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1.
Superplasticity-like Deformation of Nanocrystalline Monoclinic Zirconia at Elevated Temperatures 总被引:1,自引:0,他引:1
Michiyuki Yoshida Yutaka Shinoda Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2004,87(6):1122-1125
The deformation behavior of nanocrystalline monoclinic ZrO2 polycrystals (nanocrystalline MZP) was studied at 1273–1373 K in compression tests. The deformation of nanocrystalline MZP was characterized by stress exponent ( n = 2.5), grain-size exponent ( p = 2.5), and apparent activation energy ( Q = 350 kJ/mol). The values of n and p were similar to the superplasticity of high-purity Zn-22% aluminum alloy. The strain rate of nanocrystalline MZP was faster than that of Y2 O3 -stabilized tetragonal ZrO2 (Y-TZP) at temperatures lower than the monoclinic-tetragonal transition temperature. The strain rate of MZP gradually approached to that of Y-TZP as the temperature increased to the transition temperature. The comparison of present data with published data suggested that trace amount of impurities affected the deformation behavior of MZP. 相似文献
2.
Simon C. P. Wang Samim Anghaie Clayton Collins 《Journal of the American Ceramic Society》1991,74(9):2250-2257
Alumina and zirconia are considered for potential use in uranium hexafluoride (UF6 ) based nuclear gaseous-core reactors. The corrosion reactions of these oxide ceramics in high-temperature UF6 environment were investigated. Chemical thermodynamic analysis of the reactions was performed by using a computer data base and code package, FACT, to identify stoichiometric products. An alumina reaction tube in a flowing loop test unit was used to expose alumina and calcia-stabilized zirconia samples to UF, at temperatures from 873 to 1473 K and pressures of about 20.0 to 20.7 k Pa. Chemical reaction rates were measured by a discontinuous gravimetric method. X-ray diffraction and EDS analyses and SEM microstructural examination identified corrosion products and the morphology of the exposed surfaces. Results indicate that reactions were not inhibited or slowed down for either oxide. At 1273 K and below, alumina samples formed stable AIF3 scales and showed acceptable compatibility with UF6 . The rate of UF6 reaction with alumina and weight loss dramatically increased at 1473 K. Zirconia samples failed to resist degradation and reacted rapidly with UF6 at 1073 K. The maximum service temperatures for alumina and zirconia in UF6 environment do not seem to exceed 1273 and 973 K, respectively. 相似文献
3.
ROBERT RUH 《Journal of the American Ceramic Society》1963,46(7):301-307
The reactions between zirconia and titanium were studied by (1) weight change and bulk density determinations, (2) chemical analysis, (3) metallographic and petrographic analyses, (4) microhardness determinations, (5) lattice parameter measurements, (6) electron probe analysis, and (7) thermal conductivity determinations. These studies were made on specimens which had been fired in vacuum in the temperature range 1200° to 2000°C. Experimental data indicated that titanium contents up to 4 atomic % were retained at room temperature as a substitutional solid solution in zirconia. In titanium-rich binary alloys, zirconium and oxygen were retained in solid solution in titanium for zirconia contents up to approximately 10 mole %. In this case, the zirconium entered the titanium lattice substitutionally and the oxygen went into interstitial positions. 相似文献
4.
纳米颗粒粒径对等离子喷涂法制备氧化锆纳米涂层的影响 总被引:1,自引:1,他引:0
利用扫描电镜(SEM)、场发射扫描电镜(FESEM)、透射电镜(TEM)、比表面积吸附法(BET)等分析测试技术,研究了3种不同纳米尺寸氧化锫粉粒的造粒性能、沉积效率以及对等离子喷涂涂层晶粒大小、涂层熔融性能、结合强度的影响.结果表明:纳米氧化锆粉体一次颗粒粒径大小显著影响纳米粉体的喷雾造粒性能、沉积效率、涂层表面粗糙度、涂层晶粒粒径和结合强度大小.本试验中,利用颗粒一次粒径范围为50~70 nm的纳米氧化锆粉体,等离子喷涂制备了晶粒粒径范围为80~120 nm,沉积效率为43%,涂层表面粗糙度为5.92 μm,结合强度为27 MPa的纳米结构氧化锆涂层. 相似文献
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Jagadish C. Ray Asit B. Panda Chitta R. Saha Panchanan Pramanik 《Journal of the American Ceramic Society》2003,86(3):514-516
The polymer precursor method is very useful to prepare Nb5+ -stabilized nanocrystalline powders of t -ZrO2 . The precursor solution is composed of zirconium oxalate, niobium tartrate, and poly(vinyl alcohol), which help to form a network matrix to disperse the metal ions homogeneously. Nb5+ is an effective agent to stabilize t -ZrO2 , and ease of formation of the tetragonal phase increases with increasing dopant concentration. Thermal stability of t -phase is found up to 1700°C having 15 mol% Nb5+ , prepared at 600°C with particle sizes of 35 ± 5 nm. 相似文献
7.
Arun Suresh Merrilea J. Mayo Wallace D. Porter Claudia J. Rawn 《Journal of the American Ceramic Society》2003,86(2):360-362
In pure zirconia, ultrafine powders are often observed to take on the high-temperature tetragonal phase instead of the "equilibrium" monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal → monoclinic phase transformation is examined more broadly across the yttria–zirconia system. Using dilatometry and high-temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal → monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free-energy equilibrium between two phases. 相似文献
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Prevention of Low-Temperature Surface Transformation by Surface Recrystallization in Yttria-Doped Tetragonal Zirconia 总被引:1,自引:0,他引:1
Philip J. Whalen Franz Reidinger Robert F. Antrim 《Journal of the American Ceramic Society》1989,72(2):319-321
The low-temperature (100° to 400°C) tetragonal to monoclinic transformation in yttria-doped tetragonal zirconia (Y-TZP) can be inhibited by a postsintering grinding and annealing treatment. The surface region so treated contains fine tetragonal grains which have recrystallized from the severely damaged ground surface. The various features of the recrystallized surface that may affect the lowtemperature transformation are analyzed. 相似文献
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David B. Marshall Michael R. Jarnes John R. Porter 《Journal of the American Ceramic Society》1989,72(2):218-227
The mechanical properties of high-toughness magnesia-partially-stabilized zirconia were found to be dramatically altered by a single cooling cycle between room temperature and − 196°C. Raman spectroscopy and X-ray diffraction were used to correlate the changes in mechanical properties with structural changes that occur at temperatures below ∼− 100°C. Most of the tetragonal precipitates that are responsible for toughening transformed to an orthorhombic phase with unit-cell volume intermediate between those of the tetragonal and monoclinic phases. The orthorhombic phase was stable with heating to 300°C, but it transformed back to the tetragonal structure when heated to 400°C. Surprisingly, the orthorhombic phase was not readily transformable by stress, with the consequence that, after the cooling cycle, most of the high-toughness properties of the original tetragonal-containing material were lost. 相似文献
13.
Alvise Benedetti Giuliano Fagherazzi Francesco Pinna 《Journal of the American Ceramic Society》1989,72(3):467-469
Factors concerning the stabilization of the tetragonal and cubic phases, metastable at room temperature, with respect to the monoclinic stable phase in ultrafine zirconia powders are studied. The importance of Na+ ions in the initial zirconia amorphous gel in obtaining a cubic phase has been confirmed. By an X-ray diffraction study using a new peak profile fitting procedure, the amount of the crystalline phases and their microstructural properties (crystallite size and lattice distortions) have been obtained. 相似文献
14.
Thermally stable zirconia with a large BET surface area was prepared by using zirconium atrane derivatives and commercial alkyltrimethylammonium bromide. The zirconia samples were characterized by wide-angle X-ray diffraction, thermal analysis and N2 adsorption/desorption analysis. The results showed that the present zirconia existed as a thermally stable tetragonal crystallite and consisted of mesoporous material with microporous contribution. The BET surface area was found larger than 240 m2/g even after calcination at 600 °C. The present zirconia after sulfation was applied to the skeletal isomerization of 1-butene, and its catalytic activity was found superior to that of the conventional sulfated zirconia. 相似文献
15.
Effect of Grain Size on the Sliding Wear and Friction of Alumina at Elevated Temperatures 总被引:3,自引:0,他引:3
Tetsuya Senda Eiichi Yasuda Masaki Kaji Richard C. Bradt 《Journal of the American Ceramic Society》1999,82(6):1505-1511
The sliding friction and wear of three different grain-size aluminas were studied from room temperature through 1000°C. The coefficient of friction revealed two distinct regions of decrease with increased temperature, with a transition at ∼700°C. Below 700°C, the coefficient of friction decreased rapidly with increased temperature (∼10-3 /°C). However, above 700°C, the decrease was more gradual (∼10-5 /°C). This was believed to be related to a brittle-to-ductile transition at the wear surface. The coefficient of friction was only weakly dependent on grain size, because the largest grain sizes exhibited slightly higher friction coefficients. However, the specific wear loss of the aluminas increased with increased grain size at room temperature and at 600°C, both below the 700°C transition. The primary mechanism of wear was ascertained to be brittle microfracture along grain boundaries. At 1000°C, above the 700°C transition, the specific wear loss was significantly decreased and appeared to be independent of the alumina grain size. At 1000°C, the wear surfaces developed a thin layer of fine grains formed by dynamic recrystallization. The grain size within the thin layer was in agreement with the previously reported grain-size/Zener-Hollomon parameter relationship. 相似文献
16.
Yingkai Liu Chenglin Zheng Wengzhong Wang Yiongjie Zhan Guang Hou Wang 《Journal of the American Ceramic Society》2002,85(12):3120-3122
ZrO2 nanorods are prepared by annealing precursor powders produced in the novel inverse microemulsion system. The length and diameter of ZrO2 nanorods are a few micrometers and 40–100 nm, respectively. The microstructure of the resultant nanorods are studied by XRD, TEM, selected area electron diffraction, and Raman spectroscopy. The ZrO2 nanorods are single crystalline and have monoclinic structure. The formation of ZrO2 nanorods is discussed. 相似文献
17.
Crystallite Size and Microstrain of Thermally Aged Low-Ceria- and Low-Yttria-Doped Zirconia 总被引:1,自引:0,他引:1
The final phases of zirconia powders depend on the synthesis method employed, and the amounts of stabilizer present. In this study, ceria- and yttria-doped zirconia powders were prepared by urea hydrolysis and subsequent hydrothermal treatment. The amount of tetragonal ( t ) vs monoclinic ( m ) phase in the powders increased with increasing stabilizer content, while the tetragonal phase size decreased and the microstrain of t crystals remained unchanged. The thermal degradation behavior of the metastable t phase in zirconia containing a low CeO2 or YO1.5 doping level was explored during aging treatment by means of X-ray line profile broadening analysis. Both ultrafine yttria- and ceria-doped zirconia powder pellets exhibit isothermal t → m transformation after aging at 900°C for various times. It is argued that a crystallite size effect, rather than the dopant valence, dictates the occurrence of the t → m transformation in ultrafine zirconia powders. The change in crystallite sizes of both t and m phases during aging depends significantly on the amount of stabilizer, aging time, and mechanism of t → m phase transformation. However, the change of microstrain in both t and m phases is related to the amount of stabilizers present and the matrix constraints. 相似文献
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Synthesis and Colloidal Processing of Zirconia Nanopowder 总被引:6,自引:0,他引:6
Nanosized tetragonal 3 mol% Y2 O3 -doped ZrO2 powder was produced by hydrothermal precipitation from metal chlorides and urea sol followed by a washing–drying treatment and calcination. The effects on powder properties of powder washing by water and ethanol with subsequent centrifuging, with possible deagglomeration using microtip ultrasonication, were experimentally shown. Ultrasonic irradiation induced pressure waves, which generated cavities that could violently collapse, producing intense stress. This induced stress was effective in minimizing secondary particle size, deagglomerating the powder, redispersing the ZrO2 after all the washing–centrifuging cycles, and minimizing mean aggregate size after final calcination. A uniformly aggregated tetragonal ZrO2 nanopowder with a mean secondary particle size of ∼45 nm and without hard agglomerates was prepared. The properties of the nanopowders produced by colloidal processing and CIP were studied. Determination of the best suspension parameters allowed for low-temperature sinterability, which resulted in a nanograined ∼95 nm ceramic. 相似文献
20.
An yttria-stabilized zirconia powder, free of monoclinic phase, may be prepared by an oxalate method in an ethanol solution at strong acidity. This study demonstrates that the control of pH in the preparation of precursors has a significant effect on the ability of precursors to crystallize and hence plays an important role in determining the formation and fraction of various crystalline phases in the resulting yttria-stabilized zirconia powder. With the increase of pH, a precursor with a certain crystalline form may be transformed into an amorphous precursor, and a monoclinic phase appers in the phase composition of the resulting powder. The results of XRD analysis and Raman spectroscopy are discussed. 相似文献