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1.
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
2.
Fabrication of Translucent Magnesium Aluminum Spinel Ceramics 总被引:5,自引:0,他引:5
Ji-Guang Li Takayasu Ikegami Jong-Heun Lee Toshiyuki Mori 《Journal of the American Ceramic Society》2000,83(11):2866-2868
A precursor for magnesium aluminum spinel powder, composed of crystalline ammonium dawsonite hydrate (NH4 Al(OH)2 CO3 ·H2 O) and hydrotalcite (Mg6 Al2 (CO3 )(OH)16 ·4H2 O) phases, was synthesized via precipitation, using ammonium bicarbonate as the precipitant. The precursor was characterized by differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. Reactive spinel powder, which could be densified to translucency under vacuum at 1750°C in 2 h without additives, was obtained by calcining the precursor at 1100°C for 2 h. 相似文献
3.
Monoclinic hydrous-zirconia fine particles that contained cerium(IV) hydroxide (Ce(OH)4 ) were heated from 200°C to 600°C, to investigate the phase transformation to CeO2 -doped tetragonal ZrO2 . Both ZrOCl2 ·8H2 O and CeCl3 ·7H2 O were dissolved in aqueous solutions and then boiled to prepare the hydrous-zirconia particles. The Ce(OH)4 -containing hydrous-zirconia particles were prepared by adding aqueous ammonia into the boiled solutions. The monoclinic-to-tetragonal ( m right arrow t ) phase transformation of the Ce(OH)4 -containing hydrous zirconias was observed at 300°C using X-ray diffraction (XRD). XRD and Brunauer-Emmett-Teller (BET) specific surface area measurements revealed that the Ce(OH)4 -containing hydrous zirconias had a tendency to transform from the monoclinic phase to the tetragonal phase at lower temperatures as the primary particle size of the hydrous zirconia decreased and the Ce(OH)4 content increased. These tendencies for the m right arrow t phase transformation agree with the conclusions that have been derived from thermodynamic and kinetic considerations. 相似文献
4.
Phase equi ibria in the system MgO-MgC 2 -H2 O at 2°±3°C were determined and the reactions by which the equi ibrium phases, 5Mg(OH)2 MgC 2 8H2 O and 3Mg(OH)2 MgC 2 8H2 O, deve op were studied by X-ray diffractometry. As reactive MgO is disso ved by magnesium ch oride so utions, a thixotropic suspension is converted to a ge, which then crysta izes to form the ternary oxych oride phases. Insufficient y active MgO disso ves more s ow y so that, in an open system, bu k composition can shift by evaporation of water, resu ting in crysta ization of a nonequi ibrium phase assemb age, with residua magnesium ch oride so ution and unreacted MgO. Imp ications of these nonequi ibrium reactions for the performance of magnesium oxych oride cements are discussed. 相似文献
5.
Synthesis of Mesoporous Needle-Shaped Ytterbium Oxide Crystals by Solvothermal Treatment of Ytterbium Chloride 总被引:1,自引:0,他引:1
Saburo Hosokawa Shinji Iwamoto Masashi Inoue 《Journal of the American Ceramic Society》2007,90(4):1215-1221
The reaction of rare-earth (RE; Y, Er, and Yb) chloride hydrates in 1,4-butanediol at 300°C for 2 h gave mixtures of RE(OH)2 Cl and RE2 O3 · x H2 O, and the products were composed of irregularly shaped particles. A prolonged reaction (10 h) yielded a mixture of RE(OH)2 Cl and RE2 O3 · x H2 O for Er or Y, but phase-pure RE2 O3 · x H2 O was obtained for Yb. The product for Yb comprised needle-shaped single crystals of Yb2 O3 · x H2 O with a width of 0.2–0.6 μm and a length of 5–15 μm. The Yb2 O3 · x H2 O phase decomposed to Yb2 O3 at 350°–500°C, preserving the needle-shaped morphology; this was maintained even after calcination at 1100°C. Single crystals of Yb2 O3 obtained by the calcination of Yb2 O3 · x H2 O at 500°C had very small voids and the voids were enlarged to 35 Å in diameter by calcination at 800°C. 相似文献
6.
Claus H. Rüscher Shiro Shimada Hartmut Schneider 《Journal of the American Ceramic Society》2002,85(6):1616-1618
A plane-parallel, polished, 0.9 mm thick, single-crystal (001) plate of 2:1 mullite was treated for 6 h at 1600°C in an Ar/H2 O (90/10) gas mixture at 100 kPa. Optical microscopy studies and infrared (IR) reflection spectroscopy studies of the lattice vibrations yielded no evidence for change with respect to the untreated reference crystal. However, IR absorption spectroscopy showed that structurally bound OH groups were formed by the heat treatment in the Ar/H2 O gas mixture. IR absorption depth profile analysis showed a rather homogeneous OH distribution through the crystal. Five different hydroxyl groups were separated according to dipole orientations and peak positions: E ‖ a , ω a 1 = 3447 cm−1 , ω a 2 = 3579 cm−1 ; E ‖ b , ω b 1 = 3456 cm−1 , ω b 2 = 3544 cm−1 ; and E ‖ c , ω c 1 = 3498 cm−1 . All IR peaks were strongly broadened (between 90 and 150 cm−1 ) because of a distribution in O-H binding distances caused by the real structure of mullite. 相似文献
7.
Thermal analysis has been performed on BaTiO(C2 O4 )2 .4H2 O, Ba0.6 Sr0.4 TiO(C2 O4 )2 .4H2 O, Sr(TiO(C2 O4 )2 .4H2 O, Ba0.9 Pb0.1 TiO(C2 O4 )2 .4H2 O, and BaTi0.9 Zr0.1 O(C2 O4 )2 .4H2 O. It was observed that the strontium compound decomposes differently than the others. Previous investigators have proposed conflicting mechanisms for the pyrolysis of the barium salt and these results are discussed in comparison with this work. The electrical resistivity and temperature coefficient of fired lanthanum-doped materials were found to vary with the calcination temperature. Maximum conductivity was observed in samples calcined at 900°C whereas maximum positive temperature coefficient was observed for materials calcined at 1050°C. Particle sizes of the calcined material were compared with grain sizes in the fired pieces and correlated with the electrical properties. A cursory examination was made on the effects of fabrication pressure, 1.25 to 15 tsi, on the electrical conductivity. Both the conductivity and positive temperature coefficient were found to increase with decreasing fabrication pressure. 相似文献
8.
KAZUO FUJIURA SHIGEKI SAKAGUCHI YASUTAKE OHISHI YUKIO TERUNUMA 《Journal of the American Ceramic Society》1988,71(6):460-464
This paper clarifies the formation reaction of ZrO2 crystals which appear as extrinsic scatterers in fluoride fibers. EPMA analysis indicates that BaO exists at grain boundaries of BaF2 purified by sublimation. BaO reacts with ZrF4 to form ZrO2 at 600°C during a glass-melting process. The ZrO2 formation reaction is influenced by H2 O. Ba(OH)2 , which is formed by the reaction between BaO and water vapor, melts at 370° to 420°C and reacts with ZrF4 to form ZrO2 at 450° to 520°C. When low-oxide-content BaF2 is used for fiber preparation, scatterers significantly decrease. 相似文献
9.
S. Shimada T. Onuma H. Kiyono M. Desmaison 《Journal of the American Ceramic Society》2006,89(4):1218-1225
Isothermal oxidation of dense TiC ceramics, fabricated by hot-isostatic pressing at 1630°C and 195 MPa, was performed in Ar/O2 (dry oxidation), Ar/O2 /H2 O (wet oxidation), and Ar/H2 O (H2 O oxidation) at 900°–1200°C. The weight change measurements of the TiC specimen showed that the dry, wet, and H2 O oxidation at 850°–1000°C is represented by a one-dimensional parabolic rate equation, while the oxidation in the three atmospheres at 1100° and 1200°C proceeds linearly. Cross-sectional observation showed that the dry oxidation produces a lamellar TiO2 scale consisting of many thin layers, about 5 μm thick, containing many pores and large cracks, while H2 O-containing oxidation decreases pores in number and diminishes cracks in scales. Gas evolution of CO2 and H2 with weight change measurement was simultaneously followed by heating the TiC to 1400°C in the three atmospheres. Cracking in the TiO2 scale accompanied CO2 evolution, and the H2 O-containing oxidation produced a small amount of H2 . A piece of single crystal TiC was oxidized in 16 O2 /H2 18 O to reveal the contribution of O from H2 O to the oxidation of TiC by secondary ion mass spectrometry. 相似文献
10.
Marin Cernea Elena Chirtop Dana Neacsu Iuliana Pasuk Sergiu Iordanescu 《Journal of the American Ceramic Society》2002,85(2):499-503
A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC2 O4 ·0.5H2 O and TiO(OH)2 ·1.5H2 O in a molar ratio of 1:4. Crystallized BaTi4 O9 was obtained by the thermal decomposition of a precipitate precursor at 1300°C for 2 h in air. The dimensions of the powder calcined at 1000°C are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300°C are of the order of 10 to 30 μm. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE011 mode. Excellent microwave characteristics for BaTi4 O9 —ɛ= 38 ± 0.5, Q = 3800–4000 at 6–7 GHz and τ f = 11 ± 0.7 ppm/°C—were found. 相似文献
11.
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
12.
Low-Temperature Fabrication of Transparent Yttrium Aluminum Garnet (YAG) Ceramics without Additives 总被引:12,自引:0,他引:12
Ji-Guang Li Takayasu Ikegami Jong-Heun Lee Toshiyuki Mori 《Journal of the American Ceramic Society》2000,83(4):961-963
A carbonate precursor of yttrium aluminum garnet (YAG) with an approximate composition of NH4 AlY0.6 (CO3 )1.9 (OH)2 ·0.9H2 O was synthesized via a coprecipitation method from a mixed solution of ammonium aluminum sulfate and yttrium nitrate, using ammonium hydrogen carbonate as the precipitant. The precursor precipitate was characterized using chemical analysis, differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. The sinterability of the YAG powders was evaluated by sintering at a constant rate of heating in air and vacuum sintering. The results showed that the precursor completely transforms to YAG at ∼1000°C via the formation of a yttrium aluminate perovskite (YAP) phase. YAG powders obtained by calcining the precursor at temperatures of ≤1200°C were highly sinterable and could be densified to transparency under vacuum at 1700°C in 1 h without additives. 相似文献
13.
Feng Li Xianghua Yu Liying Chen Hongjun Pan Xinquan Xin ¶ 《Journal of the American Ceramic Society》2002,85(9):2177-2180
A solid-state reaction process has been developed to synthesize perovskite-type LaCoO3 nanocrystals with grain diameters of 15–40 nm. In the first step of the preparation, ∼5 nm composite hydroxide nanoparticles are synthesized by the solid-state reaction of La(NO3 )3 · n H2 O and Co(NO3 )2 ·6H2 O with KOH at ambient temperature. A perovskite-type rhombohedral LaCoO3 phase appears at 550°C, after the hydroxide has been calcined at various temperatures. The phase transformation process is complete at ∼800°C, yielding a single-phase binary oxide. The results indicate that the new process is convenient, inexpensive, and effective for obtaining LaCoO3 nanocrystals with high yield. 相似文献
14.
Ji-Guang Li Takayasu Ikegami Toshiyuki Mori 《Journal of the American Ceramic Society》2005,88(4):817-821
We report here the fabrication of transparent Sc2 O3 ceramics via vacuum sintering. The starting Sc2 O3 powders are pyrolyzed from a basic sulfate precursor (Sc(OH)2.6 (SO4 )0.2 ·H2 O) precipitated from scandium sulfate solution with hexamethylenetetramine as the precipitant. Thermal decomposition behavior of the precursor is studied via differential thermal analysis/thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffractometry, and elemental analysis. Sinterability of the Sc2 O3 powders is studied via dilatometry. Microstructure evolution of the ceramic during sintering is investigated via field emission scanning electron microscopy. The best calcination temperature for the precursor is 1100°C, at which the resultant Sc2 O3 powder is ultrafine (∼85 nm), well dispersed, and almost free from residual sulfur contamination. With this reactive powder, transparent Sc2 O3 ceramics having an average grain size of ∼9 μm and showing a visible wavelength transmittance of ∼60–62% (∼76% of that of Sc2 O3 single crystal) have been fabricated via vacuum sintering at a relatively low temperature of 1700°C for 4 h. 相似文献
15.
Axel Nørlund Christensen Torben R. Jensen Nicola V. Y. Scarlett Ian C. Madsen Jonathan C. Hanson 《Journal of the American Ceramic Society》2004,87(8):1488-1493
The hydrolysis of pure and sodium-substituted calcium aluminates and cement clinker phases was investigated in situ in the temperature range 25°–170°C, using the angle dispersive powder synchrotron powder X-ray diffraction technique. The final hydrolysis product in all cases was Ca3 Al2 (OH)12 . The intermediate phase Ca4 Al2 O7 ·19H2 O was formed from the pure calcium aluminates, and the intermediate phases Ca4 Al2 O7 · x H2 O, x = 11, 13, or 19, were formed from the cement clinker phases. 相似文献
16.
Nanosized ZnO particles are successfully synthesized via mechanical activation of a zinc nitrate hydroxide hydrate (Zn5 (NO3 )2 (OH)8 ·2H2 O) precursor in NaCl matrix for 15 h. The ZnO particles obtained are in the nanosize range of ∼20 nm, with a well-established hexagonal morphology. They compare favorably with those derived from conventional calcination of the precursor. The decomposition of Zn5 (NO3 )2 (OH)8 ·2H2 O precursor and formation of nanocrystalline ZnO cannot be completed by mechanical activation in the absence of NaCl, which acts as both an effective dispersing matrix and drying agent although it remains chemically inert during mechanical activation. The powder derived from calcination at 400°C does not possess powder characteristics comparable to that of the powder derived from the mechanical activation in NaCl, because of the extensive particle coarsening and aggregation at the calcination temperature. 相似文献
17.
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
18.
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
19.
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
20.
Kazuhiko Kandori Naoto Horigami Akemi Yasukawa Tatsuo Ishikawa 《Journal of the American Ceramic Society》1997,80(5):1157-1164
The texture of fibrous calcium hydroxyapatite (Ca10 -(PO4 )6 (OH)2 , CaHAP) particles that were prepared by the decomposition of calcium–ethylenediaminetetraacetic acid (calcium–EDTA) chelates at 100°C under various pH conditions (pH values of 5–10) was investigated by various means. Well-crystallized fibrous CaHAPs were produced at pH .6. The stoichiometry of the CaHAPs with a chemical formula of Ca10− x (HPO4 ) x (PO4 )6− x (OH)2− x (H2 O) x was improved by increasing the decomposition pH. All the CaHAPs had unit-cell dimensions of a = 0.9436 ± 0.0003 nm and c = 0.6881 ± 0.0006 nm, exhibiting an enlarged a value. The finding of mesoporosity of CaHAPs by nitrogen gas (N2 ) adsorption measurement indicated that the CaHAPs were produced by an agglomeration of primary particles. Furthermore, the nonstoichiometric CaHAPs that formed at pH 6 developed ultramicropores, which were accessible to water (H2 O) molecules but not to N2 molecules, by the elimination of H2 O molecules that were adsorbed in interstices of primary particles in less-orderly crystallized CaHAPs and/or by dehydration of HPO4 2− groups. These findings by gas adsorption techniques could give evidence for the agglomeration mechanism to attain a polycrystalline CaHAP, although they exhibited good crystallinity with large size. 相似文献