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51.
In this work we address the optimization of mixed conductivity in fluorite compounds based on zirconia. Phase relations of the new systems YbO1.5-NbO2.5-ZrO2, and CaO-NbO2.5-ZrO2 are presented. The limit of the cubic defect fluorite phase in YbO1.5-NbO2.5-ZrO2 closely resembles that of the system YO1.5-NbO2.5-ZrO2, whilst in CaO-NbO2.5-ZrO2 is narrow extending to include composition Ca0.255Nb0.15Zr0.595O1.82 at 1500°C. The influence of dopant ion size, charge and composition on ionic conduction is assessed and parallels are drawn with the systems YO1.5-NbO2.5-ZrO2 and YO1.5-TiO2-ZrO2. Comparison of these results with published data on the Ti containing systems CaO-TiO2-ZrO2, GdO1.5-TiO2-ZrO2 shows that the highest mixed conducting compositions can only be offered in the system YO1.5-TiO2-ZrO2 out of all the systems here studied. 相似文献
52.
The isolation and structure elucidation of xyloccensin L from the stem bark of Xylocarpus granatum is described. Xyloccensin L is a highly oxidized heptacyclic A, B, D-seco limonoid with an α-8, 30-epoxy ring and a rare 1, 29 oxygen bridge. 相似文献
53.
M. Karppinen Y. Morita I. Grigoraviciute R.S. Liu 《Journal of solid state chemistry》2005,178(11):3464-3470
Superconductivity characteristics have been systematically evaluated for a two-CuO2-plane copper oxide system, (Cu,Mo)-12s2, upon increasing the number of fluorite-structured layers, s, between the two CuO2 planes. Essentially single-phase samples of (Cu0.75Mo0.25)Sr2YCu2O7+δ (s=1), (Cu0.75Mo0.25)Sr2(Ce0.45Y0.55)2Cu2O9+δ (s=2) and (Cu0.75Mo0.25)Sr2(Ce0.67Y0.33)3Cu2O11+δ (s=3) were synthesized through a conventional solid-state route in air. To make the samples superconductive an additional high-pressure oxygenation (HPO) treatment was required. Such treatment (carried out at 5 GPa and 500 °C in the presence of 75 mol% Ag2O2 as an oxygen source to maximize the Tc) compressed the crystal lattice for the three members of the (Cu0.75Mo0.25)-12s2 series equally, i.e., by 0.01 Å for the a parameter and by 0.07 Å for the c parameter per formula unit. From both Cu L-edge and O K-edge XANES spectra the s=1 sample was found to possess the highest overall hole-doping level among the HPO samples. Accordingly it exhibited the best superconductivity characteristics. With increasing s, both the Tc (s=1: 88 K, s=2: 61 K, s=3: 53 K) and Hirr values got depressed, being well explained by the trend of decreasing CuO2-plane hole concentration with increasing s as revealed from O K-edge XANES spectra for the same samples. Hence, the present results do not suggest any significant (negative) impact on the superconductivity characteristics from the gradually thickened fluorite-structured block itself. 相似文献
54.
本文采用程序升温脱附(TPD)技术研究了光沉积方法制备的Pt/TiO_2催化剂经过氧化、还原后氧、氢的脱附行为.光沉积过程中,Pt/TiO_2表面上可以生成大量的吸咐氢,在TPD中脱附;同时Pt/TiO_2表面上化学吸附的水在TPD过程中也可以分解释氢.氧化处理的Pt/TiO_2在TPD过程中于550~750K温区出现氧脱附峰,随着氧化温度升高,脱附峰位向高温移动,经实验证明,这种可脱附活泼氧物种的生成是由样品前身中留存氢引起的.还原处理的Pt/TiO_2在TPD过程中分别在300~600和大于600K出现两个氢脱附峰,认为是由于表面羟基和钛—氢(Ti~(4+)—H~-)物种的分解释氢引起的Pt/TiO_2上活泼氧物种的存在,增加了样品在室温条件下的吸氢量;在中温(473~573K)这种活泼氧物种则和氢发生反应,减少了TPD过程中的脱氢量;Pt/TiO_2在大于673K温度还原,可以消除活泼氧物种的影响. 相似文献
55.
氧弹燃烧灰化法测定有机物中磷 总被引:1,自引:0,他引:1
用氧弹燃烧法灰化有机物进行元素测定,操作简便,快速,无污染,该方法用于有机物中磷的分析,结果可靠。 相似文献
56.
Copper is a bioessential element in biology with truly unique chemical characteristics in its two relevant oxidation states +I and +II. Significant progress has been made in recent years in the elucidation of the frequently surprising biochemistry of this trace element. Those advances were especially furthered through mutual stimulation involving results from biochemistry, molecular biology, and medicine on one hand and the synthesis as well as the structural and spectroscopic characterization of low molecular weight model complexes on the other. The most notable features of protein-bound active copper are its almost exclusive function in the metabolism of O2 or N/O compounds (NO, N2O) and its frequent association with oxidizing organic and inorganic radicals such as tyrosyl, semiquinones, superoxide, or nitrosyl. This unique biological role of copper can be rationalized given its chemical and assumed evolutionary background. 相似文献
57.
在甲烷氧化偶联制C2烃的研究中,人们发现碱土金属与稀土金属组成的复合氧化物催化剂具有高的催化活性[1,2].稀土化合物作为有希望的工业催化剂之一,已受到广泛的关注.一般认为,它们含有的氧空位对活化甲烷的有效氧物种有利.Debey等在1%Sr/La2O... 相似文献
58.
P. Song W. Guan C. Yao Z. M. Su Z. J. Wu J. D. Feng L. K. Yan 《Theoretical chemistry accounts》2007,117(3):407-415
Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from
YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91,
B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed,
especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance
in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest
bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation
energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of
their corresponding neutral species. 相似文献
59.
An accurate estimation of pKa values in methanol-water binary mixtures is very important for several separation techniques such as liquid chromatography and capillary electrophoresis that use these solvent mixtures. In this study, the pKa values of 11 polyphenolic acids have been determined in methanol-water binary mixtures (10%, 20% and 30% (v/v)) by potentiometry, liquid chromatography (LC) and LC-DAD methodology.The results show a similar trend for the pKa values of all the studied compounds, as they increase with increasing concentration of organic modifier, which allows a linear relationship between pKa values and mole fraction of methanol to be obtained. The pKa values obtained in aqueous medium have been compared with those given in the literature, and also with the values predicted by the SPARC on-line pKa calculator. The data obtained have been used to test the feasibility of an estimation of dissociation constants in a methanol-water medium from the relationship between pKa values and the organic cosolvent fraction in the mixtures. 相似文献
60.
Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes,
both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model
developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for
neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the
other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water
mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity
and basicity, dipolarity/polarizability…).
This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various
journals. 相似文献