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461.
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
462.
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
463.
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
464.
465.
I. E. Animitsa 《Russian Journal of Electrochemistry》2009,45(6):668-676
Data on the thermogravimetry, spectroscopy, and electrical charge transfer as functions of T, aH2O, and aO2 for niobates and tantalates of alkali-earth metals with structure disordering of the oxygen sublattice, which can show high-temperature proton conduction, are summarized. It is shown that in the solid solution series with decreasing x (that is, with the increasing of the oxygen vacancies concentration) the proton conductivity increase, which is caused by the increasing of both the concentration of proton defects formed in the structure (in compliance with the formula Sr6 ? 2x M 2 + 2x +5 O10(OH)2?6x and their mobility. The proton transfer dominates for the compositions with x < 0.15 at temperatures below 550°C. In the solid solutions (Ba1?y Ca y )6Nb2O11 (0.23 ≤ y ≤ 0.47) characterized by equal concentration of oxygen vacancies, with the increasing of barium content (correspondingly, with the increasing of the lattice parameter) the oxygen-ion conductivity (at aH2O = 3 × 10?5) grows monotonically, which is caused by the decreasing of the oxygen atom migration energy and increasing of their mobility. In this series, the proton conductivity (at aH2O = 2 × 10?2) increased. It was shown, by using IR-spectroscopy and the 1H NMR method, that the protons exist in the complex oxide structure mainly as energy-wise nonequivalent OH? groups: isolated, closely set, and paired, whose quantitative ratios are determined by the coordination preference of the B-sublattice elements. 相似文献
466.
采用高温固相法制备了4种高纯度晶相组成的LixZryOz三元化合物,研究了焙烧温度、时间、反应物的种类和初始反应物物质的量比对产物组成的影响,进一步用XRD、SEM及BET分析方法对产物的晶相结构、表面形貌及比表面积进行了表征.实验结果表明,Li2CO3与ZrO2在适当条件下可以合成得到单斜相Li3ZrO3;以LiOH替代Li2CO3,在适当条件下可以分别合成得到四方相Li2ZrO3和三斜/单斜相Li6Zr2O7;进一步以Zr(NO3)4·5H2O代替Zr02,可将单斜相Li6Zr2O7的制备时间由96 h缩短至24 h.SEM照片显示产物硬团聚明显,粒径分布在1~10μm间,BET分析表明样品比表面积处于1.0~9.0 m2·g-1间分布,反应过程中锂的过量以及长时间高温焙烧是引起产物粒径长大和产生硬团聚的主要原因. 相似文献
467.
A. N. Nadeev S. V. Tsybulya E. Yu. Gerasimov L. A. Isupova 《Journal of Structural Chemistry》2009,50(1):108-113
Phase transformations in a sample from the series La1?x Sr x FeO3?δ (x = 0.75) with cubic symmetry and perovskite type structure were studied by high-temperature X-ray diffraction. In air, the solid solution was stable to the synthesis temperature (1200°C), despite the loss of some part of oxygen. Heating in vacuum led to a two-phase state at 900°C (or even at 600°C when a small amount of palmitic acid was added to the sample); the unit cell parameter changed abruptly. The amount of the new phase increased with temperature, and at 1000°C, the sample, as well as the starting phase, was monophase perovskite with cubic symmetry; i.e., an isosymmetric phase transition occurred, which was accompanied by an abrupt change in the cell volume. Cooling in vacuum to ~800°C led to the ordering of the oxygen vacancies and the formation of a Grenier phase type structure. When the sample was heated again in vacuum, a reversible phase transition occurred from the Grenier phase type structure to a perovskite structure (again at ~800°C). 相似文献
468.
O. A. Bulavchenko S. V. Tsybulya S. V. Cherepanova T. N. Afonasenko P. G. Tsyrulnikov 《Journal of Structural Chemistry》2009,50(3):474-478
The behavior of the manganese-alumina system with Mn:Al = 1:1 on heating in air and vacuum was studied. The starting samples were mixtures of β-Mn3O4, α-Mn2O3, and γ-Al2O3. On heating to 950°C in air, the samples were partially oxidized into α-Mn2O3, and corundum α-Al2O3 formed along with mixed manganese-alumina cubic spinel, whose composition was close to Mn2AlO4. In vacuum at 1200°C, the starting sample with a ratio of Mn:Al = 1:1 transformed into the manganese-alumina spinel Mn1.5Al1.5O4, which retained its cubic structure after slow cooling in vacuum. When cooled in air, this solid solution delaminated, and a nanocrystalline Mn2.8Al0.2O4 phase formed, whose structure was β-Mn3O4 type tetragonal spinel. 相似文献
469.
高温光纤光栅的研究进展 总被引:5,自引:3,他引:2
为了满足航空航天、导弹制导、冶炼等一些高温领域的传感测量需求,国内外学者对高温光纤光栅进行了大量的研究工作。对已报道的主要的高温光纤光栅进行了综述,按照光栅结构、特点和所用光纤的不同,将其分为Ⅱ型光纤光栅、ⅡA型光纤光栅、化学组分光纤光栅、掺杂特殊离子的光纤光栅、结构变化型长周期光纤光栅等,逐类进行了说明并对它们的制作方法、高温特性、优缺点等进行了介绍和简评,并对其发展前景和应用进行了展望。 相似文献
470.