共查询到20条相似文献,搜索用时 15 毫秒
1.
Jinho Kim Toshio Kimura Takashi Yamaguchi 《Journal of the American Ceramic Society》1989,72(8):1541-1544
Densification and microstructure de velopment in Bi2 O3 -doped ZnO have been studied with a special emphasis on the effect of the Bi2 O3 content. A small amount of Bi2 O3 in ZnO (0.1 mol%) retarded densification, but the addition of Bi2 O3 to more than 0.5 mol% promoted densification by the formation of a liquid phase above the eutectic temperature (∼740°C). The liquid phase increased grain-boundary mobility, which was responsible for the formation of intragrain pores and the decrease in the sintered density. The increase in the Bi2 O3 content increased the probability of the formation of skeleton structure, which reduced the grain growth rate and the sintered density. 相似文献
2.
Zinc oxide (ZnO) nanoparticles coated with 1–5 wt% Bi2 O3 were prepared by precipitating a Bi(NO3 )3 solution onto a ZnO precursor. Transmission electron microscopy showed that a homogeneous Bi2 O3 layer coated the surface of the ZnO nanoparticles and that the ZnO particle size was ∼30–50 nm. Scanning electron microscopy showed that ZnO grains sintered at 1150°C were homogeneous in size and surrounded by a uniform Bi2 O3 layer. When the ZnO grains were surrounded fully by Bi2 O3 liquid phases, further increases in the ZnO grain size were not affected by the Bi2 O3 content. This predesigned ZnO nanoparticle structure was shown to promote homogeneous ZnO grains with perfect crystal growth. 相似文献
3.
Grain growth in a high-purity ZnO and for the same ZnO with Bi2 O3 additions from 0.5 to 4 wt% was studied for sintering from 900° to 1400°C in air. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: G n — G n 0 = K 0 t exp(— Q/RT ). For the pure ZnO, the grain growth exponent or n value was observed to be 3 while the apparent activation energy was 224 ± 16 kJ/mol. These parameters substantiate the Gupta and Coble conclusion of a Zn2+ lattice diffusion mechanism. Additions of Bi2 O3 to promote liquidphase sintering increased the ZnO grain size and the grain growth exponent to about 5, but reduced the apparent activation energy to about 150 kJ/mol, independent of Bi2 O3 content. The preexponential term K 0 was also independent of Bi2 O3 content. It is concluded that the grain growth of ZnO in liquid-phase-sintered ZnO-Bi2 O3 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Bi2 O3 -rich liquid phase. 相似文献
4.
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
5.
Grain growth in a high-purity ZnO with systematic additions of Sb2 O3 from 0.29 to 2.38 wt% was studied for sintering in air from 1106° to 1400°C. The results are discussed and compared with previous studies of pure ZnO and ZnO with Bi2 O3 additions in terms of the kinetic grain growth expression: Gn – Gn 0 = K 0 t exp(— Q/RT ). Additions of Sb2 O3 inhibited the grain growth of ZnO and increased the grain growth exponent ( n -value) to 6 from 3 for pure ZnO and 5 for the ZnO—Bi2 O3 ceramic. The apparent activation energy for the grain growth of ZnO also increased to about 600 kJ/mol from 220 kJ/mol for pure ZnO and 150 kJ/mol for the ZnO—Bi2 O3 ceramics. Both the grain growth exponent and the activation energy were independent of the Sb2 O3 content. Particles of the Zn7 Sb2 O12 spinel were observed on the grain boundaries and at the grain triple point junctions. It was also observed that the Sb2 O3 additions caused twin formation in each ZnO grain. It is concluded that both the Zn7 Sb2 O12 particles and the twins are responsible for the ZnO grain growth inhibition by Sb2 O3 . 相似文献
6.
Jung-Hae Choi Nong-Moon Hwang Doh-Yeon Kim 《Journal of the American Ceramic Society》2001,84(6):1398-1400
Pore–boundary separation in ZnO and 99.95ZnO·0.05Bi2 O3 (in mol%) specimens during sintering at 1200°C was investigated. In pure ZnO specimens, pores were attached to the grain boundaries and disappeared during the final stage of sintering. In the Bi2 O3 -doped specimens, on the other hand, many pores were separated from the boundaries and trapped inside the grains. Observation using transmission electron microscopy showed that a thin layer of Bi2 O3 -rich phase existed at the boundaries in the Bi2 O3 -doped specimens. The pore separation in 99.95ZnO·0.05Bi2 O3 specimens was explained in terms of the dihedral angle change and the high mobility of a liquid film boundary. 相似文献
7.
Grain growth of ZnO during the liquid-phase sintering of binary ZnO–Bi2 O3 ceramics has been studied for Bi2 O3 contents from 3 to 12 wt% and sintering from 900° to 1400°C. The results are considered in combination with previously published studies of ZnO grain growth in the ZnO–Bi2 O3 system. For the Bi2 O3 contents of the present study, the rate of ZnO grain growth is found to decrease with increasing Bi2 O3 . Activation analysis, when combined with the results of similar analyses of the previous studies, reveals a change in the rate-controlling mechanism for ZnO grain growth. Following a low-Bi2 O3 -content region of nearly constant activation energy values of about 150 kJ/mol, further Bi2 O3 additions cause an increase of the activation energy to about 270 kJ/mol. consistent with accepted models of liquid-phase sintering, it is concluded that the rate-controlling mechanism of ZnO grain growth during liquid-phase sintering in the presence of Bi2 O3 changes from one of a phase-boundary reaction at low Bi2 O3 levels to one of diffusion through the liquid phase at about the 5 to 6 wt% Bi2 O3 level and above. 相似文献
8.
Effect of Heat Treatments on the Wetting Behavior of Bismuth-Rich Intergranular Phases in ZnO:Bi:Co Varistors 总被引:1,自引:0,他引:1
Jeffrey P. Gambino W. David Kingery Gordon E. Pike Lionel M. Levinson Herbert R. Philipp 《Journal of the American Ceramic Society》1989,72(4):642-645
The effect of annealing on the wetting behavior of Bi-rich intergranular phases in ZnO:Bi:Co varistors was studied. The intergranular phase exhibits temperature-dependent grain-boundary wetting, with an average equilibrium dihedral angle of 0° at 1140°C and over 55° at 610°C. The temperature-dependent wetting may be related to the temperature dependence of the ZnO concentration in the Bi2 O3 liquid phase. The effect of the intergranular phase distribation on the electrical properties of ZnO varistors is discussed. 相似文献
9.
Seeding of the Reaction-Bonded Aluminum Oxide Process 总被引:1,自引:0,他引:1
The effect of the initial α-Al2 O3 particle size in the reaction-bonded aluminum oxide (RBAO) process on the phase transformation of aluminum-derived γ-Al2 O3 to α-Al2 O3 , and subsequently densification, was investigated. It has been demonstrated that if the initial α-Al2 O3 particles are fine (∼0.2 μm, i.e., 2.9 × 1014 γ-Al2 O3 particles/cm3 ), then they seed the phase transformation. The fine α-Al2 O3 decreases the transformation temperature to ∼962°C and results in a finer microstructure. The smaller particle size of the seeded RBAO decreases the sintering temperature to as low as ∼1135°C. The results confirm that seeding can be utilized to improve phase transformations and densification and subsequently to tailor final microstructures in RBAO-derived ceramics. 相似文献
10.
Yanmei Kan Peiling Wang Tao Xu Guojun Zhang Dongsheng Yan Zhijian Shen Yi-Bing Cheng 《Journal of the American Ceramic Society》2005,88(6):1631-1633
Spark plasma sintering (SPS) was used to fabricate bismuth titanate (Bi4 Ti3 O12 ) ceramics. The densification, microstructure development and dielectric properties were investigated. It was found that the densification process was greatly enhanced during SPS. The sintering temperature was 200°C lower and the microstructure was much finer than that of the pressureless sintered ceramics, and dense compacts with a high density of over 99% were obtained at a wide temperature range of 800°–1100°C. Dielectric property measurement indicated that the volatilization of Bi3+ was greatly restrained during SPS, resulting in an unprecedented low dielectric loss for pure Bi4 Ti3 O12 ceramics. 相似文献
11.
The Bi2 O3 –Nb2 O5 –NiO phase diagram at 1100°C was determined by means of solid-state synthesis, X-ray diffraction, and scanning electron microscopy. A ternary eutectic with a melting point below 1100°C was found to exist in the field between NiO, Bi2 O3 , and the end-member of the δBi2 O3 –Nb2 O5 solid solution. The existence of the previously reported Bi3 Ni2 NbO9 phase was disproved. A pyrochlore homogeneity range around Bi1.5 Ni0.67 Nb1.33 O6.25 was determined together with all the phase relations in this phase diagram. 相似文献
12.
David W. Johnson Jr. Warren W. Rhodes 《Journal of the American Ceramic Society》1989,72(12):2346-2350
Bi2 Sr2 CaCu2 O8 was prepared using the mixed oxide-carbonate method and sintered at temperatures ranging from 850° to 911°C. The samples were characterized for density, mechanical strength, phase composition, microstructure, and superconducting transition temperatures. A unique retrograde densification characteristic is demonstrated in the temperature range 850° to 890°C whereby the material first becomes less dense as the sintering temperature is raised, and only in a narrow temperature range from 900° to 905°C does the material densify then with the formation of a liquid phase. The retrograde densification mechanism is shown to be that of the formation of thin platelike crystallites which grow in a randomly oriented fashion, thus pushing the structure apart. This retrograde densification, coupled with a narrow sintering range overlapping the melting temperature, makes this compound a difficult one to process. 相似文献
13.
C. C. Khaw C. K. Lee Z. Zainal G. C. Miles A. R. West 《Journal of the American Ceramic Society》2007,90(9):2900-2904
The subsolidus phase diagram of the system Bi2 O3 –ZnO–Ta2 O5 in the region of the cubic pyrochlore phase has been determined at 1050°C. This phase forms a solid solution area that includes the ideal composition P, Bi3 Zn2 Ta3 O14 ; possible solid solution mechanisms are proposed, supported by density measurements of Zn-deficient solid solutions. The general formula of the solid solutions is Bi3+ y Zn2− x Ta3− y O14− x − y , based on the creation of Zn2+ , O2− vacancies in Zn-deficient compositions and a variable Bi/Ta ratio. 相似文献
14.
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
15.
TAKETOSHI TAKEMURA MASAHIRO KOBAYASHI YOSHIO TAKADA KEN SATO 《Journal of the American Ceramic Society》1987,70(4):237-241
The breakdown voltage, the upturn voltage, and the nonlinearity of the ZnO varistors are significantly influenced by the Sb2 O3 and SiO2 contents, as well as by the β→γ transition of the Bi2 O3 phase. The lattice parameter of spinel is influenced by the coexisting Bi2 O3 phase. Antimony oxide disperses into the powders of ZnO and other additives in the early stage of sintering, and finally gathers again as particles of spinel which may play an important role in the improvement of the nonlinearity by stressing the interfaces of two ZnO grains. 相似文献
16.
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
17.
The effects of the oxide additives MnO2 , Co3 O4 , and Sb2 O3 , commonly incorporated in commercial Bi2 O3 -doped ZnO varistors, on the current–voltage characteristics and microstructure of 0.25 mol% V2 O5 -doped ZnO varistors have been studied. MnO2 is the most significant additive in terms of its effects on varistor performance. Varistor performance can also be improved by increasing the V2 O5 content to 0.5 mol% in a ZnO ceramic containing 1 mol% MnO2 . Further increases in the V2 O5 content of 1 mol% MnO2 -doped material cause a deterioration in varistor behavior. The microstructure of the samples consists mainly of ZnO grains with zinc vanadates as the minority secondary phases. Additional spinel phase is formed when Sb2 O3 is incorporated. 相似文献
18.
Masanori Hirano Takayuki Oda Kenji Ukai Yasunobu Mizutani 《Journal of the American Ceramic Society》2002,85(5):1336-1338
Inhibition of cubic-rhombohedral phase transformation and low-temperature sintering at 1000°C were achieved for 10-mol%-Sc2 O3 -doped cubic-ZrO2 by the presence of 1 mol% Bi2 O3 . The powders of 1-mol%-Bi2 O3 –10-mol%-Sc2 O3 -doped ZrO2 were prepared using a hydrolysis and homogeneous precipitation technique. No trace of rhombohedral-ZrO2 phase could be detected, even after sintering at 1000°–1400°C. The average grain size of the ZrO2 sintered at 1200°C was >2 μm because of grain growth in the presence of Bi3+ . Cubic, stabilized Bi-Sc-doped ZrO2 sintered at 1200°C had sufficient conductivity at 1000°C (0.33 S/cm) to be used as an electrolyte for a solid-oxide fuel cell (SOFC) and at 800°C (0.12 S/cm) for an intermediate-temperature SOFC. 相似文献
19.
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
20.
TAKESHI KIKUCHT 《Journal of the American Ceramic Society》1977,60(3-4):148-150
The subsolidus phase equilibria in the system Bi2 O3 -TiO2 -Nb2 O5 at 1100°C were determined by solid-state reaction techniques and X-ray powder diffraction methods. The system was found to contain 4 ternary compounds, i.e. Bi3 TiNbO9 , Bi7 Ti4 NbO21 , a cubic pyrochlore solid solution having a compositional range of 3Bi2 O3 · x TiO2 (7– x )Nb2 O5 where x ranges from 2.3 to 6.75, and an unidentified phase, 4Bi2 O3 ·11TiO2 ·5Nb2 O5 . 相似文献