ, 25000; loss factor tan δ, 2%; insulating resistivity ρj , 1010 Ω· cm; variation of dielectric constant with temperature Δɛ/ɛ (−25° to +85°C), +10%, −14%. ɛ and tan δ show only small changes with frequency. The study shows this ceramic can be used in multilayer technology. 相似文献
16.
The subsolidus phase equilibrium diagram for the pseudobinary join MgAl2 O4 -Ga2 O3 was determined. The shape of the exsolution boundary was obtained by heat-treating samples pre- equilibrated at 1600°C. Crystalline solubility of Ga2 O3 in MgAl2 O4 decreased from 73 mole % at 1600°C to 55 mole % at 1200°C. The crystalline solution was formed by the replacement of Mg2+ ions by Ga3+ ions to produce a cation defect spinel. The phase precipitated was the mono-clinic δ-Ga2 O3 (=δ-Al2 O3 structure). Changes in the ratios of relative X-ray diffraction intensities indicated that the crystalline solutions also disorder with temperature. 相似文献
17.
The stability of the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound has been evaluated under conditions of elevated temperature (500°-860°C) and elevated oxygen fugacity (i.e., in O2 /Ar gas mixtures containing ≤120% O2 , at total pressures of 5207 MPa). At sufficiently high oxygen fugacities and temperatures, the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound transformed into a mixture of a strontium-rich (Bi,Pb)1 -(Sr,Ca,Cu)2 Oy -type compound, a calcium-rich (Bi,Pb)2 -(Sr,Ca,Cu)2 Oy -type compound, CuO, and a small amount of (Sr,Ca)O. The decomposition of the (Bi,Pb)2 Sr2 Ca2 -Cu3 O10±δ -type compound was accompanied by a 2%-3% weight gain, which was consistent with an oxidation reaction. The conditions of oxygen fugacity and temperature leading to decomposition, and the resulting decomposition products, are compared for the (Bi,Pb)2 Sr2 Ca2 Cu2 O10±δ -type and Bi2 Sr2 Ca1 Cu2 O8±Ψ -type compounds. 相似文献
18.
Tatsuya Kodama Ken-ichi Tominaga Masahiro Tabata Takashi Yoshida Yutaka Tamaura 《Journal of the American Ceramic Society》1992,75(5):1287-1289
Active wustite (FeδO, with a δ value of 0.98) was prepared by keeping normal wustite (δ value of 0.94) in a N2 atmosphere at 300°C for 10 min. This reaction is given by (4δ2 –3)Feδ1 O→(4δ1 –3)Feδ2 O + (δ2 –δ1 )Fe3 O4 where δ1 = 0.94 and δ2 = 0.98. The equation indicates that the normal wustite undergoes eutectoid decomposition into active wustite and stoichiometric magnetite (Fe3 O4 ). Carbon dioxide (1.013 × 105 Pa) was almost completely (100%) decomposed into carbon (zero valence) by the active wustite at the low temperature of 300°C, which was associated with the transformation of the active wustite into the stoichiometric magnetite. The internal pressure of the reaction cell eventually became a vacuum. 相似文献
19.
R. G. VISSER† W. F. SCHIAVI‡ M. F. BERARD 《Journal of the American Ceramic Society》1975,58(9-10):438-441
An electron microprobe interdiffusion study was made in single crystals between 1200° and 1331°C over the solid-solution compositional range 0 to 20 mol% YF3 in CaF2 . At constant temperature, the value of δ , the interdiffusion coefficient, increased approximately exponentially with increasing YF3 content. As YF3 content increased, the temperature dependence of δ decreased. Extrapolation of δ to 0% YF3 combined with consideration of the defect formation mechanism at mite dilution allowed estimation of the impurity diffusion coefficient for Y in essentially pure CaF2 . 相似文献
20.
Osamu Yamaguchi Daijo Tomihisa Tatsuji Uegaki Kiyoshi Shimizu 《Journal of the American Ceramic Society》1987,70(11):335-C
In the system Ta2 O3 -Al2 O5 solid solutions of metastable δ-Ta2 O5 (hexagonal) are formed up to 50 mol% Al2 O3 from amorphous materials prepared by the simultaneous hydrolysis of tantalum and aluminum alkoxides. The values of the lattice parameters decrease linearly with increasing Al2 O3 , content. The to β-Ta2 O5 (orthorhombic, low-temperature form) transformation occurs at ∼950°C. The solid solution containing 50 mol% Al2 O3 transforms at 1040° to 1100°C to orthorhombic TaAlO4 . Orthorhombic TaAlO4 contains octahedral TaO6 groups in the structure. 相似文献