On the Role of Diffusion in the Oxidation of Fe, Ni, Co and the Fe-Sn Alloy by Calcium and Sodium Sulfates

2006 ◽  
Vol 258-260 ◽  
pp. 63-67
Author(s):  
V.M. Chumarev ◽  
V.P. Maryevich ◽  
V.A. Shashmurin
Keyword(s):  
Co Oxidation ◽  
Chemical Reaction ◽  
Diffusion Processes ◽  
Transport Processes ◽  
Diffusion Transport ◽  
Sodium Sulfates ◽  
Product Forms ◽  
Kinetics Of ◽  
Dominant Part

Diffusion processes play a dominant part in the macro kinetics of Fe, Ni and Co oxidation by calcium and sodium sulfates. Here, the reaction product forms a compact covering which spatially divides the reagents on the surface in the same way as in the oxidation and sulfidization of metals by oxygen and sulfur. Therefore, it is possible to assume in advance that interaction of metals with calcium and sodium sulfates will be determined not by the actual chemical reaction properly but by the diffusion transport processes.

Substituent Effect on Reactivity of Alkyl Thiolacetates

1971 ◽  
Vol 26 (7) ◽  
pp. 703-707
Author(s):  
F. Dutka ◽  
A. F. Márton ◽  
P. Vinkler
Keyword(s):  
Chemical Reaction ◽  
Sulfur Atom ◽  
Substituent Effect ◽  
Linear Structure ◽  
Common Mechanism ◽  
Reaction Site ◽  
Structure Reactivity Relationship ◽  
Kinetics Of

Kinetics of catalyzed acyl group exchange between acetic-1-14C anhydride and alkyl thiolacetates was investigated. The exchange is not accompanied by chemical reaction and demonstrates the full equivalency of anhydride acyl groups in the process. The rate of exchange is lowered by increasing branching rather than lengthening in S-alkyl substituents. The role of catalyst and structures of possible intermediates are interpreted. Upon existing linear structure-reactivity relationship a common mechanism involving sulfur atom as the reaction site seems to be operative.

The role of transport processes in crystallization kinetics of ammonium pentaborate

2003 ◽  
Vol 253 (1-4) ◽  
pp. 488-495 ◽  
Author(s):  
Ömer Şahin ◽  
Nasrettin Genli ◽  
Mustafa Özdemir
Keyword(s):  
Crystallization Kinetics ◽  
Transport Processes ◽  
Kinetics Of

scholarly journals Structural-phase transformation kinetics during sintering of alumina ceramics using metastable nanopowders

2005 ◽  
Vol 37 (1) ◽  
pp. 35-43 ◽  
Author(s):  
A.S. Kaigorodov ◽  
V.R. Khrustov ◽  
V.V. Ivanov ◽  
A.I. Medvedev ◽  
A.K. Shtol’ts
Keyword(s):  
Diffusion Processes ◽  
Structural Phase ◽  
Alumina Ceramics ◽  
Transformation Kinetics ◽  
Structural Phase Transformation ◽  
Positive Role ◽  
Polymorphous Transition ◽  
Mg Addition ◽  
Kinetics Of

The processes taking place during pressureless sintering of nano- metastable Al2O3, compacted up to high densities (0.7 of the theoretical density) using the magnetic pulsed method were studied. The influence of MgO, TiO2 and ZrO2 additives on the kinetics of Al2O3 polymorphous transition, shrinkage and microstructure evolution during annealing at temperatures up to 1450?C has been studied. We have found that the process of annealing is two-staged starting with a polymorphous transition. Doping changes the starting temperature as well as the shrinkage depth at both stages. TiO2 and ZrO2 additives decrease the temperature of the onset of shrinkage, whereas MgO increases it. The best composition contained MgO in the series of examined types of ceramics with an ?-Al2O3 matrix. The positive role of Mg addition in the production of dense and hard Al2O3 ceramics is related to the nature of Mg influence on the activation of diffusion processes in Al2O3, as well as to the way of uniform distribution of MgO dopant in the material. All these factors provide effective damping of diffusion processes and limit ?-Al2O3 crystal growth. Highly dense MgO, ZrO2 and TiO2 doped Al2O3 ceramics with a grain size of 190, 220, and 250 nm and microhardness of 22, 17 and 17 GPa, correspondingly have been obtained.

Role of CO2 methanation into the kinetics of preferential CO oxidation on Cu/Co3O4

2019 ◽  
Vol 466 ◽  
pp. 167-180 ◽  
Author(s):  
Satyapaul A. Singh ◽  
Suhas Mukherjee ◽  
Giridhar Madras
Keyword(s):  
Co Oxidation ◽  
Co2 Methanation ◽  
Preferential Co Oxidation ◽  
Kinetics Of

scholarly journals The Role of Defects in the Local Reaction Kinetics of CO Oxidation on Low-Index Pd Surfaces

2013 ◽  
Vol 117 (23) ◽  
pp. 12054-12060 ◽  
Author(s):  
D. Vogel ◽  
C. Spiel ◽  
M. Schmid ◽  
M. Stöger-Pollach ◽  
R. Schlögl ◽  
...  
Keyword(s):  
Co Oxidation ◽  
Reaction Kinetics ◽  
Local Reaction ◽  
Kinetics Of

scholarly journals Some basic mathematical features of the simultaneous convection anomalous diffusion transport processes

2014 ◽  
Vol 1 (1) ◽  
pp. 1-5
Author(s):  
Ágnes Bálint ◽  
Csaba Mészáros
Keyword(s):  
Anomalous Diffusion ◽  
Diffusion Processes ◽  
Practical Importance ◽  
Transport Processes ◽  
Bulk Materials ◽  
Engineering Applications ◽  
Diffusion Transport ◽  
Open Research

The basic mathematical features of the anomalous diffusion processes are discussed in detail, together with some of the open research subdomains belonging to it. Due to its practical importance in engineering applications, the possibilities of the necessary mathematical refinements are proposed and justified for the general case of the simultaneous convection-anomalous diffusion processes taking place through porous bulk materials.

scholarly journals The Origin of Coupled Chloride and Proton Transport in a Cl−/H+ Antiporter

2016 ◽  
Author(s):  
Sangyun Lee ◽  
Heather B. Mayes ◽  
Jessica M. J. Swanson ◽  
Gregory A. Voth
Keyword(s):  
Chemical Reaction ◽  
Proton Transport ◽  
Critical Role ◽  
Multiscale Simulation ◽  
Transport Processes ◽  
Experimental Result ◽  
Free Energy Barrier ◽  
Concentration Gradients ◽  
Extracellular Solution

AbstractThe ClC family of transmembrane proteins functions throughout nature to control the transport of Cl− ions across biological membranes. ClC-ec1 from Escherichia coli is an antiporter, coupling the transport of Cl− and H+ ions in opposite directions and driven by the concentration gradients of the ions. Despite keen interest in this protein, the molecular mechanism of the Cl−/H+ coupling has not been fully elucidated. Here, we have used multiscale simulation to help identify the essential mechanism of the Cl−/H+ coupling. We find that the highest barrier for proton transport (PT) from the intra- to extracellular solution is attributable to a chemical reaction—the deprotonation of glutamic acid 148 (E148). This barrier is significantly reduced by the binding of Cl− in the “central” site (Cl−cen), which displaces E148 and thereby facilitates its deprotonation. Conversely, in the absence of Cl−cen E148 favors the “down” conformation, which results in a much higher cumulative rotation and deprotonation barrier that effectively blocks PT to the extracellular solution. Thus, the rotation of E148 plays a critical role in defining the Cl−/H+ coupling. As a control, we have also simulated PT in the ClC-ec1 E148A mutant to further understand the role of this residue. Replacement with a non-protonatable residue greatly increases the free energy barrier for PT from E203 to the extracellular solution, explaining the experimental result that PT in E148A is blocked whether or not Cl−cen is present. The results presented here suggest both how a chemical reaction can control the rate of PT and also how it can provide a mechanism for a coupling of the two ion transport processes.

Metamorphic reaction rate laws and development of isograds

1986 ◽  
Vol 50 (357) ◽  
pp. 359-373 ◽  
Author(s):  
Antonio C. Lasaga
Keyword(s):  
Diffusion Processes ◽  
Relative Role ◽  
Mineral Surfaces ◽  
Surface Kinetics ◽  
Rate Laws ◽  
Careful Treatment ◽  
Reaction Zones ◽  
Kinetics Of ◽  
And Diffusion

AbstractNew data on the kinetics of dehydration of muscovite + quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of ‘reaction zones’ are then analysed as a function of intrusion size and kinetic parameters.

Reactive uptake governs the pulmonary air space removal of inhaled nitrogen dioxide

1990 ◽  
Vol 68 (2) ◽  
pp. 594-603 ◽  
Author(s):  
E. M. Postlethwait ◽  
A. Bidani
Keyword(s):  
Chemical Reaction ◽  
Lung Model ◽  
Independent Effect ◽  
Vascular Perfusion ◽  
Epithelial Surface ◽  
Uptake Rates ◽  
Air Space ◽  
Residual Capacity ◽  
Kinetics Of

With the use of an isolated rat lung model, we investigated pulmonary air space absorption kinetics of the reactive gas NO2 in an effort to determine the contributory role of chemical reaction(s) vs. physical solubility. Unperfused lungs were employed, because vascular perfusion had no effect on acute (0- to 60-min) NO2 absorption rates. We additionally found the following: 1) Uptake was proportional to exposure rates (2-14 micrograms NO2/min; 10-63 ppm; 37 degrees C) but saturated with exposures greater than or equal to 14 micrograms NO2/min. 2) Uptake was temperature (22-48 degrees C) dependent but, regardless of temperature, attained apparent saturation at 10.6 micrograms NO2/min. 3) Lung surface area (SA) was altered by increasing functional residual capacity (FRC). Expanded SA (8 ml FRC) and temperature (48 degrees C) both raised fractional uptakes (greater than or equal to 0.81) relative to 4 ml FRC, 37 degrees C (0.67). Uptake rates normalized per unit estimated SA revealed no independent effect of FRC on fractional uptake. However, temperature produced a profound effect (48 degrees C = 0.93; 4 and 8 ml FRC = 0.54). 4) Arrhenius plots (ln k′ vs. 1/T), which utilized derived reactive uptake coefficients (k′), showed linearity (r2 = 0.94) and yielded an activation energy of 7,536 kcal.g-1.mol-1 and Q10 of 1.43, all consistent with a reaction-mediated process. These findings, particularly the effects of temperature, suggest that acute NO2 uptake in pulmonary air spaces is, in part, rate limited by chemical reaction of NO2 with epithelial surface constituents rather than by direct physical solubility.

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