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1.
The crystal-growth process and growth conditions of β-alumina (Na2 O · Al2 O3 ) were investigated using the Na2 B4 O7 -Na3 AlF6 flux method. β-Alumina (electric fusion brick) was used as both nutrient and seed. Weight loss of the flux varied widely for various runs: ≅ 10 wt% of flux evaporated at 100 h, ≅ 17 wt% at 150 h, and 43 wt% at 600 h. When β-alumina crystal was grown, only 20 wt% Na2 B4 O7 was added to the Na3 AlF6 flux. The linear growth rates of the β-alumina single crystal grown by an Na3 AlF6 -20 wt% Na2 B4 O7 flux method at 1040°C and Δ t = 18°C were ≅ 1.0 × 10−3 mm/h ( a face) and ≅0.3 × 10−3 mm/h ( c face). The β-alumina single crystals grown were bounded by only c [001] and a [100] and were colorless and transparent. 相似文献
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CECIL M. JONES II 《Journal of the American Ceramic Society》1971,54(7):347-349
A technique for growing α-Al2 O3 crystals is described in which Na2 O·11Al2 O3 is dissolved in a liquid of composition Na2 O·4TiO2 ·3Al2 O3 . Alpha Al2 O3 is precipitated as Na2 O evaporates from the system; Na2 O·11Al2 O3 serves as a source of Al2 O3 , and Na2 O in the liquid. The content of solids in the mixture is always such that it does not melt completely. The size of the α-Al2 O3 crystals grown is related to the Na2 O content of the composition. Crystals as large as 4000 by 3000 μm in the α-axis direction and 500 μm in the c -axis direction have been grown. 相似文献
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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
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After high-temperature reaction between Al2 O3 and TiO2 crystals, precipitates found in rutile were characterized by electron microprobe and X-ray diffraction methods and by optical and electron microscopy. The precipitates were identified as α-Al2 O4 . Geometric and crystallographic orientation relations with the TiO2 matrix constitute a reverse case of rutile precipitation in star sapphire . 相似文献
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Masaru Miyayama Hiroya Terada Hiroaki Yanagida 《Journal of the American Ceramic Society》1981,64(1):19-C-
The metastable β form of bismuth sesquioxide was obtained by doping antimony oxide. The solubility of antimony was 4 to 10 at. %in β specimens, where more than 75% of the antimony atoms were valenced at 5+. 相似文献
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Sodium depth profiles were determined in water-leached glass samples with molar composition 20Na2 O · 10RO · x Al2 O3 · (70 - x)SiO2 (RO = CaO, MgO, and ZnO) using secondary ion mass spectrometry. The leaching of sodium ions decreases with increasing Al2 O3 content in all three glass systems. For x = 0 the leaching is hardly affected by the nature of the divalent cation. For x = 5 and 10 the corrosion resistance is highest for the glass containing ZnO, and for the glasses containing ZnO and MgO, respectively. These glasses correspond to those with the smallest fraction of NBOs. From all these results it is concluded that the nonbridging oxygen atoms play an important role in promoting the leaching of a glass. 相似文献
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Xue-Ning Huang Chu Kun Kuo Patrick S. Nicholson 《Journal of the American Ceramic Society》1995,78(4):892-896
An epitaxial β-alumina crystal growth method was used to modify α-AI2 O3 platelet surfaces before inclusion as a reinforcing phase in partially stabilized zirconia (3Y-TZP). The as-grown surface phase was Na-β"-AI2 O3 . This was converted to Ca-β"-AI2 O3 by ion exchange, as the latter is more temperature-stable at composite sintering temperatures. The conditions of formation, thermal stability, and chemical compatibility of these interfacial phases were examined. α-AI2 O3 platelets with Ca-β"-AI2 O3 film were incorporated into 3Y-TZP. The β"-AI2 O3 /ZrO2 interface was found to promote platelet debonding and pullout, thus enhancing the α-AI2 O3 platelet/crack interactions during the fracture process. 相似文献
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MASARU MIYAYAMA SHINICHI KATSUTA YOSHIHIRO SUENAGA HIROAKI YANAGIDA 《Journal of the American Ceramic Society》1983,66(8):585-588
Electrical conduction in tetragonal β-Bi2 O3 doped with Sb2 O3 was investigated by measuring electrical conductivity, ionic transference number, and Seebeck coefficient. The β-Bi2 O3 doped with 1 to 10 mol% Sb2 O3 was stable up to 600°C and showed an oxygen ionic and electronic mixed conduction, where the electron conduction was predominant at low oxygen pressures. The oxygen-ion conductivity showed a maximum at 4 mol% Sb2 O3 , whereas the activation energy for the ionic conduction remained unchanged for 4 to 10 mol% Sb2 O3 -doped specimens. These results were interpreted in terms of the oxygen vacancy concentration and the distortion of the tetragonal structure. The electron conductivity and its oxygen pressure dependence decreased with increasing Sb2 O3 content. The fact that Sb5+ is partially reduced by excess electrons in heavily doped β specimens at low oxygen pressures is explained. 相似文献
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The model proposed to explain the defect behavior of nominally pure β-Ta2 O5 was extended to the case of defect equilibria and charge transport in β-Ta2 O5 doped with a multivalent cation, i.e., Nb2 O5 -doped P-Ta2 O5 . This case is of practical interest in the electronics industry, where Nb2 O5 , is a dominant impurity in capacitor-grade β-Ta2 O5 . 相似文献
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Phase relations in the system Na2 O· Al2 O3 -CaO· Al2 O3 -Al2 O3 at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na2 O · 3CaO · 5Al2 O3 , known from the literature, was reformulated as Na2 O · CaO · 2Al2 O3 . A new compound with the probable composition Na2 O · 3CaO · 8Al2 O3 was found. Cell parameters of both compounds were determined. The compound Na2 O · CaO-2Al2 O3 is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na2 O · Al2 O3 up to 38 mol% Na2 O at 1200°C. The compound Na2 O · 3CaO · 8Al2 O3 is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al2 O3 is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al2 O3 make it very difficult to determine equilibrium phase relations in the high-Al2 O3 part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram. 相似文献
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The molecular dynamics computer simulation technique was used to determine the short-time dynamics behavior and resultant structures of ions at the surface of Li2 0·3SiO2 and Na2 O-3SiO2 glasses. Room temperature and elevated temperatures were used. Results are compared with similar studies of the K2 O·3SiO2 glass surface and with recent experimental ion-scattering-spectroscopy data. The simulations indicate that a localized surface rearrangement occurs within picoseconds after formation of the free surface, creating a surface excess of alkali in the Na (and K) case, but not in the Li case. Elevated temperatures, even for brief times, enhance the observed surface excess of Na and K. The results correspond to those obtained from the ion-scattering-spectroscopy studies. 相似文献
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Oxide crystallite formation and growth from freeze-dried sulfates were studied for the representative materials Al2 O3 and Fe2 O3 . Transmission and scanning electron micrographs showed the formation and growth of chainlike aggregates of crystallites. Aggregation occurred as part of the nucleation and growth of the oxide, and discrete oxide particles were never present. Orientation of the chain aggregates was related to the ice structure formed during freezing. X-ray line broadening data showed that crystallite size is a function of the 1/5 to 1/7 power of time for isothermal treatments. A qualitative analysis of material transport favored the surface diffusion mechanism. 相似文献
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R. E. CARTER 《Journal of the American Ceramic Society》1960,43(9):448-451
The dissociation pressures of solid solutions from Fe3 O4 to 0.4Fe3 O4 ·0.6CoFe2 O4 have been determined as a function of temperature. Within experimental error, solid solutions within this range are thermodynamically ideal. 相似文献
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Solid solutions of Fe304-FeV204 and Fe304-FeCr204 were prepared and equilibrated with Pt under controlled streams of CO/CO, gas mixtures at 1673 K. The concentration of Fe in Pt was used to determine the activity of Fe304 in the solid solutions. The activity of the second component was calculated by Gibbshhem integration. From these data, the Gibbs energy of mixing was derived for both systems. The experimental results and theoretical values which are determined from calculated cation distribution compare favorably in the case of vanadite solid solutions but not in the case of chromite solid solutions. The difference is attributed to a heat term arising from lattice distortion due to cation size difference. The positive heat of mixing will give rise to a miscibility gap in the system Fe304-FeCr204 at lower temperatures. 相似文献
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Yoshikazu Suzuki Héctor A. Calderón Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(6):1346-1350
The in situ formation of magnetoplumbite-type (M-type) hexaferrites within a 3Y-TZP matrix was examined for the La2 O3 –ZnO–Fe2 O3 and BaO–Fe2 O3 systems. The formation of barium hexaferrite (Ba-M) was rapid enough at a temperature of 1300°C for 2 h to result in a uniform dispersion of fine Ba-M particles in a tetragonal zirconia polycrystal (TZP) matrix. However, the formation of lanthanum-substituted hexaferrite (La-M) was rather sluggish, despite the existence of a charge-compensating divalent oxide. The 3Y-TZP/20-wt%-BaFe12 O19 in situ composite possessed good magnetic properties, as well as moderately good mechanical properties. 相似文献
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Aluminum oxide single crystals deformed by dislocation glide and deformation twinning during compressive creep at 1400° to 1700°C. The activation energy for basal slip was a function of the applied stress and agreed with activation energies previously measured by observation of yielding phenomena. The overcoming of a large Peierls-Nabarro stress is the most probable rate-controlling mechanism. Rhombohedral twinning, a significant deformation mode in creep, depends on surface damage for nucleation. The activation energy for rhombohedral twin growth, a function of the applied stress, is substantially lower than that for basal slip. When basal slip and rhombohedral twinning occur concurrently, creep by basal slip results, but the presence of twins can substantially reduce the creep rate. 相似文献