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501.
H. A. Hristov J. W. S. Hearle J. M. Schultz A. D. Kennedy 《Journal of Polymer Science.Polymer Physics》1995,33(1):125-133
The mechanical properties of poly(ethylene terephthalate) (PET) fibers at temperatures above the glass transition are investigated by means of a specially constructed device. Measurements of the deformation rate and of the “dynamic” stress-strain curves of the fibers are performed in nearly isothermal regime (after initial rapid heating) in a temperature interval 100–200°C. The results reported in the present work demonstrate that the high-temperature mechanical characteristics of rapidly crystallizing polymers can be deduced to a satisfactory precision, while keeping the crystallinity development at low level. Our investigations indicate that if the high-temperature deformation is sufficiently fast, the polymer behavior is similar to the deformation at sub-Tg temperatures. Based on this similarity, a qualitative model of the deformation in the high-temperature region is proposed. The proposed model is fundamentally equivalent to the models describing mechanical deformation of glassy polymers at temperatures below the glass transition. ©1995 John Wiley & Sons, Inc. 相似文献
502.
M. A. Valenzuela P. Bosch B. Zapata G. Aguilar-Ríos V. H. Lara E. García-Figueroa I. Schifter 《Journal of Thermal Analysis and Calorimetry》1995,44(3):639-653
ZnAl2O4 and Sn?ZnAl2O4 were synthesized by coprecipitation, sol-gel and impregnation methods. These materials were calcined and treated in H2 at 1073 K. Thermal analysis (DTA and TG), nitrogen physisorption (BET method), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used as characterization techniques. H2 treatment promoted AlxZny crystallization in the coprecipitated and impregnated samples. When tin was added to zinc aluminate, the tin acted as a protective shell against high-temperature reduction, independently of the preparation technique. 相似文献
503.
The effect of a transverse magnetic field on the oscillatory thermocapillary convection in the NaBi(WO4)2 melt was studied by using the in-situ observation system. The oscillation was attenuated when the 60 mT magnetic field was applied, as shown by the decrease in the amplitude and the frequency. Furthermore, the oscillation under smaller temperature difference was stabilized after the magnetic field was applied. The magnetic effect could be due to the Lorentz force generated by the interaction between motional ions and the vertical magnetic field. The ionic conductivities were measured to demonstrate the effect of the magnetic field. The solid ionic electrical conductivity increases with the temperature rise, and the melt ionic electrical conductivity was measured to be about 2.0×10-4 Ω-1·cm-1. Experimental results manifest that the effect of the magnetic field on anions and cations in the melt makes the flow change to the direction normal to the applied field, so the flow is more orderly and the oscillation is suppressed. 相似文献
504.
Lisa Gamperl Lukas Neudert Peter Schultz Dajana Durach Prof. Dr. Wolfgang Schnick Prof. Dr. Oliver Oeckler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12835-12844
Single-crystalline domains in intergrown microcrystalline material of the new compounds Ba22.5+xLa55−x[Si129N240−xOx]O3:Ce3+ and Ba25.5+xLa77−x[Si170N312−xO9+x]O4:Ce3+ were identified by transmission electron microscopy (TEM). Precise diffraction data from these domains were collected with microfocused synchrotron radiation so that crystal structure elucidation of the complex disordered networks became possible. They are composed of two different interconnected slabs of which one is similar in both compounds, which explains their notorious intergrowth. The distribution of Ba and La is indicated by the analysis of bond-valence sums and by comparison with isostructural Sr28.5+xLa75−x[Si170N312−xO9+x]O4. Ce3+ doping leads to yellow luminescence. This is a showcase that highlights the discovery and accurate characterization of new compounds relevant for luminescence applications from heterogeneous microcrystalline samples by exploiting the capability of the combination of TEM and diffraction using the latest focusing techniques for synchrotron radiation. 相似文献
505.
Investigations of the electrotransport and thermodynamic properties of CsH2PO4 and composite systems (1 ? x)CsH2PO4?xSiO2 (x=0–0.5) synthesized on the basis of silicon dioxide with different magnitude of the specific surface area are conducted while varying the partial pressure of water vapor. It is demonstrated that the superionic phase transition, which is observed in CsH2PO4 at a temperature of 230°C, has nothing to do with the process of dehydration. A strong surface interaction of the salt with the matrix is discovered in composites of different compositions synthesized on the basis of uniformly porous silicon dioxides with specific surface areas of 41–520 m2 g?1 and the value of pH ~7. The interaction is found to lead to dehydration and to small values of conductivity in the systems heated to temperatures in excess of 230°C. An analysis of the dehydration products is conducted and conditions conducive to the existence of phases with certain compositions are determined. 相似文献
506.
507.
文章回顾了作者和合作者三年来应用中子散射技术方法,在铁基高温超导体研究中,通过测定材料的组分、晶体结构、反铁磁序结构、相变以及结构类型激发与磁性激发谱,对这些材料的微观物理过程与机理所做的初步理解和分析. 相似文献
508.
The results of a comparative research of thermoluminescence (TL) of TLD-500 detectors based on anion-defective corundum irradiated with continuous and pulsed X-ray and pulsed electron beams in a range of doses of 0.3 ÷ 107 Gy, dose rates of 0.02–2.6·1011 Gy/s, and in a temperature range of 300–950 K are presented. It is found that, in contrast to continuous irradiation, upon pulsed irradiation with a duration of 10 ns and dose rate of PP ≥ 5·106 Gy/s, the first linear region of dose dependences for TL peaks at 450, 580 and 830 K is, instead of saturation, followed by a second one with a smaller slope at doses near 2, 200 and 103 Gy. Moreover, the slope of the second region increases with growing PP. It was also found that dose dependence for the peak at 830 K in the area of the first linear region at 10–103 Gy remains invariable at PP ≤ 1010 Gy/s. It is shown that the upper limit of doses registered by TLD-500 detectors can be increased to 2·103 and 6·106 Gy for continuous and pulsed irradiation, respectively. New broadband UV luminescence with a maximum hν = 4.1 eV and half width H = 0.85 eV was registered within the TL peak spectrum at 830 K. Besides, the optical depletion spectrum in which a single band with hν = 5.2 eV and H = 1.6 eV is observed was investigated for a trap causing a peak at 830 K. 相似文献
509.
M. Engin Ayturk E.A. Payzant S.A. Speakman Y.H. Ma 《Journal of membrane science》2008,316(1-2):97-111
Among several different approaches to form Pd/Ag alloys for hydrogen separation applications, ex situ studies carried out by conventional X-ray point scanning detectors might fail to reveal the key aspects of the phase transformation between Pd and Ag metals. In this respect, in situ time-resolved high-temperature X-ray diffraction (HTXRD) was employed to study the Pd/Ag alloy phase nucleation and growth kinetics. By the use of linear position sensitive detectors, advanced optics and profile fitting with the use of JADE-6.5 software, isothermal phase evolution of the Pd/Ag alloy at 500 °C, 550 °C and 600 °C under hydrogen atmosphere were quantified to elucidate the mechanistic details of the Pd/Ag alloy phase nucleation and growth pattern. Analysis of the HTXRD data by the Avrami model indicated that the nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The value of the Avrami exponent, n, was found to increase with temperature with the values of 0.34, 0.39 and 0.67 at 500 °C, 550 °C and 600 °C, respectively. In addition, parabolic rate law analysis suggested that the nucleation of the Pd/Ag alloy phase was through a heterogeneous nucleation mode, in which the nucleation sites were defined as the non-equilibrium defects. Indeed, the cross-sectional SEI micrographs indicated that the Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers formed by the electroless plating. Based on the Avrami model and the parabolic rate law, the estimated activation energies for the phase transformation were 236.5 kJ/mol and 185.6 kJ/mol and in excellent agreement with the literature values (183–239.5 kJ/mol). Finally, the in situ annealing of the 15.6 μm thick composite Pd/Ag/PSS membrane at 550 °C in hydrogen atmosphere indicated that the Pd/Ag alloy phase formation was not complete even after 500 h. According to the Avrami model, the increase in the hydrogen permeance from 7.1 m3/m2 h atm0.5 to 21.3 m3/m2 h atm0.5 at 550 °C over a period of 500 h corresponded to an 83% Pd/Ag alloy phase formation. 相似文献
510.
The magnetic properties of (Cox Fe1-x)A (Zn1-x Fe1+x)B O4 are studied using mean-field theory and the probability distribution law to obtain the saturation magnetization, the coercive field, the critical temperature, and the exchange interactions with different values of D (nm) and x. High-temperature series expansions (HTSEs) combined with the Pade approximant are used to calculate the critical temperature of (CoxFe1-x)A(Znl-xFe1+x)BO4, and the critical exponent associated with magnetic susceptibility is obtained. 相似文献