Search results for " Activation energy"
showing 6 items of 6 documents
Influence of the electro-optical properties of an a-Si:H single layer on the performances of a pin solar cell
2012
We analyze the results of an extensive characterization study involving electrical and optical measurements carried out on hydrogenated amorphous silicon (α-Si:H) thin film materials fabricated under a wide range of deposition conditions. By adjusting the synthesis parameters, we evidenced how conductivity, activation energy, electrical transport and optical absorption of an α-Si:H layer can be modified and optimized. We analyzed the activation energy and the pre-exponential factor of the dark conductivity by varying the dopant-to-silane gas flow ratio. Optical measurements allowed to extract the absorption spectra and the optical bandgap. Additionally, we report on the temperature dependen…
Steam catalytic cracking of naphtha over ZSM-5 zeolite for production of propene and ethene: Micro and macroscopic implications of the presence of st…
2012
One option to produce more ethene and propene can be to crack naphtha type fractions in dedicated smaller FCC units. We present here the results obtained for high temperature steam catalytic cracking (SCC) of a representative naphtha product (n-heptane) with ZSM-5. It has been found that under those conditions the presence of steam produces an irreversible dealumination of the zeolite as well as a reversible deactivation due to the interaction of water with active sites with a negative effect on protolytic cracking. A kinetic decay model that takes into account the two phenomena has been developed. The apparent activation energy is lower in the presence of steam. It appears that whilst the …
Degrees of freedom effect on fragmentation in tandem mass spectrometry of singly charged supramolecular aggregates of sodium sulfonates
2012
The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged noncovalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine-enkephalin. Positively and negatively charged aggregates be…
Ordering kinetics in synthetic Mg(Al,Fe3+)2O4 spinels: Quantitative elucidation of the whole Al-Mg-Fe partitioning, rate constants, activation energi…
2014
A novel procedure, based on the application of the kinetics simulator Gepasi, has been successfully applied for modeling the cation ordering process in two synthetic Mg(Al2-yFe3+y)O4 spinels (y~ 0.39 and 0.54, samples F39 and F54, respectively). The kinetic profiles suggested a two-stage mechanism, with rapid inter-site exchange of Fe3+ with Mg followed by slow exchange of Al with Mg. The trial to apply the classical approaches, based on the explicit solutions of the differential equations corresponding to single-cation (Sha-Chappel model) or two-cation (Müller model) exchange reactions, proved not feasible in the whole time range, thus implying a lack of information about the exchange proc…
Density Functional Theory Study of the Trans-Trans-Cis (TTC)→Trans-Trans-Trans (TTT) Isomerization of a Photochromic Spiropyran Merocyanine
2008
Density Functional Theory (DFT) calculations have been performed on the TTC→TTT isomerization reaction of the open forms of the 1',3'-dihydro-8-bromo-6-nitro- 1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-(2H)indole (8-Br-6-nitro-BIPS) system. The calculations were carried out in vacuo and in methylene chloride solution at different temperatures. Results are compared with the available experimental values of free energy difference and activation energy in solution.
A comparative thermogravimetric study of waterlogged archaeological and sound woods
2010
Waterlogged archaeological woods Pinus pinaster and Fagus sylvatica L. were analyzed by using TG technique. Degradation processes ascribable to the holocellulose decay were evidenced at nearly the same temperature for sound and archaeological samples. The residual matters at 600 and 900 °C of the sound woods are much lower than those of archaeological waterlogged woods in agreement with the presence of inorganic materials encapsulated during the burial into the marine environment. It was proposed a new protocol to rapidly calculate the maximum water content parameter, which is related to the wood degradation state. TG experiments at variable heating rates were performed to obtain kinetic pa…