Liquid phase low temperature sintering of niobate and cerate fine powders

The efficiency of simultaneous application of chemically-derived starting powders and melt-forming sintering aids in low temperature sintering has been demonstrated. Doping of cryochemically processed BiNbO₄ powders with CuO/V₂O₅ causes reducing sintering temperatures from 850–900^∘C to 700–720^∘C. Similar doping of Zn₃Nb₂O₈ fine powders allows to obtain ceramics with density 97–98% and Q × F values up to 40 000 GHz at T > 720^∘C. The sintering of solution-derived BaCeO₃ powders doped with CuO results in dense ceramics at T = 1000^∘C. Morphological evolution during sintering was observed using hot stage SEM. Low temperature liquid phase sintering of fine powders is rather sensitive to the traces of secondary phases and to the micromorphology of starting powders though observed reduction of sintering temperatures is substantially larger than for traditional liquid phase sintering of coarse-grained oxide powders.     

Microstructure and densification mechanism of low temperature sintering Bi-Substituted yttrium iron garnet

The low temperature sintering and densification mechanism of Bi-substituted yttrium iron garnet (Bi:YIG) polycrystalline samples were studied in this paper. The Bi:YIG polycrystalline samples, with the composition of Y_3?x Bi _x Fe₅O₁₂ (x?=?0–1.2), were prepared by the solid-state reaction method. The X-ray diffraction (XRD) patterns show that Bi-substitution can lower the formation temperature of garnet phase from about 1200 to 900 °C and the thermo-mechanical analysis (TMA) indicates that the sintering temperature of ceramics can be decreased from over 1350 °C to below 1000 °C. The microstructure of grains and grain boundaries was observed by high resolution electron microscopy (HREM). The bismuth distribution in grains and grain boundaries was performed by X-ray energy dispersive spectroscopy (EDS). The occurrence of liquid phase with Bi-contained oxide in the sintering process caused the decrease in sintering temperature.     

Low temperature preparation of ferroelectric SrBi2Ta2O9 thin films by a modified RF magnetron sputtering technique

Abstract

Bi–layered ferroelectric SrBi₂Ta₂O₉ (SBT) films were successfully prepared on Pt/Ti/SiO₂/Si substrates at 650°C by a modified rf magnetron sputtering technique. The SBT films annealed for 1 h in O₂ (760 torr) and again for 30 min in O₂ (5 torr) at 650°C show a average grain size of about 49 nm. The SBT films annealed at 65 0°C have a remanent polarization (P_r) of 6.0 μC/cm² and coercive field (E_c) of 36 kV/cm at an excitation voltage of 5 V. The films showed fatigue–free characteristics up to 4.0 × 10¹⁰ switching cycles under 5 V bipolar pulse. The retention characteristics of SBT films looked very promosing up to 1.0 × 10⁵ s.     

Preparation and evaluation of temperature-sensitive magnetic film with low Curie temperature

Up to now, only bulk materials and thick films were available for use as temperature-sensitive substances. However, due to the high heat capacity of these substances, their sensitivity is too low for the detection of minute temperature variations. General trends toward the miniaturization and weight reduction of electronic equipment necessitate development of thin films having magnetic properties. No technology for the preparation of temperature-sensitive magnetic thin films (TMF) has existed so far because of difficulties related to the adjustment of the mixture ratio of TMF materials composed of Fe, Mn, and Zn oxides. The authors investigated a method of fabrication of TMF by annealing of the film formed by the sputtering of a target consisting of temperature-sensitive ferrites with low Curie temperature. This method involves a two-step processing: depositing the metal components of temperature-sensitive ferrites on a substrate by sputtering and a high-temperature annealing treatment performed in a flow of argon gas in a tank containing oxygen. As a result, a ferrite thin film (thickness 1.5 μm) with spinel structure can be fabricated. The TMF characteristics closely reproduce parameters of the temperature-sensitive ferrites used in the target. The TMF so obtained also have an exceptional temperature dependence and a low heat capacity, thus providing for a prompt response to minute temperature variations of the order of 10^–1 °C. Therefore, the TMF are expected to find use in such applications as pyromagnetic sensors, optimized artificial sensors, and biosensors. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 17–23, 1999     

The effect of Bi substitution on phase formation and low temperature sintering of Y-type hexagonal ferrite

Polycrystalline Y-type hexagonal ferrite, with composition of Ba_2?x Bi _x Zn_0.8Co_0.8+x Cu_0.4Fe_12?x O₂₂ (x?=?0～0.4), was prepared by the solid state reaction method. The effect of Bi substitution on phase formation, sintering process and magnetic properties were investigated in detail. The phase formation process was characterized by the means of powder X-ray diffraction (XRD). Bi³⁺ can substitute Ba²⁺ in Y-type hexagonal ferrite as divalent metal ion Co²⁺ substitute Fe³⁺ at the same time for electrovalence balance. As Bi amount is less than 0.3, the phase formation of Y-type hexagonal ferrite will not be destroyed. As Bi amount further increases, the lattice mismatch induced by the difference in ionic radii of Bi³⁺ and Ba²⁺ ions prevents the formation of pure Y-type phase. The samples with proper Bi substitution (0.05?<?x?<?0.3) have much lower phase formation temperature than that of the samples without Bi substitution. Bi substitution can also promote the sintering process. As x?>?0.1, the samples can be sintered well under 900 °C without any other addition. These materials are suitable for multilayer chip inductive components and devices.     

The structure and dielectric properties of low temperature sintering barium titanate based x7r ceramics

In this paper we try to do systematic investigation on the structure and dielectric properties of low temperature sintered barium titanate based X7R ceramics, which are doped with rare earth oxide, Nb₂O₅, Co₃O₄ using ZnO–B₂O₃ as the sintering aids. The dielectric ceramic powder can be sintered at the temperature below 950°C to satisfy X7R requirement and also with good permittivity and low dielectric loss. The research strongly suggest that this doped BaTiO₃ based ceramic, which can be sintered at a rather low temperature, may be used in the production of MLCC with low content of Pd in the Ag–Pd electrode, and for sure, the production cost would be greatly reduced.     

阀控铅蓄电池在低温下的充放电行为

论述了阀控铅蓄电池在低温下的充放电行为，对影响铅蓄电池低温放电行为的主要因素：膨胀剂、放电电流密度、充电状态、温度、电解液密度及隔板饱和度进行了分析与讨论。由于贫液，阀控铅蓄电池更容易因电阻增大、离子扩散困难影响其低温大电流放电性能。但是，解决阀控铅蓄电池低温启动放电问题最主要的还是膨胀剂，以防止负极钝化。因低温条件下铅蓄电池的充电效率很低，为保持阀控铅蓄电池的性能，应避免对其进行低温充电。     

膨胀石墨的低温制备及储能性能研究

采用改进的Hummers法制备氧化石墨,并对氧化石墨进行水热处理和后处理,得到了最终产物样品。通过对产物样品进行X射线衍射分析(XRD)、扫描电子显微镜(SEM)、红外光谱测试(FTIR)及拉曼测试(Raman),研究了其形貌、结构和化学键结合,同时并对其电化学性能进行表征,研究结果发现,通过对氧化石墨简单水热处理后,得到了膨胀石墨。提出了一种制备膨胀石墨的新方法,即低温水热法,此方法可以避免高温烧结的过程,降低了能耗并减少了成本。将其用于锂离子电容器正极材料,在100 m A/g的电流密度下,其放电比容量达到43 m Ah/g,循环稳定性较好,容量保持率接近100%。     

阀控式密封铅蓄电池内阻与低温起动能力

阀控式密封铅蓄电池（ＶＲＬＡ）电流放电初期出现的电压降主要是由电池欧姆内阻引起的。板栅和极柱连接件的电阻是电池欧姆内阻的主要成分。合理设计板栅结构、提高正板栅铅钙合金中的锡含量和负极活性物质中的碳含量,将会有利于提高电池的低温起动力。     

密封铅酸蓄电池内阻与低温起动能力

阀控式密封铅酸蓄电池（ＶＲＬＡ）大电流放电初期出现的电压降主要是由电池欧姆内阻引起的。板栅和极柱连接件的电阻是电池欧姆内阻的主要成分。合理设计板栅结构,提高正板栅铅钙合金中的锡含量和负极活性物质中的碳含量,将会有利于提高电池的低温起动能力。     

低温下DMFC性能特性及传热传质分析

对自制有效面积为4.41cm2的直接甲醇燃料电池进行了低温(5℃)运行条件下的性能测试及分析,并着重研究了甲醇浓度,甲醇溶液流速和氧气流速等运行参数对电池性能的影响。实验结果表明,电池性能随运行温度的下降而降低。在较低运行温度下,运行参数对电池性能的影响有别于常温及以上温度条件下的规律。在运行温度为5℃时,高浓度和低流速甲醇溶液可获得较高的比功率;在本实验范围内,电池性能在氧气流速为100mL/min时达到最佳。     

ViCo0.98-xTi0.02LaxO2的高温固相法合成及其电化学性能

以Li2CO3、Co3O4为原料,采用高温囿相法制备了钮离子电池正极材料LiCo0.98-xTi0.02LaxO2(x=0,0.01,0.03,0.05).采用扫描电镜(SEM)、恒流充放电研究了材料的表面形貌和电化学性能,结果表明:掺杂La后材料的D50略有增大,放电平台电压升高;在2.75～4.20 V电位范围内,LiCo0.97Ti0.02La0.01O2的首次1 C放电比容量达到143.86 mAh/g,50次循环后容量保持率为97.0%,且具有很好的倍率性能.     

某2030 t/h W火焰锅炉低负荷下再热汽温偏低原因分析及对策

某600 MW机组W火焰锅炉75%以下负荷时存在再热汽温较设计值(541℃)偏低问题,严重影响机组运行经济性。本文通过锅炉热力计算并结合炉内温度CFD分析,对再热汽温偏低原因进行了研究。结果表明:300 MW负荷下通过常规的运行调整方式无法提升再热汽温;锅炉低负荷下再热汽温偏低是高温对流受热面积分配相对不合理所致。对此,提出了增加低温再热器和高温再热器面积,减少高温过热器面积等方案,其中增加低温再热器和高温再热器受热面虽能够提高再热汽温达到设计值,但烟道布置空间受限,工程上无法实施,而减少高温过热器受热面积2 792 m2,能够在50%负荷下提升再热汽温到设计值,且可以控制再热器减温水量在0 t/h。虽然锅炉效率下降影响发电煤耗升高,但整体对煤耗的改善明显。     

常温制备硫碳均匀复合材料

采用沉淀法制备硫溶胶,通过活性炭吸附溶胶中纳米尺度的硫颗粒,在常温下制得硫碳均匀复合材料,并将该复合材料用于锂硫电池正极。通过SEM和XRD对该复合材料进行表面形貌和内部结构表征,采用恒流充放电法和电化学阻抗测量法测试正极的电化学性能。测试结果表明,活性炭吸附的硫颗粒直径在50 nm附近,且硫在活性炭中均匀分散。在电流密度为0.2 mA/cm2时,含该复合材料正极的首次放电比容量为793 mAh/g。循环充放电50次后,正极放电比容量为460 mAh/g。     

Investigation on structural and electrical properties of BZT ceramics synthesized at low temperature

Abstract

Due to environmental concerns, lead free ceramics such as KNN- NBT and BT have growing interest in applications such as actuators and sensors. Among them Barium Zirconate Titanate (BZT) has become most attractive because it is derived from two perovskite lattice i.e. Barium Titanate (BaTiO₃) and Barium Zirconate (BaZrO₃). It has been reported that Zirconium substitution in titanium lattice enhances the material properties. In the present paper BZT was prepared using solid state route. By adding a mixture of Li₂CO₃ as a sintering aid, the sample could be sintered at 1150?°C having around 94% of the theoretical density. Prepared samples were then subjected to XRD analysis. X-ray diffraction revealed the formation of single phase material. It is observed that the electrical properties of such low-temperature sintered samples are comparable with BZT samples prepared via conventional sintering at a high temperature. It is also observed that the curie temperature shift towards room temperature for a samples sintered at low temperature.     

Characterization and properties of anatase TiO2 film prepared via colloidal sol method under low temperature

Nanocrystalline titanium dioxide particles and films with anatase structures have been prepared via solvothermal method under low temperature. The products were characterized by X-ray diffraction and transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The optical properties were characterized in the ultraviolet-visible region by optical absorption measurement. The relationship between the optical band gaps and the structures was studied.