工程陶瓷

早期的陶瓷是粘土质耐火材料。最普通的粘土砖广泛用于高炉、化铁炉、热处理炉等冶金工业,组分为20～45%的Al_2O_3和50～80%的SiO_2与常用的几种粘土、以及几种能减小烧成收缩和增加使用稳定性的添加剂。烧成温度为1500C。典型的烧结材料含有50%玻璃、35%莫来石和15%方英石。耐火粘土的承载能力直接关系到玻璃相的数量及其粘度。Al_2O_3含量较高的耐火粘土能在艰难条件下更好地使用。软化温度通常为1750     

美国高技术陶瓷持续增长

高技术陶瓷的销售额从1989年的35亿美元增加到1999年的81亿美元,平均年增长率为8.7％。据美国商业资讯公司的调查,在高技术陶瓷市场中,电子陶瓷不仅将继续占有最大市场份额,而且是未来增长的领头羊,结构陶瓷紧随其后。1999年,美国高技术陶瓷部件的总产值大约为81亿美元,预     

结构陶瓷—一个需要耐心的行业

众所周知,要制备高质量的先进陶瓷零部件、元器件,粉料的质量是个关键环节。近15年来,通过国际陶瓷界(当然还有国内)对制备方法和工艺技术的精心研究,粉料的纯度、细度、颗粒分布以及性能的重现性均有极大的进展,导致高性能结构陶瓷的性能有了显著的提高(当然还包括配方、工艺的改进,这里只是强调了粉料)。例如:①力学性能由20MPa提高到2GPa;②K_(IC)由1提高到     

陶瓷中氧化锆的研究及应用现状

综述了陶瓷中氧化锆的研究动态;介绍了氧化锆的几个主要应用领域及常用氧化锆陶瓷系列。     

对我国工程陶瓷的科研和发展的调查

几位教授介绍了我国南方几所大学有关工程陶瓷的科研情况,以及在京专家介绍了部分工程陶瓷的生产情况。     

B4C陶瓷的协同增韧

采用热压工艺制备的Ｂ４Ｃ－３５ｖｏｌ％ＴｉＢ２复相陶瓷的断裂韧性值从单体Ｂ４Ｃ的３．６ＭＰａ－ｍ＾１／２以６．５ＭＰａ．ｍ＾１／２， 游离碳后的韧性进一步提高，达７．６ＭＰａ．ｍ＾１／２，显微结构观察表明，材料韧性的改善是因第二相颗粒的ＴｉＢ２和基体Ｂ４Ｃ之间的热膨胀系数不匹配而产生的残余应力导致的偏转和游离碳的 产生的微开明纹协同增韧的结果，游离碳的存在削弱了界面的结合强度，在很强的残余应力的和     

晶内型Al2O3—SiC纳米复合陶瓷的制备

研究了沉淀法制备Ａｌ２Ｏ３－ＳｉＣ纳米复合陶瓷的工艺过程，利用Ａｌ２Ｏ３从γ相到α相的蠕虫状生长过程，使大部分纳米ＳｉＣ颗粒位于Ａｌ２Ｏ３晶粒内，用沉淀法制得的、含有５ｖｏｌ％ＳｉＣ的Ａｌ２Ｏ３－ＳｉＣ纳米复合陶瓷，其强度为４６７ＭＰａ，韧性为４．７ＭＰａ．ｍ＾１／２，与一般的Ａｌ２Ｏ３陶瓷相比有较大的提高，显示了沉淀法制备Ａｌ２Ｏ３－ＳｉＣ纳米复合陶瓷的优点。     

基于双ZnO薄膜单元并联结构的微型压电振动能量采集器(英文)

报道了一种基于ZnO压电薄膜双单元结构的压电式微型振动能量采集器,其中的双压电元件是并联结构.采用射频磁控溅射技术制备ZnO压电薄膜,同时,该压电式振动能量采集器采用微加工技术制作.测试表明该器件的共振频率为1 300 Hz,基于ZnO薄膜双单元并联结构的压电式振动能量采集器比起具有同样尺寸的传统型压电振动能量采集器有更高的输出性能.在频率为1 300 Hz,加速度为10 m/s2的外界振动激励下,该压电式振动能量采集器在1 MΩ负载电阻上产生的电压为2.06 V;当负载电阻为0.6 MΩ时,输出功率最大为1.25μW.     

宽频压电振动能量采集器的力-电输出特性分析

压电振动能量采集器是一种新型的力(加速度)-电耦合转换输出器件,为了提高单自由度悬臂梁压电振动能量采集器的输出功率和工作频带,通过在单自由度悬臂梁压电振动能量采集器模型基础上增加一个弹性放大器的方法,构造形成了具有两自由度的宽频压电振动能量采集器。利用ANSYS有限元软件建立了宽频压电能量采集器的有限元力-电耦合模型,数值分析了模型中各参数(如质量比、阻尼比以及负载电阻等)对系统力特性(速度、加速度等)和电输出特性(电压、电流、输出功率等)的影响。研究结果表明：大的质量比和小的阻尼比能够提高压电悬臂梁能量采集器的输出功率并拓展其工作频带;短路谐振状态下的匹配电阻能够使能量采集器产生较大的输出电流,而开路谐振状态的匹配电阻能够使能量采集器产生较大的输出电压,优化后的短路谐振和开路谐振最大输出功率分别达到4386.5 mW/g2和4263.4 mW/g2。频带宽度达到10 Hz,且是SDOF系统的5倍。     

球形永磁阵列振动能量收集器设计与优化

为实现多方向环境能量收集,设计球形电磁式振动能量采集器。基于二维Halbach阵列设计的球面Halbach永磁阵列,较传统永磁阵列能提高线圈中磁链变化梯度,从而提高结构输出性能;建立数学解析模型,据解析结果对模型各参数进行优化;对该模型进行有限元仿真分析及实验性能测试。结果表明,该模型能有效响应空间任意方向振动,进而转化为电能;外部激励为10 Hz、激励为水平方向、负载阻值50 Ω时,该球形振动能量采集器输出电能达最大,单个线圈中最大负载功率可达0.8 mW。     

Bimorph piezoelectric vibration energy harvester with flexible 3D meshed-core structure for low frequency vibration

This paper proposes a bimorph piezoelectric vibration energy harvester (PVEH) with a flexible 3D meshed-core elastic layer for improving the output power while lowering the resonance frequency. Owing to the high void ratio of the 3D meshed-core structure, the bending stiffness of the cantilever can be lowered. Thus, the deflection of the harvester and the strain in the piezoelectric layer increase. According to vibration tests, the resonance frequency is 15.8% lower and the output power is 68% higher than in the conventional solid-core PVEH. Compared to the solid-core PVEH, the proposed meshed-core PVEH (10 mm × 20 mm × 280 μm) has 1.3 times larger tip deflection and the maximum output power is 24.6 μW under resonance condition at 18.7 Hz and 0.2G acceleration. Hence it can be used as a power supply for low-power-consumption sensor nodes in wireless sensor networks.     

A High Average Power Dye Laser Powered by a Vortex Stabilized Flashlamp

A flashlamp pumped organic dye laser has recently been operated at an average power output of 114 W. This is the highest average power ever reported for a dye laser. The laser was excited by a high power, vortex stabilized flashlamp. In this type of lamp a fast flow of argon gas is injected near the walls. The gas swirls inward and exits through holes in the electrodes. The fast gas flow provides cooling to allow the lamp to operate at high average power and it also stabilizes the position of the discharge. The lamp was used in an elliptical pumping cavity, with the lamp at one focus. The arc length in the lamp was 10 cm. The dye was circulated through a transverse flow channel at the other focus. The lamp was fired at repetition rates up to 357 Hz and with an energy per pulse of 211 J, i.e. an average power of 75 kW. The laser output pulses had a full width at half maximum of 1·8 μ sec. The average power output increased nearly linearly with repetition rate to a maximum of 114 W at 255 Hz. The achievement of even higher powers was limited by the replacement rate of dye in the channel and a drop in the flashlamp intensity at higher repetition rates. The dye used in these experiments was Rhodamine 6G in an ethanol solution.     

On the possibility of increasing the efficiency of sealed-off nitrogen lasers

A sealed-off nitrogen laser operating in a periodic-pulse regime at a repetition rate of 40 Hz has been experimentally studied and it is demonstrated that the laser efficiency can be increased by quasi-stationary energy pumping into the active medium (pure nitrogen or its mixtures with helium or neon). The presence of a buffer gas (helium or neon) allows the energy parameters of radiation to be increased and the laser efficiency to be controlled. A small-sized sealed-off nitrogen laser is developed, which operates at a peak output power of 160 kW and a pulse energy of 0.8 mJ with an efficiency of 0.27%.     

Comprehensive modeling of the temperature-related laser performances of the amplifiers of the LUCIA laser

We present numerical simulations of the temperature-related laser performance of the amplifiers for the Lasers Ultra-Courts et Intenses et Applications (LUCIA) laser, a 100 J, 10 Hz, 10 ns diode-pumping solid-state-laser facility, which uses Yb3+:YAG as the gain medium. The simulations include energy storage and extraction efficiency, cooling of the gain medium, and wavefront distortion. The results show that, with a pumping intensity of 20 kW/cm2 at 10 Hz and a doping concentration of 10 at. % at a thickness of Yb3+:YAG of 1.6 mm, the output laser fluence and optical-to-optical efficiency are expected to be 10 J/cm2 and 25.8%, respectively, at a heat exchange coefficient of 3000 W/m2/K of water. Also, the matching thickness of undoped YAG is optimized to prevent bending deformation of the gain medium, which could be approximately 5 mm.     

Single-frequency pulsed laser source with hybrid MOPA configuration

A unique approach with a hybrid master oscillator power amplifier configuration to obtain single-frequency, high-energy laser pulses at 1064 nm is presented. The setup consists of a single-frequency seed laser, a multistage fiber amplifier, and a four-pass crystal rod amplifier. Pulse energy of 10 mJ is obtained at the repetition rate of 100 Hz. The pulse width is about 110 ns with a transform-limited linewidth of 3.2 MHz. The M(2) factor of the output beam is about 1.5. To our knowledge, this is the first report of using a hybrid amplifier to obtain 10 mJ pulses with long pulse width and transform-limited linewidth.     

All-solid-state tunable DCM dye laser pumped by a diode-pumped Nd:YAG laser

Lasing is observed near 620 nm in a DCM dye doped TiO(2)-content organically modified silicate (ORMOSIL) pumped by frequency-doubled radiation from a diode-pumped Q-switched Nd:YAG laser. The laser wavelength is tunable over 60 nm. A conversion efficiency of 18% is obtained at its central wavelength of 621 nm. The laser output energy has only a 10% reduction after 27,000 pulses at a pump repetition rate of 30 Hz and a pump intensity of 1 J/cm(2). An all-solid-state, compact, long-lifetime, and tunable dye laser has been demonstrated.     

Analysis of ac-dc conversion for energy harvesting using an electrostrictive polymer P(VDF-TrFE-CFE)

Harvesting systems capable of transforming unused environmental energy into useful electrical energy have been extensively studied for the last two decades. The recent development of electrostrictive polymers has generated new opportunities for harvesting energy. The contribution of this study lies in the design and validation of electrostrictive polymer- based harvesters able to deliver dc output voltage to the load terminal, making the practical application of such material for self-powered devices much more realistic. Theoretical analysis supported by experimental investigations showed that an energy harvesting module with ac-to-dc conversion allows scavenging power up to 7 μW using a bias electric field of 10 V/μm and a transverse strain of 0.2%. This represents a power density of 280 μW/cm(3) at 100 Hz, which is much higher than the corresponding values of most piezo-based harvesters.