Transmission of very slow neutrons through material foils and its influence on the design of ultracold neutron sources

At the Paul Scherrer Institute (PSI), a very intense source of ultracold neutrons (UCN) is being built. The UCN converter of solid deuterium must be contained in a vessel. Produced UCN leave that vessel through its top lid. To decide on the design of the vessel and the top lid, we have measured the transmission of neutrons with velocities between 3 and 20 m/s through different material foils. Contrary to expectations, we found that transmission through aluminium and aluminium alloys is equal or even higher compared to zirconium and reactor-grade zirconium alloys, respectively.     

A compact, large-diameter adiabatic spinflipper for ultracold neutrons

We report the design and test of a compact, large-diameter spinflipper for ultracold neutrons based on the principle of adiabatic spinflip. A solenoid rf coil with a high diameter-to-length ratio (d/l~1.7) is surrounded by up to three short magnet coils (d/l~0.4…1.7) to provide the static gradient field. The device is optimized for low power consumption and operation in high vacuum. The magnetic field conditions necessary for full spinflipper efficiency over the full diameter were evaluated with ultracold neutrons. The measured spinflipper efficiency vs. adiabaticity correlation is in good agreement with a calculation based on an ideally linear gradient.     

A new superleak to remove He for UCN experiments

The production of superleaks to remove He³ in helium for UCN experiments is described. Using one of these superleaks, He³/He⁴ ratio was found to be less than 3 × 10⁻⁹ as indicated by the UCN storage lifetime.     

双固化型全息用光致聚合物的研制及其全息性质研究

以环氧树脂为成膜树脂，甲基丙烯酸甲酯为光聚合活性单体，研制了一种双固化型全息用光致聚合物材料。通过成膜树脂配方的选取和光敏染料的选取优化了样片的配方组成，用457nm的蓝光在样片中记录全息光栅，用632．8nm的红光作为探针光，研究了样片的衍射效率、灵敏度、折射率调制度、预曝光量和收缩率等全息性能，测试结果表明单体的含量与组分的选取是影响样片衍射效率的主要因素，同时样片的制膜工艺对其全息性能也有很大的影响，通过配方的调整和制膜工艺的优化，部分样片的综合性能已基本达到实用化的需要。     

类金刚石磁盘保护膜的性能、应用与制备

类金刚石膜在磁盘和读写磁头之上形成一层关键的保护膜.磁存储密度的飞速发展可以使存储密度上限达到1万亿字节/英寸2.这要求读写磁头距离磁盘更近,即需要一层仅1 nm～2 nm厚的类金刚石薄膜.四面体结构的非晶碳膜能够满足磁存储技术的要求,即形成原子尺度平滑、连续、致密,只有几个原子层厚的碳膜.磁过滤阴极弧方法、等离子体增强化学气相沉积方法可用来制备符合要求的超薄碳膜.     

PiBrED—A novel bragg edge detector for neutrons

We present a single pixel prototype of a pixelated Bragg edge detector for neutron transmission measurements. The optical signal coming from a scintillator is collected by an optical fiber and is detected by an avalanche photodiode. A fast, Field Programmable Gate Array based, readout allows to obtain transmission spectra within reasonable acquisition times. The performances of the instrument have been tested by measuring the transmission spectra of iron powder samples with two different scintillators. The instrument accuracy in detecting the Bragg edges positions is comparable with the state of the art for similar devices.     

烟煤粘结纳米镁基储氢材料的制备及吸放氢性能

以Mg、烟煤和碳化无烟煤为原料,经H2反应球磨、热处理制备了烟煤粘结的纳米镁基储氢材料,研究了储氢材料结构及吸放氢性能,并计算了材料的吸氢动力学参数。结果表明,在600℃热处理时材料中的Mg容易与煤中的C发生反应生成Mg2C3;添加15%(质量分数)烟煤,经500℃热处理能有效粘结纳米Mg颗粒,且未见Mg2C3生成。储氢材料的吸氢速率随温度升高而增大,在2MPa H2下吸氢量在350℃达到最大值,约3.77%(质量分数),在400℃时吸氢量略有下降。根据Arrhenius公式得出储氢材料在300~350℃下吸氢的一级反应表观活化能为56.6kJ/mol H2。用TPD测定了储氢材料的放氢温度,表明材料在250℃开始放氢,388℃时达到放氢高峰。储氢材料中的C可结合少量H,该类H在加热时会以CH4等烃的形式释放出来。     

球磨时间对镁碳复合储氢材料结构和性能的影响

采用氢气气氛中高能球磨反应法,制备了40Mg60C镁碳复合储氢材料,研究了球磨时间对材料粒度、晶体结构和放氢性能的影响.结果表明,球磨2h材料的粒度即可达纳米级,约10～20nm,球磨时间再延长,材料团聚程度加重;球磨2h的材料为纳米晶和非晶结构,当球磨时间增加到4h时,材料几乎成为非晶结构;球磨时间4h时,材料储氢量已趋于饱和,最大放氢量为3.15%(质量分数);材料放氢温度随球磨时间的增加而降低,球磨5h材料的初始放氢温度和放氢峰温降为275.18和314.94℃.     

A novel type of Ge nanotube arrays for lithium storage material

Amorphous Ge nanotubes, featured of a top-closed tubular structure, were synthesized directly on metallic current collector substrates via a template technique. Measurement of electrochemical cycling reveals that these nanotubes can deliver reversible capacities of -1300 mAh/g (81% of the theoretical capacity) at the current density of C/20 (1C = 1600 mAh/g) and retain -700 mAh/g at 2C with columbic efficiencies over 99%. Such performance is comparable to that of the recently reported Ge nanowire anodes grown directly on the metallic substrates by the chemical vapor deposition, indicating that the present Ge nanotubes are a type of anode materials with high capacity and good rate performance for lithium storage.     

Preparation and thermal properties of lauric acid/raw fly ash/carbon nanotubes composite as phase change material for thermal energy storage

Abstract

In this study, a novel ternary system form-stable phase change material (FSPCM) composed of lauric acid (LA)/raw fly ash (RFA)/carbon nanotubes (CNT) was prepared via low cost, easy and industrially applicable fabrication process for low-temperature heat storage. Particularly, the unmodified RFA was directly acted as supporting material to prevent the leakage of the melted LA almost at no cost. A series of leakage experiments were performed to evaluate the package efficiency. The maximum mass fraction of LA absorbed in RFA and CNT was found to be 25?wt% without the LA leakage. Hence, the LA/RFA/CNT (25/75/5?wt%) composite was characterized as FSPCM. The chemical structures, microstructure thermal properties and thermal stability of the FSPCM was investigated by Fourier transformation infrared spectroscope (FTIR), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analyzer (TGA). The SEM and FTIR results indicated that LA was adsorbed on the RFA’s surface porous or into the porous structure of CNT. And there was good chemical compatibility among LA, RFA and CNT. The DSC results demonstrated that the phase change temperatures and latent heats of LA/RFA/CNT FSPCM were 45.36?°C and 37.83?J/g for melting and 40.51?°C and 36.48?J/g for freezing, respectively. TGA analysis test revealed that the composite PCM had excellent thermal stability. Moreover, the heat transfer efficiency of LA/RFA/CNT FSPCM has been improved by the addition of RFA and CNT. In short, the LA/RFA/CNT FSPCM has a promising application prospect in low-temperature application due to feasible and in large scale industrial preparation, low-cost, simple and facile process.     

Influence of PECVD parameters on the properties of diamond-like carbon films

The properties of diamond-like carbon (DLC) are strongly affected by the amount of carbon atoms bonded in sp² and sp³ electronic hybridizations. Also the amount of incorporated hydrogen and oxygen plays an important role in the final properties of DLC films. Usually, the structure and chemical composition of thin DLC films can be changed by varying the deposition parameters. Therefore, the influence of PECVD process parameters on the properties of DLC films, grown on Si substrates, was investigated in this work.Thin DLC films were deposited in a CH₄/H₂ plasma by using Ar as a gas carrier. Different ratios of gas flows were used as a variable parameter of the PECVD process. The effect of cathodic ion bombardment was also investigated.The chemical composition of DLC specimens was studied by X-ray photoelectron spectroscopy (XPS). The ratio of carbon in sp² and sp³ hybridizations was determined by analyzing the first derivative of Auger C KLL spectra. These results were also confirmed by the measurements of electrical resistivity. The changes of surface morphology and microadhesion were analyzed by Atomic Force Microscopy (AFM).     

有机相变蓄冷复合材料的研究

研制了一种新型三元复合相变蓄冷材料.利用差示扫描量热仪测量物质的性能,测得相变材料相变温度为-14℃,相变潜热为172J/g.主要成分是丙三醇、乙酸钠和水,原材料价格便宜且易购得,可以大规模应用于冷库冷藏、低温物流等领域.     

新型电子转移复合物Cu-TCNQ(C2H4 COOCH3)2的制备及其薄膜的绿光可擦重写光存储性能的研究

报道了高溶解性能的电子转移复合物铜-(2,5-二丙酸甲酯-7,7,8,8-四氰基对苯醌二甲烷);并对其紫外可见光光谱进行了研究.用旋涂工艺制备了Cu-TCNQ(C2H4COOCH3)2薄膜,并对该薄膜的可擦重写光存储性能及其机理进行了研究.短波长(514.5nm)静态可擦重写光存储性能测试结果表明在写入功率为9mW,写入脉冲为80ns,擦除功率为4mW,擦除脉冲为500ns时反射率对比度＞15%(无反射膜),循环次数可达110次以上,并且没有出现任何疲劳现象.     

Pd在超级活性炭上的负载对其储氢性能的影响

负载金属Pd和PdO都有助于提高超高比表面积活性炭的吸氢性能，并能使其吸氢能力分别提高2倍～4倍和4倍～5倍左右。同时由于过渡金属住高温下容易发生团聚和迁移现象，负载在活性炭上的金属Pd的还原温度和还原时间应分别控制在125℃和2h。在0℃和27℃常压下，Pd／AC和PdO／AC(SBET为3886m^2／g)对氢的饱和吸附量分别为：20mL／g、23mL／g和14mL／g、15．8mL／g，且它们的循环使用寿命良好。     

Investigation of the properties of diamond-like carbon thin films deposited by single and dual-mode plasma enhanced chemical vapor deposition

In this study diamond-like carbon (DLC) films were deposited by a dual-mode (radio frequency/microwave) reactor. A mixture of hydrogen and methane was used for deposition of DLC films. The film structure, thickness, roughness, refractive index of the films and plasma elements were investigated as a function of the radio frequency (RF) and microwave (MW) power, gas ratio and substrate substance. It was shown that by increasing the H₂ content, the refractive index grows to 2.63, the growth rate decreases to 10 (nm/min) and the surface roughness drops to 0.824 nm. Taking into consideration the RF power it was found that, as the power increases, the growth rate increases to 11.6 (nm/min), the variations of the refractive index and the roughness were continuously increasing, up to a certain limit of RF power. The Raman G-band peak position was less dependent on RF power for the glass substrate than that of the Si substrate and a converse tendency exists with increasing the hydrogen content. Adding MW plasma to the RF discharge (dual-mode) leads to an increase of the thickness and roughness of the films, which is attributed to the density enhancement of ions and radicals. Also, optical emission spectroscopy is used to study the plasma elements.     

一种定形相变贮能材料的制备

本实验探讨了利用熔融插层法将棕榈酸插入到蒙脱土层间制备定形相变贮能材料的方法,研究了其适宜的制备条件,用XRD、IR、DSC等方法对定形相变材料的结构和性能进行了表征与测试.研究结果表明:棕榈酸被有效地密封在蒙脱土层间,制得的材料具有良好的贮能性能,相变贮能过程中形态稳定.     

新型稀土镁基贮氢电极合金的结构与性能

系统研究了La0．7Mg0．3(Ni0．85Co0.15)x(x=2．5，3．0，3．5，4．0，4．5，5．0)贮氢电极合金的结构和储氢性能．该类型合金由(La，Mg)Ni3相(PuNi3型结构)和LaNi5相(CaCu5型结构)组成，两相的a轴参数和晶胞体积都随着x值的增大而减小．(La，Mg)Ni3相的丰度先从x=2．5时的48．4％增加到x=3．5时的78．2％，然后又减小到x=5．0时的12．2％，而LaNi5相的丰度在x=2．5-3．5时基本保持不变(-20％)，在x=4．0时突然增加到71.9％．合金的吸氢量从x=2．5时的0．86％(质量分数)增加到x=3．5时的1．50％然后又减小到x=5．0时的1．19％．合金的放氢平台压力在x=2．5-3．5时保持基本不变(-65．9kPa)，然后逐渐增加到x=5．0时的0．30MPa．随着x的增加，吸放氢过程的滞后效应先增大后减小，而合金的放氢平台变得更加平坦．     

The influence of fluorine doping on the optical properties of diamond-like carbon thin films

Optical properties of fluorine doped diamond-like carbon (F:DLC) films deposited by the direct current plasma enhanced chemical vapor deposition (PECVD) technique were studied in detail. Surface morphologies of the F:DLC films were studied by an atomic force microscope, which indicated surface roughness increased with increase in at.% of F in the films. The chemical binding was investigated by X-ray photoelectron spectroscopic studies. Fourier transformed infrared spectroscopic studies depicted the presence of CF_x (x = 1,2,3) and CH_n (n = 1,2) bonding within the F:DLC films. Optical transparency and the optical band gap decreased with the fluorine incorporation in the DLC film. Optical band gap calculated from the transmittance spectra decreased from 2.60 to 1.95 eV with a variation of 0-14.8 at.% of F concentration in the diamond-like carbon films. Urbach parameter determined from the band tail of the transmittance spectra showed that it increased with the doping concentration.     

环氧树脂-磷酸氢二钠复合相变储能材料的制备与性能研究

相变储能具有工艺简单、使用方便、成本低廉等优点,近年成为能量利用、系统控温等领域中的研究热点.研究以固化环氧树脂为载体材料、Na2HPO4·12H2O为相变功能材料,获得了一种定形复合相变储能材料.实验制备材料的热分析、IR光谱等研究表明,获得的复合材料在低于100℃的温度段具有多个相变峰;总相变潜热较高;固化环氧树脂能较好地将Na2HPO4·12H2O包裹,它们之间为简单的物理作用.