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21.
22.
A theoretical and experimental treatment of axial dispersion in coiled tubes is presented. The dispersion, δ, is related to the theoretical plate height divided by four times the radius of the tube (H/4r). This parameter, when plotted against the product of the Reynolds number and the Schmidt number (ReSc), accurately predicts maxima in dispersion curves. Variations in the boundary layer thickness and the velocity profile cause the dispersion to pass through a maximum at a constant value of log (De2Sc1·14) equal to 6.13 for unretained solutes (De is the Dean number). A new measure of dispersion is proposed; the reduced dispersion, ? = 256/(Re0.667Sc), is derived from the experimental behavior of dispersion at values of log (De2Sc1·14) smaller than 6.13. The logarithm of ? is found to be approximately zero for 2.2 < log (De2Sc1·14) < 6.1 and to decrease linearly with log (De2Sc1·14) at higher values. Experiments with four solutes that have a wide range of molecular diffusivities are reported. Results agree with theory. 相似文献
23.
Fe? Al-Isomorphism and Structural Water in Crystals of Jarosite-Alunite-Type The isomorphous relation between synthetic Alunite KAl3(OH)6(SO4)2 and Jarosite KFe3(OH)6(SO4)2 is investigated. Chemical analysis, X-ray diffraction and thermal analysis permit to draw conclusions on the stoichiometry of the solid solution. It can be shown that under the chosen synthesis conditions the following results are obtainable:
- Iron is preferably built in the crystal lattice of the solid solution.
- There are vacancies on the octahedral positions of aluminium or iron.
- There is always an excess of water in the structure.
24.
The carbodiphosphorane CO2 adduct O2CC(PPh3)2 ( 1a ) reacts with [(CO)5W(THF)] and [(CO)3W(NCEt)3] to produce the complexes [(CO)5W{η1‐O2CC(PPh3)2}] ( 2 ) and [(CO)4W{η2‐O2CC(PPh3)2}] ( 3 ), respectively. Whereas in 2 the betain‐like ligand is coordinated at the tungsten atom in a monodentate manner, in 3 it acts as a chelating ligand with formation of a WO2C four‐membered ring. As a by‐product during the reaction with the acetonitrile adduct also some crystals of the hydrolysis product [HC(PPh3)2]2[W6O19] · 3C2H4Cl2 (4 · 3C2H4Cl2) were isolated. All compounds could be characterized by X‐ray analyses and the usual spectroscopic methods. 相似文献
25.
R.V. Denys V.A. Yartys Masashi Sato R.G. Delaplane 《Journal of solid state chemistry》2007,180(9):2566-2576
A new intermetallic deuteride Ce2Ni7D4.7 with an anomalous volume expansion has been studied. Its structure was solved on the basis of in situ neutron diffraction data. Expansion proceeds along the c-axis and within the CeNi2 slabs only. All D atoms are located inside these slabs and on the border between CeNi2 and CeNi5. Ordering of D atoms in the bulk of CeNi2 is accompanied by substantial deformation of these slabs thus lowering the hexagonal symmetry to orthorhombic [space group Pmcn (No. 62); a=4.9251(3) Å, b=8.4933(4) Å, c=29.773(1) Å]. Inside the CeNi2 layer the hydrogen sublattice is completely ordered; all D-D distances exceed 2.0 Å. Local coordination of Ni by D inside the CeNi2 blocks is of “open”, saddle-like type. Hydrogen ordering is mainly determined by Ce-H and H-H interactions. The pressure-composition-temperature measurements yielded the following thermodynamic parameters of the formation of the hydride: ΔH=−22.4 kJ/molH, ΔS=−59.9 J/(K molH). 相似文献
26.
27.
van den Brand J Blajiev O Beentjes PC Terryn H de Wit JH 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6318-6326
The bonding of two types of ester group-containing molecules with a set of different oxide layers on aluminum has been investigated using infrared reflection absorption spectroscopy. The different oxide layers were made by giving typical surface treatments to the aluminum substrate. The purpose of the investigation was to find out what type of ester-oxide bond is formed and whether this is influenced by changes in the composition and chemistry of the oxide. The extent by which these bonded ester molecules resisted disbondment in water or substitution by molecules capable of chemisorption was also investigated. The ester groups were found to show hydrogen bonding with hydroxyls on the oxide surfaces through their carbonyl oxygens. For all oxides, the ester groups showed the same nu(C = O) carbonyl stretching vibration after adsorption, indicating very similar bonding occurs. However, the oxides showed differences in the amount of molecules bonded to the oxide surface, and a clear relation was observed with the hydroxyl concentration present on the oxide surface, which was determined from XPS measurements. The two compounds showed differences in the free to bonded nu(C = O) infrared peak shift, indicating differences in bonding strength with the oxide surface between the two types of molecules. The bonding of the ester groups with the oxide surfaces was found to be not stable in the presence of water and also not in the presence of a compound capable of chemisorption with the aluminum oxide surface. 相似文献
28.
F. Kastenholz E. Grell J. W. Bats G. Quinkert K. Brand H. Lanig F. W. Schneider 《Journal of fluorescence》1994,4(3):243-246
Two newly synthesized cryptands act as sensitive Na+- and K+-selective indicators for cation concentrations above 20 M. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N–H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S1–T
x
energy gap as a consequence of bridgehead nitrogen protonation.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993. 相似文献
29.
Christopher Hubrich Axel Schulz Harald Brand Alexander Villinger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):2179-2196
The silyl ethers (siloxanes) Me4? xSi(OC6H5CN)x (x = 1–4) (1–4), O(Si(OC6H4CN) (Me)2)2 (5), and Me3Si–O–C6F4CN (6) have been synthesized by the reaction of the respective p-hydroxybenzonitriles and chlorosilanes in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) as hydrogen chloride acceptor. All compounds have been fully characterized by CHN-analysis, melting point, IR, Raman, mass spectroscopy, and 1H, 13C, 29Si NMR spectroscopy. Furthermore, the crystal structures of these compounds—with the exception of Me2Si(OC6H5CN)2, which is a liquid—were determined by X-ray diffractometry. 相似文献
30.
Pavel ?iler Josef Kr��tky Iva Kol��?ov�� Jarom��r Havlica Ji?�� Brand?tetr 《Chemical Papers》2013,67(2):213-220
Possibilities of a multicell isoperibolic-semiadiabatic calorimeter application for the measurement of hydration heat and maximum temperature reached in mixtures of various compositions during their setting and early stages of hardening are presented. Measurements were aimed to determine the impact of selected components?? content on the course of ordinary Portland cement (OPC) hydration. The following components were selected for the determination of the hydration behaviour in mixtures: very finely ground granulated blast furnace slag (GBFS), silica fume (microsilica, SF), finely ground quartz sand (FGQ), and calcined bauxite (CB). A commercial polycarboxylate type superplasticizer was also added to the selected mixtures. All maximum temperatures measured for selected mineral components were lower than that reached for cement. The maximum temperature increased with the decreasing amount of components in the mixture for all components except for silica fume. For all components, except for CB, the values of total released heat were higher than those for pure Portland cement samples. 相似文献