共查询到20条相似文献,搜索用时 78 毫秒
1.
Ming Chen Bengt Hallstedt A. Nicholas Grundy Ludwig J. Gauckler 《Journal of the American Ceramic Society》2003,86(9):1567-1570
Phase equilibria in the CeO2 −CoO system at temperatures above 1500°C were investigated. The microstructures and the phase compositions of the DTA (differential thermal analysis) samples and the quenched solid pellets were analyzed using SEM (scanning electron microscope), EDX (energy dispersive X-ray), and WDX (wavelength dispersive X-ray). A eutectic reaction was found at 1645 ± 5°C. The eutectic point was calculated to be at 82 ± 1.5 mol% CoO. The eutectic phases were the CeO2 -rich phase (containing <5 mol% CoO) and the CoO-rich phase (containing ∼0.5 mol% CeO2 ). At 1580°C, the solubility of CoO in CeO2 was ∼3 mol%. 相似文献
2.
The solubility of TiO2 in tetragonal ZrO2 is 13.8±0.3 mol% ui 1300°C, 14.9±0.2 mol% at 1400°C, and 16.1±0.2 mol% at 1500°C. These solid solutions transform to metastable monoclinic solid solutions without compositional change on cooling to room temperature. 相似文献
3.
Zirconia-Stabilized Cubic Europia 总被引:1,自引:1,他引:0
The system Eu2 O3 -ZrO2 was studied, concentrating attention on the region 0 to 33 mol% ZrO2 , which is of interest for fast-reactor neutron absorber applications. The addition of ∼20% ZrO2 to Eu2 O3 resulted in stable cubic phases. Results are compared for coprecipitated powders and pellets prepared from mechanically mixed powders fired at 1300°C and 1S50°C. The thermal stability of cubic structures at 600°C and 800°C for 8000 h was also demonstrated. 相似文献
4.
YPSZ/Al2 O3 -platelet composites were fabricated by conventional and tape-casting techniques followed by sintering and HIPing. The room-temperature fracture toughness increased, from 4.9 MPa·m1/2 for YPSZ, to 7.9 MPa·m1/2 (by the ISB method) for 25 mol% Al2 O3 platelets with aspect ratio = 12. The room-temperature fiexural strength decreased 21% and 30% (from 935 MPa for YPSZ) for platelet contents of 25 vol% and 40 vol%, respectively. Al2 O3 platelets improved the high-temperature strength (by 110% over YPSZ with 25 vol% platelets at 800°C and by 40% with 40 vol% platelets at 1300°C) and fracture toughness (by 90% at 800°C and 61% at 1300°C with 40 vol% platelets). An amorphous phase at the Al2 O3 -platelet/YPSZ interface limited mechanical property improvement at 1300°C. The influence of platelet alignment was examined by tape casting and laminating the composites. Platelet alignment improved the sintered density by >1% d th , high-temperature strength by 11% at 800°C and 16% at 1300°C, and fracture toughness by 33% at 1300°C, over random platelet orientation. 相似文献
5.
Masatomo Yashima Nobuo Ishizawa Tatsuo Noma Masahiro Yoshimura 《Journal of the American Ceramic Society》1991,74(3):510-513
Stable and metastable phase relationships in the system ZrO2 –ErO1.5 were investigated using homogeneous samples prepared by rapid quenching of melts and by arc melting. The rapidly quenched samples were annealed in air for 48 h at 1690°C or for 8 months at 1315°C. Two tetragonal phases ( t - and t '-phases) were observed after quenching samples heated at 1690°C to a room temperature, whereas one t -phase and cubic ( c -) phase were found in those treated at 1315°C. Since the t '-phase is obtained through a diffusionless transformation during cooling from a high-temperature c -phase, t - and c -phases can coexist at high temperature. The t - and c -phases field spans from 4 to 10 mol% ErO1.5 at 1690°C and from 3 to 15 mol% ErO1.5 at 1315°C. The equilibrium temperature T t-m 0 between the t - and monoclinic ( m -) phases estimated from As and Ms temperatures decreased with increasing ErO1.5 contents. 相似文献
6.
The process of compaction and densification of ultrafine (40- to 60-nm grain size) powder of partially stabilized zirconia with 3 mol% of Y2 O3 (Y3-PSZ) during rapid hot-pressing was investigated. A special apparatus was designed to allow rapid application of 1.6 GPa of quasi-isostatic pressure at temperatures of 1100° to 1300°C to powder compacts encapsulated in glass under vacuum. Pressure was applied for 10 s, then the samples were rapidly cooled to room temperature, removed from the encapsulating glass, and characterized using SEM, TEM, and X-ray diffraction. Density and mechanical properties of the prepared materials were measured and compared with those of similar materials fabricated using conventional hot-pressing. SEM and TEM observations revealed that the ultrafine grains of the starting powder coarsened rapidly during the initial heating, and the compacts developed large (> 10 μm) and small (< 1 μm) pores. The process of densification under pressure consisted of closing of the large pores, whereas the small pores were relatively unaffected by the application of pressure at all investigated temperatures. The major mechanism of densification during the rapid pressing appears to be rearrangement and sliding of grains around the large pores. The material prepared by rapid pressing at 1300°C had higher hardness ( H v = 1400 versus 1300 kg/mm2 ) but somewhat lower fracture toughness ( K I C = 5.5 versus 6.0 MPa · m1/2 ) compared with the conventionally hot-pressed Y3-PSZ. Density of the material pressed at 1300°C was 97% of theoretical density. 相似文献
7.
The Li2 O-TiO2 pseudobinary phase diagram was determined from 50 to 100 mol% TiO2 by DTA, microscopy, and X-ray analysis; Li2 Ti3 O7 effectively melts congruently at 1300° and decomposes eutectoidally at 940°C. A solid solution based on Li2 TlO3 from 50 to ∼65 mol% TiO3 was observed to exist at >930°C. A new metastable phase was discovered with a composition of ∼75 mol% TiO2 and with a hexagonal unit cell (8.78 by 69.86 × 10−1 nm). Discrepancies in the literature regarding some of these phase equilibria are reconciled. 相似文献
8.
Masanori Hirano Michio Inagaki Yasunobu Mizutani Kazuhiro Nomura Masayuki Kawai Yasuhisa Nakamura 《Journal of the American Ceramic Society》2000,83(10):2619-2621
Significant improvement in the fracture strength, accompanied by an enhancement in the electrical conductivity, of zirconia polycrystals that were doped with 3–7 mol% Sc2 O3 was obtained by sintering at 1300°C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300° and 1450°C for 1.5 h in an argon-gas atmosphere. Dense bodies (with an average grain size of <0.5 μm) that were doped with 3.5 mol% of Sc2 O3 showed the highest average fracture strength up to 1770 MPa and an electrical conductivity of 0.08 S/cm at 1000°C. The present zirconia ceramics, which consisted of submicrometer-sized grains of tetragonal phases and were stabilized with 5 and 6 mol% of Sc2 O3 , exhibited high strength (1330 and 1140 MPa, respectively) and good conductivity (0.15 and 0.18 S/cm, respectively); values for both properties were greater than those previously reported. The present HIPed zirconia ceramics, which have excellent properties, are candidates for an electrolyte of planar-type solid oxide fuel cells. 相似文献
9.
A liquid phase in the Al2 O3 -1 mol% TiO2 -0.5 mol% NaO1/2 composition is confirmed at ±1300°C by an electrical conductivity measurement. The ease of the method led to a study of the Al2 O3 -2 mol% CuO-2 mol% TiO2 system and to the geologically important detection of eutectics (peritectics) in rock materials. 相似文献
10.
The system HfO2 -TiO2 was studied in the 0 to 50 mol% TiO2 region using X-ray diffraction and thermal analysis. The monoclinic ( M ) ⇌ tetragonal ( T ) phase transition of HfO2 was found at 1750°± 20°C. The definite compound HfTiO4 melts incongruently at 1980°± 10°C, 53 mol% TiO2 . A metatectic at 2300°± 20°C, 35 mol% TiO2 was observed. The eutectoid decomposition of HfO2,ss ) ( T ) → HfO2,ss ( M ) + HfTiO3 4,ss ss occurred at 1570°± 20°C and 22.5 mol% TiO2 . The maximum solubility of TiO2 in HfO2,ss ,( M ) is 10 mol% at 1570°± 20°C and in HfO2,ss ( T ) is 30 mol% at 1980°± 10°C. On the HfO2 -rich side and in the 10 to 30 mol% TiO2 range a second monoclinic phase M of HfO2 ( M ) type was observed for samples cooled after a melting or an annealing above 1600°C. The phase relations of the complete phase diagram are given, using the data of Schevchenko et al. for the 50% to 100% TiO2 region, which are based on thermal analysis techniques. 相似文献
11.
Masatomo Yashima Katsuya Ohtake Masato Kakihana Masahiro Yoshimura 《Journal of the American Ceramic Society》1994,77(10):2773-2776
Homogeneous metastable tetragonal ( t ') solid solutions of ZrO2 — x mol% CeO2 ( x = 20 and 50) were successfully synthesized by the organic polymerized complex method. The citric acid-ethylene glycol solution containing Zr and Ce ions was polymerized at about 140°C and then heat-treated at about 350°C to obtain a precursor. The black precursor was heated at 450°C and then fired up to 1300° or 1590°C, resulting in the homogeneous solid solutions. 相似文献
12.
Masanori Hirano Shinzi Watanabe Etsuro Kato Yasunobu Mizutani Masayuki Kawai Yasuhisa Nakamura 《Journal of the American Ceramic Society》1999,82(10):2861-2864
The microstructure, crystal phase, electrical conductivity, and mechanical strength of less than 7-mol%-Sc2 O3 -doped zirconia ceramics fabricated by comparatively low-temperature sintering at 1200–1300°C for 1 h were investigated. Zirconia ceramics having a uniform microstructure (grain size < 0.5 μm) stabilized with 6 mol% Sc2 O3 showed high electrical conductivity (0.15 S/cm at 1000°C) and high fracture strength (660 MPa). With the increase of Sc2 O3 content from 3.5 to 7 mol%, the grain size, fracture strength, and electrical conductivity at 1000°C changed from 0.2 to 0.5 μm, 970 to 440 MPa, and 0.07 to >0.2 S/cm, respectively. Sc2 O3 -doped zirconia polycrystals with high fracture strength and high electrical conductivity are promising candidates for the electrolyte material of solid oxide fuel cells. 相似文献
13.
Pure Ba2 Ti9 O20 (BT29) was synthesized by a solid-state reaction in one step with various amounts of ZrO2 powder additive. The transformation kinetics of BT29 were investigated by quantitative X-ray diffractometry (XRD). The results show that stoichiometric powder mixtures transform to the BT29 phase by nucleation and growth mechanism between 1200° and 1300°C with 1.0 mol% ZrO2. The activation energy of the transformation was found to be 620±60 kJ/mol, but decreases to 515±30 kJ/mol when doped with 1.0 mol% ZrO2 . The addition of ZrO2 possibly changes the phase transformation mechanism of BT29 from diffusion controlled to interface controlled. 相似文献
14.
Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al2 O3 at 1300° and 1400° C with the aim of deriving information on the thermodynamic properties of the spinel phases. Synthetic samples in selected phase assemblages of the system were equilibrated with metallic nickel and a gas phase of known oxygen partial pressures at a total pressure of 1 atm. The data on NiO activities and directions of conjugation lines between coexisting oxide and spinel phases were used to establish the activity–composition relations in spinel solid solutions at 1300° and 1400°C. The MnAl2 O4 –NiAl2 O4 solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2 O4 from its oxide components (MnO + Al2 O3 ) at 1300° and 1400°C is calculated to be −24.97 and −26.56 kJ. mol−1 , respectively. The activities determined in the stoichiometric spinel solid solutions are more negative as compared with those predicted from cation distribution models. 相似文献
15.
EIJI TANI MASAHIRO YOSHIMURA SHIGEYUKI SOMIYA 《Journal of the American Ceramic Society》1983,66(7):506-510
The phase diagram of the system ZrO2 -CeO2 was rein-vestigated using hydrothermal techniques. Cubic, tetragonal, and monoclinic solid solutions are present in this system. The tetragonal solid solution decomposes to monoclinic and cubic solid solutions by a eutectoid reaction at 1050°50°C. The solubility limits of the tetragonal and cubic solid solutions are about 18 and 70 mol% CeO2 , respectively, at 1400°C, and about 16 and 80 mol% CeO2 , respectively, at 1200°C. Solubility limits of the monoclinic and cubic solid solutions are about 1.5 and 88 mol% CeO2 at 1000°C, and 1.5 and 98 mol% CeO2 at 800°C, respectively. The compound Ce2 Zr3 O10 is not found in this system. 相似文献
16.
The subsolidus phase relations in the entire system ZrO2 -Y2 O3 were established using DTA, expansion measurements, and room- and high-temperature X-ray diffraction. Three eutectoid reactions were found in the system: ( a ) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y2 O3 and ∼490°C, ( b ) cubic zirconia solid solutiow→δ-phase Y4 Zr3 O12 +hexagonalphase Y6 ZrO11 at 45 mol% Y2 O3 and ∼1325°±25°C, and ( c ) yttria C -type solid solution→wcubic zirconia solid solution+ hexagonal phase Y6 ZrO11 at ∼72 mol% Y2 O3 and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y2 O3 with ideal formula Y4 Zr3 O12 , and another, a new hexagonal phase, at 75 mol% Y2 O3 with formula Y6 ZrO11 . They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C -type solid solution, respectively. The extent of the cubic zirconia and yttria C -type solid solution fields was also redetermined. By incorporating the known tetragonal-cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO2 -Y2 O3 . 相似文献
17.
Phase equilibria in the system MnO–CoO–Cr2 O3 were investigated at 1300°C under controlled oxygen partial pressures by using the gas equilibration technique. The CoO activities in various phase assemblages of the system were measured by determining the partial pressures of oxygen in the gas phase for coexistence with metallic cobalt. The activity data revealed that at 1300°C, MnO–CoO and MnCr2 O4 –CoCr2 O4 solid solutions exhibit mild positive departures from ideal behavior. The activities in the stoichiometric spinel solutions were found to be in good agreement with those predicted from a model based on cation distribution equilibria. The standard free energy of formation of the compound CoCr2 O4 from its oxide components at 1300°C was determined as −37 636 J/mol, while that for MnCr2 O4 was found as −44 316 J/mol. 相似文献
18.
The phase relations for the system y2 o3 –Ta2 o5 in the composition range 50 to 100 mol% Y2 O3 have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C2221 ), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y2 O3 under 17000C and O phase in 70 mol% Y2 O3 up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y2 O3 and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y2 O3 , and at about 1990°C, 62 mol% Y2 O3 . A Phase diagram including the above three phases were not identified with each other. 相似文献
19.
W. A. SCHULZE T. G. MILLER J. V. BIGGERS 《Journal of the American Ceramic Society》1975,58(1-2):21-23
The disappearing-phase method was used to determine the extent of the solid-solution region of the PLZT system for conventionally sintered ceramics prepared at 1100° and 1300°C in a PbO atmosphere provided by pbZrO3 . A decrease in the firing temperature from 1300° to 1100°C lowers the solubility limit by 5 to 8 at.% La. Beyond the limits of solubility, additional La forms La2 Zr2 O7 and/or La2 Ti2 O7 . The limit determined by the disappearing-phase method (1300°C firing) is compared to values determined by the parametric method. The Curie temperature is stabilized at 5 at.% La for modified PbZrO3 (1300°C firing). 相似文献
20.
The phase relations for the Sc2 O3 -Ta2 O5 system in the composition range of 50-100 mol% Sc2 O3 have been studied by using solid-state reactions at 1350°, 1500°, or 1700°C and by using thermal analyses up to the melting temperatures. The Sc5.5 Ta1.5 O12 phase, defect-fluorite-type cubic phase (F-phase, space group Fm 3 m ), ScTaO4 , and Sc2 O3 were found in the system. The Sc5.5 Ta1.5 O12 phase formed in 78 mol% Sc2 O3 at <1700°C and seemed to melt incongruently. The F-phase formed in ∼75 mol% Sc2 O3 and decomposed to Sc5.5 Ta1.5 O12 and ScTaO4 at <1700°C. The F-phase melted congruently at 2344°± 2°C in 80 mol% Sc2 O3 . The eutectic point seemed to exist at ∼2300°C in 90 mol% Sc2 O3 . A phase diagram that includes the four above-described phases has been proposed, instead of the previous diagram in which those phases were not identified. 相似文献