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1.
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
2.
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
3.
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
4.
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
5.
Preparation of Ultra-Fine Nickel Manganite Powders and Ceramics by a Solid-State Coordination Reaction 总被引:2,自引:0,他引:2
Dao-lai Fang Zhong-bing Wang Ping-hua Yang Wei Liu Chu-sheng Chen A. J. A. Winnubst 《Journal of the American Ceramic Society》2006,89(1):230-235
A solid-state coordination reaction was adopted to prepare negative temperature coefficient ceramics. A mixed oxalate NiMn2 (C2 O4 )3 ·6H2 O, a coordination compound, was synthesized by milling a mixture of nickel acetate, manganese acetate, and oxalic acid for 5 h at room temperature. An ultrafine NiMn2 O4 powder was obtained by calcining the mixed oxalate in air at 850°C for 2 h. Ceramics with a relative density of more than 97% were achieved by sintering powder compacts at a temperature as low as 1050°C for 5 h. The specific electrical resistivity ρ25°C and the thermal constant B 25°/85°C were 2174 Ω·cm and 3884 K, respectively. The drift of the resistivity after aging at 150°C for 1000 h was 3.0%. 相似文献
6.
FRANK SCHREY 《Journal of the American Ceramic Society》1965,48(8):401-405
Lanthanum-doped Ba0.6 Sr0.4 4TiO (OH)2 C2 O4 .4H2 O was prepared by precipitation from a pH-controlled oxalic acid solution for conversion to the titanate. TGA and DTA support the proposed formula of a hydrated, mixed hydroxyoxalate. Density and resistivity measurements of the titanates are correlated as a function of lanthanum content. 相似文献
7.
Xia Wang Wei Li Jin-lou Gu Yong-sheng Li Liang Li Jian-lin Shi 《Journal of the American Ceramic Society》2009,92(10):2412-2414
Li2.06 Nb0.18 Ti0.76 O3 powder has been successfully prepared at low temperatures via a facile and manageable, activated pretreatment on the inert raw Nb2 O5 . It is demonstrated that with triethanolamine, citric acid, and hydrogen peroxide, this simple pretreatment process could activate Nb2 O5 efficiently. Pure Li2 TiO3 solid solution phase was thus obtained by calcining the mixture of the activated Nb2 O5 , LiOH·H2 O, and Ti(C4 H9 O)4 at temperatures as low as 650°C, which is about 200°C lower than that of the traditional solid-state method. To the best of our knowledge, this temperature is the lowest one for preparing Li2 TiO3 solid solution. Additionally, the phase transformation and the morphology of the final powder are also discussed. 相似文献
8.
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
9.
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
10.
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
11.
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
12.
Synthesis of Titanate Derivatives Using Ion-Exchange Reaction 总被引:3,自引:0,他引:3
Chul-Tae Lee Myeong-Heon Um Hidehiro Kumazawa 《Journal of the American Ceramic Society》2000,83(5):1098-1102
Two types of titanate derivatives, layered hydrous titanium dioxide (H2 Ti4 O9 · n H2 O) and potassium octatitanate (K2 Ti8 O17 ) with a tunnellike structure, were synthesized using an ion-exchange reaction. Fibrous potassium tetratitanate (K2 Ti4 O9 · n H2 O) was prepared by calcination of a mixture of K2 CO3 and TiO2 with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling-water treatment of the calcined products for 10 h. The material then was transformed to layered H2 Ti4 O9 · n H2 O through an exchange of K+ ions with H+ ions using HCl. K2 Ti8 O17 was formed by a thermal treatment of KHTi4 O9 · n H2 O. Pure KHTi4 O9 · n H2 O phase was effectively produced by a treatment of K2 Ti4 O9 with 0.005 M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K2 Ti8 O17 . 相似文献
13.
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
14.
Kunio Saegusa Wendell E. Rhine H. Kent Bowen 《Journal of the American Ceramic Society》1993,76(6):1505-1512
Lead titanate, barium titanate, and lead barium titanate powders (>99.9% pure), the particle size of which varied from 0.03 to 0.15 μm depending on the calcination temperature and the composition, was prepared from barium lead titanyl oxalate, which was previously prepared by reacting high-purity ammonium titanyl oxalate with barium and lead acetate. The critical crystallite size of BaTiO3 powder from the cubic to the tetragonal phase is around 1 μm. Pb0.3 Ba0.7 TiO3 powder with an average size of 0.057 μm showed the tetragonal phase. 相似文献
15.
Do-Kyun Kwon Teppei Akiyoshi Hyeongjae Lee Michael T. Lanagan 《Journal of the American Ceramic Society》2008,91(3):906-909
Manganese dioxide (α-MnO2 ) thin films have been explored as a cathode material for reliable glass capacitors. Conducting α-MnO2 thin films were deposited on a borosilicate glass substrate by a chemical solution deposition technique. High carbon activities originated from manganese acetate precursor, (Mn(C2 H3 O2 )2 ·4H2 O) and acetic acid solvent (C2 H4 O2 ), which substantially reduced MnO2 phase stability, and resulted in Mn2 O3 formation at pyrolysis temperature in air. The α-MnO2 structure was stabilized by Ba2+ insertion into a (2 × 2) oxygen tunnel frame to form a hollandite structure. With 15–20 mol% Ba addition, a conducting α-MnO2 thin film was obtained after annealing at 600–650°C, exhibiting low electrical resistivity (∼1 Ω·cm), which enables application as a cathode material for capacitors. The hollandite α-MnO2 phase was stable at 850°C, and thermally reduced to the insulating bixbyte (Mn2 O3 ) phase after annealing at 900°C. The phase transition temperature of Ba containing α-MnO2 was substantially higher than the reported transition temperature for pure MnO2 (∼500°C). 相似文献
16.
Toshifumi Sugama Marita Allan Janet M. Hill 《Journal of the American Ceramic Society》1992,75(8):2076-2087
We investigated the characteristics of calcium phosphate cements (CPC) prepared by an exothermic acid–base reaction between NH4 H2 PO4 -based fertilizer (Poly-N) and calcium aluminate compounds (CAC), such as 3CaO · Al2 O3 (C3 A), CaO · Al2 O3 (CA), and CaO · 2Al2 O3 (CA2 ), in a series of integrated studies of reaction kinetics, interfacial reactions, in-situ phase transformations, and microstructure development. Two groups were compared: untreated and hydrothermally treated CPC specimens. The extent of reactivity of CAC with Poly-N at 25°C was in the following order: CA > C3 A ≫ CA2 . The formation of a NH4 CaPO4 · x H2 O salt during this reaction was responsible for the development of strength in the CPC specimens. The in-situ phase transformation of amorphous NH4 CaPO4 · x H2 O into crystalline Ca5 (PO4 )3 (OH) and the conversion of hydrous Al2 O3 gel →γ-AIOOH occur in cement bodies during exposure in an autoclave to temperatures up to 300°C. This phase transformation significantly improved mechanical strength. 相似文献
17.
Toshiaki Yamaguchi Wataru Sakamoto Toshinobu Yogo Shin-ichi Hirano 《Journal of the American Ceramic Society》2002,85(4):909-914
The effects of the substitution of transition-metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition-metal-substituted hexaaluminogallates (BaM(Al,Ga)11 O19 , M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NO x reduction was observed over BaM(Al,Ga)11 O19 to be around 10%. The NO x removal activity of BaM(Al,Ga)11 O19 powders was improved by addition of C3 H6 as a reductant gas. Co-, Ni- and Cu-substituted BaM(Al,Ga)11 O19 catalysts exhibited about 40% NO x reduction with C3 H6 in excess oxygen at a high space velocity of 10 000 h−1 . The NO x reduction on Mn- and Fe-substituted BaM(Al,Ga)11 O19 catalysts was less than 10% even in the presence of C3 H6 . The temperature of the effective NO x reduction on BaM(Al,Ga)11 O19 catalysts could be adjusted from 350° to 500°C by the selection of the transition-metal substitution in the catalysts. The catalysts hold high activities for NO x reduction even at 500°C in water vapor produced in the combustion system of reductant gases. 相似文献
18.
The precursor [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O is known to react with Ba(OH)2 · 8H2 O in an acid/base process that generates Ba[Ti(catecholate)3 ] · 3H2 O, a compound which undergoes low-temperatue calcination to produce BaTiO3 powder. Attempts to develop similar routes to PbTiO3 have been frustrated, since lead(II) hydroxide does not exist. The amphoteric yellow PbO and the basic oxide, Pb6 O(OH)6 4+ , are both insufficiently basic to react with [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O. Based on the large sizes of both the [Ti(catecholate)3 ]2- anion and the Pb2+ cation, a precipitation method has been developed in which lead nitrate and [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O are added together in an aqueous medium causing precipitation and leaving only NH4 NO3 in solution. The lead-titanium-catecholate complex that forms in this manner undergoes low-temperature pyrolysis to produce PbTiO3 . SEM indicates a submicrometer ultimate crystallite size. 相似文献
19.
Byoung-Kyu Kim Dae-Young Lim Richard E. Riman Jun-Seok Nho Seung-Beom Cho 《Journal of the American Ceramic Society》2003,86(10):1793-1796
Barium titanate (BaTiO3 ) nanoparticles were synthesized at the low temperature of 80°C through a glycothermal reaction using Ba(OH)2 ·8H2 O and amorphous titanium hydrous gel as precursors and a solution of 1,4-butanediol and water as solvent. This processing method provides a simple low-temperature route for producing BaTiO3 nanoparticles, which could also be extended to other systems. It is demonstrated that the size of BaTiO3 particles can be controlled by reaction conditions, such as reaction temperature and various volume ratios of 1,4-butanediol/water. 相似文献
20.
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