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排序方式: 共有1617条查询结果,搜索用时 15 毫秒
21.
Recycling of metals from low concentrated solutions. A review is given of processes used for the separation of metals from aqueous solutions, especially low concentration waste waters. Purification processes for waste water used only to reach values set by law are compared with processes that allow recovery of metals. Precipitation with and without additives, adsorption, processes with ion exchange resins, solvent extraction and membrane processes, especially liquid membrane permeation, are described. As a result of these considerations, a qualitative comparison of all the described processes becomes possible. For the separation of zinc from a waste water stream, a special economic comparison is also shown between precipitation processes and the liquid membrane permeation process. Finally, the latest developments in the fields of solvent extraction and liquid membrane permeation are discussed. 相似文献
22.
Structure and molecular dynamics of α,ω-dihydroxy terminated polybutadienes of varying number averaged molecular weight (1320-10?500 g/mol) have been investigated by Fourier-transformed infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). DSC and DRS revealed an increase in the glass transition temperature upon decrease of the molecular weight, accompanied by an increasing dynamic fragility m (or steepness index) of the dielectric α-process. This correlation between Tg and m for different molecular weights indicates the presence of a physical network, where H-bonded end-group clusters act as temporary crosslinks. From the dielectric relaxation strength Δ?α(Mn), the fraction of associated hydroxy groups (fbond) was estimated showing a peak value for the two but shortest polymers, a behaviour that strongly resembles the molecular weight dependence of the fragility. By considering the quantity fbond(Mn) in a modified Fox-Flory approach, the measured Tg(Mn) behaviour could be reproduced in a satisfying way. FTIR results support this general picture and show a considerable dependence of the extent of hydrogen bonding and formation of hydroxy groups associates on the molecular weight. Further, WAXS and DSC results disprove the idea of formation of pseudo-crystalline hydrophobic microdomains in these compounds as suggested by other authors. 相似文献
23.
A correlation for the estimation of critical micellization concentrations and temperatures of polyols in aqueous solutions 总被引:1,自引:0,他引:1
Paschalis Alexandridis Josef F. Holzwarth T. Alan Hatton 《Journal of the American Oil Chemists' Society》1995,72(7):823-826
An empirical correlation is presented for the estimation of critical micellization concentrations (CMC) and critical micellization
temperatures (CMT) for poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers in aqueous solutions. The CMC and CMT are expressed as a function of the polyol molecular
weight, composition, and temperature (for CMC determination) or concentration (in the case of CMT). The correlation was developed
from experimental CMT data for a set of 12 polyols that covered a wide range of molecular weights (2900–14600) and poly(ethylene
oxide) contents (30–80 wt%) and is based on a simple expression for the standard free energy of micellization. Such a correlation
should be useful to practitioners of the field as it allows easy prediction of CMC and CMT for a wide range of polyols with
a minimal number of input parameters. 相似文献
24.
25.
Johannes Konnerth Andreas Jger Josef Eberhardsteiner Ulrich Müller Wolfgang Gindl 《应用聚合物科学杂志》2006,102(2):1234-1239
Seven different polymers used frequently as adhesives and/or matrix polymers in wood, wood composites, and natural fiber‐reinforced composites were studied by uniaxial tensile tests and nanoindentation. It was shown that the elastic modulus, the hardness, the creep factor, and the elastic‐, plastic‐, and viscoelastic work of indentation of the seven different polymers is essentially the same regardless whether the polymers were tested in the form of pure films or in situ, i.e., in an adhesive bond line with spruce wood. An excellent correlation was found between the elastic modulus measured by tensile tests and the elastic modulus measured by nanoindentation. In spite of the good correlation, the elastic modulus measured by nanoindentation is significantly higher than the elastic modulus measured by tensile tests. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1234–1239, 2006 相似文献
26.
Ashraf El-Sayed Josef Gödde Peter Witzgall Heinrich Arn 《Journal of chemical ecology》1999,25(2):389-400
The behavioral responses of Lobesia botrana males to calling females, pheromone gland extracts, and synthetic sex pheromones were recorded in a wind tunnel. Gland extracts and synthetic pheromones were released from a pheromone evaporator. The numbers of males reaching the source and their flight tracks in response to calling females and pheromone gland extracts were compared to those of synthetic blends. Upwind flights to natural sex pheromone were straighter and faster than to a three-component blend of (E)-7,(Z)-9-dodecadienyl acetate (E7,Z9–12:Ac), (E)-7,(Z)-9-dodecadien-1-ol (E7,Z9–12:OH), and (Z)-9-docecenyl acetate (Z9–12:Ac) (100:20:5). The optimum ratio of E7,Z9–12:OH and Z9–12:Ac to E7,Z9–12:Ac was found to be 5% and 1%, respectively. An additional seven compounds identified in the sex pheromone gland were investigated for their biological activity. Two unsaturated acetates, i.e., (E)-9-dodecenyl acetate (E9–12:Ac) and 11-dodecenyl acetate (11–12:Ac), increased the number of males reaching the source as well as straightness, linear velocity, and decreased the track angle of upwind flight. Optimum response was obtained by releasing 10 pg/min E7,Z9–12:Ac in a mixture with 0.5 pg/min E7,Z9–12:OH, 0.1 pg/min Z9–12:Ac, 0.1 pg/min E9– 12:Ac and 1 pg/min 11-12–Ac. The saturated acetates previously identified in the female glands were biologically inactive. 相似文献
27.
Werner Lohwasser Maximilian Fleischer Josef Gerblinger Hans Meixner 《Journal of the American Ceramic Society》1994,77(7):1969-1972
Simultaneous Hall and conductivity measurements have been performed on sputtered polycrystalline thin films and on bulk ceramic specimens of nearly stoichiometric CeO2 in the temperature range between 900° and 1040°C. The measurements have been performed in air using low-frequency alternating current. In the case of the bulk ceramic specimens, an upper limit for the carrier mobility of ≤0.2 cm2 /(V·s) has been obtained, which is in accordance with data from the literature for bulk samples. The conductivity of the thin films (l/1Ω·m) at 1000°C) is in accordance with data from the literature for bulk ceramics. The carrier density derived from the Hall measurements (3 × 1016 /cm3 at 1000°C) increases with increasing temperature, whereas the Hall mobility (4 cm2 (V·s) at 1000°C) decreases with increasing temperature. These values differ from literature data for bulk ceramic specimens. The difference may be duelo the small grain diameters (∼200 nm) in the 1-μm-thick thin films. 相似文献
28.
Ya-Ping Sun Robert D. Miller R. Sooriyakumaran Josef Michl 《Journal of Inorganic and Organometallic Polymers》1991,1(1):3-35
A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores. 相似文献
29.
Bertrand Nathalie Konnov Igor Lazić Marijana Widder Josef 《International Journal on Software Tools for Technology Transfer (STTT)》2021,23(5):797-821
International Journal on Software Tools for Technology Transfer - Randomized fault-tolerant distributed algorithms pose a number of challenges for automated verification: (i) parameterization in... 相似文献
30.
Schwaiger Josef Hammerl Timo Florian Johannsen Leist Susanne 《Information Systems and E-Business Management》2021,19(4):1275-1320
Information Systems and e-Business Management - The digital transformation, with its ongoing trend towards electronic business, confronts companies with increasingly growing amounts of data which... 相似文献