The Electron–Phonon Interaction of Low-Dimensional and Multi-Dimensional Materials from He Atom Scattering

Atom scattering is becoming recognized as a sensitive probe of the electron–phonon interaction parameter λ at metal and metal-overlayer surfaces. Here, the theory is developed, linking λ to the thermal attenuation of atom scattering spectra (in particular, the Debye–Waller factor), to conducting materials of different dimensions, from quasi-1D systems such as W(110):H(1 × 1) and Bi(114), to quasi-2D layered chalcogenides, and high-dimensional surfaces such as quasicrystalline 2ML-Ba(0001)/Cu(001) and d-AlNiCo(00001). Values of λ obtained using He atoms compare favorably with known values for the bulk materials. The corresponding analysis indicates in addition, the number of layers contributing to the electron–phonon interaction, which is measured in an atom surface collision.     

Investigation on phase shifting for a 4 K Stirling pulse tube cryocooler with He-3 as working fluid

He-3 is generally recognized for its ability to provide more excellent thermophysical performance than He-4, especially in the 4 K temperature range. However, this was not always the case in our preliminary experiments on a three-stage Stirling-type pulse tube cryocooler (SPTC). Our ongoing studies, as reported in this paper, demonstrate that the different working fluids also affect the performance through their phase shifting capability. This feature has been passed over in large part by researchers considering refrigerant substitution. Unlike previous theoretical analyses that focus primarily on regenerator losses, this report investigates the effects of the working fluid on the phase angle at the cold end in order to quantitatively reveal the relationship between the lowest attainable temperature and the cooling capacity. The analysis agrees well with our experimental results on a three-stage SPTC. While running with the operating parameters optimized for He-3, the lowest temperature of the SPTC decreased from 5.4 K down to 4.03 K. This is the lowest refrigeration temperature ever achieved with a three-stage SPTC.     

Radiative and conductive heat transfer in a 4-K helium phase separator with minimum heat loss

Improvements in simulation and practice for the heat load of a helium phase separator are discussed. The separator cryostat (volume 100 L, cooling capacity 1.5 W at 4.2 K) re-condenses and stores liquid helium. An additional radiation shield was designed to minimize the radiative heat transfer and to decrease the heat conduction. The experimental results indicate that the heat load of the separator was decreased from 5.56 W to 1.555 W, a gain about 4 W of heat load, which is an improvement by 72%. Liquid helium (50 L) was stored in the separator stably for more than 90 h. Software implementing the finite-element method (FEM) was used to predict the temperature distribution of pipe fittings and the separator heat load with or without the additional radiation shield. The results of these simulations show that the temperatures of the pipe fittings were significantly decreased in the separator with additional radiation shields. For the heat load, the trends of simulation and experimental results were similar. This work provides a simple and effective method to minimize the radiation heat load of a separator. In this paper, we discuss in detail the improvements of the model, the experimental setup and the results of comparisons between experiments and simulations.     

氦离子预注入对钨中氘滞留行为的影响

利用高能离子注入机和直线等离子体模拟装置,本文研究了高能氦离子预注入对氘等离子体辐照后钨中氘滞留行为的影响。采用FIB-SEM、TEM、GD-OES和TDS等分析方法,分析了氦离子预注入对钨中氘滞留行为的影响。结果表明：氦离子预注入在辐照损伤区域形成大量氦泡,钨经过氘等离子体辐照后,表面的氘泡数量明显低于未经过氦离子预注入的样品。GD-OES分析中可以看到在氦捕获位处氘滞留浓度明显升高,同时氦离子预注入增加了氘在钨中的扩散深度,结合TDS分析可知氦离子预注入增加了氘在钨中的滞留总量,这是由于氦离子预注入后,形成的缺陷又为钨中氘的俘获提供大量新的位点,从而导致钨中的氘滞留量明显提高。     

利用氦流法真密度仪研究水泥水化过程

采用氦流法真密度仪测定了水泥水化过程中水泥浆体的绝对体积变化,并根据水泥浆体绝对体积变化曲线将水泥水化过程划分为极速收缩期、收缩暂停期、快速收缩期和收缩趋缓期4个阶段.结果表明:水泥浆体极速收缩期和快速收缩期发生的绝对体积变化最为明显,且变化幅度较大,其与C_3A和C_3S的水化密切相关;水泥浆体收缩暂停期的绝对体积通常呈线性规律缓慢减小,但变化幅度较小,其规律与"欠饱和度理论"相符;水泥浆体收缩趋缓期的绝对体积变化曲线通常会出现"膨胀"假象,不能反映水泥浆体绝对体积变化的实际情况,但与水泥浆体孔结构的发展有关,对水泥水化行为的表征仍具有重要的指导意义;水灰比不仅可以影响水泥水化过程,而且可以对水泥浆体各水化阶段的绝对体积变化产生明显影响.     

Separation of He/N2/CH4 ternary mixtures by a triple-reflux pressure swing adsorption process

Conventional pressure swing adsorption (PSA) processes can only produce one high purity product in a single stage, whereas the state-of-art dual-reflux PSA (DR-PSA) can produce two high purity products simultaneously. However, multicomponent gas separation is often required in the industry, targeting at recovering several valued products at the same time. In this study, we propose a novel adsorption process, namely triple-reflux PSA (TR-PSA), to separate three components simultaneously. A middle product outlet and a middle reflux stream were introduced to the adsorption columns of a conventional DR-PSA process to separate ternary mixtures of nitrogen, methane, and helium. Nonisothermal dynamic models were built to investigate the impacts of operating parameters particularly the location of the middle reflux/product stream and the middle reflux flow rates. Results showed that the TR-PSA process successfully separated ternary mixtures obtaining three enriched products simultaneously in a single stage, yielding a separation performance comparable to that of the double-stage DR-PSA with significantly lower capital and energy cost.     

氢镍电池陶瓷密封极柱正压氦检方法研究

高压氢镍电池陶瓷极柱的密封性是影响电池性能的主要原因之一。设计了一种陶瓷极柱的正压氦检方法,有效提高了极柱的检漏水平,从而进一步提高了氢镍电池使用的可靠性。     

氩霜竞争吸附实验平台的设计与验证

为了研究氩霜对氦气与氢气的混合气体竞争吸附的特性,设计并搭建了一套低温实验台,该实验台主要包括液氦恒温器、吸附室和气体缓冲室,能实现氩霜在低温下对纯氦气、纯氢气以及两种气体的混合物的吸附特性的研究。从理论上分析了液氦恒温器的热力性能,预冷恒温器低温部分所需液氦为35.3 L,系统漏热为7.109 2 W,稳定运行时液氦耗量为9.8 L/h。为了验证本实验台的可信度,以氦气为吸附质气体,研究了氩霜在液氦温度下对其吸附的吸附特性,通过与文献实验数据的对比,表明该实验台在低温下研究氩霜对不同气体的吸附研究是可信的。     

氦冷却法制备氮浆中液滴凝固过程的模拟与分析

采用氦冷却法制备氮浆的工艺所制氮浆颗粒尺寸均匀,制备过程中杜瓦内可维持正压,从而防止周围空气的漏入。通过对氦冷却法制备氮浆过程中液滴凝固时固氮颗粒的形成过程进行分析,建立起相应的物理模型以及微分方程,并对微分方程进行数值求解。着重考察了液滴的凝固过程,并对液滴群完全凝固时的氦气温度、压力、流速以及扩散腔长度进行了研究,进而探讨了采用该方法制备氮浆时氦气工作参数、喷管尺寸以及扩散腔长度等的选择问题。     

He+离子辐照Inconel 718合金表面形貌改变及机理研究

研究了3种不同剂量He⁺离子辐照后Inconel 718合金的形貌变化规律及其形成机理。结果表明，He⁺离子辐照会在合金表面形成纳米多孔结构，其孔径会随辐照剂量的增加而增大。此外，He⁺离子辐照还会破坏合金表面δ相并导致碳化物的持续溅射损耗，且这一现象会随着辐照剂量的增加而愈发严重。由于辐照过程中氦泡间微观应力σ n作用会引起毗邻材料断裂及氦泡合并长大，且辐照溅射作用又会导致氦泡上层薄膜的损耗甚至破裂，因而这也是He⁺离子辐照Inconel 718合金表面纳米多孔结构的形成机制。