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1.
A. T. PRINCE 《Journal of the American Ceramic Society》1951,34(2):44-51
The system MgO–Al2 O3 –2CaO·SiO2 comprises a plane through the tetrahedron CaO–MgO–Al2 O3 –SiO2 . A total of 108 compositions were prepared having an alumina content below the line joining 2CaO·Al2 O3 SiO2 (gehlenite) and MgO·Al2 O3 (spinel). Quenching experiments were carried out on 96 of these compositions at temperatures up to 1590°C. Three binary eutectic systems and two ternary eutectic systems are described. Compositions on this plane are of significance in an investigation of the constitution of basic refractory clinkers made from Canadian dolomitic magnesites. They also concern the compositions of certain blast furnace slags. 相似文献
2.
S. E. McCUNE T. P. GREANEY W. C. ALLEN R. B. SNOW 《Journal of the American Ceramic Society》1957,40(6):187-195
An examination was conducted to determine the mechanism of peeling of fire-clay brick in the low-temperature region of a blast furnace where 3 to 10% K2 O is the principal contaminant. In laboratory tests, as-received high-duty and superduty fire-clay brick and 70% alumina brick treated with KCl-K2 CO3 mixtures showed no peeling at a temperature of 1600°F. Cracks were found in high-duty brick that were treated with KCN at 1500°F. under partially reducing conditions. X-ray diffraction studies of mixtures of crushed brick and K2 CO3 indicated the formation of leucite (K2 O.Al2 O3 .4SiO2 ) and kaliophilite (K2 O.-Al2 O3 .2SiO2 ) at temperatures below 1700°F. These latter data, confirmed by specimens from used blast-furnace linings, showed that silica is the first constituent attacked by alkali. Since the formation of leucite and kaliophilite in fire-clay brick is the probable cause of peeling, the increased reaction of silica, in a dense Al2 O3 .SiO2 refractory of higher silica content than fire-clay brick, should confine the alkali attack to the surface of the brick in low-temperature applications. 相似文献
3.
The cell dimensions of pure triclinic 3CaO·SiO2 and monoclinic 3CaO·SiO2 solid solution (54CaO·16SiO2 ·Al2 O3 ·MgO) were determined and the powder diffraction patterns were indexed by the method of precise measurement of the spacings. The lattice constants are expressed in terms of triclinic or monoclinic cells corresponding to pseudo-orthorhombic cells derived from Jeffery's trigonal cell. The apparent lattice constants for pure 3CaO·SiO2 are a = 12.195 a.u., b = 7.104 au., c = 25.096 a.u., α= 90°, β= 89°44'γ= 89°44'; for 54CaO·16SiO2 .-Al2 O3 MgO, a = 12.246 a.u., b = 7.045 a.u., c = 24.985 a.u., β= 90°04'. Precise lattice constants of Jeffery's monoclinic lattice for 54CaO.-16SiO2 -Al2 O3 ·MgO are derived as a = 33.091 a.u., b = 7.045 a.u., c = 18.546 a.u., β= 94°08'. High-temperature X-ray patterns showed that pure triclinic 3CaO·SiO2 transformed to a monoclinic form at about 920°C. and then to a trigonal form at about 970°C. Monoclinic 54CaO.16SiO2 ·Al2 O3 –MgO transformed to trigonal at about 830°C. These transitions were reversible and reproducible and were accompanied by only slight deformation of the structure forms. 相似文献
4.
By use of electron microbeam probe analysis on quenched samples, the concentration distribution of CaO, A12 O3 , and SiO2 was determined across the boundary layer between molten calcium aluminum silicates and dissolving or growing sapphire and fused silica. A definite shift in the concentration ratios of the solvent components was found near the interface. Analysis of diffusion flux equations for a ternary system successfully related the shift in concentration ratio to the intrinsic diffusion coefficient for each component. For alumina dissolution in a melt rich in CaO, evidence of incongruent dissolution was observed with the formation of new phases, CaO· 6Al2 O3 and CaO· 2A12 O3 . 相似文献
5.
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
6.
Calcium hexa-aluminate (CaO·6Al2 O3 ) has been prepared from calcium nitrate and aluminum sulfate solutions in the temperature range of 1000°–1400°C. A 0.3 mol/L solution of aluminum sulfate was prepared, and calcium nitrate was dissolved in it in a ratio that produced 6 mol of Al2 (SO4 )3 ·16H2 O for each mole of Ca(NO3 )2 ·4H2 O. It was dried over a hot magnetic stirrer at ∼70°C and fired at 1000°–1400°C for 30–360 min. The phases formed were determined by XRD. It was observed that CaO·Al2 O3 and CaO·2Al2 O3 were also formed as reaction intermediates in the reaction mix of CaO·6Al2 O3 . The kinetics of the formation of CaO·6Al2 O3 have been studied using the phase-boundary-controlled equation 1 − (1 − x )1/3 = K log t and the Arrhenius plot. The activation energy for the low-temperature synthesis of CaO·6Al2 O3 was 40 kJ/mol. 相似文献
7.
Examination of mixtures of extremely pure silica and alumina shows that the greatest reactivity is not encountered with stoichiometric ratios to form mullite with the formula 3Al2 O3 . 2SiO2 but rather with the formula 2A12 O3 -SiO2 , and that reactivity also depends on the crystalline modification of alumina. A sharp exothermic differential thermal peak at 980°C. is attributed to three simultaneous reactions dependent on the silica-alumina ratio of the mixture: (1) the crystallization of gamma alumina, (2) the crystallization of a hydrogen aluminum spinel (HAl5 O5 ), and (3) the reaction of silica with the hydrogen aluminum spinel to form mullite. 相似文献
8.
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
9.
Bertha Alicia Vázquez Ángel Caballero Pilar Pena 《Journal of the American Ceramic Society》2005,88(7):1949-1957
Solid-state compatibility and melting relations of MgAl2 O4 in the quaternary system Al2 O3 –CaO–MgO–SiO2 were studied by firing and quenching selected samples located in the 65 wt% MgAl2 O4 , plane followed by microstructural and energy dispersive X-ray analysis. A projection of the liquidus surface of the primary crystallization volume of MgAl2 O4 was constructed from CaO, SiO2 and exceeding Al2 O3 , not involved in stoichiometric MgAl2 O4 formation; those three amounts were recalculated to 100 wt%. The temperature and character of six invariant points, where four solids co-exist with a liquid phase, were defined. One maximum point was localized and the positions of the isotherms were tentatively established. The effect of CaO, SiO2 , and Al2 O3 impurities on the high temperature behavior of spinel materials was also discussed. 相似文献
10.
Takeshi Hashishin Yasuhiro Kodera Takeshi Yamamoto Manshi Ohyanagi Zuhair A. Munir 《Journal of the American Ceramic Society》2004,87(3):496-499
The spinel (Mg,Si)Al2 O4 was synthesized from aluminum dross using an induction synthesis method. X-ray diffraction analyses on products formed at different temperatures provided an understanding of the formation mechanism of the spinel. After removal of soluble components, the induction heating of the dross resulted first in the oxidation of some of the AlN component and the subsequent formation of the spinel by the following reaction: x SiO2 + (1− x )MgO + [1−( x /3)]Al2 O3 + (2 x /3)AlN = (Mg1− x ,Si x )Al2 O4 + ( x /3)N2 ( g ). 相似文献
11.
Yoshihiro Hirata Kazuyoshi Sakeda Yumi Matsushita Kinji Shimada Yoshimi Ishihara 《Journal of the American Ceramic Society》1989,72(6):995-1002
Submicrometer SiO2 -Al2 O3 powders with compositions of 46.5 to 76.6 wt% Al2 O3 were prepared by hydrolysis of mixed alkoxides. Phase change, mullite composition, and particle size of powders with heating were analyzed by DTA, XRD, IR, BET, and TEM. As-produced amorphous powders partially transformed to mullite and Al-Si spinel at around 980°C. The compositions of mullite produced at 1400° and 1550°C were richer in Al2 O3 than the compositions of stable mullite solid solutions predicted from the phase diagram of the SiO2 -Al2 O3 system. Particle size decreased with increasing Al2 O3 content. The sintered densities depended upon the amount of SiO2 -rich glassy phase formed during sintering and the green density expressed as a function of particle size. 相似文献
12.
Luis A. M. Scudeller Elson Longo Jose A. Varela 《Journal of the American Ceramic Society》1990,73(5):1413-1416
A graphite chamber was used for the reaction between samples of 45 or 55 wt% alumina and a mixture of metallurgical coke and potassium carbonate. Thermal treatments were conducted at 1000°C. The results suggest that the potassium attack in silica-alumina bricks is controlled by the following reactions: K2 O + SiO2 → K2 O → SiO2 in the glassy matrix; 3(K2 O · 2SiO2 ) + 3Al2 O3 → 2SiO2 · 3(K2 O · Al2 O3 · 2SiO2 ) + 2SiO2 for short times; and K2 O → Al2 O3 · 2SiO2 + 2SiO2 · K2 O · Al2 O3 · 4SiO2 for long times. In 55 wt% alumina bricks containing corundum and tridymite, potassium also attacks those phases forming a glassy phase. The formation of kaliophilite at the matrix/mullite grain interface causes a volumetric expansion of 55.5%, resulting in cracks in the matrix. Because the kaliophilite phase is not in equilibrion with mullite, the former will react with free silica to form leucite that is more thermodynamically stable. 相似文献
13.
Microstructure and Bending Strength of 3Y-TZP/12Ce-TZP Ceramics Fabricated by Liquid-Phase Sintering at Low Temperature 总被引:1,自引:0,他引:1
With the addition of 1 wt% of MgO–Al2 O3 –SiO2 glass as a sintering aid, 3Y-TZP/12Ce-TZP ceramics (composed from a mixture of 3Y-TZP and 12Ce-TZP powder) have been fabricated via liquid-phase sintering at 1250°–1400°C. In the sintered bodies, the grain growth of Y-TZP is almost unaffected, whereas that of Ce-TZP is inhibited. MgO·Al2 O3 spinel and an amorphous phase that contains Al2 O3 and SiO2 (from the sintering aid) fully fill the grain junctions. The bending strength of 3Y-TZP/12Ce-TZP, when sintered at 1250°–1300°C, is ∼800–900 MPa, which is greater than that of 3Y-TZP ceramics without Ce-TZP particles. Ce-TZP grains and MgO·Al2 O3 spinel in 3Y-TZP/12Ce-TZP ceramics may impede crack growth, and the bending strength is enhanced. 相似文献
14.
Cristina Siligardi Luca Lusvarghi Monia Montorsi Cecilia Vernia 《Journal of the American Ceramic Society》2008,91(3):990-995
In this work several complementary techniques have been employed to carefully characterize the sintering and crystallization behavior of CaO–Al2 O3 –ZrO2 –SiO2 glass powder compacts after different heat treatments. The research started from a new base glass 33.69 CaO–1.00 Al2 O3 –7.68 ZrO2 –55.43SiO2 (mol%) to which 5 and 10 mol% Al2 O3 were added. The glasses with higher amounts of alumina sintered at higher temperatures (953°C [lower amount] vs. 987°C [higher amount]). A combination of the linear shrinkage and viscosity data allowed to easily find the viscosity values corresponding to the beginning and the end of the sintering process. Anorthite and wollastonite crystals formed in the sintered samples, especially at lower temperatures. At higher temperatures, a new crystalline phase containing ZrO2 (2CaO·4SiO2 ·ZrO2 ) appeared in all studied specimens. 相似文献
15.
Yexia Qin Wei Pan Rui Zhang Aibing Du 《International Journal of Applied Ceramic Technology》2008,5(1):105-109
A series of alumina-based ceramic cores sintered at 1300°C, 1400°C, and 1500°C for 5 h were prepared, and the phases and microstructures were characterized by X-ray diffraction and scanning electron microscopy. The effect of colloidal silica sols on the properties of ceramic core was discussed. The properties of these materials were determined. The results indicated that the microstructure of the core is characterized by the presence of substantially unreacted Al2 O3 particles having a polycrystalline composition consisting essentially of in situ synthesized 3Al2 O3 ·2SiO2 on the surface of the Al2 O3 particles. The colloidal silica sol contents do not have an appreciable effect on the densification and shrinkage of the alumina ceramic core. The ceramic cores of 5 wt% colloidal silica sol contents sintered at 1500°C for 5 h showed the smallest creep deformation in the present research. 相似文献
16.
J. P. HILGER D. BABEL N. PRIOUL A. FISSOLO 《Journal of the American Ceramic Society》1981,64(4):213-220
Corrosion processes of Al2 O3 -ZrO2 -SiO2 and Al2 O3 -SiO2 refractories were studied. Chemical, microscopic, and X-ray diffraction investigations are reported. The results are interpreted using the SiO2 A12 O3 -K2 O and SiO2 -Al2 O3 -PbO phase diagrams. An explanation is put forward regarding the process of corrosion by K2 O and PbO. 相似文献
17.
Thermal and X-ray studies show that there is complete solid solution between MgO.Cr2 O3 and MgO.Al2 O3 and that the spinel solid solutions are stable with no exsolution down to temperatures as low as 510°C. There is no solid solution of excess Cr2 O3 in MgO.Cr2 O3 nor of MgO.Cr2 O3 in Cr2 O3 . The join MgO.Cr2 O3 –Al2 O3 is found to be nonbinary; compositions along that join yield mixtures of a chromium oxide-alumina solid solution and a spinel solid solution on firing to temperatures high enough to promote solid-state reaction. Chromium oxide loss by volatilization increases at higher temperature. At a given temperature, chromium oxide loss is found to vary directly with the partial pressure of oxygen in the furnace atmosphere and with the ratio of MgO to SiO2 in the charges heated. 相似文献
18.
Synthesis of hexacelsian barium aluminosilicate (BaAl2 Si2 O8 or BAS) from BaCO3 , Al2 O3 , and amorphous SiO2 was examined. BaCO3 can react with SiO2 and Al2 O3 to form barium silicates (Ba2 SiO4 or B2 S, BaSiO3 or BS, and BaSi2 O5 or BS2 ) and barium aluminate (BaAl2 O4 or BA). It is shown that there are two competitive reactions leading to the formation of hexacelsian BAS. One involves a reaction between BS2 and Al2 O3 and the other involves a reaction between BA and SiO2 . In experiments with the model BS2 –Al2 O3 and BA–SiO2 systems it is shown that the reaction between BS2 and Al2 O3 is much faster than the reaction between BA and SiO2 . However, in the BAS system, Al2 O3 suppresses the reactions which form BS2 and instead reacts with B2 S and BS to form BA. The kinetics of hexacelsian BAS formation are greatly enhanced when BS2 is made separately and fired with Al2 O3 to yield BAS. 相似文献
19.
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
20.
Synthesis of AlN Powder by Carbothermal Reduction-Nitridation of Various Al2O3 Powders with CaF2 总被引:1,自引:0,他引:1
Takayuki Ide Katsutoshi Komeya Takeshi Meguro Junichi Tatami 《Journal of the American Ceramic Society》1999,82(11):2993-2998
We investigated the effect of characteristics of raw Al2 O3 powder on the synthesis of AlN by the carbothermal reduction-nitridation method, in which CaF2 was added as a catalytic material. Four types of Al2 O3 powders were selected. An Al2 O3 /C molar ratio of 0.29 was fixed, and the amount of CaF2 was varied from 3 to 30 wt%. The carbothermal reduction-nitridation was conducted from 1350° to 1450°C in N2 flow. The nitridation rate tended to increase with decreasing particle size of raw Al2 O3 and was found to depend on the Al2 O3 synthesizing method. The particle sizes of the synthesized AlN increased somewhat with increasing reaction temperatures. However, even though different particle sizes of Al2 O3 powders were used, AlN powders synthesized under the same conditions exhibited almost the same particle size, round shape, and narrow size distribution. From XRD analysis, CaO·6Al2 O3 and CaO·2Al2 O3 were identified as intermediate compounds during these reactions. The above phenomena suggest that the synthesis mechanism of AlN powder by carbothermal reduction-nitridation of Al2 O3 with CaF2 addition was the nitridation of the intermediate compounds through the liquid phase of the system CaF2 -CaO·6Al2 O3 -CaO·2Al2 O3 . 相似文献