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1.
P. Duran M. Gonzalez C. Moure J. R. Jurado C. Pascual 《Journal of Materials Science》1990,25(12):5001-5006
The phase relationships over a wide range of temperature and compositions in the ZrO2-CeO2 system have been reinvestigated. From DTA results, thermal expansion measurements andK
IC determinations it was established that additions of CeO2 to ZrO2 decreases the monoclinic to tetragonal ZrO2 transition temperature, from 990 ° C to 150 50 ° C, and an invariant eutectoid point at approximately 15 mol% CeO2 exists. The extent of the different single- and two-phase fields were determined with precise lattice parameter measurements on quenched samples. Evidence for the existence of a binary compound Ce2Zr3O10 (ø-phase) was obtained by X-ray diffraction. The ø-phase was stable below approximately 800 ° C, above which it decomposes into tetragonal zirconia + fluorite ceria solid solutions. Taking into account the polymorphic tetragonal-cubic transition and the narrowness of the two-phase tetragonal zirconia + fluorite ceria field above 2000 ° C, the existence of a new invariant eutectoid point was assumed, in which the metastable fluorite zirconia solid solution decomposes into tetragonal zirconia + fluorite ceria solid solutions. From the results obtained, the phase diagram also incorporates a eutectic point located at approximately 2300 ° C and 24 mol % CeO2. 相似文献
2.
S. Inamura H. Miyamoto Y. Imaida M. Takagawa K. Hirota O. Yamaguchi 《Journal of Materials Science》1994,29(18):4913-4917
In the system of ZrO2-Al2O3, cubic ZrO2 solid solutions containing up to 40 mol% Al2O3 crystallize at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of zirconium and aluminium alkoxides. At higher temperatures, they transform into tetragonal solid solutions. Metastable ZrO2 solid solution powders containing 25 mol% Al2O3 have been sintered at 1000–1150 °C under 196 M Pausing the hot isostatic pressing technique. The solid solution ceramics consisting of homogeneous microstructure with an average grain size of 50 nm exhibited a very high fracture toughness of 23 MN m –1.5. They have been characterized by X-ray diffraction and electron probe surface analyses. 相似文献
3.
ZrO2–CeO2 solid solutions (12 and 13 mol % CeO2) were prepared by mechanochemical synthesis in different media. The mechanical activation medium was shown to have a significant effect on the phase composition and particle size of the resultant powders. The conditions for sintering the powders were optimized. 相似文献
4.
Ceria–samaria (CeO2–Sm2O3) is one of the most interesting fluorite oxides since its ionic conductivity is higher than that of yttria-stabilized zirconia in air. However, these CeO2 -based oxides are partially reduced and develop electronic conductivity under fuel cell operating conditions. In their application to the SOFC system, their current densities and power densities are not at a satisfactory level. For the development of high-performance CeO2 electrolytes, it is important that the fluorite lattice of CeO2-based oxide be improved from the viewpoint of crystallography. In this study, it is assumed that the reduction of Ce4+ in the fluorite lattice was inhibited by expansion of the CeO2 lattice. In order to investigate the contribution of the expanded CeO2 lattice to reduction resistance, CeO2–Sm2O3 solid solution, calcia-doped CeO2–Sm2O3 solid solution, and a small amount of alkali element-doped CeO2–Sm2O3 -based oxide were prepared for comparison. It was found that the calcia or a small amount of alkali element-doped CeO2 solid solution enhanced the oxide ionic conductivity. The power density of the latter showed a high value at 800°C. It is concluded that the improved fuel cell performance can be attributed to the good reduction resistance in the fuel cell atmosphere. 相似文献
5.
The phase composition, electrical conductivity, and structural and electrical stability of ZrO2–Sc2O3–Cr2O3 solid electrolytes prepared by solid-state reactions involving three-step firing at 1350, 1850 (vacuum), and 1300°C were studied for compositions along two lines: x(0.91ZrO2 + 0.09Sc2O3)–yCr2O3 (I) andx(0.89ZrO2 + 0.11Sc2O3)–yCr2O3 (II), x + y = 1, y = 0–0.04. The results indicate that the ternary solid solutions withy= 0.01–0.02 retain a cubic structure in a broad temperature range, down to room temperature. This increases the low-temperature (<600°C) conductivity of the solid electrolytes, especially in system II. In both systems, Cr2O3 solubility is about 3 mol %. Stability tests at 900°C for 200 h reduce the conductivity of the solid electrolytes, particularly at the lower Sc2O3 content and in the presence of Cr2O3. The reduction in conductivity is due to the decomposition of the high-temperature tetragonal phase and the formation of a tetragonal phase with a low stabilizer content. 相似文献
6.
We prepared weakly agglomerated powders of ZrO2-CeO2 and HfO2-CeO2 solid solutions 5–8 nm in particle size, consisting of monoclinic and tetragonal phases. After heat treatment at 1200°C, the crystallite size was 30 and 14 nm, respectively. We also examined the effect of precipitate freeze drying on the crystallization of hafnia-based solid solutions containing up to 20 mol % CeO2. 相似文献
7.
L. I. Podzorova A. A. Il'icheva N. A. Mikhailina V. Ya. Shevchenko L. I. Shvorneva 《Inorganic Materials》2002,38(12):1235-1240
Data are presented on the phase composition of ZrO2–Al2O3–CeO2 powders containing 10, 30, and 70 mol %, prepared via coprecipitation and successive precipitation. The precipitation procedure is shown to have a strong effect on the phase composition of the heat-treated powders and the state (inter- or intracrystalline) of the T-ZrO2 phase, thereby changing its stability. At an Al2O3 content of 30 mol %, the M-ZrO2 content is independent of the precipitation procedure. 相似文献
8.
Glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems containing up to 33 wt% ZrO2 were prepared by a non-melting technique using zirconium n-propoxide, sodium methoxide and silicon tetraethoxide as raw materials. The mixed alkoxide solutions were exposed to moist air for hydrolysis. The fibrous gels were drawn from these solutions in the course of hydrolysis, and converted to the corresponding oxide glass fibres by heating at 500 to 700° C. It was found that chemical durability of the fibres toward alkaline solution increased with ZrO2 content. The weight loss due to the corrosion by 2 N NaOH solution at 96° C for 4 h was around 14 mg dm–2 for the fibres containing 17 to 26 wt% ZrO2, which was comparable to the alkali-resistant glasses so far obtained by the conventional melting technique. The glass fibres containing 33 wt% ZrO2 showed higher resistance. 相似文献
9.
H. Watanabe K. Hirota O. Yamaguchi S. Inamura H. Miyamoto N. Shiokawa K. Tsuji 《Journal of Materials Science》1994,29(14):3719-3723
In compositions having ZrO2/Y2O3=(74.25–71.25)/(0.75–3.75) (mol% ratio) with 25 mol% Al2O3, metastable t-ZrO2 solid solutions crystallize at 780° to 860°C from amorphous materials prepared by the simultaneous hydrolysis of zirconium, yttrium and aluminium acetylacetonates. Hot isostatic pressing has been performed for 1 h at 1130 and 1230°C under 196 MPa using their powders. Two kinds of material are fabricated: (i) perfect ZrO2 solid-solution ceramics and (ii) composites of ZrO2 solid solution and -Al2O3. Their mechanical properties are examined, in connection with microstructures and t/m ZrO2 ratios. Composites with a homogeneous dispersed -Al2O3 derived from solid-solution ceramics result in a remarkable increase of strength. 相似文献
10.
Ultrafine powders of cubic ZrO2 were obtained at about 270° C by heating hydrated amorphous ZrO2 in greater than 0.2 molal calcium acetate solutions. Ca2+ ions played a role as nucleii for crystallization and were introduced into distinct sites of the crystalline phases, that is, substituted for Zr4+ ions. Mn2+ ions produced almost the same effects on the crystallization of ZrO2·EPR spectra for powder samples containing Mn2+ ions apparently showed two types as follows: for tetragonal ZrO2 with a trace of monoclinic ZrO2, the central fine structure transitions (M=+1/2–1/2) showed a well-resolved hyperfine structure. In addition to the m=0 transition, forbidden m=±1 transitions were observed. For cubic ZrO2, the broad underlying response was observed as well as the hyperfine structure composed of six main peaks. 相似文献
11.
The mechanisms and kinetics of the solid-state reactionx ZrO2+yY2O3+(1–x–y) Ln2O2 ternary fluorite solid solution was studied in the temperature range 1350 to 1650° C by quantitative X-ray diffraction analysis. In the ZrO2-Y2O3-CeO2 system the fluorite formation process starts with the simultaneous interaction of CeO2 and Y2O3 with ZrO2, although the reaction rate of ceria with zirconia is more rapid. In the ZrO2-Y2O3-Nd2O3 system, the formation of a pyrochlore, Nd2Zr2O7, responsible for the formation process of the ternary fluorite solid solution. Finally, in the ZrO2-Y2O3-Er2O3 system, a competitive interaction of yttria and erbia occurred in the formation process of the ternary solid solution. The kinetic data were treated using the Avrami equation, and activation energies for the processes studied calculated. 相似文献
12.
The relationship between the starting temperature of the martensitic transformation, M
s, and the grain size of the parent phase, d, in ZrO2-containing ceramics was investigated. The experimental results showed that in tetragonal zirconia polycrystals doped with CeO2 (8 mol%) and Y2O3 (0.25 mol%) (8Ce, 0.25Y-TZP), the M
s temperature displays a linear relationship with d
–1/2, its slope being negative. A new explanation for this phenomenon, the so-called the size effect, has been presented, in which the grain size of the parent phase affects the M
s temperature through the strength of the parent phase. Thermodynamic calculation of the relationship between M
s and d gives a result consistent with the experimental ones. 相似文献
13.
Chih-Ming Lee Yi-Hao Pai Tzu-Piao Tang Chih-Cheng Kao Gong-Ru Lin Fuh-Sheng Shieu 《Materials Chemistry and Physics》2010,119(1-2):15-18
Blue-green emission of ZrO2:Ce3+ phosphor, prepared by solid-state reaction, is demonstrated. The phosphor presents a strong and broad photoluminescence band centered at 496 nm with excitation at 291 nm. The optimized Ce content is 2.5 mol% for the strongest emission of ZrO2:Ce3+ phosphors prepared without B2O3. The PL intensity is enhanced by at least 3 dB by adding 5.0 mol% B2O3 within the ZrO2:Ce3+ containing 5.0 mol% Ce during synthesis. Increase of the B2O3 flux effectively induces the Ce ions to substitute the Zr ions in ZrO2 lattice and causes the ZrO2 lattice distortion. The formation of Ce0.75Zr0.25O2 compound within the ZrO2:Ce3+ occurred when the Ce content is greater than or equal to 2.5 mol% for the phosphors prepared without B2O3 and leads to a degradation of the phosphor PL intensity due to the host effect. The addition of B2O3 during the preparation of phosphors containing Ce ions lower than or equal to 5.0 mol% essentially restrains the Ce0.75Zr0.25O2 formation and then enhances the blue-green PL. 相似文献
14.
The solubility limits of MgO in tetragonal zirconia were studied by combining the differential thermal analysis data and X-ray disappearing phase method. From these experiments a eutectoid reaction, tetragonal ZrO2 solid solution monoclinic ZrO2 solid solution + MgO, at 1120±10 °C and 1.6±0.2 mol% MgO was established. The solubility of MgO in tetragonal ZrO2 diminished as the temperature increased, and at 1700 °C the solubility was less than 0.5 mol% MgO. The extent of the cubic zirconia solid solution single field was determined by using precise lattice parameter measurements and SEM observations. In this way an invariant eutectoid point, cubic ZrO2 solid solution tetragonal ZrO2 solid solution + MgO, was located at 1420±10 °C and 14.8±0.5 mol% MgO. 相似文献
15.
Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y2O3·84(Zr1–x
Hf
x
)O2 withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol–1)/RT] cm2 sec–1 and the grain-boundary diffusion parameters byD=1.5×10–6exp [–309(kJ mol–1)/RT] cm3 sec–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O2 and MgO-(Zr+Hf)O2 indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO2 solid solutions. 相似文献
16.
Xiaohong Wang Guanzhong Lu Yun Guo Liangzhu Jiang Yanglong Guo Chunzhong Li 《Journal of Materials Science》2009,44(5):1294-1301
M
y
O
x
-modified CeO2–ZrO2 (M = Al, Ba, Cu, La, Nd, Pr, Si) solid solutions with the atomic ratio of Zr/Ce = 1 were prepared by the reverse microemulsion
method, and the effect of different additives on the structure characteristics, thermal stability, reducibility, and catalytic
activity of CeO2–ZrO2 solid solution for methane combustion were investigated. According to their different effects, M
y
O
x
can be classified into three groups. The first group includes SiO2 and Al2O3 which do not vary the crystalline phase of CeO2–ZrO2 solid solution but distort the crystal lattice obviously. They are the most effective additives for improving the surface
area, thermal stability, and reducibility of CeO2–ZrO2, and they can also promote the catalytic activity of Pd/CeO2–ZrO2 for methane combustion. The second group includes La2O3, Pr2O3, and Nd2O3, which can also keep the same crystalline phase, distort the crystal lattice, and improve the surface area and thermal stability
of the solid solution, but their effects are much weaker and they decrease the reducibility of the solid solution. The third
group includes BaO and CuO, whose effects on the property of CeO2–ZrO2 are much different. BaO and CuO, especially CuO, can decrease the thermal stability, and reduction extent of CeO2–ZrO2. CuO-modified CeO2–ZrO2 calcined at 550 °C shows the comparable high activity for the methane combustion, but after being calcined at 900 °C, CuO-modified
CeO2–ZrO2 would separate into three phases as CeO2, ZrO2, and CuO, resulting in the much lower activity for the methane catalytic combustion. 相似文献
17.
S. Kittaka K. Matsuno K. Tanaka Y. Kuroda M. Fukuhara 《Journal of Materials Science》2001,36(10):2511-2522
The interactions between vanadium pentoxide hydrate (V2O5·nH2O) sol and colloid solutions of ultra fine titanium dioxide TiO2 and zirconium dioxide particles ZrO2 were studied. When mixed with an intrinsic V2O5·nnH2O sol, TiO2 particles in the mixed sol are sandwiched by V2O5·nH2O layer sheets to form intercalation compounds. An Interlayer distance of V2O5·nH2O was increased by this treatment and the surface area was also increased from 7.9 m2 g–1 for the V2O5·nH2O to ca. 50 m2 g–1. When the TiO2 sol was contacted with K-type V2O5·nH2O, microporous nature appeared in the sample and the surface area incrased up to ca. 100 m2 g–1. The porous structure was maintained up to 300°C, above which materials were separated into two phases, anhydrous V2O5 and anatase type TiO2. Ultrafine ZrO2 particles were intercalated stoichiometrically in both intrinsic and K-type V2O5·nH2O giving ZrO2-V2O5·nH2O for all the mixing ratios from ZrO2/V2O5 = 5 to 20. Physico-chemical properties were almost unvaried and the materials were nonporous. Their surface areas are around 50 m2 g–1 for the former and around 60 m2 g–1 for the latter. The layered structure was maintained up to 300°C above which the sample was crystallized into ZrV2O7. The reaction temperature is about 150°C lower than that the heated mixture of ZrO2 and V2O5 powders. The electron microscope observations of the prepared materials showed that the number of the stacked layers was decreased from more than 10 sheets for the sample before intercalation to about 2–4 sheets by exfoliation. This indicates that V2O5·nH2O is exfoliated by ion exchangeably reacting to ultrafine titanium oxide and zirconium oxide particles. 相似文献
18.
V. Grover 《Materials Research Bulletin》2004,39(6):859-866
The phase relation in CeO2-Gd2O3 system has been established under slow cooled conditions from 1400 °C. Two phase regions, namely F-type cubic and C-type cubic, were observed in this system. A striking observation of this investigation is the stabilization of C-type gadolinia after Ce4+ substitution, which is attributed to decrease in average cationic size on Ce4+ substitution at Gd3+ site. The lattice thermal expansion behaviour of C-type gadolinia samples was investigated by High temperature-XRD. The lattice thermal expansion coefficient was found to gradually increase on increasing the Ce4+ content, within the C-type homogeneity range, in Ce1−xGdxO2−x/2 series. 相似文献
19.
The (metastable) tetragonal phase in 3–4 mol% Y2O3-ZrO2 alloys undergoes a transition to the monoclinic form in the 200–300 °C temperature range. Microcracking due to the volume change at this transition has been detected in these compositions by sharp acoustic emission during heating. The phase change was confirmed by X-ray diffraction, dilatometry and scanning electron microscopy. The monoclinic tetragonal transition in ZrO2-1 mol% Y2O3 alloy at 850–750 °C and the same phase change in 2, 3, 4 and 6 mol% Y2O3 compositions at the eutectoid temperature of about 560 °C was also clearly signalled by the acoustic emission counts during heating and cooling. There was no significant acoustic emission activity on heating and cooling the 9 and 12 mol% Y2O3 compositions, which are cubic. The acoustic emission data thus confirm the phase relations in the 1–12 mol% Y2O3 region, established by conventional methods such as differential thermal analysis, dilatometry and X-ray diffraction. 相似文献
20.
Lee TM Tsai RS Chang E Yang CY Yang MR 《Journal of materials science. Materials in medicine》2002,13(3):281-287
Plasma-sprayed hydroxyapatite (HA) coating, applied to metal substrates, can induce a direct chemical bond with bone and hence achieve a biological fixation of the implant. However, the poor bonding strength between the HA coating and the substrate has been a concern for the orthopedists. In a previous study, the zirconia-reinforced hydroxyapatite composite coatings (HA/ZrO2) could significantly improve the mechanical strength before and after soaking in simulated body fluid. This study aims to investigate the biological responses of osteoblasts on plasma-sprayed HA/ZrO2 coating. The osteoblasts derived from neonatal rat calvarial were cultured in Dulbeccos modified Eagle medium (DMEM) with fetal bovine serum (FBS) on the surface of plasma-sprayed HA coating, HA/ZrO2 coating, and ZrO2 coating, respectively. The biological responses were investigated by the cell growth (1, 3, 5, and 10 days) and the cell morphology under scanning electron microscopy (SEM) (3, 6, 12, 24 and 48 h). Examination by SEM revealed that osteoblasts on HA coatings exhibit less spreading during the medium phase (6 and 12 h), while, better morphologies were observed at the latter phases (24 and 48 h). This should be derived by the dissolution of HA coating in the culture medium. On HA/ZrO2 coating, the cells showed the poor morphologies at the latter phases (24 and 48 h). This could be explained by the no apatite formed at the surface HA/ZrO2 coating after soaking in simulated body fluid. The lower contents of ZrO2 coating in HA coating and the addition of other solid solution (ZrO2–MgO, CaO–ZrO2, ZrO2–CeO2) in HA coating are the two possible methods to improve the cytocompatibility of HA/ZrO2 coating. 相似文献