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1.
P. L. ROEDER F. P. GLASSER† E. F. OSBORN 《Journal of the American Ceramic Society》1968,51(10):585-593
Liquidus phase equilibrium data are presented for the system Al2 O3 -Cr2 O3 -SiO2 . The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al2 O3 -ICr2 O3 -93SiO2 ) coexists with a mullite solid solution (61Al2 O3 -10Cr2 O3 -29SiO2 ), a corundum solid solution (19Al2 O3 -81Cr2 O3 ), and cristobalite (SO2 ). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases. 相似文献
2.
SiO2 -Al2 O3 melts containing 42 and 60 wt% A12 O3 were homogenized at 2090°C (∼10°) and crystallized by various heat treatment schedules in sealed molybdenum crucibles. Mullite containing ∼78 wt% A12 O3 precipitated from the 60 wt% A12 O3 melts at ∼1325°± 20°C, which is the boundary of a previously calculated liquid miscibility gap. When the homogenized melts were heat-treated within this gap, the A12 O3 in the mullite decreased with a corresponding increase in the Al2 O3 content of the glass. A similar decrease of Al2 O3 in mullite was observed when crystallized melts were reheated at 1725°± 10°C; the lowest A12 O3 content (∼73.5 wt%) was in melts that were reheated for 110 h. All melts indicated that the composition of the precipitating mullite was sensitive to the heat treatment of the melts. 相似文献
3.
The chemical composition of mullite which was termed from 2SiO2 3Al2 O3 xerogel by firing was examined by analytical TEM. Mullite formed at 950°C firing showed around 66 mol% Al2 O3 , which was fairly Al2 O3 rich compared with the bulk composition. The chemical composition of mullite gradually approached the bulk composition as the firing temperature increased to 1400°C and slightly departed again above that firing temperature. 相似文献
4.
Pierre E. Debély Eric A. Barringer H. Kent Bowen 《Journal of the American Ceramic Society》1985,68(3):76-C-
A fine, uniform A12 O3 -SiO2 powder was prepared by heterocoagulation of narrow Al2 O3 and SiO2 powders. This composite powder was dispersed, compacted, and fired in air at 900° to 1580°C for 1 to 13 h. Full density was achieved at 1550°C with the formation of a mullite phase. Relative densities of 83% and 98% (0.3 μm grain size) were measured for samples sintered at 1200°C for 13 h and at 1400°C for 1 h, respectively. 相似文献
5.
Stoichiometric mullite (71.38 wt% Al2 O3 -28.17 wt% SiO2 ) and 80 wt% Al2 O3 -20 wt% SiO2 gels were prepared by the single-phase and/or diphasic routes. Dense sintered bodies were prepared from both sets of gels in the Al2 O3 -SiO2 system. Apparent densities of 96% and 97% of theoretical density were measured for the diphasic (using two sols) mullite samples sintered at 1200° and 1300°C for 100 min, respectively; this compared with 85% and 94% for the single-phase xerogels under the same conditions, and to much lower values for mullite prepared from conventional mixed powders. The microstructure of the mullite pellets from diphasic xerogel precursors is also considerably finer. 相似文献
6.
The compositional range for glass formation below 1600°C in the Sm2 O3 ─Al2 O3 ─SiO2 system is (9–25)Sm2 O3 ─(10–35)Al2 O3 ─(40–75)SiO2 (mol%). Selected properties of the Sm2 O3 ─Al2 O3 ─SiO2 (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm2 O3 content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm2 O3 content and with increasing temperature to 70°C. The transformation temperature ( T g ) and dilatometric softening temperature ( T d ) of the SmAS glasses exceeded 800° and 850°C, respectively. 相似文献
7.
A study of the solid solution of TiO2 , Fe2 O3 , and Cr2 03 in mullite was made by measuring the changes in lattice parameters and unit-cell volume. Synthetic mullite (3O3 -2SiO2 ) was reacted with up to 12 weight % of the oxides at temperatures ranging from 1000° to 17000C. The approximate minimum temperature required for the formation of solid solution was 12000C. for Fe2 03 and 1400°C. for Cr2 O3 and TiO3 . The maximum amount of solid solution found was 2 to 4% TiO2 at 1600°C., 10 to 12% Fe2 Os at 1300°C., and 8 to 10% CrZ O3 at 1600OC. Lattice parameters and unit-cell volumes for each solid solution series increased with increasing amounts of foreign oxide. There was good agreement between the calculated and observed increase in cell dimensions for the iron oxide series. Except in the case of titania, there was good agreement between X-ray data and petrographic observations. 相似文献
8.
ARTHUR S. WATTS 《Journal of the American Ceramic Society》1951,34(2):63-63
The results of a study of deformation temperatures and rates within the composition area 25 to 45% SrO, 5 to 25% Al2 O3 , 50 to 70% SiO2 are presented. A eutectic of the composition 30% SrO, 10% Al2 O3 , 60% SiO2 is indicated with "1 o'clock" deformation at 1155°C. and "6 o'clock" deformation at 1165°C. A low-temperature area surrounding this eutectic includes 27.5 to 32.5% SrO, 10 to 12.5% Al2 O3 , 57.5 to 62.5% SiO2 . Compositions within this range reach "6 o'clock" deformation at approximately 1180°C. 相似文献
9.
ROBERT H. THOMAS 《Journal of the American Ceramic Society》1950,33(2):35-44
Phase-equilibrium relations on the liquidus surface in the system Ba0-A12 O3 -SiO2 have been investigated by the quenching method. The compositions investigated within the ternary area were those containing less than 30%, A12 O3 and more than 20% SiO2 by weight. Petrographic and X-ray techniques were employed in the determination of the crystalline phases.
The crystal phases that separate from melts within the area investigated are barium orthosilicate (2BaO. SiO2 ,), barium metasilicate (BaO 2SO2 ,), solid solutions, sanbornite (BaO 2SiO2 ), tridymite and cristobalite (SO2 ), mullite (3A12 O3 2SiO2 ), and celsian (BaO A12 O3. 2SiO2 ). Diagrams show the isotherms and indices of refraction of the glasses.
Five quintuple points and eleven boundary curves have been determined within = .5yo compositional variations. The liquidus-surface temperatures have been obtained within limits of ± 125°C. 相似文献
The crystal phases that separate from melts within the area investigated are barium orthosilicate (2BaO. SiO
Five quintuple points and eleven boundary curves have been determined within = .5yo compositional variations. The liquidus-surface temperatures have been obtained within limits of ± 125°C. 相似文献
10.
The thermal evolution of a mullite gel of composition 2Al2 O3 ·SiO2 has been investigated. The gel crystallized at 1300°C into an alumina-rich mullite and corundum, instead of single-phase 2Al2 O3 ·SiO2 mullite. The amount of Al2 O3 that dissolved in the mullite structure has been determined in the 1300–1780°C temperature range by measuring the mullite lattice parameters. A maximum limit for the amount of Al2 O3 in solid solution has been observed. Densification of the gel powders has been analyzed up to temperatures of 1780°C. The microstructure of dense materials always showed the presence of residual Al2 O3 particles. 相似文献
11.
John R. Moyer 《Journal of the American Ceramic Society》1996,79(11):2965-2968
Alumina reacts with 1 atm of SiF4 below 660°± 7°C to form A1F3 and SiO2 . At higher temperatures the product is a mixture of fluorotopaz and AIF3 . Mixtures of fluorotopaz and AIF3 decompose in 1 atm of SiF4 at 973°± 8°C and form tabular α-alumina. The equilibrium vapor pressure of SiF4 above mixtures of fluorotopaz and AlF3 is log p (atm) = 9.198 – 11460/ T (K). Fluorotopaz itself decomposes at 1056°± 5°C in 1 atm of SiF4 to give acicular mullite, 2Al2 O3 . 1.07SiO2 . Alumina and mullite are stable in the presence of 1 atm of SiF4 above 973° and 1056°C, respectively. The phase diagram of the system SiO2 -Al2 O3 -SiF4 shows only gas-solid equilibria. 相似文献
12.
R. R. DAYAL R. E. JOHNSON† ARNULF MUAN‡ 《Journal of the American Ceramic Society》1967,50(10):537-540
The free energy of reaction for the formation of mullite from its oxide components was derived from equilibrium studies in the system CoO-Al2 O3 -SiO2 . Within this system there appears, at solidus temperature in a certain composition area, the phase assemblage mullite + silica + spinel (= cobalt aluminate) + liquid. Determination of the oxygen pressure of a gas phase at which metallic cobalt precipitates from this phase assemblage and from the phase assemblage spinel (= cobalt aluminate) + corundum in the system CoO-Al2 O3 permits calculation of ΔG° for the reaction 3Al2 O3 + 2SiO2 = Al6 Si2 O13 . The value obtained at 1422°C is -5.8 kcal. 相似文献
13.
Adam J. G. Ellison Paul C. Hess Gerald C. Naski 《Journal of the American Ceramic Society》1998,81(12):3215-3220
The saturation surface of cassiterite, SnO2 , was determined for liquids in the system K2 O–Al2 O3 –SiO2 as a function of bulk composition and temperature. At fixed K2 O/Al2 O3 cassiterite solubility varies weakly with SiO2 concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f O 2 ) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K2 O/Al2 O3 lessthan equal to 1 (peraluminous liquids). As K2 O/Al2 O3 increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K2 O in excess of Al2 O3 . It is proposed that potassium in excess of aluminum combines with Sn4+ to form quasi-molecular complexes with an effective stoichiometry of K4 SnO4 . 相似文献
14.
The crystallization of Al2 O3 -rich glasses in the system SiO2 -Al2 O3 which were prepared by flame-spraying and/or splat-cooling was studied by DTA, electron microscopy, and X-ray diffraction. Over a wide range of compositions, the crystallization temperature ( Tx ) remained near 1000°C, changing smoothly with composition. In all cases crystallization of mullite was detected by X-ray diffraction. In the low-Al2 O3 region, coarsening of the microstructure during crystallization was observed by electron microscopy. In the high-Al2 O3 region mullite and γ-Al2 O3 cocrystallized; this behavior may be interpreted as evidence of a cooperative process of crystallization at the respective Tx 's. The crystallite size of the mullite immediately after rapid crystallization increased continuously with increasing Al2 O3 content. In light of the Tx data, the adequacy of the evidence for the proposed metastable miscibility gap in the SiO2 -Al2 O3 system is questioned. 相似文献
15.
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
16.
James W. Palko Ali Sayir Stanislav V. Sinogeikin Waltraud M. Kriven Jay D. Bass 《Journal of the American Ceramic Society》2002,85(8):2005-2012
Directionally solidified mullite fibers have been grown by the laser-heated, float-zone method from starting materials with a nominal composition of 3Al2 O3 ·2SiO2 . The fibers used in this study have large single-crystal regions with composition 2.5Al2 O3 ·SiO2 and (001) fiber axis orientation. The complete elastic tensor of these samples has been determined by Brillouin spectroscopy at room temperature and elevated temperatures up to 1200°C. Isotropic moduli (bulk, shear, and Young's) have been calculated using the Voigt–Reuss–Hill averaging scheme. The room-temperature values obtained are K VRH = 173.5 ± 6.9 GPa, G VRH = 88.0 ± 3.5 GPa, E VRH = 225.9 ± 9.0 GPa. All moduli show gradual, linear decreases with temperature. The temperature derivatives obtained for the equivalent, isotropic moduli are d K VRH /d T =−17.5 ± 2.5 MPa/°C, d G VRH /d T =−8.8 ± 1.4 MPa/°C, d E VRH /d T =−22.6 ± 2.8 MPa/°C. Substantial differences between bulk properties calculated from the single–crystal measurements in this study and the properties reported in the literature for polycrystalline sintered mullite are identified, indicating the importance of factors such as microstructure, intergranular phases, and composition to the elasticity of mullite ceramics. 相似文献
17.
Marion Bartsch Bilge Saruhan Martin Schmücker Hartmut Schneider 《Journal of the American Ceramic Society》1999,82(6):1388-1392
Dense mullite ceramics were successfully produced at temperatures below 1300°C from amorphous SiO2 -coated gamma-Al2 O3 particle nanocomposites (AS-gammaA). This method reduces processing temperatures by similar/congruent300°C or more with respect to amorphous SiO2 -coated alpha-Al2 O3 particle microcomposites (AS-alphaA) and to other Al2 O3 -SiO2 reaction couples. The good densification behavior and the relatively low mullite formation temperature make AS-gammaA nanocomposites an excellent matrix raw material for polycrystalline aluminosilicate fiber-reinforced mullite composites. 相似文献
18.
Phase equilibria along the nonbinary join between cordierite (2MgO · 2Al2 O3 · 5SiO2 ) and spodumene (Li2 O · Al2 O3 · 4SiO2 ) were investigated in the temperature range 800° to 1550°C. using the quench technique on fourteen compositions. The phase diagram at high temperatures is characterized by a very small region of solid solution on the cordierite side, appreciable solid solution on the spodumene side, and regions of three and four phases toward the center of the system, including liquid, α-cordierite, mullite, spinel, corundum, and β-spodumene and its solid solutions. The liquidus has a flat minimum between 40 and 50% cordierite at 1347°, and rises on one side to the congruent melting point of β-spodumene (1421°) and on the other side to the temperature of complete melting of cordierite (1530°). The lowest temperature at which liquid appears is 1325°. At low temperatures a complete series of metastable solid solutions exists between μ-cordierite and β-spodumene. The significance of the data in the preparation of thermal-shock-resisting bodies is discussed. 相似文献
19.
Akshoy Kumar Chakravorty Dilip Kumar Ghosh 《Journal of the American Ceramic Society》1987,70(3):46-C-
The independent crystallization sequence of an Al2 O3 component is modified in the presence of SiO2 and vice versa. Mixed SiO2 -Al2 O3 , gel (28 wt% SiO2 and 72 wt% Al2 O3 ) forms neither cristobalite nor γ-Al2 O3 and corundum at 1000°C but forms Si-Al spinel; an amorphous aluminosilicate phase invariably also forms after the gel is heated. However, the composition of this amorphous aluminosilicate phase is not as yet known. 相似文献
20.
The UO2 –Al2 O3 phase equilibrium system was found to contain no new compounds or solid solutions. Uranium dioxide melted at 2878°± 22°C. and Al2 O3 melted at 2034°± 16°C. The eutectic temperature was approximately 1930°C. There is an indication that two immiscible liquids formed above the eutectic temperature between 53 and 74 mole % Al2 O3 . 相似文献