Diffusion of water in crystalline and glassy oxides: Diffusion–reaction model

1999 ◽  
Vol 14 (9) ◽  
pp. 3754-3758 ◽  
Author(s):  
R. H. Doremus
Keyword(s):  
Activation Energy ◽  
Oxygen Isotopes ◽  
Reaction Model ◽  
Water Diffusion ◽  
Diffusion Reaction ◽  
Molecular Water ◽  
Oh Groups ◽  
Hydrogen And Oxygen Isotopes ◽  
Activation Energy For Diffusion ◽  
And Diffusion

Diffusion of water in oxides is modeled as resulting from the solution and diffusion of molecular water in the oxide. This dissolved water can react and exchange with the oxide network to form immobile OH groups and different hydrogen and oxygen isotopes in the oxide. The model agrees with many experiments on water diffusion in oxides. The activation energy for diffusion of water in oxides correlates with the structural openness of the oxide, suggesting that molecular water is the diffusing species.

Diffusion of water in silica glass

1995 ◽  
Vol 10 (9) ◽  
pp. 2379-2389 ◽  
Author(s):  
Robert H. Doremus
Keyword(s):  
Reaction Mechanism ◽  
Silica Glass ◽  
Diffusion Reaction ◽  
Molecular Water ◽  
Oh Groups ◽  
First Order ◽  
Apparent Diffusion ◽  
Unified Description ◽  
Silicon Oxygen ◽  
Diffusion Profiles

The diffusion of water into silica glass is modeled to result from the diffusion of molecular water into the glass and its reaction with the silicon-oxygen network to form SiOH groups. Equations for this diffusion-reaction mechanism are presented and compared with experimental diffusion profiles. At temperatures above about 500 °C the reaction goes to equilibrium, but at lower temperatures it does not, leading to a time dependence of the concentration of surface-reacted OH groups and of their apparent diffusion coefficient. At higher temperatures, the OH groups are nearly immobile, but diffuse far enough to sample neighboring OH groups, leading to a bimolecular reverse reaction. At lower temperatures only OH pairs react, giving a first-order reaction. When water tagged with O18 diffuses into silica, the O18 exchanges with O16 in the silicon-oxygen network of the glass. This process is also controlled by the rate of diffusion of molecular water into the glass, and the rate of O18-O16 exchange. This diffusion-reaction mechanism gives a unified description of the diffusion of water in silica glass from 160 °C to 1200 °C at least.

Evaluation of the energy barrier for dehydration of homoionic (Li, Na, Cs, Mg, Ca, Ba, Alx(OH)yz+ and La)-montmorillonite by a differentiation method

Clay Minerals ◽  
2000 ◽  
Vol 35 (2) ◽  
pp. 357-363 ◽  
Author(s):  
M. Zabat ◽  
H. Van Damme
Keyword(s):  
Activation Energy ◽  
Hydration Shell ◽  
Mechanical Tests ◽  
Molecular Water ◽  
Water Molecules ◽  
Water Removal ◽  
Differentiation Method ◽  
Physisorbed Water ◽  
Activation Energy For Diffusion ◽  
The Individual

AbstractThe thermal energy necessary for the removal of molecular water from Li+-, Na+-, Cs+-, Mg2+-, Ca2+-, Ba2+-, Alx(OH)yz+- and La3+-homoionic montmorillonite powders was determined by thermogravimetric analysis under atmospheric pressure. The weight loss curves and their derivatives exhibit one or several features related to the various populations of water molecules. The activation energy for water removal, which is the sum of the adsorption energy and the activation energy for diffusion, was calculated in each case using a simple first-order differentiation method. The results allow the physisorbed water and the water coordinated to the cations to be clearly separated. For the later population and with the exception of the Na-clay, a good correlation was found between the temperatures and activation energies for water removal and the polarizing power of the cations. Comparison with the results of mechanical tests performed on similar samples suggests that the creep of smectite clays is not controlled by mobility of the individual water molecules but by the mobility of the interlayer cations surrounded by their hydration shell.

Study on Unreacted Nuclear Model of Iron Oxide Pellet Reduction

2020 ◽  
Vol 980 ◽  
pp. 404-409
Author(s):  
Jing Yi Zhu ◽  
Xiao Lei Zhou ◽  
Ning Bin Liu
Keyword(s):  
Activation Energy ◽  
Iron Ore ◽  
Reaction Rate ◽  
Reaction Model ◽  
Nuclear Model ◽  
Speed Limit ◽  
Single Interface ◽  
Kinetic And Thermodynamic Parameters ◽  
Iron Ore Pellet ◽  
And Diffusion

For the unreacted nuclear model, predecessors have established a more complete theoretical model under the assumption of steady-state conditions. And deduced the general equation of the rate of reduction of pellets. In this paper, we focus on the model of iron ore pellet reduction, not only establishing a single-interface unreacted nuclear model but also establishing a three-interface unreacted nuclear model. The activation energy and diffusion coefficient of iron ore reaction under certain conditions are obtained. According to the fitted images, the speed limit factors in the iron ore pellet reaction model are analyzed completely. In this paper, a pellet decomposition model was established to try to determine the kinetic and thermodynamic parameters of the pellet reaction without the need for experimentation, to simulate the reduction of pellets, and to determine the process of limiting the reaction rate and the process Strengthen.

Gas Cell Infrared and Attenuated Total Reflection Infrared Spectroscopic Studies for Organic–Inorganic Interactions in Adsorption of Fulvic Acid on the Goethite Surface Generating Carbon Dioxide

2021 ◽  
pp. 000370282199121
Author(s):  
Yuki Nakaya ◽  
Satoru Nakashima ◽  
Takahiro Otsuka
Keyword(s):  
Carbon Dioxide ◽  
Activation Energy ◽  
Fulvic Acid ◽  
Spectroscopic Studies ◽  
Reaction Model ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Gas Cell ◽  
Rate Determining Step ◽  
Ir Spectroscopic

The generation of carbon dioxide (CO2) from Nordic fulvic acid (FA) solution in the presence of goethite (α-FeOOH) was observed in FA–goethite interaction experiments at 25–80 ℃. CO2 generation processes observed by gas cell infrared (IR) spectroscopy indicated two steps: the zeroth order slower CO2 generation from FA solution commonly occurring in the heating experiments of the FA in the presence and absence of goethite (activation energy: 16–19 kJ mol–1), and the first order faster CO2 generation from FA solution with goethite (activation energy: 14 kJ mol–1). This CO2 generation from FA is possibly related to redox reactions between FA and goethite. In situ attenuated total reflection infrared (ATR-IR) spectroscopic measurements indicated rapid increases with time in IR bands due to COOH and COO– of FA on the goethite surface. These are considered to be due to adsorption of FA on the goethite surface possibly driven by electrostatic attraction between the positively charged goethite surface and negatively charged deprotonated carboxylates (COO–) in FA. Changes in concentration of the FA adsorbed on the goethite surface were well reproduced by the second order reaction model giving an activation energy around 13 kJ mol–1. This process was faster than the CO2 generation and was not its rate-determining step. The CO2 generation from FA solution with goethite is faster than the experimental thermal decoloration of stable structures of Nordic FA in our previous report possibly due to partial degradations of redox-sensitive labile structures in FA.

scholarly journals Gas-phase detonation propagation in mixture composition gradients

2012 ◽  
Vol 370 (1960) ◽  
pp. 567-596 ◽  
Author(s):  
D. A. Kessler ◽  
V. N. Gamezo ◽  
E. S. Oran
Keyword(s):  
Activation Energy ◽  
Reaction Model ◽  
Single Step ◽  
Mixture Composition ◽  
Composition Gradient ◽  
Detonation Properties ◽  
High Activation ◽  
Zone Structure ◽  
Detonation Cell ◽  
High Activation Energy

The propagation of detonations through several fuel–air mixtures with spatially varying fuel concentrations is examined numerically. The detonations propagate through two-dimensional channels, inside of which the gradient of mixture composition is oriented normal to the direction of propagation. The simulations are performed using a two-component, single-step reaction model calibrated so that one-dimensional detonation properties of model low- and high-activation-energy mixtures are similar to those observed in a typical hydrocarbon–air mixture. In the low-activation-energy mixture, the reaction zone structure is complex, consisting of curved fuel-lean and fuel-rich detonations near the line of stoichiometry that transition to decoupled shocks and turbulent deflagrations near the channel walls where the mixture is extremely fuel-lean or fuel-rich. Reactants that are not consumed by the leading detonation combine downstream and burn in a diffusion flame. Detonation cells produced by the unstable reaction front vary in size across the channel, growing larger away from the line of stoichiometry. As the size of the channel decreases relative to the size of a detonation cell, the effect of the mixture composition gradient is lessened and cells of similar sizes form. In the high-activation-energy mixture, detonations propagate more slowly as the magnitude of the mixture composition gradient is increased and can be quenched in a large enough gradient.

scholarly journals Metamorphism of Air Bubbles in a Snow Crystal

1967 ◽  
Vol 6 (46) ◽  
pp. 561-564
Author(s):  
Norikazu Maeno ◽  
Daisuke Kuroiwa
Keyword(s):  
Activation Energy ◽  
Diffusion Processes ◽  
Atomic Diffusion ◽  
Mechanical Relaxation ◽  
Air Bubbles ◽  
A Value ◽  
Snow Crystal ◽  
Activation Energy For Diffusion ◽  
Snow Crystals ◽  
Natural Snow

RésuméObservations have been made of the modification produced by a temperature gradient in the shape of air bubbles in natural snow crystals, and also of the shrinkage of the bubbles with time. The rate of shrinkage is governed by a constant which is strongly temperature dependent with an activation energy of about 15.1 kcal./mole, a value sufficiently similar to the activation energy for diffusion of tritium, dielectric relaxation and mechanical relaxation to suggest that atomic diffusion processes may be responsible for all of these phenomena.

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