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1.
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
2.
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
3.
Debao Zhang Baoyu Chen Zhuping Liu Shunguang Li Lili Hu 《Journal of the American Ceramic Society》2004,87(12):2228-2231
Er3+ -doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO2 ·0.3Al2 O3 )· x Na2 O·8.2La2 O3 · 0.6Er2 O3 ·0.2Yb2 O3 ·1Sb2 O3 (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω t ( t = 2, 4, 6) decreases with increasing Na2 O. Ω2 decreases rapidly with increasing Na2 O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2 O. Fluorescence spectra of the 4 I 13/2 to 4 I 15/2 transition have been measured and the change with Na2 O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2 O. 相似文献
4.
Takashi Wakasugi Rikuo Ota Jiro Fukunaga 《Journal of the American Ceramic Society》1992,75(11):3129-3132
In order to evaluate the crystallization tendency of glasses, the ratio of the crystallization temperature to the liquidus temperature ( T c / T L ) was obtained by DTA measurement for the Na2 O–B2 O3 and Na2 O–B2 O3 –Al2 O3 systems. The critical cooling rate for glass formation ( Q *) was also measured. The measurements were performed in the composition range of (100 − x )Na2 O–( x )B2 O3 , ( x = 25–35 and 60–100 mol%), and (100 − y )0.5Na2 O·0.5B2 O3 −( y )Al2 O3 , ( y = 6–34 mol%). The relationship between T c / T L and Q * was discussed. A linear relationship between T c / T L and log Q * for these systems was found. Furthermore, the relationship between T c / T L and Q * was verified by computer simulation based on the crystallization kinetics of glass or supercooled liquid. 相似文献
5.
E. F. RIEBLING P. E. BLASZYK D. W. SMITH 《Journal of the American Ceramic Society》1967,50(12):641-647
Density and viscosity results are presented for ternary Na2 O·GeO2 ·B2 O3 melts (∼600° to 1300°C) and glasses containing as much as 35 mole % Na2 O. Synthetic partial molar volume models indicate a fairly broad stability region for BO4 tetrahedra in the B2 O3 -rich melts. Similar models for GeO2 -rich melts reveal a more limited stability region for GeO6 octahedra. The expansion coefficient contours and viscosity isotherms confirm the volume-based conclusions for the liquid state. The high-temperature volume models were used to develop glass volume models that agree to within several percent of experiment. It has been concluded that the melts and glasses possess similar structures. The relatively greater compositional stability of GeO6 octahedra in the presence of B2 O3 (compared to Al2 O3 ) can be related to the smaller average number of oxygens around boron (III), at a fixed O/Ge ratio, compared to aluminum (III). Evidence is presented for a slight decrease of the thermal stability of GeO6 octahedra in the GeO2 -rich melts above about 1000°C. 相似文献
6.
The preparation of near stoichiometric spinel and alumina-rich spinel composites from Al2 O3 and MgO powders with the addition of Na3 AlF6 up to 4 wt% in the temperature range 700°–1600°C was studied; 98 wt% spinel containing 72 wt% Al2 O3 can be produced from the mixture of 72 wt% (50 at.%) Al2 O3 + 28 wt% (50 at.%) MgO powders with the addition of 1 wt% Na3 AlF6 fired at 1300°C for 1 h. Spinels containing 81–85 wt% Al2 O3 can be produced from either the mixture of 90 wt% (78 at.%) Al2 O3 + 10 wt% (22 at.%) MgO or the mixture of 95 wt% (88 at.%) Al2 O3 + 5 wt% (12 at.%) MgO powders with the addition of 4 wt% Na3 AlF6 in the temperature range 1300°–1600°C by using a torch-flame firing for 3 min, followed by quenching in water, while the same system under slow cooling in a furnace results in spinel containing 74–76 wt% Al2 O3 . Microscopic studies indicate that the alumina-rich spinel composites consist of a continuous majority spinel phase and an isolated minority corundum phase, regardless of slow cooling in a furnace or quenching in water. 相似文献
7.
The system Na3 AlF6 -AlF3 -Al2 O3 was investigated by a combination of quenching, optical microscopy, and X-ray powder diffraction techniques in order to define liquidus temperatures, univariant lines, and invariant points. Phase fields for the primary crystallization of cryolite, chiolite, aluminum fluoride, α-alumina, and η-alumina were located. A ternary peritectic point contained 28.3% AlF3 -4.4% Al2 O3 -67.3% Na3 AlF6 at 723°C. A eutectic point of composition 37.3% AlF3 -3.2% Al2 O3 -59.5% Na3 AlF6 occurs at 684°C. 相似文献
8.
This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li2 O·9Al2 O3 ·38 TiO2 ·39P2 O5 glass–ceramic and polyethylene. The processing involved tape casting of 14Li2 O·9Al2 O3 ·38TiO2 ·39P2 O5 glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 950°–1100°C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150–350 μm thick membranes were characterized and are discussed in this paper. The crystallites of the glass–ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO4 at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity. 相似文献
9.
G. Bhattacharya S. Zhang D. D. Jayaseelan W. E. Lee 《Journal of the American Ceramic Society》2007,90(1):97-106
Lithium borate (Li2 B4 O7 ) and sodium borate (Na2 B4 O7 ) mineralize spinel formation from stoichiometric MgO and Al2 O3 between 1000° and 1100°C. Mineralization with both compounds is shown to be mediated by B-containing liquids which form glass on cooling. However, the liquid compositions depend on the type of mineralizer and temperature, suggesting that templated grain growth or dissolution–precipitation mechanisms are operating, one dominating over the other under certain conditions. Na2 B4 O7 -mineralized compositions show predominantly templated grain growth at 1000°C, which changes to dissolution–precipitation at 1100°C, whereas Li2 B4 O7 -mineralized compositions show dissolution–precipitation from 1000°C. Li2 B4 O7 is a stronger mineralizer as spinel formation is complete with 3 wt% Li2 B4 O7 at 1000°C and with ≥1.5 wt% addition at 1100°C, whereas Na2 B4 O7 -mineralized compositions are found to retain some unreacted corundum even at 1100°C. 相似文献
10.
Phase equilibrium relations in the system Na2 O-GeO2 have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na2 O·GeO2 and 2Na2 O·9GeO2 , exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO2 and 2Na2 O·9GeO2 is 950°±f 10°C at 94.5 wt GeO2 . The eutectic temperature between 2Na2 O · 9GeO2 and Na2 O·GeO2 is 790° f 10°C at about 75 wt% GeO2 . Both the refractive index and the density of glasses in the system Na2 O-GeO2 exhibit maximum values at about 16 to 18 mole % Na2 O. The Ge-O-Ge absorption band at 890 cm−1 shifts toward lower wave numbers with the addition of Na2 O. 相似文献
11.
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
12.
Kazuhiro Narita Yoshihiro Takahashi Yasuhiko Benino Takumi Fujiwara Takayuki Komatsu Takeshi Hanada Yoshihiko Hirotsu 《Journal of the American Ceramic Society》2004,87(1):113-118
Some K2 O-Nb2 O5 -GeO2 glasses are prepared, and their crystallization behaviors are examined. 25K2 O·25Nb2 O5 ·50GeO2 glass with the glass transition temperature T g = 622°3C and crystallization onset temperature T x = 668°3C shows a prominent nanocrystallization. The crystalline phase is K3,8 Nb5 Ge3 O20,4 with an orthorhombic structure. The sizes of crystals in the crystallized glasses heat-treated at 630° and 720°3C for 1 h are °10 and 20–30 nm, respectively, and the crystallized glasses obtained by heat treatments at 620°-850°3C for 1 h maintain good transparency. The density of crystallized glasses increases gradually with increasing heat-treatment temperature, and the volume fraction of crystals in the sample heat-treated at 630°3C for 1 h is estimated to be ∼35%. The usual Vickers hardness and Martens hardness (estimated by nanoindentation) of 25K2 O·25Nb2 O5 ·50GeO2 glass change steeply by heat treatment at T g , i.e., at around 35% volume fraction of nanocrystals. The present study demonstrates that the composite of nanocrystals and the glassy phase has a strong resistance against deformation during Vickers indenter loading in crystallized glasses. 相似文献
13.
J. P. COUTURES 《Journal of the American Ceramic Society》1985,68(3):105-107
A tentative phase diagram for the system Al2 03 -Nd2 O3 is presented. Three compounds were obtained: a β -A12 O3 -type compound, the perovskite NdAlO3 , and Nd4 Al2 O9 . The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al2 O3 , mp 1900°C; Nd4 Al2 O9 , mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al2 O3 , 1750°C; 23 mol% Al2 O3 ,1800°C. Nd4 Al2 O9 decomposes in the solid state at 1780°C. 相似文献
14.
Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na2 O-Nb2 O5 . Five compounds corresponding to the formulas 3Na2 O.1Nb2 06 , lNa2 O. 1Nb2 O5 , lNa2 O 4Nb2 O6 , lNaz O.7Nb2 O5 , and lNa2 O. 10Nb2 O6 have been found. The compound 3Naz 0.lNb2 O5 melts congruently at 992°C. The compounds 1Na2 O. 4Nb2 O6 , lNa2 O.7Nb2 O, and 1Na2 O. 1Onb2 O5 melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO3 was found to melt congruently at 1412°C. The transition temperatures in NaNbO5 were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO3 could be preserved to room temperature by very rapid quenching. 相似文献
15.
The crystallization and phase transformation of glassy Na2 O·2B2 O3 have been studied by X-ray diffraction, infrared spectroscopy, thermal analysis, and density measurement. By employing proper thermal treatment methods, three metastable and two relatively stable polymorphs of Na2 O·2B2 O3 are obtained, as well as two other compounds, Na2 O·B2 O3 and 2Na2 O·5B2 O3 . The possible structural groups of these phases are deduced, which are found to be similar to that existing in the glass. Current glass models which imply the existence of structural "granularity" satisfactorily describe the crystallization behavior. The phase transformation is observed to depend not only on temperature, but also on the density of the phase. 相似文献
16.
Fine-particle beta sodium ferrite (β-NaFeO2 ), rather than α-Fe2 O3 , may be responsible for superparamagnetic behavior in a glass of composition (in mole fractions) 0.37Na2 O-0.26Fe2 O3 -0.37SiO2 . The 700°C isothermal section of the phase diagram of the Na2 O-Fe2 O3 -SiO2 system is given, showing a three-phase field bounded by Na2 SiO3 -NaFeO2 -Fe2 O3 ; there is no evidence for the existence (at 700°C) of compounds of molar composition 6Na2 O-4Fe2 O3 -5SiO2 or 2Na2 O-Fe2 O3 -SiO2 . The Moessbauer spectrum of β-NaFeO2 has an internal magnetic field of 487 kOe at room temperature. 相似文献
17.
Sashi Tandon Ranchhor D. Agrawal Madan L. Kapoor 《Journal of the American Ceramic Society》1994,77(4):1032-1036
The viscosity of sodium borate slags at high Na2 O concentrations (37.3 to 49.4 mol%) and high temperatures (1000° to 1300°C) follows an Arrhenius-type relationship. This relationship was also observed for sodium borate slags (mass% Na2 O/mass% B2 O3 = 0.86) containing CaO and CaF2 for the same temperature range. There has been a reduction in viscosity of the sodium borate slags (mass% Na2 O3 mass% B2 O = 0.53 to 0.86) with increase in Na2 O concentration. On adding CaO (10 to 50 mass%) to the sodium borate slag (mass% Na2 O/mass% B2 O3 = 0.86), the viscosity increased considerably, while an addition of CaF2 (S to 15 mass%) to the slag (30.9 mass% Na2 O3 35.8 mass% B2 O3 , 33.3 mass% CaO) decreased the viscosity. The average activation energies of Na2 O─B2 O3 , Na2 O─B2 O3 ─CaO3 and Na2 O─B2 O3 ─CaO─CaF2 slag systems have been estimated as 14.6, 124.7, and 41.4 kJ/mol, respectively, for the given composition ranges and 1000° to 1300°C temperature range. 相似文献
18.
The internal friction of R2 O·Al2 O3 ·6SiO2 glasses was measured from-180° to 700°C at 0.4 Hz. Glasses containing Li2 O or Na2 O exhibited only the one internal friction peak characteristic of the stress-induced movement of the alkali ions. Substitution of a second alkali resulted in two significant changes in the internal friction: (1) a rapid reduction in the magnitude of the original alkali peak and (2) the appearance of a new internal friction peak whose magnitude was especially sensitive to the concentration of the second alkali. Each combination of two alkali ions resulted in a new peak, with peaks being observed for the combinations Li-Na, Na-K, and Li-K. A mechanical damping spectrum is predicted for aluminosilicate glasses containing more than two alkali ions. 相似文献
19.
Protons were introduced into the surface of an Li2 O·Al2 O3 ·2SiO2 glass fiber (0.5 mm in diameter) by ion exchange in NH4 HSO4 at 366°C for 21 h. Infrared absorption measurements established that the protons were associated with bridging oxygen ions. After ion exchange, the magnitude of the alkali internal friction peak decreased and a new peak appeared at ∼220°C. This new peak is attributed to the interaction of alkali and hydrogen ions, independent of the presence of nonbridging oxygen ions. 相似文献
20.
Osamu Yamaguchi Daijo Tomihisa Tatsuji Uegaki Kiyoshi Shimizu 《Journal of the American Ceramic Society》1987,70(11):335-C
In the system Ta2 O3 -Al2 O5 solid solutions of metastable δ-Ta2 O5 (hexagonal) are formed up to 50 mol% Al2 O3 from amorphous materials prepared by the simultaneous hydrolysis of tantalum and aluminum alkoxides. The values of the lattice parameters decrease linearly with increasing Al2 O3 , content. The to β-Ta2 O5 (orthorhombic, low-temperature form) transformation occurs at ∼950°C. The solid solution containing 50 mol% Al2 O3 transforms at 1040° to 1100°C to orthorhombic TaAlO4 . Orthorhombic TaAlO4 contains octahedral TaO6 groups in the structure. 相似文献