共查询到20条相似文献,搜索用时 31 毫秒
1.
G. Bhattacharya S. Zhang M. E. Smith D. D. Jayaseelan W. E. Lee 《Journal of the American Ceramic Society》2006,89(10):3034-3042
B2 O3 mineralizes spinel formation from stoichiometric (1:1 mole ratio) calcined magnesia and alumina. After 3 h at 1100°C, X-ray diffraction (XRD) shows the mineralization effect of B2 O3 is limited to 1.5 wt% additions with higher B2 O3 contents leading to Mg3 B2 O6 formation and reduced spinel content. Boron nuclear magnetic resonance, electron probe microanalysis (EPMA), scanning electron microscopy, transmission electron microscopy (TEM) and XRD reveal formation of a boron-containing liquid. Energy dispersive spectroscopy in the TEM and EPMA of the glassy phases formed from solidification of the liquid reveal that initially it is Mg borate, later becoming a magnesia-modified boroaluminate, composition suggesting dissolution–precipitation as opposed to templated growth as the mechanism of this liquid phase mediated mineralization. 相似文献
2.
The temperature dependence of the rate of growth of Na2 B4 O7 from its melt was determined between 1° and 192°C of undercooling. The maximum rate of growth was 2000 μm/min at 57°C of undercooling. Analysis of the growth data indicated that growth could occur by a screw dislocation mechanism over the entire range of undercooling. When this mechanism was assumed, there was good correlation between the experimental data and the predictions of the Turnbull and Cohen equation. 相似文献
3.
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
4.
LEON MAYA 《Journal of the American Ceramic Society》1977,60(7-8):323-328
The system B2 O3 -NaF-NaBF, has been studied by subjecting selected compositions to thermal treatment in the range 400° to 600°C. Weight losses, chemical analyses, ir, Raman, and X-ray diffraction techniques were used to define the composition of the crystalline phases and the structural units being formed in the system. The stoichiometry of the BF3 evolved from NaBF4 -B2 O3 mixtures indicated that a composition corresponding to Na2 B3 F5 O3 was formed in mixtures containing up to 33.3 mol% B2 O3 . At higher boron oxide concentrations, Na2 B3 F5 O3 was consumed, yielding 2NaF.3B2 O3 . The crystalline compounds Na3 B3 F6 O3 , 2NaF.3B2 O3 , and phase B (apparently NaF.B2 O3 ) were formed in the system. The compound Na3 B3 F6 O3 appeared as the stable oxygen-containing species in NaBF4 -NaF mixtures of low oxide content. The main fluorine-containing structural units of the system are BF4 , (–O)3 BF, (–O)2 BF2 , (–O)2 BF, whereas the main structure for binary NaF-B2 O3 mixtures is (–O)3 BF. 相似文献
5.
The effect of Al8 B4 C7 used as an antioxidant in MgO–C refractories and the behavior of Al8 B4 C7 in CO gas were investigated in the present study. Al8 B4 C7 was found to react with CO gas, to form Al2 O3 ( s ), B2 O3 ( l ), and C( s ), at temperatures >1100°C. The Al2 O3 reacts with MgO to form MgAl2 O4 near the surface of the material. At the same time, B2 O3 ( l ) evaporates and reacts with MgO, to form a liquid phase, at >1333°C, the eutectic point between 3MgO·B2 O3 and MgO. The coexistence of the liquid and MgAl2 O4 makes the protective layer more dense, thus inhibiting oxidation of the refractory. At >1333°C, the process apparently is controlled by oxygen diffusion, whereas it is controlled by chemical reaction when the temperature is <1333°C. 相似文献
6.
Hiroya Yamashita Toshinobu Yoko Sumio Sakka 《Journal of the American Ceramic Society》1991,74(7):1668-1674
Li2 B4 O7 films, a promising material for surface acoustic wave devices, were prepared by the sol—gel method using metal alkoxide precursors as starting materials. The Li2 B4 O7 films on silicon (100) and (111) single crystals prepared from a coating solution to which acetic or hydrochloric acid was added were highly oriented along the (122) plane, whereas those without acid additive were randomly oriented. The results were interpreted based on the basic sol-gel chemistry and the lattice matching between the film and substrate. 相似文献
7.
The glassforming region in the system was roughly outlined and liquidus data were obtained for the three joins LiPO3 -BPO4 , Li4 P2 O7 -BPO4 , and Li3 PO4 -Li2 B4 O7 . Compatibility relations for the ternary subsystems Li4 P2 O7 -BPO4 -P2 O5 and Li2 O-Li3 PO4 -Li2 B8 O13 were established. Two ternary compounds with the probable compositions 22Li2 O - 11B2 O3 - 13P2 O5 and 2Li2 O 3B2 O3 P2 O5 were detected. 相似文献
8.
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
9.
Above 755°C, compounds along the spinel join LiFe5 O8 -Li4 Ti5 O12 form a complete solid solution and below that temperature a two-phase region separates the ordered LiFe5 O8 and the disordered spinel phase. At 800° and 900°C, cubic LiFeO2 ( ss ) and monoclinic Liz Ti03 ( ss ) exist on the monoxide join LiFeO2 -Li2 TiO3 . The distributions of cations in both the spinel and monoxide structures were calculated as a function of equilibrium temperature and composition. Sub-solidus equilibria in the system Li2 O-Fe2 O3 -TiO2 at 800° and 900°C were determined for compositions containing ∼50 mol% Li2 O. 相似文献
10.
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
11.
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
12.
A type of new low sintering temperature ceramic, Li2 TiO3 ceramic, has been found. Although it is difficult for the Li2 TiO3 compound to be sintered compactly at temperatures above 1000°C for the volatilization of Li2 O, dense Li2 TiO3 ceramics were obtained by conventional solid-state reaction method at the sintering temperature of 900°C with the addition of ZnO–B2 O3 frit. The sintering behavior and microwave dielectric properties of Li2 TiO3 ceramics with less ZnO–B2 O3 frit (≤3.0 wt%) doping were investigated. The addition of ZnO–B2 O3 frit can lower the sintering temperature of the Li2 TiO3 ceramics, but it does not apparently degrade the microwave dielectric properties of the Li2 TiO3 ceramics. Typically, the good microwave dielectric properties of ɛr =23.06, Q × f =32 275 GHz, τf = 35.79 ppm/°C were obtained for 2.5 wt% ZnO–B2 O3 frit-doped Li2 TiO3 ceramics sintered at 900°C for 2 h. The porosity was 0.08%. The Li2 TiO3 ceramic system may be a promising candidate for low-temperature cofired ceramics applications. 相似文献
13.
γ-Y2 Si2 O7 is a promising candidate material both for high-temperature structural applications and as an environmental/thermal barrier coating material due to its unique properties such as high melting point, machinability, thermal stability, low linear thermal expansion coefficient (3.9 × 10−6 /K, 200°–1300°C), and low thermal conductivity (<3.0 W/m·K above 300°C). The hot corrosion behavior of γ-Y2 Si2 O7 in thin-film molten Na2 SO4 at 850°–1000°C for 20 h in flowing air was investigated using a thermogravimetric analyzer (TGA) and a mass spectrometer (MS). γ-Y2 Si2 O7 exhibited good resistance against Na2 SO4 molten salt. The kinetic curves were well fitted by a paralinear equation: the linear part was caused by the evaporation of Na2 SO4 and the parabolic part came from gas products evolved from the hotcorrosion reaction. A thin silica film formed under the corrosion scale was the key factor for retarding the hot corrosion. The apparent activation energy for the corrosion of γ-Y2 Si2 O7 in Na2 SO4 molten salt with flowing air was evaluated to be 255 kJ/mol. 相似文献
14.
J. D. HODGE 《Journal of the American Ceramic Society》1984,67(3):183-185
A subsolidus phase diagram for the system Li2 O-Na2 O-Al2 O3 at 1500°C is presented. Unlike the analogous system MgO-Na2 O-Al2 O3 , β" was the only ternary compound observed in the section of the lithia-based system examined in this study. A fairly extensive region of β solid solution was found. In contrast, the range of compositions where β" exists is small and does not extend into the Na2 O-Al2 O3 binary. 相似文献
15.
Nine compositions containing 40 to 68% B2 O3 were used to study the high-lithia portion of the system Li2 O-B2 O3 by quenching and differential thermal analysis methods. The compounds 3Li2 O 2B2 O3 and 3Li2 O B2 O3 melted incongruently at 700°± 6°C, and 715°± 15°C., respectively. The compound 2Li2 O B2 O3 is assumed to dissociate slightly below 650°± 15° C., although the data could also be interpreted as in-congruent melting. Below 600°± 6°C. it does dissociate to the 3:2 and 3:1 compounds. In this narrow temperature interval the 2:1 compound had an inversion at 618°± 6°C. Both forms of the 2:1 compound could be quenched to room temperature. X-ray diffraction data for the compounds are tabulated, and the complete phase diagram for the system Li2 O-B2 O3 is presented. 相似文献
16.
A solid electrolyte electrochemical cell of the type Pt|Ni:NiO a =1 ∥ZrO2 +7.5% CaO∥Ni:NiO a <1 +glass|Pt was used to measure the activities of NiO in sodium disilicate glass from 750° to 1100°C. The data indicate a solubility varying from 11 mol% (5.0 wt%) at 800° to 20 mol% (9.3 wt%) at 1100°C. From the variation in NiO activity, the activity of sodium disilicate in glass solution was estimated; from these combined data partial molar free energies and entropies of solution of NiO and Na2 Si2 O5 and free energies and entropies of mixing were calculated. A partial phase diagram for the system NiO-Na2 Si2 O5 proposed from solubility data indicates a eutectic at ∼12 mol% (5.3 wt%) NiO at 830°C. 相似文献
17.
The quenching technique was used to study subliquidus and subsolidus phase relations in the pseudobinary system Na2 Ti2 Si2 O11 -Na2 Ti2 Si2 O9 . Both narsarukite (Na2 TiSi4 O11 ) and lorenzenite (Na2 Ti2 Si2 O9 ) melt incongruently. Narsarsukite melts at 911°±°C to SiO2 +liquid, with the liquidus at 1016°C. Lorenzenite melts at 910°±5°C to Na2 Ti6 O13 +liquid; Na2 Ti6 O13 reacts with liquid to form TiO2 and is thus consumed by 985°±5°C. The liquidus occurs at 1252°C. 相似文献
18.
E. F. RIEBLING 《Journal of the American Ceramic Society》1967,50(1):46-53
Density (and some viscosity) data are presented for binary sodium borate melts containing as much as 60 mole % Na2 O and for ternary sodium silicoborate melts with B/Si <2.0 between 1000°C and 1300°C. The high-temperature partial molar volume analysis of the binary sodium borate melts reveals about 50% BO4 tetrahedra at the 40 mole % Na2 O composition, in agreement with recent NMR estimates for the binary glasses. No "boron anomaly" was found near 18 mole % Na2 O at high temperature. The synthetic partial molar volume model that agrees best with experiment for all ternary melts studied involves the presence of some BO4 tetrahedra, the percentage of which varies with composition. This ternary model involves a high degree of internal consistency. No tendency toward extensive micro-immiscibility was observed for ternary melts near the SiO2 ·B2 O3 binary. 相似文献
19.
Mi-Ri Joung Jin-Seong Kim Myung-Eun Song Jae-Hong Choi Jong-Woo Sun Sahn Nahm Jong-Hoo Paik Byung-Hyun Choi 《Journal of the American Ceramic Society》2009,92(9):2151-2154
Li2 CO3 was added to Mg2 V2 O7 ceramics in order to reduce the sintering temperature to below 900°C. At temperatures below 900°C, a liquid phase was formed during sintering, which assisted the densification of the specimens. The addition of Li2 CO3 changed the crystal structure of Mg2 V2 O7 ceramics from triclinic to monoclinic. The 6.0 mol% Li2 CO3 -added Mg2 V2 O7 ceramic was well sintered at 800°C with a high density and good microwave dielectric properties of ɛ r =8.2, Q × f =70 621 GHz, and τf =−35.2 ppm/°C. Silver did not react with the 6.0 mol% Li2 CO3 -added Mg2 V2 O7 ceramic at 800°C. Therefore, this ceramic is a good candidate material in low-temperature co-fired ceramic multilayer devices. 相似文献
20.
Tentative phase relations in the binary system BnOa-A12 O3 are presented as a prerequisite to the understanding of the system Li2 O-B2 O3 -Al2 O3 . Two binary compounds, 2A12 O3 .B2 O3 and 9A12 O3 .-2B2 O3 , melted incongruently at 1030° f 7°C and about 144°C, respectively. Two ternary compounds were isolated, 2Li2 O.A12 O3 .B2 O3 and 2Li2 O. 2AI2 O3 . 3B2 03 . The 2:1:1 compound gave a melting reaction by differential thermal analysis at 870°± 20° C, but the exact nature of the melting behavior was not determined. The 2:2:-3 compound melted at 790°± 20° C to Liz O.-5Al2 O3 and liquid. X-ray diffraction data for the compounds are presented and compatibility triangles are shown. 相似文献