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1.
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
2.
Ji-Guang Li Takayasu Ikegami Toshiyuki Mori Yoshiyuki Yajima 《Journal of the American Ceramic Society》2004,87(6):1008-1013
Hydroxyl-type Sc2 O3 precursors have been synthesized via precipitation at 80°C with hexamethylenetetramine as the precipitant. The effects of starting salts (scandium nitrate and sulfate) on powder properties are investigated. Characterizations of the powders are achieved by elemental analysis, X-ray diffractometry (XRD), differential thermal analysis/thermogravimetry (DTA/TG), high-resolution scanning electron microscopy (HRSEM), and Brunauer-Emmett-Teller (BET) analysis. Hard-aggregated precursors (γ-ScOOH·0.6H2 O) are formed with scandium nitrate, which convert to Sc2 O3 at temperatures ≥400°C, yielding nanocrystalline oxides of low surface area. The use of sulfate leads to a loosely agglomerated basic sulfate powder having an approximate composition of Sc(OH)2.6 (SO4 )0.2 ·H2 O. The powder transforms to Sc2 O3 via dehydroxylization and desulfurization at temperatures up to 1000°C. Well-dispersed Sc2 O3 nanopowders (∼64.3 nm) of high purity have been obtained by calcining the basic sulfate at 1000°C for 4 h. The effects of SO4 2− on powder properties are discussed. 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.
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
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.
Stephen Kwan Judith LaRosa Michael W. Grutzeck 《Journal of the American Ceramic Society》1995,78(7):1921-1926
Strätlingite (2CaO·Al2 O3 ·SiO2 ·8H2 O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag-containing cements or other cements enriched in alumina. Strätlingite can coexist with the hydrogarnet solid solution [hydrogarnet (3CaO·Al2 O3 ·6H2 O)-katoite (3CaO·Al2 O3 ·SiO2 ·4H2 O)] and calcium silicate hydrate (C-S-H). Since Strätlingite is present in many blended cements, the knowledge of strätlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important. Phase pure Strätlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using 29 Si, with and without cross-polarization (CP), and 27 Al solid-state magic angle nuclear magnetic resonance spectroscopy (MASNMR). For the most part, NMR data for these strätlingites corroborate structural information available in the literature. The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q2 , Q2 (1Al), and Q2 (2Al) species. The presence of alkali affects the structure of strätlingite in subtle ways, significantly reducing the AlIV /A1VI ratio. 相似文献
7.
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
8.
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
9.
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
10.
The morphological changes accompanying the conversion of the hexagonal CaO·Al2 O3 ·10H2 O phase to the cubic 3CaO·Al2 O3 ·6H2 O phase were studied by scanning electron microscopy. The hydration and conversion reactions were monitored by X-ray diffraction analysis. From the micrographs, it was inferred that changes in the pore structure and the presence of large cubic crystals of questionable adhesive value were probably the principal factors responsible for the loss of strength in converted calcium aluminate cement pastes. 相似文献
11.
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
12.
Kinetics of the Early Hydration of Tricalcium Aluminate in Solutions Containing Calcium Sulfate 总被引:1,自引:0,他引:1
PAUL WENCIL BROWN LAWRENCE O. LIBERMAN GEOFFREY FROHNSDORFF 《Journal of the American Ceramic Society》1984,67(12):793-795
The rates of reaction of 3CaO. Al2 O3 , in sulfate-containing solutions of three compositions were investigated. It was observed that the rates of calcium and sulfate uptake decreased with increasing calcium hydroxide concentration. In a further experiment using a calcium sulfate solution, which also contained NaOH, it was established that the kinetics of calcium sulfoaluminate hydrate formation are strongly dependent on the hydroxyl ion concentration. The rate of sulfate ion consumption per unit surface area of 3CaO·Al2 O3 was observed to be constant during the period in which a calcium sulfoaluminate hydrate is a reaction product. The ratio of calcium-to-sulfate ions consumed in the hydration reactions investigated exceeded unity suggesting the formation of 4CaO·Al2 O3 · n H2 O in addition to ettringite. 相似文献
13.
The formation of ettringite (3CaO·Al2 O3 ·3CaSO4 ·32H2 O) from monosulfate (3CaO·Al2 O3 ·CaSO4 ·12H2 O) and gypsum (CaSO4 ·2H2 O) was investigated by isothermal calorimetry and X-ray diffraction (XRD) analyses. Hydration was carried out at constant temperatures from 30° to 80°C using deionized water and 0.2 M , 0.5 M , and 1.0 M sodium hydroxide (NaOH) solutions. Ettringite was found to be the dominant crystalline phase over the entire temperature range and at all sodium hydroxide concentrations. A sodium-substituted monosulfate phase was formed as a hydration product in the 1.0 M sodium hydroxide solution regardless of temperature. XRD and calorimetry demonstrate that hydration in increasing sodium hydroxide concentrations decreases the amount of ettringite formed and retards the rate of reaction. The apparent activation energy for the conversion of the monosulfate/gypsum mixture to ettringite was observed to vary depending on the sodium hydroxide concentration. Ettringite formation was observed to depend upon the concentration of calcium in solution; thus the formation of calcium hydroxide and sodium-substituted monosulfate phase competes with ettringite formation. 相似文献
14.
Zhong Zhuang Xian Ping Wang Dan Li Tao Zhang Qian Feng Fang 《Journal of the American Ceramic Society》2009,92(4):839-844
Dense, crack-free, and uniform La2 Mo2− x W x O9 ( x =0, 0.1, and 0.2) nanocrystalline films were successfully synthesized on poly-alumina substrates via a modified sol–gel method, with inorganic salt of La(NO3 )3 ·6H2 O, (NH4 )6 Mo7 O24 ·4H2 O, and (NH4 )6 H2 W12 O24 as precursors. Pure La2 Mo2 O9 phase was confirmed by X-ray diffractometer when the annealing temperature was >500°C. The average grain size of the La2 Mo2− x W x O9 films is in the range of 90–400 nm, depending upon the conditions of thermal treatment, and the thickness of films can reach 1 μm by repetitive spin-coating. The electrical conductivity increases with decreasing grain size and reaches 0.074 S/cm at 600°C in the film with a grain size of 90 nm, which is one order of magnitude higher than that in the corresponding bulk materials. W-doping can suppress the phase transition that occurs at 580°C in pure La2 Mo2 O9 and enhance the low-temperature ionic conductivity. Furthermore, the activation energy of conductivity in the nanocrystalline La2 Mo2 O9 films decreases to about 0.6 eV in comparison with 1.0 eV in the bulk ones, which implies that the grain resistance prevails in the total resistance, when grain size reduces to nanometer domain. 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.
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
17.
The phase diagram for the ternary system MgO─P2 O5 ─H2 O at 25°C has been constructed. The magnesium phosphates represented are Mg(H2 PO4 )2 · n H2 O ( n = 4, 2, 0), MgHPO4 ·3H2 O, and Mg3 (PO4 )2 · m H2 O ( m = 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P2 O5 as their 10th roots has been employed. With the exception of MgHPO4 ·3H2 O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic-like reaction, the phase Mg2 (PO4 )3 · 8H2 O persists metastably for an extended period. 相似文献
18.
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
19.
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
20.
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