Theory of the Gorsky effect for low interstitial concentrations

The formalism of the preceding paper is applied to work out the theory of the Gorsky effect, or anelastic relaxation due to the long-range diffusion of interstitials in a host lattice, for non-interacting (low-concentration) interstitials (e.g., H in Nb). It is shown how linear response theory (LRT) provides a number of advantages that simplify the solution of the problem and permit the handling of complications due to specimen geometry and stress inhomogeneity. The multiple-relaxation time creep function of Alefeldet al is first re-derived. Next, the dynamic responseand the short-time behaviour of the creep function are deduced exactly, and theω ^−1/2 fall-off of the internal friction at high frequencies is exhibited. Finally, it is pointed out that the true asymptotic behaviour of the dynamic response must be found by going beyond the diffusion equation model. A two-state random walk analysis is used to predict a cross-over to a trueω ⁻¹ asymptotic behaviour, and the physical reasons for this phenomenon are elucidated.     

An internal friction study of the vanadium-deuterium system

The internal friction of deuterium-doped vanadium has been investigated in the temperature range from 65 to 350 K. At low deuterium concentrations (≦0.18 at.−%) a relaxation effect has been observed near 90 K; its activation energy and its limiting relaxation tiem are 0.17 eV and 2×10⁻¹² sec, respectively. A second internal friction peak (precipitation peak) appears in more heavily doped samples; the position of this second peak shifts to higher temperatures as the deuterium content is increased. Possible mechanisms for the two peaks are discussed. The phase diagram of the vanadium-deuterium system at low temperatures has been deduced from the correlation between the deuterium concentration and the position of the precipitation peak.     

Effect of nonlocal elasticity on internal friction peaks observed during martensite transformation

The internal friction associated with martensite is calculated using elastic interaction energy between dislocations and solute atoms in nonlocal elasticity during low temperature aging process. The relaxation strength depends on the lattice parameter of the crystal as well as the temperature and the heating rate. The peak heights increase with increasing lattice parameter. The proposed model can demonstrate more realistically the shape of the change of internal friction versus temperature when nonlocal elasticity is included.     

Diffusion in a bistable potential at intermediate and high friction

We study the motion of a Brownian particle in a bistable potential for intermediate and high-friction . Following ideas of Titulaer we perform a high-friction expansion of the distribution functionP(v,x,t) in velocity and space. We show (for arbitrary potential) that the expansion coefficients obey simple recursion relations, which allow them to be calculated easily. When terms of order ^–5 are neglected the resulting differential equations can be transformed into Hermitian Schrödinger-type equations. Using the WKB technique we solve these equations analytically for the case of the bistable potential and discuss the various time regimes involved in the system, in particular we show that the final approach to equilibrium is governed by the Kramers rate. Our results become exact in the limit of low temperatures.     

The temperature dependence of internal friction in SicPCS/Al composites

In this study the relationship between Q^-1 and the microstructural characteristics of SiC_PCS/Al composites was investigated. Seven specimens made by various processes were divided into three groups and their Q^-1-T spectra were compared. The temperature dependence of internal friction up to 500°C was measured by vacuum inverse torsional pendulum apparatus. For the SiC_PCS/Al composite fabricated by the liquid infiltration method, Q^-1 increased more and more rapidly with rising temperature when the extent of fiber-matrix interfacial reaction intensified. For hot-pressed plates fabricated from preform wires and Al(1050) foils, poor diffusion bonding between the preform wires and A1 foils was introduced; this new interface is primarily responsible for the temperature dependence of Q^-1.     

Coherency stresses and diffusion in solids: neutron spectroscopic versus Gorsky effect measurements of deuterium diffusion in niobium

Published neutron scattering and Gorsky effect results on the diffusion and spatial fluctuations of D interstitials in NbD _x (x0.5) reveal striking differences. It is shown that these differences are caused by coherency stresses which raise the elastic energy of the short-wavelength D fluctuations studied by coherent neutron scattering. Gorsky effect measurements, on the other hand, probe long-range fluctuations which were coherencystress free in the experiments above. The observed differences can quantitatively be explained within the elasticity-theoretical concepts of Cahn, Krivoglaz, and Wagner and Horner. This represents the first successful application of these concepts to a diffusion coefficient. The correlation factor for D diffusion is, finally, determined from a comparison of the Gorsky effect and neutron scattering data.     

Anomaly of the internal friction in helium-4 crystals prepared with the burst-like growth method

The internal friction is measured in the ⁴He crystals prepared with the conventional and burst-like methods at temperature 0.65 K and frequency 75 kHz. It is observed that the crystals, grown too rapidly, have an excess damping and smaller dynamic elastic modulus. The magnitude of the effect enhances as the initial overpressure increases. The contribution to the excess damping vanishes at the critical overpressure 3.5 mbar separating the regions of the normal and anomalous crystal growth at the corresponding temperature. Corrections to the modulus and decrement relax with the time constant of about 3 ms. The regime of the burst-like growth may result in the crystals with the internal state different from that of equilibrium crystals.     

快冷Fe_(71)Al_(29)合金中的两个内耗峰

用一个计算机控制的倒扭摆研究了快冷Fe71 Al2 9合金中的两个内耗峰 .在快冷的Fe71 Al2 9样品中分别在 180℃(P1 ) ,340℃ (P2 )和 5 10℃ (P3)出现了内耗峰 ,而在慢冷的Fe71 Al2 9样品中只发现了P3峰 .快冷样品中的P1 和P2峰在从 6 5 0℃冷却下来的测量过程中或在 35 0℃经过较长时间的时效后消失 ,其峰高随时效时间的增加而下降 ,直至消失 .P1 和P2 峰都有弛豫特征 ,它们的激活能分别为 :H1 =1.0 3± 0 .0 8eV(P1 峰 ) ;H2 =1.6 4± 0 .0 5eV(P2 峰 ) .P1 峰被认为是无序合金中Al原子在四面体点阵内的最近邻运动所引起 ,P2 峰则是无序合金中Al原子在四面体点阵内的次近邻运动所引起     

A study of the effects of deuteride precipitation in tantalum by frequency and internal friction measurements

The effects of deuteride precipitation from Ta-D solid solution was investigated by vibration frequency and internal friction measurements in the temperature range (80–300) K. Initiation of deuteride precipitation is indicated by the inflexion of the frequency curve, whereas the onset of the dislocation-loops formation around the deuteride particles is correlated with the internal friction growth (precipitation peak). The dislocation interstitial drag model which seems to better account for the precipitation peak, is discussed. The phase diagram of the Ta-D system was determined in the range of (0.2–7.5) at.～%.     

The effect of a nitrogen-rich surface layer on the sub-surface deuterium (hydrogen) concentration distribution in titanium

Deuterium and nitrogen depth profiles in Ti with modified surfaces have been measured with Auger electron spectroscopy, secondary ion mass spectroscopy, and D(³He,p)⁴He nuclear reaction analysis. Nitrogen-rich surfaces layers of varying thicknesses were created on Ti by exposure to N₂ gas at 650°C. Deuterium loading was performed by exposure to 1 Torr of D₂ gas at 500°C. The deuterium distribution was influenced by nitrogen in the near-surface regions of all samples. Specifically, deuterium solubility was suppressed in surface regions of high (greater than 1%) nitrogen concentration. The deuterium solubility also remained low within the first few microns, well beyond the region of high nitrogen concentration. This effect is attributed to internal elastic stresses imposed by the non-deuterium absorbing nitrogen-rich layer on the Ti. These stresses prohibit the volume expansion associated with deuterium absorption. We estimate stresses on the order of 3–4 GPa are required to suppress the deuterium solubility to the values observed. The deuterium absorption kinetics were observed to depend systematically on the thickness of the nitrogen-rich layer. This is consistent with limited solubility near the surface or a surface poisoning effect influencing the overall deuterium diffusion from the gas phase into the Ti bulk.     

Angular distribution of desorbing/permeating deuterium from modified Pd(1 1 1) surfaces

The angular distribution of desorbing deuterium molecules was investigated for the clean Pd(1 1 1) surface and for modified Pd(1 1 1) surfaces, either pre-covered with 0.2 ML potassium or with an ultra-thin V₂O₃ surface oxide. The palladium sample was part of a permeation source and the angular distribution was measured by lateral displacement of the sample in front of a differentially pumped flux detector. For the clean surface at 523 K, the angular distribution is close to a cosine distribution, but changes to a cos^1.9Θ distribution at 700 K. Potassium on the surface alters the angular distribution to a cos³Θ function at 523 K. The ultra-thin vanadium oxide layer on the Pd(1 1 1) surface has no significant influence on the angular distribution of deuterium desorption. The experimental results were compared with existing data of the energy dependent sticking coefficient and the energy distribution of the desorption flux as measured by time-of-flight spectroscopy. This made it possible to get information on the applicability of detailed balance and normal energy scaling.     

颗粒物质内部滑动摩擦力的非线性振动现象

实验研究了探测棒竖直穿过圆筒中颗粒物质运动时所受的滑动摩擦阻力.研究发现，厚度为容器直径的0.5到2倍之间，粒径为2 mm的颗粒堆，对探测棒的滑动摩擦力在一个平均水平上随时间作非线性振动.当探测棒以小于2×10^-3 m/s的匀速率上升时，滑动摩擦力平均水平超过初始最大静摩擦力F₀的0.2到0.5倍，变化范围可从F₀到2F₀.频率低于1.35 Hz时，各种频率成分的强度随频率增加按幂函数方式衰减，其主要部分的平均周期T与探测棒运动速率v成反比关系. 关键词： 颗粒物质 滑动摩擦力 非线性振动     

Influence of the moment of inertia of the pendulum on the internal friction (loss tangent) measured by free decay

Summary The internal friction (loss tangent) of solids is normally measured, as a function of temperature, with a torsion pendulum operating in free decay. Curves of the internal friction and the oscillation frequency, against temperature, are obtained at various moments of inertia, to extract the parameters characteristic of the relaxation process (relaxation time and strength). In all these experiments only the temperature is considered as an independent variable and the moment of inertia of the pendulum is mainly used to shift the internal friction peaks in the temperature scale. It is pointed out in the paper that the moment of inertia is also an independent variable which can be used to determine, with high accuracy, if the measured peak is of the Debye type or not. A new torsion pendulum, with continuously variable moment of inertia is presented, which allows measurements of the partial derivative of the internal friction and the oscillation frequency with respect to the moment of inertia, at constant temperature. Finally, some measurements of the Snoek relaxation in Nb-O alloys are presented, to show the applicability of the concepts developed in the paper. The authors of this paper have agreed to not receive the proofs for correction.     

Diffusion of deuterium in GaAs from a molecular gas source

It is shown for the first time that deuterium can diffuse into GaAs from a gaseous source. Experiments performed at 500° C show two-component diffusion profiles with diffusion coefficients in the range 10^–15–4×10^-1cm²s^–1 depending on the conductivity type of the samples. These diffusion coefficients are considerably lower than those determined after RF plasma hydrogenation. Such a slow diffusion process is related to the reaction of molecular deuterium with the sample surface leading to the dissociation of the deuterium molecules.     

Ni2MnGa单晶马氏体相变过程摩擦耗能的热动力学计算

根据相界面摩擦原理 ,在推导出计算Ni2 MnGa系统热动力学参量的一般表示式的基础上 ,结合马氏体相变温度分别在室温以下、室温附近、室温以上三种非正配分比Ni2 MnGa单晶自发相变应变和交流磁化率随温度变化的测量结果 ,计算了三种样品马氏体相变过程中界面摩擦所消耗的能量 .结果进一步表明正是相变过程中的界面摩擦导致了相变的热滞后 ,而三种样品马氏体相变过程的摩擦耗能和相变热滞后存在较大差别的原因在于三种样品马氏体相变生成物具有不同的结构     

The effect of deuterium substitution in the amino group on the internal-rotation barrier of acetamide

Peptide molecules XCO-NYY′ are characterized by low potential barrier V₃ to internal rotation of a methyl group substituted for X and/or Y. A most conspicuous example is acetamide, for which V₃ was previously reported to be 25.043857(19) cm⁻¹[8]. The present study intended to clarify why V₃ is so low in acetamide, by examining the effect of the out-of-plane bending or inversion of the amino group on the molecular structure through deuterium substitution for amino hydrogens. The potential barrier V₃ in acetamide was found to decrease by 2.630, 2.986, and 5.532 cm⁻¹, when H′s at cis, trans, and both positions in the amino group were replaced by deuterium atoms, respectively. The reduction was proportional to the effective mass of the out-of-plane bending mode of the amino group (hereafter referred to as the amino inversion), which was in turn ascribed to the change in electronic resonance character of the peptide linkage. The amino inversion is coupled with the CH₃ internal rotation, producing an interaction term proportional to τ sin 3α, where τ and α denote the amino inversion and methyl internal rotation angles, respectively. This coupling term, when the inversion is treated by second-order perturbation, yields a V₆ term in the internal-rotation potential function of the methyl group, in agreement with the finding of Ilyushin et al. [8], who derived an unusually large V₆ term of −10.044874(73) cm⁻¹. It is quite interesting that even a small perturbation such as deuterium substitution causes a substantial change in electronic structure of the peptide linkage.     

烧结过程中Ni-Al金属间化合物形成的内耗

Ni-Al金属间化合物是一类重要的高温结构材料,在多种领域具有明确的目标需求.粉末冶金技术是制备Ni-Al金属间化合物的一种重要选择.探索烧结过程中Ni-Al金属间化合物形成和转变过程,明确固相扩散反应发生温度和金属间化合物种类对调控烧结工艺和优化产品质量至关重要.本文采用内耗技术系统研究了Ni-Al粉末混合物压坯烧结...     

内耗技术在软物质研究中的一些应用

软物质物理已成为物理学发展迅速的重要前沿学科。描述软物质复杂非平衡态动力学及其运动规律是理解其宏观性质的关键。内耗与力学谱作为材料缺陷与力学性质研究的重要实验技术,它能够很灵敏地探测和研究材料中发生的复杂相变和弛豫动力学过程。文章结合作者近年来的典型工作,介绍了内耗技术在软物质研究中的一些应用,阐述了内耗手段发挥的独特作用。随着内耗测试新方法、新技术和内耗新理论的不断出现和完善,相信未来内耗技术在材料科学和凝聚态物理研究领域将起到越来越重要的作用。     

Ni2MnGa单晶马氏体相变过程摩擦耗能的热动力学计算

根据相界面摩擦原理，在推导出计算Ni₂MnGa系统热动力学参量的一般表示式的基础上，结合马氏体相变温度分别在室温以下、室温附近、室温以上三种非正配分比Ni₂MnGa单晶自发相变应变和交流磁化率随温度变化的测量结果，计算了三种样品马氏体相变过程中界面摩擦所消耗的能量.结果进一步表明正是相变过程中的界面摩擦导致了相变的热滞后，而三种样品马氏体相变过程的摩擦耗能和相变热滞后存在较大差别的原因在于三种样品马氏体相变生成物具有不同的结构. 关键词： 马氏体相变 应变 界面摩擦     

Diffusion of Butylated Hydroxy Toluol (BHT) in PVC Films

Abstract

The diffusion coefficient of butylated hydroxy toluol (BHT) in solvent casted PVC films from tetrahydrofurane (THF) was studied by UV spectroscopy. Diffusion coefficient of BHT in PVC at 140, 160 and 180°C were determined as 1.0 × 10^?12 3.0 × 10^?12 and 6.0 × 10^?12 m²/s. The activation energy of diffusion (E_a) was 66 kj/mol.

IR spectroscopic work showed that the complete removal of THF was possible by heating films 15 minutes at 140 °C, but that caused formation of C=0 groups in PVC. No dehydrochlorination of films was observed even for heating them at 180 °C for 60 minutes.

Antioxidant BHT is volatile at high temperatures, so it is not advisable to use it for high temperature applications.