Effect of Temperature and Bicarbonate Concentration on the Kinetics of UO2(s) Dissolution Under Oxidizing Conditions

1996 ◽  
Vol 465 ◽  
Author(s):  
J. de Pablo ◽  
I. Casas ◽  
J. Giménez ◽  
M. Molera ◽  
M. E. Torrero
Keyword(s):  
Dissolution Rate ◽  
Solid Particles ◽  
Effect Of Temperature ◽  
Bicarbonate Concentration ◽  
Rate Laws ◽  
Carbonate Concentration ◽  
Hydrogen Carbonate ◽  
Different Temperatures ◽  
Flow Through ◽  
Kinetics Of

ABSTRACTThe dissolution rate of unirradiated UO2 (s) has been studied as a function of hydrogen carbonate concentration at three different temperatures (298.15 K, 313.15 K and 333.15 K) under oxidizing conditions in a continuous flow-through reactor with a thin layer of solid particles (particle size from 100 to 300 μm). From the results of these experiments, two different rate laws have been determined. At high temperature (313.15 K and 333.15 K), we obtained a dissolution rate proportional to hydrogen carbonate concentration while at 298.15 K, the rate almost depends on the square root of the hydrogen carbonate concentration. This indicates a different reaction mechanism depending on temperature which can be related to the oxidation step of the overall process. The apparent activation energy obtained was 41 kJ mo1−1.

Dissolution kinetics of meta-torbernite under circum-neutral to alkaline conditions

2009 ◽  
Vol 6 (6) ◽  
pp. 551 ◽  
Author(s):  
Dawn M. Wellman ◽  
Bruce K. McNamara ◽  
Diana H. Bacon ◽  
Elsa A. Cordova ◽  
Ruby M. Ermi ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Coupled Processes ◽  
Effect Of Temperature ◽  
Subsurface Environments ◽  
Alkaline Conditions ◽  
Flow Through ◽  
Uranium Phosphate ◽  
The Stability ◽  
Kinetics Of

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].

THE REACTION BETWEEN CYANATE AND HYPOCHLORITE

1956 ◽  
Vol 34 (4) ◽  
pp. 489-501 ◽  
Author(s):  
M. W. Lister
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Rate Constant ◽  
Hypochlorous Acid ◽  
Effect Of Temperature ◽  
Slow Step ◽  
True Activation Energy ◽  
Rate Of Reaction ◽  
Different Temperatures ◽  
Kinetics Of

The reaction between sodium hypochlorite and potassium cyanate in the presence of sodium hydroxide has been examined. The main products are chloride, and carbonate ions and nitrogen; but, especially if much hypochlorite is present, some nitrate is formed as well. The rate of reaction is proportional to the cyanate and hypochlorite concentrations, but inversely proportional to the hydroxide concentration: the rate constant is 5.45 × 10−4 min.−1 at 65 °C, at an ionic strength of 2.2. The rate constant increases somewhat as the ionic strength rises from 1.7 to 3.5. The effect of temperature makes the apparent activation energy 25 kcal./gm-molecule. The kinetics of the reaction suggest that the slow step is really a reaction of hypochlorous acid and cyanate ions, and possible intermediate products of this reaction are suggested. Allowing for the different extent of hydrolysis of hypochlorite at different temperatures, the true activation energy is found to be 15 kcal./gm-mol., which is consistent with the observed rate of reaction.

Nanoparticles aggregation in nanofluid flow through nanochannels: Insights from molecular dynamic study

2014 ◽  
Vol 25 (11) ◽  
pp. 1450066 ◽  
Author(s):  
Habib Aminfar ◽  
Mohammad Ali Jafarizadeh ◽  
Nayyer Razmara
Keyword(s):  
Poiseuille Flow ◽  
Pt Nanoparticles ◽  
Potential Interaction ◽  
Solid Particles ◽  
Dynamics Simulation ◽  
Intermolecular Potential ◽  
Cluster Morphology ◽  
Flow Through ◽  
Solid Walls ◽  
Kinetics Of

This paper deals with the molecular dynamics simulation (MDS) of nanofluid under Poiseuille flow in a model nanochannel. The nanofluid is created by exerting four solid nanoparticles dispersed in Argon ( Ar ), as base fluid, between two parallel solid walls. The flow is simulated by molecules with the Lennard-Jones (LJ) intermolecular potential function. Different simulations are done with two different types of solid particles and two cut-off radii. In each case, Copper ( Cu ) and Platinum ( Pt ) LJ parameters are applied for the nanoparticles and solid walls particles with cut-off ratios of 2.2σ and 2.5σ. The microstructure of the system at different time steps is investigated to describe the aggregation kinetics of nanofluid on Poiseuille flow. When a few nanoparticles or a cluster of them reach each other, they stick together and the interaction surface of the solid–fluid interface reduces, so the potential energy of the system decreases at these time steps. Therefore, the system enthalpy reduces at the aggregation time steps. Results show that the simulations with cut-off radius 2.5σ indicate minimum clustering effect at the same time. Based on the obtained results, the system with Cu nanoparticles makes it to aggregate later than that of Pt nanoparticles which is due to differences in potential interaction of two materials. The new simulation results enhance our understanding of cluster morphology and aggregation mechanisms.

The kinetics of specific organic reactions in the zone of catagenesis

1985 ◽  
Vol 315 (1531) ◽  
pp. 107-122 ◽  
Keyword(s):  
Biological Marker ◽  
Rate Coefficients ◽  
Rate Laws ◽  
Oil Generation ◽  
Different Temperatures ◽  
History Of ◽  
Exponential Factors ◽  
Marker Compounds ◽  
Configurational Isomerization ◽  
Kinetics Of

Recently it has been shown that the measured extent of reactions in sedimentary biological marker compounds during catagenesis (for example, steroid aromatization, sterane isomerization) can assist in providing information about the extent of maturation of sedimentary organic matter before and during oil generation and also the thermal history of sediments. In the present study, aromatization of a C 27 C-ring aromatic steroid and isomerization at the chiral centres of an isoprenoid alkane, 6( R ),10( S )-pristane, have been brought about under laboratory conditions, elemental sulphur being used as the source of radicals. Precise rate laws have been determined and rate coefficients measured at different temperatures. The pre-exponential factors and activation energies were found to be 6.7 x 10 12 s -1 and 145 kJ mol -1 for the aromatization, and 2.1 x 10 7 s -1 and 120 kJ mol -1 for the configurational isomerization of pristane. These values reflect the relative behaviour of the two types of reactions in sediments, the aromatization being the more temperature-dependent reaction.

scholarly journals Kinetics of dissolution of calcium phosphate (Ca-P) bioceramics

2008 ◽  
Vol 2 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Lukas Brazda ◽  
Dana Rohanova ◽  
Ales Helebrant
Keyword(s):  
Calcium Phosphate ◽  
Dissolution Rate ◽  
Dissolution Kinetics ◽  
Weight Changes ◽  
Enhanced Dissolution ◽  
Different Temperatures ◽  
Sbf Solution ◽  
Kinetics Of Dissolution ◽  
Unexpected Findings ◽  
Kinetics Of

Hydroxyapatite (HAp) and ?-tricalcium phosphate (?-TCP) are widely used bioceramics for surgical or dental applications. This paper is dealing with dissolution kinetics of synthetically prepared ?-TCP and four types of HAp granules. Two groups of HAp, treated at different temperatures, each of them with two different granule sizes, were tested. Three corrosive solutions with different pH and simulated body fluid (SBF) were used for immersing of the samples. Changes in concentrations of calcium and phosphate ions, pH level and weight changes of the samples were observed. It was found that presence of TRIS buffer enhanced dissolution rate of the ?-TCP approximately two times. When exposed to SBF solution, calcium phosphate (most probably hydroxyapatite) precipitation predominates over ?-TCP dissolution. Results from HAp samples dissolution showed some unexpected findings. Neither heat treatment nor HAp particle size made any major differences in dissolution rate of the same mass of each HAp sample.

Phenomenological effect of temperature on the order n of the reaction of the curing kinetics in an EPDM polymer

2021 ◽  
pp. 1-12
Author(s):  
Salvador Gomez-Jimenez ◽  
Ana Maria Becerra-Ferreiro ◽  
Eduardo D Jareño-Betancourt ◽  
Jose M Vazquez-Penagos
Keyword(s):  
Cure Kinetics ◽  
Analytical Description ◽  
Curing Kinetics ◽  
Effect Of Temperature ◽  
Crosslinking Reaction ◽  
Precise Control ◽  
The Best Approximation ◽  
Short Period ◽  
Different Temperatures ◽  
Kinetics Of

Abstract The precise control of curing reaction parameters allows a better crosslinking polymer. Modeling and optimization of this process require a correct kinetic of curing model. The kinetics of the crosslinking reaction is studied for the ethylene propylene diene monomer (EPDM) synthetic elastomer by movile die rheometer (MDR). The kinetic parameters of reaction were calculated from Kamal-Ryan, Sestak-Berggren, and the Isayev-Deng methods at different temperatures. An Arrhenius-type function for the order of reaction n is introduced to improve the adjusting. A comparative study of Sestak-Berggren and Isayev-Deng models was made to validate and determine which model best describes the behavior of vulcanization. The best approximation was obtained with the model Isayev-Deng. Finally, taking the model with the best fit, a graphical and analytical description of the cure kinetics was developed. The order of reaction is predicted to better establishment of processing time. It was noted that for EPDM at higher temperatures, the increase of the rate of reaction occurs in short period of time, which could cause premature curing if the supply system is inadequate.

scholarly journals Kinetics of winter deacclimation in response to temperature determines dormancy status and explains budbreak in differentVitisspecies

2018 ◽  
Author(s):  
Alisson P. Kovaleski ◽  
Bruce I. Reisch ◽  
Jason P. Londo
Keyword(s):  
Cold Hardiness ◽  
Effect Of Temperature ◽  
Good Prediction ◽  
Chilling Requirement ◽  
Perennial Plant ◽  
Different Temperatures ◽  
Winter Cold ◽  
Response To Temperature ◽  
The Relationship ◽  
Kinetics Of

2.AbstractBud dormancy and cold hardiness are critical adaptations for surviving winter cold stress for temperate perennial plant species, with shifting temperature-based responses during the winter. The objective of this study was to uncover the relationship between dormancy transition (chilling requirement) and temperature on the loss of cold hardiness and budbreak. Dormant cuttings ofVitis vinifera,V. aestivalis,V. amurensis, andV. ripariawere examined to determine the relationship between chilling requirement and temperature on rate of deacclimation (kdeacc). Differential thermal analysis was used to determinekdeaccusing mean low temperature exotherms. Effect of chill was evaluated as the deacclimation potential (ψdeacc), which was the change inkdeaccdue to chill accumulation. Budbreak was also evaluated in fully chilled buds at different temperatures. Results indicate that ψdeaccvaries dependent on dormancy state, following a logarithmic response to chill accumulation. The effect of temperature onkdeaccwas exponential at low and logarithmic at high temperatures. The combination of ψdeaccandkdeaccresulted in good prediction of deacclimation. Budbreak phenology was also explained by differences inkdeacc. Deacclimation rates can be used as a quantitative determinant of dormancy transition and budbreak, and to refine models predicting effects of climate change.

5-hydroxymethyl furfural formation and reaction kinetics of different pekmez samples: effect of temperature and storage

2012 ◽  
Vol 8 (4) ◽  
Author(s):  
Rasim Alper Oral ◽  
Mahmut Dogan ◽  
Kemal Sarioglu ◽  
Ömer Said Toker
Keyword(s):  
Reaction Kinetics ◽  
Arrhenius Equation ◽  
Storage Period ◽  
Effect Of Temperature ◽  
Temperature Changes ◽  
Juniperus Communis ◽  
Hydroxymethyl Furfural ◽  
Different Temperatures ◽  
And Storage ◽  
Kinetics Of

Abstract Pekmez (molasses) is a traditional food commonly produced from grape and other kind of fruit juices by evaporation processes. In this study, 5-Hydroxymethylfurfural (HMF) level of various pekmez samples was investigated during storage at different temperatures. HMF content of apricot, mulberry, carob, grape, Juniperus communis pekmez changed from 133.0 ppm to 1060.5 ppm, from 88.2 to 1921.5 ppm, from 11.1 to 1153.6 ppm, from 75.5 to 2077.0 ppm, from 19.9 to 280.1 ppm throughout eight months storage period, respectively. Samples of pekmez from the Juniperus communis had the minimum k values for each temperature that means HMF formation in these samples were slower than other pekmez types. The kinetic data analysis for HMF formation during storage was performed and an Arrhenius equation was used to determine the effect of temperature on reaction kinetics of 5-HMF formation in pekmez samples. Ea values were found between 10.58–37.73 (kcal/mol). Apricot pekmez was found as the least sensitive sample to HMF formation resulted from temperature changes.

Kinetics of UO2 (s) Dissolution in the Presence of Hypochlorite, Chlorite, and Chlorate Solutions

2008 ◽  
Vol 1107 ◽  
Author(s):  
Rosa Sureda ◽  
Ignasi Casas ◽  
Javier Giménez ◽  
Joan de Pablo
Keyword(s):  
Dissolution Rate ◽  
Continuous Flow ◽  
Empirical Equation ◽  
Uranium Concentration ◽  
Experimental Methodology ◽  
Dissolution Rates ◽  
Experimental Conditions ◽  
Flow Through ◽  
Kinetics Of ◽  
Hypochlorite Anion

AbstractThe influence of hypochlorite, chlorite and chlorate in the UO2 dissolution rate has been studied experimentally using a continuous flow-through reactor. Uranium concentration in each outflow solution was measured as a function of time and dissolution rates were determined once the steady-state was reached. The results obtained show that the influence of the hypochlorite anion concentration on the UO2 dissolution rate can be expressed by the following empirical equationrdiss = 10-8.7±0.1•[ClO-]0.28±0.04The dissolution rates obtained in this work were higher than those previously determined in presence of either oxygen or hydrogen peroxide using the same experimental methodology.In contrast, neither chlorate nor chlorite had any significant effect on the UO2 dissolution rates under the experimental conditions of this work.

Effect of Temperature on Microparticle Rebound Characteristics at Constant Impact Velocity—Part I

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
J. M. Delimont ◽  
M. K. Murdock ◽  
W. F. Ng ◽  
S. V. Ekkad
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
Target Material ◽  
Road Dust ◽  
Solid Particles ◽  
Effect Of Temperature ◽  
Different Temperatures ◽  
Materials Used ◽  
Wall Interaction ◽  
Engine Components

Many gas turbine engines operate in harsh environments where the engines ingest solid particles. Ingested particles accelerate the deterioration of engine components and reduce the engine's service life. Understanding particle impacts on materials used in gas turbines at representative engine conditions leads to improved designs for turbomachinery operating in particle-laden environments. Coefficient of restitution (COR) is a measure of particle/wall interaction and is used to study erosion and deposition. In this study, the effect of temperature (independent of velocity) on COR was investigated. Arizona road dust (ARD) of 20–40 μm size was injected into a flow field to measure the effects of temperature and velocity on particle rebound. Target coupon materials used were Stainless Steel 304 (SS304) and Hastelloy X (HX). Tests were performed at three different temperatures: 300 K (ambient), 873 K, and 1073 K. The velocity of the flow field was held constant at 28 m/s. The impingement angle of the bulk sand on the coupon was varied from 30 deg to 80 deg for each temperature tested. The COR was found to decrease substantially from the ambient case to the 873 K and 1073 K cases. The HX material exhibits a larger decrease in COR than the SS304 material. The results are also compared to previously published literatures. The decrease in COR is believed to be due to the changes in the surface of both materials due to oxide layer formation which occurs as the target material is heated.

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