共查询到20条相似文献,搜索用时 31 毫秒
1.
Yongsheng Zhang Litian Hu HaoKun Li Jianmin Chen 《Journal of the American Ceramic Society》2008,91(4):1332-1334
ZrO2 –Y2 O3 –CuO nanocrystalline powders have been synthesized using a chemical coprecipitation method. Nano-powders were compacted uniaxially and densified in a muffle furnace. Densification studies show that the presence of CuO accelerates the densification process of ZrO2 (3Y). A fully dense (>96%) pellet of ZrO2 (3Y)/5 mol% CuO was obtained after sintering at 900°C, with a very small grain size of 44 nm calculated by X-ray line broadening. 相似文献
2.
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
3.
Khalil Abdelrazek Khalil Sug Won Kim 《International Journal of Applied Ceramic Technology》2006,3(4):322-330
High-frequency induction heat sintering (HFIHS) is a comparatively new technique that consolidates metals and ceramics very rapidly to full density. In this work, superfast densification behavior and the attendant microstructural features of Al2 O3 –(ZrO2 +8% mol Y2 O3 ) composites processed by HFIHS were investigated. The effects of processing parameters such as sintering temperatures, pressures, and heating rate, on the mechanical and microstructural properties were studied. The results indicated that HFIHS was effective in the preparation of fine-grained, nearly fully dense Al2 O3 –8YSZ ceramics from the powder with a smaller particle size by optimizing the overall processing parameters. 相似文献
4.
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
5.
Cristina Siligardi Luca Lusvarghi Monia Montorsi Cecilia Vernia 《Journal of the American Ceramic Society》2008,91(3):990-995
In this work several complementary techniques have been employed to carefully characterize the sintering and crystallization behavior of CaO–Al2 O3 –ZrO2 –SiO2 glass powder compacts after different heat treatments. The research started from a new base glass 33.69 CaO–1.00 Al2 O3 –7.68 ZrO2 –55.43SiO2 (mol%) to which 5 and 10 mol% Al2 O3 were added. The glasses with higher amounts of alumina sintered at higher temperatures (953°C [lower amount] vs. 987°C [higher amount]). A combination of the linear shrinkage and viscosity data allowed to easily find the viscosity values corresponding to the beginning and the end of the sintering process. Anorthite and wollastonite crystals formed in the sintered samples, especially at lower temperatures. At higher temperatures, a new crystalline phase containing ZrO2 (2CaO·4SiO2 ·ZrO2 ) appeared in all studied specimens. 相似文献
6.
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
7.
Andreas Krell 《Journal of the American Ceramic Society》1995,78(5):1417-1419
Monolithic alumina bodies with a grain size of 0.5 μm and submicrometer tetragonal ZrO2 (3 mol% Y2 O3 ) polycrystals were produced and investigated. With decreasing indentation load, the hardness increases but may again decrease below about 5 N; relevant measurements require the application of fairly high loads. Decreasing grain sizes increase the hardness of alumina and zirconia ceramics even for very small grain sizes in the submicrometer range. 相似文献
8.
Dae-Joon Kim Paul F. Becher Camden R. Hubbard 《Journal of the American Ceramic Society》1993,76(11):2904-2908
Tetragonal ZrO2 ( t -ZrO2 ) solid solutions were prepared with addit ons of 2 mol% Y2 O3 plus up to 0.45 mol% Nb2 O5 . The thermal expansion coefficients in both the a- and c -axis lattice directions increased with Nb2 O5 alloying and the thermal expansion in the c -axis direction was greater than that in the a -axis direction over the entire composition range. This anisotropic thermal expansion behavior was related to the 4-fold coordination of Nb5+ with oxygen ions in t -ZrO2 solid solutions in the system ZrO2 –Y2 O3 –Nb2 O5 . The fracture toughness continuously increased with Nb2 O5 alloying and suggested that the c/a axial ratio is a more significant factor than the internal stress that arises from the thermal expansion anisotropy, in the determination of the transformability of t -ZrO2 in this system. 相似文献
9.
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
10.
Ehrenfried Zschech Paris N. Kountouros Günter Petzow Peter Behrens Alex Lessmann Ronald Frahm 《Journal of the American Ceramic Society》1993,76(1):197-201
Valence state and site symmetry of Ti ions in TiO2 –Y2 O3 –ZrO2 powders with 2 mol% Y2 O3 and 5, 10, 15, and 20 mol% TiO2 , respectively, are studied by X-ray absorption near-edge spectroscopy (XANES). Tetravalent Zr4+ ions are replaced predominantly by Ti4+ ions. Within the solubility region of Ti ions, a subsequent displacement of Ti ions from the center of symmetry is observed with increasing TiO2 content in TiO2 –Y2 O3 -stabilized tetragonal ZrO2 polycrystals (Ti-Y-TZP) under investigation. This behavior cannot be interpreted with a random substitution of Ti4+ ions on Zr4+ lattice sites. On the contrary, this correlation between the TiO2 content in Ti-Y-TZP and the shift of Ti ions indicates an increasing interaction between the Ti ions with growing TiO2 content, caused by a subsequent clustering of Ti ions. 相似文献
11.
Koji Matsui Nobukatsu Ohmichi Michiharu Ohgai Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2005,88(12):3346-3352
The sinterabilities of fine zirconia powders including 5 mass% Y2 O3 were investigated, with emphasis on the effect of Al2 O3 at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al2 O3 increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al2 O3 was lower than that of a powder compact without Al2 O3 . The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al2 O3 included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al2 O3 enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage. 相似文献
12.
Nithyanantham Thangamani Ashutosh S. Gandhi Vikram Jayaram Atul H. Chokshi 《Journal of the American Ceramic Society》2005,88(10):2696-2701
This study examined pressure consolidation of amorphous Al2 O3 –15 mol% Y2 O3 powders prepared by co-precipitation and spray pyrolysis. The two amorphous powders had similar true densities and crystallization sequences. Uniaxial hot pressing was carried out at 450°–600°C with a moderate pressure of 750 MPa. The co-precipitated powder could be hot pressed to a maximum relative density of 98% and remained amorphous. Pressure adversely affected the densification of the spray-pyrolyzed powder by favoring an early crystallization of γ-Al2 O3 phase at 580°C. Plastic deformation of the amorphous phase is believed to be responsible for the large densification of the amorphous powders. 相似文献
13.
Composite ceramic materials based on Si3 N4 and ZrO2 stabilized by 3 mol% Y2 O3 have been formed using aluminum isopropoxide as a precursor for the Al2 O3 sintering aid. Densification was carred out by hot-pressing at temperatures in the range 1650° to 1800°C, and the resulting micro-structures were related to mechanical properties as well as to oxidation behavior at 1200°C. Densification at the higher temperatures resulted in a fibrous morphology of the Si3 N4 matrix with consequent high room-temperature toughness and strength. Decomposition of the ZrO2 grains below the oxidized surface during oxidation introduced radial stresses in the subscalar region, and from the oxidation experiments it is suggested that the ZrO2 incorporated some N during densification. 相似文献
14.
Koji Matsui Kenji Tanaka Takanori Yamakawa Masato Uehara Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2007,90(2):443-447
The shrinkage behavior of fine zirconia powders containing 2.9 and 7.8 mol% Y2 O3 was investigated to clarify the effect of Y2 O3 concentration on the initial sintering stage. The shrinkage of powder compact was measured under both conditions of constant rates of heating (CRH) and constant temperatures. CRH measurements revealed that when the Y2 O3 concentration of fine zirconia powder increased, the starting temperature of shrinkage shifted to a high temperature. Isothermal shrinkage measurements revealed that the increase in Y2 O3 concentration causes the shrinkage rate to decrease. The values of activation energy ( Q ) and frequency-factor term (β0 ) of diffusion at initial sintering were estimated by applying the sintering-rate equation to the isothermal shrinkage data. When the Y2 O3 concentration increases, both Q and β0 of diffusion increase. It is, therefore, concluded that the increase in Y2 O3 concentration of fine zirconia powder decreases the shrinkage rate because of increasing Q of diffusion at the initial stage of sintering. 相似文献
15.
Koji Tsukuma 《Journal of the American Ceramic Society》2000,83(12):3219-3221
Composites of β-Ce2 O3 ·11Al2 O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2 , ZrO2 (2 mol% Y2 O3 ), and Al2 O3 . The composites had microstructures composed of elongated grains of β-Ce2 O3 ·11Al2 O3 in a Y-TZP matrix. The β-Ce2 O3 ·11Al2 O3 decomposed to α-Al2 O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β-Ce2 O3 ·11Al2 O3 divided into several grains of α-Al2 O3 and ZrO2 doped with Y2 O3 and CeO2 . High-temperature bending strength of the oxygen-annealed α-Al2 O3 composite was comparable to the β-Ce2 O3 ·11Al2 O3 composite before annealing. 相似文献
16.
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
17.
Kentaro Fukuda Teiichi Hanada Setsuhisa Tanabe Takeshi Yao 《Journal of the American Ceramic Society》2002,85(4):915-920
Amorphous films in the system Al2 O3 –Y2 O3 were prepared by the rf sputtering method in the range of 0–76 mol% Y2 O3 , and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al2 O3 –Y2 O3 films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y2 O3 content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al2 O3 –Y2 O3 films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y2 O3 content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y2 O3 , the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y2 O3 content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al2 O3 –Y2 O3 , the change of the coordination state of aluminum ions has an important effect on physical properties. 相似文献
18.
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
19.
Jae Ryong Kim Do-Hyeong Kim Chong Hee Kim 《Journal of the American Ceramic Society》1990,73(8):2567-2569
The effects of ZrO2 and Y2 O3 on the densification of hotpressed Si3 N4 -Zr(Y)O2 composites have been studied. High density could not be obtained by the addition of pure or 3-mol%-Y2 O3 -doped ZrO2 in this composite; however, nearly full density (>97%) could be obtained in Si3 N4 using 6- and 8-mol%-Y2 O3 -doped ZrO2 . It is concluded that Y2 O3 diffusing out from the added Zr(Y)O2 promoted the densification and that ZrO2 also had some role in the formation of an oxynitride glass. 相似文献
20.
M. C. Caracoche J. A. Martínez P. C. Rivas A. M. Rodríguez D. G. Lamas G. E. Lascalea N. E. Walsöe de Reca 《Journal of the American Ceramic Society》2005,88(6):1564-1567
A nanocrystalline ZrO2 –10 mol% Y2 O3 powder synthesized by a nitrate–citrate gel-combustion process and stabilized in the metastable t '-form of the tetragonal phase has been characterized using mainly the Perturbed Angular Correlations technique. The determined hyperfine interaction allows a clear distinction between the zirconium surroundings in the t '-form and those already known of the other forms of the tetragonal phase. Oxygen vacancies movement is revealed as a slow diffusion involving a very small activation energy. As the powder is heated, a transformation is observed to occur around 560°C, which is consistent with a t '-to-cubic transition. 相似文献