共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Ritesh Rawal Antonio Feteira Alberto Arenas Flores Neil C. Hyatt Anthony R. West Derek C. Sinclair Kumaravinothan Sarma Neil McN. Alford 《Journal of the American Ceramic Society》2006,89(1):336-339
The dielectric properties of dense ceramics of the "twinned" 8H-hexagonal perovskite Ba8 Nb4 Ti3 O24 are reported. Single-phase powders were obtained from the mixed-oxide route at 1325°C and ceramics (>92% of the theoretical X-ray density) by sintering in air or flowing O2 at 1400°–1450°C. The ceramics are dc insulators with a band gap >3.4 eV that resonate at microwave frequencies with relative permittivity, ɛr ∼44–48, quality factor, Q × f r ∼21 000–23 500 GHz (at f r ∼5.5 GHz) and temperature coefficient of resonant frequency, TC f ,∼+115 ppm/K. 相似文献
3.
Shuichi Kawano Junichi Takahashi Shiro Shimada 《Journal of the American Ceramic Society》2003,86(9):1609-1611
Nano-sized TiO2 powders were prepared by controlled hydrolysis of TiCl4 and Ti(O-i-C3 H7 )4 solutions and nitrided in flowing NH3 gas at 700°–1000°C to form TiN. Nano-sized TiN was densified by spark plasma sintering at 1300°–1600°C to produce TiN ceramics with a relative density of 98% at 1600°C. The microstructure of the etched ceramic surface was observed by SEM, which revealed the formation of uniformly sized 1–2 μm grains in the TiCl4 -derived product and 10–20 μm in the Ti(O-i-C3 H7 )4 -derived TiN. The electric resisitivity and Vickers micro-hardness of the TiN ceramics was also measured. 相似文献
4.
Liang Fang Hui Zhang Qian Yu Heping Su Bolin Wu Xueming Cui 《Journal of the American Ceramic Society》2009,92(2):556-558
The microwave dielectric properties of dense ceramics of a new A4 B3 O12 type cation-deficient hexagonal perovskite Sr3 LaNb3 O12 are reported. Single-phase powders can be obtained from the mixed-oxide route at 1320°C and dense ceramics (>96% of the theoretical X-ray density) with uniform microstructures (5–12 um) can be obtained by sintering in air at 1430°C. The ceramic exhibits a moderate dielectric constant ɛr ∼36, a high quality factor Q × f ∼45 327 GHz, and a low temperature coefficient of resonant frequency τ f of −9 ppm/°C. 相似文献
5.
Yong Jun Wu Naofumi Uekawa Yoshinori Sasaki Kazuyuki Kakegawa 《Journal of the American Ceramic Society》2002,85(8):1988-1992
The microstructures and pyroelectric properties of multicomposition 0.9PbZrO3 · x PbTiO3 ·(0.1− x )Pb(Zn1/3 Nb2/3 )O3 (PZ–PT–PZN) ceramics were investigated. The PZ–PT–PZN ceramics with nearly theoretical density were prepared by spark plasma sintering at low temperature (800°C) for a very short time (10 min) from two original compositions with x = 0.025 and x = 0.050. The heat treatment was successfully used to control the diffusion between the different compositions in such ceramics. For ceramics heat-treated at 900°C, two pyroelectric peaks corresponding to the original compositions were observed. When the heat-treatment temperature was increased to 1200°C, these two pyroelectric peaks combined into one sharp pyroelectric peak, which corresponds to average composition. When the spark-plasma-sintered ceramics were heat-treated at 950°C, a high and stable pyroelectric coefficient (>100 nC·cm−2 ·K−1 ) over a wide temperature range (23°–47°C) was obtained. It was found that the pyroelectric properties strongly depended on the microstructures. 相似文献
6.
T. S. R. Ch. Murthy B. Basu R. Balasubramaniam A. K. Suri C. Subramanian R. K. Fotedar 《Journal of the American Ceramic Society》2006,89(1):131-138
The densification of non-oxide ceramics like titanium boride (TiB2 ) has always been a major challenge. The use of metallic binders to obtain a high density in liquid phase-sintered borides is investigated and reported. However, a non-metallic sintering additive needs to be used to obtain dense borides for high-temperature applications. This contribution, for the first time, reports the sintering, microstructure, and properties of TiB2 materials densified using a MoSi2 sinter-additive. The densification experiments were carried out using a hot-pressing and pressureless sintering route. The binderless densification of monolithic TiB2 to 98% theoretical density with 2–5 μm grain size was achieved by hot pressing at 1800°C for 1 h in vacuum. The addition of 10–20 wt% MoSi2 enables us to achieve 97%–99%ρth in the composites at 1700°C under similar hot-pressing conditions. The densification mechanism is dominated by liquid-phase sintering in the presence of TiSi2 . In the pressureless sintering route, a maximum of 90%ρth is achieved after sintering at 1900°C for 2 h in an (Ar+H2 ) atmosphere. The hot-pressed TiB2 –10 wt% MoSi2 composites exhibit high Vickers hardness (∼26–27 GPa) and modest indentation toughness (∼4–5 MPa·m1/2 ). 相似文献
7.
Ching-Fang Tseng Cheng-Liang Huang Wen-Ruei Yang Cheng-Hsing Hsu 《Journal of the American Ceramic Society》2006,89(4):1465-1470
The microwave dielectric properties and the microstructures of Nd(Zn1/2 Ti1/2 )O3 (NZT) ceramics prepared by the conventional solid-state route have been studied. The prepared NZT exhibited a mixture of Zn and Ti showing 1:1 order in the B-site. The dielectric constant values (ɛr ) saturated at 29.1–31.6. The quality factor ( Q × f ) values of 56 700–170 000 (at 8.5 GHz) can be obtained when the sintering temperatures are in the range of 1300°–1420°C. The temperature coefficient of resonant frequency τf was not sensitive to the sintering temperature. The ɛ r value of 31.6, the Q × f value of 170 000 (at 8.5 GHz), and the τf value of −42 ppm/°C were obtained for NZT ceramics sintering at 1330°C for 4 h. For applications of high selective microwave ceramic resonators, filters, and antennas, NZT is proposed as a suitable material candidate. 相似文献
8.
Lead-based piezoelectric ceramics typically require sintering temperatures higher than 1000°C at which significant lead loss can occur. Here, we report a double precursor solution coating (PSC) method for fabricating low-temperature sinterable polycrystalline [Pb(Mg1/3 Nb2/3 )O3 ]0.63 -[PbTiO3 ]0.37 (PMN–PT) ceramics. In this method, submicrometer crystalline PMN powder was first obtained by dispersing Mg(OH)2 -coated Nb2 O5 particles in a lead acetate/ethylene glycol solution (first PSC), followed by calcination at 800°C. The crystalline PMN powder was subsequently suspended in a PT precursor solution containing lead acetate and titanium isopropoxide in ethylene glycol to form the PMN–PT precursor powder (second PSC) that could be sintered at a temperature as low as 900°C. The resultant d 33 for samples sintered at 900°, 1000°, and 1100°C for 2 h were 600, 620, and 700 pm/V, respectively, comparable with the known value. We attributed the low sintering temperature to the reactive sintering nature of the present PMN–PT precursor powder. The reaction between the nanosize PT and the submicrometer-size PMN occurred roughly in the same temperature range as the densification, 850°–900°C, thereby significantly accelerating the sintering process. The present PSC technique is very general and should be readily applicable to other multicomponent systems. 相似文献
9.
A possibility to produce microwave (MW) dielectric materials by liquid-phase sintering of fine particles was investigated. Zn3 Nb2 O8 powders with a grain size 50–300 nm were obtained by the thermal decomposition of freeze-dried Zn–Nb hydroxides or frozen oxalate solutions. The crystallization of Zn3 Nb2 O8 from amorphous decomposition products was often accompanied by the simultaneous formation of ZnNb2 O6 . Maximum sintering activity was observed for single-phase crystalline Zn3 Nb2 O8 powders obtained at the lowest temperature. The sintering of as-obtained powders with CuO–V2 O5 sintering aids results in producing MW dielectric ceramics with a density 93%–97% of the theoretical, and a Q × f product up to 36 000 GHz at sintering temperature ( T s )≥680°C. The high level of MW dielectric properties of ceramics was ensured by intensive grain growth during the densification and the thermal processing of ceramics. 相似文献
10.
Gui-hua Peng Min Liang Zhen-hua Liang Qing-yu Li Wen-lan Li Qian Liu 《Journal of the American Ceramic Society》2009,92(9):2122-2124
Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°–1600°C for 3–12 min, using α-Si3 N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%α-Si3 N4 phase left in the sintered material. α-Si3 N4 was completely transformed to β-Si3 N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K)−1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate β-Si3 N4 ceramics with high thermal conductivity when appropriate additives are used. 相似文献
11.
Xiaohui Wang Longtu Li Shuiyuan Su Zhilun Gui 《Journal of the American Ceramic Society》2005,88(2):478-480
The Zn-substituted planar hexaferrite Ba3 Co2− x Zn x Fe24 O41 ( x =0–1.2) powders were prepared via a citrate precursor method. With an appropriate sintering aid, ceramics with high density could be obtained after sintering at a temperature of less than 900°C. These ceramics exhibit excellent high-frequency properties such as high initial permeability up to 10.0 with cut-off frequencies above 1.1 GHz. The results show that we have exploited novel promising ferrimagnetic materials well suited for multilayer chip inductors or multilayer chip beads applications in the high-frequency range. 相似文献
12.
Jae-Yuk Kim Takayoshi Iseki Toyohiko Yano 《Journal of the American Ceramic Society》1996,79(10):2744-2746
The effect of aluminum and yttrium nitrate additives on the densification of monolithic Si3 N4 and a Si3 N4 /SiC composite by pressureless sintering was compared with that of oxide additives. The surfaces of Si3 N4 particles milled with aluminum and yttrium nitrates, which were added as methanol solutions, were coated with a different layer containing Al and Y from that of Si3 N4 particles milled with oxide additives. Monolithic Si3 N4 could be sintered to 94% of theoretical density (TD) at 1500°C with nitrate additives. The sintering temperature was about 100°C lower than the case with oxide additives. After pressureless sintering at 1750°C for 2 h in N2 , the bulk density of a Si3 N4 /20 wt% SiC composite reached 95% TD with nitrate additives. 相似文献
13.
Hyun-Jai Kim Sergey Kucheiko Seok-Jin Yoon Hyung-Jin Jung 《Journal of the American Ceramic Society》1997,80(5):1316-1318
Dielectric properties of the system (1 − x)(La1/2 Na1/2 )TiO3 – x Ca(Fe1/2 Nb1/2 )O3 , where 0.4 # x # 0.6, have been investigated at microwave frequencies. The temperature coefficient of resonant frequency (τf ), nearly 0 ppm/°C, was realized at x = 0.58. These ceramics had perovskite structure and showed relatively low dielectric losses. A new dielectric material applicable to microwave devices having Q · f of 12000–14000 GHz and a dielectric constant (εr ) of 59–60 has been obtained at 1300–1350°C for 5–15 h sintering. 相似文献
14.
Jau-Ho Jean Chia-Ruey Chang Cheng-Dao Lei 《Journal of the American Ceramic Society》2004,87(7):1244-1249
Effects of Ag addition on sintering of a crystallizable CaO-B2 O3 -SiO2 glass have been investigated at 700°–900°C in different atmospheres. With Ag content increasing in the range of 1–10 vol%, the softening point, the densification, the onset crystallization temperature, and the total amount of crystalline phase formed of the crystallizable glass are reduced when fired in air. A bloating phenomenon is observed when the crystallizable CaO-B2 O3 -SiO2 glass doped with 1–10 vol% Ag is fired at 700°–900°C for 1–4 h. Fired in N2 or N2 + 1% H2 , however, the above phenomena disappear completely. It is thus believed that the diffusion of Ag into the crystallizable glass, which is caused by the oxidation of Ag in air, is the root cause for the above results observed. 相似文献
15.
Lead-based ferroelectric (FE) ceramics exhibit superior electromechanical properties; therefore, there has been an increased focus on developing new lead-based FE materials with high Curie temperature ( T c ) and enhanced properties. The aim of this study was to investigate new compositions in the Pb(Mg1/3 Nb2/3 )O3 –Pb(Yb1/2 Nb1/2 )O3 –PbTiO3 ( PMN–PYbN–PT) system to enhance the electromechanical properties while increasing the T c and lowering the sintering temperature. The 0.575[0.5PMN–0.5PYbN]–0.425PT composition at PMN/PYbN (50/50) mole ratio were prepared by reactive sintering PMNT and PYbNT powder mixtures at 950°–1200°C for 4 h. PMNT and PYbNT powders were calcined via the columbite method. Samples were prepared by cold isostatic pressing at 80 MPa. Dense and fully perovskite 0.575[0.5PMN–0.5PYbN]–0.425PT ceramics were fabricated at 975°C for 4 h, and these samples displayed a remnant polarization ( P r ) of 32 μ C/cm2 , coercive field ( E c ) of 17 kV/cm, and a piezoelectric charge coefficient ( d 33 ) of 475 pC/N. It is proposed that this ternary system can be tailored for various applications. 相似文献
16.
Shun J. Wu Lutgard C. De Jonghe Mohamed N. Rahaman 《Journal of the American Ceramic Society》1996,79(8):2207-2211
The sintering of ultrafine γ-Al2 O3 powder (particle size ∼10–20 nm) prepared by an inert gas condensation technique was investigated in air at a constant heating rate of 10°C/min. Qualitatively, the kinetics followed those of transition aluminas prepared by other methods. Measurable shrinkage commenced at ∼ 1000°C and showed a region of rapid sintering between ∼1125° and 1175°C followed by a transition to a much reduced sintering rate at higher temperatures. Starting from an initial density of ∼0.60 relative to the theoretical value, the powder compact reached a relative density of 0.82 after sintering to 1350°C. Compared to compacts prepared from the as-received powder, dispersion of the powder in water prior to compaction produced a drastic change in the microstructural evolution and a significant reduction in the densification rate during sintering. The incorporation of a step involving the rapid heating of the loose powder to ∼1300°C prior to compaction (which resulted in the transformation to α-Al2 O3 ) provided a method for significantly increasing the density during sintering. 相似文献
17.
Ki-Woong Chae† Doh-Yeon Kim Koichi Niihara 《Journal of the American Ceramic Society》1995,78(1):257-259
The results obtained from the sintering of Al2 O3 –50TiC (in weight percent) composite in the temperature range from 1650° to 1800°C with addition of Y2 O3 are presented. Densification is accelerated by the formation of liquid at temperatures above 1750°C, and 99% of theoretical density can be achieved by vacuum sintering at 1800°C for 15 min. The liquid presented at the sintering temperature is crystallized to YAG (Y3 Al5 O12 ) during cooling. 相似文献
18.
Janez Bernard reja Benan Tadej Rojac Janez Holc Barbara Mali Marija Kosec 《Journal of the American Ceramic Society》2008,91(7):2409-2411
The objective of this work was to lower the sintering temperature of K0.5 Na0.5 NbO3 (KNN) without reducing its piezoelectric properties. The KNN was sintered using 0.5, 1, 2, and 4 mass% of (K, Na)-germanate. The influence of the novel sintering aid, based on alkaline germanate with a melting point near 700°C, on the sintering, density, and piezoelectric properties of KNN is presented. The alkaline-germanate-modified KNN ceramics reach up to 96% of theoretical density at sintering temperatures as low as 1000°C, which is approximately 100°C less than the sintering temperature of pure KNN. The relative dielectric permittivity (ɛ/ɛ0 ) and losses (tanδ), measured at 10 kHz, the piezo d 33 coefficient, the electromechanical coupling and mechanical quality factors ( k p , k t , Q m ) of KNN modified with 1 mass% of alkaline germanate are 397, 0.02, 120 pC/N, 0.40, 0.44, and 77, respectively. These values are comparable to the best values obtained for KNN ceramics sintered above 1100°C. 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.
CaCu3 Ti4 O12 (CCTO) ceramics with high dielectric constant (2–4 × 104 ) and low loss (0.04) were prepared by the sol–gel process and sintered at 1050°C for different times. The sintering time has a sensitive influence on the values of the dielectric constant and nonlinear coefficient. Tailored dielectric constant and nonlinear coefficient can be obtained by selecting a suitable sintering time according to different desired device application. The result of current–voltage characteristics and Cole–Cole plots in a broad temperature range (60–400 K) provide more effective evidence of the high dielectric constant supported by the grain boundary barrier layer (GBBL) capacitors model. Below 150 K, the GBBL capacitors effect weakens and gradually disappears with further decrease of temperature, thus leading the dielectric constant to decrease rapidly. Two values of grain activation energy acting at different temperature for each sample were obtained. 相似文献