Effects of ball-milling conditions and additives on the hydrogen sorption properties of Mg + 5 wt% Cr2O3 mixtures

2006 ◽  
Vol 21 (7) ◽  
pp. 1747-1752 ◽  
Author(s):  
J-L. Bobet ◽  
M. Kandavel ◽  
S. Ramaprabhu
Keyword(s):  
Particle Size ◽  
Sorption Process ◽  
Rate Equations ◽  
Desorption Kinetics ◽  
Yield Information ◽  
Order Of Magnitude ◽  
Effect Of Particle Size ◽  
Kinetics Of ◽  
And Diffusion

Effects of particle size of Cr2O3 catalyst on the hydrogen absorption/desorption kinetics of Mg + 5 wt% Cr2O3 mixtures have been studied. To explain the effect of particle size of Cr2O3 and also to yield information about the role of Cr2O3 during the sorption process, the kinetics data have been analyzed using Avrami–Erofeev rate equations. The activation energies and diffusion coefficients of these mixtures are in the ranges of 50.6–63.2 kJ/mol and 1.2.10−11 to 8.9.10−10 cm2/s, respectively. The addition of nano-oxides led to an increase of the diffusion coefficient of hydrogen by one order of magnitude.

scholarly journals Reduction Mechanism of Fine Hematite Ore Particles in Suspension

2021 ◽  
Author(s):  
Zhiyuan Chen ◽  
Christiaan Zeilstra ◽  
Jan van der Stel ◽  
Jilt Sietsma ◽  
Yongxiang Yang
Keyword(s):  
Particle Size ◽  
Temperature Drop ◽  
Reduction Rate ◽  
Reduction Process ◽  
Reciprocal Relationship ◽  
Drop Tube ◽  
Surface Nucleation ◽  
Order Of Magnitude ◽  
Relationship Of ◽  
Kinetics Of

AbstractIn order to understand the pre-reduction behaviour of fine hematite particles in the HIsarna process, change of morphology, phase and crystallography during the reduction were investigated in the high temperature drop tube furnace. Polycrystalline magnetite shell formed within 200 ms during the reduction. The grain size of the magnetite is in the order of magnitude of 10 µm. Lath magnetite was observed in the partly reduced samples. The grain boundary of magnetite was reduced to molten FeO firstly, and then the particle turned to be a droplet. The Johnson-Mehl-Avrami-Kolmogorov model is proposed to describe the kinetics of the reduction process. Both bulk and surface nucleation occurred during the reduction, which leads to the effect of size on the reduction rate in the nucleation and growth process. As a result, the reduction rate constant of hematite particles increases with the increasing particle size until 85 µm. It then decreases with a reciprocal relationship of the particle size above 85 µm.

scholarly journals Biosorption and Diffusion Modeling of Pb(II) by Malt Bagasse

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Klaiani B. Fontana ◽  
Giane Gonçalves Lenzi ◽  
Erica R. L. R. Watanabe ◽  
Ervin Kaminski Lenzi ◽  
Juliana A. M. T. Pietrobelli ◽  
...  
Keyword(s):  
Sorption Process ◽  
Isotherm Models ◽  
Diffusion Modeling ◽  
Biosorption Capacity ◽  
Kinetic And Thermodynamic Parameters ◽  
Pseudo Second Order ◽  
Ph Optimization ◽  
Kinetics Of ◽  
And Diffusion

The removal of Pb(II) from water by biosorption processes onto malt bagasse was investigated and the kinetic and thermodynamic parameters were obtained; additionally a diffusion modeling was proposed. The characterization of malt bagasse was performed by FTIR and SEM/EDS. The experiments were conducted in batch system and an experimental design based response surface methodology was applied for agitation speed and pH optimization. The kinetics of biosorption followed pseudo-second-order model and the temperature of the process affected the biosorption capacity. Isotherm models of Langmuir, Freundlich, and Elovich were applied and the Langmuir model showed better fit and the estimated biosorption capacity was 29.1 mg g−1. The negative values obtained for ΔG° and positive values of ΔH° confirm, respectively, the spontaneous and endothermic nature of the process. The diffusion modeling was performed based on experiments in the absence of agitation to investigate the influence of the biosorbent on the sorption process of Pb(II) ions.

KINETICS OF ELECTROCHEMICAL REACTIONS ON MODEL SUPPORTED CATALYSTS: READSORPTION AND MASS TRANSPORT

2008 ◽  
Vol 15 (06) ◽  
pp. 745-751
Author(s):  
VLADIMIR P. ZHDANOV ◽  
BENGT KASEMO
Keyword(s):  
Mass Transport ◽  
Supported Catalysts ◽  
Reaction Scheme ◽  
Electrochemical Reactions ◽  
Subsequent Reaction ◽  
Flow Cells ◽  
2D And 3D ◽  
Kinetics Of ◽  
And Diffusion

To bridge the structure gap, electrochemical reactions can be studied in flow cells with nm-sized catalyst particles deposited or fabricated on the cell walls. The understanding of the role of mass transport in such cells is now limited. To clarify the likely effects in this field, we analyze the simplest reaction scheme including intermediate desorption, readsorption, and subsequent reaction and show how the net rate of the formation of intermediate can be influenced by its diffusion in the liquid phase. With certain approximations, we derive analytical results describing reaction and diffusion near catalyst particles and in more remote regions in the simplest 1D case and more complex 2D and 3D situations.

scholarly journals Kinetics of proton transfer in the zeolitic tuff

2009 ◽  
Vol 7 (3) ◽  
pp. 508-511
Author(s):  
Fehime Çakıcıoğlu-Özkan ◽  
İlker Polatoğlu
Keyword(s):  
Particle Size ◽  
Proton Transfer ◽  
Size Fraction ◽  
Proton Transfer Reaction ◽  
Reaction Model ◽  
Zeolitic Tuff ◽  
Particle Size Fractions ◽  
Model Equations ◽  
Kinetics Of ◽  
And Diffusion

AbstractThe kinetics of a proton transfer into dilute acid solutions containing natural zeolitic tuff was studied by following the pH evolution of the liquid phase. Four different solutions with tuff contents of 9, 3, 1 and 0.5 (% wt) and three different particle size fractions (≤ 2000 μm) were studied. The proton concentration of the solution was decreased by increasing the zeolite amount and decreasing the particle size fraction. The proton transfer reaction was analyzed with chemical reactions and diffusion model equations. Analysis shows that the adsorption and/or ion exchange are possible mechanisms and are expressed by a second order reaction model.

Sorption Kinetics of Non-Ionic Organic Pollutants Onto Suspended Sediments

1991 ◽  
Vol 23 (1-3) ◽  
pp. 447-454 ◽  
Author(s):  
H. M. Liljestrand ◽  
Y. D. Lee
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Experimental Studies ◽  
Size Fraction ◽  
Organic Matter Content ◽  
Suspended Sediments ◽  
Spherical Particles ◽  
Particle Model ◽  
Desorption Kinetics ◽  
Kinetics Of

The results of controlled batch experimental studies of the adsorption and desorption kinetics of dichlorobenzene to 1) size fractionated, washed sediments, 2) aggregate, washed sediment, 3) dissolved/colloidal sediment materials, and 4) bulk sediments,are used to determine the effect of inhomogeneous mixtures on the overall sorption rates. The size-segregated sediments are modeled as spherical particles with a porous outer shell of organic matter for sorption and an inert, inorganic core. The characteristic times of intraparticle diffusive transport are found to vary with particle size by about two orders of magnitude. The distribution of natural organic matter content with particle size results in sorption rates which differ greatly from that predicted by the monodisperse, homogeneous particle model. Coupled, reversible reactions between the solute and each solid size fraction are presented as a conceptual model for the interpretation of the empirical results of batch experiments.

scholarly journals Effect of particle size on adsorption kinetics of water vapor on porous aluminium oxide material

2019 ◽  
Vol 1145 ◽  
pp. 012033 ◽  
Author(s):  
S Reshetnikov ◽  
Zh Budaev ◽  
A Livanova ◽  
E Meshcheryakov ◽  
I Kurzina
Keyword(s):  
Particle Size ◽  
Water Vapor ◽  
Adsorption Kinetics ◽  
Aluminium Oxide ◽  
Oxide Material ◽  
Effect Of Particle Size ◽  
Kinetics Of
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