Semi-empirical calculation of activation energy for a number of bimolecular reactions. Part I

The effects of F− concentration, leaching temperature, and time on the Ti leaching from Ti-bearing electric furnace slag (TEFS) by [NH4+]-[F−] solution leaching process was investigated to reveal the leaching mechanism and kinetics of titanium. The results indicated that the Ti leaching rate obviously increased with the increase of leaching temperature and F− concentration. The kinetic equation of Ti leaching was obtained, and the activation energy was 52.30 kJ/mol. The fitting results of kinetic equations and calculated values of activation energy both indicated that the leaching rate of TEFS was controlled by surface chemical reaction. The semi-empirical kinetics equation was consistent with the real experimental results, with a correlation coefficient (R2) of 0.996. The Ti leaching rate reached 92.83% after leaching at 90 °C for 20 min with F− concentration of 14 mol/L and [NH4+]/[F−] ratio of 0.4. The leaching rates of Si, Fe, V, Mn, and Cr were 94.03%, 7.24%, 5.36%, 4.54%, and 1.73%, respectively. The Ca, Mg, and Al elements were converted to (NH4)3AlF6 and CaMg2Al2F12 in the residue, which can transform into stable oxides and fluorides after pyro-hydrolyzing and calcinating.

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Review and Analysis of Bluff Body Flame Stabilization Data

Volume 3: Combustion, Fuels and Emissions, Parts A and B ◽

10.1115/gt2008-50375 ◽

2008 ◽

Cited By ~ 1

Author(s):

Sajjad A. Husain ◽

Ganesh Nair ◽

Santosh Shanbhogue ◽

Tim C. Lieuwen

Keyword(s):

Activation Energy ◽

Kinetic Modeling ◽

First Principles ◽

Bluff Body ◽

Large Range ◽

Flame Stabilization ◽

Local Extinction ◽

Data Set ◽

Flame Sheet ◽

Semi Empirical

This paper compiles and analyzes bluff body stabilized flame blowoff data from the literature. Many of these studies contain semi-empirical blowoff correlations that are, in essence, Damko¨hler number correlations of their data. This paper re-analyzes these data, utilizing various Damko¨hler number correlations based upon detailed kinetic modeling for determining chemical time scales. While the results from this compilation are similar to that deduced from many earlier studies, it demonstrates that a rather comprehensive data set taken over a large range of conditions can be correlated from “first-principles” based calculations that do not rely on empirical fits or adjustable constants (e.g., global activation energy or pressure exponents). The paper then discusses the implications of these results on understanding of blowoff. Near blowoff flames experience local extinction of the flame sheet, manifested as “holes” that form and convect downstream. However, local extinction is distinct from blowoff — in fact, under certain conditions the flame can apparently persist indefinitely with certain levels of local extinction. We hypothesize that simple Damko¨hler number correlations contain the essential physics describing this first stage of blowoff; i.e., they are correlations for the conditions where local extinction on the flame begins, but do not fundamentally describe the ultimate blowoff condition itself. However, such correlations are reasonably successful in correlating blowoff limits because the ultimate blowoff event appears to be correlated to some extent to the onset of this first stage.

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Calculation of The Diffusion Parameters in an Ordered Ni3Al-Alloy for A Relaxed Lattice

MRS Proceedings ◽

10.1557/proc-527-165 ◽

1998 ◽

Vol 527 ◽

Cited By ~ 11

Author(s):

C. Schmidt ◽

J.L. Bocquet

Keyword(s):

Activation Energy ◽

Gradient Algorithm ◽

Al Alloy ◽

Self Diffusion ◽

Barrier Heights ◽

Diffusion Parameters ◽

Exponential Factors ◽

Diffusion Mechanisms ◽

Body Potential ◽

Semi Empirical

ABSTRACTUsing atomistic computer simulations, we calculate the diffusion parameters of an Ll2-ordered Ni3Al-alloy. A conjugate gradient algorithm under constant zero pressure and a semi-empirical N-body potential are applied to evaluate potential barrier heights and pre-exponential factors. We focus our investigation on those diffusion mechanisms that have been proposed to account for the experimentally observed but theoretically still disputed fast self-diffusion of Al in Ni3Al: antisite bridge mechanisms and correlated six-jump cycles. Our results demonstrate that the most competitive jumps or jump sequences involve AlNJ-antistructure atoms which are shown to play a key role in the diffusion process by either actively or passively lowering the activation energy of migration.

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Theoretical Inversion of Amino Acids (Alanine and Aspartic Acid) by Semi-Empirical Methods

International Letters of Chemistry Physics and Astronomy ◽

10.18052/www.scipress.com/ilcpa.12.37 ◽

2013 ◽

Vol 12 ◽

pp. 37-44

Author(s):

Musa E. Mohamed

Keyword(s):

Activation Energy ◽

Amino Acids ◽

Transition State ◽

Gas Phase ◽

Aspartic Acid ◽

Aqueous Phase ◽

Free Amino ◽

Membered Ring ◽

Empirical Methods ◽

Semi Empirical

The inversion reaction coordinate of free amino acids (alanine, aspartic acid) have been computationally calculated by semi-empirical methods AM1. A transition state for free alanine and aspartic acid were obtained as a three membered ring in which the α-C-H and α-C-CH3 are slightly elongated, 1.2 and 2.17 Å respectively in the alanine transition state. The activation energy of alanine is 77.52 kcal/mol in the gas phase and 76.66 kcal/mol in aqueous phase, and for aspartic acid is 54.87 kcal/mol in the gas phase and 50.86 kcal/mol in aqueous phase.

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