Photovoltaic effect of organic devices at low temperature and under high magnetic field

The photocurrent responses of organic MIM junctions were investigated for light chopped at various frequencies in the temperature range between 300 K and 1.5 K. The responses to different chopping frequencies exhibited different temperature dependences. A light-chopped photocurrent markedly decreased under magnetic fields at low temperatures. An experiment of photoinduced charge extraction by linearly increasing voltage (photo-CELIV) was performed at 1.4 K to reveal the origin of this phenomenon. A drastic increase in the lifetime was observed for trapped carriers under applied magnetic field.     

Nucleation kinetics of paramagnetic and diamagnetic metal melts under a high magnetic field

The influence of a high magnetic field (HMF) on the nucleation kinetics of paramagnetic aluminum and diamagnetic zinc melts has been investigated by differential thermal analysis (DTA).It is found that the application of an HMF increases the undercooling of pure aluminum and pure zinc at the same heatingcooling rates.Moreover,the quantitative analysis of activation energy calculated from the DTA results using the Kissinger method manifests that the HMF reduces the activation energy of pure aluminum and pure zinc.Regardless of magnetism,the nucleation frequency under an HMF is higher than that without an HMF.Furthermore,the increase in undercooling under the HMF is mainly attributed to the increase of the contact angle,calculated by the functional relationship between the cooling rate and undercooling.This result is consistent with the increase of the calculated nucleation work for pure aluminum and pure zinc.Additionally,the increase in undercooling caused by the HMF is partly ascribed to the magnetic field-induced suppression of thermal convection in the undercooled melt.     

Strong static magnetic field processing of metallic materials: A review

Metallic materials processing in an imposed strong static magnetic field (SSMF) has attracted widely attention in the last decade since a magnetic field of 10 T or higher becomes easily attainable. Fundamentals including magnetic energy, magnetic anisotropy and magnetic forces influence significantly the research and development of this technology by means of both scientific and engineering paths. The ability to control metallic materials processing depends crucially on the understanding of the fundamentals and subsequently the engineering of the strong magnetic field effects. This review provides a critical examination of different SSMF effects together with the fundamentals that can be used in liquid/solid metal controlling and the subsequent metallic materials preparation. These effects are discussed by integrating them into different technologies or experimental results and accompanied by theoretical considerations of the fundamentals. Comprehensive comparisons are then carried out for each series of SSMF effects. It is aiming to provide an overview of the recent progress in SSMF processing of metallic materials.     

The density and interdiffusion coefficients of bismuth-tin melts of eutectic and near-eutectic composition

The method of gamma-raying of samples by a narrow beam of gamma radiation is used to investigate the temperature dependences of the density of bismuth-tin liquid alloys, which contain 30.0, 44.0, and 54.0 at.% Bi, at temperatures from the liquidus line to 920 K. The density jump in the case of solid-liquid phase transition is directly measured for the first time for an alloy of eutectic composition (44.0 at.% Bi). The temperature and concentration dependences of the thermal properties of the liquid Bi-Sn system are constructed. The kinetics of homogenization are studied of melts with average composition of 44.0 and 54.0 at.% Bi at temperatures from 550 to 850 K. The interdiffusion coefficients are determined from the results of these experiments.     

Crystallization of amorphous carbon at high static pressure and high temperature

Amorphous carbons prepared from furfuryl alcohol resin have been studied in a high-pressure apparatus of octahedral anvil type at pressures up to 18 GPa and at temperatures up to 2000° C. The amorphous carbons, when heated under pressure, crystallized first into graphite at 450 to 600°C and then into diamond at 1120 to 2000° C. The temperatures for the onset of these crystallizations,T ₉ andT _d, were determined by a simple technique. As the temperature for the preparation of the amorphous carbons was raised from 700 to 1000° C,T ₉ at 15 GPa increased slightly whereasT _d at the same pressure turned from a decrease into an increase beyond 750° C for the preparation temperature. For amorphous carbon prepared at 850° C,T _g increased a little whileT _d decreased markedly with increasing pressure.     

Surface tension measurements of metallic melts under microgravity

The surface tension of liquid metals and alloys was measured for the first time in microgravity using the oscillating drop technique. Data for pure gold, a congruently melting gold copper alloy, and an eutectic zirconium nickel alloy are presented. We find excellent agreement with available results obtained on Earth by the same technique, but only if the latter are corrected to account for gravity effects. This is not only shows the necessity for the correction of the surface tension data derived from Earth-bound oscillating drop experiments, but also proves its correctness.DeceasedPaper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Efficiency and behavior of textured high emissivity metallic coatings at high temperature

Three metallic coatings with textured surfaces, made of rhenium, tungsten and molybdenum, were studied in the frame of the Solar Probe Plus mission (NASA) as candidate materials. The role of these coatings is to dissipate a maximum of energy from a hot instrument facing the Sun, by the mean of their high total hemispherical emissivity. The total hemispherical emissivity of the three coatings was measured in the temperature range 1100–1900 K, as well as over time in order to study their high temperature stability. Various emissivity levels were obtained depending on the surface texture. The highest total hemispherical emissivity was obtained on a rhenium coating, with an emissivity of 0.8 in the temperature range 1300–1700 K. However, this rhenium coating with a fine, sharp surface texture, presented an instability at high temperature, which might limit its optimal operating temperature to about 1500 K. As for the tungsten coating, the total hemispherical emissivity was increased by a factor 2 due to the enhanced surface texturation and its great stability over the whole temperature range was shown.     

Electrodeposited hydroxyapatite coatings in static magnetic field

Uniform hydroxyapatite (HA) coatings were deposited electrochemically on titanium in magnetic fields. The structure and morphology of the deposited films were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy (SEM, XRD and TEM). It was found that the morphology of HA deposits could be altered by direction and intensity of applied magnetic field. Needle-like crystals formed when magnetic field was applied perpendicularly to electric field (B⊥ J), whereas spherical nanocrystals formed when magnetic and electric fields were in parallel (B||J). In addition, the nucleation rate of the HA crystals was proportional to the magnetic field intensity. Therefore, the resultant crystal size decreased with increasing magnetic field intensity.     

Acoustic emission and lifetime prediction during static fatigue tests on ceramic-matrix-composite at high temperature under air

The present work deals with two types of ceramic matrix composites CMC: SiC_f/[Si–B–C] and C_f/[Si–B–C], loaded in static fatigue at high temperature. An acoustic emission-based technique is proposed to predict the residual fatigue life. Indeed, two approaches based on the analysis of released energy are applied. A coefficient denoted R_AE is evaluated. Moreover, a cumulative Benioff law commonly used for pre-seismic activations is applied. Under constant stress, micro-cracks are created, which generate elastic waves in a manner similar to earthquakes. The law predicted satisfactorily the time-to-failure of SiC_f/[Si–B–C] composite under a constant load.     

A new model of DLA under high magnetic field

A new Monte Carlo model is introduced to describe diffusion-limited aggregation (DLA) with extra forces arising from Lorentz's and/or Coulomb forces. Furthermore, we simulate a behavior of multiparticle diffusive aggregation to examine the resultant pattern of crystal in electrochemical deposition. Different patterns grown under various external forces are produced by Monte Carlo simulations. In the present model, the basic movement of particles is a random walk, with different transition probabilities in different directions, which characterizes stochastically the effect of extra forces. In case of assuming a high magnetic field, pattern formations which are qualitatively different from the standard DLA model are observed and they are successfully compared with preexisting experiments (Mogi et al., 1991). The present numerical results of electrochemical deposition show that the generated patterns strongly depend on the force acting on ions and their concentration (Sawada et al., 1986).     

Transport of paramagnetic liquids under nonuniform high magnetic field

From recent investigations, the magnetic force generated by a heterogeneous high magnetic field has been highlighted, in particular by levitating systems. This paper is devoted to describing a new method for the analysis of the magnetic properties of liquids by using the magnetic force. This technique has consisted of observing and measuring the transport of a paramagnetic or diamagnetic liquid under the gradient of high magnetic fields. The theoretical approach of this phenomenon has been developed taking into account the fluid motion expanding in an axially symmetrical magnetic field. From this investigation, a typical experiment has been carried out by injecting a small amount of paramagnetic copper sulfate solution in a cell settled inside the bore of a superconducting magnet. Consequently, the accordance between the experimental results and the theoretical expectations has led to the determination of the magnetic susceptibility of the solution in a short time.     

3D physical modeling of anisotropic grain growth at high temperature in local strong magnetic force field

Abstract

A new mechanism based on the effect of local magnetic forces on diffusing ions around a growing ferromagnetic precipitate is proposed. A 3D simulation based only on physical parameters is undertaken in which main assumption is of interface limited growth controlled by the effect of both curvature and local magnetic field distortion. Although usually neglected in magnetic field effect mechanisms, it is shown that these local magnetic forces acting on a single paramagnetic ion can change markedly affect the growth process and induce strong shape anisotropy.     

3D physical modeling of anisotropic grain growth at high temperature in local strong magnetic force field

A new mechanism based on the effect of local magnetic forces on diffusing ions around a growing ferromagnetic precipitate is proposed. A 3D simulation based only on physical parameters is undertaken in which main assumption is of interface limited growth controlled by the effect of both curvature and local magnetic field distortion. Although usually neglected in magnetic field effect mechanisms, it is shown that these local magnetic forces acting on a single paramagnetic ion can change markedly affect the growth process and induce strong shape anisotropy.     

施加水平磁场下电磁声发射与裂纹指向特征分析

声发射检测方法对金属构件进行健康检测的关键问题:通过合适的载荷使得构件产生声发射信号。现阶段大部分声发射检测均采用接触式离线加载,声发射检测采用可在线检测的非接触式电磁加载。从电致位错、自由电子运动理论出发,在微观层面探究电磁声发射的机理特征;研究静磁场与涡流分布作用下电磁声发射特征差异;基于声发射信号的非平稳特征,利用希尔伯特黄变换方法分析电磁声发射特征。通过改变水平磁场激励方向,实现本征模态函数的能量比值、互相关系数、特征本征模态函数时频图与裂纹指向特征之间的关系联立。     

Electrocodeposition of magnetic nickel matrix nanocomposites in a static magnetic field

The effect of an external magnetic field on the electrocodeposition of composites consisting of either Co or magnetite nanoparticles in a Ni matrix has been studied. An alkaline Ni pyrophosphate bath containing citrate was used. The magnetic particles were prepared by thermal decomposition (Co) or chemical precipitation (magnetite) and characterized by transmission electron microscopy, X-ray diffraction, dynamic light scattering, zeta potential and vibrating sample magnetometry measurements. The particle incorporation showed a distinct dependency on the orientation of an externally applied magnetic field. While the particle incorporation increased in a perpendicular field (perpendicular with regard to the electrode surface), it decreased in a parallel orientation. This result is explained with the dominating action of the magnetophoretic force. The structure and the properties of the Ni layers were significantly affected by the particle codeposition. A refinement of the Ni grains was found with increasing plating current density and as a result of the nanoparticle incorporation. The magnetic hardness and the Vickers microhardness of the films increased significantly due to the incorporation of the nanoparticles.     

Superconducting cylinder in a static longitudinal magnetic field

A study of the calculation of the magnetic field forces acting on a superconducting cylinder in a longitudinal magnetic field is reported. A computation algorithm and the results of field calculation by means of the boundary integral method, taking account of the cylinder edge singularity, are presented. The method makes it possible to compute the forces pressing the cylinder with a relative error below 1%     

Thin film interdiffusion of Au and In at room temperature

Results on the thin film interdiffusion of Au and In at room temperature are presented. Indium films 56–3000 Å thick were deposited by vacuum evaporation onto previously deposited gold films of thicknesses ranging from 200 to 1600 Å. The interdiffusion of Au and In occurs quickly at room temperature and the intermetallic compounds AuIn₂, AuIn, Au₇In₃ and Au₄In are formed. Which compound will be formed depends on the Au:In ratio in the layer and on the diffusion time.     

Approximation of the temperature dependence of the coefficients of interdiffusion of vapor—gas systems

The correctness of an approximation equation for the temperature dependence of the coefficients of interdiffusion of vapor-gas systems with a mean deviation of 2% is confirmed by numerous experimental data.Translated from Inzhenerno-Fizicheskoi Zhurnal, Vol. 49, No. 2, pp. 266–270, August, 1985.