Metallothermic reduction as an electronically mediated reaction

1998 ◽  
Vol 13 (12) ◽  
pp. 3372-3377 ◽  
Author(s):  
Toru H. Okabe ◽  
Donald R. Sadoway
Keyword(s):  
Mass Transfer ◽  
Electron Transfer ◽  
Electron Transport ◽  
Chemical Reaction ◽  
Reaction Pathway ◽  
Tantalum Powder ◽  
Metallothermic Reduction ◽  
Rate Of Reaction

The commonly held view that metallothermic reduction is strictly a chemical reaction and that the process is rate limited by mass transfer has been found to be incomplete. In a study of the production of tantalum powder by the reaction of K2TaF7 with sodium, it has been shown that there are two dominant kinetic pathways, both involving electron transfer. Furthermore, the overall rate of reaction is limited by electron transport between the reactants. This indicates that metallothermic reduction is an “electronically mediated reaction” (EMR). Experiments found that the location of the tantalum deposit and its morphology are governed by the reaction pathway.

scholarly journals The Kinetics of Electron Transfer Reaction of Methylene Blue and Titanium Trichloride in different Solvents

2017 ◽  
Vol 6 (2) ◽  
pp. 940-957 ◽  
Author(s):  
Rehana Saeed Saeed
Keyword(s):  
Activation Energy ◽  
Methylene Blue ◽  
Electron Transfer ◽  
Transfer Reaction ◽  
Reaction Pathway ◽  
Reaction Medium ◽  
Electron Transfer Reaction ◽  
Rate Of Reaction ◽  
Titanium Trichloride ◽  
Kinetics Of

The kinetics of the electron transfer reaction of methylene blue and titanium trichloride was studied in water and aqueousalcoholic solvents at various temperatures by spectrophotometry. The rate of reaction was observed by taking change inabsorbance as a function of time at λmax 660 nm. The reaction is pseudo-first order, dependent on concentration of titaniumtrichloride at fixed concentration of methylene blue.The effect of solvent was studied in the pH/Ho range from 4 to 7. It was observed that the rate of reaction increased withincrease in polarity of the reaction medium. The rate of reaction was high in acidic condition and decreased with furtherincrease in hydrogen ions activity. The increase in temperature increased the rate of electron transfer reaction of methyleneblue and titanium trichloride. Activation energy (Ea) was calculated by Arrhenius relation. The absence of any reactionintermediate was confirmed by spectroscopic and kinetic investigations. A plausible mechanism for the reaction in line withouter-sphere reaction pathway has been proposed. Thermodynamic parameters such as activation energy (Ea), enthalpychange (∆H), free energy change (∆G) and entropy change (∆S) were also evaluated.

Unsteady MHD Free Convective Heat and Mass Transfer Flow Past a Vertical Porous Plate in the Presence of Radiation and Chemical Reaction

2017 ◽  
Vol 6 (10) ◽  
pp. 116
Author(s):  
J. Buggaramulu ◽  
M. Venkatakrishna ◽  
Y. Harikrishna
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Chemical Reaction ◽  
Porous Plate ◽  
Physical Parameters ◽  
Governing Equations ◽  
Vertical Porous Plate ◽  
Flow Past ◽  
Transfer Flow

The objective of this paper is to analyze an unsteady MHD free convective heat and mass transfer boundary flow past a semi-infinite vertical porous plate immersed in a porous medium with radiation and chemical reaction. The governing equations of the flow field are solved numerical a two term perturbation method. The effects of the various parameters on the velocity, temperature and concentration profiles are presented graphically and values of skin-frication coefficient, Nusselt number and Sherwood number for various values of physical parameters are presented through tables.

A Paramedic Treatment for Modeling Explicitly Solvated Chemical Reaction Mechanisms

2018 ◽  
Author(s):  
Yasemin Basdogan ◽  
John Keith
Keyword(s):  
Reaction Mechanism ◽  
Chemical Reaction ◽  
Reaction Mechanisms ◽  
Reaction Pathway ◽  
Optimization Procedure ◽  
Cost Effective ◽  
Chemical Reaction Mechanisms ◽  
Solvent Molecules ◽  
Dynamics Simulations ◽  
Mbh Reaction

<div> <div> <div> <p>We report a static quantum chemistry modeling treatment to study how solvent molecules affect chemical reaction mechanisms without dynamics simulations. This modeling scheme uses a global optimization procedure to identify low energy intermediate states with different numbers of explicit solvent molecules and then the growing string method to locate sequential transition states along a reaction pathway. Testing this approach on the acid-catalyzed Morita-Baylis-Hillman (MBH) reaction in methanol, we found a reaction mechanism that is consistent with both recent experiments and computationally intensive dynamics simulations with explicit solvation. In doing so, we explain unphysical pitfalls that obfuscate computational modeling that uses microsolvated reaction intermediates. This new paramedic approach can promisingly capture essential physical chemistry of the complicated and multistep MBH reaction mechanism, and the energy profiles found with this model appear reasonably insensitive to the level of theory used for energy calculations. Thus, it should be a useful and computationally cost-effective approach for modeling solvent mediated reaction mechanisms when dynamics simulations are not possible. </p> </div> </div> </div>

Interfacial mass transfer in turbulent flow accompanied by irreversible first order chemical reaction

1979 ◽  
Vol 44 (5) ◽  
pp. 1388-1396
Author(s):  
Václav Kolář ◽  
Zdeněk Brož
Keyword(s):  
Mass Transfer ◽  
Turbulent Flow ◽  
Chemical Reaction ◽  
Experimental Results ◽  
Theoretical Concepts ◽  
First Order ◽  
Order Chemical Reaction ◽  
Interfacial Mass Transfer ◽  
First Order Chemical Reaction

Relations describing the mass transfer accompanied by an irreversible first order chemical reaction are derived, based on the formerly published general theoretical concepts of interfacial mass transfer. These relations are compared with experimental results taken from literature.

scholarly journals Electrical characteristics of amyloid beta peptides in vertical junctions

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Sohyeon Seo ◽  
Jinju Lee ◽  
Jungsue Choi ◽  
G. Hwan Park ◽  
Yeseul Hong ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electron Transport ◽  
Amyloid Beta ◽  
Field Effect Transistors ◽  
Brain Diseases ◽  
Electrical Characteristics ◽  
Transport Pathway ◽  
Sequence Dependence ◽  
Aβ Oligomers ◽  
Aβ Peptides

AbstractAssembled amyloid beta (Aβ) peptides have been considered pathological assemblies involved in human brain diseases, and the electron transfer or electron transport characteristics of Aβ are important for the formation of structured assemblies. Here, we report the electrical characteristics of surface-assembled Aβ peptides similar to those observed in Alzheimer’s patients. These characteristics correlate to their electron transfer characteristics. Electrical current–voltage plots of Aβ vertical junction devices show the Aβ sequence dependence of the current densities at both Aβ monomers (mono-Aβs) and Aβ oligomers (oli-Aβs), while Aβ sequence dependence is not clearly observed in the electrical characteristics of Aβ planar field effect transistors (FETs). In particular, surface oligomerization of Aβ peptides drastically decreases the activity of electron transfer, which presents a change in the electron transport pathway in the Aβ vertical junctions. Electron transport at oli-Aβ junctions is symmetric (tunneling/tunneling) due to the weak and voltage-independent coupling of the less redox-reactive oli-Aβ to the contacts, while that at mono-Aβ junctions is asymmetric (hopping/tunneling) due to redox levels of mono-Aβ voltage-dependently coupled with contact electrodes. Consequently, through vertical junctions, the sequence- and conformation-dependent electrical characteristics of Aβs can reveal their electron transfer activities.

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