玻璃纤维/环氧树脂复合材料热分解动力学参数的确定

采用热重分析仪对空气和氮气气氛中的玻璃纤维增强环氧树脂基复合材料进行热分析,得到该材料在空气气氛中的烧蚀热为3 125～3 440 J/g,而在氮气气氛中并未出现明显的氧化放热峰。基于阿伦纽斯形式的多步分解模型和直接解法,计算了该材料在空气气氛中的热分解动力学参数。分析表明：阿伦纽斯形式的多步分解模型能够较好地描述该材料的热分解过程;直接解法适用于计算复合材料的热分解动力学参数;确立的热分解动力学参数是正确有效的。     

玻璃纤维/环氧树脂复合材料热分解动力学参数的确定

采用热重分析仪对空气和氮气气氛中的玻璃纤维增强环氧树脂基复合材料进行热分析,得到该材料在空气气氛中的烧蚀热为3125～3440J/g,而在氮气气氛中并未出现明显的氧化放热峰。基于阿伦纽斯形式的多步分解模型和直接解法,计算了该材料在空气气氛中的热分解动力学参数。分析表明:阿伦纽斯形式的多步分解模型能够较好地描述该材料的热分解过程;直接解法适用于计算复合材料的热分解动力学参数;确立的热分解动力学参数是正确有效的。     

Multi-site kinetic Monte Carlo simulations of thermal desorption spectroscopy data

Presented is a kinetic Monte Carlo simulation (KMCS) algorithm for simulating experimental thermal desorption spectroscopy (TDS) data. The KMCS is based on the Master equation approach and applies a first-passage-time analysis, i.e., the time dependence of the kinetics is matched correctly. The KMCS–TDS scheme used here includes multiple kinetically distinct adsorption sites and the effect of lateral interactions as required for fitting experimental data. After the results of extensive tests of the algorithm by means of synthetic data are discussed, experimental TDS curves are reproduced by the KMCS. Two applications are demonstrated: iso-butane adsorption on ZnO(0 0 0 1)–Zn and n-pentane adsorption on carbon nanotubes.     

Crystallization of a eutectic Pb-Sn melt in the thermal field of a temperature gradient

The crystallization of a eutectic Pb-Sn melt is investigated under nonuniform conditions in vacuum, in air, and in water. It is found that the structure of the solid-state systems formed depends on the cooling conditions. A structural inhomogeneity in volume and a correlation between the microstructure and the coordinate in a thermal field are revealed. Results of technological, electron-microscopic, and statistical investigations are reported. It is shown that the experiment is consistent with the crystallization theory of eutectic melts.     

Electrophysical parameters of variband AlGaAs films made in a temperature gradient

Results are presented on the distributions of the carriers and the hole mobility in undoped Al_zxGa_1–xAs variband films made by zone recrystallization in a temperature gradient on n-GaAs or p-GaAs crystals. It is shown that this method can give a structure of p⁺-n-p type with the n-p junction in the variband layer and a compensated n region.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 63–66, July, 1984.     

Determination of kinetic temperature of a gas from spectral lineshape

Journal of Applied Spectroscopy -     

回热器功产生的临界温度梯度研究

热声机械作为一种能量转化装置，能够不通过运动部件将热量转变成压力波输出，实现这一功能的关键部件就是回热器，本文讨论了丝网型回热器能在纯行波状态下起振的临界温度梯度与结构参数及运行参数的关系。     

Electron thermal diffusivity due to the electron temperature gradient mode

Charge neutrality breaks down in the short wavelength toroidal electron temperature gradient mode. In contrast to the ion temperature gradient mode, the wave number normalized by the Debye wave number, k/k(De), appears as a natural scale parameter, rather than the finite Larmor radius parameter k( perpendicular )rho(e). The growth rate and consequent mixing length estimate yields an electron thermal diffusivity large enough to be relevant to tokamaks.     

Combination of temperature-programmed thermal desorption and laser-induced thermal desorption

The combination of temperature-programmed thermal desorption with heating rates of the order of 1 K s^–1 and laser-induced thermal desorption with of the order of 10¹⁰ K s^–1 has proved to be a suitable method to determine both the frequency factor v and the activation energy E _d of desorption. The systems Ni(110)/N₂ and Ni(110)/CO serve as examples.     

Single-particle thermal diffusion of charged colloids: Double-layer theory in a temperature gradient

The double-layer contribution to the single-particle thermal diffusion coefficient of charged, spherical colloids with arbitrary double-layer thickness is calculated and compared to experiments. The calculation is based on an extension of the Debye-Hückel theory for the double-layer structure that includes a small temperature gradient. There are three forces that constitute the total thermophoretic force on a charged colloidal sphere due to the presence of its double layer: i) the force F _W that results from the temperature dependence of the internal electrostatic energy W of the double layer, ii) the electric force F _el with which the temperature-induced non-spherically symmetric double-layer potential acts on the surface charges of the colloidal sphere and iii) the solvent-friction force F _sol on the surface of the colloidal sphere due to the solvent flow that is induced in the double layer because of its asymmetry. The force F _W will be shown to reproduce predictions based on irreversible-thermodynamics considerations. The other two forces F _el and F _sol depend on the details of the temperature-gradient-induced asymmetry of the double-layer structure which cannot be included in an irreversible-thermodynamics treatment. Explicit expressions for the thermal diffusion coefficient are derived for arbitrary double-layer thickness, which complement the irreversible-thermodynamics result through the inclusion of the thermophoretic velocity resulting from the electric- and solvent-friction force.     

Au deposits on graphite: On the nature of high temperature desorption peaks in CO thermal desorption spectra

Due to the discovery of Au as a catalyst for low temperature CO oxidation, the adsorption of CO on Au surfaces has attracted a lot of attention recently. On stepped and rough single crystal surfaces as well as on deposited particles two characteristic desorption states above 100 K have been observed via TPD. We have studied Au deposits on graphite in order to elucidate the nature of these desorption peaks in more detail. For this purpose, Au was deposited at 100 K and 300 K on HOPG as a weakly interacting support. In analogy to other supports, we obtain two desorption states (∼140 K and ∼170 K) whose relative intensities depend strongly on the deposition temperature with the high temperature peak being much more pronounced for the 100 K deposits. After annealing to 600 K, both states drastically lose intensity. XP spectra, on the other hand, show virtually no decrease of the Au 4f intensity as would be expected for desorption or significant changes of the particle morphologies. We conclude that both desorption peaks are defect-related and connected with under-coordinated Au atoms that are lost for the most part upon annealing. These sites could be located at the perimeter of dendritic islands or on small, defect-rich particles in addition to larger particles not adsorbing CO at 100 K. Preliminary STM results are in favour of the second interpretation.     

A comparison of desorption rate parameters obtained by the variation of heating rate and the threshold temperature programmed desorption methods

Coverage dependent activation energies and preexponential factors for desorption of CO on Ni(110) have been obtained by the variation of heating rate and the threshold temperature programmed desorption (TTPD) methods. With the TTPD technique the initial coverage was varied by an adsorption and a desorption method. All three measurements yield nearly identical rate parameters at low coverages, but significant deviations are observed for higher coverages. In particular, abnormally low binding energies are observed in TTPD analysis of high coverages surfaces, where coverage is controlled by adsorption. These anamolous binding energies are attributed to desorption of CO which has not equilibrated to the tight binding sites on the surface. Better agreement is obtained between the variation of heating rate results and those obtained from TTPD analysis of surfaces where coverage is controlled by desorption. Remaining differences are considered to be a result of fundamental limitations in the TTPD technique as shown by comparison of the results with a calculated correction factor.     

Method for investigation of parameters of X-ray beams diffracted from a single crystal in the presence of temperature gradient

A method for investigation of the parameters of X-ray beams pumped from the transmission direction into the reflection one depending on the value of applied temperature gradient is proposed. An increase in the integral intensity of diffracted X-ray beam is due to both the overthrowing effect inside the Darwin table and an increase in the angular width of beam. It is shown that it is possible to determine to a high accuracy the value of temperature gradient, beginning with which the angular width of the pumped X-ray beam increases.     

Determination of heat sources from the thermal radiation of a half space with steady-state temperature distribution

Scientific-Research Radiophysics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 4, pp. 381–385, April, 1991.     

Electronic phenomena in semi-conductors with a temperature gradient

Phenomena connected with the transfer of current carrier concentrations as a result of a temperature gradient in semi-conductors with two kinds of current carriers are theoretically studied. The paper first deals with the general equations which are valid at a certain point of the semi-conductor with a temperature gradient for the concentrations of current carriers and density of electric and thermal current. From this the distribution of the concentrations of current carriers is found for a typical case, the phenomenon of thermal emission of minority current carriers is discussed, relations are derived for the dependence of the thermal emf on the magnitude of the temperature gradient, the possibility is discussed of thermal rectification and equations are given for the thermal conductivity of a semi-conductor with non-equilibrium concentrations of current carriers.     

Mechanisms of heteroepitaxial growth of cadmium telluride thin films in a thermal field of a temperature gradient

The processes of forming cadmium telluride films upon vapor-phase deposition onto a substrate in a thermal field of the temperature gradient along the substrate plane are studied. The results of technological, geometric, electron diffraction, and electron microscopic investigations are reported. It is found that the thermal field of temperature gradient leads to a change in the duration of the Ostwald ripening stage and, under certain conditions, enhances the perfection of the formed structure. The mechanism of the influence of a thermal field on the Ostwald ripening is established. The results obtained are in agreement with the current theory of film formation.     

Measurements of electron thermal transport due to electron temperature gradient modes in a basic experiment

Production and identification of electron temperature gradient modes have already been reported [X. Wei, V. Sokolov, and A.?K. Sen, Phys. Plasmas 17, 042108 (2010)]. Now a measurement of electron thermal conductivity via a unique high frequency triple probe yielded a value of χ(⊥e) ranging between 2 and 10 m(2)/s, which is of the order of a several gyrobohm diffusion coefficient. This experimental result appears to agree with a value of nonlocal thermal conductivity obtained from a rough theoretical estimation and not inconsistent with gyrokinetic simulation results for tokamaks. The first experimental scaling of the thermal conductivity versus the amplitude of the electron temperature gradient fluctuation is also obtained. It is approximately linear, indicating a strong turbulence signature.     

Light scattering from a fluid with a stationary temperature gradient

The spectrum of light, scattered from a fluid with a stationary temperature gradient, is calculated on the basis of fluctuating hydrodynamics. Explicit expressions are obtained for the spectrum of the scattered light which is no longer symmetric around the frequency of the incident light. In particular the difference in height and intensity of the Brillouin lines is given. Furthermore the shift in the position of the maximum of the Rayleigh line is calculated.