Dimensional analysis for Gorter-Mellink counter flow convection in pressurized superfluid helium

Dimensional analysis of the heat transport through ducts filled with saturated He II is extended to pressurized conditions up to 20 bar. Simplified models are also presented for the ease of first order estimation of the GM-transport heat flux density, the temperature gradient and the limiting heat flux densities by relating calculations to reduced thermo physical properties, with respect to the properties at the lambda point. The data available show good support for the dimensionless GM-equation in pressurized He II within data scatter and thermo physical property uncertainty.     

Studies on the structural properties of SiO:H films prepared from (SiH4+CO2+He) plasma in RF-PECVD

A comprehensive report on the structural studies on SiO:H films prepared at high growth rate from He-diluted (SiH₄+CO₂) plasma has been presented and extraction of some intriguing ideas that deserve high relevance for the potential development of nano-crystalline hydrogenated silicon oxide (nc-SiO:H) films has been tried. Poly-hydrogenation has been found as inherent to increasing alloying of the network; however, the bonded H-content reduces linearly with the degree of oxygen incorporation, i.e., the solubility of H in the SiO:H network decreases as the O-content increases in the presence of He. This result happens to be opposite to the conventional H₂-diluted plasma condition and appears to be attractive as well. In addition, He-dilution contributes to a high growth rate of the material. Dynamic interaction of He* in the formation of activated oxygen atoms in the plasma and their efficient mobilization on the surface reaction process at the growing network induces abstraction of H from the SiH_n groups and the terminal H atoms are replaced by bridging O atoms to form the SiO:H network. Abstraction of H from the network being an essential criteria for developing nanocrystallinity and it being inherent to oxygenation in Si network when prepared from He-diluted (SiH₄+CO₂) plasma in PECVD, the process could provide an appropriate pathway for preparing nc-SiO:H structures for solar cells, from such plasma in suitable parametric conditions.     

Structural study of CH3S self-assembled monolayers on Au(111)

We present preliminary results of an experimental investigation of ordered phases of CH₃S chemisorbed on Au(111). The self-assembled monolayer has been grown by dosing dimethyl disulfide in ultrahigh vacuum at different substrate temperatures between 200 K and 320 K and following different protocols. The monolayers have been characterized by means of low-energy He atom scattering with time-of-flight detection in a temperature range between 150 K and 300 K. The observed diffraction patterns show that the main periodicity is well-described by the (3 × 4) overlayer of the Au(111) lattice, coexisting with the (√3 × √3) periodicity, in agreement with previous results obtained by means of low-energy electron diffraction.     

钚材料的α能谱以及氦气累积的蒙特卡罗计算

本文根据钚材料的元素成分和放射性核素的级联衰变规律,编程计算了共涉及11种核素杂质以及氦气的生成.采用蒙特卡罗方法计算,得到了自辐照α粒子能谱及其演化规律.在编制的计算程序中设计了独立的随机数发生器,并利用Fortran95的MODULE功能进行模块化封装.这一以封装模块为主体的程序具有良好的通用性和扩展性,可方便地作为一个功能实现部分嵌入钚材料老化研究的其他程序之中.     

射频容性耦合等离子体阻抗影响因素研究

为了进一步探索射频容性耦合放电等离子体,本文建立了以容性耦合等离子体(CCP)为基础的板-板电极一维轴线简化仿真模型。仿真采用氦气为工作气体,使用约化电子传递属性并忽略重粒子对流,利用有限元算法,综合讨论了一定范围内放电参数(气体压强、输入功率、电极直径以及间隙长度)变化时,放电等离子体阻抗的变动情况,并根据仿真所得数据进行理论分析。结果表明:四种仿真条件下的等离子体均呈现容抗特性;当气压升高、放电间隙长度变大时,初期均有利于碰撞电离的发生,而后将成为限制因素,使得等离子体阻抗呈现先减小后升高的变化趋势;当电极直径增大、输入功率增加时,初期等离子体阻抗均呈下降趋势,但后续变化趋于平稳。     

Blistering and flaking of amorphous alloys bombarded with He ions

The blistering and flaking behavior of many kinds of amorphous alloys under helium ion bombardment at room temperature was investigated.Helium ions with energies of 40keV and 60keV were implanted within the fluence range (1.0-4.0)013310^18ions/cm^2.The surface topography of samples after irradiation was observed by using a scanning electron microscope.The diameter of blister and the thickness of exfoliated blister lids were measured.The results showed that many kinds of surface topography characteristics appeared for different fluences,energies and amorphous alloys,such as flaking,blistering,exfoliation,blister rupture,secondgeneration blistering and porous structure.The dependence of surface damage modes and the critical fluence for the onset of blistering and flaking on the sort of materials and ion energy was discussed.     

Performance of low-friction coatings in helium environments

The aim of this research work was to investigate the possibility of replacing soft PTFE‐based coatings on components operating in helium atmosphere. Focus was on maintaining low friction and improving surface wear resistance. Therefore two commercial DLC coatings (a-C:H and Me-C:H), CrN coating and reference PTFE‐based Rulon and Xylan coatings were included in this investigation. Coatings were deposited on hardened 100Cr6‐bearing steel discs and tested against uncoated steel balls in pin-on-disc contact configuration under dry reciprocating and unidirectional sliding in helium atmosphere. Investigation was concentrated on the effect of running-in, contact pressure, sliding speed and counter-material type and surface treatment on the tribological behaviour of hydrogenated DLC coatings when running‐in in helium.     

锆复合板换热器制造工艺技术

介绍了锆复合板换热器制造特点和技术难点,在实际制造中,通过详细的试验对比,制定了合理的加工技术参数,为下一步大型锆复合板容器的制造提供了依据。     

Helium-driven element depletion and phase transformation in irradiated Ti3SiC2 at high temperature

Future nuclear reactors and advanced power generators require materials with good stability and damage tolerance under harsh conditions, including high temperatures and high-dose radiation. Ti₃SiC₂ MAX phase has good physical properties and mechanical strength. It can remain crystalline under serious microstructure damage due to the nanolaminate structure. In this study, the effects of helium in irradiated Ti₃SiC₂ at up to 1100 °C were investigated by microstructural and chemical composition analysis. The concentrated helium can grow into large bubbles without significant confinement or capture by the nano-laminated layers. A new hexagonal to fcc phase transformation mechanism, driven mainly by the evolution of the helium bubbles accompanied by Si diffusion and depletion, is found and investigated. Si interstitials are forced to move out from the peak helium region by the helium evolution and segregate at the outermost surface, forming a thin Si-O layer, at 1100 °C. The formation of the fcc phase is the result of chemical compositional changes and local compressive stress contributed by He bubbles.     

In-situ transmission electron microscopy observation of the helium bubble evolution in pre-irradiated fluorapatite during annealing

The polycrystalline fluorapatite Ca₁₀(PO₄)₆F₂ ceramic synthesized by a standard solid-state sintering method was pre-irradiated with 80 keV He⁺ ions to a fluence of 5 × 10¹⁶ ions/cm² at room temperature. After that, an in-situ annealing experiment was performed inside a transmission electron microscope to monitor the evolution of helium bubbles during heating to 723 and 823 K. Initially, no helium bubble formation was observed in the damage layers of the pre-irradiated samples. However, as the temperature increased, helium bubbles first became visible and then began coarsening, ultimately reaching an asymptotic radius during annealing. The migration and coalescence of helium bubbles in the fluorapatite matrix was complete at a temperature of 823 K, and its likely mechanism involved the existence of two different types of coalescing bubbles.