A Monte Carlo model for determination of binary diffusion coefficients in gases

A Monte Carlo method has been developed for the calculation of binary diffusion coefficients in gas mixtures. The method is based on the stochastic solution of the linear Boltzmann equation obtained for the transport of one component in a thermal bath of the second one. Anisotropic scattering is included by calculating the classical deflection angle in binary collisions under isotropic potential. Model results are compared to accurate solutions of the Chapman–Enskog equation in the first and higher orders. We have selected two different cases, H₂ in H₂ and O in O₂, assuming rigid spheres or using a model phenomenological potential. Diffusion coefficients, calculated in the proposed approach, are found in close agreement with Chapman–Enskog results in all the cases considered, the deviations being reduced using higher order approximations.     

The viscosity and diffusion coefficients of the binary mixtures of xenon with the other noble gases

This paper presents new experimental data for the viscosity of binary mixtures of xenon with the remaining monatomic gases, helium, neon, argon, and krypton. The measurements have been performed in a high precision oscillating-disk viscometer at atmospheric pressure and within the temperature range 25–500°C. The data have an estimated uncertainty of ±0.1% at 25°C increasing to ±0.3% at 500°C. The collision integrals for the interactions of xenon with the other monatomic species conform to the extended law of corresponding states formulated by Kestin, Ro and Wakeham. For each binary interaction the scaling parameters σ_ij and ∈_ij have been obtained. The ensemble of experimental results can be correlated by means of the appropriate kinetic theory expressions reinforced by the extended law of corresponding states. The deviations do not exceed 0.5%. The binary diffusion coefficients were calculated from the measured mixture viscosity and compared with the available experimental results. The standard deviation was estimated as ±2% which is within the mutual uncertainty of the two sets.     

光热偏转检测技术自动测量的研究

介绍了光热偏转技术自动测量材料热物性的原理及实验方法。根据光热偏转检测理论建立了一套自动检测系统,从自动控制、数据采集和数据处理等方面实现了光热偏转检测技术的自动化测量。设计出了步进电机自动控制和数据处理软件。利用该系统对钛酸锶钡材料的热扩散率进行了测量,发现随着掺杂量铈的增加,钛酸锶钡的热扩散率逐渐减小,当掺杂量铈增加到一定值时,其热扩散率又开始增加。     

Characterization of photovoltaic cells using the photothermal deflection spectroscopy

The equilibrium segregation coefficientK ₀ of the following impurities has been measured in high-purity tellurium: Ag, Al, As, Cr, Cu, Fe, In, Mn, Ni, Pb, Pd, Ti, V, and their diffusion coefficient in liquid tellurium determined at 550 °C.     

Probe-beam incidence angle-effects on thermal diffusivity measurement by photothermal deflection technique

Received: 27 February 1998     

用共线光热偏转技术测量光学薄膜的微弱吸收

用具有高灵敏的共线光热偏转技术研究SiO_2、ZrO_2、MgF_2、ZnS等单层光学薄膜的吸收特性,测得它们的吸收率.实验结果与激光量热法及横向光热偏转技术符合良好,表明共线光热偏转技术是测量光学薄膜弱吸收的较理想方法.     

光学薄膜激光损伤的光热偏转法实时研究

本文首次把调制与脉冲光热偏转技术同时置于激光损伤测试装置之中,用以进行光学薄膜激光损伤的实时研究.初步实验结果表明,该方法不仅有助于确定损伤阀值,也有助于分析损伤形貌和损伤过程,包括样品损伤前的行为及样品在重复频率激光作用下损伤的累积效应.     

IR spectral depth profiling using fourier transform photothermal beam deflection

FTIR photothermal beam-deflection spectroscopy (PBDS) was used to make spectral depth-profiling measurements with synthetic bilayer samples of polyethylene/nitrocellulose, with a commercial plastic having surface printing and with a single human hair. A Digilab interferometer modified to operate at several scan speeds was used to record the spectra, without the cell-resonance problems found with photoacoustic spectroscopy (PAS). The utility of spectral depth profiling is discussed; significant S/N improvements seem to be needed and, with either PBDS or PAS, a wider range of modulation frequencies is required for the methods to be useful.     

Micromechanical photothermal spectroscopy of trace gases using functionalized polymers

We demonstrate a novel method to spectroscopically detect and identify trace gases. Micromechanical photothermal spectroscopy (MPS) with functionalized sorbent materials provides trace gas spectra in an optical interaction length of only a few micrometers. We use microcavity interferometry to read out displacements as low as 25 fm/√Hz, heating as low as 200 pW/√Hz, and analyte concentrations as low as 65 parts-per-billion for the nerve agent simulant DMMP. MPS integrated with functional materials represents an important new tool in chip-scale optical sensing.     

Pharmaceutical applications of photothermal beam deflection

We report the potential use of a noninvasive method of photothermal beam deflection (PBD) in pharmaceutical research exemplifying the determination of drug content in semisolid formulations and mapping the lateral drug diffusion into an artificial membrane. PBD exhibits a high sensitivity. The requirement of only minimal sample preparation makes this spectroscopic technique advantageous. PBD in conjunction with an appropriate scanner device and depth profiling is a promising technique for in vivo studies of three-dimensional drug diffusion into biological membranes. A short introduction to the basic principles of PBD is given.     

Measurement of diffusion coefficients using a quick echo split NMR imaging technique

A new method for the ultrafast generation of diffusion-weighted images is reported. The technique combines a quick echo split NMR imaging sequence with the principle of Stejskal and Tanner. It allows to determine the diffusion constant with nearly the same accuracy as the conventional spin-echo technique, requiring only a fraction of the time. The determined values for water doped with 1 g Cu(NO₃)₂ per liter of H₂O and pure acetone were D_water = (1.95 ± 0.02) × 10⁻⁹ m²/s and D_acetone = (4.05 ± 0.02) × 10⁻⁹ m²/s at 18.5°C. They are in good agreement both with literature and our own reference measurements using a diffusion-weighted spin-echo sequence. In addition, the temperature dependence of D_water was measured in the range of 18.5–45.9°C and a good correspondence with reported data was found.     

Application of the diffraction theory for photothermal deflection to measurements of thermophysical and mass-diffusion properties of gases

The application of recently developed diffraction theory for cw transverse photothermal deflection spectroscopy (normal deflection only) to the measurements of thermophysical and mass-diffusion properties of gases is presented. Compared with the traditional ray-optics theory, the diffraction theory has one more term in the phase signal. This term quantitatively exhibits the probe-beam size effect on the phase signal. Experimental results demonstrated that even if the ratio of the probe-beam radius to the thermal diffusion length of a deflecting medium was as low as about 0.22, the probe-beam size effect could not be ignored when measuring the distance between the probe beam and a solid sample using the phase signal. With the measured distance, the thermal diffusivity α_g and the temperature coefficient of the refractive index dn/dT of pure gases (O₂, N₂, and CO₂) and binary gas mixtures (CO₂-O₂ and CO₂-O₂) were precisely measured, resulting in good agreement with literature values. Furthermore the measured dn/dT values of the pure gases had one more significant figure than the literature ones. The concentration dependences of α_g and dn/dT were employed for the determination of mass-diffusion coefficients of CO₂-O₂ and CO₂-N₂, and the results were consistent with literature values.     

Thermal analysis of a part of circuit board card by the photothermal deflection technique

Photothermal deflection which is a non-destructive technique is widely used to study defects in materials. However, high spatial resolution and high sensitivity are required to detect them. To validate the theoretical model that we developed in the case, the sample is immersed in a paraffin oil-filled cell and heated with a laser beam of a diameter less than the dimensions of defects and of power 2 mW instead of several 100 mW power frequently used. Our model was tested on a part of a circuit board card having copper strips spaced periodically and embedded in the resin. The experimental curves of amplitude and phase variations according to displacement of the sample are in good agreement with the corresponding theoretical ones; and their coincidence permit us to deduce several parameters such as the width of the copper and resin strips, their thicknesses and their thermal properties. These comparisons allowed also to detect some anomalies in the structure such as inhomogeneity in the width, the shape and the thicknesses of copper and resins strips.     

利用光热偏转技术实施光学薄膜弱吸收的多波长测量

介绍了光热表面形变光束偏转技术用于测量光学薄膜弱吸收的基本原理,简述多波长吸收测量装置的建立和测试过程,最后给出简单的测量实例.     

An investigation of the photothermal deflection spectroscopy technique for temperature measurements in a flame

The technique of photothermal deflection spectroscopy (PTDS) is investigated for temperature measurements in a flame. The spatial distribution of temperature is measured in two different types of burners operating with methane and oxygen, and methane and air. The spatial distributions of the temperature are in qualitative agreement with our expectations. At two points, the temperatures measured by PTDS have been compared with those measured by Boltzmann distributions. The measurements agree within their uncertainties. All the effects that affect the reliability of this technique are investigated and discussed. Finally, the pros and cons of the PTDS technique for temperature measurement are discussed. Received: 31 January 2002 / Published online: 8 August 2002     

The density and the binary diffusion coefficients of silver-tin melts

Temperature dependences of the density of liquid silver-tin melts containing 61.6 and 96.5 wt. % Sn (59.3 and 96.15 at. % Sn) have been determined using gamma-ray attenuation technique over the temperature range from liquidus line to 950 K. The density changes during solid-liquid transition have been directly measured for the first time for eutectic alloy (96.5 wt. % Sn). The temperature and concentration dependences of the thermal properties for Ag-Sn system have been constructed. Kinetics of homogenization of the melts with mean composition of 61.6 wt. % Sn has been investigated in the temperature range from 770 to 950 K. The coefficients of binary diffusion have been derived from these experiments.     

The viscosity and diffusion coefficients of eighteen binary gaseous systems

The paper reports accurate measurements of the viscosity of the eighteen binary gaseous systems: CF₄ with He, Ne, Ar, N₂, CO₂, CH₄; SF₆ with He, Ne, Ar, N₂, CO₂, CH₄, CF₄ and O₂ with He, Ne, CO₂, CF₄, SF₆. The measurements were performed in a high-precision oscillating-disk viscometer at atmospheric pressure and in the temperature range 25–200°C for the systems containing CH₄ or SF₆ and in the temperature range 25–400°C for the remainder. The reported viscosities are believed to be accurate to within ±0.1% at room temperature and to within ±0.2% at 400°C.It is shown that the data conform to the extended law of corresponding states developed by Kestin, Ro and Wakeham despite the complexity of some of the component gases. The standard deviation between the experimental values and those calculated from the law of corresponding states is only 0.3% which is commensurate with the uncertainty in the experimental results.Binary diffusion coefficients derived from the mixture viscosity data are also presented; they have an estimated uncertainty of ±2%.     

Vector model analysis in nondestructive imaging by using the photothermal deflection methods

The noncontact imaging of the buried structures is carried out in the open-air atmosphere by using the photothermal deflection (PTD) method. We applied these techniques to the layered samples. Besides the PTD images for the optically opaque buried structures, the parameters of the materials such as thermal diffusivity can also be calculated from the PTD amplitude and phase signal in the PTD scanning images. When the PTD signals at two different modulation frequencies are used, the thermal diffusivity of the buried structure can be obtained from the PTD signal outside of the sample nondestructively. Received: 27 November 1998 / Accepted: 18 March 1999 / Published online: 7 July 1999