低温等离子体对铝弹性体表面改性的研究及其应用

铝弹性体表面用低温等离子体处理后 ,极大地提高了铝弹性体与应变片的粘结强度和防潮性能。与未经低温等离子体处理时相比 ,用相同的粘结剂 ,在拉伸试验过程中应变片不脱落的最大应变提高4倍以上 ,绝缘电阻高出一个数量级。此项成果已在金属材料拉伸实验和测力称重传感器中得到应用     

Low Temperature Elastic Constants of Polycrystalline MgB2

We have used a resonant ultrasound spectroscopy technique to measure the bulk and shear modulus of fully dense, polycrystalline MgB₂ between 4 and 300 K. Both moduli show good agreement with published first principle calculations. The internal friction shows a broad maximum around 40 K.     

Low Temperature Anomalies of Vitreous Silica and the Tunneling Model

The thermal conductivity, the relative change of sound velocity, the heat capacity and the heat release of Suprasil have been measured at low temperatures. The spectral density was determined in the range of relaxation time between 10^–10 and 10⁵s. The spectral density is nearly constant for relaxation times shorter 1s and longer 500s. However, the absolute value at short time is roughly a factor four larger than in the long-time range. The obtained dependence of the spectral density on the relaxation time disagrees with the Standard Tunneling Model as well as with the Soft Potential Model.     

Heat Capacity of Low Temperature Solid 3He

We have calculated the spin wave spectra and from these the specific heats of CNAF and UUDD solid ³He at low temperatures. We compare with experiment and find good agreement even though we also find major deviations from simple T³ behavior. The calculation included the six-spin exchange terms now recognized to be important for quantitative calculations. The inclusion of these terms was made more tractable by application of an algebraic technique from nuclear theory (Random Phase Approximation) for execution of the spin wave calculation, which nevertheless involved lengthy analysis.     

Low Temperature Heat Capacities of Submonolayer Solid 3He

Heat capacities (C) of ³ He submonolayer solids adsorbed on a graphite surface are measured down to 100 K, a factor of twenty lower temperatures than previous work. At a real densities near the commensurate solid (6.4 nm ^–2 ), an anomalous temperature dependence, C 1/T, is observed in a wide temperature range over two orders of magnitude (0.1 T 20mK). Similar behavior was observed for the commensurate solid in the second-layer with the same density, suggesting a common microscopic mechanism. It is, however, a puzzle that the solid is ferromagnetic according to recent magnetization measurements by ISSP group, while the solid is known to be antiferromagnetic. Possible explanations for this conflict, such as vacancy effects or multiple-spin exchanges modulated by a substrate potential corrugation, are discussed.     

Low Temperature Elastic Constants of Polycrystalline MgB2

We have used a resonant ultrasound spectroscopy technique to measure the bulk and shear modulus of fully dense, polycrystalline MgB₂ between 4 and 300 K. Both moduli show good agreement with published first principle calculations. The internal friction shows a broad maximum around 40 K.     

碳纳米纤维低温下的石墨化转变

“实心”碳纳米纤维在高温下的微结构转变分别利用电子显微镜和激光Raman光谱进行了表征。研究发现当热处理温度高于1000℃时，原来为无序结构的碳纳米纤维开始发生石墨化转变，有序化程度提高；而且随着热处理温度越高，石墨化程度越明显。分析认为碳纳米纤维的石墨化转变温度低是由于纳米结构小尺寸效应引起的。     

微波ECR—CVD低温SiNx薄膜的氢含量分析

利用红外光谱技术研究了微波电子回旋共振（ＥＣＲ）等离子体化学气相沉积（ＣＶＤ）法在低温条件下制备的ＳｉＮ。膜的键的结构和氢含量，分析了微波 功率和后处理条件对膜含量的影响及其成因，提出适当提高微波功率是降低微波ＥＣＲ－ＣＶＤ低温ＳｉＮｘ膜中氢含量的可能途径。     

Low Temperature Adsorption of Helium on Quench-Condensed Solid Neon Probed by Electron Emission from the Solid

Cyclotron resonance of free electrons (ECR) emitted from the solid Ne under VUV irradiation is observed. A flow of He gas supplied to the substrate avoiding a gas discharge zone is found to decrease the ECR amplitude. The decrease has been attributed to different mechanisms at the sample temperatures of 4.2 K and 1.6 K. He monolayer formation on the Ne surface is suggested in the low temperature region.      

Isotopic Effects in Solid LiH and LiD at Very Low Temperature

The ground state of the ionic solids LiD and LiH is theoretically studied using the Variational Monte Carlo (VMC) method. Our main focus has been the calculation of relevant properties of the H⁻ and D⁻ ions using a fully quantum approach. In particular, we report results on their kinetic energies, mean-squared displacements, Einstein frequencies, radial distribution functions, and density profiles around the sites. The microscopic results obtained for both isotopes show corrections beyond trivial isotopic effects due to their quantum behavior. Finally, the VMC results are compared with predictions from self consistent average phonon (SCAP) theory at T = 0 K.PACS numbers: 61.12 −q, 67.80 Cx, 63.20 −e, 02.70 Ss     

Elastic Energy and Elastic Interaction Ordering of Binary Solid Solutions

A theory in the framework of continuum elasticity has been developed to calculate the totalcontribution of "atomic size effect" or "strain energy effect" to free energy of binary solidsolutions. It is found that elastic free energy consists of two parts f elastic self energy (ESE),and elastic interaction energy(EIE). The former is a function of composition alone, the latter isalso a function of atomic configuration. Minimization of total elastic free energy with respect toatomic arrangement resuIts in an ordered arrangement of atoms, which is caIIed elastic interactionordering (EIO), as it originates from elastic interaction among atoms. EIO is a kind of localordering within a "characteristic range", and it is found to be important in determining the Stateof solid solutions and structures of superlattices. The present theory also gives good explanationto the coexistence of ordering and decomposition which can not be understood in conventionaltheories.     

Computer Modeling of Ionic Conductivity in Low Temperature Doped Ceria Solid Electrolytes

Solid oxides, such as ceria (CeO₂) doped with cations of lower valance, are potential electrolytes for future solid oxide fuel cells. This is due to the theoretically high ionic conductivity at low operation temperature. This paper investigates the feasibility of two potential electrolytes which are samarium-doped ceria (SDC) and gadolinium-doped ceria (GDC) to replace the traditional yttria-stablized zirconia (YSZ). Molecular simulation techniques were employed to study the influence of different dopant concentrations at different operation temperatures on the ionic conductivity from the atomistic perspective. Simulation results show that the optimized ionic conductivity occurs at 11.11mol% concentration using both dopants of Gd₂O₃ and Sm₂O₃. The temperature effect was also examined under a fixed concentration simulation to check how low temperature they still function. The predicted ionic conductivities have been verified with published experimental results and show reasonable agreements. This simulation technique reveals a clear picture with qualitative and quantitative connection between the choice of the dopant and the improvement of the ionic conductivity of fuel cell electrolytes.     

Elastic Properties of Polycrystalline Solid Helium

Recent experiments have shown that the shear modulus of solid helium undergoes a large temperature variation in the range 20 to 200 mK, possibly due to changes in the pinning of dislocations. In this note we report on computer simulations of the elastic properties of polycrystalline solid helium. We calculate how the elastic coefficients of a sample made up of a large number of randomly oriented grains are affected by the changes in the shear modulus c ₄₄ of the individual grains.     

Elastic Properties of Solid 4He

The shear modulus of solid ⁴He increases below 200 mK, with the same dependence on temperature, amplitude and ³He concentration as the frequency changes recently seen in torsional oscillator (TO) experiments. These have been interpreted as mass decoupling in a supersolid but the shear modulus behavior has a natural explanation in terms of dislocations. This paper summarizes early ultrasonic and elastic experiments which established the basic properties of dislocations in solid helium. It then describes the results of our experiments on the low temperature shear modulus of solid helium. The modulus changes can be explained in terms of dislocations which are mobile above 200 mK but are pinned by ³He impurities at low temperature. The changes we observe when we anneal or stress our crystals confirm that defects are involved. They also make it clear that the shear modulus measured at the lowest temperatures is the intrinsic value—it is the high temperature modulus which is reduced by defects. By measuring the shear modulus at different frequencies, we show that the amplitude dependence depends on stress in the crystal, rather than reflecting a superfluid-like critical velocity. The shear modulus changes shift to lower temperatures as the frequency decreases, showing that they arise from a crossover in a thermally activated relaxation process rather than from a true phase transition. The activation energy for this process is about 0.7 K but a wide distribution of energies is needed to fit the broad crossover. Although the shear modulus behavior can be explained in terms of dislocations, it is clearly related to the TO behavior. However, we made measurements on hcp ³He which show essentially the same modulus stiffening but there is no corresponding TO anomaly. This implies that the TO frequency changes are not simply due to mechanical stiffening of the oscillator—they only occur in the Bose solid. We conclude by pointing out some of the open questions involving the elastic and TO behavior of solid helium.     

Surface Diffusion of Solid Hydrogen

A number of experiments have shown that hydrogen molecules can migrate on films of solid hydrogen. This was thought to be a diffusive process but recent experimental findings have led others to a different conclusion, so a question remains about the process by which the hydrogen molecules migrate over their own solid surface. We report new measurements using a hole-burning technique which confirm these recent experiments but we interpret them differently. We have developed a model for the recovery of the hydrogen which accounts for these results and shows that the H₂ does move diffusively. The diffusion is thermally activated and we have determined the diffusion constant, D ₀=4.03×10^–4±2.5×10^–5 m²s^–1, and the activation energy, E=43±7 K, for hydrogen.     

低温吸附法生产高纯氢浅析

采用低温吸附法生产高纯氢,在国内已是很成熟的方法。但实际上仍然有许多问题影响着装置不能正常稳定地生产。该文就生产过程中出现的一些问题进行了浅析。     

Elastic Anomalies of Crystalline 4He at T=0

A new effort has been undertaken to model the effect of μd _1s muonic atom loss on the number of X-rays generated by combination of negative slow muons with ions implanted in the two-layer hydrogen setup of H₂/D₂–D₂. Until now, this effect has not been investigated theoretically. Here a solid hydrogen-deuterium layer (H₂/D₂) has been used for μd _1s production. For ion implantation and characteristic muonic X-ray generation, a small amount of solid deuterium (a mixture of ortho and para states) has been kept on the solid H₂/D₂ at temperature 3 K. The μd _1s loss rate and the integrated number of X-photons have been determined. Our results of X-ray yields are in good accord with those experimental reported by Strasser et al. We expect the effect of μd _1s loss to provide a scaling of about 10 %, making overall agreement better, compared to our previous work.     

硫化氢低温脱除技术的研究进展及趋势

硫化氢是一种存在于天然气,焦炉煤气等工业气体中的有害杂质,吸附脱硫法作为有效的硫化氢低温脱除方法被广泛研究。结合国内外低温脱硫剂的研究现状,主要讨论以下几类吸附剂:活性炭吸附剂,金属氧化物吸附剂,胺/氧化硅类吸附剂。分析了每种脱硫剂的脱硫原理及优缺点,探讨了低温脱硫剂的研究方向。     

Solid Hydrogen for Nonlinear Optics

We recently developed a new method of preparing a parahydrogen crystal which is suitable for experiments on nonlinear optical processes. The crystal was grown slowly from pressurized liquid–phase in order to avoid internal stress from the thermal constriction, and was cooled down to 4.2 K. The obtained crystal was uncracked and perfectly transparent with a high damage threshold. To evaluate the quality, the vibrational coherence decay was measured using the time–resolved coherent anti–Stokes Raman spectroscopy (CARS) technique. The decay process showed a nonexponential behavior, with an asymptotic limit characterized by a single time constant of 2.6 s, which corresponds to a linewidth of less than 0.1 MHz. This decay time is extremely slow compared to the previously published work.     

FTIR Study of Electronic Transitions in Solid Oxygen at High Pressure and Low Temperature

We report near-IR measurements of the electronic ^3– _g¹ _g(0,1) transitions of solid oxygen at high pressure and low temperature. Most of the P-T diagram was investigated up to the phase by means of isothermal and isobaric scans. The electronic spectra are a powerful tool to investigate the unique properties of solid oxygen, which is a localized-spin system. Magnetism of the high pressure phase plays a major role in determining the frequency of these bands, which are strongly temperature and density dependent. The analysis of this dependence allows us to model the spin correlation function and the intermolecular exchange integral.