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71.
Xue-Kai Lan Jie Li Jia-Pu Li Fei Wang Wen-Zhong Lu Xiao-Chuan Wang Wen Lei 《Journal of the American Ceramic Society》2020,103(2):1105-1112
Novel LiAl5−xZnxO8−0.5x microwave dielectric ceramics were synthesized through a solid-state reaction route. Phase evolution of LiAl5−xZnxO8−0.5x was determined by XRD analysis. The XRD results indicated that the phase compositions had a P4332 space group when 0 ≤ x ≤ 0.2 and a spinel structure when 0.3 ≤ x ≤ 0.5. The dielectric constant (εr) of this series’ solid solutions decreased with the increase in Zn doping content, which was in good agreement with the Clausius-Mossotti relation. Oxygen vacancy and the decreased degree of order degraded the quality factor (Q × f) of the two structures. The deterioration in quality factor was further verified by impedance spectroscopy. The temperature coefficient of the resonant frequency (τf) decreased with the increase in x and was correlated with the unit cell volume. Finally, CaTiO3 was used as a compensation material to obtain a near-zero τf of the LiAl5O8 ceramic. 相似文献
72.
Modification of the microwave dielectric properties in Ba6−3 x Nd8+2 x Ti18 O54 ( x = 0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near-zero temperature coefficient combined with high Qf values were obtained in modified Ba6−3 x Nd8+2 x Ti18 O54 solid solutions where an enlarged solid solution limit of Bi in Ba6−3 x Nd8+2 x Ti18 O54 was observed. Excellent microwave dielectric characteristics (ɛ= 105, Qf = 4110 GHz, and very low τf ) were achieved in the composition Ba6−3 x (Nd0.7 Bi0.18 Sm0.12 )8+2 x Ti18 O54 . 相似文献
73.
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
74.
Electric-Field-Controlled Permittivity Ferroelectric Composition for Microwave LTCC Modules 总被引:1,自引:0,他引:1
Tao Hu Heli Jantunen Anatoli Deleniv Seppo Leppävuori Spartak Gevorgian 《Journal of the American Ceramic Society》2004,87(4):578-583
A low-temperature cofired ferroelectric ceramic composition for electrically tunable radio frequency devices is introduced. A sintering temperature of 950°C for BaSrTiO3 –MgO was obtained following the combined addition of B2 O3 and Li2 CO3 . The effects of these sintering aids on densification, microstructure, and ferroelectric properties were investigated. The permittivity and dissipation factor values were 234 and 0.0010, respectively, measured at 286.3 K, 1 kHz. The electrically tunable ferroelectric structure for microwave measurement was fabricated throughout the tape-casting process. Measured permittivity was 130 at 26 GHz and tunability >15% (4 V/μm). 相似文献
75.
用流动注射法测量含颗粒物水样中总氮,采用较粗管路和快速微波消解法,水样经预处理后,再使用自制在线过滤装置除去消解残渣。总氮的检出限为0.040mg/L,检测范围为0~10.0mg/L。本方法连续测定含悬浮颗粒水样,流路无堵塞,对湖水、生活污水和工业废水实际含悬浮颗粒水样中总氮的测定,加标回收率为99.6%~103.5%。 相似文献
76.
Villa C Baldassari S Gambaro R Mariani E Loupy A 《International journal of cosmetic science》2005,27(1):11-16
Solid-liquid solvent-free phase transfer catalysis (PTC) and acidic catalysis in dry media were applied, with noticeable improvement and simplification over classical procedures in a Green Chemistry context, to the synthesis of some aromatic esters useful as cosmetic ingredients: 3-methylbutyl 4-methoxycinnamate, 2-ethylhexyl 4-methoxycinnamate, 2-ethylhexyl 4-(dimethylamino)benzoate and 2-ethylhexyl salicylate, well-known ultraviolet B sunscreen filters; 4-isopropylbenzyl salicylate, UV absorber and cutaneous antilipoperoxidant; propyl 4-hydroxybenzoate and butyl 4-hydroxybenzoate (parabens), antimicrobial agents. The reactions were performed under microwave (MW) activation and conventional heating. The best results for the synthesis of cinnamic, salicylic and 4-(dimethylamino)benzoic esters were achieved by in situ preformed carboxylates alkylation with alkyl bromides using PTC. The 4-hydroxybenzoates were obtained in good yields by classical esterification of the acid with alcohols using a simple heterogeneous mixture of reagents with catalytic amounts of p-toluenesulfonic acid (PTSA). The comparisons of yields and thermal profiles under either MW or conventional heating were studied and reported. 相似文献
77.
Hisako Hirai Osamu Fukunaga Osamu Odawara 《Journal of the American Ceramic Society》1991,74(7):1715-1718
The effect of microwave power on the hydrogen and amorphous carbon contents of diamond films is investigated by the plasma chemical vapor deposition method. The input microwave power during diamond synthesis is varied between 330 and 500 W by using different holder materials, while a constant substrate temperature of 850°C is maintained. The hydrogen content in the synthesized diamond is measured by secondary ion mass spectrometry, and the relative amount of amorphous carbon is estimated from the Raman spectra. The hydrogen count normalized against that of carbon decreases logarithmically with increasing input power; the amorphous carbon amount also decreases with higher input power. The present experimental results prove that hydrogen content can be controlled by varying input microwave power during diamond deposition. 相似文献
78.
Tatsuo Ohgushi Kazushi Ishimaru Sridhar Komarneni 《Journal of the American Ceramic Society》2001,84(2):321-27
The thermal disintegration processes of A-type zeolites and the properties of the materials that were formed after microwave heating (at 2.45 GHz) were studied. The thermal disintegration of 4A-type zeolite proceeded as follows: disintegration at ∼880°C, followed by transformations to high-carnegieite 1 at ∼920°C, nepheline (in nepheline(4A) form) at ∼990°C, and high-carnegieite 2 at ∼1254°C (further heating led to melting at ∼1526°C). High-carnegieite 1, nepheline(4A), and high-carnegieite 2 efficiently absorbed microwaves. Cooling of the molten material yielded low-carnegieite that contained some impurities. The change of 3A-type zeolite proceeded as follows: disintegration at ∼910°C and transformation to nepheline (in nepheline(3A) form) at ∼1006°C. In 3A-type zeolite, in contrast to 4A-type zeolite, carnegieite did not form before the crystallization of nepheline(3A). Nepheline of high purity and carnegieite with some impurities were synthesized easily by heating 3A- and 4A-type zeolites, respectively, using microwaves. These results suggest that the microwave heating of zeolites can be used to prepare some ceramic materials. 相似文献
79.
80.
Hirotsugu Takizawa Kyota Uheda Tadashi Endo 《Journal of the American Ceramic Society》2000,83(9):2321-2323
(In0.67 Fe0.33 )2 O3 with the bixbyite structure was synthesized via 28 GHz microwave irradiation, using multimode microwave heating equipment. Indium sesquioxide strongly absorbs 28 GHz microwaves, and this strong coupling with microwave energy can be used to drive a reaction with iron sesquioxide. A mixture of In2 O3 and α-Fe2 O3 powders (In:Fe ratio of 2:1) was irradiated with microwaves at a frequency of 28 GHz. The mixture was heated to 1400°C during the microwave irradiation. The formation of a solid solution was completed within a minute, which indicated a drastic enhancement of the reaction rate. Scanning electron microscopy revealed remarkable grain growth under microwave irradiation. 相似文献