共查询到20条相似文献,搜索用时 31 毫秒
1.
Keith G. Brooks Yolande Berta Vasantha R. W. Amarakoon 《Journal of the American Ceramic Society》1992,75(11):3065-3069
Preventing the incorporation of impurities in Li-Zn ferrite grains during sintering is essential for production of ceramics with reproducible magnetic and electrical properties. Li-Zn ferrites of composition Li0.3 Zn0.4 Mn0.05 Fe2.25 O4 were prepared with Bi2 O3 and borosilicate sintering additives. The distribution of impurity ions in the sintered ferrites was investigated using transmission electron microscopy (TEM) coupled with energy dispersive spectroscopy (EDS). Ceramics prepared with Bi2 O3 contained Si, Ca, and S impurities, located at grain boundaries and triple point regions. The low viscosity and good wetting properties of the Bi2 O3 and to a lesser extent the borosilicate liquid phase allowed impurities to be selectively removed from the growing ferrite phase during sintering, thus improving sample resistivities. 相似文献
2.
Sea-Fue Wang Chiang-Chuang Chung Chai-Hui Wang Jinn P. Chu 《Journal of the American Ceramic Society》2002,85(6):1619-1621
Preparation of dense and phase-pure Ba2 Ti9 O20 is generally difficult using solid-state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba2 Ti9 O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. In this study, the effects of B2 O3 on the densification, microstructural evolution, and phase stability of Ba2 Ti9 O20 were investigated. It was found that the densification of Ba2 Ti9 O20 sintered with B2 O3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid-state sintering became dominant because of the evaporation of B2 O3 . With the addition of 5 wt% B2 O3 , the ceramic yielded a pure Ba2 Ti9 O20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO2 or ZrO2 . The facilities of B2 O3 addition to the stability of Ba2 Ti9 O20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species. 相似文献
3.
Mark I. Jones Maria-Cecilia Valecillos Kiyoshi Hirao Motohiro Toriyama 《Journal of the American Ceramic Society》2001,84(10):2424-2426
Si3 N4 powders were sintered using a 28 GHz gyrotron source, with Y2 O3 , Al2 O3 , and MgO as sintering aids, in an attempt to investigate the effect of microwave radiation on densification behavior. The microwave-sintered samples were compared with identical samples produced by conventional pressureless sintering. The effect of sintering on the microstructural development and grain growth of the samples was assessed using scanning electron microscopy. Phase transformation behavior was assessed using X-ray diffractometry. In the microwave-sintered samples, densification and α→β transformation occurred at temperatures ∼200°C lower than those of the conventionally sintered samples. More importantly, at comparable stages of densification, the microstructures of the microwave-sintered and conventionally sintered samples were significantly different, with the microwave-sintered samples showing the development of elongated β grains at a much earlier stage of the α→β transformation. It was concluded that the effect of microwave radiation on sintering was not simply a decrease in sintering temperatures, but in possibly a different sintering mechanism, clearly related to localized heating within the grain-boundary phase. 相似文献
4.
Edelio Bermejo Thierry le Mercier Michel Quarton 《Journal of the American Ceramic Society》1995,78(2):365-368
The effects of sintering temperature above 1000°C and of cooling rate on the microstructual development of pure and Zn-substituted spinel lithium ferrites are discussed. The strong dependence of microstructural features on cooling rate can be explained on the basis of the precipitation of α-Fe2 O3 or the formation of a solid solution of ferrite phase with Fe3 O4 occurring during sintering above 1000°C. These two phenomena are studied by detailed characterization analyses: SEM, XRD, magnetization, and ac electrical resistivity measurements. 相似文献
5.
Jin-Seong Kim Ngoc-Huan Nguyen Jong-Bong Lim Dong-Soo Paik Sahn Nahm Jong-Hoo Paik Jong-Hee Kim Hwack-Joo Lee 《Journal of the American Ceramic Society》2008,91(2):671-674
B2 O3 was added to nominal composition Zn1.8 SiO3.8 (ZS) ceramics to decrease their sintering temperature for application to low-temperature cofired ceramic (LTCC) devices. B2 O3 reacted with SiO2 to form a liquid phase containing SiO2 and B2 O3 . The composition and melting temperature of the liquid phase depended on the sintering temperature and the B2 O3 content. The specimen containing 20.0 mol% of B2 O3 sintered at 900°C exhibited high microwave dielectric properties of Q × f =53 000 GHz, ɛ r =5.7, and τf =−16 ppm/°C, confirming the promising potential of the B2 O3 -added ZS ceramics as candidate materials for the LTCC devices. 相似文献
6.
Jin-Seong Kim Ngoc-Huan Nguyen Myung-Eun Song Jong-Bong Lim Dong-Soo Paik Sahn Nahm Jong-Hoo Paik Byung-Hyun Choi Soon-Jae Yu 《International Journal of Applied Ceramic Technology》2009,6(5):581-586
Bi2 O3 was added to a nominal composition of Zn1.8 SiO3.8 (ZS) ceramics to decrease their sintering temperature. When the Bi2 O3 content was <8.0 mol%, a porous microstructure with Bi4 (SiO4 )3 and SiO2 second phases was developed in the specimen sintered at 885°C. However, when the Bi2 O3 content exceeded 8.0 mol%, a liquid phase, which formed during sintering at temperatures below 900°C, assisted the densification of the ZS ceramics. Good microwave dielectric properties of Q × f =12,600 GHz, ɛr =7.6, and τf =−22 ppm/°C were obtained from the specimen with 8.0 mol% Bi2 O3 sintered at 885°C for 2 h. 相似文献
7.
Two compositions of the Y2 O3 –MgO (YM) and Yb2 O3 –MgO (YbM) systems were chosen to study the effect of the sintering additive composition on the processing and thermal conductivity of sintered reaction-bonded silicon nitride (SRBSN). The nitridation, postdensification, microstructural evolution, and thermal conductivity of SRBSN were found to depend strongly on the sintering additive composition. The RBSN materials with YbM exhibited a poor sinterability, whereas those with YM exhibited an excellent sinterability. However, the SRBSN materials with YbM showed a higher thermal conductivity than those with YM. This was associated primarily with the isolated distribution and lower amount of secondary phase and the higher percentage of large grains in the former materials. 相似文献
8.
Synthesis of BaCu(B2 O5 ) Ceramics and their Effect on the Sintering Temperature and Microwave Dielectric Properties of Ba(Zn1/3 Nb2/3 )O3 Ceramics 总被引:1,自引:0,他引:1
Min-Han Kim Jong-Bong Lim Jae-Chul Kim Sahn Nahm Jong-Hoo Paik Jong-Hee Kim Kyeong-Soon Park 《Journal of the American Ceramic Society》2006,89(10):3124-3128
BaCu(B2 O5 ) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B2 O5 ) phase was formed at 700°C and melted above 850°C. The BaCu(B2 O5 ) ceramic sintered at 810°C had a dielectric constant (ɛr ) of 7.4, a quality factor ( Q × f ) of 50 000 GHz and a temperature coefficient of resonance frequency (τf ) of −32 ppm/°C. As the BaCu(B2 O5 ) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B2 O5 ) was added to the Ba(Zn1/3 Nb2/3 )O3 (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B2 O5 ) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q × f =16 000 GHz, ɛr =35, and τf =22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B2 O5 ) ceramic sintered at 875°C for 2 h. 相似文献
9.
Laura C. Stearns Martin P. Harmer Helen M. Chan 《Journal of the American Ceramic Society》1991,74(9):2175-2179
Dense, polycrystalline YBa2 Cu3 O6+x inclusions were incorporated into YBa2 Cu3 O6+x: powder in order to investigate the effect of nondensifying inclusions on the sintering behavior of the matrix. The presence of these inclusions caused a significant reduction in the densification rate of the matrix, as well as some microstructural damage. However, when approximately 2.5 vol% of a liquid phase was present during sintering, there was some retardation of densification in the early stages, but this disappeared with time. Also, the final sintered microstructures were damage-free and essentially identical to those of samples containing no inclusions. Possible roles for the liquid phase in correcting this microstructural damage are briefly discussed. 相似文献
10.
Qun Zeng Wei Li Jian-lin Shi Jing-kun Guo 《Journal of the American Ceramic Society》2006,89(10):3305-3307
The effects of V2 O5 addition on the sintering behavior, microstructure, and the microwave dielectric properties of 5Li2 O–0.583Nb2 O5 –3.248TiO2 (LNT) ceramics have been investigated. With addition of low-level doping of V2 O5 (≤2 wt%), the sintering temperature of the LNT ceramics could be lowered down to around 920°C due to the liquid phase effect. A secondary phase was observed at the level of 2 wt% V2 O5 addition. The addition of V2 O5 does not induce much degradation in the microwave dielectric properties but lowers the τf value to near zero. Typically, the excellent microwave dielectric properties of ɛr =21.5, Q × f =32 938 GHz, and τf =6.1 ppm/°C could be obtained for the 1 wt% V2 O5 -doped sample sintered at 920°C, which is promising for application of the multilayer microwave devices using Ag as an internal electrode. 相似文献
11.
Mg–Cu–Zn ferrites can be sintered at T ≤950°C to sufficient density and display adequate permeability profiles for application in multilayer ferrite inductors. The permeability and Curie temperature have to be optimized by proper selection of composition. Ferrites with <50 mol% Fe2 O3 reveal enhanced densification behavior. Submicrometer powders prepared by fine milling show good sintering activity and density after firing at 900°C. Nano-size ferrite powders prepared by coprecipitation or flame synthesis lead to high density; maximum shrinkage already occurs at T <800°C. The use of Bi2 O3 as a sintering additive further improves the densification, but also affects the microstructure and, hence, the permeability. A maximum permeability of μi =450–500 is obtained. 相似文献
12.
M. F. YAN 《Journal of the American Ceramic Society》1980,63(7-8):443-447
Sintering and microstructural evolution were studied in Fe3 O4 as a model system for spinel ferrites. Fe3 O4 powder, purified by the salt-crystallization method, was sintered to ∼99.5% density in a CO-CO2 atmosphere. The p O2 Of the sintering atmosphere drastically affects the microstructure (grain size) of sintered Fe3 O4 without significantly affecting density. The measured grain-boundary mobilities, M , of Fe3 O4 fit the equation M=M 0 ( T ) p O2 −1/2 with M 0 ( T ) = 2.5×105 exp[-(609kJ·mol-1 / RT ](m/s)(N/m2 )−l . The grain-boundary migration process appeared to be pore-drag controlled, with lattice diffusion of oxygen as the most likely rate-limiting step. 相似文献
13.
Pavel Diko Paul.-H. Duvigneaud Alain Lanckbeen ré Van Moer Georges Naessens Robert Deltour 《Journal of the American Ceramic Society》1993,76(11):2859-2864
Porosity, grain growth, phase composition, and microstructural defects were studied in sintered YBa2 (Cu1−x )3 O7−x ceramics for x values up to 0.3. The porosity of the samples, related to the sintering mechanism, was independent of iron concentration. A linear dependence of the grain size with the inverse of the iron concentration was found, strongly suggesting grain boundary segregation of iron. The solubility limit was estimated to be x = 0.18 at 950°C in O2 . Beyond this limit, a new microstructural component was found consisting of YBa2 (Cu1−x Fex )3 O7−δ , YBaCuFeO5 and Ba(Cu,Fe)O2 . The transition from an orthorhombic twin to an orthorhombic tweed phase and a tetragonal phase was detected by polarized light microscopy. 相似文献
14.
Thermal Conductivity of Gas-Pressure-Sintered Silicon Nitride 总被引:3,自引:0,他引:3
Naoto Hirosaki Yusuke Okamoto Motohide Ando Fumio Munakata Yoshio Akimune 《Journal of the American Ceramic Society》1996,79(11):2878-2882
Si3 N4 with high thermal conductivity (120 W/(m. K)) was developed by promoting grain growth and selecting a suitable additive system in terms of composition and amount. β-Si3 N4 doped with Y2 O3 -Nd2 O3 (YN system) or Y2 O3 -A12 O3 (YA system) was sintered at 1700°-2000°C. Thermal conductivity increased with increased sintering temperature because of decreased two-grain junctions, as a result of grain growth. The effect of the additive amount on thermal conductivity with the YN system was rather small because increased additive formed multigrain junctions. On the other hand, with the YA system, thermal conductivity considerably decreased with increased additive amount because the aluminum and oxygen in the YA system dissolved into β-Si3 N4 grains to form a β-SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si3 N4 were the sintering temperature and additive composition. 相似文献
15.
Sung Min Rhim Seokmin Hong Heungjin Bak Ok Kyung Kim 《Journal of the American Ceramic Society》2000,83(5):1145-1148
The effects of B2 O3 addition on the sintering behavior and the dielectric and ferroelectric properties of Ba0.7 Sr0.3 TiO3 (BST) ceramics were investigated. The dielectric and ferroelectric properties of a BST sample with 0.5 wt% B2 O3 sintered at <1150°C were as good as those of undoped BST sintered at 1350°C, and the dielectric loss was better. When >1.0 wt% B2 O3 was added to BST, the overdoped B2 O3 did not form a liquid phase or volatilize; it remained in the samples and formed a secondary phase that lowered the sintering behavior and the dielectric and ferroelectric properties of the BST. 相似文献
16.
A double–inverse microemulsion (IME) process is used for synthesizing nano-sized Ba2 Ti9 O20 powders. The crystallization of powders thus obtained and the microwave dielectric properties of the sintered materials were examined. The IME-derived powders are of nano-size (∼21.5 nm) and possess high activity. The BaTi5 O11 , intermediate phase resulted when the IME-derived powders were calcined at 800°C (4 h) in air. However, high-density Ba2 Ti9 O20 materials with a pure triclinic phase (Hollandite like) can still be obtained by sintering such a BaTi5 O11 dominated powders at 1250°C/4 h. The phase transformation kinetics for the IME-derived powders were markedly enhanced when air was replaced by O2 during the calcinations and sintering processes. Both the calcination and densification temperatures were reduced by around 50°C compared with the process undertaken in air. The microwave dielectric properties of sintered materials increase with the density of the samples, resulting in a large dielectric constant ( K ≅39) and high-quality factor ( Q × f ≅28 000 GHz) for samples possessing a density higher than 95% theoretical density, regardless of the sintering atmosphere. Overfiring dissociates Ba2 Ti9 O20 materials and results in a poor-quality factor. 相似文献
17.
Anna-Karin Axelsson Yuya Pan Matjaz Valant Neil Alford 《Journal of the American Ceramic Society》2009,92(8):1773-1778
Studies of a synthesis of KTaO3 displayed a two-step reaction path with the intermediate formation of K2 Ta4 O11 . Thermal and X-ray diffraction analysis showed that the synthesis is completed at 900°C. Sintering studies showed that KTaO3 powder can produce single phase ceramics with 85% of relative density with the addition of 5% of potassium excess when sintered at 1330°C for 1 h. Longer sintering times or higher temperatures result in enhanced potassium loss and consequent formation of K6 Ta10.8 O30 secondary phase with tetragonal tungsten bronze structure. Room- and low-temperature microwave dielectric properties of KTaO3 ceramics compare well with measurements performed on single crystals. We evaluated the influence of microstructural features (porosity, structural defects, secondary phases) on the dielectric properties of the ceramic samples. 相似文献
18.
Densification of Calcia-Stabilized Zirconia with Borates 总被引:1,自引:0,他引:1
Densification studies of submicrometer ZrO2 powders stabilized with 6.5 wt% CaO (CSZ) showed borate additions (1 to 10 wt%) to be effective sintering aids. Estimated densities >99% of theoretical were obtained on sintering at 1200°Cfor 4 h with 2 wt% B2 O3 or 5 wt% CaO·2B2 O3 additions to the CSZ powders. Average grain sizes obtained were typically <1 μm. Partial development of a monoclinic ZrO2 phase was observed in the sintered samples. The amount of this phase varied from ∼7 to 75 wt% and was approximately linearly dependent on the additive concentration. The effect was most marked for the B2 O3 additions. Development of the monoclinic phase was attributed to progressive leaching of Ca from the CSZ phase by B2 O3 , in effect partially destabilizing the ZrO2 . 相似文献
19.
Tape-cast slurries of Ba2 YCu3 O7 powders offer a convenient means of preparing sintered ceramic samples for critical current density (Jc ) measurements where the transport cross section is small and the current electrode areas are large. Samples were sintered from 900° to 1000°C and characterized for bulk density, grain size, phase composition, Tc , and Jc . Bulk density and grain size both increase with sintering temperature while all samples were single-phase perovskite except for those sintered at 900°C. The onset temperature for superconductivity is constant at about 93 K while the transition sharpens to R=0 at about 92 K for the densest samples. Jc rises with sintering temperature to a maximum of ∼103 A/cm2 . A linear relationship between Jc and bulk density is predicted from microstructural considerations. 相似文献
20.
The composition effects on the sintering behavior, microstructure evolution, dielectric, and magnetic properties of BaO·(Nd0.8 Bi0.2 )2 O3 ·4TiO2 (BNBT)+Bi2 O3 –B2 O3 –SiO2 –ZnO (BBSZ) glass–(Ni0.28 Cu0.12 Zn0.6 O)–(Fe2 O3 )0.99 (NiCuZn ferrite) composites were investigated in developing low-temperature-fired composites for high-frequency electromagnetic interference devices. An X-ray diffractometer, a scanning electron microscope, and a dilatometer were used to examine the BNBT+BBSZ glass powder to NiCuZn ferrite ratio effect on the composites densification and chemical reaction between BNBT and NiCuZn ferrite. The results indicate that these composites can be densified at 950°C with no significant chemical reactions occurring between BNBT and NiCuZn ferrites during sintering. The BNBT+BBSZ glass–NiCuZn ferrite composites sintered at 950°C exhibit excellent dielectric and magnetic properties over a wide frequency range. 相似文献