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951.
K. Rossmanith 《Monatshefte für Chemie / Chemical Monthly》1995,126(5):543-547
Summary The Separation Factors for Pr/La, Nd/Pr, and Sm/Nd, characterizing the crystallization of ammonium and magnesium double nitrates under practical conditions, were determined analytically and are discussed. They confirm that La and Pr can be separated better by fractional crystallization of ammonium double nitrates, whereas in the presence of Sm the magnesium double nitrates are preferable. 相似文献
952.
T. Saraidarov R. Reisfeld A. Sashchiuk E. Lifshitz 《Journal of Sol-Gel Science and Technology》2003,26(1-3):533-540
PbS nanocrystals (NCs) ranging between 4–8 nm were incorporated into Zirconium-Silica-Urethane (ZSUR) matrix obtained by the sol-gel method. The sizes of the particles were controlled by temperature treatment and by concentration of PbS in ZSUR matrix. The sizes of PbS NCs were determined by TEM measurements. The quantum size effect could also be extracted from optical absorption and photoluminescence spectra. The new matrix allows incorporation of up to 40% PbS forming a characteristic structure of dendrite by reacting lead acetate with ammonium thiocyanate in sol-gel matrix. The sol precursors of the matrix for Zirconium-Silica-Urethane contained zirconium oxide (ZrO2) matrix solution, tetramethoxysilane (TMOS), 3-glycid oxypropyl trimethoxysilane (GLYMO) and polyethylene urethane silane (PEUS) synthesized separately. The ZrO2 matrix solution was obtained from zirconium n-tetrapropoxide in propanol and acetic acid was used as a chelating agent to stabilize the zirconium oxide precursor. 相似文献
953.
Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B2F4 and MenN(SiMe3)3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me3SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)n. The course of the reactions was studied by means of 11B and 19F NMR spectroscopy and by measuring the vapor pressures. According to the 11B and 31P NMR spectra the reaction of B2Cl4 with PCl5 or [Me4N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl4]2+[B2Cl6]2? or [Me4N]2+[B2Cl6]2? but gives [PCl4]+[BCl4]?, PCl3 and BCl3 or [Me4N]+[BCl4]? and BCl3 besides (BCl)n. 相似文献
954.
Gert Brandl Fritz Kastner Rainer Fritsch Herbert Zinner Albrecht Mannschreck 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):1059-1069
Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke. 相似文献
955.
A new synthetic route for the preparation of the betain-like compound (CH3N)6P4F8 from (CH3NPF3)2,N-methyl-hexamethyldisilazane andN,N-dimethyl-urea has been found. The steps of this multi-stage reaction could be rationalized to a far extent.
10. Mitteilung:Kubjacek M., Utvary K., Mh. Chem.112, 305 (1981). 相似文献
956.
Summary A micro carbon rod atomizer has been employed for specific and quantitative bromine determinations. This Br-specific gas-chromatographic detector works by help of InBr-bands and measurement at 372.7 nm. The performance of this flame band emission detector (FBD) is demonstrated by calibration curves and the detection limits of 2 examples (ethyl bromide, ethylene dibromide), the latter being 5 and 36 ng of bromine, respectively. The reproducibility has been found to be 4.3%. An example of this detector in comparison with a thermoconductivity detector (TCD) is presented.
Verwendung einer Mikro-Graphitküvette als Br-spezifischer Detektor für die Gas-Chromatographie
Zusammenfassung Eine Mikro-Graphit-Küvette wird für spezifische quantitative Brombestimmungen nach der Indium-Methode bei 372,7 nm benützt und in Verbindung mit einem Gas-Chromatographen als Br-spezifischer Detektor eingesetzt. Die Leistungsfähigkeit dieses Detektors wird an 2 Beispielen (Äthylbromid, Dibromäthan) mit Hilfe von Eichkurven, Bestimmung von Nachweisgrenzen u. ä. demonstriert. Die Nachweisgrenzen liegen bei 5 bzw. 36 ng Brom für die 2 genannten Substanzen. Die Reproduzierbarkeit der Messungen liegt bei 4,3%. Ein Beispiel für die Registrierung eines Gemisches verschiedener Substanzen, gemessen mit dem GC + Flammen-Banden-emissions-Detektor (FBD) und zum Vergleich mit einem Wärmeleitfähigkeitsdetektor (TCD), wird dargestellt.
This research work was supported by financial help of the Bundesminister für Forschung und Technologie in Bonn (GFR). 相似文献
957.
J. Umemura 《Journal of Molecular Structure》1977,36(1):35-54
Temperature dependence of the IR spectra of crystalline propionic acid were examined in the temperature range 242–50 K. The intensities of most absorption bands increased on lowering the temperature, but some bands diminished until they disappeared at temperatures lower than about 120 K. Normal coordinate analyses indicate that the former bands are due to the stable cis dimer and the latter due to the less stable trans dimer which would be produced from the cis dimer by simultaneous proton transfer along two hydrogen bonds. 相似文献
958.
Band structure calculations at the level of LMTO-ASA provide insight into the electronic structure of BaV10O15 and the origin of the structural phase transition. A crystal orbital Hamiltonian population/integrated crystal orbital Hamiltonian population analysis provides evidence that the crystallographic phase transition is driven by V-V bond formation. As well, the energy bands near the Fermi level are very narrow, <1 eV, consistent with the fact that the observed insulating behavior can be due to electron localization via either Mott-Hubbard correlation and/or Anderson disorder. The partial solid solution, BaV10−xTixO15, was examined to study the effect of Ti-doping at the V sites on the structure and electronic transport properties. In spite of the non-existence of “BaTi10O15”, the limiting x=8, as indicated by a monotonic increase in the cell volume and systematic changes in properties. This limit may be due to the difficulty of stabilizing Ti2+ in this structure. For x=0.5 both the first order structural phase transition and the magnetic transition at 40 K are quenched. The samples obey the Curie-Weiss law to x=3 with nearly spin only effective moments along with θ values which range from −1090 K (x=0.5) to −1629 K (x=3). For x>3 a very large, ∼2×10−3 emu/mol, temperature independent (TIP) contribution dominates. Conductivity measurements on sintered, polycrystalline samples show semiconducting behavior for all compositions. Activation energies for Mott hopping derived from high temperature data range from ∼0.1 eV for x=0-1 and fall to a plateau of 0.06 eV for x=3-7. Low temperature data for x=3, 5 and 7 show evidence for Mott variable range hoping (VRH) with a T1/4 law and in one case between 5 and 17 K, a Efros-Shklovskii correlated hopping, T1/2 law, was seen, in sharp contrast to BaV10O15 where only the E-S law was observed up to 75 K. Seebeck coefficients are small (<35 μV/K), positive, roughly TIP and increase with increasing x up to x=5. This may point to a Heikes hopping of holes but a simple single carrier model is impossible. The compositions for x>3 are remarkable in that local moment behavior is lost, yet a metallic state is not reached. The failure of this system to be driven metallic even at such high doping levels is not fully understood but it seems clear that disorder induced carrier localization plays a major role. 相似文献
959.
Tautomerism of Nunsubstituted benzohydroxamic acids and their anions in the gas phase was investigated by the semiempirical AM1 method. The possibility of estimating pK
a in aqueous solutions using calculated characteristics of molecules is demonstrated. 相似文献
960.
以金属硝酸盐为原料,分别采用高分子前驱体法、柠檬酸盐凝胶法制备了纳米级的Ce-Zr-Ba-O复合氧化物超细粒子,采用X-射线衍射(XRD)、透射电镜(TEM)、BET比表面测定、热重-差热(TG-DTA)技术对催化剂进行了表征,并考察了催化剂的CO氧化活性和热稳定性。实验结果表明,高分子前驱体法和柠檬酸盐凝胶法制备的催化剂粉体都达到了纳米级。两种方法中,高分子前驱体法所制得的催化剂的BET比表面达118.96m2·g-1,CO氧化反应活性较高,同时该方法制得的催化剂分散性好,无团聚,经1000℃高温焙烧后仍基本无烧结、无团聚现象,具有较高的热稳定性。 相似文献