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1.
Phase relations in the system Bi2 O3 -WO3 were studied from 500° to 1100°C. Four intermediate phases, 7Bi2 O3 · WO3 , 7Bi2 O3 · 2WO3 , Bi2 O3 · WO3 , and Bi2 O3 · 2WO3 , were found. The 7B2 O · WO3 phase is tetragonal with a 0 = 5.52 Å and c 0 = 17.39 Å and transforms to the fcc structure at 784°C; 7Bi2 O3 · 2WO3 has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi2 O3 · WO3 and Bi2 O3 · 2WO3 are orthorhombic with (in Å) a 0 = 5.45, b 0 =5.46, c 0 = 16.42 and a 0 = 5.42, b 0 = 5.41, c 0 = 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO3 , 907°± 3°C and 70 mol% WO3 , and 965°± 5°C and 10 mol% WO3 . 相似文献
2.
Phase relations, with special emphasis on the formation of wolframite-type phases, were determined in 12 ternary systems, each containing an alkali oxide (Li2 O, Na2 O), a polyvalent oxide (Fe2 O3 , Cr2 O3 , SnO2 , ThO2 , ZrO2 , V2 O5 ), and WO3 . Among 12 ternary phases characterized, 5 have the wolframite-type structure. They are LiFe(WO4 )2 , LiCr(WO4 )2 , NaFe(WO4 )2 , NaCr(WO4 )2 , and Li2 Zr(WO4 )3 . Complete series of solid solutions exist along Li(Fe,Cr) (WO4 )2 and Na(Fe,Cr)(WO4 )2 joins but not along other wolframite joins. Both LiFe(WO4 )2 and LiCr(WO4 )2 were also found to form complete solid solution series with MgWO4 , a compound used hi this study to represent the simple wolframite-type phase. 相似文献
3.
The dissolution of (Al, Cr)2 O3 into CaO—MgO—Al2 O3 —SiO2 melts, under static and forced-convective conditions was investigated at 1550°C in air. With sufficient MgO in the melt, or sufficient Cr2 O3 in (Al, Cr)2 O3 , a layer consisting of a spinel solid solution, Mg(Al, Cr)2 O4 , formed at the (Al, Cr)2 O3 /melt interface. The dissolution kinetics of 1.5 and 10 wt% Cr2 O3 specimens were determined as a function of immersion time, specimen rotation rate, and magnesia content of the melt. Electron microprobe analysis was used to characterize concentration gradients in the (Al, Cr)2 O3 sample, the Mg(Al, Cr)2 O4 spinel, or in the melt after immersion of specimens containing 1.5 to 78 mol% Cr2 O3 . The dissolution kinetics and microprobe analyses indicated that a steady-state condition was reached during forced-convective, indirect (Al, Cr)2 O3 dissolution such that spinel layer formation was rate limited by solid-state diffusion through the spinel layer and/or through the specimen, and spinel layer dissolution was rate limited by liquid-phase diffusion through a boundary layer in the melt. This is consistent with a model previously developed for the indirect dissolution of sapphire in CMAS melts. 相似文献
4.
Transmission electron microscopy (at 100 and 1000 kV potential) and analytical scanning transmission electron microscopy were used to study α-Al2 03 second-phase particles and their interactions with grain boundaries in two high-conductivity Y2 03 /Yb2 03 stabilized zirconia ceramics containing deliberate additions of the alumina as a sintering aid. Most of the Al2 03 particles were intragranular and microanalysis showed that they contained inclusions rich in Zr or Si plus Zr. Al2 O3 particles at grain boundaries were frequently associated with amorphous cusp areas rich in Si and Al. The results suggest that the Al2 03 acts as a scavenger for SiO2 , removing it from grain-boundary localities. A model is proposed whereby this process occurs as the boundaries meet the second-phase particles, assisted by rapid grain-boundary diffusion. Such an ZrO2 -Al2 O3 -SiO2 interaction and partitioning is predicted thermodynamically and offers a possible explanation for the improvements in ionic conductivity brought about by Al2 O3 additions, as reported in the literature. 相似文献
5.
Chaitanya K. Narula M. Matti Maricq Brian G. Demczyk Irving T. Salmeen Willes H. Weber 《Journal of the American Ceramic Society》1993,76(11):2727-2733
Irradiation of Ti[N(CH3 )2 ]4 by the 1.064-μm line of a pulsed Nd: YAG laser in the presence of TiO2 , Al2 O3 , or Si3 N4 particles has been found to form amorphous deposits on the oxide particles. The resulting materials can be processed into TiN/TiO2 , TiN/Al2 O3 , or TiN/Si3 N4 composites with the TiN component on the surface of the particles. The powders have been characterized by Raman spectroscopy and X-ray powder diffraction studies. The surface analysis of the composites by X-ray photoelectron spectroscopy and high-resolution electron microscopy is presented. 相似文献
6.
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
7.
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
8.
A single-phase material (HfMg)(WO4 )3 with an orthorhombic structure, A2 (WO4 )3 -type tungstate, has been successfully prepared for the first time by the calcination of HfO2 , MgO, and WO3 , substituting Hf4+ and Mg2+ for A3+ cations in A2 (WO4 )3 . The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc2 (WO4 )3 . 相似文献
9.
Shyan-Lung Chung Yu-Cheng Sheu Ming-Shyong Tsai 《Journal of the American Ceramic Society》1992,75(1):117-123
SiO2 , Al2 O3 , and 3Al2 O3 .2SiO2 powders were synthesized by combustion of SiCl4 or/and AlCl3 using a counterflow diffusion flame. The SiO2 and Al2 O3 powders produced under various operation conditions were all amorphous and the particles were in the form of agglomerates of small particles (mostly 20 to 30 nm in diameter). The 3Al2 O3 .2SiO2 powder produced with a low-temperature flame was also amorphous and had a similar morphology. However, those produced with high-temperature flames had poorly crystallized mullite and spinel structure, and the particles, in addition to agglomerates of small particles (20 to 30 nm in diameter), contained larger, spherical particles 150 to 130 nm in diameter). Laser light scattering and extinction measurements of the particle size and number density distributions in the flame suggested that rapid fusion leading to the formation of the larger, spherical particles occurred in a specific region of the flame. 相似文献
10.
The existence of stable and metastable forms of 2ZrO2 ·P2 O5 and the subsolidus phase relations in the system ZrO2 -ZrP2 O7 were confirmed before investigation of the ternary system. The synthesis and thermal behavior of ZrW2 O8 were reinvestigated, and the system WO3 -P2 O5 was examined cursorily. A ternary compound, 2ZrO2 ·WO3 ·P2 O5 , was found, and compatibility triangles for the system between 1105° and 1150°C were established. The ternary compound is compatible with ZrO2 , WO3 , and three binary compounds, giving rise to five composition triangles. In addition, ZrP2 O7 , WO3 , and "W2 O3 (PO4 )2 " were compatible. 相似文献
11.
Yoshikazu Suzuki Masahiro Tsukatsune Susumu Yoshikawa Peter E. D. Morgan 《Journal of the American Ceramic Society》2005,88(11):3283-3286
Porous Al2 O3 /20 vol% LaPO4 and Al2 O3 /20 vol% CePO4 composites with very narrow pore-size distribution at around 200 nm have been successfully synthesized by reactive sintering at 1100°C for 2 h from RE2 (CO3 )3 · x H2 O (RE = La or Ce), Al(H2 PO4 )3 and Al2 O3 with LiF additive. Similar to the previously reported UPC-3Ds (uniformly porous composites with a three-dimensional network structure, e.g. CaZrO3 /MgO system), decomposed gases in the starting materials formed a homogeneous open porous structure with a porosity of ∼40%. X-ray diffraction, 31 P magic-angle spinning nuclear magnetic resonance, scanning electron microscopy, and mercury porosimetry revealed the structure of the porous composites. 相似文献
12.
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
13.
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
14.
On the basis of 190 runs made up to 1860°C in sealed noble-metal containers the following revisions have been made in the equilibrium diagram for the system A12 O3 –SiO2 . Mullite melts congruently at 1850°C. The extent of equilibrium solid solution in mullite at solidus temperature is from approximately 60 mole % Al2 O3 (3/2 ratio) to 63 mole % A12 O3 . Metastable solid solutions can be prepared up to about 67 mole % Al2 O3 . There is no evidence for stable solubility of excess SiO2 beyond the 3/2 composition at pressures below 3 kbars. Refractive indices are presented for glasses containing up to 60 mole % Al2 O3 and from them the composition of the eutectic is confirmed at 5 mole % SiO2 . The variation in lattice constants of the mullite solid solution is not an unequivocal guide to composition since mullites at one composition produced at different temperatures show differences in spacing, no doubt reflecting Al-Si ordering phenomena. The possibility of quartz and corundum being the stable assemblage at some low temperatures and pressures cannot be ruled out. A new anhydrous phase in the system is described, which was previously thought to be synthetic andalusite; it is probably a new polymorph of the Al2 SiO5 composition with ortho-rhombic unit-cell dimensions a =7.55 A, b =8.27 A, and c = 5.66 A. 相似文献
15.
Phase relations in the system Sc2 O3 -WO3 were characterized. Two stable binary compounds were, found. The 1:3 compound, SC2 (WO4 )3 , melts congruently at 1640°±10°C and forms a simple eutectic with WO3 at ∼90 mol% WO3 and 1309°+10°C. The 3 : 1 compound, Sc6 WO12 , forms a simple eutectic with the 1:3 compound at -69 mol% WO2 , and 1580°+10°C. The melting temperature of SC6 WO12 was >1600°C. 相似文献
16.
An Xie Ximing Yuan Yu Shi Fengxiang Wang Juanjuan Wang 《Journal of the American Ceramic Society》2009,92(10):2254-2258
A series of novel red phosphors LiEu1− x Bi x (WO4 )0.5 (MoO4 )1.5 ( x =0, 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, and 0.50) were synthesized by the conventional solid-state reaction method. The spectrum and the crystal structure of the phosphors were characterized by Fluorescence spectrophotometry and X-ray diffraction, respectively. The photoluminescent results show that all samples can be excited efficiently by UV (396 nm) and blue (467 nm) light and that they emit red light at 615 nm with line spectra, which are coupled well with the characteristic emissions from UVLED and blue light-emitting diode (LED), respectively. There is an efficient energy transfer from Bi3+ to Eu3+ ions, leading to the emission intensity of Eu3+ being enhanced by 1.5 times, and even more when Bi3+ ions are introduced into LiEu (WO4 )0.5 (MoO4 )1.5 . The introduction of Bi3+ ions broadened the excitation band of the phosphor, and the optimum doping concentration is found to be 10 mol% of Bi3+ . 相似文献
17.
An isothermal section of the ternary system MgO–Al2 O3 -Cr2 O3 was determined at 1700°± 15°C to delineate the stability field for spinel crystalline solutions (cs). Crystalline solutions were found between the pseudobinary joins MgAl2 O4 –Cr2 O3 and MgCr2 O4 -Al2 O3 , and the binary join MgAl2 O4 -MgO. The first two crystalline solutions exhibit cation vacancy models while the latter can probably be designated as a cation interstitial model. Precipitation from spinel cs may proceed directly to an equilibrium phase, (Al1-x Crx )2 O3 , with the corundum structure or through a metastable phase of the probable composition Mg(Al1-x Cr )26 O40 . The composition and temperature limits were defined where the precipitation occurs via metastable monoclinic phases. The coherency of the metastable monoclinic phase with the spinel cs matrix can be understood by considering volume changes with equivalent numbers of oxygens and known crystallographic orientation relations. Electron probe and metallographic microscope investigations showed no preferential grain boundary precipitation. 相似文献
18.
Solid-state reactions between Li2 O and Al2 O3 were studied in the region between Li2 O.Al2 O 3 and Al2 O 3 . The compound Li2 O Al2 O 3 melts at 1610°± 15°C. and undergoes a rapid reversible inversion between 1200° and 1300°C. Vaporization of Li2 O from compositions in the system proceeds at an appreciable rate at 1400°C, as shown by fluorescence. Lithium spinel, Li2 O -5Al2 O3 , was the only other compound observed. The effect of Li2 O on the sintering of alumina was investigated. 相似文献
19.
Federica Bondioli Anna Maria Ferrari Cristina Leonelli Tiziano Manfredini Laura Linati Piercarlo Mustarelli 《Journal of the American Ceramic Society》2000,83(8):2036-2040
The aim of this work is to study the structural characteristics and properties of the solid solution (Al,Cr)2 O3 . XRD analysis, 27 Al MAS-NMR measurements, and microstructural characterization were used to determine the relationship between color and crystallochemical properties of the compounds formed. In particular, to determine more accurately the mechanism of solid solution formation above the miscibility gap of the system, the marker technique was used. In order to define the behavior of the system for temperatures below the miscibility gap at 1 bar pressure, the composition Al2 O3 :Cr2 O3 1:1 was studied with high-temperature XRD. 相似文献
20.
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