Influence de la température sur les constantes B.E.T. de dissolution de l'eau dans un mélange fondu [AgNO3 + TlNO3]

1980 ◽  
Vol 58 (14) ◽  
pp. 1480-1483 ◽  
Author(s):  
Marie-Christine Abraham ◽  
Maurice Abraham ◽  
James Sangster
Keyword(s):  
Temperature Dependence ◽  
Adsorption Sites ◽  
Adsorption Of Water ◽  
The Difference ◽  
Molar Energy

The temperature dependence of the B.E.T. constants for water dissolved in the melt (0.515 AgNO3 + 0.485 TlNO3) has been studied in the range 85–110 °C at water mole fractions between 0 and 0.5. The B.E.T. constants are: r: the mole ratio of adsorption sites to salt; ΔE: the difference between the molar energy of adsorption of water on an available site in the melt and the molar energy of liquefaction of water.It was found in this work that (1) r increases linearly with temperature and (2) the product rΔE is perceptibly independent of temperature.

Effect of ring substituents on the fluorescence spectra of substituted diarylcarbenes

1988 ◽  
Vol 66 (3) ◽  
pp. 491-494 ◽  
Author(s):  
J. C. Scaiano ◽  
D. Weir
Keyword(s):  
Free Radical ◽  
Temperature Dependence ◽  
Fluorescence Spectra ◽  
Excellent Correlation ◽  
Emission Data ◽  
The Difference

The fluorescence spectra of a series of ring-substituted diarylcarbenes have been examined. The solution spectra are generally red shifted by 25–30 nm with respect to the band positions in matrices at 77 K. The difference is believed to reflect emission from non-relaxed conformations at 77 K. Both electron-withdrawing and -donating substituents lead to red shifts in the emission. These shifts are essentially additive, and the carbene emission data show an excellent correlation with free radical fluorescence data for the corresponding diarylmethyl radicals. The temperature dependence of excited carbene lifetimes have been examined for a few representative examples.

Water Adsorption on Ideal Anatase-TiO2(101) – An Embedded Cluster Model for Accurate Adsorption Energetics and Excited State Properties

2020 ◽  
Vol 234 (5) ◽  
pp. 813-834 ◽  
Author(s):  
Thorben Petersen ◽  
Thorsten Klüner
Keyword(s):  
Excited State ◽  
Cluster Model ◽  
Dissociative Adsorption ◽  
Molecular Adsorption ◽  
Hydrogen Electrode ◽  
Adsorption Sites ◽  
First Results ◽  
Adsorption Of Water ◽  
Hybrid Functionals ◽  
High Level

AbstractA combined theoretical approach towards the accurate description of water on anatase-TiO2(101) was pursued in this study. Firstly, periodic slab calculations on the basis of density hybrid functionals (PBE0, HSE06) were performed in order to gain insight into the adsorption sites and geometric structure of the surface. For submonolayer coverage of H2O, the molecular adsorption of water is found to be the most stable one with quite similar energetics in PBE0 and HSE06. Moreover, the transition states towards the less preferred dissociative adsorption forms are predicted to be greater than 0.7 eV. Thus, water will not spontaneously dissociate and based on the Computational Hydrogen Electrode model an overpotential of about 1.71 V is needed to drive the overall oxidation. In addition, to validate our results for molecular adsorption of H2O, an embedded cluster model is carefully evaluated for the a-TiO2(101) surface based on the periodic slab calculations. Subsequent high-level DLPNO-CCSD(T) results are in close agreement with our periodic slab calculations since the interaction is found to mainly consist of electrostatic contributions which are captured by hybrid functionals. Finally, first results on optimized geometries in the excited state based on the photogenerated charge-transfer state are presented.

Evaluation of Low-Temperature Properties and the Fragility of Asphalt Binders with Non-Arrhenius Viscosity–Temperature Dependence

2005 ◽  
Vol 1901 (1) ◽  
pp. 44-51 ◽  
Author(s):  
Huachun Zhai ◽  
Delmar Salomon
Keyword(s):  
Temperature Dependence ◽  
Asphalt Binders ◽  
Arrhenius Behavior ◽  
Direct Tension ◽  
Different Temperatures ◽  
Rotational Viscosity ◽  
Liquid Fragility ◽  
The Difference ◽  
Critical Cracking Temperature ◽  
Experimental Values

Rotational viscosities of different asphalt binders were determined at temperatures between 80°C and 185°C. Viscosity–temperature dependence of asphalt binders was described with the use of the Vogel–Tammann–Fulcher (VTF) and the William–Landel–Ferry (WLF) equations. The Vogel temperature ( Tv) and the glass transition temperature ( Tg) for different asphalt binders were determined by fitting experimental values of viscosity at different temperatures with these two equations. For asphalt binders, the difference between Tv and Tg was about 40K. Effects of asphaltenes, aging, chemical modification, and polymer content on these temperatures were evaluated. As asphaltene content increased, both temperatures, Tv and Tg, increased. Different polymers showed different effects on these temperatures. The values of Tv and Tg were correlated with the critical cracking temperature ( Tcr) determined through use of a bending beam rheometer and a direct tension tester. The results suggested that the correlations between Tv, Tg, and Tcr could be used to determine Tcr from the rotational viscosity results tested at high temperature. With simple rotational measurements, a quick estimation of Tcr of asphalt binders could be obtained. Liquid fragility theory was also used to study Tg of asphalt binders. Parameters determined with the VTF and WLF equations indicated that asphalt binders behaved as fragile liquids because of their non-Arrhenius behavior in the temperature range studied.

Methodology for Measurement of Density of Liquid Oxides

2020 ◽  
Vol 7 (2) ◽  
Author(s):  
Jan Hrbek ◽  
Bence Mészáros ◽  
Mykhaylo Paukov ◽  
Martin Kudláč
Keyword(s):  
High Temperature ◽  
Temperature Dependence ◽  
Extreme Conditions ◽  
Nuclear Accidents ◽  
System A ◽  
Different Temperatures ◽  
Density Values ◽  
Properties Of Materials ◽  
The Difference

Abstract Measurement of physical properties of materials in extreme conditions, such as high temperature, is limited by technological challenges. Nevertheless, modeling of several phenomena relies on the existence of experimental data for their validation. In this study, a method suitable for determination of density in a liquid phase at high temperature is proposed and tested on Al2O3–ZrO2 system. A methodology for acquiring the temperature dependence of density for radioactive materials is proposed and is aimed to refine severe nuclear accidents modeling. The oxide was melted in an induction furnace with a cold crucible. The measurement was based on evaluation of the volume of the melt at different temperatures, in a range from 2100 to 2400 °C. The densities of the oxide in the solid-state and the skull-layer were measured using a pycnometer. A temperature dependence of the density was established and the results were compared with literature. The difference between existing data and the measured values in this work was less than 5%. Thus, the proposed methodology provides reliable density values in extreme conditions.

scholarly journals Temperature Dependence and Anisotropic Effects in the Thermal Properties of Hen Egg-White Lysozyme Crystals

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1279
Author(s):  
Syou Maki ◽  
Seiji Fujiwara ◽  
Seiichi Tanaka ◽  
Eka Erzalia ◽  
Mizuki Kato ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thermal Properties ◽  
Temperature Dependence ◽  
Superconducting Magnet ◽  
Egg White ◽  
Hen Egg White Lysozyme ◽  
Egg White Lysozyme ◽  
Hen Egg White ◽  
The Difference ◽  
Hen Egg

We measured the thermal conductivity (λ) and thermal diffusivity (α) of tetragonal hen egg-white lysozyme (HEWL) crystals by the transient short-hot wire method. The crystals were grown by two different methods: Magnetically levitated crystals were realized with a superconducting magnet, the c-axis of which was perpendicularly orientated in the direction of the wire, and naturally grown crystals realized by the two-liquid method, grown randomly. We confirmed the temperature dependence in both the λ and α properties by measuring the variations in temperature and by statistical analysis. These properties differed slightly depending on the presence or absence of a magnetic field applied during the crystal growth. We hypothesize that the difference originated from the orientation of the crystals caused by the magnetic field. The statistical analyses demonstrated the possibility that asymmetric thermal conduction in the protein crystals provides anisotropic effects of the thermal properties.

Rutile- and anatase-type temperature-dependent pre-edge peak intensities in K-edge XANES spectra for AO (A = Mn), A 2O3 (A = Sc, Cr and Mn) and AO2 (A = Ti and V)

2018 ◽  
Vol 25 (4) ◽  
pp. 1129-1134 ◽  
Author(s):  
Tsubasa Tobase ◽  
Akira Yoshiasa ◽  
Tatsuya Hiratoko ◽  
Akihiko Nakatsuka
Keyword(s):  
Temperature Dependence ◽  
Difference Spectrum ◽  
True Temperature ◽  
Energy Position ◽  
Edge Structure ◽  
Peak Intensity ◽  
Transition Metal Element ◽  
Peak Energy ◽  
Bending Mode ◽  
The Difference

Pre-edge peaks in 3d transition-metal element (Sc, Ti, V, Cr and Mn) K-edge XANES (X-ray absorption near-edge structure) spectra in AO2 (A = Ti and V), A 2O3 (A = Sc, Cr and Mn) and AO (A = Mn) are measured at various temperatures. Quantitative comparisons for the XANES spectra were investigated by using absorption intensity invariant point normalization. The energy position of the difference peak (D peak) is obtained from the difference between the low- and high-temperature XANES spectra. There are two kinds of temperature dependence for pre-edge peak intensity: rutile- and anatase-type. The true temperature dependence of a transition to each orbital is obtained from the difference spectrum. In both anatase and rutile, the pre-edge peak positions of A2 and A3 are clearly different from the D1- and D2-peak positions. The A1 peak-top energies in both phases of VO2 differ from the D1 peak-top energies. The D-peak energy position determined by the difference spectrum should represent one of the true energies for the transition to an independent orbital. The peak-top positions for pre-edge peaks in XANES do not always represent the true energy for independent transitions to orbitals because several orbital transitions overlap with similar energies. This work suggests that deformation vibration (bending mode) is effective in determining the temperature dependence for the D-peak intensity.

Chemisorption of Ammonia on Silica

1973 ◽  
Vol 51 (11) ◽  
pp. 1771-1781 ◽  
Author(s):  
G. A. Blomfield ◽  
L. H. Little
Keyword(s):  
Adsorption Process ◽  
Ammonia Adsorption ◽  
Adsorption Sites ◽  
Added Water ◽  
Adsorption Of Water ◽  
Amine Groups

The interaction of ammonia with silicas prepared by a variety of methods was studied to resolve conflicting reports of the mode of ammonia adsorption and to determine the role of chlorine impurities (present in the silica) in the adsorption process. Results for the adsorption of water on silica assisted in making band assignments and competition between ammonia and water for silica adsorption sites was observed. It was concluded that dehydroxylated silicas contain sites which dissociate ammonia to form Si—NH2 groups having infrared bands at 3540, 3450, and 1550 cm−1 (the surface amine groups are not displaced by added water). The presence of chlorine in the silica is not a prerequisite for chemisorption of ammonia.

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