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141.
This paper reports a first approach on the kinetics parameters of terbium-activated magnesium orthosilicate using various methods. A deconvolution has also used for taking into account a more complex glow-curve structure.
Zusammenfassung Mittels verschiedener Methoden werden in erster Näherung die kinetischen Parameter von terbiumaktiviertem Magnesiumorthosilikat ermittelt Zur Berücksichtigung einer komplexeren Thermolumineszenzkurve wurde auch eine Dekonvolution angewendet.相似文献
142.
A Pluta polarizing interference microscope with a fibre stretching device attached was used to detect the changes in molecular structure that occur during the fibre cold drawing process. Fibres drawn with low draw ratios show different types of deformation mechanisms. The interference patterns recorded at different draw ratios are used to relate the deformation mechanisms with the measured structural parameters. Some optical parameters are measured such as; refractive indices nand n birefringence n, the polarizability per unit volume , the orientation distribution function f(θ), the angle θ between the stretching direction and the chain axis, and the angle θm which the transition dipole moment of the molecular species makes with the molecular axis (chain axis). Three polymeric fibres (Polyethylene terephthalate PET, Polypropylene PP and Polyamide PA) were used in this study and their interferograms are illustrated. 相似文献
143.
Potentiometric investigations on metal complexes of various bivalent metal ions, viz. UO2(II), Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Mn(II) with benzilmonol(lepidy!)hydrazone (BLH) have been carried
out at different ionic strengths and at different temperatures in order to determine stability constants of the complexes.
Thermodynamic parameters ΔC, ΔH and ΔS have also been evaluated from temperature coefficient data. The effect of varying the
dielectric constant of the medium on the stability constants of complexes has also been investigated at 30±0.5°C and μ = 0.1MNaCl.
Thermodynamic stability constants and thermodynamic stabilization energies for the first transition metals have also been
discussed. 相似文献
144.
In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is
investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to
20°C min−1 . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during
dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference,
a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic
parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere
for each step is between 40–50 kJ mol−1 upper than E
a calculated in inert atmosphere.
The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E
a ≈130 kJ mol−1 ) even though the thermal degradation in nitrogen flow presents a maximum E
a for 15% mass loss (E
a ≈60 kJ mol−1 ).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
145.
The mechanism of proton exchange between semiquinone neutral radicals 3,6-di-tert-butyl-2-hydroxyphenoxyl (1), 6-tert-butyl-3-chloro-2-hydroxy-4-triphenylmethylphenoxyl, and hydrochloric acid in toluene solutions has been studied. The rate of proton exchange with hydrochloric acid is less than that with acetic acid owing to the higher thermodynamic stability of the radical cation formed upon semiquinone radical protonation by hydrochloric acid. The formation of radical cations and their dimers has been proven by spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 1, pp. 84–87, January, 1993. 相似文献
146.
I. B. Sharma V. Singh M. Lakhanpal 《Journal of Thermal Analysis and Calorimetry》1992,38(6):1345-1355
Thermal decomposition of ammonium cerium sulphate has been studied by differential scanning calorimetry and thermogravimetry. The results show that the material decomposes in five steps in the temperature region 364–1116 K in oxygen. Based on the thermal data, elemental analysis and magnetic susceptibility measurements, sequence of decomposition has been established. The final product has been identified as CeO2 by X-ray diffractometry. Ammonium cerium sulphate and the products of the first and the final transitions contain cerium ion in 4+ oxidation state, while the three intermediate phases have cerium ion in 3+ oxidation state. From the non-isothermal DSC studies, kinetic parameters have been computed. The isothermal data show that the dehydration process follows Ginstling-Brounshtein mechanism, while the next three steps are governed by Mampel's unimolecular law of random nucleation.
Zusammenfassung Mittels DSC und TG wurde die thermische Zersetzung von Ammoniumzersulfat untersucht. Die Ergebnisse zeigen in Sauerstoff einen fünfstufigen Zersetzungsprozeß im Temperaturbereich 364–1116 K. Ausgehend von den thermoanalytischen Angaben, der Elementaranalyse und den Messungen der magnetischen Suszeptibilität wurde eine Sequenz für die Zersetzung erstellt. Das Endprodukt wurde mittels Röntgendiffraktion als CeO2 identifiziert. Ammoniumzersulfat und die Produkte des ersten und des letzten Überganges enthalten Zerionen mit der Oxydationsstufe +4, während in den drei Zwischenschritten Zerionen mit der Oxydationsstufe +3 vorkommen. Anhand der nichtisothermen DSC-Untersuchungen wurden die kinetischen Parameter berechnet. Die isothermen Angaben zeigen, daß der Dehydratationsprozeß einem Ginstling-Brounstein Mechanismus folgt, während die folgenden drei Schritte durch das Mampelsche unimolekulare Gesetz der Randomkeimbildung bestimmt werden.相似文献
147.
A. A. El-Khouly M. A. H. Hafez I. M. M. Kenawy 《Russian Journal of Electrochemistry》2006,42(3):225-232
Some kinetic and activation thermodynamic functions for the electrodeposition of palladium, thallium, and tellurium from the
best selected baths, viz. niclosamide bath [5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide] for Pd, alizarin red bath
for Tl, and salicylaldehyde bath for Te, are determined. Reaction rate constant (k), half-lifetime (t
1/2), activation energy (E
a), and such activation thermodynamic parameters as entropy change (ΔS*), enthalpy change (ΔH*), and Gibbs free energy (ΔG*) are calculated by applying the rate theory of the first-order reaction and the Eyring theory of the reaction rate. The
effect of temperature change in the range of 30–60°C on the above parameters is studied and thoroughly discussed. The effect
of metal type on both the reaction rate and the activation energy is also investigated.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 3, pp. 264–271.
The text was submitted by the authors in English. 相似文献
148.
许多标准和公开出版物中都用双指数函数描述高空核电磁脉冲典型波形。通过数值方法,研究了双指数函数一项重要的性质。根据该性质,详细讨论了高空核电磁脉冲模拟波形数值拟合中,双指数函数特征参数与脉冲峰值、前沿、后沿以及半宽等物理参数的关系,从而提出一种简单有效的脉冲参数计算方法。通过IEC标准中规定的高空核电磁脉冲参数的估计与一个实测高空核电磁脉冲模拟波形的数值拟合,验证了该方法的有效性和可靠性。该方法能够适应多种峰值、前沿和半宽的高宽核电磁脉冲模拟波形的数值拟合。 相似文献
149.
Deña M. Agra-Kooijman Gautam Singh Michael R. Fisch M. R. Vengatesan Jang-Kun Song 《Liquid crystals》2017,44(1):191-203
ABSTRACTThe discovery of the oblique chiral (or, the twist-bend, NTB) nematic phase predicted for bent-core mesogens has engendered much interest due to its unique structure and physical properties, and the possibility of use in the next generation of fast electro-optic technology. Bimesogenic calamitic as well as bent-core mesogens are found to form the NTB phase. Here, we report direct measurements of the temperature dependence of the conical tilt and the evidence of volcano-like orientational distribution of molecules in the NTB phase. Optical and x-ray scattering investigations of two single-component calamitic bimesogens and their mixtures show that, while the Maier–Saupe orientational distribution function (ODF) is valid for the higher temperature nematic phase, a generalised expansion in terms of even Legendre functions is needed for the NTB phase. Temperature dependence of the ODFs and the order parameters 〈P2(cosβ)〉, 〈P4(cosβ)〉, and 〈P6(cosβ)〉 has been measured in both phases. The parameters 〈P2(cosβ)〉 and 〈P4(cosβ)〉 increase/decrease in the N/NTB phase with decreasing temperature, while 〈P6(cosβ)〉 remains vanishingly small for all samples. The value of 〈P4(cosβ)〉 becomes negative in the NTB phase confirming a conical distribution of molecules as they follow a helical trajectory keeping the local director tilted at an angle α wrt the macroscopic director. The heliconical tilt calculated from ODFs, exhibits a power law behaviour with temperature, vanishing at the transition to the N phase. 相似文献
150.
Treewidth is a graph parameter of fundamental importance to algorithmic and structural graph theory. This article surveys several graph parameters tied to treewidth, including separation number, tangle number, well‐linked number, and Cartesian tree product number. We review many results in the literature showing these parameters are tied to treewidth. In a number of cases we also improve known bounds, provide simpler proofs, and show that the inequalities presented are tight. 相似文献