Gd2SiO5纳米粉体的并流化学共沉淀法合成

以Gd₂O₃和正硅酸乙酯(TEOS)为原材料,采用并流化学共沉淀法合成Gd₂SiO₅粉体材料。研究Gd₂SiO₅前驱体的热响应特征、Gd₂SiO₅粉体的物相组成和微观形貌,并对Gd₂SiO₅粉体的合成机理进行初步探讨。结果表明:前驱体的低Gd/Si摩尔比和反应体系的高pH值会导致Gd₂SiO₅粉体生成Gd_9.33(SiO₄)₆O₂杂质相,相反则会导致生成Gd2O3杂质相。当Gd/Si摩尔比为20∶11、pH值为9~10、合成温度为1000~1300℃时,合成的粉体纯度较高,Gd₂SiO₅颗粒呈不规则形貌特征,平均粒度为100~200 nm。Gd₂SiO₅合成过程中,前驱体以一种—[Si—O—Gd]—网络结构存在,在煅烧过程中逐渐转化为Gd₂SiO₅晶体以及Gd_9.33(SiO₄)₆O₂和Gd₂O₃杂相。     

Nickel-hydrogen multicell common pressure vessel batterydevelopment update

Flight qualification of the multicell common pressure vessel (CPV) nickel-hydrogen (Ni-H₂) battery is discussed. The battery has completed full flight qualification, including random vibration at 19.5 g for two minutes in each axis, electrical characterization in a thermal vacuum chamber, and mass-spectroscopy vessel leak detection. A first launch is scheduled in 1992. Several design variations, ranging from 9 Ah to 125 Ah and 12 to 32 V, have been developed and prototypes fabricated. Designs for smaller capacity, smaller diameter (6.4-8.9 cm), and higher voltage (up to 100 V) are in progress. The CPV battery offers cost and weight savings of up to 30% as compared to traditional nickel-cadmium (Ni-Cd) and individual pressure vessel (IPV) Ni-H₂ batteries. The fully qualified design provided a 50% weight savings over its Nd-Cd predecessor for the same application. Its reduced volume also provides a significant advantage over IPV technology. Resistance data show a further advantage     

Galileo probe Li-SO2 battery cell life testing

Several hundred D-sized, Li-SO₂ battery cells have been in a carefully controlled quiescent storage test for up to 14 years, starting at Honeywell but completing at the NASA Ames Research Center, in support of the Atmospheric Probe portion of the Galileo Mission to the planet Jupiter. This population of cells includes similar samples from 8 different manufacturing lots; the earliest from October 1981, the latest from October 1988. The baseline samples have been divided among several storage chambers, each having its own constant temperature, respectively, set between 0°C to 40°C. Non-invasive measurements have been made repeatedly of open circuit voltage and internal resistance (at 1000 Hz). At intervals, a small portion of the cells has been removed from storage and fully discharged under repetitive conditions, thus assessing any storage related loss of discharge capacity. The results show that for storage up to 20°C the cells have excellent stability. Above 20°C noticeable degradation occurs     

Prismatic lithium-ion batteries

Lithium-ion (Li-ion) batteries have demonstrated the ability to fulfill the energy storage needs of many new technologies. The most significant drawbacks of currently available technologies, such as LiCoO ₂ based Li-ion cells, is their high cost and significant environmental hazards. Li-ion cells which use a lithium manganese oxide (LiMn₂O₄) spinel based cathode material should be much less costly and safer than LiCoO₂ based cells. Performance data from prismatic design cells which use a LiMn₂O₄ based cathode material is presented and shown to meet many military performance criteria. The most significant drawback of this technology is the short cycle life     

阳极氧化膜厚度对TB8钛合金表面特性及其粘结性能的影响

采用以酒石酸钠为主盐的电解体系对TB8钛合金进行阳极氧化,研究阳极氧化膜厚度对TB8钛合金表面特性及其与环氧树脂粘结性能的影响。采用SEM、XRD和EDS分析了阳极氧化膜的微观形貌和晶体结构,采用角接触测量仪和三维视频显微镜分别对阳极氧化膜的表面润湿性和粗糙度进行测量。研究了不同厚度TB8钛合金阳极氧化膜的粘结性能与表面形貌、相组成、润湿性及粗糙度的关系。结果表明:采用以酒石酸钠为主盐的电解体系对TB8钛合金进行阳极氧化处理,氧化时间为15 min,电压为1~30 V时,能够在钛合金表面形成一层1~4μm厚的阳极氧化膜;氧化膜主要由金红石型和锐钛型TiO₂混合晶体组成,其表面具有微纳多孔的粗糙结构;随着厚度的增加,阳极氧化膜对水的润湿性能逐渐增强。当氧化膜厚度为3μm时,可获得最大粘结强度为19.6 MPa,相对于母材提高了88.5%,同时,水接触角为43.2°,相对于其母材减少了56.1%;粗糙度为2.14μm,相对于母材提高了137.8%。     

固体火箭发动机Al_2O_3凝结及颗粒破碎的数值模拟

Al2O3凝结对固体火箭发动机Al颗粒的燃烧效率及燃气流动有很大影响。结合拉格朗日方法,建立Al2O3凝结模型,分析了在Al2O3烟雾凝结及颗粒自身破碎作用下,不同初始直径Al颗粒的燃烧效率及燃烧室流场的变化规律。计算结果与同条件下的测试数据有较好的吻合,颗粒分布符合相关实验现象。结果表明,小颗粒燃烧后,流场温度及Al2O3烟雾分布均匀;随颗粒初始直径的增加,径向出现明显分层现象;在发动机出口,小颗粒燃烧效率较高,颗粒中Al2O3质量分数较大,但破碎程度较小;随初始直径增加,颗粒燃烧效率逐渐降低,颗粒中仍含有大量未燃烧的Al,破碎程度提高,颗粒数目急剧增加。     

Lithium micro-battery development at the Jet Propulsion Laboratory

Recent successes in the effort to miniaturize spacecraft components using MEMS technology, integrated passive components, and low power electronics have driven the need for very low power, low profile, low mass micro-power sources for micro/nanospacecraft applications. Recent work at JPL has focused upon developing thin film/micro-batteries compatible with temperature sensitive substrates. A process to prepare crystalline LiCoO₂ films with RF sputtering and moderate (<700°C) annealing temperature has been developed. Thin film batteries with cathode films prepared with this process have specific capacities approaching the practical limit for LiCoO₂, with acceptable rate capabilities and discharge voltage profiles. Solid-state micro-scale batteries have also been fabricated with feature sizes on the order of 50 microns     

钛基稀土激光熔覆层组织细化机制及性能

采用通快TruDisk 4002光纤激光器在TC4合金表面分别制备了0wt% Y₂O₃和3wt% Y₂O₃的TC4+Ni45+Co-WC钛基耐磨复合涂层。利用XRD、SEM、EDS、EPMA、显微硬度计和摩擦磨损试验机等分析了涂层组织、显微硬度和摩擦学性能。结果表明，两种涂层表面均无裂纹孔隙等缺陷，且生成相一致，主要包括TiC、TiB₂、Ti₂Ni、WC和α-Ti；0wt% Y₂O₃涂层组织存在明显偏析，析出相尺寸粗大且方向性明显；3wt% Y₂O₃涂层组织呈均匀弥散状态分布，细化特征明显；经Bramfitt二维点阵错配度计算，（100）_Y2O3和（100）_Ti2Ni、（111）_Y2O3和（110）_TiC、（110）_Y2O3和（1010）_TiB2间的错配度分别为5.75%、6.72%和10.10%，Y₂O₃作为异质形核核心对Ti₂Ni、TiC和TiB₂的细化能力依次为Ti₂Ni > TiC > TiB₂；0wt% Y₂O₃和3wt% Y₂O₃涂层显微硬度分别为600~630 HV_0.5和470~480 HV_0.5，较基材分别提高了约62%和26%；3wt% Y₂O₃涂层耐磨减摩性最优，其磨损体积和摩擦系数较0wt% Y₂O₃涂层分别下降了约47.8%和5.0%，磨损机制主要为磨粒磨损。     

TiC-TiB2复合相钛基稀土激光熔覆层组织与性能

采用通快同轴送粉4002光纤激光器,在TC4表面熔覆制备了不同含量Y₂O₃的TC4+Ni45+Co-WC+Y₂O₃钛基复合耐磨涂层。采用XRD、SEM、EDS、EPMA测试研究了涂层微观组织,利用显微硬度计、摩擦磨损实验机和白光轮廓仪分析评价了涂层的显微硬度和摩擦学性能。结果表明,涂层生成相不随Y₂O₃含量变化而改变,主要包括Ti₂Ni、TiC、TiB₂以及α-Ti;未添加Y₂O₃涂层,生成相尺寸粗大,方向性明显;随着Y₂O₃的加入,涂层组织逐步细化,生成相方向性减弱;当Y₂O₃为3wt%时,涂层析出相以颗粒和短棒状相为主,合成了大量TiC-TiB₂依附生长复合相,经二维点阵错配度计算,TiB₂（0001）与TiC （111）错配度δ为0.912%,TiC与TiB₂形成了共格界面,可有效增加涂层组织分布均匀性;Y₂O₃含量为0wt%、1wt%和3wt%时,涂层显微硬度逐渐减小,磨损体积先增大后减小,摩擦系数逐渐降低;在TiC-TiB₂复合相的作用下,3wt% Y₂O₃涂层的耐磨、减摩性最优,涂层磨损机理为磨粒磨损。     

阳极氧化对TiAl合金高温氧化行为和力学性能的影响

采用电化学阳极氧化技术在含NH4F的乙二醇电解液中对TiAl合金进行阳极氧化处理。研究阳极氧化对TiAl合金高温氧化行为和力学性能的影响。结果表明:由于“卤素效应”,阳极氧化处理的TiAl合金经高温氧化后表面形成致密、连续的Al₂O₃氧化膜,有效阻止了氧的内扩散,进而显著提高合金的抗高温氧化性能。经1000℃氧化100 h后,阳极氧化试样增重由未经阳极氧化处理试样的85.86 mg/cm²降至0.67 mg/cm²。另一方面,阳极氧化TiAl合金表面硬度和弹性模量随高温氧化时间延长呈先降低后升高的趋势。阳极氧化TiAl合金在高温服役后,合金的摩擦系数较未经阳极氧化处理试样上升,但表面耐磨性先降低后升高。这是由于TiAl合金经阳极氧化后,表面形成了一层富铝含氟氧化膜,由于氧化膜中F元素在高温氧化过程中与Ti、Al结合形成卤化物,卤化物蒸气选择性扩散在原始氧化膜处形成致密的Al₂O₃保护膜。阳极氧化对TiAl合金力学性能的影响主要是由于氧化膜中Al₂O₃的含量变化所致。     

Lightweight (AlGaAs)GaAs/CuInSe2 tandem junction solarcells for space applications

Mechanically stacked tandem cells consisting of GaAs thin-film upper cells and CuInSe₂ thin-film lower cells have been developed to meet the increasing power needs projected for future spacecraft. The authors report the fabrication of the first highly efficient lightweight GaAs/CuInSe₂ tandem cell on a 2-mil thick substrate, update recent performance improvements in thin-film GaAs/CuInSe₂ tandem cells, and discuss their application to space power systems. The efficiency of 4-cm² cells has improved to 21.6% AM0, the highest ever reported for a thin-film photovoltaic cell. Lightweight 4-cm² tandem cells have been successfully fabricated with efficiencies as high as 20.8%. These cells weighed about 180 mg without optimized substrate trimming. Radiation and operating temperature effects on GaAs/CuInSe₂ tandem cells are also discussed, and an interconnect scheme to form a voltage-matched string is described     

Need and effect of reconditioning of nickel/hydrogen batteries

There has been a debate about the need for reconditioning nickel/hydrogen batteries in geosynchronous satellites. A study was done as part of life cycling, to determine the necessity of reconditioning and its effect on the cell performance. A 36 Ah nickel/hydrogen cell was put on a GEO simulated cycling at 15°C without reconditioning up to four eclipse seasons. The effect of reconditioning on the fifth and sixth eclipse seasons was studied. The study has conclusively proven the need for reconditioning and has shown the benefits of a high rate reconditioning. It has also been possible to draw some conclusions about the effect of a long duration trickle charge on the positive electrode     

药柱含扰流板H2O2/HTPB固液火箭发动机 两相流数值计算

研究了药柱中添加扰流板对固液火箭发动机燃烧性能的影响,以北京航空航天大学φ100mm标准固液火箭发动机为计算模型,针对98%H₂O₂/HTPB(过氧化氢/端羟基聚丁二烯)推进剂组合,采用二维轴对称气液两相模型计算了不同药柱位置、不同孔径尺寸的扰流板对固液火箭发动机燃烧性能的影响.结果表明:孔径尺寸更小的扰流板且置扰流板于药柱长度的50%~70%时,平均燃料退移速率最大,燃烧效率最高,这将为扰流板设计提供理论依据.      

航天飞行器轻质纳米材料高温隔热性能

纳米隔热材料是一种新型航天飞行器热防护材料。本文使用自行研制的高速飞行器热试验系统,对Al₂O₃纳米材料的高温隔热性能进行试验研究及数值计算,为高速航天器热防护系统的安全可靠性设计提供重要依据。研究结果表明,厚度仅为10 mm的Al₂O₃纳米材料板,当前表面温度为1 200℃时（1 800 s）,前后表面的温度差高达880.9℃,后表面温度降低了73.4%,且隔热性能稳定。另外与某空天飞行器轻质陶瓷材料进行了隔热性能的对比试验,结果显示轻质陶瓷材料板的背壁温度要比Al₂O₃纳米材料板高56%。说明Al₂O₃纳米材料的高温隔热性能非常优异,在航天器和高超声速飞行器热防护中具有重要的应用价值。由扫描电镜（SEM）图像知,当温度超过1 200℃后,Al₂O₃纳米材料颗粒快速聚集生长,颗粒间的空洞尺寸显著增大,材料内部纤维出现熔融现象,裂纹数量增多、深度及宽度显著增大,影响材料表观导热率。另外,当温度高于1 200℃时,纳米材料板边界出现了较大的收缩变形和弯曲变形。基于试验结果可知,Al₂O₃纳米隔热材料应该在小于1 200℃的热环境中使用。     

TMO复合催化剂对AP推进剂燃速催化作用研究

系统地考察了4种TMO催化剂(CuO、Fe₂O₃、Co₂O₃和Cr₂O₃)及其等质量比(1∶1)的6种TMO复合催化剂对AP/HTPB和AP/Al/HTPB两类复合固体推进剂燃烧性能的影响。实验结果表明, TMO复合催化剂对推进剂燃速的影响可分为正协同效应、无协同效应和负协同效应3类;具有正协同效应的TMO复合催化剂提高燃速效果最佳, TMO复合催化剂对AP复合推进剂燃速的影响取决于推进剂的种类, 协同效应的类属和单一TMO催化剂的催化活性。      

CrON扩散阻挡层对NbCrAl涂层与Nb基高温合金元素互扩散的影响

利用磁控溅射技术在C103型Nb基高温合金上制备了含和不含CrON扩散阻挡层的NbCrAl涂层,对比研究了2种涂层分别经900℃和1000℃真空热处理后的元素扩散行为。结果表明:NbCrAl涂层以Cr₂Nb和AlNb₂相为主,含非晶态组织;真空热处理后生成了NbAl₃和(Nb,Cr)沉淀相。热处理温度由900℃升至1000℃时,NbCrAl涂层中元素扩散速度加快。不含扩散阻挡层样品中Cr和Al元素扩散至基体的含量分别为2.76wt%和1.21wt%,而含扩散阻挡层样品中Cr和Al元素扩散到基体的含量分别仅为2.52wt%和0.84wt%。扩散阻挡层保持连续,且与涂层及基体的界面结合良好,经高温处理后主要以密排六方结构的Cr₂O₃和Al₂O₃相为主,有效地抑制了元素互扩散。     

Performance characteristics of lithium-ion cells for NASA's Mars2001 Lander application

NASA requires lightweight rechargeable batteries for future missions to Mars and the outer planets that are capable of operating over a wide range of temperatures, with high specific energy and energy densities. Due to the attractive performance characteristics, lithium-ion batteries have been identified as the battery chemistry of choice for a number of future applications, including Mars rovers and landers. The Mars 2001 Lander (Mars Surveyor Program MSP 01) will be one of the first missions which will utilize lithium-ion technology. This application will require two lithium-ion batteries, each being 28 V (eight cells), 25 Ah and 8 kg. In addition to the requirement of being able to supply at least 200 cycles and 90 days of operation on the surface of Mars, the battery must be capable of operation (both charge and discharge) at temperatures as low as -20°C. To assess the viability of lithium-ion cells for these applications, a number of performance characterization tests have been performed, including: assessing the room temperature cycle life, low temperature cycle life (-20°C), rate capability as a function of temperature, pulse capability, self-discharge and storage characteristics, as well as mission profile capability. This paper describes the Mars 2001 Lander mission battery requirements and contains results of the cell testing conducted to-date in support of the mission,     

GPS C/N/sub 0/ estimation in the presence of interference and limited quantization levels

The carrier-to-noise density ratio (C/N₀) is considered an important parameter describing the GPS receiver performance. This paper compares the performance of two popular coarse-acquisition (C/A) C/N₀ algorithms appearing in literature: the variance summing method (VSM) (Psiaki et al., 2003, Psiaki, 2001), and the power ratio method (PRM) (Van Dierendonck, 1996, Sayre, 2003), in terms of their estimates in 1) additive white Gaussian noise (AWGN), 2) narrowband continuous wave interference (CWI), 3) their response to quantization and saturation effects, and their 4) dynamic range. The algorithms were implemented as a part of a software receiver. Two LI GPS data sets are examined; one was obtained from a GPS raw data collection setup, while the other was obtained from a GPS signal simulator. The collected set was stored with almost constant C/N₀ level while the simulated one contained variable C/N₀ levels. The effect of adding AWGN on the C/N₀ estimate was directly proportional with the noise power. The C/N₀ estimates suffered more when the CWI frequency was closer to the IF of the receiver. The PRM suffered from saturation at higher C/N₀ levels. The VSM showed good tracking at high C/N₀ levels and better immunity to limited quantization levels, while its C/N₀ estimate suffered from rapid fluctuations in power levels when sudden power steps occurred     

Sm2Zr2O7基热障涂层材料研究现状

由于航空发动机不断向高效率、高推重比方向发展,发动机热端部件表面热障涂层的服役条件也越来越苛刻。稀土锆酸盐作为新型热障涂层材料,其开发和应用受到越来越多国内外学者的关注。Sm₂Zr₂O₇材料在一系列稀土锆酸盐中具有烧绿石结构稳定、低热导率和高热膨胀系数等优点,具有良好的应用前景。为满足热障涂层更高的服役要求,Sm₂Zr₂O₇的掺杂改性及性能研究也成为了研究热点。首先,对热障涂层材料进行了简要概述,然后就Sm₂Zr₂O₇基陶瓷材料及其涂层的晶体结构、热物理性能、力学性能以及抗腐蚀性能等的研究进展进行了详细的介绍,为该材料在热障涂层领域的研究及应用提供参考。     

半潜入喷管收敛段碳/酚醛材料烧蚀特性

采用流固热耦合数值方法,以及Abaqus的ALE（arbitrary Lagrangian-Eulerian,任意拉格朗日欧拉方法）自适应网格技术,对位于半潜入喷管收敛段的碳/酚醛的烧蚀现象进行了预估,与试验结果进行了对比分析。结果表明:在收敛段,Al/Al₂O₃液滴或颗粒对材料的传热烧蚀起到了关键作用,当气流与材料表面平行时,液滴或颗粒的影响很小;从碳/酚醛热分解角度出发,基于完全碳化即被剥蚀的假设,基本能够预估碳/酚醛材料的烧蚀特征,烧蚀速率大约为0.3 mm/s;后效碳化对材料碳化过程的影响明显,发动机工作期间,分解层的厚度大约为2.0 mm,考虑后效作用,分解层厚度可能会增加至4.0 mm左右;与喉衬接触的材料区域,喉衬的传热会明显加剧材料的碳化过程。