Selective Growth Of Decagonal Ai-Co Thin Films By Reactive Diffusion: Kinetic And Thermodynamic Aspects

1998 ◽  
Vol 553 ◽  
Author(s):  
E. Emeric ◽  
C. Bergman ◽  
G. Clugnet ◽  
P. Gas
Keyword(s):  
Activation Energy ◽  
Reactive Diffusion ◽  
Multilayer Structures ◽  
Peritectoid Reaction ◽  
Dsc Analysis ◽  
Reaction Step ◽  
Diffusion Kinetic ◽  
Decagonal Quasicrystal ◽  
The Enthalpy Of Formation

AbstractWe report on the formation by reactive diffusion of a pure decagonal quasicrystalline film in Al/Co bilayer and multilayer structures of overall composition Al13CO4. We show that this method is highly selective since several stable phases which exist around this composition are never observed. The quasicrystal is not the first reaction product but is obtained as a second reaction step by a peritectoid reaction between Al9Co2 and the remaining cobalt. DSC analysis allows the determination of both the enthalpy of formation of the decagonal quasicrystal (ΔHf = -31500 ± 2000 J/g-atom) and its activation energy of growth (2.6 ± 0.5 eV).

Development of HPLC Method for the Purity Test by Design of Experiments and Determination of Activation Energy of Hydrolytic Degradation Reactions of Sofosbuvir

2020 ◽  
Vol 16 (7) ◽  
pp. 976-987
Author(s):  
Jakub Petřík ◽  
Jakub Heřt ◽  
Pavel Řezanka ◽  
Filip Vymyslický ◽  
Michal Douša
Keyword(s):  
Activation Energy ◽  
Design Of Experiments ◽  
Mobile Phase ◽  
Hydrolytic Degradation ◽  
Isoconversional Method ◽  
Hplc Method ◽  
Organic Modifier ◽  
Calculation Methods ◽  
Degradation Reactions

Background: The present study was focused on the development of HPLC method for purity testing of sofosbuvir by the Design of Experiments and determination of the activation energy of hydrolytic degradation reactions of sofosbuvir using HPLC based on the kinetics of sofosbuvir degradation. Methods: Following four factors for the Design of Experiments were selected, stationary phase, an organic modifier of the mobile phase, column temperature and pH of the mobile phase. These factors were examined in two or three level experimental design using Modde 11.0 (Umetrics) software. The chromatographic parameters like resolution, USP tailing and discrimination factor were calculated and analysed by partial least squares. The chromatography was performed based on Design of Experiments results with the mobile phase containing ammonium phosphate buffer pH 2.5 and methanol as an organic modifier. Separation was achieved using gradient elution on XBridge BEH C8 at 50 °C and a flow rate of 0.8 mL/min. UV detection was performed at 220 nm. The activation energy of hydrolytic degradation reactions of sofosbuvir was evaluated using two different calculation methods. The first method is based on the slope of dependence of natural logarithm of the rate constant on inverted thermodynamic temperature and the second approach is the isoconversional method. Results and Conclusion: Calculated activation energies were 77.9 ± 1.1 kJ/mol for the first method and 79.5 ± 3.2 kJ/mol for the isoconversional method. The results can be considered to be identical, therefore both calculation methods are suitable for the determination of the activation energy of degradation reactions.

Cathodoluminescence of SiO2/Si System

2009 ◽  
Vol 156-158 ◽  
pp. 487-492 ◽  
Author(s):  
M.V. Zamoryanskaya
Keyword(s):  
Activation Energy ◽  
Electron Beam ◽  
Rise Time ◽  
Silicon Oxide ◽  
Beam Current ◽  
Electron Beam Current ◽  
Electron Traps ◽  
Definition Of ◽  
Luminescent Centers

In this paper the new method for determination of luminescent centers concentration are discussed. While the possibility of electron traps determination and definition of its activation energy are suggested. The cathodoluminescent (CL) method was used. The determination of luminescent centers concentration in silicon oxide is based on the measurements of dependences of CL intensity on electron beam current. The presence and energy of activation of electron traps were studied by measurement of rise time and decay of luminescent band during the stationary irradiation of silica by electron beam.

scholarly journals Determination of the membrane hydraulic permeability of MSCs

2016 ◽  
Vol 2 (1) ◽  
pp. 323-327
Author(s):  
Jennifer Contreras Lopez ◽  
Lothar Lauterböck ◽  
Birgit Glasmacher
Keyword(s):  
Activation Energy ◽  
Bone Marrow ◽  
Cooling Rate ◽  
Mesenchymal Stromal Cells ◽  
Stromal Cells ◽  
Hydraulic Permeability ◽  
Osmotic Behaviour ◽  
Additional Influence ◽  
Dimethyl Sulfoxid

AbstractA successful cryopreservation is based on knowledge of the optimal cooling rate. So far, this is often determined by way of complex parameter studies. Alternatively, the identification of cell specific characteristics, such as osmotic behaviour, membrane hydraulic permeability and activation energy could be used to calculate the optimal cooling rate. These parameters should be determined for supra-zero and sub-zero temperatures. In this study cryomicroscopy was used. Mesenchymal stromal cells (MSCs) from bone marrow were analysed. The determined membrane hydraulic permeability for sub-zero temperatures is significantly lower than that for supra-zero temperatures. On the contrary the activation energy is significantly higher in the presence of ice. The addition of a cryoprotective agent (CPA) such as dimethyl sulfoxid (DMSO) shows an additional influence on the characteristics of the membrane of the cell. The optimal cooling rate was determined with these parameters. For cryopreservation without DMSO the optimal cooling rate was found to be 12.82 K/min. If the MSCs were frozen with 5% (v/v) DMSO the optimal cooling rate is 16.25 K/min.

scholarly journals Determination of the Activation Energy of Polar Firn by D.C. Resistivity Measurements

1967 ◽  
Vol 6 (48) ◽  
pp. 911-915 ◽  
Author(s):  
M. P. Hochstein ◽  
G. F. Risk
Keyword(s):  
Activation Energy ◽  
Resistivity Measurements ◽  
Temperature Range

The activation energy ϵe1 of polar firn samples determined by D.C. resistivity measurements is a function of temperature and density. In the temperature range −2° C. to −10° C. ϵe1 decreases with decreasing temperature reaching a nearly constant value for temperatures colder than −10°C.; in the temperature range −10°C. to −21°C. ϵe1 was found to decrease with increasing density and to lie between 0.7 eV. and 0.4 eV.

scholarly journals Formation of metal oxide-based hydroxysodalite by alkali-activation of kaolinite

Chemija ◽  
2020 ◽  
Vol 31 (3) ◽  
Author(s):  
Ehab AlShamaileh ◽  
Muayad Esaifan ◽  
Qusay Abu-Afifeh
Keyword(s):  
Activation Energy ◽  
Metal Oxide ◽  
Alkali Activation ◽  
Dsc Analysis ◽  
X Ray Diffraction ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Xrd Study ◽  
Dsc Curves

The formation of metal oxide-based hydroxysodalite by alkali-activation of kaolinite is studied using X-ray diffraction (XRD) study and differential scanning calorimetry (DSC) analysis. Different metal oxides (CoO, MgO, FeO and SiO2) were used to form the metal oxide-based hydroxysodalite. The transformation from kaolinite into hydroxysodalite is confirmed by XRD. In the thermodynamic study, the maximum peak temperatures for DSC curves at various heating rates were used to determine the activation energy (Ea) of the hydroxysodalite formation. With magnesium oxide and cobalt oxide, the formation process was found to be exothermic while it was endothermic with iron oxide.

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