Some electrical feedthroughs to be used at low temperatures

A type of low temperature feedthrough is described for use by low temperature physicists     

Electronic transport in RuO2-based thick film resistors at low temperatures

The electrical conductivity of various RuO₂-based thick film paste resistors was investigated in the temperature range between 50 mK and 20K. It is shown that models based on variable range hopping and simple models based on tunnelling of charge carriers between conductive grains do not provide a satisfactory explanation for the temperature dependence of the electrical conductivity in these materials at very low temperatures. We suggest a new mechanism based on tunnelling of electrons through graded barriers between conductive particles.     

Hydrogen transport through thin palladium-copper alloy composite membranes at low temperatures

Hydrogen permeation performance of three thin palladium-copper composite membranes with different thicknesses had been studied between 398 K and 753 K. Hydrogen permeance was obtained up to 2.7 × 10^− 6 mol/(m² s Pa) with an ideal selectivity over 1000 at 753 K. The hydrogen permeation exhibited two different activation energies over the temperature range: lower activation energy of about 9.8 kJ/mol above 548 K, while higher activation energy of about 26.4 kJ/mol below 548 K. After permeation tests, the alloy membranes were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and in situ X-ray diffraction. Palladium segregation on the surface of these palladium-copper alloys may induce changes of hydrogen permeation performance and thus influence the activation energies.     

Gas-phase transport phenomena at low temperatures: Thermal diffusion in an Ar-Kr system

A metal two-bulb apparatus for the measurement of the thermal diffusion factor, _T , especially at temperatures below room temperature, has been designed and constructed. The results for the argon-krypton system are reported, and these cover five mixture compositions (25, 40, 50, 60, and 75% of krypton). The top bulb is maintained at 293.2 K, while the temperature of the lower bulb is varied in the range 102–250 K. The measured _T values are estimated to be accurate within ±4%. The positive minimum in the present _T values is less pronounced than that reported by some other workers, and this is attributed to the operating conditions and to the apparatus geometry.     

具有正负系数的二阶非线性中立型方程的非振动准则

中立型泛函微分方程的振动性在理论和应用中有着重要意义。本文研究了一类具有正负系数的二阶非线性中立型时滞泛函微分方程的振动性,利用Banach空间的压缩映象原理和一些分析技巧,建立了该方程非振动的一些新的准则,并给出了定理应用的例子。所得结论推广和改进了现有文献中的一系列结果。     

Nonlinear Effects in Laser Flash Thermal Diffusivity Measurements

The numerical solution of the nonlinear heat conduction equation is used to analyze nonlinear effects in the laser flash method, when the thermophysical parameters of the sample depend on the temperature. A parameter estimation technique is proposed to determine the temperature dependence of the thermal diffusivity from a response curve. Computer generated data, as well as real experimental data, were used to demonstrate the reliability of the technique.     

Impurity ionization in MOSFETs at very low temperatures

The physics of freeze-out in conventionally doped silicon is examined. A dynamic equilibrium theory, similar to that used in deep level transient spectroscopy, is developed to describe the time dependence of thermal ionization. The theory is extended to include field-dependent ionization, which accounts for impurity ionization at very low temperatures. The specific mechanisms (Poole - Frenkel ionization and tunnelling) are discussed, and the temperature and field dependences of the mechanisms are described. It is then shown that MOS capacitors and MOSFETs have very different behaviour at very low temperatures. Experimental results are examined, showing a distinct change in the behaviour of long term current transients at very low temperatures, as predicted by the model. The theoretical model developed here, when used in a simple one-dimensional simulation, agrees with substrate current measurements. Finally, some implications for very low temperature MOSFET operation are considered.     

SiCl4/H2为气源低温沉积多晶硅薄膜低温电学特性的研究

对用SiCl4/H2为源气体、采用等离子体增强化学气相沉积(PECVD)技术制备的多晶硅薄膜进行了低温电学特性的研究.实验结果表明,多晶硅薄膜的暗电导强烈依赖于温度,在300～90K的温度范围内呈现不同的导电特性.对多晶硅薄膜,其导电特性还与晶化率有关,晶化率越大电导率越大.测量数据表明,低晶化率薄膜电输运主要由电子热发射跃过势垒所贡献,但对于高晶化率的薄膜要同时考虑电子隧穿对电导的影响.     

炭材料在低温型磷酸铁锂材料中的应用分析及展望

磷酸铁锂为正极的锂离子电池是目前电动汽车和储能领域应用最为广泛的电池体系之一,具有成本低廉、循环寿命长、安全性好等特点。但磷酸铁锂为正极的锂离子电池在低温下的容量和循环寿命衰减问题一直制约了其在寒冷地区的推广和应用。因此磷酸铁锂材料本身低温放电性能的提高,对于改善磷酸铁锂为正极的锂离子电池体系的低温放电特性具有重要意义。本文首先分析了磷酸铁锂为正极的锂离子电池的低温衰减机制,从炭材料作用的角度评述了低温型磷酸铁锂材料的研究进展,同时也关注了高倍率型磷酸铁锂材料。因磷酸铁锂的高倍率性能与低温特性具有很大的相似之处,两者对材料的要求基本接近,材料的设计原则和方法也基本相同。本文也重点分析了纳米炭材料,如碳纳米管和石墨烯等在低温型磷酸铁锂材料领域的应用。     

含有n个无关变元的Mate-Nevai型非线性积分不等式

讨论了Mate-Nevai型积分不等式,得到几个含有n个无关变元的Mate-Nevai型非线性积分不等式。利用所得结论讨论某些非线性偏微分方程解的有界性。     

Mode I fatigue delamination growth in GFRP woven laminates at low temperatures

The cryogenic fatigue delamination behavior of glass fiber reinforced polymer woven laminates under Mode I loading has been investigated experimentally and numerically. Fatigue delamination tests were conducted using double cantilever beam specimens at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). Fracture surface examination using scanning electron microscopy revealed delamination mechanisms under fatigue loading. A finite element analysis was also employed to calculate the J-integral range and damage distributions. The effects of temperature and loading condition on the fatigue delamination growth rates were discussed.     

Thermal stability of retained austenite in Cr–Ni weld metals at low temperatures

Abstract

As environmental temperature decreases, the amount of retained austenite is more likely to greatly reduce due to the thermal austenite–martensite transformation caused by the decreased thermal stability of retained austenite, probably making its amount lower than the required content. In the present study, the thermal stability of retained austenite in Cr–Ni weld metals was investigated to see whether sufficient retained austenite can be maintained at low temperatures. The specific experimental procedure is as follows: briefly, the samples were cooled in turn from room temperature to 0, ?20, ?40, ?60, ?80, ?100 and ?196°C; the amount of retained austenite at the above temperatures was measured using X-ray diffraction. Through investigating the dependence of the content of retained austenite on temperature, it was revealed that when the content of retained austenite is <20%, retained austenite can be maintained until ?196°C.     

Dynamic singular stresses in glassfiber reinforced plastics with a broken layer at low temperatures

The plane strain dynamic singular stress problem for glassfiber reinforced plastics with a broken layer at low temperatures is considered. With the order of stress singularity around the tip of the crack which is normal to and ends at the interface between orthotropic elastic materials, Laplace and Fourier transforms are used to formulate the problem in terms of a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and the dynamic stress intensity factors at different temperatures are shown graphically.     

A mechanical measurement of textural relaxation in superfluid3He-A at very low temperatures

We have studied superfluid³He-A textures by a mechanical method in the very low temperature limit, T/T_c 0.14. The damping of a vibrating wire viscometer is affected by the structure of the 1-vector texture near the wire. The texture is disturbed by a violent motion of the wire. The relaxation of the texture, back to equilibrium, is then observed through changes in the damping of the wire's motion.We gratefully acknowledge discussions with G.R. Pickett and J.R. Hook. J.D.Close helped with early preparation of the experiment. This work was supported by NSF grant DMR 9120277.     

Tensile behaviour of type 304 austenitic stainless steels in hydrogen atmosphere at low temperatures

Abstract

The tensile behaviour of solution annealed type 304L, solution annealed type 304, and solution annealed and sensitised type 304 stainless steels was investigated in hydrogen and helium under a pressure of 1·1 MPa over the temperature range 300–80 K at strain rates ranging from 4·2×10^-5 to 4·2×10^-2 s^-1. For 304L steel, hydrogen environment embrittlement (HEE) increased with decreasing strain rate. For 304L and 304 steels, HEE increased with decreasing temperature, reached a maximum, and then decreased with further decrease in temperature: the decrease was particularly rapid near the minimum temperature for HEE. Sensitisation enhanced the HEE of 304 steel. Above the maximum HEE temperature, the HEE behaviour was similar to the hydrogen embrittlement behaviour of materials in previous studies, but near the minimum temperature for HEE it was different. Three types of hydrogen induced brittle fracture were observed as a result of HEE: transgranular fracture along strain induced martensite laths and twin boundary fracture on the fracture surfaces of solution annealed 304L and 304 steels, and grain boundary fracture on the sensitised 304 steel. It was found that from room temperature to the maximum HEE temperature, the HEE of the materials depended on the transformation of strain induced martensite and below the maximum HEE temperature it depended on the diffusion of hydrogen.     

Damage evolution and characterisation of crack types in CF/EP laminates loaded at low temperatures

Tensile testing of CF/EP AS4/8552 cross-ply laminates at room (RT) and cryogenic (around −150 °C) temperatures has been performed to study the effect of temperature on damage (intralaminar cracking) evolution. Microscopy studies of the specimen edges showed a significant difference in damage pattern for the two different temperatures. At the low temperature (LT), more complex crack types were obtained that could not be found in specimens tested at the RT. The effect of these crack types on the laminate tensile modulus was studied by FEM. In analytical stiffness modelling complex shape crack was replaced by an “effective” normal (straight) crack with an “effective” crack opening displacement (COD) that leads to the same reduction in laminate stiffness. A crack efficiency factor was introduced to characterize the significance of complex crack shapes for stiffness reduction. The reduction of tensile modulus for a laminate damaged at low temperature was measured and compared with model predictions.     

低温与真空条件下1Cr18Ni9Ti钢的疲劳行为

分别在室温大气、室温真空及低温真空几种环境条件下,对1Cr18Ni9Ti钢进行对称载荷拉-压疲劳试验,利用TEM观察疲劳断口附近的显微组织,研究了环境因素对疲劳性能的影响,并对影响的原因进行了分析和讨论.研究表明:1Cr18Ni9Ti钢在低温真空条件下疲劳性能显著提高;疲劳断口附近出现大量板条马氏体;真空与低温显著提高1Cr18Ni9Ti钢疲劳性能的原因与真空对裂纹表面的净化效应,以及低温促进疲劳裂纹前沿形成板条马氏体有关.     

The structure of electrical double layer of silica in the presence of polyvinyl alcohol (PVA) at different temperatures

The effect of polyvinyl alcohol (PVA) adsorption on the structure of the electrical double layer of silica (SiO₂) in the temperature range 15-35 °C was studied. The potentiometric titrations were applied in the experiments, which enable determination of the surface charge density of silica systems without and with adsorbed polymer. The preferential adsorption of acetate groups of not fully hydrolysed PVA chains (degree of hydrolysis 97.5%) through hydrogen bridges is mainly responsible for bonding process of polymer with adsorbent surface. The obtained results indicate that temperature increase causes more stretched conformation of adsorbed macromolecules and the greater number of acetate groups can be adsorbed on the solid surface. It leads to changes in structure of polymer adsorption layer on the solid surface and the increase of the SiO₂ surface charge with the rising temperature was observed.     

CO2 flow condensation heat transfer and pressure drop in multi-port microchannels at low temperatures

CO₂ flow condensation heat transfer coefficients and pressure drop are investigated for 0.89 mm microchannels at horizontal flow conditions. They were measured at saturation temperatures of −15 and −25 °C, mass fluxes from 200 to 800 kg m⁻² s⁻¹, and wall subcooling temperatures from 2 to 4 °C. Flow patterns for experimental conditions were predicted by two flow pattern maps, and it could be predicted that annular flow patterns could exist in most of flow conditions except low mass flux and low vapor quality conditions. Measured heat transfer coefficients increased with the increase of mass fluxes and vapor qualities, whereas they were almost independent of wall subcooling temperature changes. Several correlations could predict heat transfer coefficients within acceptable error range, and from this comparison, it could be inferred that the flow condensation mechanism in 0.89 mm channels should be similar to that in large tubes. CO₂ two-phase pressure drop, measured in adiabatic conditions, increased with the increase of mass flux and vapor quality, and it decreased with the increase of saturation temperature. By comparing measured pressure drop with calculated values, it was shown that several correlations could predict the measured values relatively well.