共查询到20条相似文献,搜索用时 15 毫秒
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Nina Daneu Aleksander Renik Slavko Bernik Drago Kolar 《Journal of the American Ceramic Society》2000,83(12):3165-3171
The effects of adding small quantities of SnO2 to the basic ZnO–Bi2 O3 varistor composition were studied in terms of phase reactions, microstructural development, and the formation of inversion boundaries. Scanning and transmission electron microscopy studies showed that the inversion boundaries, triggered by the addition of SnO2 , cause anisotropic grain growth in the early stages of sintering. ZnO grains that include inversion boundaries grow exaggeratedly, at the expense of normal grains, until they dominate the microstructure. Higher additions of SnO2 lead to an increase in number of grains with inversion boundaries and to a more fine-grained microstructure. The increasing amount of secondary phases is also related to a higher level of SnO2 addition; however, the influence of these phases on ZnO grain growth is subordinate to the role of inversion boundaries. 相似文献
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Effects of a liquid-phase-sintering aid, BaCuO2 + CuO (BCC), on densification and microwave dielectric properties of (Zr0.8 Sn0.2 )TiO4 (ZST) ceramics have been investigated. The densification kinetics of ZST are greatly enhanced with the presence of 2.5–5 wt% BCC, but become retarded when the amount of BCC increases further. At a given BCC content, moreover, slower densification kinetics are observed with a larger particle size of ZST. The above results are attributed to a chemical reaction taking place at the interface of BCC/ZST during firing. The ZST dissolves into BCC, forming crystalline phases of ZrO2 , SnO2 , CuO, and BaTi8 O16 which reduce the amount of BCC flux available for liquid-phase sintering. The crystallization kinetics become more significant, compared with densification kinetics, with increasing the amount of BCC and the particle sizes of ZST. For samples with 2.5–5 wt% BCC, a high relative sintered density is obtained at 1000°C and the resulting microwave ceramics have a dielectric constant and a value of Q at 7 GHz in the ranges of 35–38 and 2800–5000, respectively. 相似文献
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Akiteru Watanabe Takeshi Kikuchi Masayuki Tsutsumi Satoshi Takenouchi Kenji Uchida 《Journal of the American Ceramic Society》1983,66(7):c104-c105
Subsolidus equilibrium relations were reexamined in the SnO2 -rich portion of the system GeO2 -SnO2 (60 to 98 mol% SnO2 ). A limited solid solution based on SnO2 was confirmed; 4mol% GeO2 dissolved in SnO2 at 1250 C, and glass was formed on quenching over the compositional range above 4mol% GeO2 . Phase relutions in the system are discussed with reference to the polymorphism of GeO2 and its glass-forming ability, and a possible phase diagram is given . 相似文献
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The Knoop microhardness anisotropy of single-crystal cassiterite (SnO2 ) was measured on the (100), (110), (001), and (111). That anisotropy is depicted as the microhardness profiles for those planes. The results are addressed first in terms of the elastic anisotropy of SnO2 and then on the basis of the effective resolved shear stress (ERSS), the latter an approach initially advanced by Brookes and co-workers. The load dependence of the Knoop microhardness is also evaluated in terms of the classical Meyer's law for which it is demonstrated that the Meyer's law coefficient and Meyer's law exponent are related. 相似文献
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Yong Liu Yuan-Hua Lin Bo-Ping Zhang Hong-Min Zhu Ce-Wen Nan Jinle Lan Jing-Feng Li 《Journal of the American Ceramic Society》2009,92(4):934-937
La2 − x R x CuO4 (R: Pr, Y, Nb) polycrystalline ceramics have been prepared by a spark plasma sintering process. Analysis of the microstructure and phase composition shows that pure La2 CuO4 ceramics with a high density can be obtained, and no impurity phases appear. All the samples exhibit a metal–semiconductor transition behavior at ∼750 K, which could be ascribed to the decreasing charge density as a result of loss of oxygen atoms and various conduction mechanisms in these La2 CuO4 -based ceramics. Our results indicate that the La1.98 Y0.02 CuO4 ceramics show large thermoelectric power ∼1.0 × 10−3 μW·(m·K2 )−1 , and the evaluated ZT can reach 0.17 at 330 K, which potentially make them useful for thermoelectric applications. 相似文献
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Madhumita Goswami Vasanthakumaran Sudarsan Vilas K. Shrikhande Govind P. Kothiyal Shailendra K. Kulshreshtha 《Journal of the American Ceramic Society》2008,91(3):986-989
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The effect of crystal phase in the starting powder of (Ba, Nb)-doped TiO2 ceramics on abnormal grain growth was investigated. The abnormal grain growth took place mainly during the cooling period after the second phase precipitated. The extent of abnormal grain growth is higher in an anatase powder sample than in a rutile powder sample and is highest at an intermediate rate of cooling for both powders. The nature of abnormal grain growth is suggested to be the Ba flow resulting from the concentration gradient of Ba between neighboring grains as the second phase precipitated. The reason for the greater abnormal grain growth in the anatase powder sample is proposed to be the higher dissolution of Ba in the grain which can be explained by the more open crystal structure of anatase with respect to rutile. The amount of second phase on the surface is greater than that in the interior, especially in the anatase powder sample. Characteristic features of the structure of anatase were calculated. 相似文献
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Variations in electrical conduction which were caused by heat treatment of SnO2 films vapor-deposited on glass were studied. In the range 20° to 230°C, the relative importance of semiconduction processes attributed to 3 types of donors (probably O vacancies, interstitial Sn ions, and Cl ions) was determined as a function of heat treatment. A decrease in conductivity at constant temperature above 230°C was ascribed to grain growth of the SnO2 crystals deposited initially. 相似文献
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NIKOS K. FLEVARIS 《Journal of the American Ceramic Society》1987,70(5):301-304
Expressions are given for the coherency-strain elastic free energy of systems with tetragonal symmetry in the framework of the continuum theory. This theory is applied for SnO2 -TiO2 and the results are compared with known experimental observations. Calculations for other tetragonal systems are also presented. Finally, the results of these calculations for systems of tetragonal symmetry are discussed in the light of the Cahn and Hilliard theory of spinodal decomposition. 相似文献
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Masaru Yoshinaka Ken Hirota Masayuki Ito Hiroshi Takano Osamu Yamaguchi 《Journal of the American Ceramic Society》1999,82(1):216-218
Tin(IV) oxide (SnO2 ) crystallizes at room temperature by adding hydrazine monohydrate ((NH2 )2 · H2 O) to a hydrochloric acid solution of tin, followed by washing and drying. Well-densified SnO2 ceramics (99.8% of theoretical) with an average grain size of 0.9 μm have been fabricated by hot isostatic pressing for 2 h at 900°C and 196 MPa. Their Vickers hardness and bending strength are 14.4 GPa and 200 MPa, respectively. They exhibit an electrical conductivity of 2 × 10−3 −9 × 10−3 S·cm−1 at room temperature. 相似文献
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An investigation of the ternary systems BaO-TiO2 -SnO2 and BaO-TiO2 -ZrO2 led to the discovery of two new compounds belonging to the system BaO-TiO2 . These compounds, Ba2 Ti9 -O20 and Ba2 Ti9 O20 , are stabilized by minute additions of SnO2 or ZrO2 . The known compound BaTi2 O5 can be obtained only from the molten phase and decomposes below 1300°C. into Ba2 Ti5 O12 and BaTiO2 . In these systems no ternary compounds are found. The ternary phase diagrams can be divided into regions with high and low dielectric losses, which are in accordance with the phase relations. Tables with crystallographic data of the new compounds are included. 相似文献
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Niall J. Donnelly Thomas R. Shrout Clive A. Randall 《Journal of the American Ceramic Society》2009,92(6):1203-1207
It is demonstrated that the use of ∼0.9 mol% Li2 CO3 (LC) as a sintering aid for Sr, K, Nb modified Pb(Zr1− x ,Ti x )O3 (PZT) ceramics is effective only in the presence of excess PbO (∼2 mol%). It is shown that LC and PbO react to form the compound, Li2 PbO3 (LPO) which has a melting temperature of ∼836°C. Using dilatometry, we were able to correlate shrinkage during heating of a green ceramic to the melting of the LPO. Consequently, complete densification and sizeable grain growth are achieved by solution-precipitation of the ceramic through the liquid phase. Importantly, sintering is not particularly effective with such small additions of either LC or PbO alone. In confirmation of this model, the LPO compound was presynthesized and used as the only sintering aid in the same PZT composition. The densification behavior of this mixture compared well with the case of separate additions. 相似文献
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Fumio Kawamura Itaru Yasui Masayuki Kamei Ichiro Sunagawa 《Journal of the American Ceramic Society》2001,84(6):1341-1346
SnO2 single crystals have short prismatic habits bounded by well-developed {110} and {111} faces in a pure SnO2 –Cu2 O flux system. When trivalent cations are added to the system, the habits drastically change to needle, acicular, or whisker forms with large aspect ratios. The addition of trivalent cations also greatly increases the nucleation rate and drastically decreases the crystal size. SEM observations and EPMA investigations reveal that the flat {111} faces transform to rounded or rough { hkl } faces by the addition of trivalent cations. This roughening transition of {111} faces, keeping {110} faces unchanged, is the cause of drastic habit modification that is attributed to the breaking of the periodic bond chain in {111} faces by impurity cations. 相似文献
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The grain size-microcracking relation was examined for low thermal expansion NaZr2 (PO4 )3 family ceramics. By measurements of the strength, Young's modulus, thermal expansion, and grain size of polycrystalline ceramics sintered at appropriate conditions, the critical grain size for microcracking was determined. The critical grain size was proportional to the inverse square of the maximum thermal expansion difference. 相似文献
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TiO2 /SnO2 nanonecklace-structured hybrid nanofibers have been prepared via an electrospinning method. These hybrid nanofibers are characterized with SnO2 -rich beads and pure TiO2 chains. It is found that TiO2 in the beads shows a rutile structure, and the one in the chains is entirely composed of anatase phase. This novel microstructure enhanced the photocatalytic activity, as well as its ideal recyclable character. We believe that this fire-new type of nanofiber may potentially serve as a new generation photocatalyst in environmental remediation. 相似文献
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Fumio Kawamura Masayuki Kamei Itaru Yasui Ichiro Sunagawa 《Journal of the American Ceramic Society》1999,82(3):774-776
The effects of a small amount of cations with valence states ranging from mono- to hexavalent on the growth and habits of SnO2 crystals growing in the SnO2 -Cu2 O flux system were systematically investigated. Trivalent cations having ionic radii closer to that of Sn4+ had a conspicuous effect upon the size and habits of SnO2 . Pentavalent cations with ionic radii similar to those of Sn4+ had some effect, whereas cations of other valence states showed no effect at all. 相似文献
18.
P. R. Bueno J. A. Varela C. M. Barrado E. Longo E. R. Leite 《Journal of the American Ceramic Society》2005,88(9):2629-2631
We performed a comparative study of electrical and thermal properties of ZnO- and SnO2 -based varistor. The electrical properties of commercial ZnO-based varistor are equivalent to that found in SnO2 -based varistor system. In spite of this, the SnO2 showed a thermal conductivity higher than commercial samples of ZnO-based varistor, which allied with its simpler microstructure and lower dopant concentration is a remarkable result that point out to the use of this system to compete commercially with ZnO-based varistor devices. 相似文献
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PAUL F. BECHER 《Journal of the American Ceramic Society》1983,66(7):485-488
Significant increases in the critical fracture toughness (K IC ) over that of alumina are obtained by the stress-induced phase transformation in partially stabilized ZrO2 particles which are dispersed in alumina. More importantly, improved slow crack growth resistance is observed in the alumina ceramics containing partially stabilized ZrO2 particles when the stress-induced phase transformation occurs. Thus, increasing the contribution of the ZrO2 phase transformation by tailoring the Y2 O3 stabilizer content not only increases the critical fracture toughness (KIC ) but also the K Ia to initiate slow crack growth. For example, crack velocities ( v )≥10–9 m/s are obtained only at K Ia ≥5 MPa.m1/2 in transformation-toughened ( K IC =8.5 MPa.m1/2 ) composites vs K Ia ≥2.7 MPa.m1/2 for comparable velocities in composites where the transformation does not occur ( K IC =4.5 MPa.m1/2 ). This behavior is a result of crack-tip shielding by the dissipation of strain energy in the transformation zone surrounding the crack. The stress corrosion parameter n is lower and A greater in these fine-grained composite materials than in fine-grained aluminas. This is a result of the residual tensile stresses associated with larger (≥1 μm) monoclinic ZrO2 particles which reside along the intergranular crack path. 相似文献