共查询到20条相似文献,搜索用时 31 毫秒
1.
B. I. Bogdanov Iv. Chomakov Y. Iliev P. Tanev 《Journal of the American Ceramic Society》1986,69(8):179-C
The effect of Al(NO3 )3 ·9H2 O, AlCl3 ·6H2 O, Al(CH3 COO)3 , and NH4 F on the specific surface of Al2 O3 obtained from aluminum-ammonium alum by calcining was studied. It was found that the use of these additives makes it possible to obtain Al2 O3 with specific surface varying from 1 to 135 m2 /g after thermal treatment in the interval from 1273 to 1423 K. The changes in the morphology and structure of powederd Al2 O3 obtained from alum containing these additives were studied by electron microscope observations. 相似文献
2.
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
3.
SAMUEL J. SCHNEIDER 《Journal of the American Ceramic Society》1959,42(4):184-193
The compound compositions of four aluminous cements were determined on anhydrous as well as hydrated specimens which had been heat-treated at temperatures between room temperature and 1400° C. Phases were identified by X-ray diffraction and differential thermal analysis. Specimens were also tested for transverse strength, dynamic modulus of elasticity, and thermal length change. A study of the dehydration characteristics of CaO - Al2 O8 - 10H2 O3 3CaO.Al2 O3 . 6H2 O, and Al2 O3 . 3H2 O was included. The data indicated that CaO. Al2 O3 10H2 O was the primary crystalline hydrate formed in the cements at room temperature. At 50° C., 3 CaO Al2 O3 -6H2 O and Al2 O3 . 3H2 O were formed as by-products of the dehydration of CaO.Al2 O3 .10H2 O. When heated alone in an open system, CaO.Al2 O3 .10H2 O did not convert to 3CaO. Al2 O3 . 6H2 O and A12 O3 . 3H2 O. A correlation between the mechanical properties and compound compositions was noted. 相似文献
4.
F. G. BUTTLER L. S. DENT GLASSER H. F. W. TAYLOR 《Journal of the American Ceramic Society》1959,42(3):121-126
Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al2 O3 . 13H2 O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca2 (OH)7 - 3H2 O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12 O3 .13H2 O, from which it is derived by substitution of CO3 2- for 20H- + 3H2 O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2 O3 .Ca Y 2 - xH2 O and 3CaO Al2 O3 Ca Y xH2 O. On dehydration, 4CaO.Al2 O3 .13H2 O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2 O3 .3H2 O are formed and, by 1000°C., CaO and 12CaO.7Al2 O8 . The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2 O3 .3H2 O is formed. 相似文献
5.
A study of the system Al2 O3 –Ga2 O3 –H2 O has resulted in the determination of equilibrium diagrams for the systems Al2 O3 –Ga2 O3 and Al2 O3 .-H2 O–Ga2 O3 .H2 O. Extensive solid solution characterizes the α -Al2 O3 and β -Ga2 O3 structures at high temperatures, but it is shown that below 810°C. a compound, GaAlO3 , and a new series of (Al, Ga)2 O3 structures are stable. Among the hydrates, a complete series of diaspore solid solutions extends from Al2 O3 .H2 O to Ga2 O3 .H2 O. Boehmite solid solutions extend to approximately the composition 70Al2 O3 .H2 O, 30Ga2 O3 .H2 O. 相似文献
6.
Phase equilibria have been determined in the system CaO-Al2 O3 -H2 O in the temperature range 100° to 1000°C. under water pressures of up to 3000 atmospheres. Only three hydrated phases are formed stably in the system: Ca(OH)2 , 3CaO·Al2 O3 ·6H2 O, and 4CaO·3Al2 O3 -3H2 O. Pressure-temperature curves delineating the equilibrium decomposition of each of these phases have been determined, and some ther-mochemical data have been deduced therefrom. It has been established that both the compounds CaO·Al2 O3 and 3CaO·Al2 O3 have a minimum temperature of stability which is above 1000°C. The relevance of the new data to some aspects of cement chemistry is discussed. 相似文献
7.
Tohru Sekino Toshio Nakajima Satoru Ueda Koichi Niihara 《Journal of the American Ceramic Society》1997,80(5):1139-1148
High-density nickel–dispersed-alumina (Al2 O3 /nickel) composites with superior mechanical properties were obtained by the hydrogen reduction and the hot pressing of alumina–nickel oxide (Al2 O3 /NiO) mixed powders. The mixtures were prepared by using NiO or nickel nitrate (Ni(NO3 )2 · n H2 O) as a dispersion source of nickel metal. Microstructural investigations of the composite fabricated using nitrate powder revealed that fine nickel particles, } 100 nm in diameter, dispersed homogeneously at the matrix grain boundaries, forming the intergranular nanocomposite. High strength (.1 GPa) and high-temperature hardness were registered for the composite that contained a small amount of nickel dispersion. The ferromagnetic properties of nickel, such as high coercive force, were observed, because of the fine magnetic dispersions, which indicates a functional value of structural composites. 相似文献
8.
Qingmei Lu Wensheng Dong Haojing Wang Xinkui Wang 《Journal of the American Ceramic Society》2002,85(2):490-492
Yttrium aluminum garnet (YAG, Y3 Al5 O12 ) was synthesized by sol–gel processing from the stoichiometric amounts of aluminum pellets, Y(NO3 )3 ·6H2 O, and Al(NO3 )3 ·9H2 O or AlCl3 ·6H2 O, with suitable kinds of acid (citric acid, acetic acid, etc.) as catalysts. Polycrystalline YAG powder was obtained by drying the YAG precursor followed by calcination at temperatures above 900°C. Thermogravimetry/differential thermal analysis and Fourier transform infrared specotrscopic analyses in air showed an exothermic peak at ∼900°C, attributed to the formation of a polycrystalline YAG phase and weight loss of 60% at 1000°C, caused by the decomposition of hydroxyl and NO3 − , etc. X-ray diffraction analysis showed that YAG can be formed at 900°C, and no other intermediate was observed. In particular, the YAG sol can be used for dry-spinning fibers with the aid of some organic polymer. 相似文献
9.
Sinterable cubic aluminum oxy nitride (ALON) has been prepared by carbon reduction of aluminum oxide inflowing nitrogen. Three different sources of Al2 O3 (A12 O3 from clay, commercial A12 O3 , and A12 O3 derived from AlCl3 .6H2 O) and two different sources of carbon (carbon black and starch) were used. Pressed pellets of ALON powder were sintered in N2 at 1950°C greater than 95% of theoretical density. 相似文献
10.
Chi-Shiung Hsi Hong-Yang Lu Fu-Su Yen 《Journal of the American Ceramic Society》1989,72(11):2208-2210
Xerogels of 3Al2 O3 ·2SiO2 mullite were prepared by hydrolyzing Al(NO3 )3 ·9H2 O and Si(OC2 H5 )4 solutions with pH values of 8.3, 9.4, 10.1, and 10.4; the xerogels were composed of a combination of singlephase and diphasic materials. A strong alkaline solution enhanced bayerite formation in the gels. Mullite from the diphasic xerogels was produced by reacting θ-Al2 O3 with amorphous SiO2 , whereas mullite from the single-phase xerogels was transformed from Al-Si spinel. For the single-phase xerogel, the DTA curve closely resembled the kaolinite-to- mullite reaction. For the diphasic xerogels, the Al3+ -containing solution gelled to pseudoboehmite, which transformed to bayerite in solution. The bayerite then decomposed to η-Al2 O3 and to θ-Al2 O3 sequentially on heating. 相似文献
11.
Akira Kato Hisao Yamashita Hiroshi Kawagoshi Shimpei Matsuda 《Journal of the American Ceramic Society》1987,70(7):157-C
Mixtures of La2 O3 and Al2 O3 with various La contents were prepared by co-precipitation from La(NO3 )3 and Al(NO3 )3 solutions and calcined at 800° to 1400°C. The addition of small amounts of La2 O3 (2 to 10 mol%) to Al2 O3 gives rise to the formation of lanthanum β-alumina (La 2 O3 ·11–14Al2 O3 ) upon heating to above 1000°C and retards the transformation of γ-Al2 O3 to α-Al2 O3 and associated sintering. 相似文献
12.
An exothermic transition is observed near 400°CC on thermal dehydration of highly crystalline AI2 (SO4 )3.16H2 O, Al2 (S04 )3 14H2 O, and Al2 (S04 )3 9H2 O when the early stages of heating are carried out in vacuum. Amorphous or partially crystalline hydrates do not show the exotherm. No systematic relation is apparent between the decomposition behavior and the pore volume distribution of the various anhydrous A12 (SO4 )3 products. 相似文献
13.
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
14.
The thermal decompositions of BaTiO(c2 O4 )2 .- 4H2 O, BaTiO(OH)2 C2 O4 .2H2 O, SrTiO(C2 O4 )2 .- 4H2 O, and SrTiO(OH)2 C2 O4 .H2 O were investigated using TGA, DTA, and effluent gas analysis. The stoichiometry of the decompositions is discussed and it is proposed that a reduced state of titanium is formed as an intermediate. 相似文献
15.
Paste samples of tricalcium aluminate alone, with CaCl2 , with gypsum, and with gypsum and CaCl2 were hydrated for up to 6 months and the hydration products characterized by SEM, XRD, and DTA. Tricalcium aluminate hydrated initially to a hexagonal hydroaluminate phase which then changed to the cubic form; the transformation rate depended on the size and shape of the sample and on temperature. The addition of CaCl2 to tricalcium aluminate resulted in the formation of 3CaO · Al2 O3 · CaCl2 ·10H2 O and 4CaO · Al2 O3 · 13H2 O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al2 O3 · 6H2 O; the addition of gypsum resulted in the formation of monosulfoaluminate with a minor amount of ettringite. When chloride was added to tricalcium aluminate and gypsum, more ettringite was formed, although 3CaO · Al2 O3 · CaSO4 · 12H2 O and 3CaO · Al2 O3 · CaCl2 · 10H2 O were the main hydration products. 相似文献
16.
Junying Zhang Zhongtai Zhang Zilong Tang Yuanhua Lin 《Journal of the American Ceramic Society》2002,85(4):998-1000
A (Ce0.67 Tb0.33 )Mn x Mg1− x Al11 O19 phosphor powder was synthesized, using a simple sol–gel process, by mixing citric acid with CeO2 , Tb4 O7 , Al(NO3 )3 ·9H2 O, Mg(OH)2 ·4MgCO3 ·6H2 O, and Mn(CH3 COO)2 . The phosphor crystallized completely at 1200°C, and the phosphor particle size was between 1 and 5 μm. The excitation spectrum was characteristic of Ce3+ , while the emission spectrum was composed of lines from Tb3+ and Mn2+ . The Mn2+ gave a green fluorescence band, and concentration quenching occurred when x > 0.10. The luminescent properties of the phosphor were explained by a configurational coordinate model. 相似文献
17.
The influence of citric acid on paste hydration of 3CaO· Al2 O3 in the presence of CaSO4 ·2H2 O and Ca(OH)2 was studied using X-ray diffraction, scanning electron microscopy, and conduction calorimetry. The time at which the citric acid is added (either prior to or with the mixing water) determines how it affects the reactivity of the aluminate. Immediately after the paste is gaged citric acid promotes a more rapid reaction, but later reactions are retarded. Hexagonal calcium aluminate hydrates, ettringite, and monosulfate were all detected as early hydration products. The influence of citric acid on the hydration of 3CaO·Al2 O3 slabs immersed in saturated CaSO4 ·2H2 O solutions was also studied and a reaction scheme proposed. 相似文献
18.
Tsang-Tse Fang Horng-Bin Lin Jim-Bin Hwang 《Journal of the American Ceramic Society》1990,73(11):3363-3367
Thermal analysis was performed on coprecipitated materials and on individual components. The detailed decomposition schemes of coprecipitates and individual components are proposed and discussed. According to the proposed decomposition schemes, the values of the observed weight loss are in good agreement with those of the theoretical values of the coprecipitated materials and individual components. The results indicate that barium titanyl oxalate is an inserting compound, i.e., a structure of distorted barium hydrogen oxalate hydrate being inserted by Ti(OH)3 + . The results also verify that copreciptation of barium and titanium ions in an oxalate aqueous solution at pH 7 is a mixture of BaC2 O4 · 0.5H2 O and TiO(OH)2 · 1.5H2 O and coprecipitation of barium and titanium ions using the process of Yamamura et al. is a mixture of Ba(NO3 )2 and Ti(OH)2 C2 O4 . 相似文献
19.
Masayuki Nogami Naoya Hayakawa Naoya Sugioka Yoshihiro Abe 《Journal of the American Ceramic Society》1996,79(5):1257-1261
Samarium ions (Sm2+ ) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2 O-Al2 O3 SiO2 synthesized by the hydrolysis of Si(OC2 H5 )4 , Al(OC4 H9 )3 , CH3 COONa, and SmCl3 ·6H2 O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2 O3 -SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2 O2 -SiO2 glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min. 相似文献
20.
Weon-Pil Tai Tadahiko Watanabe Nathan S. Jacobson 《Journal of the American Ceramic Society》1999,82(1):245-248
The high-temperature stability of alumina (Al2 O3 ) in argon and argon/water-vapor (Ar/H2 O) environments has been investigated. Samples were exposed at temperatures of 1300°C–1700°C for 10 h. The microstructure, flexural strength, and volume all showed significant changes in the Ar/H2 O environment at 1700°C. Samples also became whiter, because of the oxidation of graphite impurities that had diffused from the hot-processing dies. In the Ar/H2 O environment at 1700°C, grain-boundary etching occurred and was much more severe than in the pure-argon environment, which was very likely caused by the enhanced formation of gaseous Al(OH)3 and Al(OH)2 along grain boundaries. In addition, in the Ar/H2 O environment, substantial grain growth occurred in the surface vicinity. This grain growth, together with grain-boundary etching, led to a decrease in flexural strength. 相似文献