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1.
The vapor pressure of plutonium dioxide (PuO2 ) was investigated in the range 1450° to 1775°C in air, argon, and oxygen atmospheres by a transpiration technique. There were strong indications that PuO2 can vaporize congruently or as a suboxide species, depending on the atmosphere. The δH°298 for vaporization in 1 atm of oxygen is approximately 154,000 cal per mole. The estimated standard free energy of formation (δG°f ) of gaseous PuO2 is −121,000 + 10.7 T from 1227° to 1827°C. 相似文献
2.
C. N. Pleczulewski J. E. McAdams T. O. Mason 《Journal of the American Ceramic Society》1990,73(10):3088-3090
Phase composition and compatibilites at 930° to 950°C were determined for the system Eu2 O3 –BaO–CuO in air. The binary compound Eu2 CuO4 dissolves Ba to the extent 0 x 0.02 in Eu2-x Bax CuO4 , whereas the other binary compounds, Eu2 BaO4 and BaCuO2 , do not exhibit solid solubility. Three ternary compounds were obtained, Eu2 BaCuO5 and two solid solution phases. The first contains the 90 K '123' superconductor and has solubility limits represented by Eu1+x Ba2-x Cu3 O7±y , where 0 x 0.5. The second has a solubility limit represented as Eu1+x Ba8-x Cu4 Oy , where 0 x 0.44. The limited solid solution range of this phase provides insight concerning the probable solid solution range of the analogous phase in the Y2 O3 -BaO-CuO system. 相似文献
3.
Subsolidus phase relations in the La2 O3 –BaO–CuO system were studied at 950°C. Three previously reported binary compounds exist (La2 CuO4 , BaLa2 O4 , and BaCuO2 ) and five previously reported ternary phases occur (La2-x Bax CuO4-(x/2)+δ , La4-2x Ba2+2x Cu2-x O10-2x , La2-x Ba1+x Cu2 O6-(x-2) , La3-x Ba3+x Cu6 O14±δ , and La4 BaCu5 O13+δ ). Of the seven phases in the diagram, all but BaLa2 O4 , BaCuO2 , and La4 BaCu5 O13+δ were shown to exhibit significant ranges of solubility. The diagram is important in that both >30 K (La2-x Bax CuO4-(x/2)+δ ) and >90 K (La3-x Ba3+x Cu6 O14+δ , x=1) superconductors occur. 相似文献
4.
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
5.
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
6.
Phase equilibria of the La2 O3 -SrO-CuO system have been determined at 950°C and 10 kbar (1 GPa). Stable phases at the apices of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 CuO4 in the LaO1.5 -CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO-SrO binary. The La2-x Sr x CuO4-δ solid solution is stable where 0.0 ≤ x ≤ 1.3, the La2-x Sr1+x Cu2 O6+δ solid solution is stable where 0.0 ≤ x ≤ 0.2, the La8-x Sr x Cu8 O20-δ solid solution is stable where 1.3 ≤ x ≤ 2.7, the La x Sr14-x -Cu24 O41 solid solution is stable where 0 ≤ x ≤ 6, and the La1+x Sr2-x Cu2 O5.5+δ phase is stable where 0.04 ≤ x ≤ 0.16. The La2 O3 -SrO-CuO phase diagram at 950°C and 10 kbar is almost identical to that determined by other authors at 950°C and 1 atm, in terms of phase stability and solid-solution ranges. 相似文献
7.
Ferroelectric twin domains resulting from the cubic ( c ) to tetragonal ( t ) phase transformation at the Curie point T C ≈130°C in pressureless-sintered BaTiO3 ceramics, using TiO2 -excess powder, have been investigated using scanning and transmission electron microscopy. Both 90° and 180° domains were identified by spot splitting along characteristic crystallographic directions in the selected-area diffraction patterns and/or from the shape of domain boundaries. Lamellar domains were found predominantly with the 90° types. The 180° domain boundaries mostly appeared wavy in shape, while the 90° ones, having sharpened ends, attained a dagger shape. Failure of Friedel's law in the non-centrosymmetric t -BaTiO3 was adopted to validate the existence of the 180° domains. The 90° domains with boundaries lying in are reflection–inversion twins, and the 180° domains lying in {100) t and }220) t are inversion twins. Convergent-beam electron diffraction was performed to ensure that changing of the polar direction [001] t across the 90° and the 180° domain boundaries was consistent with the domain type. It was also used to confirm whether the 180°-type walls are inversion domain boundaries produced by the loss of an inversion center when the cubic phase transforms into tetragonal symmetry. The formation of such ferroelectric domains is discussed with reference to the crystal symmetry reduction from ( c -phase) to P 4 mm ( t -phase) with a loss of mirror plane (m) and roto-inversion axis upon c → t phase transformation. 相似文献
8.
J. M. LEITNAKER T. B. LINDEMER C. M. FITZPATRICK 《Journal of the American Ceramic Society》1970,53(9):479-481
The reaction of nitrogen with arc-melted UC was studied from 1475° to 1700°C at an N2 pressure of about 400 torr. The reaction appeared to proceed toward equilibrium in distinct stages: (1) UC and N2 reacted to form UC2 and UC0.8 N0.2 ; (2) UC2 reacted with N2 to produce more UC0.3 N0.2 and free C; and (3) this U(C,N) reacted with N2 to produce more free C and the equilibrium product, a high-N U(C,N). These results are consistent with known thermodynamic and phase behavior in the U-C-N system. 相似文献
9.
JULIE CHI-SUN YANG 《Journal of the American Ceramic Society》1960,43(10):542-549
Reactions in the ternary system MgO-SiO2 -H2 O were studied over the temperature range 100° to 300° C. and were found to produce only two phases. Under conditions of 100° to 200° C. and atmospheric pressure up to 20,000 lb. per sq. in., and regardless of the initial MgO/SiO2 ratio, the predominant magnesium silicate product was found to have a MgO/SiO2 ratio of 1.5. In the range 200° to 300°C. at 210 to 20,000 lb. per sq. in. two stable phases, 3MgO.2SiO2 .2H2 O (I) and 3MgO.4SiO2 .H2 O (II), were observed. In this case the phase that was favored was determined by the molar ratio of MgO/SiO2 of the reaction mixture at the start of the run. The physical and chemical properties of phases (I) and (II) resembled those of the natural minerals serpentine and talc respectively. Two different morphologies were observed in electron micrographs of phase (I). From 100° to 160°C. it occurred as crumpled foils, and at 170°C. fibrous crystallites, which resembled the natural asbestos mineral chrysotile, appeared at the expense of some of the foils. 相似文献
10.
A diffusion couple of 3 mol% Y2 O3 –ZrO2 and titanium was isothermally annealed in argon at temperatures between 1100° and 1550°C. The phases and microstructure in the ceramic side were investigated using scanning electron microscopy and transmission electron microscopy, both attached to an energy-dispersive spectrometer. After annealing at 1100°C/6 h, zirconia grains did not grow conspicuously and evolved only traces of oxygen, resulting in t -ZrO2− x but not α-Zr. At temperatures above 1300°C, a significant amount of oxygen evolved from zirconia, reducing the O/Zr ratio, such that α-Zr was excluded from t -ZrO2− x during cooling, yielding a higher O/Zr ratio (≈2). When held at 1550°C/6 h, zirconia grains grew rapidly. The α-Zr was segregated on grain boundaries during cooling by the exsolution of zirconium from ZrO2− x , while twinned t '-ZrO2− x or lenticular t -ZrO2− x , which was embedded in ordered c- ZrO2− x , was found. The ordered c -ZrO2− x was identified by the {113} superlattice reflections of its electron diffraction patterns. 相似文献
11.
Electrical conductivity was measured from 850° to 1400°C for β-sialon and pure X phase as well as for the sintered system Si3 N4 -Al2 O3 , containing β-sialon, X phase, β-Si3 N4 , and glassy phase. Ionic conductivity was measured at >1000°C. The charge carriers were identified by electrolysis. The results showed that pure β-sialon is ionically conducting because of Si4+ migration for the temperature range studied. Pure X phase shows ionic conduction by Si4+ above 1000°; below 1000°C, it shows electronic conduction because of impurities. The conductivity of the sintered system Si3 N4 -Al2 O3 containing β-sialon, β-Si3 N4 X phase, and glassy phase changes as the relative quantities of β -sialon and X phase change. The apparent activation energies for the ionic and electronic conductivities are 45 and 20 kcal/mol, respectively. 相似文献
12.
Yongsheng Liu Laifei Cheng Litong Zhang Wenbin Yang Yongdong Xu 《International Journal of Applied Ceramic Technology》2008,5(3):305-312
Methane (CH4 ) and propylene (C3 H6 ) were used to fabricate a boron–carbon coating by a low-pressure chemical vapor deposition (LPCVD) technique. The effects of carbon precursors on the phase, microstructure, and bonding state of the deposits have been investigated. X-ray diffraction results show that the 2θ value of the deposit from the C3 H6 precursor shifts to 25.78° when the coating is deposited at 1223 K, and shifts to 26.1° when deposited at 1273 K, compared with the 2θ value of the pyrocarbon (PyC) peak deposited by LPCVD, which is 25.42°, and no boron–carbon (B–C) compound peak exists. However, the phases of coating deposited from CH4 include B25 C, B13 C2 , elemental carbon, and boron. X-ray photoelectron spectroscopy (XPS) results show that the percent contents of boron atom in the coatings from the CH4 precursor are 61.18% and 67.78% when deposited at 1223 and 1273 K, respectively, much higher than that from the C3 H6 precursor, 10.85% and 15.30%, respectively. Scanning electron microscopy (SEM) results show that the coatings deposited from CH4 have a coarse crystal-like morphology; however, the coatings deposited from the C3 H6 precursor are smooth. The formation of PyC from C3 H6 is more facile than that from CH4 , which leads to differences in the phase, atom content, and microstructure of coatings from CH4 and C3 H6 precursors. 相似文献
13.
Dense, single-phase β-sialon ceramics were sintered at 1700°C and 200 MPa using the glass-encapsulated hot isostatic pressing technique. The materials were very hard, 1500 to 1700 kg / mm2 (98 N load), but were fairly brittle, with an indention fracture toughness of about 3 MPa · m1/2 . The addition of 1 wt% Y2 O3 before sintering had a positive effect on the toughness, especially at the low x compositions of Si3-x Alx Ox N4-x , where KIC ∼4 MPa · m1/2 . 相似文献
14.
A. C. TURNOCK 《Journal of the American Ceramic Society》1966,49(7):382-384
Subsolidus phase relations among oxides in the system Mn–Ta–O were experimentally determined by the quenching method. The conditions during the heating period were 1200°C, 1 atm total pressure, and various partial pressures of oxygen between 10–17 atm and 1 atm. At the limits of this range, the stable assemblages at f -= 10–17 atm are: MnO, Mn6 Ta2 O11 , Mn4 -Ta2 O9 , Mn1.4 TaO3.9 , MnTa2 O6 , and β-Ta2 O5 ; at p o2 = 1 atm they are: Mn3 O4 , Mn1.4 TaO4.2 , MnTa2 O6 , and β-Ta2 O5 . There are five univariant assemblages of three solid phases plus vapor in the phase diagram. 相似文献
15.
Charles N. Pieczulewski Kelly S. Kirkpatrick Thomas O. Mason 《Journal of the American Ceramic Society》1990,73(7):2141-2143
The phase relations involving the 24 K n -type Nd2- x Ce x CuO4 superconductor were investigated at 1000°C in air. The terminal solid solubility was confirmed to be x = 0.2. This solid solution is the only ternary phase in the Nd2 O3 –CeO2 –CuO diagram. A binary (1 − y )CeO2 – y NdO1.5 solid solution exists out to y = 0.4. Phase diagrams for NdO1.5 –CeO2 –CuO (1000°C) and NdO1.5 –CeO2 (900° to 1500°C) are presented. 相似文献
16.
Phase Equilibria in the Quaternary System Ti-Al-C-N 总被引:2,自引:0,他引:2
The quaternary system Ti-Al-C-N and its binary and ternary boundary systems are investigated using powder methods and XRD analysis. Phase equilibria at 1375°C are presented in an isothermal network for alloys up to 50 at.% Ti. In the vertical section Ti2 AIC1-x -Ti2 AlN1-x a complete series of solid solutions exists at 1495°C, but a wide miscibility gap occurs at 1375°C. The vertical section Ti3 AlC1-x -Ti3 AlN1-x is more complex because of the occurrence of the quaternary, tetragonally distorted phase Ti3 Al(C,N)1-x ( a = 0.41135(4) nm, c = 0.41366(5) nm) and the transformation of perovskite-type Ti3 AlN1-x into filled Re3 B-type Ti3 AlN1-x below 1200°C. 相似文献
17.
Equilibrium relations in the system NiO–TiO2 –SiO2 in air have been investigated in the temperature range 1430° to 1660°C. The most conspicuous feature of the phase relations is the existence of a cation-excess spinel-type phase, in addition to NiO and NiTiO3 , on the liquidus surface and at subsolidus temperatures down to 1430°C. Three invariant points have been located on the liquidus. There is a peritectic at 1540°C characterized by coexisting NiO ( ss ), spinel( ss ), cristobalite, and liquid of composition 47 wt% NiO, 29 wt% TiO2 , and 24 wt% SiO2 . Two eutectics are present, one at 1480°C, with spinel( ss ), NiTiO3 , cristobalite, and liquid (42 wt% NiO, 43 wt% TiO2 , and 15 wt% SiO2 ), as the coexisting phases. The other is at 1490°C with NiTiO3 , rutile, cristobalite, and liquid (32 wt% NiO, 56 wt% TiO2 , and 12 wt% SiO2 ). A liquid miscibility gap extends across the diagram from the two bounding binary systems NiO–SiO2 and TiO2 –SiO2 . 相似文献
18.
In the synthesis of the superconducting compound Ba2 YCu3 O7-x from a stoichiometric mixture containing BaCO3 , Y2 O3 , and CuO In air, a low-melting liquid phase is formed at about 890°C. The liquid phase was identified as a ternary eutectic located within the compatibility triangle Ba2 YCu3 O7-x –BaCuO2 –CuO. The implication of this finding for the processing of Ba2 YCu3 O7-x is discussed. 相似文献
19.
S. M. LANG 《Journal of the American Ceramic Society》1964,47(12):641-644
The lattice constants for three samples of tetragonal ZrO2 were measured in a high-temperature X-ray diffractometer in the range 1150° to 1700°C in an ambient air atmosphere. The unrefined lattice constants were the same for these materials only after each had been previously heat-treated at 1550° to 1750°C in an ambient air atmosphere. The thermal expansions of the two axes are linear and are given by: a value, A = 3.5882 + 4.50 X 10+(T) , within 0.0013 A; and c value, A = 5.1882 + 7.57 × 10−5 (T), within 0.0022 A, where T is in °C for the range 1150° to 1700°C. The lattice constant values are a = 3.6399 A and c = 5.2758 A at 1150°C and a = 3.6782 A and c = 5.3397 A at 1700°C. 相似文献
20.
A. C. TURNOCK 《Journal of the American Ceramic Society》1966,49(4):177-180
Subsolidus phase relations of the oxides in the system Fe–Nb–O were experimentally determined at 1180°C, 1 atm total pressure, and variable partial pressures of oxygen. Niobium pentoxide reacts readily with either ferrous or ferric oxide at subsolidus temperatures and the following ternary compounds were synthesized: Fe4 Nb2 O9 , FeNbO4 , and FeNb2 O6 . It is shown that the rutile structure of NbO2 will take Fe-Nb2 O6 into solid solution and that the spinel structure of Fe3 O4 will incorporate up to 7 at.% Nb. 相似文献