Fabrication of nano-sized grains by pulsed laser surface melting

In this work, the formation and characterization of nano-sized grains on the modified surfaces of GCr15 and H13 steels have been investigated. The material was processed by pulsed laser surface melting (LSM) under different depths of de-ionized water. The microstructures and phases of the melted zones were examined by x-ray diffraction, environmental field emission scanning electron microscopy and high resolution transmission electron microscopy. The results indicate that LSM under water can successfully fabricate nano-scaled grains on the surfaces of steel, due to the rapid solidification and crystallization by heterogeneous nucleation. The elemental segregation of chromium and activated heterogeneous nucleation mechanism of austenite in liquid metal play a key role in the formation of nano-sized grains at high cooling rates. This one-step technique provides us a new way to prepare uniform nano-scaled grains, and is of great importance for further understanding the growth of nano-materials under extreme conditions.

Modeling study on the flow, heat transfer and energy conversion characteristics of low-power arc-heated hydrogen/nitrogen thrusters

A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets). 1:0 (pure hydrogen), 3:1 (to simulate decomposed ammonia), 2:1 (to simulate decomposed hydrazine) and 0:1 (pure nitrogen) hydrogen/nitrogen mixtures are chosen as the propellants. Both the gas flow region inside the thruster nozzle and the anode-nozzle wall are included in the computational domain in order to better treat the conjugate heat transfer between the gas flow region and the solid wall region. The axial variations of the enthalpy flux, kinetic energy flux, directed kinetic-energy flux, and momentum flux, all normalized to the mass flow rate of the propellant, are used to investigate the energy conversion process inside the thruster nozzle. The modeling results show that the values of the arc voltage, the gas axial-velocity at the thruster exit, and the specific impulse of the arcjet thruster all increase with increasing hydrogen content in the propellant, but the gas temperature at the nitrogen thruster exit is significantly higher than that for other three propellants. The flow, heat transfer, and energy conversion processes taking place in the thruster nozzle have some common features for all the four propellants. The propellant is heated mainly in the near-cathode and constrictor region, accompanied with a rapid increase of the enthalpy flux, and after achieving its maximum value, the enthalpy flux decreases appreciably due to the conversion of gas internal energy into its kinetic energy in the divergent segment of the thruster nozzle. The kinetic energy flux, directed kinetic energy flux and momentum flux also increase at first due to the arc heating and the thermodynamic expansion, assume their maximum inside the nozzle and then decrease gradually as the propellant flows toward the thruster exit. It is found that a large energy loss (31-52%) occurs in the thruster nozzle due to the heat transfer to the nozzle wall and too long nozzle is not necessary. Modeling results for the NASA 1-kW class arcjet thruster with hydrogen or decomposed hydrazine as the propellant are found to compare favorably with available experimental data.

Modeling study to compare the flow and heat transfer characteristics of low-power hydrogen, nitrogen and argon arc-heated thrusters

A modelling study is performed to compare the plasma °ow and heat transfer char- acteristics of low-power arc-heated thrusters (arcjets) for three di®erent propellants: hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equa- tions, which take into account the e®ects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, veloc- ity and Mach number distributions calculated within the thruster nozzle obtained with di®erent propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the °ow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appear- ing near the cathode tip; the °ow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant °ows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, speci¯c enthalpies and thermal conductivities, are di®erent, there are appreciable di®er- ences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest speci¯c impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.

A fixed arc length direct current plasma torch for reduced pressure deposition of thin films

Because of its high energy density direct current(dc)thermal plasmas are widely accepted as a processing medium which facilitates high processing rates high fluxes of radical species the potential for smaller jnstallations a wide choice of reactants and high quench rates[1].A broad range of industrial processing methods have been developed based on dc plasma technology. However,nonstationary features limited new applications of dc plasma in advanced processing, where reliability£¬reproducibility and precise controllability are required£. These challenges call for better understanding of the arc and jet behavior over a wide range of generating parameters and a comprehensive control of every aspect of lhe plasma processing.

Melting of Au and Al in nanometer Fe/Au and Fe/Al multilayers under swift heavy ions: A thermal spike study

Knowing that Fe is sensitive to swift heavy ion irradiations whereas Au and Al are not, the behavior of nanometric metallic multilayer systems, like [Fe(3 nm)/Au(x)](y) and [Fe(3 nm)/Al(x)](y) with x ranging between 1 and 10 mn, were studied within the inelastic thermal spike model. In addition to the usual cylindrical geometry of energy dissipation perpendicular to the ion projectile direction, the heat transport along the ion path was implemented in the electronic and atomic sub-systems. The simulations were performed using three different values of linear energy transfer corresponding to 3 MeV/u of Pb-208, Xe-132 and Kr-84 ions. For the Fe/Au system, evidence of appearance of a molten phase was found in the entire Au layer, provided the Au thickness is less than 7 nm and 3 nm for Pb and Xe ions, respectively. For the Fe/Al(x) system irradiated with Pb ions, the Al layers with a thickness less than 4 nm melt along the entire ion track. Surprisingly, the Fe layer does not melt if the Al thickness is larger than 2 nm, although the deposited energy surpasses the electronic stopping power threshold of track formation in Fe. For Kr ions melting does not occur in any of the multilayer systems.

关于偶偶核的形变及对~(124)Te的ARC研究

本文展现了一个从实验谱提取核形变值的唯象方法，并用该方法提取了某些偶偶核的基态形变值。根据Bohr和Mottelson关于对关联对转动惯量的影响的近似考虑及转动惯量对于形变的依赖关系，从实验有效转动惯量提取了核的形度值，并与最近发现的两组理论计算值以及从电四极矩提取的形变数值作了系统比较，结果取得一致，同时表明Bohr和Mottelson关于对关联效应的近似考虑是合理的。本文并计算了一镧系区偶偶核和锕系区偶偶核的α带的形变值。本论文工作利用近年来发展起来的平均共振俘获（ARC）的核谱技术，对~(124)Te核作了探讨和研究。平均能量为24kev中子被~(123)Te靶核俘获后退激放出的γ初级射线，用电子对谱仪进行测量，获得ARC γ谱。通过对2kev、24kev ARC谱数据处理，获取了~(124)Te核2.6Mer下所有O~+、1~+、2~+能级，证明长期以来没确定的2~+态的2倍能量附近的0~+态不存在。在IBMI模型框架下对~(124)Te结构作了探讨，认为最近Robinson等人通过拟合实验谱的理论计算，得出~(124)Te是O（6）核的结论是不合理的。而认为~(124)Te核具有非谐振子能谱的特征，并初步提出~(124)Te可能是接近U（5）结构的核

GIS接受外部空间数据的初步探讨——兼论ARC/INFO~的数据接受方式

数据是地理信息系统 (GIS)应用的核心。现实世界的数据具有普遍的多样性 ,关于 GIS接受不同数据的研究已成为当前 GIS研究中的一个难点和热点。从常见空间数据类型的格式、GIS接受外部空间数据的方式以及 GIS接受外部空间数据中的数据精度、比例尺、坐标变换等几个方面 ,对外部空间数据处理系统的数据向 GIS转换的问题进行了探讨 ,同时以通用 GIS工具软件 ARC/INFO为例分析了其接受外部矢量空间数据的方式。

ARC/INFOR~接受Surfer图文数据的实现

数据是地理信息系统 (GIS)应用的核心。现实世界的数据具有普遍的多样性 ,关于 GIS接受不同数据的研究已成为当前 GIS研究中的一个难点和热点。本文根据通用 GIS工具软件 ARC/INFO接受外部空间数据的方式和图形分析软件 Surfer的数据格式特征 ,运用特定的处理方法实现了由 Surfer格式数据向 ARC/ INFO矢量格式数据 (Coverage)的转换 ,使 ARC/ INFO接受外部数据格式的范围拓宽 ,数据处理能力增强。

Improved Melting Strength of Polypropylene by Reactive Compounding With Ultrafine Full-Vulcanized Polybutadiene Rubber (UFBR) Particles

Ultrafine full-vulcanized polybutadiene rubber (UFBR) in particle sizes of ca. 50-100 nm has been used for modifying mechanical and processing performances of polypropylene (PP), and PP-g-maleic anhydride (PP-MA) has been used as a compatibilizer for enhancing the interfacial adhesion between the two components. The results show that PP/UFBR possesses rheological behaviors such as highly branched PP when UFBR content in blends reaches 10 wt%, while in contrast, the much low content of UFBR combining small amount of PP-MA endows the material with rheological characteristics of high melt strength materials like highly branched PP.

The effect of Co-60 gamma-rays on the crystal structure, melting and crystallization behavior of poly(butylene succinate)

The results obtained for poly(butylene succinate) (PBS) after Co-60 gamma-ray irradiation, studied by wide-angle X-ray diffraction (WAXD), differential scanning calorimeter (DSC) and polarizing optical microscopy (POM), revealed that the degree of crystallinity, melting temperature and enthalpy decreased with increasing irradiation dose, but that the crystal structure of PBS did not vary when compared to non-irradiated PBS. By using Scherrer equation, small changes occurred in the crystal sizes of L-020, L-110 and L-111. The spherulitic morphology of PBS was strongly dependent on irradiation dose and changed significantly at higher irradiation dosages. The crystallization kinetics of PBS indicated that the Avrami exponent (n) for irradiated PBS was reduced to 2.3, when compared to non-irradiated PBS (3.3).

Effect of poly(propylene carbonate) on the crystallization and melting behavior of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate)

The crystallization and melting behavior of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (PHBV) and a 30/70 (w/w) PHBV/poly(propylene carbonate) (PPC) blend was investigated with differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The transesterification reaction between PHBV and PPC was detected in the melt-blending process. The interaction between the two macromolecules was confirmed by means of FTIR analysis. During the crystallization process from the melt, the crystallization temperature of the PHBV/PPC blend decreased about 8 degreesC, the melting temperature was depressed by 4 degreesC, and the degree of crystallinity of PHBV in the blend decreased about 9.4%; this was calculated through a comparison of the DSC heating traces for the blend and pure PHBV. These results indicated that imperfect crystals of formed, crystallization was inhibited, and the crystallization ability of PHBV was weakened in the blend. The equilibrium melting temperatures of PHBV and the 30/70 PHBV/PPC blend isothermally crystallized were 187.1 and 179 degreesC, respectively.

Multiple melting and crystallization behavior of nylon 1212

The wide-angle X-ray diffraction (WAXD) patterns of isothermally crystallized Nylon 1212 show that gamma-form crystals form below 90 degrees C and the alpha-form crystals call exist above 140 degrees C. In the temperature range of 90-140 degrees C, the a-form gamma-form crystals coexist. Variable-temperature WAXD exhibits that the nylon 1212 gamma-form does not show crystal and transition on heating, while a-form isothermally crystallized at 160 degrees C exhibits Brill transition at a little higher than 180 degrees C on heating. The multiple melting behaviors of Nylon 1212 isothermally crystallized from melt come from a complex mechanism of different crystal structures, dual lamellar population and melting-recrystallization. In polarized optical microscope (POM) observations, Nylon 1212 isothermally crystallized at 175 degrees C shows the ringed banded spherulites. However, at temperatures below 160 degrees C the ringed handed image disappears, and cross-extinct spherulites are formed.

Melting behaviors, isothermal and non-isothermal crystallization kinetics of nylon 1212

Isothermal crystallization, subsequent melting behavior and non-isothermal crystallization of nylon 1212 samples have been investigated in the temperature range of 160-171 degreesC using a differential scanning calorimeter (DSC). Subsequent DSC scans of isothermally crystallized samples exhibited three melting endotherms. The commonly used Avrami equation and that modified by Jeziorny were used, respectively, to fit the primary stage of isothermal and non-isothermal crystallizations of nylon 1212. The Avrami exponent n was evaluated, and was found to be in the range of 1.56-2.03 for isothermal crystallization, and of 2.38-3.05 for non-isothermal crystallization. The activation energies (DeltaE) were determined to be 284.5 KJ/mol and 102.63 KJ/mol, respectively, for the isothermal and non-isothermal crystallization processes by the Arrhenius' and the Kissinger's methods.

Crystallization and melting behaviors of PPC-BS/PVA blends

The isothermal crystallization and melting behaviors of poly(propylene carbonate) end-capped with benzenesulfonyl/poly (vinyl alcohol) (PPC-BS/PVA) blends over rich PVA composition range were first investigated by differential scanning calorimetry (DSC). PPS-BS/PVA interaction parameter, chi(12), calculated from equilibrium melting temperature depression was -0.44, revealing miscibility of PPC-BS with PVA in the melt and favorable interactions. The temperature dependence of crystallization rate constant at initial crystallization stage was analyzed using the modified Lauritzen-Hoffman expression. The chain width, a(0), the thickness of a monomolecular layer, b(0), the fold and lateral surface-free energies, sigma(e) and sigma, and the work of chain folding, q, for neat PVA were first reckoned to be 4.50 Angstrom, 4.78 Angstrom, 76.0 erg.cm(-2), and 4.70 kcal.mol(-1), respectively. The values of sigma(e) and q for PVA in PPC-BS/PVA blends exhibited a maximum in the neighborhood of 10/90 PPC-BS/PV, respectively.