共查询到20条相似文献,搜索用时 15 毫秒
1.
Hongguo Zhang Longtu Li Yongli Wang Ji Zhou Zhenxing Yue Zhilun Gui 《Journal of the American Ceramic Society》2002,85(5):1180-1184
The influence of the substitution of copper for cobalt on the low-sintering densification, microstructure, lattice parameters, and electromagnetic properties of planar Z-type hexaferrites, which have a stoichiometric composition of Ba3 Co2(10.8− x ) -Zn0.4 Cu2 x Fe24 O41 , were investigated. The experimental results show that densification of the copper-substituted hexaferrite is dependent on the amount of copper substitution and sintering temperatures. XRD analysis reveals that the solid solubility of copper in Z-type hexaferrite is limited to x ≤ 0.30. At the same time, the lattice parameters ( a and c ) of Z-type hexaferrites with copper substitution showed a small change, that is, decrease of a parameter in the basal plane and increase of the c axial. Moreover, the microstructure becomes more homogeneous and intragranular pores decrease considerably, but the temperature-stable range of the Z-type phase formation is narrow. The copper-substituted hexaferrites, with x = 0.20 and sintered at ∼1125°C for 4 h, resulted in a high density sample of ∼4.68 g/cm3 as the optimal value, good magnetic properties, and the enormous potentiality for fabrication of multilayer chip inductors used in hyper-frequencies. 相似文献
2.
Antonio Barba Carolina Clausell Carlos Felíu María Monzó 《Journal of the American Ceramic Society》2004,87(4):571-577
A study has been conducted on the sintering of a ceramic ferrite having the composition (Cu0.25 Ni0.25 Zn0.50 )Fe2 O4 . The study analyzes the evolution of ferrite relative to density and microstructure with peak sintering temperature and dwell time at peak temperature. The densification and grain-growth rates are correlated with average grain size, relative density, and temperature. Corresponding rate-controlling diffusion mechanisms are proposed. 相似文献
3.
Hyo Tae Kim Thomas Shrout Clive Randall Michael Lanagan 《Journal of the American Ceramic Society》2002,85(11):2738-2744
The sintering behavior and dielectric properties of perovskite Ag(Nb1− x Ta x )O3 (0 < x < 1) solid solutions and two-phase composite assemblages were explored. A small amount of CuO (1 wt%) was used for liquid-phase sintering and led to high densification at temperatures <950°C. The temperature coefficient of capacitance, TCC, was adjusted by varying the Nb:Ta ratio within the solid-solution series and by creating composite microstructures. Two-phase assemblages consisting of Ag(Nb3/4 Ta1/4 )O3 and Ag(Nb1/4 Ta3/4 )O3 were synthesized to achieve a temperature-stable dielectric material for high-frequency applications. The composite dielectric with CuO addition had an average dielectric constant of 390 and a Q × f factor of 410 GHz at 2 GHz, with a stable TCC (0 to −180 ppm/°C) in the temperature range from −20° to +60°C. In addition, process compatibility with a silver conductor was confirmed by high-frequency ring-resonator measurements and microstructural characterization. The Ag(Nb1− x Ta x )O3 solid solutions and composites are promising candidates as embedded capacitors for radio-frequency/microwave applications. 相似文献
4.
Zélia Soares Macedo Antonio Carlos Hernandes 《Journal of the American Ceramic Society》2002,85(7):1870-1872
A solid-state route to synthesize bismuth germanate (Bi4 Ge3 O12 , or BGO) ceramics, and the optimum conditions for the laser sintering of these ceramics, were investigated. Special emphasis was placed on the influence of laser power and irradiation time on densification and microstructure evolution. The procedure that was used involved preheating the samples and a laser-irradiation program, which resulted in sintered, crack-free BGO ceramics with good pore shrinkage and a relative density of 95% (±3%). 相似文献
5.
Samuel M. Salamone Laura C. Stearns Rajendra K. Bordia Martin P. Harmer 《Journal of the American Ceramic Society》2003,86(6):883-892
The presence of rigid inclusions in a powder compact leads to a reduction in the densification rate of the compact and may also lead to processing defects. In this paper, the densification rate and the constitutive parameters of both homogeneous YBa2 Cu3 O6+ x and composite powder compacts (YBa2 Cu3 O6+ x powder with 10 vol% dense inclusions of YBa2 Cu3 O6+ x ) are reported. A small amount of liquid phase, which formed during sintering, was present in the samples. However, even with the presence of a liquid phase, the addition of inclusions still reduces the densification rate of the composite and increases its viscosity. The results have been compared with a published analysis of the problem using measured values of the constitutive parameters. Both the viscosity and viscous Poisson's ratio of the porous body have been measured. 相似文献
6.
Hae-Won Kim Young-Hag Koh Hyoun-Ee Kim 《Journal of the American Ceramic Society》2000,83(11):2863-2865
The densification behavior and mechanical properties of B4 C hot-pressed at 2000°C for 1 h with additions of Al2 O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2 O3 . The improvement was attributed to the enhanced mobility of elements through the Al2 O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2 O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4 C and Al2 O3 . 相似文献
7.
D. Doni Jayaseelan N. Kondo D. Amutha Rani S. Ueno T. Ohji S. Kanzaki 《Journal of the American Ceramic Society》2002,85(11):2870-2872
The pulse electric current sintering technique (PECS) was demonstrated to be effective in rapid densification of fine-grained Al2 O3 /3Y-ZrO2 using available commercial powders. The composites attained full densification (>99% of TD) at 1450°C in less than 5 min. The composites sintered at a high heating rate had a fine microstructure. The incorporation of 3 vol% 3Y-ZrO2 substantially increased the average fracture strength and the toughness of alumina to as high as 827 MPa and 6.1 MPa·m1/2 , respectively. A variation in the heating rate during the PECS process influenced grain size, microstructure, and strength, though there was little or no variation in the fracture toughness. 相似文献
8.
Gas pressure sintering kinetics of silicon nitride powder coated with 10 wt% (9:1) Al2 O3 and TiO2 have been studied at 1850°C with a pressure schedule of 0.3 MPa in the first stage and 1 MPa in the second stage. The rates have been analyzed with a liquid-phase sintering model. Diffusion-controlled intermediate-stage kinetics have been observed. The role of second-step pressurization with nitrogen and argon has been determined by monitoring the kinetics. Pressurization at an earlier stage (∼90% relative density) reduces the densification rate but produces a denser material at the final stage. Although final density is greater, a porous surface layer forms on samples sintered with argon pressurization at the second stage. No such porous layer is formed in the case of pressurization with nitrogen. The mechanism of the intermediate-stage kinetics has been discussed with respect to the nature of the product analyzed by XRD after sintering. 相似文献
9.
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
10.
The effect of the addition of V2 O5 on the structure, sintering and dielectric properties of M -phase (Li1+ x − y Nb1− x −3 y Ti x +4 y )O3 ceramics has been investigated. Homogeneous substitution of V5+ for Nb5+ was obtained in LiNb0.6(1− x ) V0.6 x Ti0.5 O3 for x ≤ 0.02. The addition of V2 O5 led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]r = 66, Q × f = 3800 at 5.6 GHz, and τf = 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V2 O5 -doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications. 相似文献
11.
An addition of just 0.4 wt% Li2 O to (Ba0.6 Sr0.4 )TiO3 powder was able to reduce the sintering temperature to ≤900°C and produce ceramics with a relative density of 97%. Small amounts of two secondary phases were formed during this process: Li2 TiO3 and Ba2 TiO4 . The addition of Li2 O depresses the ferroelectric character of the (Ba0.6 Sr0.4 )TiO3 and, as a result, reduces the permittivity, improves the temperature coefficient of permittivity, and reduces the dielectric losses. The tunability shows no significant variation with Li2 O concentration and remains between 16.5% and 13.5%. A low-temperature sintering mechanism was proposed. The mechanism involves the intermediate formation of BaCO3 , its melting and the incorporation of Li+ into the BST. The sintering mechanism can be characterized as reactive liquid-phase sintering. 相似文献
12.
13.
Eirik Hagen Yingda Yu Tor Grande Ragnvald Høier Mari-Ann Einarsrud 《Journal of the American Ceramic Society》2002,85(12):2971-2976
The densification of aluminum nitride using Ca12 Al14 O33 as a sintering aid has been studied with emphasis on the effect of using coarse or fine powder, the amount of sintering aid, the sintering temperature, and embedding. Both crystalline and amorphous grain boundary phases were observed. Significant weight losses were observed for coarse-grained samples, and if suitable embedding was not used. Porous and coarse-grained ceramics with high contiguity and minor amounts of secondary phases were obtained by enhanced evaporation while dense ceramics were obtained limiting the evaporation. High weight losses in the graphite environment resulted in formation of a dense AlN surface layer. 相似文献
14.
Koji Tsukuma 《Journal of the American Ceramic Society》2000,83(12):3219-3221
Composites of β-Ce2 O3 ·11Al2 O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2 , ZrO2 (2 mol% Y2 O3 ), and Al2 O3 . The composites had microstructures composed of elongated grains of β-Ce2 O3 ·11Al2 O3 in a Y-TZP matrix. The β-Ce2 O3 ·11Al2 O3 decomposed to α-Al2 O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β-Ce2 O3 ·11Al2 O3 divided into several grains of α-Al2 O3 and ZrO2 doped with Y2 O3 and CeO2 . High-temperature bending strength of the oxygen-annealed α-Al2 O3 composite was comparable to the β-Ce2 O3 ·11Al2 O3 composite before annealing. 相似文献
15.
The sintering behavior and surface microstructure of PbNi1/3 Nb2/3 O3 –PbTiO3 –PbZrO3 (PNiNb-PT-PZ) ceramics were investigated. The PNiNb-PT-PZ ceramics with the stoichiometric composition and the addition of excess lead oxide (PbO-rich ceramics) were sintered by liquid-phase sintering in accordance with the solution-reprecipitation mechanism at temperatures below the melting point of PbO. The temperature at which the liquid phase forms fell to near the eutectic point of the PbO–Nb2 O5 and the PbO–TiO2 system (868°C) with the addition of 5 mol% PbO. As the calcination temperature influenced the sinterability of the stoichiometric PNiNb-PT-PZ ceramic, unreacted PbO was considered to be the source of the liquid phase in the sintering of the stoichiometric powder. The secondary phase was observed at the surface of PbO-rich ceramics and was suggested to be a liquid phase expelled from inside the ceramic. A sintering scheme of PNiNb-PT-PZ ceramics was proposed, and the high sinterability of PNiNb-PT-PZ ceramics was attributed to the low formation temperature of the liquid phase. 相似文献
16.
The preparation of near stoichiometric spinel and alumina-rich spinel composites from Al2 O3 and MgO powders with the addition of Na3 AlF6 up to 4 wt% in the temperature range 700°–1600°C was studied; 98 wt% spinel containing 72 wt% Al2 O3 can be produced from the mixture of 72 wt% (50 at.%) Al2 O3 + 28 wt% (50 at.%) MgO powders with the addition of 1 wt% Na3 AlF6 fired at 1300°C for 1 h. Spinels containing 81–85 wt% Al2 O3 can be produced from either the mixture of 90 wt% (78 at.%) Al2 O3 + 10 wt% (22 at.%) MgO or the mixture of 95 wt% (88 at.%) Al2 O3 + 5 wt% (12 at.%) MgO powders with the addition of 4 wt% Na3 AlF6 in the temperature range 1300°–1600°C by using a torch-flame firing for 3 min, followed by quenching in water, while the same system under slow cooling in a furnace results in spinel containing 74–76 wt% Al2 O3 . Microscopic studies indicate that the alumina-rich spinel composites consist of a continuous majority spinel phase and an isolated minority corundum phase, regardless of slow cooling in a furnace or quenching in water. 相似文献
17.
Takayuki Nagano Kenji Kaneko Guo-Dong Zhan Mamoru Mitomo 《Journal of the American Ceramic Society》2000,83(10):2497-2502
Compression and tension tests were performed on liquid-phase-sintered β-SiC fabricated by hot-pressing, using ultrafine powders, at 1973–2048 K in an N2 atmosphere. Amorphous phases were observed at the grain boundaries and at multigrain junctions in the as-sintered material. Strain hardening was observed under all experimental conditions. Stress exponents in the compression test were 1.7–2.1 in the temperature range 1973–2023 K. A maximum tensile elongation of 170% was achieved at the initial strain rate of 2 × 10− 5 s− 1 at 2048 K. 相似文献
18.
Our analysis of the microwave dielectric properties of the δ-Bi2 O3 –Nb2 O5 solid solution (δ-BNss ) showed a continuous increase in permittivity and dielectric losses with an increasing concentration of Nb2 O5 . The only discontinuity was found for the temperature coefficient of resonant frequency, which is negative throughout the entire homogeneity range but reaches a minimum value for the sample with 20 mol% Nb2 O5 . At the same composition there is a discontinuity in the grain size of the δ-BNss ceramics. For the sample containing 25 mol% Nb2 O5 two structural modifications were observed. A single-phase tetragonal Bi3 NbO7 , in the literature referred to as a Type-III phase, is formed in a very narrow temperature range from 850° to 880°C. A synthesis performed below or above this temperature range resulted in the formation of the end member of the δ-BNss homogeneity range. Compared with the δ-BNss the Bi3 NbO7 ceramics exhibit lower microwave dielectric losses, an increased conductivity, and a positive temperature coefficient of resonant frequency. 相似文献
19.
Bikramjit Basu Jong-Heun Lee Doh-Yeon Kim 《Journal of the American Ceramic Society》2004,87(2):317-319
In the present work, we report the processing of ultrahard tungsten carbide (WC) nanocomposites with 6 wt% zirconia additions. The densification is conducted by the spark plasma sintering (SPS) technique in a vacuum. Fully dense materials are obtained after SPS at 1300°C for 5 min. The sinterability and mechanical properties of the WC–6 wt% ZrO2 materials are compared with the conventional WC–6 wt% Co materials. Because of the high heating rate, lower sintering temperature, and short holding time involved in SPS, extremely fine zirconia particles (∼100 nm) and submicrometer WC grains are retained in the WC–ZrO2 nanostructured composites. Independent of the processing route (SPS or pressureless sintering in a vacuum), superior hardness (21–24 GPa) is obtained with the newly developed WC–ZrO2 materials compared with that of the WC–Co materials (15–17 GPa). This extremely high hardness of the novel WC–ZrO2 composites is expected to lead to significantly higher abrasive-wear resistance. 相似文献
20.
Andrei N. Salak Maria Paula Seabra Victor M. Ferreira 《Journal of the American Ceramic Society》2004,87(2):216-220
Low-frequency dielectric response of air- and oxygen-sintered ceramics with the composition 0.9BaTiO3 –0.1La(Mg1/2 Ti1/2 ) O3 (0.9BT–0.1LMT) has been studied in the temperature range of 12–550 K. In comparison with pure BT, in 0.9BT–0.1LMT the dielectric permittivity maximum is shifted by almost 300 K toward lower temperatures. Both real and imaginary parts of dielectric permittivity of the solid solution, in the range 12–150 K, show a strong frequency-dependent behavior, which is typical of relaxors. On the basis of the model of exponential cluster size distribution and the Cole–Cole equation, the degree of interaction between the polar clusters was estimated. It was shown that the oxygen vacancies arising during sintering at high temperatures did not affect noticeably the relaxor properties of the material. The role of heterovalent La3+ /Ba2+ and Mg2+ /Ti4+ substitutions in the relaxor behavior formation is discussed. 相似文献