共查询到20条相似文献,搜索用时 31 毫秒
1.
Elliott B. Slamovich Frederick F. Lange 《Journal of the American Ceramic Society》1990,73(11):3368-3375
Micrometer size polydispersed spheres of zirconia were produced via electrostatic atomization and pyrolysis of aqueous zirconium acetate-yttrium acetate precursors. Varying the precursor composition in the ZrO2 -rich region of the ZrO2 -Y2 O3 binary system resulted in the production of either single-crystal (0 and 10 mol% Y2 O3 O or dense polycrystalline (3 mol% Y2 O3 ) zirconia spheres of similar size distribution for densification studies. Powders of either the singlecrystal or the polycrystalline particles exhibited contrasting densification behavior; viz., powder compacts composed of polycrystalline particles obtained significantly higher endpoint densities than their single-crystal counterparts. Microstructural observations showed that while necks between single-crystal particles reached a stable size, necks between polycrystalline particles continued to grow. 相似文献
2.
Kousuke Yamamoto Toshihiro Kasuga Yoshihiro Abe 《Journal of the American Ceramic Society》1997,80(3):822-824
A novel porous glass-ceramic with a skeleton of CuTi2 (PO4 )3 was prepared by controlled crystallization of a glass and subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic composed of CuTi2 (PO4 )3 and Cu3 (PO4 )2 whose surface was covered by a CuO thin layer was prepared by reheating a glass with a nominal composition of 50CuO·20TiO2 30P2 O5 (in mol%) glass in air. When the resultant glass-ceramic was leached with dilute H2 SO4 , Cu3 (PO4 )2 and CuO phases were dissolved out selectively, leaving a crystalline CuTi2 (PO4 )3 skeleton. The specific surface area and the average pore radius of the porous glass-ceramic obtained were approximately 45 m2 g-1 and 9 nm, respectively. The porous glass-ceramic showed catalytic activity in the conversion reaction of propene into acrolein. 相似文献
3.
A novel porous glass-ceramic with a skeleton of a NASICON-type copper(II) titanium phosphate was prepared via the controlled crystallization of a glass and the subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic comprised of CuTi2 (PO4 )3 and Cu3 (PO4 )2 , whose surface was covered by a thin layer of CuO, was prepared by reheating a glass with a nominal composition of 50CuO20TiO2 30P2 O5 (in mol%) in air. When the resulting glass-ceramic was leached with dilute HCl, the Cu3 (PO4 )2 and CuO phases were dissolved out selectively, and a cuprous NASICON crystal of CuTi2 (PO4 )3 was converted to its cupric type, CuTi4 (PO4 )6 , which was left as a skeleton of the porous materials. The specific surface area and the average pore radius of the porous glass-ceramic obtained were ∼70 m2 /g and ∼7 nm, respectively. The porous glass-ceramic showed high catalytic activities for the dehydration of 2-propanol. 相似文献
4.
Etsuro Kato Masanori Hirano Yuichi Kobayashi Keisuke Asoh Makoto Mori Masato Nakata 《Journal of the American Ceramic Society》1996,79(4):972-976
Monodisperse zirconia particles were prepared by the thermal hydrolysis of mixtures of zirconyl chloride, zirconium hydroxide, and water at high concentrations corresponding to about 5 mol/L Zr. The particles, as first prepared, were temporarily agglomerated spheres composed of primary ultrafine zirconia crystals. The agglomerated particles collapsed and dispersed in water to form a translucent sol. When vacuum dried and followed by heat treatment, they were not dispersible. The size of the agglomerated particles increased with increasing molar ratio of the zirconium chloride in the starting mixture, varying from about 0.2 to 0.6 μm. Using the sample thus obtained, monodisperse tetragonal zirconia particles of about 0.35 μm containing 3 mol% Y2 O3 with a relatively uniform composition were obtained by homogeneous precipitation of YOHCO3 by heating with urea and calcination at 800°C. 相似文献
5.
Preparation of Zirconia-Toughened Bioactive Glass-Ceramic Composite by Sinter–Hot Isostatic Pressing
Toshihiro Kasuga Kiichi Nakajima Tomoko Uno Masahiro Yoshida 《Journal of the American Ceramic Society》1992,75(5):1103-1107
High-strength bioactive ceramics, MgO-CaO-SiO2 -P2 O5 glass-ceramic composites toughened by zirconia, were prepared by sinter-hot isostatic pressing (sinter-HIPing) to achieve easier mass production and higher reliability. Raw materials for preparing a dense presintered body were investigated to obtain almost complete densification by sinter-HIPing. It was found that the densification of a presintered body was influenced by residual glassy phases in the crystallized glass particles. By using a controlled crystallized glass powder and a zirconia powder as raw materials, a presintered body with a relative density higher than 94% was prepared, and then it was densified to near its theoretical density by sinter-HIPing. This bioceramic exhibited an extremely high bending strength of 400 to 1000 MPa and fracture toughness of 3 to 5 MPa.m1/2 for 30 to 80 vol% of zirconia. 相似文献
6.
High-Strength Mica-Containing Glass-Ceramics 总被引:13,自引:0,他引:13
Tomoko Uno Toshihiro Kasuga Kiichi Nakajima 《Journal of the American Ceramic Society》1991,74(12):3139-3141
Glass-ceramics containing barium–mica in the system Ba0.5 Mg3 (Si3 AIO10 )F2 –2MgO · 2Al2 O3 · 5SiO2 –Ca3 (PO4 )2 are two to three times stronger than conventional mica-containing glass-ceramics. Moreover, the barium-mica glass-ceramics are easier to machine, as confirmed by a drilling test using conventional steel tools. Such mechanical properties are attributable to the microstructure of the barium–mica glass-ceramics. Very fine, interlocking mica crystals are precipitated in the glass, and a crack-deflection mechanism is observed by scanning electron microscopy. 相似文献
7.
Mei-Hwa Lee Hung-Yin Lin James L. Thomas 《Journal of the American Ceramic Society》2006,89(12):3624-3630
A novel synthesis of amorphous hydrous zirconia nanoparticles was performed in a supercritical carbon dioxide (scCO2 ) reverse microemulsion, converting a high concentration of a very inexpensive starting material (zirconyl nitrate hydrate) into a product that was then calcined to yield monoclinic zirconia nanoparticles. The amorphous hydrous zirconia precursor particles were obtained by simply adding a precipitating agent to [Zr4+ (aq) ]/perfluoropolyether/scCO2 . Calcination converts the amorphous hydrous zirconia precursor into the oxide, and the corresponding phase changes that occur were confirmed by differential thermal analysis. Some control of particle size and shape (ellipticity) could be achieved by selecting the reaction pressure from within the range over which stable microemulsions are obtained (13.9–17.3 MPa): a higher reaction pressure yields smaller and more spherical particles. This novel route for the synthesis of zirconia nanoparticles is both "green" (environmentally friendly) and economical. 相似文献
8.
ELIHU A. SCHATZ 《Journal of the American Ceramic Society》1963,46(2):71-73
Attempts to substitute for silicon in the fluorphlogopite structure resulted in the synthesis of a fluorgermanium mica and a boron phosphate micalike orthorhombic crystal. The batch material contained Al2 O3 , MgO, MgF2 , K2 CO3 , plus GeO2 for forming the fluorgermanium mica and BPO4 for forming the boron phosphate crystal. Optical analysis with a polarizing microscope and by X-ray diffraction verified the mica structure of the germanium crystal and disproved the mica structure of the boron phosphate crystal. The indices of refraction and unit-cell constants were determined for both crystals. A study of the electrical properties up to temperatures of 1000°F showed that the dielectric properties of the fluorgermanium mica were very similar to that of fluorphlogopite. 相似文献
9.
Thomas Höche Martin Deckwerth Christian Rüssel 《Journal of the American Ceramic Society》1998,81(8):2029-2036
Nitrogen (via a polymeric AlN precursor) and ZrO2 are introduced into a MgO-CaO-Al2 O3 -SiO2 -glass. Subsequent crystallization of the glass results in a fine-grained oxynitride glass-ceramic. The microstructure of the latter is found to be entirely different for nitrogen concentrations of 4.85 and 9.94 mol%. Not only do the phase contents differ, but also tetragonal zirconia is more effectively stabilized at higher nitrogen concentrations. Partial stabilization of tetragonal zirconia is not due to nitrogen incorporation but is based on an indirect effect: the spherical morphology of tetragonal zirconia precipitated at higher nitrogen contents suppresses the nucleation of the martensitic transformation. The beneficial effects of the introduction of nitrogen and the simultaneous incorporation of zirconia into a glass-ceramic result in overall improved mechanical properties. 相似文献
10.
Toshihiro Kasuga Masayuki Nogami Mitsuo Niinomi 《Journal of the American Ceramic Society》2003,86(6):1031-1033
A bioactive calcium phosphate invert glass-ceramic containing β-Ca3 (PO4 )2 crystals could be joined strongly with a Ti–29Nb–13Ta–4.6Zr alloy consisting of a β-titanium phase by heating the metal on which the mother glass powders with a composition 60CaO·30P2 O5 ·7Na2 O·3TiO2 (mol%) were placed, at 800°C for 1 h in air; the tensile joining strength was estimated to be ∼26 MPa on average. A compositionally gradient layer was developed on the metallic substrate during the heating. When the metal with glass powders on it was heated at 850°C in air, the phosphate glassy phase flowed viscously, permeating the oxide layer formed around the surface of the metal, which was thicker than that formed by heating at 800°C; a compositionally gradient layer was not developed, and a strong joining was not realized. The joining between the glass-ceramic and the metal is suggested to be controlled by viscous flow of the glassy phase in the glass-ceramic and by reaction of the glassy phase with the oxide phase formed around the surface layer of the metal. 相似文献
11.
D. A. DUKE J. E. MEGLES JR. J. F. MACDOWELL H. F. BOPP 《Journal of the American Ceramic Society》1968,51(2):98-101
Glasses in the Na2 O–Ba0–A12 O3 -Si02 system, nucleated with TiO2 , were heat-treated to effect controlled crystallization. Resulting materials consisted of a dense, micro-crystalline mixture of nepheline (Na2 0–A12 O3 -2SiO2 ) and barium feldspar (BaO-A12 O3 -2Si02 ) in a glassy matrix. Thermal expansion coefficients (O° to 300° C) of these bodies ranged from 75 to 125 × 10 –7/°C. Glazes in the Na2 O-CaO-PbO-B2 O2 -A12 03 -SiO2 system having expansion coefficients of about 40 to 80 × 10 -7/0 °C were applied to the glass-ceramics. On firing, the glazes matured well and reacted with the bodies to form interlocking crystals at the interface. This interfacial region was investigated using several instrumental techniques, and the crystals were identified as plagioclase feldspar. Applying these compressive glazes resulted in modular of rupture up to five times that of the initial glass-ceramic. Calculated strengths correlated well with experimental values. 相似文献
12.
Wei-Hsing Tuan Shi-Ming Liu Chan-Ju Ho Tsong-Jen Yang 《Journal of the American Ceramic Society》2006,89(2):754-758
Previous studies demonstrated that the strength of zirconia (ZrO2 ) could be enhanced or reduced by respectively adding micrometer-sized alumina (Al2 O3 ) or nickel (Ni) particles. In the present study, 5 vol% micrometer-sized Al2 O3 particles and 1 vol% nanometer-sized Ni particles are incorporated into the ZrO2 matrix, which is subsequently densified by pressureless sintering. The biaxial strength of the ZrO2 /(Ni+Al2 O3 ) nanocomposite is nearly double that of the monolithic ZrO2 . The increase in strength correlated with a reduction in the critical flaw size and not with any change in toughness, which may be a result of grain boundary strengthening. 相似文献
13.
Mixtures of Zr(OH)4 and ZrO2 particles, ∼10 nm in size, were hydrothermally treated in 0.25–1.5 mol/L H2 SO4 solutions at a temperature of 200°C. After 3 h, very short ZrO2 fibers, 10–30 nm in length, were obtained, with no other zirconium compounds observed. The particles grew with treatment time and resulted in whisker particles. In a higher concentration (3 mol/L) H2 SO4 solution, ZrO2 whiskers were not obtained, and clear solutions resulted with the starting ZrO2 particles remaining. It was concluded that Zr(OH)4 was useful as a starting material and that nanosized ZrO2 particles served as seed crystals for whisker formation. 相似文献
14.
Bertrand Dubois Daniel Ruffier Philippe Odier 《Journal of the American Ceramic Society》1989,72(4):713-715
Fine yttria-stabilized zirconia powders were prepared by the spray pyrolysis of aqueous solutions of ZrOCl2 ·8H2 O and Y(NO3 )3 ·5H2 O (3 mol%). An appropriate thermal treatment resulted in slightly porous spherical particles with a narrow size distribution. The sintering ability of these powders was evaluated. 相似文献
15.
The microstructures of α-Al2 O3 seeded sol–gel-derived alumina-zirconia composites containing 20 wt% unstabilized zirconia (processed from zirconium n-propoxide) were very fine, with submicrometer alumina grains and small, mainly intergranular zirconia particles, the latter having a critical size for the tetragonal-to-monoclinic phase transformation of 0.45 μm. The corresponding ratios of the toughening contribution to the matrix toughness are relatively low (δKc /K0 <1). This finding is confirmed by an analysis of the tetragonal zirconia particle size dependence of the stress-induced transformation toughening. 相似文献
16.
Raman Spectroscopic Studies on the Formation Mechanism of Hydrous-Zirconia Fine Particles 总被引:1,自引:0,他引:1
Koji Matsui Hajime Suzuki Michiharu Ohgai Haruo Arashi 《Journal of the American Ceramic Society》1995,78(1):146-152
The Raman spectra of hydrous-zirconia fine particles produced by the hydrolysis of various ZrOCl2 solutions were investigated. The Raman spectra of hydrous zirconia synthesized at HCl concentrations below 1 mol/L were similar to those of monoclinic, crystalline ZrO2 ; those of hydrous zirconia synthesized at HCl concentrations greater than 1 mol/L showed a crystal structure change. The line width of the Raman bands increased with increasing H+ ion concentration. Analyzing the relationship between Raman band width and particle size revealed that the primary particle size of hydrous zirconia was controlled by the H+ and Cl− ions, because these ions interfered with the polymerization in a hydrolysis reaction. Based on the experimental results, the formation mechanism for primary particles of hydrous zirconia was determined. 相似文献
17.
The nucleation and crystallization of Li2 O-Al2 O3 -SiO2 glasses containing TiO2 were investigated using transmission electron microscopy of thin sections produced from bulk samples. Phase separation occurs during cooling from the melt, and on heating, a large number of titanium-aluminum crystals approximately 50 A in diameter are formed. These crystals are the heterogeneous nuclei for the crystallization of the remaining glass. Photomicrographs of various stages of crystallization show the development of the fine-grained glass-ceramic. 相似文献
18.
Yoshikazu Suzuki Masanobu Awano Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》1999,82(9):2557-2559
Composites of BaFe12 O19 particles dispersed throughout a 3-mol%-yttria-doped zirconia (3Y-TZP) matrix have been prepared using the pressureless reactive sintering of 3Y-TZP, BaCO3 , and γ-Fe2 O3 powders. The reaction behavior of the mixed powder was studied with an in situ , high-temperature powder X-ray diffraction technique. The composite that was sintered at 1300°C consisted of submicrometer-sized 3Y-TZP grains and BaFe12 O19 particles; the size of the 3Y-TZP grains was ∼100-300 nm, and the size of the BaFe12 O19 particles was ∼200-500 nm. Based on the grain size, most of the BaFe12 O19 grains presumably had a single-magnetic-domain structure. The 3Y-TZP/20-wt%-BaFe12 O19 composite showed high magnetization and coercivity values, despite the low concentration of ferromagnetic phase. Preliminary mechanical tests revealed that the composite possessed moderately good mechanical properties. 相似文献
19.
Internal Stresses and the Martensite Start Temperature in Alumina-Zirconia Composites: Effects of Composition and Microstructure 总被引:1,自引:0,他引:1
Kathleen B. Alexander Paul F. Becher Xun-Li Wang Chun-Hway Hsueh 《Journal of the American Ceramic Society》1995,78(2):291-296
n alumina-based composites containing ceria-stabilized tetragonal zirconia, the martensite start temperature ( Ms ) of the tetragonal-to-monoclinic zirconia phase transformation exhibits a grain size dependence that becomes increasingly pronounced as the zirconia content decreases. Neutron diffraction experiments confirm earlier dilatometry measurements of M s in composites containing ≥20 vol% ZrO2 and were instrumental in obtaining M s values in lower zirconia content (i.e., 10 vol%) composites. The dependence of M s on zirconia content is related to the internal stresses that arise from differences in thermal expansion coefficients between the two phases. Neutron diffraction measurements show that the internal tensile stresses in the zirconia grains increase with decreasing zirconia content. The measured internal stresses are in quantitative agreement with predictions based on models assuming isolated ZrO2 particles at low zirconia contents and a continuous ZrO2 "matrix" phase at higher zirconia contents. This assumption is consistent with the observed microstructural development in which the low zirconia contents result in isolated zirconia grains, whereas higher zirconia contents result in more interconnected zirconia grains. 相似文献
20.
DAVID J. GREEN 《Journal of the American Ceramic Society》1982,65(12):610-614
The internal strains asSociated with the martensitic phase transformation of zirconia were used to introduce microcracks into Al2 O3 /ZrO2 composites. The degree of transformation was found to be dependent on the volume fraction of ZrO2 and its size, the latter of which could be controlled by suitable heat treatments. The microstructural changes that occurred during the heat treatments were studied using quantitative microscopy and X-ray diffraction. For materials containing more than 7.5 vol% Zr02 , the ZrO2 particles were found to pin the Al2 O3 grain boundaries, thus limiting the Al2 O3 grain growth. The limiting grain size was found to be dependent on size and volume fraction of ZrO2 . Heat treatments for the higher volume fraction materials (>7.5 vol% ZrO2 ) caused micro-structural changes which resulted in increased amounts of monoclinic ZrO2 at room temperature; elastic modulus measurements indicated that this was occurring concurrently with microcracking. By combining the ZrO2 grain-size distributions with the X-ray analysis it was possible to calculate the critical ZrO2 size required for the transformation. The critical size was found to decrease with increasing amounts of ZrO2 . Hardness and indentation fracture toughness were measured on the composites. Grain fragmentation was observed at the edge of the indentations and microcracks were observed directly, using an AgNO3 decoration technique, near the indentations. 相似文献