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1.
Hyo Seok Lee Jai Joon Lee Tae Sun Chang Jeong Wook Kim Sang Man Koo 《Journal of the American Ceramic Society》2007,90(9):2995-2997
Monodisperse and spherical barium titanate (BaTiO3 ) powders with diameters of 200–470 nm were directly prepared by a low-temperature hydrothermal method at 90°C. Spherical titania (TiO2 ) powders, ranging in size from 150 to 420 nm, were initially prepared by a controlled hydrolysis and condensation reaction, aged in a highly alkaline solution for 12 h, and then hydrothermally reacted with barium hydroxide to be converted to BaTiO3 without a morphological change. The aging step of the TiO2 , where the surface of TiO2 was highly densified through elimination of the pores, was indispensable to retain the sizes and shapes of TiO2 in the resulting BaTiO3 . This was due to the fact that the formation of BaTiO3 proceeded by an in situ reaction mechanism. The resulting BaTiO3 powders exhibited dense and nonporous structures even after calcination at 1000°C. 相似文献
2.
Fabrication of Millimeter-Wave Electromagnetic Bandgap Crystals Using Microwave Dielectric Powders 总被引:1,自引:0,他引:1
Xuesong Lu Yoonjae Lee Shoufeng Yang Yang Hao Rick Ubic Julian R. G. Evans Clive G. Parini 《Journal of the American Ceramic Society》2009,92(2):371-378
Electromagnetic bandgap (EBG) structures active in the 90–110 GHz region widely used by security imaging radar were created using different ceramics by a rapid prototyping method informed by finite difference time domain modeling. This solid free-forming method uses a high volatility solvent-based ceramic paste extruded through fine nozzles allowing ceramic powders to be assembled on a multiaxis building platform avoiding machining, etching, or the alignment of loose rods and created to designs downloaded directly from a computer file. Lattices were made from two high dielectric constant ceramics: La(Mg0.5 , Ti0.5 )O3 and (Zr0.8 , Sn0.2 )TiO4 and compared with those of Al2 O3 demonstrating three EBG structures with different dimensions and dielectric constants but with the same bandgap. The effects of manufacturing tolerances on bandgap frequency are investigated by simulation. 相似文献
3.
Interstitial titanium-chromium oxynitrides in the solid solution series Ti1− z Cr z (O x N y ) ( z = 0.2, 0.4, 0.5, 0.6, 0.8) have been obtained by ammonolysis of the TiO2 /Cr2 O3 precursors resulting from the coprecipitation method. The precursors and the resulting oxynitrides were characterized by auger electron spectroscopy, X-ray diffraction analysis, electron probe microanalysis, transmission electron microscopy, and BET surface area techniques. Compounds in the Ti1− z Cr z (O x N y ) series are prepared as single phases by nitridation at 1073 K for 8 h. The as-synthesized oxynitride powders contain only Ti1− z Cr z (O x N y ) with cubic structure and the particle size is in the nanometer scale. 相似文献
4.
Formation of the Pb(Zr,Ti)O3 solid solution in the system PbO-TiO2 -ZrO2 was studied by chemical analysis and X-ray powder diffrac-tometry. Only PbTiO3 and Pb(Zr,Ti)O3 were found as reaction products. The following three elementary reactions seemed to be reasonable for the formation of the Pb(Zr,Ti)O3 phase: PbO + TiO2 → PbTiO3 , PbTiO3 + PbO + ZrO2 →Pb(Zr1-λ Tiλ )O3 , and Pb(Zrl-λ Tiλ )O3 + PbTiO3 → Pb(Zr1-λ' Tiλ' )O3 (λ<λ'). 相似文献
5.
Masanori Hirano Keisuke Ota Takaharu Ito 《Journal of the American Ceramic Society》2005,88(12):3303-3310
Anatase-type TiO2 powder containing sulfur with absorption in the visible region was directly formed as particles with crystallite in the range 15–88 nm by thermal hydrolysis of titanium(III) sulfate (Ti2 (SO4 )3 ) solution at 100°–240°C. Because of the presence of ammonium peroxodisulfate ((NH4 )2 S2 O8 ), the yield of anatase-type TiO2 from Ti2 (SO4 )3 solution was accelerated, and anatase with fine crystallite was formed. Anatase-type TiO2 doped with ZrO2 up to 9.8 mol% was directly precipitated as nanometer-sized particles from the acidic precursor solutions of Ti2 (SO4 )3 and zirconium sulfate in the presence and the absence of (NH4 )2 S2 O8 by simultaneous hydrolysis under hydrothermal conditions at 200°C. By doping ZrO2 into TiO2 and with increasing ZrO2 content, the crystallite size of anatase was decreased, and the anatase-to-rutile phase transformation was retarded as much as 200°C. The anatase-type structure of ZrO2 -doped TiO2 was maintained after heating at 1000°C for 1 h. The favorable effect of doping ZrO2 to anatase-type TiO2 on the photocatalytic activity was observed. 相似文献
6.
Conventionally Prepared Submicrometer Lead-Based Perovskite Powders by Reactive Calcination 总被引:6,自引:0,他引:6
Thomas R. Shrout Philippe Papet Sunuk Kim Gye-Song Lee † 《Journal of the American Ceramic Society》1990,73(7):1862-1867
Submicrometer powders of various Pb-based perovskites, including PbTiO3 , PbZrO3 , Pb(Zr0.53 Ti0.47 )O3 , and Pb(Mg1/3 Nb2/3 )O3 were prepared by a reactive calcination process. Using only reagent-grade raw materials and conventional processing techniques, highly reactive powders were produced by reacting the materials near the temperature of maximum volumetric expansion. At this point, the morphological development results in a skeletal-type structure consisting of ultrafine particulates that can be readily broken down further by milling. Powder sizes less than 0.3 μm and as small as 70 nm generally only achievable using chemical processing techniques were achieved. The highly reactive powders allowed densification to occur at temperatures as low as ∼900°C with correspondingly small grain sizes. A model describing the physiochemical behavior and associated morphological development of Pb-based perovskites was herein proposed. 相似文献
7.
Andreja Gajovi Kreimir Furi Svetozar Musi Igor Djerdj Antun Tonejc Anelka M. Tonejc Dangsheng Su Robert Schlögl 《Journal of the American Ceramic Society》2006,89(7):2196-2205
High-energy ball milling initiates a solid-state reaction in an equimolar mixture of TiO2 and ZrO2 . The first stage of ball milling induced the transformation of anatase TiO2 to high-pressure phase TiO2 (II), isostructural with ZrTiO4 . The formation of solid solutions monoclinic ZrO2 /TiO2 and TiO2 (II)/ZrO2 was observed in the intermediate stage. Afterward, a nanosized ZrTiO4 phase was formed in the milled product from the TiO2 (II)/ZrO2 solid solution. The sintering of the milled product at a temperature <1100°C was examined in situ by Raman spectroscopy. The full solid-state reaction toward ZrTiO4 ceramic is completed at a temperature considerably lower than reported in the literature. 相似文献
8.
Hyunjung Shin Monika Agarwal Mark R. De Guire Arthur H. Heuer 《Journal of the American Ceramic Society》1996,79(7):1975-1978
Thin films of crystalline TiO2 were deposited on self-assembled organic monolayers from aqueous TiCl4 solutions at 80°C; partially crystalline ZrO2 films were deposited on top of the TiO2 layers from Zr(SO4 )2 solutions at 70°C. In the absence of a ZrO2 film, the TiO2 films had the anatase structure and underwent grain coarsening on annealing at temperatures up to 800°C; in the absence of a TiO2 film, the ZrO2 films crystallized to the tetragonal polymorph at 500°C. However, the TiO2 and ZrO2 bilayers underwent solid-state diffusive amorphization at 500°C, and ZrTiO4 crystallization could be observed only at temperatures of 550°C or higher. This result implies that metastable amorphous ZrTiO4 is energetically favorable compared to two-phase mixtures of crystalline TiO2 and ZrO2 , but that crystallization of ZrTiO4 involves a high activation barrier. 相似文献
9.
Detlev F. K. Hennings B. Seriyati Schreinemacher Herbert Schreinemacher 《Journal of the American Ceramic Society》2001,84(12):2777-2782
BaTiO3 and Ba(Ti,Zr)O3 dielectric powders have been prepared from submicrometer BaCO3 , TiO2 , and ZrO2 . By use of submicrometer BaCO3 the intermediate formation of Ba2 TiO4 second phase can be widely suppressed. Monophase perovskites of BaTiO3 were already formed at 900°C and Ba(Ti,Zr)O3 at 1050°C. Aggregates of very small subgrains could be easily disintegrated to particle sizes <0.5 μm. 相似文献
10.
Jai Joon Lee Kum Jin Park Kang Heon Hur Sung Chul Yi Sang Man Koo 《Journal of the American Ceramic Society》2006,89(10):3299-3301
A novel synthetic method for the preparation of spherical, homogeneous, and ultrafine barium titanate (BaTiO3 ) powders is described. An aqueous titania nano-sol was prepared by peptizing coarse aggregate of hydrous titania with nitric acid. BaTiO3 powders could be synthesized through a simple reflux method using the titania nano-sol and barium hydroxide. As decreasing the titanium concentration, the particle size of the resulting spherical BaTiO3 powder was increased from 40 to 130 nm and the porosity also increased. It was revealed that the smaller as-prepared BaTiO3 powder was less porous and became more tetragonal with less intragranular pores after annealing. With this method, a highly tetragonal BaTiO3 powder ( c / a ∼1.008) with a particle size of 120.0 nm was successfully prepared and would be very suitable for the thinner dielectrics in higher capacitance multilayer ceramic capacitors. 相似文献
11.
Formation of Zirconia Titanate Solid Solution from Alkoxides 总被引:2,自引:0,他引:2
In the system ZrO2 –TiO2 , ZrTiO4 solid solutions prepared by the simultaneous hydrolysis of zirconium and titanium alkoxides crystallize at low temperatures from amorphous materials between 30 and 70 mol% TiO2 . As zirconium is substituted for titanium, the solid solutions can be indexed in an orthorhombic unit cell with a and c decreasing linearly from 0.4832 to 0.4778 nm and from 0.5063 to 0.5002 nm, respectively, and b increasing linearly from 0.5401 to 0.5478 nm. The volume of the unit cell decreases continuously with increasing TiO2 content. At higher temperatures the solid solutions decompose into ZrTiO4 and either ZrO2 (monoclinic) or TiO2 (rutile), depeanding on the starting composition. 相似文献
12.
Chemical Preparation of Lead-Containing Niobate Powders 总被引:2,自引:0,他引:2
A chemical precipitation method was developed for synthesis of typical relaxor compounds—Pb(Mg1/3 Nb2/3 )O3 (PMN), Pb(Fe1/2 Nb1/2 )O3 (PFN), and Pb(Sc1/2 Nb1/2 )O3 (PSN)—from nitrate solutions. To obtain a niobium precursor compatible with the aqueous chemical routes, peroxo-niobium complex solutions were prepared by dissolving hydrated niobia precipitates in a dilute nitric acid solution with hydrogen peroxide. Powders that consisted of small particles ranging from 20 to 40 nm were successfully precipitated from the mixed nitrate solutions by hydrolysis with aqueous ammonia solutions. On calcination, these powders were highly reactive. For example, PMN precursor powder began to crystallize simultaneously to cubic pyrochlore and perovskite phases at ∼400°C and yielded ∼95% of the perovskite phase after calcination at 800°C for 1 h. PFN and PSN precursor powders calcined under similar conditions formed single perovskite phases. 相似文献
13.
Grain-oriented Bi0.5 (Na0.85 K0.15 )0.5 TiO3 -Pb(Zr1− x Ti x )O3 (BNKT-PZT) ceramics were prepared via the reactive templated grain growth method, using platelike Bi4 Ti3 O12 particles. Factors that determine the degree of orientation were examined. Prereacted PZT gave a larger degree of orientation than PZT raw materials (PbO, ZrO2 , and TiO2 ) in the 75BNKT-25PZT ( x = 0.5) system. Increases in the titanium concentration in the PZT of the 75BNKT-25PZT system and in the BNKT concentration in the y BNKT-(100 − y )PZT ( x = 0.5) system increased the degree of orientation. The direction of material transport between BNKT and PZT was important to obtain ceramics with a large degree of orientation. 相似文献
14.
Kazushige Kohno Yasuo Takeda Nobuyuki Imanishi Yoshinori Sakaki Katsuyuki Sakamoto Osamu Yamamoto 《Journal of the American Ceramic Society》1993,76(1):192-196
Pt–ceramaic (TiO2 , ZrO2 , and ZrO2 –5 mol% Y2 O3 (PSZ)) composite powders were prepared by liquid-phase reaction. These composite powders show highly functional properties such as the following. The sintered films of these powders are good metallic conductors. The resistivity of the Pt–PSZ film at room temperature is about 1.5 × 10−5 Ω·cm, which is almost comparable to that of pure platinum (1.05 × 10−5 Ω·cm). This film shows excellent cathodic oxygen reduction. The overpotential for the oxygen reduction at 750°C is less than 20 mV even at a high current density of 0.1 A/cm2 . The Pt–TiO2 composite powders have highly catalytic activity for the reduction of NO gas. 相似文献
15.
Reaction Sequence in the Formation of Lead Zirconate-Lead Titanate Solid Solution: Role of Raw Materials 总被引:1,自引:0,他引:1
B. V. HIREMATH ANGUS I. KINGON† JAMES V. BIGGERS 《Journal of the American Ceramic Society》1983,66(11):790-793
The reaction sequence in the formation of Pb(Zr0.6 Ti0.4 )O3 (PZT 60/40) was investigated as a function of PbO and ZrO2 raw material variations, using powder X-ray diffraction. Particular emphasis was placed on the final stages of reaction in the formation of PZT solid solution. Based on the present work, a more detailed reaction sequence is being proposed for Pb(Zr0.6 Ti0.4 )O3 and similar compositions. This reaction sequence is believed to account for many of the apparent discrepancies which have appeared in the literature. 相似文献
16.
Shuichi Arakawa Kenji Mogi Ko-ichi Kikuta Toshinobu Yogo Shin-ichi Hirano Yoji Seki Mitsutoshi Kawamoto 《Journal of the American Ceramic Society》1997,80(11):2864-2668
Oriented (Ti,Sn)O2 thin films with modulated microstructure were successfully synthesized on sapphire substrates by using sol–gel processing combined with spinodal decomposition. The degree of orientation of (Ti0.5 Sn0.5 )O2 thin films increased in the following order: sapphire (0001), (11 0), and (01 2). (Ti0.5 Sn0.5 )O2 thin films underwent spinodal decomposition at 900°C by annealing. The variation of the 2theta value of the 202 reflection of (Ti0.5 Sn0.5 )O2 films showed the typical behavior of spinodal decomposition. The rate of spinodal decomposition of the (Ti0.5 Sn0.5 )O2 films on sapphire (11 0) was faster than that on sapphire (01 2) substrates. The characteristic modulated microstructure was observed for the spinodally decomposed (Ti0.5 Sn0.5 )O2 films on sapphire (01 2) substrates by transmission electron microscopy. (Ti0.3 Sn0.7 )O2 films on sapphire (01 2) substrates were binodally decomposed during annealing at 1300°C. 相似文献
17.
L. M. Peng 《Journal of the American Ceramic Society》2007,90(4):1312-1314
A layered ternary carbide phase, Ti3 AlC2 , was synthesized by hot pressing from the starting materials of Ti, aluminum, and activated carbon at 1400°C for 2 h. Its composites were also fabricated through addition of micro-sized SiC and partially stabilized zirconia particulates to the pulverized Ti3 AlC2 powders. The polycrystalline Ti3 AlC2 ceramic obtained has a flexural strength of 172 MPa and a fracture toughness of 4.6 MPa·m1/2 , respectively. This compound is relatively soft (Vikers hardness of 2.7 GPa) and exhibits good electrical conductivity with an electrical resistivity of 8.2 μΩ·m. Both the Ti3 AlC2 /SiC and Ti3 AlC2 /ZrO2 composites are superior to the monolithic Ti3 AlC2 ceramic in strength, fracture toughness, and micro-hardness. 相似文献
18.
New titanium–niobium oxynitride (Ti1− z Nb z O x N y ) powders were synthesized by ammonolysis of nanosized TiO2 /Nb2 O5 composite powders at 700°–900°C for 5 h. The products were characterized by X-ray diffraction (XRD), chemical analysis, and transmission electron microscopy. The results indicated that the as-synthesized powders were pure cubic structures with sizes of 30–60 nm. With increasing value of z , XRD peaks of Ti1− z Nb z O x N y powders tended to shift toward low 2θ angle and the cell parameter showed a linear increase. 相似文献
19.
Jae Young Choi Young Tae Moon Do Kyung Kim Chong Hee Kim In-Sig Seog 《Journal of the American Ceramic Society》1998,81(9):2294-2300
Monodisperse, spherical Si3 N4 powder composed of fine particulates was synthesized by pyrolyzing spherical organo-silica powder under nitrogen. The organo-silica powder was prepared by hydrolyzing a mixture of phenyltrimethoxysilane (PTMS) and tetraethoxysilane (TEOS) in a methanol solution of water and ammonia. The organo-silica powder consisted of 81.3 at.% silicon units derived from PTMS and 18.7 at.% silicon units derived from TEOS. During the pyrolysis under nitrogen, the organo-silica powder decomposed to a mixture of free carbon and silica, with an increase of the surface area, at 500°-600°C, followed by the formation of alpha-Si3 N4 , with ß-Si3 N4 as a minor phase, at 1450° and 1500°C and ß-SiC at 1550°C. The pyrolyzed powders, which retained the spherical shape and monodispersity of the organo-silica powders, with a reduction in mean particle diameter, were composed of fine particulates that were ~40 nm in size. 相似文献
20.
Takayuki Tsukada Sridhar Venigalla Augusto A. Morrone James H. Adair 《Journal of the American Ceramic Society》1999,82(5):1169-1174
The feasibility of low-temperature synthesis of yttrium-doped zirconia (Y-ZrO2 ) crystalline powders in aqueous solutions at lessthan equal to100°C has been evaluated, and the hydrothermal crystallization mechanism for Y-ZrO2 powders also has been investigated. Coprecipitated (Y,Zr) hydroxide gel, mechanical mixtures of Y(OH)3 and Zr(OH)4 gel, and Y(OH)3 gel have been reacted in boiling alkaline solutions. Coprecipitated (Y,Zr) hydroxide gel crystallized to cubic or tetragonal Y-ZrO2 at pH 13.9. The yttrium content in the powder synthesized from coprecipitated (Y,Zr) hydroxide is consistent with the initial precursor solution composition, as expected from the similarity in solubility of Zr(OH)- 5 and Y(OH)- 4 . A diffusionless mechanism for the transformation of the (Y,Zr) hydroxide gel to Y-ZrO2 is proposed, and the phase stability in aqueous solution is discussed in terms of an in situ crystallization model. It is also demonstrated through thermodynamic arguments with experimental verification that the stable form of the Y-ZrO2 at 25°C is the anhydrous phase, not the metal hydroxide as previously thought. 相似文献