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1.
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
2.
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
3.
The phase diagram for the system ZrO2 -Y2 O3 was redetermined. The extent of the fluorite-type ZrO2 -Yz O3 solid solution field was determined with a high-temperature X-ray furnace, precise lattice parameter measurements, and a hydrothermal technique. Long range ordering occurred at 40 mol% Y2 O3 and the corresponding ordered phase was Zr3 Y4 OL12 . The compound has rhombohedra1 symmetry (space group R 3), is isostructural with UY6 Ol2 and decomposes above 1250±50°C. The results indicate that the eutectoid may occur at a temperature <400°C at a composition between 20 and 30 mol% Y2 O3 Determination of the liquidus line indicated a eutectic at 83± 1 mol% Y2 O3 and a peritectic at 76 ± 1 mol% Y2 O3 . 相似文献
4.
The dc conductivities of ZrO2 –Y2 O3 ceramic alloys (in the range 3–12 mol% of Y2 O3 ) have been obtained from ac impedance measurements at temperatures between 250° and 370°C. The Almond–West ac conductivity model has been applied to evaluate hopping rates in this system. The migration enthalpies were evaluated and shown to increase with yttria concentration, but all values determined were shown to be lower than the corresponding activation enthalpies for conductivity. The association enthalpies thus calculated were shown to be very small in 3 mol% Y2 O3 –ZrO3 and to increase with yttria concentration until the yttria contents were high enough to form fully stabilized cubic zirconia. For these samples the association enthalpies are about 0.19 eV, and no longer sensitive to yttria content. The low hopping rate at high yttria concentration might be attributed to low entropy in the system, which might be attributed to the formation of vacancy clusters and/or an ordering of the structure. 相似文献
5.
The Phase relationships in the system ZrO2 -MgO were reinvestigated over a wide range of temperatures and compositions. The extent of the cubic solid solution field was determined with precise lattice parameter measurements and a high-temperature X-ray furnace using analyzed samples. DTA results show that the addition of MgO to ZrO2 decreases the transition temperature for monoclinic ⇌ tetragonal ZrO2 and 1 mol% of MgO is soluble in the monoclinic zirconia at ∼1070°C.The invariant eutectiod point is at 13.5 ± 0.3 mol% MgO at 1406°± 7°C, which is in fair agreement with previous results by Grain. The ordered phase Mg2 Zr5 O12 (δ-phase) can form metastably in cubic solid solutions at temperatures as low as 800°C after prolonged annealing. Evidence for the existence of the ordered phase MgZr6 O13 (γ-phase) was obtained by electron diffraction technique. Conditions for the formation of this phase are described. The ordered phases in this system are metastable and their formation is an intermediate step in the eutectoid decomposition of the cubic phase. 相似文献
6.
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
7.
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
8.
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
9.
Kuan Zong Fung Anil V. Virkar David L. Drobeck 《Journal of the American Ceramic Society》1994,77(6):1638-1648
Cubic solid solutions in the Y2 O3 -Bi2 O3 system with ∼25% Y2 O3 undergo a transformation to a rhombohedral phase when annealed at temperatures ≤ 700°C. This transformation is composition-invariant and is thermally activated, and the product phase can propagate across matrix grain boundaries, indicating that there is no special crystallo-graphic orientation relationship between the product and the parent phases. Based on these observations, it is proposed that cubic → rhombohedral phase transformation in the Y2 O3 -Bi2 O3 system is a massive transformation. Samples of composition 25% Y2 O3 -75% Bi2 O3 with and without aliovalent dopants were annealed at temperatures ≤ 700°C for up to 10000 h. ZrO2 as a dopant suppressed while CaO and SrO as dopants enhanced the kinetics of phase transformation. The rate of cubic/rhombohedra1 interface migration (growth rate or interface velocity) was also similarly affected by the additions of dopants; ZrO2 suppressed while CaO enhanced the growth rate. Diffusion studies further showed that ZrO2 suppressed while CaO enhanced cation interdiffusion coefficient. These observations are rationalized on the premise that cation interstitials are more mobile compared to cation vacancies in cubic bismuth oxide. The maximum growth rate measured was ∼10−10 m/s, which is orders of magnitude smaller than typical growth rates measured in metallic alloys. This difference is explained in terms of substantially lower diffusion coefficients in these oxide systems compared to metallic alloys. 相似文献
10.
Subsolidus phase relations were established in the system Si3 N4 -SiO2 -Y2 O3 . Four ternary compounds were confirmed, with compositions of Y4 Si2 O7 N2 , Y2 Si3 O3 N4 , YSiO2 N, and Y10 (SiO4 )6 N2 . The eutectic in the triangle Si3 N4 -Y2 Si2 O7 -Y10 (SiO4 )6 N2 melts at 1500°C and that in the triangle Si2 N2 O-SiO2 -Y2 Si2 O7 at 1550°C. The eutectic temperature of the Si3 N4 -Y2 Si2 O7 join was ∼ 1520°C. 相似文献
11.
The chemical equilibrium for the system ZrO2 -CaO was rede termined for temperatures above ∼1000°C by heating reactive powders for extended periods of time. The eutectoid decom position of the cubic solid solution was found to occur at 1140°±40°C and 17.0±0.5 mol% CaO. Decomposition reac tions in sintered cubic solid solutions were studied using elec tron diffraction and transmission techniques. Decomposition follows metastable extensions of the boundary lines which sena rate two-phase regions from the adjacent cubic solid solution region. The appearance of the diffuse diffraction features in the electron diffraction patterns of cubic solid solutions Seems to be associated with short-range ordering of oxygen vacancies.'Duo ordered phases, CaZr4 O9 and Ca6 Zr19 O44 , were syn thesized and their upper limits of stability were determined to be 1235°±15° and 1355°±15°C, respectively. 相似文献
12.
J. LLorca José Y. Pastor Pedro Poza José I. Peña Isabel de Francisco Angel Larrea Victor M. Orera 《Journal of the American Ceramic Society》2004,87(4):633-639
The effect of Y2 O3 content on the flexure strength of melt-grown Al2 O3 –ZrO2 eutectics was studied in a temperature range of 25°–1427°C. The processing conditions were carefully controlled to obtain a constant microstructure independent of Y2 O3 content. The rod microstructure was made up of alternating bands of fine and coarse dispersions of irregular ZrO2 platelets oriented along the growth axis and embedded in the continuous Al2 O3 matrix. The highest flexure strength at ambient temperature was found in the material with 3 mol% Y2 O3 in relation to ZrO2 (Y2 O3 ). Higher Y2 O3 content did not substantially modify the mechanical response; however, materials with 0.5 mol% presented a significant degradation in the flexure strength because of the presence of large defects. They were nucleated at the Al2 O3 –ZrO2 interface during the martensitic transformation of ZrO2 on cooling and propagated into the Al2 O3 matrix driven by the tensile residual stresses generated by the transformation. The material with 3 mol% Y2 O3 retained 80% of the flexure strength at 1427°C, whereas the mechanical properties of the eutectic with 0.5 mol% Y2 O3 dropped rapidly with temperature as a result of extensive microcracking. 相似文献
13.
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
14.
α-Al2 O3 -doped (8 mol % Sc2 O3 )ZrO2 composite solid electrolyte has been investigated in the fabrication of solid-state ceramic gas sensors. The microstructure and electrical conductivity of the composite solid electrolyte have been measured over a range of temperature from 240°C to 596°C. The composite solid electrolyte has been found to exhibit a higher conductivity compared with the commonly used (8 mol% Y2 O3 )ZrO2 at temperatures above ∼448°C. The sensing characteristics for NO2 detection have been studied in the temperature range of 500–650°C at the low concentration from 10 to 30 ppm and at high concentration from 100 to 500 ppm of NO2 . The NO2 sensor was found to respond reproducibly and rapidly to the variations of NO2 , concentration, indicating that the composite solid electrolyte has promising application as a solid electrolyte for on-board exhaust gas monitoring. 相似文献
15.
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
16.
Nicole R. Harlan Rosa I. Merino José I. Peña Angel Larrea Victor M. Orera Carlos González Pedro Poza Javier LLorca 《Journal of the American Ceramic Society》2002,85(8):2025-2032
Al2 O3 -ZrO2 eutectics containing 0 to 12.2 mol% Y2 O3 (with respect to zirconia) were produced by directional solidification using the laser floating zone (LFZ) method. Processing variables were chosen to obtain homogeneous, colony-free, interpenetrating microstructure for all of the compositional range, optimum from the viewpoint of mechanical properties. The amount of cubic, tetragonal, or monoclinic zirconia phases was determined using a combination of Raman and X-ray diffraction techniques. Monoclinic zirconia was present up to concentrations of 3 mol% Y2 O3 , while the amount of tetragonal zirconia gradually increased with yttria content up to 3 mol%. Cubic zirconia was the only phase detected when the yttria content reached 12 mol%. The residual stresses in alumina were measured using the shift of the ruby R lines. Compressive stresses were isotropic when measured in the samples containing tetragonal and cubic zirconia, while higher tensile, anisotropic stresses were found when monoclinic zirconia was present. They were partially relieved in the eutectic sample without yttria. These results were compared with a thermoelastic analysis based on the self-consistent model. 相似文献
17.
MgO addition to 3 mol% Y2 O3 –ZrO2 resulted in enhanced densification at 1350°C by a liquid-phase sintering mechanism. This liquid phase resulted from reaction of MgO with trace impurities of CaO and SiO2 in the starting powder. The bimodal grain structure thus obtained was characterized by large cubic ZrO2 grains with tetragonal ZrO2 precipitates, which were surrounded by either small tetragonal grains or monoclinic grains, depending on the heat-treatment schedule. 相似文献
18.
F.F. LANGE 《Journal of the American Ceramic Society》1986,69(3):240-242
The average grain size of ZrO2 (+Y, o,) materials sintered at 1400°C was observed to depend significantly on the Y2 O3 content. The average grain size decreased by a factor of 4 to 5 for Y2 O3 contents between 0.8 and 1.4 mol% and increased at Y2 O3 contents of 6.6 mol%. Grain growth control by a second phase is the concept used to interpret these data; compositions with a small grain size lie within the two-phase tetragonal + cubic phase field, and the size of the tetragonal grains is believed to be controlled by the cubic grains. This interpretation suggests that the Y2 O3 -rich boundary of the two-phase field lies between 0.8 and 1.4 mol% Y2 O3 . Transformation toughened materials fabricated in this binary system must have a composition that lies within the two-phase field to obtain the small grain size required, in part, to retain the tetragonal toughening agent. 相似文献
19.
The tetragonal ( t ) and cubic ( c ) ZrO2 solid solutions in two-phase ZrO2 -8 wt% Y2 O3 ceramics have low and high solute content, respectively. Annealing samples sintered at 1600°C between 700° and 1400°C requires a change in the volume fraction of the coexisting phases, as well as their equilibrium Y2 O3 content. The enrichment in Y2 O3 content of the c -ZrO2 grains is accomplished by liquid-film migration involving the ubiquitous silicate grain-boundary phase, while the volume fraction of t -ZrO2 increases by the nucleation and growth of cap-shaped t -ZrO2 lenses. The interfaces between the c -ZrO2 matrix and the growing t -ZrO2 lenses are semicoherent. 相似文献
20.
Single-phase, cubic solid solutions of baseline composition 25% Y2 O3 —75% Bi2 O3 with and without aliovalent dopants were fabricated by pressureless sintering of powder compacts. CaO, SrO, ZrO2 , or ThO2 was added as an aliovalent dopant. Sintered samples were annealed between 600° and 650°C for up to 4000 h. Samples doped with ZrO2 or ThO2 remained cubic, depending upon the dopant concentration, even after long-term annealing. By contrast, undoped, CaO-doped, and SrO-doped samples transformed to the low-temperature, rhombohedral phase within ∼ 200 h. Conductivity measurements showed no degradation of conductivity in samples that did not undergo the transformation. In samples that underwent the transformation, a substantial decrease in conductivity occurred. The enhanced stability of the ZrO2 - and ThO2 -doped samples is rationalized on the basis of suppressed interdiffusion on the cation sublattice. 相似文献