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991.
Based on the data for the initial stage of aging of metal hydroxides that exhibit nitrogen fixation properties and the exact solution of the model kinetic problem for the association of aqua and hydroxo complexes, the regularities of the formation of the structure of primary amorphous particles of metal hydroxides have been revealed. The primary particles consist of chain hydroxo polymers that containca. 10 units and are chemically bound to each other by 3-OH bridging groups in sites at chaotically arranged intersections.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 12, pp. 2852–2857, December, 1996. 1996. 相似文献
992.
Samples with the nominal composition Nd2B5 contain strongly disordered crystals composed of nanosized (100) lamellae. Most commonly, a polysynthetic twinning based on a fourfold rotation separates the lamellae at coherent boundaries. The structure of the twin interface contains a pseudo fourfold arrangement of B atoms as derived from electron microscopy techniques. Such pseudo-symmetry serves for a rationalization of the twinning. Additionally, a chemical intergrowth of Nd2B5 and NdB4 lamellae based on related structural building units can be observed. Further HRTEM examinations allow the identification of a new structural variant of neodymium borides. 相似文献
993.
用固相反应法制备出LaBa_2Cu_2MO_7(M=Ga,Co)新相。X射线衍射分析认为其属四方晶系,La-Ba_2Cu_2GaO_7的;LaBa_2Cu_2CoO_7的。电阻和温度关系曲线测定表明均为半导体。 相似文献
994.
A previously established model of a system of series-coupled columns, incorporating the effects of temperature and mobile phase compressibility, is generalized to take the temperature dependence of the mobile phase viscosity coefficient into account. Expressions are reported for the linear flow velocity, the effective partition coefficient, and the retention time for both the case of constant mass flow rate and that of constant overall pressure drop. Numerical results indicate that the temperature dependence of the viscosity coefficient affects the retention time and pressure drop while the effective mass distribution coefficient remains essentially unchanged. 相似文献
995.
The tuning of selectivity by changing the flow rate has been investigated in HPLC: two columns with different retention characteristics were coupled in series via a T-piece and the relative retention of components chromatographed on the system were changed by varying the individual flow rates in the coupled columns. The flow rate alteration was performed by adding a second flow after the first column. The flow rate ratio necessary for optimum resolution can be easily calculated on the basis of the capacity factors measured on the individual columns. The performance of this method for adjusting selectivity has been demonstrated by using different column combinations to separate several mixtures containing chlorophenols, nitroaromatic compounds, and aromatic hydrocarbons. 相似文献
996.
《Journal of separation science》2003,26(14):1273-1283
The conformational dynamics of home‐made monomeric and polymeric (octadecyl – C18 and alkylamide – AP) stationary phases have been investigated by analyzing the dependence of retention on the reciprocal temperature for different organic compounds. Theoretical considerations were based on the results of methylene selectivity determination. Two selected PAHs – naphthacene and benzo[a]anthracene, whose structures differ in the position of the ring – were chosen as solutes to study the thermodynamics of retention behavior. Standard enthalpies (ΔH 0) were obtained from the slope of the plots of the capacity factor logarithm (ln k) against the reciprocal temperature (1/T), i. e. van't Hoff plots, in a temperature range from 285 to 315 K. The conformation of the stationary phase (monomeric and polymeric) structure and the length of bonded ligands with their specific functional (N‐acylamide) groups had a significant effect on retention. 相似文献
997.
Summary The changes in the heat of solution of polar compounds and xylene isomers in methylsilicone fluid OV-101 deposited on Chromosorb W AW DMCS were studied. It was shown that the heat of solution increases with an increase of the percentage loading of the OV-101 up to 10%. Solution and adsorption thermodynamic characteristics of the studied system are briefly discussed. 相似文献
998.
利用溶胶-凝胶分配理论对氢键溶液的模型体系进行研究, 给出了凝胶点后氢键网络中各结构参数的计算方案, 并进行相应的数值计算. 结果表明, 因受体基团本身的性质及两类质子受体基团的数量比不同, 受体基团的竞争作用对网络结构有明显影响, 这提供了控制氢键网络结构特征的可能方法. 相似文献
999.
Polymer gels with high water content are made by polymerization of hydrophilic/hydrophobic monomer mixtures in bicontinuous microemulsions. These structures can be described as a heterophasic, bicontinuous polymer colloid-in-water structure, the characteristic length of which is only indirectly influenced by the original microemulsion mixture.The structure formation and phase changes throughout the polymerization reaction are followed with rheology, polarization microscopy, and scanning and transmission electron microscopy. It is shown that already the very first formed polymer changes disturb the bicontinuous phase structure and nucleate a vesicular phase; with further consumption of the monomer mixture, at least three other phase transitions can be detected, ending with a simple globular surfactant structure.Although direct templating of the original mesomorphous structure does not occur, the existence of the diverse lyotropic phases influences the final structure. It is shown that simple dilution changes the characteristic length of the network elements from about 2 m down to 50 nm. This is explained by a combination of a nucleation-and-growth mechanism with the influence of a restricted colloidal stability in anisometric lyotropic phases. 相似文献
1000.
Brigitte Koppelhuber-Bitschnau Franz A. Mautner Klaus Yvon 《Monatshefte für Chemie / Chemical Monthly》1990,121(6-7):505-509
Lattice parameters as a function of temperature for, and atomic coordinates of the low-temperature phase of, SrMo6S8 are reported from X-ray powder diffraction. The structure transforms atT
1=135(3) K from the rhombohedral high-temperature modification (R
,a
rh=6.5630 (3) Å, rh=88.9982(2)°,V
rh=282.55(5)Å3 at 298 K) into the triclinic low-temperature modification (P
,a
tr=6.481(1)Å,b
tr=6.572(1)Å,c
tr=6.611(1)Å, tr=89.246(4)°, tr=89.304(4)°, tr=88.169(4)°,V
tr=281.4(2)Å3 at 20K). The triclinic distortion is larger than in the Ca analogue, and similar to the Ba and Eu analogues.
Untersuchung des Tieftemperatur-Phasenübergangs von SrMo6S8 mittels Röntgenpulverdiffraktometrie (Kurze Mitt.)
Zusammenfassung Die Temperaturabhängigkeit der Gitterparameter und die Atomlagen der Tieftemperaturphase von SrMo6S8 wurden mittels Röntgenpulverdiffraktometrie bestimmt. Die rhomboedrische Hochtemperaturmodifikation (R ,a rh=6.5630(3)Å, rh=88.9982(2)°,V rh=282.55(5)Å3,T=298 K) wandelt beiT 1=135(3) K in die trikline Tieftemperaturmodifikation (P ,a tr=6.481(1)Å,b tr=6.572(1)Å,c tr=6.611(1)Å, tr=89.246(4)°, tr=89.304(4)°, tr=88.169(4)°,V tr=281.4(2)Å3,T=20 K) um. Die trikline Deformation ist stärker ausgeprägt als in der Ca-Verbindung und ähnlich jener der Ba- and Eu-Verbindung.相似文献