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61.
Summary The dependence of the chloride distribution coefficient on the co-ion of solutions of different alkali fluorides, MF, up to 11M is tested on the strongly basic anion-exchange resin AG1-X10. Under the same experimental conditions the distribution coefficient decreases in the following order for M+: Na+>K+>Rb+>Cs+. This can be explained by the different co-ion-chloride interactions. The consequence of this interaction for a chromatographic separation of chloride is shown with 5M KF and CsF solutions, used as eluants. Depending on the fluoride concentration, the distribution coefficient passes through a minimum value to increase again at higher electrolyte concentration. The non-exchange electrolyte in the resin phase is responsible for this effect. In addition, the bromide and the iodide distribution coefficients up to 10M KF solutions are determined. One results is that the selectivity coefficient between halide ions increases at higher electrolyte concentrations. 相似文献
62.
A. Lainez M. M. Rodrigo Emmerich Wilhelm J. -P. E. Grolier 《Journal of solution chemistry》1992,21(1):49-65
Excess molar volumes V
E
and excess molar heat capacities C
P
/E
at constant pressure have been obtained, as a function of mole fraction x1, for several binary liquid mixtures belonging either to series I: pyridine+n-alkane (ClH2l+2), with l=7, 10, 14, 16, or series II: piperidine+n-alkane, with l=7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. V
E
of pyridine+n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x1>0.90). All the other systems show positive V
E
only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine+n-heptane in the region rich in piperidine (x1>0.87). The C
P
/E
at the respective minima, C
P
/E
(x1,min
), become more negative with increasing l, and the x1,min
values range from about 0.26 (l=7) to 0.39 (l=14). Most interestingly, mixtures of series I exhibit curves of C
P
/E
against x1 with two minima and one maximum, the so-called W-shape curves.Dedicated to Professor A. Néckel on the occasion of his 65th birthday. Communicated in part at the XVIIèmes Journées de Calorimétrie, d'Analyse Thermique et de Thermodynamique Chimique, Ferrara, Italy, 27–30 October, 1986. 相似文献
63.
Hiltrud Breitenfelder-Manske Friedrich Kohler 《Monatshefte für Chemie / Chemical Monthly》1985,116(11):1247-1261
The second virial coefficients of homonuclear three-centerLennard-Jones molecules are calculated with various parameters of the isosceles triangle connecting the three sites. A special effort is made to establish the reducedBoyle temperaturesT
B and the values of the second virial coefficients atT/T
B=0.3 for the sake of comparison with one- and two-centerLennard-Jones molecules. It is shown that it is possible to find parameter values of the interaction potential of one- and two-centerLennard-Jones molecules which give very similar values of second virial coefficients forT/T
B0.3, and the equivalence conditions are established. These conditions might not only give a basis for a microscopic scaling of state variables, but also some restrictions for the validity of the group contribution concept.Presented in part at the DFG-Colloquium at Paderborn, 19th April 1982, and at the 5th Conference on Mixtures of Nonelectrolytes and Intermolecular Interactions, April 18–22, 1983, at Halle (GDR). 相似文献
64.
Rabindra N. Roy James J. Gibbons Guilio LaCross Jr. Charles W. Krueger 《Journal of solution chemistry》1976,5(5):333-343
The two thermodynamic dissociation constants of glycine at 11 temperatures from 5 to 55°C in 50 mass % methanol-water mixed solvent have been determined from precise emf measurements with hydrogen-silver bromide electrodes in cells without liquid junction. The first acidic dissociation constant (K
1)for the process HG+H++G± is expressed as a function ofT(oK) by the equation pK
1 = 2043.5/T – 9.6504 + 0.019308T. At 25°C, pK
1is 2.961 in the mixed solvent, as compared with 2.350 in water, with H°=1497 cal-mole–1, G°=4038 cal-mole–1, S°=–8.52 cal-°K–1-mole–1, and C
p
o
=–53 cal-°K–1-mole–1. The second acidic dissociation constant (K
2)for the process G±H++G– over the temperature range studied is given by the equation pK
2 = 3627.1/T – 7.2371 + 0.015587T. At 25°C, pK
2is 9.578 in MeOH–H2O as compared with 9.780 in water, whereas H° is 10,257 cal-mole–1, G° is 13,063 cal-mole–1, S° is –9.41 cal-°K–1-mole–1, and C
p
o
is –43 cal-°K–1-mole–1. The protonated glycine becomes weaker in 50 mass % methanol-water, whereas the second dissociation process becomes stronger despite the lower dielectric constant of the mixed solvent (=56.3 at 25°C). 相似文献
65.
The adsorption equilibrium of water on microporous adsorbents (zeolites of NaA-, NaY- and NaX-type as well as their ion exchanged
forms) and on mesoporous adsorbents (different silica gels and composite material i.e. silica gel + salt hydrate) has been
studied experimentally and theoretically. Using the Dubinin theory of pore filling the characteristic curves of the adsorption
systems and other relevant dependences such as isotherms, isobars, isosteres and the curve of the differential heat of adsorption
were calculated. For all systems investigated the adsorption were calculated. Aads and the desorption potential Ades of the closed heat storage system were estimated. These values define the working range of the adsorption/desorption cycle
and allow to calculate the specific heat storage density Δ hsp. On the basis of Δ hsp the different adsorbents were compared in order to select the optimal porous storage material for a given application.
The presented experimental and theoretical investigations show that the adsorption systems water-zeolite and water-composites
are promising working pairs for thermochemical heat storage processes for hot tap water supply and space heating of single
family dwellings. The advantage of the water-composite system is the low desorption temperature (solar energy) the main shortcoming
the low temperature lift. The advantage of the water zeolite system is the high temperature lift, the shortcoming are the
relative high desorption temperatures. 相似文献
66.
A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed. 相似文献
67.
Rachael Padman Richard E. Hills 《International Journal of Infrared and Millimeter Waves》1991,12(6):589-599
Multiple reflections in large radiotelescopes used for astronomical spectroscopy cause characteristic modulations of the observed spectrum (baseline ripple). For a given mechanism, the magnitude of the effect depends primarily on the reflection coefficient, which for the most important paths is proportional to . Although ripple is thus generally negligible at mm-wavelengths, there are some instances where it may still be significant, and a recent experiment at the15 m James Clerk Maxwell Telescope was severely affected. We describe a technique which has proved effective in reducing the ripple to an acceptable level.The purpose of this research note is to draw this technique to the attention of the astronomical community. We calculate the reflection coefficient for a typical instrument and show that it can be greatly reduced over a very broad bandwidth by means of a tapered absorber in the centre of the secondary mirror. The graphical analysis of the tapered absorber also demonstrates that the scattering cones and circular absorbers widely used in radioastronomy donot in fact reduce the reflection coefficient significantly. 相似文献
68.
《Surface and interface analysis : SIA》2006,38(10):1336-1342
XPS was used to characterize the chemical changes occurring after drying or applying a heat‐treatment to beech wood samples. Our results indicate that the surface of this air‐exposed material could be strongly affected either by the ambient atmosphere during storage or by the complex atmosphere in the oven during drying or heat‐treatment. However, the O/C ratio measured after removal of a thin slice of a few millimetres of an untreated sample is in reasonable agreement with that calculated from the well‐established chemical composition of beech. Through this methodology (equivalent to scraping for hard materials) it is expected to get a realistic characterization of the wood. The reliability and repeatability of the XPS measurements have been checked and the method applied to the study of the chemical changes of the beech samples subjected to heat‐treatment. Heating at 240 °C induces a significant decrease of the O/C ratio from 0.55 before to 0.44 after the treatment. Heat‐treatment induces also a decrease of the C2 carbon contribution (carbon atom bound to a single non‐carbonyl oxygen) associated with an increase of the C1 carbon contribution (carbon atoms bound only to carbon or hydrogen atoms), in agreement with chemical modifications reported previously in the literature. Thanks to the small analysed area of the equipment used in this study, different spots were analysed to demonstrate the presence or absence of a gradient of chemical composition due to thermal degradation or migration of extractives from within the wood structure to its surface. At the scale of our observations, the different wood samples investigated (dried or heat treated) appear to be homogeneous. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
69.
大功率LD封装技术的研究 总被引:1,自引:0,他引:1
提出一种新的LD列阵封装方法。把热沉形状改为台阶式,使稳态工作条件下的芯片前腔面散热速度提高,前后腔面温差大幅度降低,因此可以提高COD阈值,降低腔面退化率,且更方便于光纤耦合封装。利用Ansys软件对大功率LD稳态工作的温度分布进行模拟。结果发现:改进前的芯片前、后腔面温差为9.0K,改进后温差降为3.5K,降低了60%;热沉前、后端面的温差由原来的18.2K降为8.0K,降低了56%。 相似文献
70.