激光烧蚀掺杂金属粉工质的推进性能

 为结合金属高比冲和聚合物工质高冲量耦合系数的优点,为激光推进光船优选工质,对掺入金属粉末的聚甲醛(POM)工质在CO₂激光辐照下的推进性能开展了实验研究。结果表明：在一定的条件下金属粉末能提高工质的推进性能。掺入微米铝粉的聚甲醛工质的冲量耦合系数最大值由12×^-5 N/W提高到21.72×10^-5 N/W,在直筒结构的约束下,最高冲量耦合系数和比冲分别提高到61.64×^-5 N/W和727.32 s,能量利用率超过了100%,表明工质参与了化学反应。     

激光烧蚀硬铝产生等离子体温度和力学效应测量

 为了研究激光推进技术中激光与材料相互作用的机制，获取等离子体状态参数及力学参数，采用Nd:YAG被动调Q固体激光器烧蚀硬铝，通过激光诱导等离子体光谱技术测得等离子体光谱和温度，由冲量摆测得力学参数。实验结果显示：在激光功率密度0.534×10⁸ W/cm²时，靶材表面的等离子体温度在等离子体辐射过程中呈二次曲线衰减；改变靶材等离子体点燃阈值附近的激光功率密度时，随着功率密度的增加，等离子体温度、冲量耦合系数也随着增大，当功率密度达到靶材的等离子体点燃阈值时，各参数达到最大，此后随着功率密度增加，由于等离子体对能量的屏蔽作用，导致靶材表面的等离子体温度降低，等离子体获得的动能减少，靶材耦合的冲量降低。     

等离子体屏蔽和稀疏波对冲量耦合系数的影响

 利用脉冲Nd:YAG激光作用在铝、铜靶上，研究了不同入射激光能量下冲量耦合系数和离焦量之间的关系，以及不同功率密度情况下冲量耦合系数和光斑直径的关系。实验表明铝靶在入射激光脉冲能量由75.8 mJ增加到382.3 mJ时，冲量耦合系数峰值对应的最佳离焦量由－10 mm处远离焦点向透镜方向移到－18 mm，而对应的激光功率密度仅由2.0×10⁹ W/cm²增加到3.9×10⁹ W/cm²；铜靶实验规律和铝靶类似。等离子体屏蔽的吸收作用导致了冲量耦合系数达到最大值后迅速降低。铝靶在入射激光功率密度由0.7×10⁹ W/cm²增大到1.0×10¹⁰W/cm²时，冲量耦合系数随光斑直径增大而增大，对应变化斜率由5.2×10^-5N·s/（mm·J）增大到49.2×10^-5N·s/（mm·J），表明了稀疏波对冲量耦合系数的削弱作用随入射激光功率密度增加而增加，随光斑直径增大而减小。     

气压对吸气式激光推进冲量耦合系数的影响

 保持CO₂激光的单脉冲能量为61.4~64.6 J，采用高精度冲击摆系统进行了不同气压下吸气模式激光推进冲量耦合系数的实验测试，分析了对应的高度特性。结果表明：气压为2.8×10⁴～1×10⁵ Pa，即距离地面0～10 km时，冲量耦合系数大约3.5×10^-4 N·s·J^-1，上下波动幅度低于5%；气压低于2.8×10⁴ Pa，即高度大于10 km时，冲量耦合系数呈二次曲线显著下降；当气压降至1×10³ Pa，即距离地面约31 km高度时，耦合系数仅为9.7×10-5 N·s·J^-1。     

Ag-Cu纳米颗粒修饰的N掺杂TiO2纳米棒阵列及其高效光催化CO2还原应用

本文采用微纳加工方法制备了负载高密度Ag-Cu纳米颗粒的N掺杂TiO₂纳米棒阵列样品. 通过TiO₂的N掺杂,可将其吸光范围调控至与Ag纳米颗粒的等离激元吸收频率相匹配的波段,从而实现复合材料中肖特基结与共振能量转移过程的协同作用. 与此同时,Cu纳米颗粒可以为CO₂还原提供活性位点. 在全谱光照射下,复合样品光催化CO₂还原的活性显著提高,CH₄生成速率可达720 μmol·g^-1·h^-1.     

物理掺杂用纳米Fe粉的制备与结构表征

 根据惯性约束聚变靶材料研究的需要采用自悬浮定向流技术制备了金属纳米Fe粉,通过透射电子显微镜和X射线衍射分析技术研究了颗粒的形貌、粒度和相组成。结果表明,所制备的纳米Fe粉为规则的球状颗粒,其粒径分布在30~70 nm之间,在空气中颗粒表面有氧化膜生成,其氧化产物为Fe₃O₄。     

超声喷雾共沉淀法制备的Lu3Al5O12∶Eu3+ 纳米粉体发光特性

采用新型超声喷雾共沉淀法技术,以Lu₂O₃、Eu₂O₃、Al(NO₃)₃·9H₂O为原料,制备了不同浓度Eu³⁺离子掺杂的Lu₃Al₅O₁₂纳米粉体.用X射线粉末衍射表征了获得纳米粉体的相,用扫描电镜观察了纳米粒子的形貌.测定了粉体的激发光谱、⁷F₀-⁵D₂声子边带谱与发射光谱.研究了不同高温烧结温度与Eu³⁺掺杂浓度对纳米粒子的发光强度与粒子形貌的影响规律.研究表明,当烧结温度高于900 ℃时,粉体发光强度明显增强,并且随着煅烧温度的增加,发光强度有所增强.Eu³⁺离子的最佳掺杂浓度为5~7 mol%.根据稀土离子Eu³⁺光学跃起矩阵元的特点,从发射光谱获得Eu³⁺光学跃起的J-O参量Ω₂与Ω₄.在Eu³⁺掺杂浓度均为5 mol%时,其强度参量达最小,电-声子耦合最强.然后随着掺杂浓度的进一步提高,强度参量略有增加,电-声子耦合减弱.说明Eu-O键强增加,共价性增强,Eu³⁺的局域环境对称性降低.Ω₂值低于Eu³⁺在玻璃与晶体基质中的情况,这是由于纳米粒子中存在着大量的缺陷以及晶体的结构畸变导致纳米粒子的对称性下降所致.     

鼓型CoB16-团簇电子结构的探索：罕见的Co(-1)氧化态

本文发现CoB₁₆^-团簇由两个对称、上下错位相连的B₈环和位于中心的Co原子组成,它代表了金属掺杂硼纳米管结构的潜在雏形,这一发现为设计一维金属-硼纳米结构提供了机会. 本文报道了CoB₁₆^-新的实验光电子能谱,并采用量子化学方法对其电子结构和化学成键特性进行了详细的电子结构分析,为进一步了解金属掺杂硼纳米管结构的化学键和稳定性提供了深入的见解. 有趣的是,发现该类体系的中心Co原子具有异常低的氧化态,即负一价钴(-1). 因此中性CoB₁₆分子可以被视为配体到金属的电荷转移化合物(Co^-@BB₁₆⁺). 研究表明,掺杂金属和硼管之间的相互作用来源于共价和静电作用的相互协调,硼元素低的电负性使得硼团簇成为形成各种低价态化合物的重要化学配体.     

掺杂浓度和烧结温度对CaWO4:Eu3+发光性能的影响

采用微乳液法合成掺杂浓度不同和烧结温度不同的CaWO₄:Eu³⁺系列荧光体, 这些荧光体都具有Eu³⁺离子的特征荧光发射. 在不同温度烧结后, 高浓度掺杂的样品(Eu³⁺掺杂30或50 mol%)可获得最大的发光强度, 低浓度掺杂的样品(掺杂0.5—2 mol%)在800 ℃烧结时也可获得优异的发光强度. 实验结果表明, Eu³⁺离子高浓度掺杂的CaWO₄:Eu³⁺在紫外光激发下可成为高效发光的荧光粉.     

高性能MgB2长线材制备及性能表征

采用原位粉末装管工艺，分别以Mg粉(99.5%)，无定形B粉(99.9%)为原料，以纳米SiC(10—30nm)作为掺杂材料制备铁基MgB₂线.首先将已混合的原料在丙酮介质中球磨，真空干燥后，将粉末填入铁管内，然后通过孔型轧制、旋锻和拉拔等冷加工工艺得到11m长外径Ф1.75mm铁基MgB₂超导线.用扫描电镜，电子能谱，X射线衍射仪和超导量子干涉仪测试发现，样品微观结构整齐，晶粒大小均匀，内部仅含微量MgO，T_C(onset)=35.1K，ΔT_C＝5.3K.纳米SiC掺杂后，其中C造成MgB₂晶格畸变，形成有效磁通钉扎中心，C元素在MgB₂中分布均匀.标准四引线测试结果表明，11m线均分10段后，各点的J_c(4.2K,10T)均超过1.0×10⁴A/cm^{2，最高值达到1.2×104A/cm2.在10—18T范围各点临界电流值分布均匀，变化率小于10%.}     

Multi-use laser impulse pendulum and laser propulsion parameters measurement

In order to investigate the mechanisms of both the air-breathing and the ablation modes of laser propulsion under laboratory conditions, a multi-use laser impulse pendulum (MULIP) is developed. The measurable impulse range is from 1.0×10-4 to 3.8×10-3 N.s. The experimental calibration data agree well with the theoretical calculated data. With MULIP, the ablation mode has been performed, in which a high power pulsed Nd:glass laser (λ= 1.06μm,Τ= 20 ns) and a gray PVC film sample are used. The experimental results show that the maximum momentum coupling coefficient Cm is 7.73×10-5 N/W, and the maximum specific impulse Isp is 208.6 s.     

Characteristics of droplets ejected from liquid glycerol doped with carbon in laser ablation propulsion

The characteristics of droplets ejected from liquid glycerol doped with carbon are investigated in laser ablation propulsion. Results show that carbon content has an effect on both the coupling coefficient and the specific impulse. The dopedcarbon moves the laser focal position from the glycerol interior to the surface. This results in a less consumed glycerol and a high specific impulse. An optimal propulsion can be realized by varying carbon content in glycerol.     

Laser plasma propulsion generation in nanosecond pulse laser interaction with polyimide film

The plasma propulsion generated in nanosecond pulse laser interaction with polyimide film is investigated. A comparison of coupling coefficient and specific impulse with glass layer and water layer confinement is given. It shows that polyimide has a higher efficiency in water confinement ablation. Through doped carbon black in polyimide film, a higher coupling coefficient is obtained. In ablated surface images, less re-deposited products on polyimide surface have been observed compared with other polymers at the same laser intensity.     

Design and characterization of nozzles and solid propellants for IR laser propulsion

In this article, we present an experimental study of the effect of conical section nozzles coupled to solid targets on laser ablation propulsion. The impulse produced on the target by laser ablation was measured in terms of the coupling coefficient C _m using a piezoelectric (PZT) sensor. The standard deviation of the PZT signal was used as an estimator of the transferred impulse. The ablation was performed with a TEA CO₂ laser at room temperature and atmospheric pressure. The targets were pellets of 90/10 % w/w Zn/CaCO₃ concentration ratio. Aluminum nozzles with conical section were coupled to these propellant pellets. A comparative study of the variation of C _m using nozzles of different inlet and outlet diameters of the ejected material as well as of different heights was made. The results demonstrate that for the pellet composition analyzed, as the nozzle’s height increases and its diameter decreases improvements up to 250 % respect to the target without nozzle are obtained. These are promising results for the potential development of laser ablation microthrusters.     

Model analysis of supermode generation in active 5-core optical fibre

In the paper, the phase-locked emitters in multi-core optical fibres for high power fibre lasers are presented. The influence of the normalized frequency and diameters of the cores on the shape of the pattern in the Fraunhofer diffraction region has been analysed. The simulation of coupling coefficient between cores influences on phase-locking and in the consequence on the far-field pattern of the fibre laser, based on the analyzed multi-core optical fibre, were performed. In the analyzed fibre laser, while exchanging power of the generated radiation between two adjacent cores on the fibre length (L = 5 m) within the range of 4–10%, the radiation becomes phased. Having satisfied this condition, in the far-field low-divergence, high-power laser beam (supermode) is attained. 5-core double clad optical fibre doped with neodymium ions was fabricated. Luminescence spectra of the manufactured fibre were measured.     

Effects of laser energy density on impulse coupling coefficient of laser ablation of water for propulsion

Time-resolved force sensing and intensified charge-coupled device (ICCD) imaging techniques were applied to the study of the effects of laser energy density on impulse coupling coefficient of laser ablation of water for propulsion. A Transversely Excited at Atmospheric pressure (TEA) CO₂ laser operated at 10.6 μm, 30 J pulse energy was used to ablate water contained in a quadrate quartz container. Net imparted impulse and coupling coefficients were derived from the force sensor data and relevant results were presented for various laser energy densities. ICCD imaging was used in conjunction with the dynamic force techniques to examine the dependencies on laser energy density. Results showed that the impulse coupling coefficient could reach a maximum value when laser energy density was about 10⁵ J/m², and it would increase before laser energy got to this point and would decrease after this point, and ICCD imaging supplied important phenomenon to explain this variation, which were water ablation before laser energy density got to 10⁵ J/m² and laser-induced air-breakdown with water as an induction when laser energy density was higher than 10⁵ J/m².     

激光熔覆中金属粉末粒子与激光相互作用模型

为了对同轴激光熔覆过程中运动的金属粉末粒子的速度和温度进行理论分析,并研究各工艺参量的影响,建立了运动中金属粉末粒子的运动模型和热模型.模拟结果表明,粉嘴几何尺寸、粒子直径以及气/粉两相流初始速度是影响粒子运动行为的重要因素;粉嘴几何尺寸、激光焦点位置、激光发散角、激光功率、粒子直径以及气/粉两相流初始速度是影响粒子热行为的重要因素.在相同的工艺参量下(粉嘴出口内径r=2 mm,粉嘴倾角α=60°,初始气流速度v0=0.8 m/s),基于数字粒子图像测速(DPIV)技术,对316L不锈钢粉末粒子运动模型进行了实验验证.结果表明,运动理论模型是可靠的.该模型是掌握同轴激光熔覆过程中金属粉末粒子运动行为的有效工具;同时,热模型也是分析粉末粒子温度随不同参量变化的重要工具.     

不同气体工质对激光推力器冲量耦合系数的影响

通过冲击摆实验,测量了激光推力器在不同气体工质(氩气,氦气)、不同工作压力条件下的冲量耦合系数,比较了不同气体对激光推力器冲量耦合系数的影响.实验结果表明:冲量耦合系数随着环境压力的下降而下降,并且下降趋势越来越快;在氩气中测量的冲量耦合系数比氦气的高;实验产生误差的主要因素是摆角的测量误差.