scholarly journals Chemisorption of Hydrogen Ions on Aminosilica Surfaces at Different Temperatures

2003 ◽  
Vol 21 (1) ◽  
pp. 53-66 ◽  
Author(s):  
Yuriy V. Kholin ◽  
Sergiy A. Myerniy ◽  
Yutta V. Shabaeva ◽  
Inna V. Khristenko ◽  
Anton A. Samoteikin ◽  
...  
Keyword(s):  
Equilibrium Constants ◽  
Subsurface Layer ◽  
Background Electrolyte ◽  
Sorption Kinetics ◽  
Hydrogen Ions ◽  
Amino Groups ◽  
Second Stage ◽  
Diffusion Controlled ◽  
Different Temperatures ◽  
And Diffusion

The chemisorption of hydrogen ions by silicas chemically modified with aliphatic amines was discussed. The sorption kinetics followed the model of sorption from a semi-infinite solution, with sorption being of a two-stage nature. The first stage, involving the overwhelming majority of sorption centres, was very fast. In contrast, the second stage was rather slow and diffusion-controlled. A proper description of the protolytic equilibria on the aminosilica surface required account to be taken not only of the protonization of the grafted amino groups but also of their homoconjugation. The latter reaction resulted from interactions between neighbouring groups and led to the non-random (islandlike) coverage of the surface by amino groups. Both the nature of the background electrolyte in the solution and its concentration had no effect on the model structure. The thermodynamic equilibrium constants for the heterogeneous protonization reaction were determined from the dependencies of the mixed equilibrium constants on the concentration of the background electrolyte in solution. Chemisorption of H+ ions, accompanied by penetration of the counterions into the subsurface layer, was of an endothermic nature and associated with increasing entropy.

scholarly journals Adsorption of H+, OH− and Background Electrolyte Ions on Alumina — Point of Zero Charge, Triple Layer Model (TLM) Parameters and Thermodynamic Parameters

1997 ◽  
Vol 15 (6) ◽  
pp. 455-463 ◽  
Author(s):  
Chu Taiwei ◽  
Du Jinzhou ◽  
Tao Zuyi
Keyword(s):  
Surface Charge ◽  
Equilibrium Constants ◽  
Background Electrolyte ◽  
Point Of Zero Charge ◽  
Aqueous Suspensions ◽  
Gibbs Energies ◽  
Zero Charge ◽  
Different Temperatures ◽  
Proton Adsorption ◽  
Titration Data

The surface charge σ0 on aqueous suspensions of alumina was measured as a function of pH in various NaNO3 concentrations and at different temperatures. The values of the point of zero charge (p.z.c.), pK1(int), pK2(int), pKNa+(int) and pKNO3–(int) for alumina suspended in NaNO3 solutions were obtained in the temperature range 17–45°C from potentiometrie titration data. The values of ΔS0 and ΔH0 of the dissociation equilibria and complexation equilibria were calculated from these equilibrium constants. Standard Gibbs energies, enthalpies and entropies for proton adsorption on alumina were also obtained. The surface charge σ0 on aqueous suspensions of alumina was measured as a function of pH and concentration of Ca(NO3)2 or Na2SO4 solution.

Kinetic investigation of a complex curing of the guaiacol bio-based benzoxazine system

e-Polymers ◽  
2016 ◽  
Vol 16 (3) ◽  
pp. 199-206 ◽  
Author(s):  
Aleš Ručigaj ◽  
Špela Gradišar ◽  
Matjaž Krajnc
Keyword(s):  
Curing Kinetics ◽  
Second Stage ◽  
Diffusion Controlled ◽  
Polymerization Behavior ◽  
Overlapped Peaks ◽  
Friedman Method ◽  
Apparent Activation Energies ◽  
Stage 1 ◽  
Kinetics Of ◽  
And Diffusion

AbstractCuring kinetics of guaiacol based benzoxazine synthesized from guaiacol, furfurylamine and formaldehyde forming bio-based polybenzoxazine was investigated. The curing process showed complex polymerization behavior, as the exothermal signal consisted of several overlapped peaks. Differentiation and fitting of overlapped peaks was performed by Pearson VII distribution obtaining two separate exothermal signals further associated to stage 1 and stage 2. The apparent activation energies of both stages were determined to be 113.8 kJ mol-1 and 117.5 kJ mol-1, respectively, according to Kissinger. The first could be explained by benzoxazine ring-opening and electrophilic substitution, whereas the second stage corresponds to the rearrangement and diffusion-controlled step. Kinetics of each stage was studied separately. As a result, the first stage was described by Šesták-Berggren autocatalytic model, whereas the second stage appeared to follow nth order kinetics proved by the Friedman method. Application of both kinetic models demonstrated that the predicted curves fit well with the non-isothermal DSC thermograms and as such sufficiently describes the complex curing behavior of guaiacol based benzoxazine.

Vacancy-Mediated Diffusion and Diffusion-Controlled Processes in Ordered Binary Intermetallics by Kinetic Monte Carlo Simulations

2021 ◽  
Vol 29 ◽  
pp. 95-115
Author(s):  
Rafal Kozubski ◽  
Graeme E. Murch ◽  
Irina V. Belova
Keyword(s):  
Monte Carlo ◽  
Kinetic Monte Carlo ◽  
Simulation Studies ◽  
Self Diffusion ◽  
Monte Carlo Techniques ◽  
Diffusion Controlled ◽  
Kinetic Monte Carlo Simulations ◽  
Kinetic Effects ◽  
Kinetics Of ◽  
And Diffusion

We review the results of our Monte Carlo simulation studies carried out within the past two decades in the area of atomic-migration-controlled phenomena in intermetallic compounds. The review aims at showing the high potential of Monte Carlo methods in modelling both the equilibrium states of the systems and the kinetics of the running processes. We focus on three particular problems: (i) the atomistic origin of the complexity of the ‘order-order’ relaxations in γ’-Ni3Al; (ii) surface-induced ordering phenomena in γ-FePt and (iii) ‘order—order’ kinetics and self-diffusion in the ‘triple-defect’ β-NiAl. The latter investigation demonstrated how diverse Monte Carlo techniques may be used to model the phenomena where equilibrium thermodynamics interplays and competes with kinetic effects.

Kinetics and Mechanism of Oxidation of Aliphatic Secondary Alcohols by Benzimidazolium Fluorochromate in Dimethyl Sulphoxide Solvent

2021 ◽  
Vol 37 (3) ◽  
pp. 626-633
Author(s):  
Bhawana Arora ◽  
Jitendra Ojha ◽  
Pallavi Mishra
Keyword(s):  
Activation Parameters ◽  
Sigmatropic Rearrangement ◽  
Dimethyl Sulphoxide ◽  
Secondary Alcohols ◽  
Hydrogen Ions ◽  
Reaction Conditions ◽  
First Order Kinetics ◽  
Aqueous Solvent ◽  
Ester Formation ◽  
Different Temperatures

Oxidation of secondary alcohols is an important part of synthetic organic chemistry. Various studies are carried out at different reaction conditions to determine the best mechanistic pathways. In our study, oxidation of different secondary alcohols was done by using Benzimidazolium Fluorochromate in Dimethyl Sulphoxide, which is a non-aqueous solvent. Oxidation resulted in the formation of ketonic compounds. The reaction showed first order kinetics both in BIFC and in the alcohols. Hydrogen ions were used to catalyze the reaction. We selected four different temperatures to carry out our study. The correlation within the activation parameters like enthalpies and entropies was in accordance with the Exnerʼs criterion. The deuterated benzhydrol (PhCDOHPh) oxidation exhibited an important primary kinetic isotopic effect (kH / kD = 5.76) at 298 K. The solvent effect was studied using the multiparametric equations of Taft and Swain. There was no effect of addition of acrylonitrile on the oxidation rate. The mechanism involved sigmatropic rearrangement with the transfer of hydrogen ion taking place from alcohol to the oxidant via a cyclic chromate ester formation.

scholarly journals Electrochemical Behaviour of N′-(p-toluenesulphonyl)-3-methyl-4-(4′-substituted arylhydrazono) pyrazolin-5-ones

2012 ◽  
Vol 9 (4) ◽  
pp. 1864-1874
Author(s):  
V. Nagaraju ◽  
R. Sreenivasulu ◽  
P. Venkata Ramana
Keyword(s):  
Electrochemical Behaviour ◽  
Reduction Process ◽  
Effect Of Solvent ◽  
Buffer Solutions ◽  
Diffusion Controlled ◽  
Controlled Potential Electrolysis ◽  
Dc Polarography ◽  
Controlled Potential ◽  
Ph Range ◽  
And Diffusion

The electrochemical behaviour of N′-(p-toluenesulphonyl)-3-methyl-4-(4′-substituted arylhydrazono) pyrazolin-5-ones has been investigated at dme and gc electrodes in buffer solutions of pH 2.0, 4.0, 6.0, 8.0 and 10.0 using dc polarography and cyclic voltammetry and coulometry. The compounds exhibit one well defined wave in the entire pH range of study. The process is irreversible and diffusion controlled. Controlled potential electrolysis indicates the involvement of four electrons in the reduction process. The effect of solvent, cations and anions, temperature and substitutents on the mechanism of reduction has been studied. Based on the results obtained the mechanism of reduction has been suggested.

scholarly journals Thermodynamic Investigations on the Inclusion Complexation of Piroxicam with Cyclodextrin Derivatives

2005 ◽  
Vol 73 (3) ◽  
pp. 147-161 ◽  
Author(s):  
Charumanee S. ◽  
Weiss-Greiler P. ◽  
Wolschann P. ◽  
Viernstein H. ◽  
Titwan A. ◽  
...  
Keyword(s):  
Ph Value ◽  
Equilibrium Constants ◽  
Inclusion Complexation ◽  
Solubility Diagram ◽  
Phase Solubility ◽  
Cyclodextrin Derivatives ◽  
Ph Values ◽  
Solubility Behavior ◽  
Solubility Method ◽  
Different Temperatures

Thermodynamic studies of piroxicam in aqueous solution complexed with β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD) and two β-cyclodextrin derivatives, hydroxypropyl-β-cyclodextrin (HP-P-CD) and methyl-β-cyclodextrin (Me-β-CD) were performed at different temperatures and pH values using the phase solubility method. The phase solubility diagrams of β-CD, γ-CD and HP-β-CD is of AL-type behavior, indicating the formation of 1:l complexes. The related stability constants range from β-CD > γ-CD > Me-β-CD > HP-β-CD, respectively. An Ap-type solubility diagram is observed for Me-β-CD, indicating the formation of 1:2 complexes at higher CD concentrations. From the temperature dependence of the equilibrium constants the reaction enthalpies and entropies have been determined. The contributions of the reaction entropies are small and no enthalpy-entropy-compensation is observed, except for γ-CD, where a very small negative reaction entropy could be estimated. Moreover, the influence of the pH value is rather high because the differently charged forms of piroxicam show different solubility behavior in water.

Refinement of Size Distributions for Primary Crystallizations

1997 ◽  
Vol 481 ◽  
Author(s):  
E. Pineda ◽  
T. Pradell ◽  
D. Crespo ◽  
N. Clavaguera ◽  
J. ZHU ◽  
...  
Keyword(s):  
Grain Size ◽  
Metastable Phase ◽  
Primary Crystallization ◽  
Controlled Growth ◽  
Diffusion Controlled ◽  
Average Grain Size ◽  
Soft Impingement ◽  
Single Grain ◽  
Kinetics Of ◽  
And Diffusion

ABSTRACTThe microstructure developed in primary crystallizations is studied under realistic conditions. The primary crystallization of an amorphous alloy is modeled by considering the thermodynamics of a metastable phase transition and the kinetics of nucleation and crystal growth under isothermal annealing. A realistic growth rate, including an interface controlled growth at the beginning of the growth of each single grain and diffusion controlled growth process with soft impingement afterwards is considered. The reduction in the nucleation rate due to the compositional change in the remaining amorphous matrix is also taken into account. The microstructures developed during the transformation are obtained by using the Populational KJMA method, from the above thermodynamic and kinetic factors. Experimental data of transformed fraction, grain density, average grain size, grain size distribution and other related parameters obtained from annealed metallic glasses are modeled.

scholarly journals SOLVATION OF THE [Cr(NCS)4(IMIDAZOLE)2] ION IN ETHANOL-WATER MIXTURES

2002 ◽  
Vol 10 (11) ◽  
pp. 63-72
Author(s):  
lon Ganescu ◽  
George Bratulescu ◽  
Ion Papa ◽  
Anca Ganescu ◽  
Alin Barbu ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Order Reaction ◽  
Water Molecules ◽  
Hydrogen Ions ◽  
Second Order Reaction ◽  
Acidic Solutions ◽  
The Third ◽  
Competitive Reactions ◽  
Different Temperatures ◽  
Kinetics Of

Salvation kinetics of [Cr(NCS)4(imidazole)2]- has been studied in ethanol-water mixtures at different temperatures. The first stage of the solvation consists of two competitive reactions: two NCS- ions are exchanged, presumably, by water molecules and simultaneously an imidazole molecule by ethanol, the latter in a second-order reaction, accelerated by hydrogen ions. The exchange of the amine is followed by the substitution of the first two NCS- ions. The third and fourth NCS- ions are substituted only in neutral and slightly acidic solutions. Kinetic parameters have been determined for reactions (1), (2), and (4). The influence of the solvent composition and acidity is discussed

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