Investigation of microwave dielectric properties in the BaO–Nb2O5–P2O5 system

BaNb₂P₂O₁₁ and Ba₃Nb₂P₄O₁₈ compounds with corner-sharing NbO₆ octahedra and PO₄ tetrahedra were prepared by a conventional solid-state reaction method. The crystal structure and microstructure were investigated by X-ray powder diffraction and field emission scanning electron microscope, respectively. The microwave dielectric properties were measured using a network analyzer. Both ceramics were sintered at a relatively low temperature of 1150 °C and had a relative density of ～96%. Compared to Ba₃Nb₂P₄O₁₈, BaNb₂P₂O₁₁ had a higher permittivity of 31.7. However, the quality factor of BaNb₂P₂O₁₁, was smaller than Ba₃Nb₂P₄O₁₈. Furthermore, the effect of the crystal structure on the microwave dielectric properties was investigated.     

Effects of ZnO–xV2O5 substitution on the microstructure and microwave dielectric properties of ZnNb2O6 ceramics

The ZnO–xV₂O₅ substituted ZnNb₂O₆ ceramics with chemical formula Zn(Nb_0.9V _x )₂O_5.5+5x (0?<?x?≤?0.10) were prepared by solid-state reaction route. The densities, microstructures and microwave dielectric properties were investigated according to the different substitution amount of V₂O₅ and sintering temperature. A small amount of substitution of ZnO–xV₂O₅ was effective to lower sintering temperature of ZnNb₂O₆ ceramics from 1,150 °C to 900 °C. The V₂O₅ substitution led to growth of rod-like grains with the help of liquid phase formed from ZnO and V₂O₅. The dielectric properties depended largely on the amount of V₂O₅ substitution and sintering temperature. The dense ceramics with x?=?0.05 were obtained at 950 °C, which had excellent dielectric properties: ?_r?=?24, Q?×?f?=?72,800 GHz and τ_f?=??63.5 ppm/°C. The interface analysis for cofired multilayer composites composed of the present LTCC and metal Ag demonstrated good co-firing chemical compatibility at co-sintering temperature.     

On O16–O18 Isotope Effects in Manganese Perovskites

Large isotope effects which have been found by others [1,2] in some colossal magneto resistance manganite perovskites, AMnO₃, are evidence of unusually strong interactions between the lattice and magnetism. We offer a model which is based upon the approximate degeneracy of two Mn⁺³ states: one with high spin S = 2, and the other with low spin S = 1. These states have different radii and different electron form factors. They thus have different force constants governing the interaction with neighboring oxygen ions which provide the sought for link between magnetism and oxygen mass. The experiments can be understood with the reasonable assumption that the LS has greater force constants than HS. The dependence of changes in T_c with isotopic substitution as a function of the A-ion radius, the metal insulator transitions and the Mossbauer effect changes, are discussed in terms of this model.     

Synthesis and dielectric properties of Ba2TiSi2O8 glass-ceramics from the sol–gel process

The Ba₂TiSi₂O₈ glass-ceramics were prepared by sol–gel process using barium acetate, titanium butoxide, tetraethoxyorthosilicate and boric acid as raw materials. Because of the existence of glass and sintering additive, the Ba₂TiSi₂O₈ glass-ceramics can be sintered at 880 °C in air. The structure of sintered sample was characterized by means of XRD and SEM. XRD patterns showed that fresnoite Ba₂TiSi₂O₈ is the dominant crystalline phase in the sintered samples. SEM images indicated that the shape of Ba₂TiSi₂O₈ grains varied with the molar ratio of ([Ba(Ac)₂/Ti(OBuⁿ)₄/Si(OEt)₄]). With an increase of Si(OEt)₄ content, the length/diameter ratio of Ba₂TiSi₂O₈ grains decreases. The Ba₂TiSi₂O₈ glass-ceramics studied in this work have ?_r in the range of 6–12 (100 MHz) and demonstrate very low dielectric losses (tanδ <2?×?10^?3, 100 MHz). The experimental results suggested that the Ba₂TiSi₂O₈ glass-ceramics could be used as dielectric materials for low temperature co-fired ceramics (LTCC) process.     

Characterization of luminescent properties of Sr–Ca–Al–O multi-phases oxide phosphors

Multi-phases phosphors, which could exhibit red, green, and blue emission bands simultaneously, were synthesized by the solid-state reaction method with a flux. Starting materials of SrCO₃, CaCO₃, and Al₂O₃ were mixed and fired. H₃BO₃ and Eu₂O₃ were added as a flux and a dopant, respectively. Effects of the excitation energy and the mixing ratio of starting materials on the luminescent properties were investigated. Phase transformations and variations of luminescent properties were also observed as a function of H₃BO₃ flux amounts. Emission wavelength and intensity depended on the excitation energy as well as H₃BO₃ flux amounts. The mixture of 8SrCO₃–4CaCO₃–11Al₂O₃–0.8H₃BO₃–0.18Eu₂O₃ showed red, green, and blue emission by exciting at near UV, while 8SrCO₃–4CaCO₃–11Al₂O₃–1.2 and 1.6H₃BO₃–0.18Eu₂O₃ exhibited strong red emissions.     

CuO/g-Al2O3和CuO-CeO2-Na2O/g-Al2O3催化吸附剂的脱硝性能

利用改进的溶胶凝胶法制备纳米孔径的CuO/γ-Al2O3和CuO-CeO2-Na2O/γ-Al2O3催化吸附剂颗粒,在固定床上测试其催化脱硝活性。两类催化吸附剂250～400℃范围内脱硝效率稳定在70％以上。在350℃时效率稳定在最高值。利用程序升温方法研究了两类催化剂对NH3和NO的氧化性能,发现NH3在高于400℃下急剧氧化,是脱硝效率下降的主要原因。CuO/γ-Al2O3催化剂能将NO氧化生成NO2,NO2生成有利于脱硝反应的进行。NO在催化剂上的吸附对脱硝过程有重要作用。改进的CuO-CeO2-Na2O/γ-Al2O3催化剂能使NH3在高温400℃下不被氧化,也促进了NO在催化剂表面的吸附,从而提高催化剂了脱硝效率。催化剂反应的机理为NO吸附在催化剂表面,氧化生成吸附态的NO2,其再与吸附催化剂上的NH3反应。     

V2O5含量对Bi2O3-V2O5复合添加NiCuZn铁氧体性能的影响

用传统陶瓷工艺制配了(Ni0.16Cu0.2Zn0.64O)1.02(Fe2O3)0.98铁氧体材料,研究了Bi2O3-V2O5复合添加对材料烧结特性和磁性能的影响.结果表明,复合添加bi2O3-V2O5能促进样品致密化、提高起始磁导率和品质因数.当添加0.3wt%Bi2O3、0.15wt%V2O5时,930℃烧结起始磁导率μi＞800、品质因数(94)、密度(5.12 g/cm3)都达到较大值,比同样配方只掺杂Bi2O3的NiCuZn材料明显提高.     

Y2O3/La2O3/Al2O3/Cu复合材料的制备与性能

采用含氧氮气(N2/O2)雾化喷射沉积技术制备Y-La-Al-Cu系多元系合金,通过化学反应原位生成(内氧化法)Y2O3/La2O3/Al2O3/Cu多相氧化物颗粒增强铜基复合材料,并对材料的显微组织、力学物理性能和电学性能进行研究.结果表明,通过喷射沉积技术并结合内氧化工艺,可制得具有较好微观组织、形成的增强相弥散分布于基体、组织致密的Y2O3/La2O3/Al2O3/Cu多相氧化颗粒增强铜基复合材料;随着冷加工变形量的增加,Y2O3/La2O3/Al2O3/Cu多相氧化颗粒增强铜基复合材料的抗拉强度和硬度提高,而材料的延伸率与导电率逐渐降低     

2O12-2O13中国消费电子领先品牌TOP1O名单火热出炉

本刊最新消息,2013年1月9日,第46届国际消费电子展（CES）现场,由美国国际数据集团IDG主办,被誉为“中国消费电子产业的奥斯卡”的2012．2013中国消费电子领先品牌TOPl0评选揭晓了最终的评选结果,海尔、海信、长虹、TcL、长城、康佳、联想、京东方、     

Piezoelectric properties of MnO2 doped low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr0.50Ti0.50)O3 ceramics

In this study, in order to develop the composition ceramics for low loss and low temperature sintering multilayer piezoelectric actuator, Pb(Mn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.50Ti_0.50)O₃ (abbreviated as PMN-PNN-PZT) ceramics were fabricated using Li₂CO₃ and Na₂CO₃ as sintering aids, and their piezoelectric and dielectric characteristics were investigated according to the amount of MnO₂ addition. At the 0.2 wt% MnO₂ doped specimen sintered at 900 °C, density and mechanical quality factor (Q _m) showed the maximum values of 7.81[g/cm³]and 1186, respectively. And also, at 0.1 wt% MnO₂ doped specimen, electromechanical coupling factor (k _p), piezoelectric constant (d ₃₃) of specimen showed the maximum values of 0.608 and 377[pC/N], respectively. Dielectric constant (? _r) slightly decreased with increasing MnO₂. Taking into consideration the density of 7.81[g/cm³], electromechanical coupling factor (k _p)of 0.597 the mechanical quality factor (Q _m) of 1,186, and piezoelectric constant (d ₃₃) of 356[pC/N], it could be concluded that 0.2 wt% MnO₂ doped composition ceramics sintered at 900 °C was best for low loss and low temperature sintering multilayer piezoelectric actuator application.     

杂相Mn2O3对尖晶石LiMn2O4容降的影响

用扫描电镜、X-射线衍射、等离子体原子发射光谱、热重分析、循环伏安、恒电流充放电、交流阻抗法研究作了比较.熔盐法制备的样品的了溶胶-凝胶法合成的尖晶石锂锰氧化物的物理化学性能,并与熔盐法合成样品颗粒为不规则块状,初始容量低（99.6 mAh/g）,而溶胶-凝胶法制备样品的颗粒细小、均匀,初始容量较高（112.5 mAh/g）.但是熔盐法制备的样品经30次循环后容降为15%,而溶胶-凝胶的却高达40%.熔盐法制备的样品中实际Li/Mn为0.506,与原料中Li/Mn摩尔比相近,而溶胶-凝胶法只有0.473,比原料中的小.熔盐法制备的样品为纯尖晶石结构,而溶胶-凝胶法制备的有杂相Mn2O3生成.热处理过程中部分Li的挥发损失和非电化学活性Mn2O3的生成导致锂锰氧化物容量快速下降.     

CJO-2O铁芯生产自动线

长期以来,低压电器中的铁芯生产是整个行业中较薄弱环节之一。以往的手工生产不仅效率低,而且操作上很不安全。过去我们也作了一些努力,但一直没有解决。这次我们在上级党委领导下,厂院结合,组成了以工人为主体的三结合设计小组,按照毛主席关于"一个正确的认识,往往需要经过由物质到精神,由精神到物质,即由实践到认识,由认识到实践这样多次的反复,才能     

Al2O3包覆LiMn2O4阴极材料的动力学研究

在尖晶石LiMn2O4颗粒表面包覆Al2O3,获得结构稳定、循环性能优异的锂离子蓄电池阴极材料。采用X射线衍射研究材料晶体结构,通过恒流充放电、循环伏安和交流阻抗(EIS)来研究锂离子在材料中脱嵌和嵌入的动力学机理。电极材料包覆Al2O3以后,交流阻抗图谱上显示有两个半圆和一条斜线,而未包覆的LiMn2O4只有一个半圆和一条斜线。这表明经过Al2O3包覆后,LiMn2O4活性材料与电解液的直接接触被隔断。相应的等效电路也给出,以评估反应动力学。     

O2/CO2和O2/N2气氛下不同煤种的热解与燃烧试验研究

采用热重-质谱联用仪分别研究了3种煤在O2/N2和O2/CO2气氛下的热解和燃烧特性.结果表明,与N2气氛相比,CO2气氛下煤粉的热解过程可分为水分的蒸发、挥发分的释放以及较高温度下煤焦与CO2的气化反应;随燃烧气氛中氧浓度的增加,煤粉的TG-DTG曲线移向低温区,着火温度和燃尽温度降低,煤粉综合燃烧特性指数增大;在相同的燃烧气氛及氧浓度下,PRB次烟煤的着火温度和燃尽温度明显低于Illinois烟煤和Utah烟煤.     

Structure and properties of Zn-doped CoFe2O4 thin films via a sol–gel method

Zn-doped cobalt ferrite Co_0.9Zn_0.1Fe₂O₄ (CZFO) films with the spinel structure were fabricated on Pt(111)/Ti/SiO₂/Si(100) using a sol-gel method, and the effect of annealing temperature and time on structure and magnetic properties of the CZFO thin films were investigated. The coercivity and saturation magnetization of the films are not sensitive to annealing time, and increase with a rise in the annealing temperature below 800 °C. The CZFO thin films annealed at 800 °C show the best crystallization and the highest coercivity (3.5 kOe), and above 800 °C, the coercivities of the films decrease as a result of formation of multi-domains, while the saturation magnetization comes to stable.     

Ni–Mn–Fe–Cr–O negative temperature coefficient thermistor compositions: Correlation between processing conditions and electrical characteristics

A study has been carried out to correlate the effect of sintering temperature on the microstructural, electrical and reliability aspects of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ (x = 0 to 0.3 and y = 0 to 0.3) negative temperature coefficient thermistor compositions prepared by solid-state route. The calcined and sintered compositions were characterized by X-ray diffraction and Scanning Electron Microscopy. The existence of cubic spinel single-phase region was determined by sintering Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ samples in air at temperatures 1150 to 1250 °C. X-ray diffraction patterns of samples sintered above 1200 °C shows additional Bragg reflections of a rock salt structured NiO phase besides normal cubic spinel. A maximum B-value of 4044 K was obtained for Ni_0.75Mn_1.95Cr_0.25Fe_0.05O₄ composition at a sintering temperature 1250 °C/3 h. The reliability of the thermistor compositions were evaluated by performing accelerated ageing based on thermal cycling test. We found that chromium enhances the reliability of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ (x = 0 to 0.3 and y = 0 to 0.3) based NTC thermistor compositions. A maximum reliability of +0.25% resistance drift was observed at sintering temperature 1200 °C for 0.25 mol% chromium content. Excellent reliability of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ NTC thermistor compositions makes it ideal candidates for high-performance thermal sensor applications.     

Piezoelectric and dielectric characteristics of low-temperature-sintering Pb(Mg1/2W1/2)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics according to the amount of PNN substitution

In this study, in order to develop low-temperature-sintering ceramics for multilayer piezoelectric actuator, Pb(Mg_1/2W_1/2)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (abbreviated as PMW–PNN–PZT) ceramics were fabricated using Li₂CO₃ and CaCO₃ as sintering aids and their dielectric and piezoelectric properties were investigated with the amount of Pb(Ni_1/3Nb_2/3)O₃ (abbreviated as PNN) substitution. PMW–PNN–PZT composition ceramics could be sintered up to 870°C by adding sintering aids. At the sintering temperature of 900°C, electromechanical coupling factor (k _p), piezoelectric constant (d ₃₃) and Curie temperature (Tc) in the composition ceramics with 9 ;mol% PNN substitution showed the optimal value of 0.64 517 ;pC/N and 317°C, respectively for multilayer actuator application.     

Dielectric and pyroelectric properties of Li2CO3 doped 0.2Pb(Mg1/3Nb2/3)O3–0.5Pb(Zr0.48Ti0.52)O3–0.3Pb(Fe1/3Nb2/3)O3 ceramics

Relaxor ferroelectric compositions of 0.2Pb(Mg_1/3Nb_2/3)O₃–0.5Pb(Zr_0.48Ti_0.52)O₃–0.3Pb(Fe_1/3Nb_2/3)O₃ (0.2PMN–0.5PZT–0.3PFN) ceramics were doped with different concentrations of Li₂CO₃ and were prepared by a columbite precursor process. Their structural, dielectric and pyroelectric properties were studied. A phase analysis was performed using the X-ray diffraction patterns from 2θ?=?44° to 46°, over which the tetragonal phase displays two peaks, (002)_T and (200)_T, while the rhombohedral phase displays one peak, (200)_R. A well saturated P–E hysteresis loop was obtained for the 0.2PMN–0.5PZT–0.3PFN ceramic doped with 0.2 wt.% Li₂CO₃, and the values for the remnant polarization (P _r) and coercive field (E _c) were 30 μC/cm² and 5.4 kV/cm, respectively. A maximum value of the pyroelectric coefficient, 518 μC/m²K, was obtained for the 0.2PMN–0.5PZT–0.3PFN ceramic doped with 0.3 wt.% Li₂CO₃ at the maximum temperature (T _max) due to the decrease of the binding energy for the polarization charge which in formed at the surface.     

O2/N2和O2/CO2氛围下丙烷层流扩散火焰中碳烟生成数值模拟

富氧燃烧因其在强化燃烧和减少污染物排放方面的优势,被认为是一种极具潜力的清洁燃烧和碳捕集技术。基于有限速率化学反应模型,采用GRI-Mech3.0气相反应机理结合详细的热力学及输运数据,数值研究了2种富氧条件下丙烷同向流动扩散火焰中碳烟的生成,构建非反应性物质FCO2,探究了CO2化学效应对丙烷火焰碳烟生成的影响。结果表明:随着氧体积分数的增加,火焰温度和碳烟体积分数显著增加,火焰高度显著降低,但与O2/N2相比,O2/CO2氛围下火焰温度和碳烟体积分数显著降低,火焰高度显著增加;O2/CO2氛围下通过CO2热效应和化学效应影响火焰形态并降低关键组分H、OH自由基和C2H2的摩尔分数,CO2主要通过降低H自由基摩尔分数从而影响碳烟质量成核率和表面生长速率,而不是通过促进碳烟氧化过程来抑制碳烟的生成。