Hydrogen trapped at intermetallic particles in aluminum alloy 6061-T6 exposed to high-pressure hydrogen gas and the reason for high resistance against hydrogen embrittlement

Hydrogen (¹H) trapped at intermetallic particles (IPs) in an aluminum alloy, 6061-T6, was visualized with secondary ion mass spectrometry (SIMS) by precisely excluding the false signal which is caused by background hydrogen (H_BG). The interference of the H_BG was avoided by a unique continuous pre-sputtering (pre-digging) by a primary ion beam of SIMS into a sample in combination with silicon sputtering prior to the SIMS measurement of the sample and we succeeded in visualizing the exact signal of ¹H trapped by IPs at subsurface layer of the sample charged in high-pressure hydrogen gas. The thermal desorption analysis clarified that the desorption energy (E_d) of the IPs was 200 kJ/mol or higher, which was extremely higher than E_d for lattice interstice, dislocations, and vacancies. High density hydrogen was concentratedly trapped at IPs in the subsurface layer in contact with the hydrogen gas. This nature causes an extremely low effective hydrogen diffusivity of 6061-T6 of the order of 10^?14 m²/s even at 200 °C and may eventually give a high HE resistance to 6061-T6.     

Outgassing measurement of an LHC collimator and estimation for the NEG performances

The outgassing rate of the collimators in the Large Hadron Collider (LHC) at CERN has an important role for the life-time of the Non-Evaporable Getter (NEG), and an accurate analysis allows the definition of future activities, like NEG vacuum activation. For these reasons, both, total outgassing rate and gas composition of a secondary collimator have been measured in the laboratory. The outgassing rate decreases by about two orders of magnitude by after bake-out and moreover, repeated bake-out further reduced the outgassing rate. The gas transmission through the NEG coated beam pipes and the resulting pressure distributions near the collimator were also measured in a dedicated setup. It is found that the main gas component after just 2 m of NEG coated beam pipe is CH₄ due to the extreme pumping speed of NEG for the other gases. Large amount of outgassing for H₂ and carbon related molecules are released when moving the collimator jaws. It is found that the NEG is very effective even in such case with large gas load.     

Facile fabrication of all-SWNT field-effect transistors

Field-effect transistors (FETs) have been fabricated using as-grown single-walled carbon nanotubes (SWNTs) for the channel as well as both source and drain electrodes. The underlying Si substrate was employed as the back-gate electrode. Fabrication consisted of patterned catalyst deposition by surface modification followed by dip-coating and synthesis of SWNTs by alcohol chemical vapor deposition (CVD). The electrodes and channel were grown simultaneously in one CVD process. The resulting FETs exhibited excellent performance, with an I _ON/I _OFF ratio of 10⁶ and a maximum ON-state current (I _ON) exceeding 13 μA. The large I _ON is attributed to SWNT bundles connecting the SWNT channel with the SWNT electrodes. Bundling creates a large contact area, which results in a small contact resistance despite the presence of Schottky barriers at metallic-semiconducting interfaces. The approach described here demonstrates a significant step toward the realization of metal-free electronics.      

Interactions of supported nickel and nickel oxide catalysts with methane and steam at high temperatures

The catalytic performance of cermets made of 10% nickel or nickel oxide supported on YSZ (yttria-stabilized zirconia) for chemical looping combustion (CLC) and steam reforming (SR) of methane at 700 °C is investigated. Steam reforming of methane over the reduced catalyst resulted in a syngas containing more than 70% hydrogen and about 15% carbon monoxide. Chemical looping combustion of methane with insufficient lattice oxygen could potentially lead to 40–65% hydrogen rich gas products. Prolonged induction period (e.g. 30–80 min) in reduction of nickel oxide by methane has been observed in the presence of steam. The span of induction period increases by increasing steam partial pressure. It is hypothesized that the delayed reduction of nickel oxide is related to the retarding effect of steam on autocatalytic reactions of methane and hydrogen with lattice oxygen of nickel oxide and the subsequent reforming reactions.     

Effects of sintering additives on dispersion properties of Al2O3 slurry containing polyacrylic acid dispersant

The effects of sintering aid adsorption on the dispersion properties of aluminum oxide slurries were investigated. We considered Al₂O₃ slurry without additives and Al₂O₃ slurry with a Mg additive with 0.1 mass% in oxide equivalent as a sintering aid. In this study, we evaluated the adsorption isotherm of polyacrylic acid (PAA) onto Al₂O₃ and the dispersion degree of Al₂O₃ slurries in sedimentation tests under gravity. The adsorption isotherm featured a characteristic adsorption isothermal line with a maximum value when Mg additive was present in Al₂O₃. In addition, the packing fractions did not correspond to the apparent viscosity. However, in slurry that was allowed to settle for several days, both of them agreed.Therefore, the disagreement between the packing fraction and the apparent viscosity immediately after preparation arose from changes of the dispersion state, such as the decrease of the distance between particles with time.     

High‐Ampacity Power Cables of Tightly‐Packed and Aligned Carbon Nanotubes

The current‐carrying capacity (CCC), or ampacity, of highly‐conductive, light, and strong carbon nanotube (CNT) fibers is characterized by measuring their failure current density (FCD) and continuous current rating (CCR) values. It is shown, both experimentally and theoretically, that the CCC of these fibers is determined by the balance between current‐induced Joule heating and heat exchange with the surroundings. The measured FCD values of the fibers range from 10⁷ to 10⁹ A m^?2 and are generally higher than the previously reported values for aligned buckypapers, carbon fibers, and CNT fibers. To the authors’ knowledge, this is the first time the CCR for a CNT fiber has been reported. The specific CCC value (i.e., normalized by the linear mass density) of these CNT fibers are demonstrated to be higher than those of copper.     

Accurate determination of the Landau parameter F o a for3He

Results of measurements of the low temperature magnetic susceptibility of normal liquid³He have been performed as a function of pressure from which we have calculated the Fermi Liquid parameter F _o ^a .     

A High-Sensitivity Microwave-Single-Photon Detector with Rydberg Atoms at Low Temperature

A high-sensitivity microwave-single-photon detector was developed in Kyoto, in which microwave photons in a resonant cavity cooled at very low temperatures are absorbed by highly excited Rydberg atoms and the Rydberg atoms thereby promoted to a higher excited state are then selectively field-ionized and detected. This scheme allows us to count microwave photons one by one, thus provide a single-photon counting without the limit of standard quantum limit (SQL). The apparatus “CARRACK” for the single-photon detector was constructed based on this scheme, where the cavity was cooled down to 10 mK range to reduce the background of thermal blackbody photons from the cavity wall. The apparatus has served for years to search for dark matter axions in the 10 μeV (∼2.4 GHz) mass region. Thermal blackbody photons in a microwave resonant cavity at temperatures as low as 70 mK have been measured, the sensitivity being below the SQL limit. A number of improvements in the detection efficiency and sensitivity have been planned and will be reported. Applications of the detector to fundamental physics are also discussed shortly.      

焦炭过滤床在线分离电炉粉尘中氧化锌的研究

采用电炉粉尘与焦炭粉的混合试样,对利用焦炭过滤床在线回收电炉粉尘,在CO/CO2混合气体中氧化锌的还原分离工艺进行了模拟研究.热力学分析表明,在所设焦炭过滤床的温度及气氛条件下,固-固还原和气-固还原反应都可以发生,氧化锌的还原分离是可以实现的.实验结果表明,与单独被固体碳或CO还原时相比较,混合试样在固体碳和CO同时存在时的初期减重率变化最快,最终还原率最高.在粉尘颗粒表面,被还原的金属铁生成及聚积长大后,将对还原气体向颗粒内部进一步扩散起到阻碍作用,对颗粒内部残存的微量ZnO的还原产生不利影响.如何加快氧化锌的还原分离而抑制氧化铁的还原及聚集长大将成为提高氧化锌回收率的关键.