THERMODYNAMIC AND PARTICLE-DYNAMIC STUDY FOR COMBUSTION SYNTHESIS OF TITANIA NANOPARTICLES

Recent referential studies on combustion synthesis of titania nanoparticles were briefly reviewed. Computations based on the minimization of Gibbs free energy were conducted to find the equilibrium compositions, the optimal reaction temperature, the suitable mole ratio of oxygen to titanium tetrachloride, and the best inlet positions of titanium tetrachloride. The mean particle diameter was obtained from particle-dynamic simulation. A combustion apparatuswas setup to synthesize titania nanoparticles by the oxidation and hydrolysis of titanium tetrachloride at high temperatures. Experimental investigation verified some results obtained from thermodynamic and particle-dynamic computations.     

THERMODYNAMIC ANALYSIS AND EXPERIMENTAL VERIFICATION FOR SYNTHESIZING SILICON NITRIDE NANOPARTICLES USING RF PLASMA CVD

Silicon nitride nanoparticles were synthesized by radio-frequency (RF) plasma chemical vapor deposition (PCVD) using silicon tetrachloride and ammonia as precursors, and argon as carrier gas. By assuming chemical thermodynamic equilibrium in the system, a computer program based on chemical thermodynamics was used to calculate the compositions of the system at different initial concentrations and final temperatures. At first, five elements and thirty-four species were considered. The effects of temperatures, and concentrations of ammonia, hydrogen and nitrogen on the equilibrium compositions were analyzed. It was found that the optimal reaction temperature range should be 1200 to 1500 K to obtain the highest conversion and yield of Si3N4. The inlet position of ammonia should be lower than that of silicon tetrachloride, and both should be located at the tail of the plasma torch. The best moleratio of ammonia to silicon tetrachloride was found to be about 6. Later, the influences of water (.and oxygen) were considered, and 17 additional species were included in the computations. It was found that oxygen or water content in the raw materials should be as low as possible in order to have high nitride content in the produced Si3N4. Nitrogen or hydrogen might be used to replace some or even all the argon to improve the yield of silicon nitride and reduce the cost. The ratio of ammonia to silicon tetrachloride should be high enough to obtain high conversion, but not excessively high to reduce the oxygen content due to the existence of water in ammonia. The simulated results were verified bv experiments.     

电热化学发射中等离子体发生器放电特性的实验研究

从实验方面研究了电热化学发射中等离子体发生器随毛细管的几何尺寸和ＰＦＮ网络的初始充电电压等参数变化的放电规律，结果将有助于改进等离子体发生器的设计和提高放电的效能。     

SYNTHESIS OF HIGH PURITY TiO2 NANOPARTICLES FROM Ti（SO4）2 IN PRESENCE OF EDTA AS COMPLEXING AGENT

TiO2 nanoparticles were synthesized by a homogeneous controlled precipitation method using industrial titanium sulfate （Ti（SO4）2）. The obtained powders were characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, Fourier transform infrared spectroscopy （FTIR） and ICP plasma spectrometer. EDTA was used as complexing agent to improve the purity and the formation of TiO2 nanoparticles. Experimental results indicated that the high-purity TiO2 nanoparticles were 20 nm in mean size and nearly monodispersed.     

热等离子体科学技术的现状和发展

概述了热等离子体科学技术的现状和发展,介绍了一些工业应用和等离子体发生器。      

化爆冲击波和炮口冲击波对生物致伤效应的对比研究

通过TNT化爆和火炮现场试验,探讨了化爆冲击波和炮口冲击波的异同点,结果发现两者的频谱大致相似。但化爆冲击波只有一次激波,而炮口冲击波有两次激波,有时甚至可见到三次激波。生物效应致伤的靶器官也有所不同,化爆冲击波以肺损伤较为多见,而炮口冲击波似乎以上呼吸道更为敏感,结果提示化爆可以模拟炮口冲击波,但又不完全等同于炮口冲击波,必要的火炮现场试验是必不可少的。     

RHT-902和Octol炸药爆轰产物JWL状态方程研究

本文对RHT-902和Octol两种炸药做了标准圆筒试验,运用能量守恒原理分析处理试验结果,用解析关系式确定了这两种炸药爆轰产物的JWL状态方程参数。这些参数与国外发表的相应参数基本一致。     

高应变率下的矿岩特性研究

本文采用霍普金森杆（S.H.P.B.）装置对三种磁铁矿和一种化岗岩在应变率为102～103S-1范围内的力学特性进行了研究。文中给出了矿岩在不同应变率下的动态破坏强度,动态弹性模量、动态应力-应变曲线和分析结论。     

准静态压力作用下岩体爆破成缝方向与机理的研究

本文在讨论了现有的爆破成缝理论以后,首先将岩体在爆生气体作用下的成缝过程分为开裂、扩展和止裂三个阶段,建立了这三个阶段的力学模型。然后,着重分析了爆破成缝方向和机理,提出了相应的断裂判据。最后,结合在大理石试块上进行的爆破成缝试验,通过计算分析,验证了本文提出的成缝机理。     

EXPERIMENTAL AND NUMERICAL STUDIES ON PERFORMANCE OF MACRO FIBER COMPOSITES FOR BEAM TWISTING APPLICATIONS

This paper presents the use of macro-fiber composites (MFC) as actuators for twisting control of pre-twisted beams, which is one efficient method of vibration suppression techniques of helicopter rotors. An MFC is a piezoelectric fiber composite which has an interdigitated electrode, rectangular cross-section and unidirectional piezoceramic (PZT) fibers embedded in the polymer matrix. An MFC actuator has much higher actuation performance, flexibility and durability than a traditional piezoceramic (PZT) actuator. This study showed that an MFC could be used as an actuator to change the displacement and twist tip-angle of a pre-twisted beam. In the test, an MFC patch was pasted on the beam’s upper surface to twist the pre-twisted beam actively. Different twist tip-angle changes of the pre-twisted beam were measured under a series of actuation voltages, and a good agreement was observed when experimental results were compared with numerical results. In addition, the actuation performance of MFC was compared with those of PZT4 and PVDF and the influence of anisotropic property of the MFC on its actuation performance was also studied. The experimental and numerical results presented in this paper show the potential of MFC for use in the vibration control of helicopter rotors.     

低频螺旋状压电俘能器结构性能分析

利用螺旋状双晶片压电梁式俘能器可以有效地从低频工作环境中提取能量.由于这种俘能结构振动中存在弯曲振动和伸缩振动两种模态,确定俘能器的最优工作模态非常重要,这样外载作用型式(即面内受载还是面外受载)对俘能器的影响较大.数值结果表明:外激励方向不同时,最大输出功率密度出现在不同阶数的固有频率处,并且最大输出功率密度的大小也显著不同,面内加载方式明显优于面外加载方式.最后还详细讨论了储能电路的阻抗,自由端悬挂的集中质量对俘能器性能的影响规律.     

一种确定压剪全息干涉条纹级数的理论与实验研究

针对全息干涉条纹判读的难点,结合断裂力学知识、焦散线法和实时全息干涉,探讨了一种计算含有预制裂纹试样实时全息干涉条纹强度值的理论方法.并进行实验验证,结果表明这种分析对于相关研究有一定的参考意义.     

电流变液研究进展及最新动态──第5届国际电流变液、磁悬浮体 及相关技术研讨会评介

通过评介第５届国际电流变液、磁悬浮体以及相关技术研讨会，指出电流变液和磁流变液的应用研究有重要进展；磁流变液的剪切应力比电流变液大一个数量级，近来又受到重视；在机理研究中，要注意电流变液的表面效应、损耗对电流变效应的影响．本文还归纳了一些电流变液材料设计的思路．