共查询到20条相似文献,搜索用时 31 毫秒
1.
The phase relations of the systems ZrO2 –TiO2 and ZrO2 –TiO2 –SiO2 were investigated. X-ray diffraction techniques served as the principal means of analysis. The binary system ZrO2 –TiO2 was found to be one of partial solid solutions with no intermediate compounds. A eutectic point was found to exist at 50 to 55 weight % ZrO2 and 1600°C. A preliminary investigation of the ternary system ZrO2 –TiO2 –SiO2 , although not extensive, resulted in a better understanding of this system, with a fairly accurate location of some of its boundary lines. A eutectic point was located at 2% ZrO2 , 10% TiO2 , and 88% SiO2 at approximately 1500°C. 相似文献
2.
A furnace for use in conjunction with the X-ray spectrometer was developed which was capable of heating small powdered specimens in air to temperatures as high as 1850°C. This furnace was also used for the heating and quenching of specimens in air from temperatures as high as 1850°C. An area of two liquids coexisting between 20 and 93 weight % TiO2 above 1765°± 10°C. was found to exist in the system TiO2 –SiO2 , which is in substantial agreement with the previous work of other investigators. The area of immiscibility in the system TiO2 –SiO2 was found to extend well into the system TiO2 –ZrO2 –SiO2 . The two liquids were found to coexist over a major portion of the TiO2 (rutile) primary-phase area with TiO2 (rutile) being the primary crystal beneath both liquids. The temperature of two-liquid formation in the ternary was found to fall about 80°C. with the first additions of ZrO2 up to 3%. With larger amounts of ZrO2 the change in the temperature of the boundary of the two-liquid area was so slight as to be within the limits of error of the temperature measurement. Primary-phase fields for TiO2 (rutile), tetragonal ZrO2 , and ZrTiO4 were found to exist in the system TiO2 –ZrO2 –SiO2 . SiO2 as high cristobalite is known to exist in the system TiO2 –ZrO2 –SiO2 . 相似文献
3.
Hyun M. Jang Jong H. Moon Cheol W. Jang 《Journal of the American Ceramic Society》1992,75(12):3369-3376
Al2 O3 –ZrO2 –SiC whisker composites were prepared by surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2 O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2 O3 matrix. The fracture toughness values of the Al2 O3 –15 vol% ZrO2 –20 vol% SiC whisker composites (∼12 MPa.m1/2 ) are substantially greater than those of comparable Al2 O3 –SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot-pressed composites. 相似文献
4.
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
5.
Ana M. Espino Luis A. Díaz Adolfo Fernández Ramón Torrecillas José S. Moya 《Journal of the American Ceramic Society》2005,88(4):1000-1003
The wettability of binary and ternary glasses belonging to SiO2 –Al2 O3 –ZrO2 diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO2 –Al2 O3 –ZrO2 (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO2 slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo5+ , Mo4+ , and Mo6+ . After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo6+ . 相似文献
6.
A thermodynamic evaluation of the ZrO2 -MgO system has been developed and combined with previous assessments of the ZrO2 –YO1.5 and YO1.5 –MgO systems to describe the ZrO2 –YO1.5 -MgO Systems to describe the ZrO2 –YO1.5 -MgO system by means of Bonnier's equation. The calculated results are shown by isothermal and vertical sections, a projection of the liquidus surfaces, and the reaction scheme. Comparisons between calculated and experimental diagrams demonstrate that the calculations satisfactorily account for most of the available experimental data. 相似文献
7.
Mohsen Mahmoudysepehr Vahak K. Marghussian 《Journal of the American Ceramic Society》2009,92(7):1540-1546
Zirconolite (CaZrTi2 O7 ) is a mineral that has a high containment capacity for actinides and lanthanides and is considered to be a good candidate for the immobilization of radioactive wastes. The glass–ceramic technique seems to be a very suitable and convenient method to produce zirconolite crystals by precipitating them in a specific glass matrix. In this study, development of a new zirconolite-based glass–ceramic belonging to SiO2 –PbO–CaO–ZrO2 –TiO2 –(B2 O3 –K2 O) system was investigated. The presence of PbO, together with B2 O3 and K2 O, allowed the preparation of a X-ray diffraction (XRD) amorphous glass with a relatively high concentration of ZrO2 and TiO2 , which was successfully converted to a glass–ceramic containing 34 wt% of zirconolite after heating at 770°C for 4 h. Differential thermal analysis, XRD, scanning electron microscope, and energy dispersive X-ray spectroscopy were used to determine the crystallization conditions, identify the crystallized phases, determine their compositions and quantities and observe and analyze the microstructures. The zirconolite crystals showed a platelet morphology with a monoclinic structure characterized by a =1.246 nm, b =0.7193 nm, c =1.128 nm, and β=100.508°. 相似文献
8.
Mikio Fukuhara 《Journal of the American Ceramic Society》1989,72(2):236-242
The effect of Al2 O3 and (Ti or Si)C additions on various properties of a (Y)TZP (yttria-stabilized tetragonal zirconia polycrystal)–Al2 O3 –(Ti or Si)C ternary composite ceramic were investigated for developing a zirconia-based ceramic stronger than SiC at high temperatures. Adding Al2 O3 to (Y)TZP improved transverse rupture strength and hardness but decreased fracture toughness. This binary composite ceramic revealed a rapid loss of strength with increasing temperature. Adding TiC to the binary ceramic suppressed the decrease in strength at temperatures above 1573 K. The residual tensile stress induced by the differential thermal expansion between ZrO2 and TiC therefore must have inhibited the t - → m -ZrO2 martensitic transformation. It was concluded that a continuous skeleton of TiC prevented grain-boundary sliding between ZrO2 and Al2 O3 . In contrast, for the ternary material containing β-SiC in place of TiC, the strength decreased substantially with increasing temperature because of incomplete formation of the SiC skeleton. 相似文献
9.
Francisco del Monte Willa Larsen John D. Mackenzie 《Journal of the American Ceramic Society》2000,83(6):1506-1512
Metastable tetragonal ZrO2 phase has been observed in ZrO2 –SiO2 binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO2 tetragonal stabilization in binary oxides such as Y3 O2 –ZrO2 , MgO–ZrO2 , or CaO–ZrO2 . In these binary oxides, oxygen vacancies cause changes or defects in the ZrO2 lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO2 –SiO2 binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO2 crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O− groups). In this paper, FT-IR and 29 Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O− is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples. 相似文献
10.
The energetics of martensitic transformation in ZrO2 is studied using a thermodynamic approach, with particular reference to Al2 O3 –ZrO2 composites. The different characters of three types of transformation-toughened ceramics are analyzed, and several factors affecting the t → m transformation in Al2 O3 –ZrO2 composites are discussed. The expression of transformation temperature dependence on particle size is derived and has good agreement with experimental results. The energetics concerned with nucleation of martensitic transformation is also discussed. 相似文献
11.
Data obtained by quenching, thermal, and high-temperature X-ray techniques are presented for the three binary systems CaF2 –BeF2 , MgF2 –BeF2 , and LiF–MgF2 . The systems CaF2 –BeF2 and MgF2 –BeF2 are presented as weakened models of the systems ZrO2 –SiO2 and TiO2 –SiO2 , respectively. The compound CaBeF4 is a model of ZrSiO4 (zircon). New data obtained for the system LiF–MgF2 explain many discrepancies among the results of previous authors. Solid solution is almost complete between LiF and MgF2 at elevated temperatures, but a small gap occurs at the eutectic (735°C.) with extensive exsolution at lower temperatures. 相似文献
12.
Zirconia-rich subsolidus phase relationships in the ZrO2 –Sc2 O3 and ZrO2 –In2 O3 systems were investigated. Phase inconsistencies in the ZrO2 –Sc2 O3 system resulted from a diffusionless cubic-to-tetragonal ( t' ) phase transformation not being recognized in the past. Through three different measuring techniques, along with microstructural observations, the solubility limits of the tetragonal and cubic phases were determined. 相似文献
13.
Phase equilibrium relations in the system PbO–TiO2 –ZrO2 were studied by quenching in the range where the PbO content is 50 mole % and more. Isotherms were examined at 1100°, 1200°, and 1300°C and tie lines were determined between the liquid and solid solution in equilibrium. The incongruent melting point of PbZrO3 was 1570°C and the equilibrium between liquid, PbO-type solid, and PbZrO3 is peritectic. Pb(Zr,Ti)O3 solid solutions containing more than 14 mole % PbZrO3 decomposed to liquid, ZrO2 , and Pb(Zr,Ti)O3 and the decomposition temperature rises from 1340° to 1570°C with increasing PbZrO3 content. The system PbTiO3 –PbZrO3 should not be treated as a binary, but as a section of the ternary system. 相似文献
14.
Vibrational spectra were measured and analyzed for HfO2 –ZrO2 solid solutions. Some Raman bands in the high–wave–number region shift almost linearly with changes in ZrO2 concentration between the pure end–members; their band locations can be used to determine ZrO2 concentrations in annealed solid solutions. The Raman bands of pure ZrO2 and HfO2 can be correlated using the band shifts of the solid solutions. Induced stress causes band shifts for the solid solutions. 相似文献
15.
Bikramjit Basu T. Venkateswaran Doh-Yeon Kim 《Journal of the American Ceramic Society》2006,89(8):2405-2412
In a recent work, 1 we have reported the optimization of the spark plasma sintering (SPS) parameters to obtain dense nanostructured 3Y-TZP ceramics. Following this, the present work attempts to answer some specific issues: (a) whether ZrO2 -based composites with ZrB2 reinforcements can be densified under the optimal SPS conditions for TZP matrix densification (b) whether improved hardness can be obtained in the composites, when 30 vol% ZrB2 is incorporated and (c) whether the toughness can be tailored by varying the ZrO2 –matrix stabilization as well as retaining finer ZrO2 grains. In the present contribution, the SPS experiments are carried out at 1200°C for 5 min under vacuum at a heating rate of 600 K/min. The SPS processing route enables retaining of the finer t -ZrO2 grains (100–300 nm) and the ZrO2 –ZrB2 composite developed exhibits optimum hardness up to 14 GPa. Careful analysis of the indentation data provides a range of toughness values in the composites (up to 11 MPa·m1/2 ), based on Y2 O3 stabilization in the ZrO2 matrix. The influence of varying yttria content, t -ZrO2 transformability, and microstructure on the properties obtained is discussed. In addition to active contribution from the transformation-toughening mechanism, crack deflection by hard second phase brings about appreciable increment in the toughness of the nanocomposites. 相似文献
16.
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
17.
Hidehiko Kobayashi Kenichi Shimosaka Miki Saitoh Takashi Mitamura 《Journal of the American Ceramic Society》1993,76(9):2389-2392
We investigated the conditions for low-temperature synthesis of ZrC fine powder from ZrO2 –Mg–CH4 . The synthesis utilizes a thermite-type reaction, with Mg as the reducing agent, and a reaction between Mg and CH4 gas as a carbon source. The Mg/ZrO2 molar ratio as well as the heating rate were varied. Because C can be continuously fed into the reaction group by the cyclic reaction of Mg through the formation and decomposition of Mg2 C3 (2Mg + 3CH4 → Mg2 C3 + 6H2 → 2Mg + 3C), a molar ratio of 2.2 for Mg/ZrO2 was sufficient for the synthesis of single-phase ZrC. ZrC powders were synthesized under the following conditions: Mg/ZrO2 molar ratio = 2.2, heating rate = 20°C/min, and temperature maintained at 750°C for 30 min. The amount of reaction heat produced in the reduction reaction of ZrO2 by Mg depended on the Mg/ZrO2 molar ratio, specifically, the amount of ZrO2 contained. Moreover, the cyclic reaction of Mg-Mg2 C3 –Mg was influenced by the amount of reaction heat described above and by the heating rate. The ZrC fine powder showed little aggregation and high dispersibility. 相似文献
18.
Sreekumar Chockalingam David A. Earl Vasantha R. W. Amarakoon 《International Journal of Applied Ceramic Technology》2009,6(1):102-110
A 2.45 GHz microwave-sintered Si3 N4 –Y2 O3 –MgO system containing various amounts of ZrO2 secondary additives have been studied with respect to phase transformation and densification behavior. The temperature dependent dielectric properties were measured from 25°C to 1400°C using a conventional cavity perturbation technique. Phase transformation behavior was studied using X-ray diffractometry. Microwave sintered results were compared with those of conventional sintered results. It has been found that α to β phase transformation was completed at a lower temperature in microwave-sintered samples than those of the conventionally sintered samples. Density of the microwave-sintered samples increased up to 2.5 wt% of ZrO2 addition and thereafter it showed a tendency to decrease or remain constant. The decrease in density is attributed to the pore generation caused by decomposition due to the localized over heating. 相似文献
19.
Yu Jia Yuji Hotta Kimiyasu Sato Koji Watari 《Journal of the American Ceramic Society》2006,89(3):1103-1106
ZrO2 –Al2 O3 nanocomposite particles were synthesized by coating nano-ZrO2 particles on the surface of Al2 O3 particles via the layer-by-layer (LBL) method. Polyacrylic acid (PAA) adsorption successfully modified the Al2 O3 surface charge. Multilayer coating was successfully implemented, which was characterized by ξ potential, particle size. X-ray diffraction patterns showed that the content of ZrO2 in the final powders could be well controlled by the LBL method. The powders coated with three layers of nano-ZrO2 particles, which contained about 12 wt% ZrO2 , were compacted by dry press and cold isostatically pressed methods. After sintering the compact at 1450°C for 2 h under atmosphere, a sintered body with a low pore microstructure was obtained. Scanning electron microscopy micrographs of the sintered body indicated that ZrO2 was well dispersed in the Al2 O3 matrix. 相似文献
20.
Conventional ramp-and-hold sintering with a wide range of heating rates was conducted on submicrometer and nanocrystalline ZrO2 –3 mol% Y2 O3 powder compacts. Although rapid heating rates have been reported to produce high density/fine grain size products for many submicrometer and smaller starting powders, the application of this technique to ZrO2 –3 mol% Y2 O3 produced mixed results. In the case of submicrometer ZrO2 –3 mol% Y2 O3 , neither densification nor grain growth was affected by the heating rate used. In the case of nanocrystalline ZrO2 –3 mol% Y2 O3 , fast heating rates severely retarded densiflcation and had a minimal effect on grain growth. The large adverse effect of fast heating rates on the densification of the nanocrystalline powder was traced to a thermal gradient/differential densification effect. Microstructural evidence suggests that the rate of densification greatly exceeded the rate of heat transfer in this material; consequently, the sample interior was not able to densify before being geometrically constrained by a fully dense shell which formed at the sample exterior. This finding implies that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO2 –3 mol% Y2 O3 specimens. 相似文献