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21.
As an alternative to acid pretreated UCON and FFAP capillaries for the analysis of wide-boiling free fatty acid mixtures, OV-1 : FFAP phase mixtures were used on high-temperature silylated inert glass capillary columns. The HETP-carrier gas velocity curves, peak asymmetry factors, coating efficiency, gas phase and stationary phase contributions to the mass transfer resistance were determined for various OV-1 : FFAP ratios. Mixed-phase capillaries showed optimum performance at a 2 : 1 OV-1 : FFAP ratio. The thermal and long-term stability of OV-1-stabilized FFAP columns surpassed those of the UCON and pure FFAP reference column used. 相似文献
22.
Yoshiyuki Oishi Shoichi Nakata Masa-Aki Kakimoto Yoshio Imai 《Journal of polymer science. Part A, Polymer chemistry》1992,30(10):2217-2221
New segmented aromatic poly(ether sulfone)-amide and poly(ether sulfone)-imide copolymers were synthesized by the chain extension of α,w-diamine-terminated poly(ether sulfone) oligomer with both aromatic dicarboxylic acid chlorides and tetracarboxylic dianhydrides, respectively. Crystallization of the poly(ether sulfone)unit was suppressed by the introduction of amide or imide linkage along the polymer backbone, giving amorphous copolymers that were +eadily soluble in various organic solvents. The copolymers had somewhat higher glass transition temperatures than the parent poly(ether sulfone). They afforded transparent and tough films by solution casting. © 1992 John Wiley & Sons, Inc. 相似文献
23.
The decomposition of EDTA gel precursors for BSCCO superconductor manufacture has been studied using STA (TG/DTA) and dilatometry in conjunction with FTIR. Ther thermoanalytical data are discussed in relation to the sequence of phase formation necessary for the production of the 2223 BSCCO superconducting phase. Thin film preparation of Bi-based highT c superconductors have been carried out on MgO (100). Grain orientation of oxide thin films has been investigated. Well orientated 2212 grains have been achieved, with the (001) planes parallel to the substrate. The EDTA-gel method has been modified by the addition of glycerol to achieve the appropriate viscosity for spin coating. STA has been used to study the decomposition of these modified gels for the formation of thin films. 相似文献
24.
Ch. Krüger H. Schwer J. Karpinski K. Conder E. Kaldis C. Rossel M. Maciejewski 《无机化学与普通化学杂志》1994,620(11):1932-1936
Structural investigations on powder samples of Y2Ba4Cu7O15–x with different carbonate content have been performed. Powder x-ray Rietveld refinements showed the remarkable influence of carbonate incorporation on the lattice parameters. Most important is the decrease of Tc with increasing carbonate content. We assign these effects to an incorporation of the carbonate ion into the crystal lattice, copper vacancies at the Cu(1) position and a possible misorientation of the copper oxygen single chains. No change of the structure (e. g. superstructure) could be found. 相似文献
25.
57Fe Mossbauer spectroscopy was used to investigate the evolution of Fe-Zn binary metal oxide sorbent in the process of high-temperature fuel gas desulfurization. The results of phase analyses show that Fe-Zn binary metal oxide sorbent is rapidly reduced in hot fuel gas and decomposed to new phases of highly dispersed microcrystalline elemental iron and zinc oxide, both of which become the active desulfurization constituents. A complementary and synergistic effect between active iron acting as a high sulfur capacity constituent and active zinc oxide acting as a deep refining desulfurization constituent exists in this type of sorbent for hot fuel gas desulfurization. 相似文献
26.
Staszczuk P. Sternik D. Chądzyński G. W. 《Journal of Thermal Analysis and Calorimetry》2003,71(1):173-182
Using thermo-analytical and sorptometric methods physicochemical properties and especially surface heterogeneity of HgBa2Ca2Cu3O8+, (Hg-1223) was investigated. The desorption energy distribution was derived from mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption in quasi-isothermal conditions of pre-adsorbed n-octane and water vapour. It is shown that the superconducting Hg-1223 phase is highly sensitive to water vapours. The mechanism of water adsorption depends largely on the activation time. By water vapour saturation in a period of 90 min, physisorption takes place. Prolonged periods result in a chemical decomposition. From nitrogen ad- and desorption isotherms the fractal dimension of superconductors were calculated. A new approach is proposed to calculate fractal dimension from Q-TG curves.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
27.
G. E. Nikiforova V. B. Lazarev I. S. Shaplygin 《Journal of Thermal Analysis and Calorimetry》1993,40(1):373-378
The termal stabilities of several families of high-T c superconductors (HTSC), as well as the dependence of phase transitions on temperature and stoichiometry, have been studied by X-ray diffraction, DTA, TG and DSC. Experimental results are discussed in the context of decomposition models. 相似文献
28.
Larsson S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(21):5276-5283
High-temperature superconductivity exists in layered, square-planar cuprates, but is almost absent in most other Cu(II) compounds and in most Ag(II) and Au(II) compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III ("negative-U compounds"). The two-electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III. 相似文献
29.
J. Horn H. -Ch. Semmelhack H. Börner F. Schlenkrich 《Journal of Thermal Analysis and Calorimetry》1994,41(5):995-1005
We propose a reaction model for the synthesis of YBa2Cu4O8 under normal pressure conditions, which contains 4 partial reaction steps. In a first step bariumnitrate and copperoxide react to Ba2Cu3O5+δ. This substance will be formed for each mixtures Ba:Cu=2∶3...3∶2. The following two partial reaction steps are connected to Ba2Cu3O5+δ, which reacts with Y2O3 and CuO to YBa2Cu4O8 or decomposes to BaCuO2 and CuO. In a last step parts of BaCuO2 reacts with Y2O3 and CuO to YBa2Cu4O8. 相似文献
30.
J.V. Acrivos 《Microchemical Journal》2005,81(1):98-107
The onset of electro-magnetic optic effects, observed at the Ba L2,3 edges synchrotron X-ray absorption by a YBa2Cu3O7 single crystal, 20 K above the transition temperature to superconductivity, Tc ∼ 92 K is used to identify the role played by the Ba donor layer in the transition to superconductivity in the CuO2 layers. Negative permeability leads to Faraday rotation of the transmitted beam below T = 112 to 56 K for the 22 μm thick single crystal (c-axis orientation of 8π/18 relative to εX-rays) and sharp changes in the density of empty final states lead to zero transmitted radiation in an interval ΔE at the given orientation. The temperature dependence: ΔE(L2) = 1.4, 3.5 and 3.9 eV, while ΔE(L3) = 5.3, 6 and 7 eV at T = 92, 74 and 63 K, respectively, indicates that the width of the empty final states bands increases as T decreases. ΔE(L3)/ΔE(L2) = 3.8 at 92 K to 1.8 at 63 K also indicates that the d5/2 symmetry bands fill faster than those of d3/2 symmetry below Tc, providing the first experimental evidence of unpaired spin-orbit states in the Ba donor layer of a superconductor. These effects, characteristic of ferromagnetic and anti-ferromagnetic materials near a resonance absorption, signal the onset of a Mott transition. The interaction between the layer states is described using 1D conjugate molecular orbitals. 相似文献