Search results for "Arrhenius plot"
showing 10 items of 11 documents
Thermokinetic Investigation of the Drying Conditions on Amorphous Calcium Phosphate
2017
The present work investigated dried calcium phosphate powders which still retain an amorphous or poorly crystalline structure under a variety of conditions. In previous studies, freeze-drying was found to be the optimum drying condition. However, several publications, as well as our previous studies, have shown that calcium phosphate amorphous, or a poorly crystalline structure, can retain their structure even if the samples are dried immediately after synthesis up to 200°C. In our study, we used the thermokinetic studies FTIR and XRD and showed that the samples are amorphous, or poorly crystalline, but were unable to answer the questions: Is there a difference between the differently dried…
Stability of vacuolar betaxanthin pigments in juices from Moroccan yellow Opuntia ficus indica fruits
2008
Pigment stability of yellow juices prepared from Moroccan cactus pear (Opuntia ficus indica) was determined as a function of temperature and pH. The experiments were carried out at temperatures ranging from 80 to 100 °C with juices at pH 3.5, 5 and 6.5. The degree of pigment retention decreased when the temperature increased. The degradation constant rates were determined for thermal degradation rates of pseudo-first order. The Arrhenius plot obtained for the degradation of betaxanthin from the yellow fruits was not linear. Regardless of the temperature treatment, the lowest degradation was obtained for pH 5. Where some stabilizers were tested for the protection of pigments, the results sho…
Correlation spectroscopy in molten and supercooled antimony trichloride.
1990
Correlation spectroscopy measurements performed on molten and supercooled antimony trichloride with the homodyne technique show correlation functions that have a nonexponential behavior. Two well-defined distributions of correlation times can be observed in different temporal regions. This behavior is discussed in terms of a structural relaxation of clusters dynamically formed by intermolecular and interchain bonds. The Arrhenius plot of these correlation times shows a linear behavior with the same activation energy for both. In contrast, the activation energy of shear viscosity has a different value, showing that the processes determining the temperature behavior of \ensuremath{\tau} and $…
Kinetischer nachweis zweier arten von ionenpaaren bei der anionischen polymerisation von styrol in tetrahydropyran
1967
Die durch Na-Naphthalin angeregte Polymerisation des Styrols in THP wurde im Temperaturbereich von -40 bis +50°C kinctisch verfolgt. Die Geschwindigkeitskonstante kw(±) der uber das lonenpaar erfolgenden Polymerisation wurde gemessen, indem die elektrolytische Dissoziation durch Zusatz von Tetraphenylbornatrium unterdruckt wurde. Oberhalb von 20°C ergibt sich bei Auftragung nach ARRHENIUS eine Gerade, aus welcher Aktivierungsenergie Ec und Frequenzfaktor Ac des Kontaktionenpaares zu berechnen sind. Diese Parameter stimmen in guter Naherung mit den E- und A- Werten uberein, die in sehr schwach polaren Losungsmitteln fur die anionische Polymerisation erhalten werden. Unterhalb von +20°C weich…
Re-investigation of the conformational interconversion of the 1,2,3,6,7,8-hexahydropyrene cation radical by EPR, ENDOR and TRIPLE spectroscopy
1985
The conformational interconversion of the 1,2,3,6,7,8-hexahydropyrene cation radical has been re-examined by EPR, ENDOR and TRIPLE spectroscopy, and the Arrhenius plot is presented for a wider temperature range than that used earlier. The EPR spectra were measured from 143 to 369 K and the ENDOR spectra from 143 to 263 K. The thermodynamic constants of the conformational interconversion of the cation radical were determined on the basis of the temperature-dependent spectra. The high-resolution spectra clearly show that there are two overlapping spectra at low temperature, and this is confirmed by simulation.
The influence of pseudohalide ligands on the SIM behaviour of four-coordinate benzylimidazole-containing cobalt(ii) complexes.
2018
Three, mononuclear complexes of the formula [Co(bmim)2(SCN)2] (1), [Co(bmim)2(NCO)2] (2) and [Co(bmim)2(N3)2] (3) [bmim = 1-benzyl-2-methylimidazole] were prepared and structurally analyzed by single-crystal X-ray crystallography. The cobalt(ii) ions in 1-3 are tetrahedrally coordinated with two bmim molecules and two pseudohalide anions. The angular distortion parameter δ was calculated and the SHAPE program (based on the CShM concept) was used for 1-3 to estimate the angular distortion from an ideal tetrahedron. The molecules of 1-3 are effectively separated, and the values of the shortest distance of cobalt-cobalt are 8.442(6) and 6.774(8) A for 1, 10.349(8) and 10.716(8) A for 2 and 6.7…
Oxidation mechanism of the Inconel 601 alloy at high temperatures
2010
The Inconel 601 alloy oxidation was performed in air, in the temperature range 1000-1150 °C, during 90 h. Kinetic results show that the parabolic behavior is always followed in this temperature range. The Arrhenius plot of the kp values shows two different activation energies. Between 1000 and 1050 °C the activation energy is E a1 = 160 ± 10 kJ/mol. In the 1050-1150 °C temperature range a higher value is calculated E a2 = 252 ± 20 kJ/mol. The E a2 value and the X-ray diffraction (XRD) results and scanning electron microscope (SEM) energy dispersive X-ray spectroscopy (EDS) examinations are in accordance with a scale growth mechanism limited by a growing Cr 2 O 3 scale acting as a diffusion …
Photoluminescence study of excitons in homoepitaxial GaN
2001
High-resolution photoluminescence spectra have been measured in high-quality homoepitaxial GaN grown on a free-standing GaN substrate with lower residual strain than in previous work. Unusually strong and well-resolved excitonic lines were observed. Based on free- and bound exciton transitions some important GaN parameters are derived. The Arrhenius plot of the free A exciton recombination yields a binding energy of 24.7 meV. Based on this datum, an accurate value for the band-gap energy, EG(4.3 K) = 3.506 eV, can be given. From the donor bound excitons and their “two-electron” satellites, the exciton localization energy and donor ionization energy are deduced. Finally, estimates of the ele…
Dielectric investigation of sodium potassium niobate ceramic doped 7% of antimony
2012
Abstract Electric properties of sodium potassium niobate ceramic doped antimony (Na0.5K0.5)(Nb0.93Sb0.07)O3 with sintering aid MnO2 (0.5 mol% MnO2) (KNNSbx + 0.5Mn) were investigated in a broad frequency (from 1 Hz to 54 GHz) and temperature (from 110 K to 800 K) ranges. The mean relaxation times calculated from the dielectric permittivity measurements fulfill Arrhenius relationship with dipole activation energy EA = 3409 K (EA/kB = 0.29 eV). The DC conductivity has been extracted from experimental results and the activation energy was calculated EA = 11733.78 K (EA/kB = 1.011 eV).
Broadband Dielectric Investigation of Sodium Potassium Niobate Ceramic Doped 8% of Antimony
2012
In this work we present dielectric permittivity measurement results of KNN ceramic doped antimony (K0.5Na0.5)(Nb0.92Sb0.08)O3 with sintering aid MnO2 (0.5 mol% MnO2) (KNNSbx + 0.5Mn). Its dielectric properties were investigated in broad frequency (from 20 Hz to 32 GHz) and temperature (from 26 K to 780K) ranges. Above room temperature obtained results show two diffused phase transitions. Below room temperature investigation revealed dielectric permittivity dispersion similar to the relaxor one. The obtained mean relaxation times fulfills Arrhenius relationship with dipole activation energy Ea/kB = 2282 K.