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31.
The conditional solubility of scheelite CaWO4 in molten NaCl?KCl (1:1) has been studied either in oxobasic or oxoacidic media. In the former case it is increased by formation of sparingly soluble CaO according to:Ca2+ + O2CaO(s), pKsCaO = 10800/T ? 5.8 (molality scale) In the later case, WO42- behaves as an oxobase according to the following equilibria:WO42?WO3 (s) + O2? pK0 = 10.0 at 1000 K3 WO42?W3O102? pK3 = 12.7 at 1000KThe latter equilibrium favours an increase in the WVI solubility when pO2- is increased, for instance by injection of HCl. The whole set of results has been summarized by a conditional solubility diagram of scheelite versus pO2-. 相似文献
32.
B. Montanari B. Civalleri C. M. Zicovich‐Wilson R. Dovesi 《International journal of quantum chemistry》2006,106(7):1703-1714
The equilibrium structural parameters, high‐ and low‐frequency dielectric tensors, Born effective charges, and Γ‐point vibrational frequencies of bulk Al2O3 corundum are calculated by using the periodic, ab initio program CRYSTAL, which adopts an all‐electron Gaussian‐type basis set. The effect of basis set and the performance of three different functionals, i.e., LDA, PW91, and B3LYP, are discussed. The mean absolute deviation from the measured frequencies is as small as 7 cm?1 for both the LDA and B3LYP functionals, indicating that these functionals perform extremely well in this case. The mean absolute deviation increases to 18 cm?1 when the PW91 functional is used. All three functionals reproduce the equilibrium geometry of corundum to a high level of accuracy, with LDA and B3LYP outperforming PW91 slightly. The comparison of the current all‐electron calculations with previous plane‐wave, pseudo‐potential calculations shows an overall similar performance. The results of isotopic substitution for both Al and O are also presented. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
33.
The infrared spectra in the OH-stretching and HOH-bending regions of H2O, and in the OH-stretching region of HDO dissolved in a number of ketones and ethers have been recorded. The number of component bands and their wavenumbers, halfwidths and intensities, as well as the total OH-stretching intensity in each solvent, have been interpreted in terms of a model for the types of hydrogen bonded solvent:water complexes formed in these systems.The effect of temperature on the spectra of H2O in some of the ketones has been rationalized on the basis of the equilibrium existing between the different hydrogen bonded species present in solution. 相似文献
34.
NMR spectral data of some (E)-α-phenyl-β-(2-thienyl) acrylic acids indicate that these compounds exist in the preferred s-trans conformation. In the case of (E)-α-phenyl-β-(2-furyl)acrylic acids and their methyl esters the presence of only s-cis rotamer has been established. 相似文献
35.
Thermal- and photo-stabilities of unstabilized acrylonitrile-butadiene-styrene terpolymer, ABS, have been investigated by i.r. spectroscopy. Degradation of ABS samples is initiated by attack on the polybutadiene (PB) component; oxidation products containing hydroxyl and carbonyl groups are produced. The effect of prior thermal processing is to introduce into the polymer hydroperoxides arising from oxidative destruction of PB-unsaturation; these hydroperoxides act as catalysts during subsequent u.v. irradiation. The insolubility of degraded samples of ABS is associated with the formation of cross-linked structures and occurs mainly in the PB segment. It is concluded that the degradation characteristics of ABS are essentially those of the polybutadiene component. 相似文献
36.
Malose J. Mphahlele Ahmed M. El-Nahas Tarek M. El-Gogary 《Journal of Molecular Structure》2004,690(1-3):151-157
The geometries of the title compounds were probed in solution, solid and gas states using spectroscopic methods, X-ray crystallography and quantum chemical techniques. The exclusive existence of the NH-4-thiones in solution (NMR and PCM-B3LYP(MP2)/6-31+G(d) calculations) and solid state (FT-IR and X-ray) is also corroborated by comparison of their spectroscopic data with those of the corresponding 2-aryl-1-methylquinoline-4(1H)-thione derivatives. The co-existence of the quinoline-4-thione and quinoline-4-thiol (4-mercaptoquinoline) isomers in the gas phase is confirmed by mass spectrometry and the preponderance of the 4-thiol is supported by quantum chemical techniques (PM3, MP2 and B3LYP). 相似文献
37.
Frank Herwig Köhler Hans Jürgen Kalder Ernst Otto Fischer 《Journal of organometallic chemistry》1975,85(2):C19-C22
Carbon-13 NMR data are reported for trimethyltin derivatives containing ERn groups where E C, Si, Ge, Sn, N, O and S including a series of cyclic amines with ring sizes from three to seven. Coupling constant values for the homologous series of fourth group derivatives give goood correlations with the electronegativity of E. The observation of the two-bond, ¦ 2J(119SnE13C) ¦ couplings only in the derivatives containing bulky R groups is rationalized by a bimolecular exchange of ERn groups in the concentrated solutions studied. 相似文献
38.
Colorimetric peroxidase-coupled procedures for the determination of several cerebrospinal fluid (CSF) lipid classes are described. These methods were modified to increase the effectiveness of each cerebrospinal fluid lipid assay by using the sample as the primary diluent for a highly concentrated reagent in an inverse concentration technique. Direct enzymic assays for the determination of CSF cholesterol (free and total), choline phospholipids, and triglycerides were adapted from existing assays to require less than 0.5 ml of sample per assay. This made determinations of the several lipid analytes possible even when samples were from pediatric specimens. In a study model, 51 pediatric CSF samples were analyzed for these lipid constituents. Mean values and standard deviations were determined. Within and between-run studies were performed by sampling from a pool of cerebrospinal fluid specimens. Within-run coefficients of variation for the several proposed procedures were less than 3% while the between-run findings for all of the procedures were less than 5%. 相似文献
39.
The magnetic susceptibility of UO2ThO2 solid solutions has been measured from room temperature to 2.0 K. The magnetic moment and the Weiss constant have been determined in the temperature range in which the Curie-Weiss law holds. For the solid solutions showing antiferromagnetic transition, the Néel temperature has been also determined. These values decrease monotonically with increasing ThO2 concentration. The results were analyzed using the molecular field theory which includes the interaction between next-nearest neighbor spins. The interactions between nearest neighbor spins, J1, and those between next-nearest neighbor spins, J2, both decrease with increasing ThO2 concentration. The change of J1 with composition is larger than that of J2. The effect of magnetic dilution with ThO2 is considered to be stronger on the interaction between nearest neighbor uranium ions. 相似文献
40.
The heat capacities of MnBr2 · 4D2O and MnCl2 · 4D2O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°TH°0) and S°T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl2 · 4D2O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K. 相似文献