Low temperature sintering of high performance KNN-based lead-free piezoelectric ceramic using BCBM frit as sintering aid

High performance lead-free (K_0.49Na_0.51)_0.98Li_0.02(Nb_0.77Ta_0.18Sb_0.05)O₃?+?0.5 mol%BaZrO₃ piezoelectric ceramic was selected as base material, while BaO-CuO-B₂O₃-MnO₂ frit was used as sintering aid to lower the sintering temperature. The effect of BaO-CuO-B₂O₃-MnO₂ frit doping amount on the sintering behavior, structure and electrical properties of the ceramics was investigated. The optimal sintering temperature of the ceramics decreased with the increase of frit doping amount. The ceramic with frit doping amount of 1.0 wt.%, sintered at a reduced temperature of 1100°C, exhibited optimal electrical properties as follows: piezoelectric constant d ₃₃?=?345 pC/N, planar electromechanical coupling coefficient k _p?=?44.5 %, mechanical quality factor Q _m?=?135, dielectric constant ε ₃₃ ^T ?=?1210, and dielectric loss tanδ?=?0.018. Together with its relatively high T _c?=?195°C, this ceramic was an excellent candidate for replacing the lead-based piezoceramics in practical applications.     

掺杂物对瓷介电容瓷料性能的影响

研究了La2O3,WO3对于0.90(Sr0.54Pb0.26Ca0.20)TiO3———0.1Bi2O3·3.5TiO2和0.90(Sr0.64Pb0.20Ca0.16)TiO3———0.1Bi2O3·3.5TiO2为系统的中高压瓷介电容瓷料的介电性能的影响,研究表明掺加La2O3对于前者的ε-t曲线有压峰作用,并能降低损耗;WO3的添加对于后者也具有压峰作用,并且同时可以降低高温段(的温度系数。     

Dielectric and sintering properties of NaNbO3 ceramic prepared by Pechini method

NaNbO₃ powders and ceramics were prepared by Pechini method. The pure phase NaNbO₃ was obtained at temperature as low as 350 °C, and then they obtained fine powders were used to prepared ceramics through conventional sintering process. The effect of sintering temperature on microstructure evolution and dielectric properties of NaNbO₃ ceramics has been determined. Results shown that the microstructure of NaNbO₃ ceramics consisted of stacked plates, which was related the liquid phase. It was important to note that the stacked plate configuration forming the grain has not been emphasized before, and these grains support adequate wetting characteristics for the liquid phase in order to achieve fully dense microstructure. Above 1195 °C, a number of angular grains with flat interfaces started to appear, and joined to each other with the sintering temperature increase. The effect of grains morphology on dielectric properties of the NaNbO₃ ceramics was also detected.     

基于脉冲形成线的脉冲方波电源设计

为研究某种高压氧化锌(ZnO)陶瓷压敏电阻的特性,设计了用于该电阻测试所需的高压脉冲方波电源。利用脉冲形成开关和高压脉冲形成线网络相结合的原理,采用固体半导体开关器件来产生触发脉冲信号。运用场畸变火花开关作为脉冲形成开关,去控制由脉冲形成线网络构建的储能单元进行放电。再通过应用脉冲变压器进行传输与能量变换后,最终在这种高压ZnO陶瓷压敏电阻负载上,实现输出电压幅度不大于40 kV、脉冲宽度不小于4μs、脉冲前沿不大于1μs的高压脉冲方波信号。     

Influence of sintering temperature on the flashover performance of alumina insulators in vacuum

This paper reports on the influence of sintering conditions on the flashover/pre-flashover characteristics of alumina insulators in vacuum under an impulse voltage. Four kinds of alumina insulator were studied, which were prepared using the same formula with different sintering conditions. The surface pre-flashover and flashover phenomena of different samples in vacuum have been observed under impulse voltage. Based on the experimental results, the characteristics of pre-flashover and flashover vary with different kinds of test samples. It was found that the insulators with a higher sintering temperature had a lower flashover voltage, and more active preflashover. From a scanning electron microscope (SEM) analysis of alumina insulators, we conclude that the methods of preparing alumina samples can affect their microstructure resulting in a change in the pre-flashover and flashover performance as alumina insulators.     

烧结温度对LiMn2O4结构和性能的影响

采用己二酸辅助溶胶-凝胶法在350～900℃制备了一系列LiMn2O4样品。运用SEM和XRD分析技术研究了不同烧结温度对LiMn2O4结构的影响。结果表明:烧结温度对LiMn2O4正极材料的晶相结构、电化学性能有显著影响,LiMn2O4正极材料晶粒的生成和长大的控制步骤为其合成的温度,材料合成的最佳温度为800℃。在800℃条件下合成的LiMn2O4具有较高的电化学活性和较好的晶相结构,首次放电比容量超过130mAh·g-1,40次循环后,放电容量保持率仍在85%以上。高温合成有利于提高LiMn2O4正极材料的放电容量,低温合成有利于提高其循环性能。     

烧结工艺对纳米Li4Ti5O12性能的影响

以醋酸锂和钛酸四丁酯为原料、冰醋酸和无水乙醇为水解抑制剂和溶剂,采用溶胶-凝胶法经高温烧结制备了纳米Li4Ti5O12负极材料,系统研究了烧结工艺对材料组成、结构和电化学性能的影响.研究表明,烧结温度是影响材料性能的最主要因素,恒温时间次之.采用两步烧结法,将所得前驱体以5C/min的速率升温到600℃,保温6h,然后...     

Influence of sintering temperatures on the electrical property of bismuth sodium titanate based piezoelectric ceramics

A systematic investigation of cerium and stannum doped 0.94(Bi_0.5Na_0.5)TiO₃−0.06BaTiO₃ (Sn&Ce-BNT6BT) based lead-free piezoelectric ceramics is undertaken to understand the influence of sintering temperature on electrical properties. The X-ray diffraction patterns showed that all of the Sn&Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The smaller grain size of Sn&Ce-BNT6BT ceramics was obtained at lower sintering temperature, and more cubical grains of Sn&Ce-BNT6BT ceramics were obtained at higher sintering temperature. The temperature dependence of dielectric permittivity of the compositions exhibited strong dispersion with the increasing temperature, and the dielectric loss tangent increased dramatically while the temperature over 225^∘C. The depolarization temperature T _d of Sn&Ce-BNT6BT ceramics sintered at 1160^∘C was 92.6^∘C. The remnant polarizations P _r for Sn&Ce-BNT6BT ceramics sintered at 1120 and 1200^∘C were found to be 28.8 and 33.4 μC/cm² at room temperature, respectively.     

Leakage current characterization for estimating the conditions of ceramic and polymeric insulating surfaces

Leakage current produced on contaminated ceramic and polymeric insulating surfaces was analyzed using a wavelet transform technique providing time-frequency domain information. Salt-fog tests with and without the deposition of non-soluble contamination were conducted in a laboratory, during which the leakage current was separated into sinusoidal, local arc, or their transition components per halfwave of power frequency. The wavelet transform allowed the detection of the zero-cross point of the base current at 50 Hz without the need for voltage information. The source information regarding the distortion level (I/sub 150 Hz//I/sub 50 Hz/) of the current half-wave separated by the zero-cross point and a time lag to onset in current attributable to arcs are used in order to obtain the above three components. The time-integrated values (cumulative charges) of these components were found to correlate with hydrophobicity and contamination level. It was shown that time variations of the cumulative charges and of their component ratios were useful for estimating the conditions of ceramic and polymeric insulating surfaces.     

DIR-MCFC性能影响因素研究

将甲烷水蒸气重整制氢反应与熔融碳酸盐燃料电池技术相结合,构成了以甲烷为燃料气的直接内重整熔融碳酸盐燃料电池(D IR-M C FC)。考察了影响电池性能的条件,发现反应气压力增加会提高电池性能,反应气压力由0.1M Pa升至0.6 M Pa,在150 m A/cm 2下,电池电压约提高200 m V;增加甲烷流量利于提高电池性能,但需要合理选择甲烷的利用率;常压下,进气水碳比为1时同等电流下电池初始电压较进气水碳比为2时高30～50 m V,而在0.6 M Pa下这两种进气水碳比对电池初性能影响不大;0.6 M Pa、水碳比为1时,催化剂容易积碳,从而降低电池运行的稳定性,因此,电池在较高压力下运行时应适当提高进气水碳比。     

Influence of switching conditions on the VFTO magnitudes in a GIS

Estimation of very fast transient overvoltage (VFTO) has been carried out using EMTP for various switching conditions in a 420 kV gas insulated substation. The variation of VFTO peak along the GIS bus nodes for disconnector and circuit breaker switching operations as well as the variation of VFTO peak with different magnitudes of trapped charges have been studied. The results indicate a distinct pattern of variation of VFTO peak along the nodes of the GIS bus in the case of disconnector switch operation as compared to that of circuit breaker operation. It has also been noticed that the variation of VFTO peak levels are not in direct proportion to the trapped charge present on the HV bus     

Influence of high-energy impact on the physical and technical characteristics of coal fuels

Currently, in the world’s large-scale coal-fired power industry, the combustion of pulverized coal is the most widely spread technology of combusting the coals. In recent years, the micropulverization technology for preparation and combustion of the coal has been developed in this field. As applied to the small-scale power industry, the method of combusting the coal in the form of a coal–water slurry has been explored for years. Fine coal powders are produced and used in the pulverized-coal gasification. Therefore, the coal preparation methods that involve high-dispersion disintegration of coals attract the greatest interest. The article deals with the problems of high-energy impact on the coal during the preparation of pulverized-coal fuels and coal–water slurries, in particular, during the milling of the coal in ball drum mills and the subsequent regrinding in disintegrators or the cavitation treatment of the coal–water slurries. The investigations were conducted using samples of anthracite and lignite from Belovskii open-pit mine (Kuznetsk Basin). It is shown that both the disintegration and the cavitation treatment are efficient methods for controlling the fuel characteristics. Both methods allow increasing the degree of dispersion of the coal. The content of the small-sized particles reground by cavitation considerably exceeds the similar figure obtained using the disintegrator. The specific surface area of the coal is increased by both cavitation and disintegration with the cavitation treatment producing a considerably greater effect. Being subjected to the cavitation treatment, most coal particles assume the form of a split characterized by the thermodynamically nonequilibrium state. Under external action, in particular, of temperature, the morphological structure of such pulverized materials changes faster and, consequently, the combustion of the treated coal should occur more efficiently. The obtained results are explained from the physical point of view.     

温度对LiNi0.45Co0.15Mn0.4O2性能的影响

采用共沉淀法先合成出前驱体Ni0.45Co0.15Mn0.4(OH)2,然后将其与Li2CO3均匀混合后在三种温度下烧结制得正极材料LiNi0.45Co0.15Mn0.4O2。用XRD、SEM和电池测试仪研究了烧结温度对材料结构、形貌和电化学性能的影响。结果表明:材料合成的最佳温度为900℃,在900℃条件下合成的LiNi0.45Co0.15Mn0.4O2具有较好的层状结构和较高的电化学活性,首次放电容量超过130mAh/g,8个循环后,容量保持率为99.1%,而且颗粒形貌呈球形并大小均匀适中。     

运行参数对单体直接甲醇燃料电池性能的影响

分别在不同温度、不同燃料浓度、不同燃料进料速度下测试了单体直接甲醇燃料电池的极化曲线、功率密度曲线以及阴、阳极的极化曲线.结果表明:随着电池操作温度升高电池性能逐渐提高,阳极极化过电位明显减小;但甲醇的渗透速率也同时增大,在阴极产生混合电位,增大了阴极极化;随着进料浓度升高,阳极出现浓差极化的电流密度增大,甲醇渗透速率增加,阴极电化学极化过电位增大;在电池运行温度、阳极燃料浓度一定情况下,进料速度对电池性能影响相对较小;在所研究的电池运行参数范围内,电池温度为60℃、阳极燃料浓度为1.0 mol/L、进料速度为2.5 mL/min时电池的性能最佳,最大功率密度为61.7 mW/cm2.     

合成气氛对LiNi0.75Co0.25O2性能的影响

利用溶胶-凝胶方法分别在氧气和空气气氛下合成了锂离子蓄电池正极材料LiNi0.75Co0.25O2,并对该材料进行了XRD分析、Rieveld结构精修以及电化学测试,初步探讨了合成气氛对LiNi0.75Co0.25O2结构及其电化学性能的影响。结果证实,当采用溶胶-凝胶预处理固相合成方法时,在氧气气氛下合成的锂离子蓄电池正极材料LiNi0.75Co0.25O2的电化学性能要好于在空气中合成的LiNi0.75Co0.25O2,并通过对该材料进行Rieveld结构精修进一步解释了该现象。     

烧制工艺对氧化镁活性的影响

为获取高活性氧化镁，以提供镁铝水滑石阻燃剂制备的实验依据，采用X射线衍射研究烧制工艺与氧化镁的结晶状态的关系，结果发现烧制温度和烧制时间对氧化镁的活性有较大的影响，而不同活性的氧化镁对镁铝水滑石有决定性影响。在500℃-750℃的范围内，镁盐的烧制温度为500℃-550℃，保温时间2h，这样的氧化镁的活性最大，用其制备镁铝水滑石试样纯度较高。     

基于ARM9+CPLD的嵌入式数据采集系统在PFN中的应用

为了实时精确的检测PFN脉冲的放电电流,根据PFN脉冲网络电流的形成特点,设计了一种专用型、采集频率高的嵌入式数据采集系统,该系统以ARM9+ CPLD作为硬件平台,采用Linux操作系统和Xilinx ISE9.1作为软件开发工具,能够同时完成对PFN放电电流的实时数据采集和处理、电流幅值及脉宽的计算,并协同控制后台进行数据通信和远程控制.系统采用5μs/次的采样频率,达到了0.1％的采样精度,从而实现了对PFN放电电流的实时检测,以及对PFN运行状况的有效监测.     

水沙条件变化对三峡水库泥沙淤积的影响

三峡水库上游来水来沙变化必然影响水库淤积发展过程,进而影响航运状况。本文运用一维及二维泥沙数学模型计算分析了上游水沙条件变化对三峡水库泥沙淤积及航运的影响,一维计算结果表明,90年代相对于60年代来沙变少变细后,三峡水库的淤积发展过程将明显减慢,淤积部位偏下,并且平衡淤积量也相对于60年代水沙情况下减小;上游建库的综合作用将延缓三峡水库的淤积发展过程,上游建库情况下,变动回水区河段在三峡水库运用40年内不会出现泥沙淤积问题;重庆河段整体呈现冲的趋势,100年内基本不发生淤积。二维计算结果表明,相对于上游无库情况下,上游干流建库后,重庆河段长江干流泥沙淤积量及淤积厚度明显减少,甚至出现冲刷,航运条件明显改善;金沙碛河段受上游干流建库影响较小,仍会出现碍航问题,需要进一步整治。     

运行条件对小型直接甲醇燃料电池性能影响

采用转压法制作4 cm2的膜电极,装配出小型直接甲醇燃料(DMFC)单体电池,对电池最佳运行条件进行实验研究.结果表明:电池经过70℃热水循环24 h后性能基本稳定,电池的性能受温度和甲醇浓度影响较大.23℃时.用1.5 mol/L甲醇溶液电池性能较好;在60℃时,用1.0 mol/L甲醇溶液电池性能较好;80℃时,在低电流密度区,用0.2mol/L的甲醇溶液电池性能较好,在高电流密度区,用0.5 mol/L的甲醇溶液电池性能较好.60℃工作温度下,电池运行所需要的最佳甲醇流速为1 mL/mIn.最佳氧气流量为250 mL/min.