排序方式: 共有55条查询结果,搜索用时 10 毫秒
1.
Darja?Rudan-Tasic Cveto?KlofutarEmail author 《Monatshefte für Chemie / Chemical Monthly》2004,135(7):773-784
Summary. The freezing temperatures of dilute aqueous solutions of some poly(oxyethylene) glycols (PEG, HO–(CH2CH2O)
n
–H, n varying from 4 to 117) were measured over a solute to solvent mass ratio from 0.0100 to 0.3900. The second and third osmotic virial coefficient (A
22 and A
222) of poly(oxyethylene) glycols in aqueous solution were determined. The molecular weight dependence of the second virial coefficient can be described by a simple relation A
22=2×10–5
M
n
1.86, and the third virial coefficient is A
222=0.038A
22
2. The activity coefficients of the solute were calculated using the Gibbs-Duhem equation as applied by Bjerrum. From the osmotic and activity coefficients the excess Gibbs energies of solution, as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were estimated. The second and the third osmotic virial coefficients are correlated with the Mc-Millan-Mayer virial coefficients. 相似文献
2.
The densities of ethanol and ethanol–water mixtures were measured with a vibrating tube densimeter at 25.0, 50.0 and 75.0 °C in the pressure range from 0.10 to 40.00 MPa. Densities were correlated using an empirical model. Partial molar volumes, excess molar volumes, isothermal compressibilities, cubic expansion coefficients and internal pressures were calculated from obtained densities. This study reports the dependence of densities, partial molar volumes, excess molar volumes, isothermal compressibilities, cubic expansion coefficients and internal pressures on composition, temperature and pressure. 相似文献
3.
4.
Cveto Klofutar Mateja Ajnihar Nata?a Poklar Ulrih Darja Rudan-Tasic 《Monatshefte für Chemie / Chemical Monthly》2010,80(2):23-30
Abstract
The density, refractive index, and electrical permittivity of cyclohexylsulfamic acid in 1,4-dioxane solutions were measured at 298.15 K. The limiting apparent specific volume, refraction, and polarization were calculated from the experimental data. The electrical dipole moment of cyclohexylsulfamic acid was estimated using the Debye, Onsager, and Kirkwood equations. The dipole association of cyclohexylsulfamic acid was treated with the assumption that the dipole moment of dimeric species is zero. The dimerization constant and dipole moment of monomeric species were evaluated. 相似文献5.
Darja Govekar-Leban 《Mathematische Zeitschrift》2000,233(2):265-286
6.
Glasses with the basic compositions 10Na2O · 10CaO · xAl2O3 · (80 − x)SiO2 (x=0, 5, 15, 25) and 16Na2O · 10CaO · xAl2O3 · (74 − x)SiO2 (x=0, 5, 10, 15, 20) doped with 0.25-0.5 mol% SnO2 were studied using square-wave-voltammetry at temperatures in the range from 1000 to 1600 °C. The voltammograms exhibit a maximum which increases linearly with increasing temperature. With increasing alumina concentration and decreasing Na2O concentration the peak potentials get more negative. Mössbauer spectra showed two signals attributed to Sn2+ and Sn4+. Increasing alumina concentrations did not affect the isomer shift of Sn2+; however, they led to increasing quadrupole splitting, while in the case of Sn4+ both isomer shift and quadrupole splitting increased. A structural model is proposed which explains the effect of the composition on both the peak potentials and the Mössbauer parameters. 相似文献
7.
Differential scanning calorimetry study of the solidification sequence of austenitic stainless steel
Darja Steiner Petrovič Grega Klančnik Miran Pirnat Jožef Medved 《Journal of Thermal Analysis and Calorimetry》2011,105(1):251-257
The solidification sequence of austenitic stainless steels can be predicted with thermodynamic calculations. Another way is
to use models where the value of the Creq./Nieq. ratio determines the relationship between the solidification mode and the composition factor. In this study the solidification
of AISI 304LN stainless steel at different cooling rates was studied using differential scanning calorimetry (DSC). The samples
were linearly heated above the liquidus temperature to 1550 °C at heating rates of 5, 10, and 25 K/min. The solidification
(cooling) scans from 1550 °C involved the same selected ramps. After the DSC measurements the samples were metallographically
analyzed to reveal the variations in the solidification microstructures. The microhardness of the solidified samples was also
measured. It was found that the cooling rate critically influenced the solidification. The solidification behavior, which
depends on the cooling rate, determines the evolution of the microstructure. At the slowest cooling rates a relief-cell morphology
was observed, and at the fastest cooling rate the formation of dendrites was evident. With an increasing cooling rate the
liquidus temperature decreased and the reaction enthalpy increased. 相似文献
8.
Darja Jenko Andreja Bencan Barbara Malic Janez Holc Marija Kosec 《Microscopy and microanalysis》2005,11(6):572-580
Using electron microscopy, K0.5Na0.5NbO3 (KNN) ceramics sintered at 1030 degrees C for 8 h and 1100 degrees C for 2 and 24 h was studied. The scanning electron microscopy and X-ray spectrometry revealed that the materials consisted of a matrix phase in which the (Na+K)/Nb ratio corresponded closely to the nominal composition and a small amount of Nb-rich secondary phase. A bimodal microstructure of cube-shaped grains was revealed in the fracture and thermally-etched surfaces of the KNN. In the ceramics sintered at 1100 degrees C, the larger grains (up to 30 mum across), contained angular trapped pores. The transmission electron microscopy analysis revealed that the crystal planes of the grains bordering the intragranular pore faces were of the {100} family with respect to the simple perovskite cell. Ferroelectric domains were observed in the grains of this material. 相似文献
9.
Negar Maafi Abdullah Al Mamun Ondej Janourek Jana Maíkov Kateina Breiterov Adla Diepoltov Klra Kone
n Anna Holkov Daniela Hulcov Jií Kune Elika Kohelov Darja Koutov Marcela afratov Lucie Novkov Lucie Cahlíkov 《Molecules (Basel, Switzerland)》2021,26(19)
The search for novel antimycobacterial drugs is a matter of urgency, since tuberculosis is still one of the top ten causes of death from a single infectious agent, killing more than 1.4 million people worldwide each year. Nine Amaryllidaceae alkaloids (AAs) of various structural types have been screened for their antimycobacterial activity. Unfortunately, all were considered inactive, and thus a pilot series of aromatic esters of galanthamine, 3-O-methylpancracine, vittatine and maritidine were synthesized to increase biological activity. The semisynthetic derivatives of AAs were screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Ra and two other mycobacterial strains (M. aurum, M. smegmatis) using a modified Microplate Alamar Blue Assay. The most active compounds were also studied for their in vitro hepatotoxicity on the hepatocellular carcinoma cell line HepG2. In general, the derivatization of the original AAs was associated with a significant increase in antimycobacterial activity. Several pilot derivatives were identified as compounds with micromolar MICs against M. tuberculosis H37Ra. Two derivatives of galanthamine, 1i and 1r, were selected for further structure optimalization to increase the selectivity index. 相似文献
10.
The monoesterification of ethylene glycol under isothermal conditions was conducted using benzoic acid in methane‐sulfonic acid/Al2O3 as a catalyst. Using this reagent, glycol was selectively monoesterified with high yield. The reactions were performed within an automated batch reactor under equimolar conditions, constant rotational frequency of the stirrer, and within the temperature range from 65 to 85°C. The rate constant related to this reaction and to the corresponding reverse reaction, activation energy, and preexponential factor was derived from experimental data. It has been concluded that under these conditions the formation of dibenzoate was successfully prevented. 相似文献