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1.
Thermal and X-ray studies show that there is complete solid solution between MgO.Cr2 O3 and MgO.Al2 O3 and that the spinel solid solutions are stable with no exsolution down to temperatures as low as 510°C. There is no solid solution of excess Cr2 O3 in MgO.Cr2 O3 nor of MgO.Cr2 O3 in Cr2 O3 . The join MgO.Cr2 O3 –Al2 O3 is found to be nonbinary; compositions along that join yield mixtures of a chromium oxide-alumina solid solution and a spinel solid solution on firing to temperatures high enough to promote solid-state reaction. Chromium oxide loss by volatilization increases at higher temperature. At a given temperature, chromium oxide loss is found to vary directly with the partial pressure of oxygen in the furnace atmosphere and with the ratio of MgO to SiO2 in the charges heated. 相似文献
2.
Liquidus equilibrium relations for the air isobaric section of the system Y2 O3 –Fe2 O3 –FeO–Al2 O3 are presented. A Complete solid-solution series is found between yttrium iron garnet and yttrium aluminum garnet as well as extensive solid solutions in the spinel, hematite, orthoferrite, and corundum phases. Minimum melting temperatures are raised progressively with the addition of alumina from 1469°C in the system Y–Fe–O to a quaternary isobaric peritectic at 1547°C and composition Y 0.22 Fe 1.08 Al 0.70 O 2.83 * Liquidus temperatures increase rapidly with alumina substitutions beyond this point. The thermal stability of the garnet phase is increased with alumina substitution to the extent that above composition Y 0.75 Fe 0.65 Al 0.60 O 3 garnet melts directly to oxide liquid without the intrusion of the orthoferrite phase. Garnet solid solutions between Y 0.75 Fe 1.25 O 3 and Y 0.75 Fe 0.32- Al 0.93 O 3 can be crystallized from oxide liquids at minimum temperatures ranging from 1469° to 1547°C, respectively. During equilibrium crystallization of the garnet phase, large changes in composition occur through reaction with the liquid. Unless care is taken to minimize temperature fluctuations and unless growth proceeds very slowly, the crystals may show extensive compositional variation from core to exterior. 相似文献
3.
C. C. Khaw C. K. Lee Z. Zainal G. C. Miles A. R. West 《Journal of the American Ceramic Society》2007,90(9):2900-2904
The subsolidus phase diagram of the system Bi2 O3 –ZnO–Ta2 O5 in the region of the cubic pyrochlore phase has been determined at 1050°C. This phase forms a solid solution area that includes the ideal composition P, Bi3 Zn2 Ta3 O14 ; possible solid solution mechanisms are proposed, supported by density measurements of Zn-deficient solid solutions. The general formula of the solid solutions is Bi3+ y Zn2− x Ta3− y O14− x − y , based on the creation of Zn2+ , O2− vacancies in Zn-deficient compositions and a variable Bi/Ta ratio. 相似文献
4.
The phase diagrams in the Al2 O3 –Cr2 O3 and V2 O3 –Cr2 O3 systems have been assessed by thermodynamic modeling with existing data from the literature. While the regular and subregular solution models were used in the Al2 O3 –Cr2 O3 system to represent the Gibbs free energies of the liquid and solid phases, respectively, the regular solution model was applied to both phases in the V2 O3 –Cr2 O3 system. By using the liquidus, solidus, and/or miscibility gap data, the interaction parameters of the liquid and solid phases were optimized through a multiple linear regression method. The phase diagrams calculated from these models are in good agreement with experimental data. Also, the solid miscibility gap and chemical spinodal in the V2 O3 –Cr2 O3 system were estimated. 相似文献
5.
pela Kunej Sreo D. kapin Danilo Suvorov 《Journal of the American Ceramic Society》2009,92(10):2373-2377
In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi2 O3 −TiO2 −Nd2 O3 system at 1100°C. The samples were analyzed using X-ray powder diffraction and scanning electron microscopy with energy- and wavelength-dispersive spectroscopy. A single-phase pyrochlore ceramic was obtained with the addition of 4.5 mol% of Nd2 O3 . We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi(1.6–1.08 x ) Nd x Ti2 O(6.4+0.3 x ) , where 0.25< x <0.96; (ii) the solid solution Bi4− x Nd x Ti3 O12 , where 0< x <2.6; and (iii) the Nd2− x Bi x Ti2 O7 solid solution, where 0< x <0.35. The determined phase relations in the pyrochlore-rich part are presented in a partial phase diagram of the Bi2 O3 −TiO2 −Nd2 O3 system in air at 1100°C. 相似文献
6.
ROBERT RUH K. S. MAZDIYASNI P. G. VALENTINE H. O. BIELSTEIN 《Journal of the American Ceramic Society》1984,67(9):190-C
Subsolidus phase relations in the low-Y2 O3 portion of the system ZrO2- Y2 O3 were studied using DTA with fired samples and X-ray phase identification and lattice parameter techniques with quenched samples. Approximately 1.5% Y2 O3 is soluble in monoclinic ZrO2 , a two-phase monoclinic solid solution plus cubic solid solution region exists to ∼7.5% Y2 O3 below ∼500°C, and a two-phase tetragonal solid solution plus cubic solid solution exists from ∼1.5 to 7.5% Y2 O3 from ∼500° to ∼1600°C. At higher Y2 O3 compositions, cubic ZrO2 solid solution occurs. 相似文献
7.
Elena R. Andrievskaya Lidia M. Lopato Vasily P. Smirnov 《Journal of the American Ceramic Society》1996,79(3):714-720
A mathematical model of the liquidus surface based on a reduced polynomial method was proposed for the system HfO2 -Y2 O3 -Er2 O3 . The results of calculations according to this model agree fairly well with the experimental data. Phase equilibria in the system HfO2 -Y2 O3 -Er2 O3 were studied on melted (as-cast) and annealed samples using X-ray diffraction (at room and high temperatures) and micro-structural and petrographic analyses. The crystallization paths in the system HfO2 -Y2 O3 -Er2 O3 were established. The system HfO2 -Y2 O3 -Er2 O3 is characterized by the formation of extended solid solutions based on the fluorite-type (F) form of HfO2 and cubic (C) and hexagonal (H) forms of Y2 O3 and Er2 O3 . The boundary curves of these solid solutions have the minima at 2370°C (15. 5 mol% HfO2 , 49. 5 mol% Y2 O3 ) and 2360°C (10. 5 mol% HfO2 , 45. 5 mol% Y2 O3 ). No compounds were found to exist in the system investigated. 相似文献
8.
P. L. ROEDER F. P. GLASSER† E. F. OSBORN 《Journal of the American Ceramic Society》1968,51(10):585-593
Liquidus phase equilibrium data are presented for the system Al2 O3 -Cr2 O3 -SiO2 . The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al2 O3 -ICr2 O3 -93SiO2 ) coexists with a mullite solid solution (61Al2 O3 -10Cr2 O3 -29SiO2 ), a corundum solid solution (19Al2 O3 -81Cr2 O3 ), and cristobalite (SO2 ). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases. 相似文献
9.
Koichiro Fukuda Ken-ichi Matsunaga Takahiro Bessho Hideto Yoshida 《Journal of the American Ceramic Society》2005,88(4):954-962
The phase stability in part of the P2 O5 -bearing pseudoquaternary system CaO–SiO2 –Al2 O3 –Fe2 O3 has been studied by electron probe microanalysis, optical microscopy, and powder X-ray diffractometry. At 1973–1653 K, the α-Ca2 SiO4 solid solution [α-C2 S(ss)] and melt coexisted in equilibrium, both chemical variations of which were determined as a function of temperature. The three phases of melt, calcium aluminoferrite solid solution (ferrite), and C2 S(ss) coexisted at 1673–1598 K. On the basis of the chemical compositions of these phases, a melt-differentiation mechanism has been, for the first time, suggested to account for the crystallization behavior of Ca3 Al2 O6 solid solution [C3 A(ss)]. When the α-C2 S(ss) and melt were cooled from high temperatures, the melt would be induced to differentiate by the crystallization of ferrite. Because the local equilibrium would be continually attained between the rims of the precipitating ferrite and coexisting melt during further cooling, the melt would progressively become enriched in Al2 O3 with respect to Fe2 O3 . The resulting ferrite crystals would show the zonal structure, with the Al/(Al+Fe) value steadily increasing up to 0.7 from the cores toward the rims. The C3 A(ss) would eventually crystallize out of the differentiated melt between the zoned ferrite crystals in contact with their rims. 相似文献
10.
The dissolution of (Al, Cr)2 O3 into CaO—MgO—Al2 O3 —SiO2 melts, under static and forced-convective conditions was investigated at 1550°C in air. With sufficient MgO in the melt, or sufficient Cr2 O3 in (Al, Cr)2 O3 , a layer consisting of a spinel solid solution, Mg(Al, Cr)2 O4 , formed at the (Al, Cr)2 O3 /melt interface. The dissolution kinetics of 1.5 and 10 wt% Cr2 O3 specimens were determined as a function of immersion time, specimen rotation rate, and magnesia content of the melt. Electron microprobe analysis was used to characterize concentration gradients in the (Al, Cr)2 O3 sample, the Mg(Al, Cr)2 O4 spinel, or in the melt after immersion of specimens containing 1.5 to 78 mol% Cr2 O3 . The dissolution kinetics and microprobe analyses indicated that a steady-state condition was reached during forced-convective, indirect (Al, Cr)2 O3 dissolution such that spinel layer formation was rate limited by solid-state diffusion through the spinel layer and/or through the specimen, and spinel layer dissolution was rate limited by liquid-phase diffusion through a boundary layer in the melt. This is consistent with a model previously developed for the indirect dissolution of sapphire in CMAS melts. 相似文献
11.
The electrical conductivity of M2 O3 -ZrO2 compositions containing 6 to 24 mole % M2 O3 , where M represents La, Sm, Y, Yb, or Sc, was examined. Only Sm2 O3 , Y2 O3 , and Yb2 O3 formed cubic solid solutions with ZrO2 over most of this substitutional range. Scandia forms a wide cubic solid solution region with ZrO2 at temperatures above 130°C whereas the cubic solid solution region at room temperature is narrow (6 to 8 mole % Sc2 O3 ). Lanthana additions to ZrO2 produced no fluorite-type cubic solid solutions within the compositional range investigated. Generally, the electrical conductivity of these cubic solid solutions increased as the size of the substituted cation decreased and the electrical conductivity for each binary system attained a maximum at about 10 to 12 mole % M2 O3 . 相似文献
12.
MADELEINE H. WARZEE MARCEL MAURICE FRANZ HALLA WALTER R. RUSTON 《Journal of the American Ceramic Society》1965,48(1):15-17
In the binary system PbO–Laz O3 only one compound, 4PbO.La2 O3 , exists; it is flanked by two eutectics. The structure of the compound, although of lower symmetry, is intimately related to the C modification of the rare earths. Below 800° to 1000°C, metastable solid solutions are formed from oxide mixtures coprecipitated from mixed solutions of the nitrates, the cubic parameter a = 5.66 A, if extrapolated to pure La2 O3 , corresponding to half the a parameter of the C form of La2 O3 . The solid solutions existing between the compositions La2 O3 –2Pb0 and pure La2 O3 have a cubic face–centered lattice and obey Vegard's rule. The systems of PbO with Sm2 O3 and Gd2 O8 are quite similar to that with La2 O3 . The compound Sm2 O3 .4Pb0 decomposes at 1000°C with evaporation of PbO; Sm2 O3 remains in the B modification. 相似文献
13.
R. E. CARTER 《Journal of the American Ceramic Society》1960,43(9):448-451
The dissociation pressures of solid solutions from Fe3 O4 to 0.4Fe3 O4 ·0.6CoFe2 O4 have been determined as a function of temperature. Within experimental error, solid solutions within this range are thermodynamically ideal. 相似文献
14.
Activity–composition relations of FeCr2 O4 –FeAl2 O4 and MnCr2 O4 –MnAl2 O4 solid solutions were derived from activity–composition relations of Cr2 O3 –Al2 O3 solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr2 O3 –Al2 O3 and MnO–Cr2 O3 –Al2 O3 . Moderate positive deviations from ideality were observed. 相似文献
15.
Subsolidus equilibrium relations in a portion of the system Li2O-Fe2 O3 -Al2 O3 in the temperature range 500° to 1400°C. have been determined near po2 = 0.21. Of particular interest in this system is the LiFe5 O8 -LiAl5 O8 join, which shows complete solid solution above 1180°C. Below this temperature the solid solution exsolves into two spinel phases. At 600°C. approximately 15 mole % of each compound is soluble in the other. The high-temperature solid solution and the low-temperature exsolution dome extend into the ternary system from the 1:5 join. There is no appreciable crystalline solubility of LiFeO2 or of α-Fe2 O3 in LiFe5 O8 . An attempt to confirm HFe5 O8 as the correct formulation of the magnetic ferric oxide "γ-Fe2 O3 " was inconclusive, but in the absence of positive evidence, the retention of γ-Fe2 O3 is recommended. All the metallic oxides of the Group IV elements increase the temperature of the monotropic conversion of -γ-Fe2 O3 to α-Fe2 O3 . Silica and thoria have a greater effect on this conversion than does titania or zirconia. 相似文献
16.
Phase relations in air at 1300°C were determined for the system MgO-Cr2 O3 −Fe2 O3 by conventional quenching techniques. Details of the phase equilibria were established for: (1) the sesquioxide solid solution between Cr2 O3 and Fe2 O3 , (2) the spinel solid solution field between MgCr2 O4 and MgFe2 O4 , and (3) the periclase solid solution field for MgO. Selected tie lines connecting coexisting compositions were established with X-ray diffractometer data. Diffuse reflectance spectra, diffractometer intensity ratios, and lattice parameter measurements were obtained for quenched samples to study the structural inversion in the spinel series MgCr2 O4-MgFe2 O4 . 相似文献
17.
ALEXANDRA NAVROTSKY BARRY A. WECHSLER KAREN GEISINGER FRIEDRICH SEIFERT 《Journal of the American Ceramic Society》1986,69(5):418-422
Solution calorimetry of MgAl2 O4 -Al8/3 O4 solid solutions was performed in a molten 2PbO · B2 O3 solvent at 975 K. The results indicate small negative heats of mixing, relative to spinel standard states for both end-members. These data were combined with information on the energetics of the α-γ transition in Al2 O3 and on the MgAl2 O4 -Al8/3 O4 (MgO-Al2 O3 ) subsolidus phase relations to estimate the partial molar entropy of mixing of γ-Al8/3 O4 in the solid solution. This entropy is much less positive than that calculated from several models for the configurational entropy of mixing of magnesium, aluminum, and vacancies on octahedral and/or tetrahedral sites. The data suggest a good deal of local order to be present in the solid solutions, consistent with negative enthalpies of mixing and entropies of mixing far less than ideal configurational values. 相似文献
18.
Masahiro Yoshimura Manikpurage Jayaratna Shigeyuki Smiya 《Journal of the American Ceramic Society》1982,65(10):c166-c168
The pseudoternary system ZrO2 -Y2 O3 -Cr2 O3 was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO3 , was observed on the Y2 O3 −Cr2 O3 join. ZrO2 and Y2 O3 formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO2 , Cr2 O3 , and YCrO3 three-phase region was located at =17 mol% Y2 O3 (83 mol% ZrO2 ). Below 17 mol% Y2 O3 , ZrO2 solid solution coexisted with Cr2 O3 . Cr2 O3 appears to be slightly soluble in ZrO2 (ss). 相似文献
19.
Thermally crystallized glasses of compositions (Li2 ,O2 , MgO).Al2 O3 .nSiO2 were studied by X-ray powder diffraction methods. High-quartz solid solution phases developed at relatively low temperatures and, for n 3.5, transformed at higher temperatures to keatite solid solution phases. Associated phases, if present, were Mg spinel and/or cordierite, or a few other trace phases. The a crystallographic axis (a0 ) of high-quartz solid solutions decreased with increase of MgO and/or SiO2 . The c crystallographic axis (c0 ) decreased with increasing MgO; it also decreased with increasing SiO2 , but only when MgO content was low. X-ray diffraction photographs of single crystals of high-quartz solid solutions of compositions LiaO.Al2 O3 .nSiO3 demonstrated that the maintenance of a basic high-quartz structure is the basis of the solid solution relation. Three modifications of the high-quartz structure were recognized in the Li2 O-Al2 O3 −SiO3 system. These modifications were based on the occurrence and positions of superlattice reflections. The high-quartz solid solution from Li2 O Al2 O3 −2SiO2 , showing streaky reflections in its precession photographs, suggested a defective structure. The term "high-quartz solid solution," with or without additional prefixes specifying the compositional series and modification, was considered the preferred nomenclature for these solid solution phases. 相似文献
20.
Carmen Barrera-Solano Luis Esquivias Gary L. Messing 《Journal of the American Ceramic Society》1999,82(5):1318-1324
In situ development of La-ß-Al2 O3 (LBA) platelets in alpha-Al2 O3 was studied as a function of the preparation method: a conventional solid-state reaction of commercial Al2 O3 powder and La(NO3 )3 as well as a sol-gel method starting with boehmite and the same La2 O3 precursor. In both cases, homogeneous distribution of the reinforcing phase was achieved, and a noteworthy inhibition of Al2 O3 grain growth resulted. However, samples prepared by solid-state reaction densified more easily than those prepared via sol-gel, but the formation of the LBA phase occurred at a lower temperature in samples prepared by the sol-gel approach. Results on the correlation of the onset of LBA grain growth and densification to microstructure are discussed. 相似文献