Multiparticle effects in the kinetics of diffusion-controlled reactions

1985 ◽  
Vol 21 (1) ◽  
pp. 31-35
Author(s):  
V. N. Kuzovkov
Keyword(s):  
Diffusion Controlled ◽  
Kinetics Of

scholarly journals Synthesis and Polymerization Kinetics of Rigid Tricyanate Ester

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1686
Author(s):  
Andrey Galukhin ◽  
Roman Nosov ◽  
Ilya Nikolaev ◽  
Elena Melnikova ◽  
Daut Islamov ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Single Step ◽  
Polymerization Kinetics ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Diffusion Controlled ◽  
Polymerization Product ◽  
The One ◽  
Kinetics Of

A new rigid tricyanate ester consisting of seven conjugated aromatic units is synthesized, and its structure is confirmed by X-ray analysis. This ester undergoes thermally stimulated polymerization in a liquid state. Conventional and temperature-modulated differential scanning calorimetry techniques are employed to study the polymerization kinetics. A transition of polymerization from a kinetic- to a diffusion-controlled regime is detected. Kinetic analysis is performed by combining isoconversional and model-based computations. It demonstrates that polymerization in the kinetically controlled regime of the present monomer can be described as a quasi-single-step, auto-catalytic, process. The diffusion contribution is parameterized by the Fournier model. Kinetic analysis is complemented by characterization of thermal properties of the corresponding polymerization product by means of thermogravimetric and thermomechanical analyses. Overall, the obtained experimental results are consistent with our hypothesis about the relation between the rigidity and functionality of the cyanate ester monomer, on the one hand, and its reactivity and glass transition temperature of the corresponding polymer, on the other hand.

Primary products and processes in the γ-radiolysis of 2-methyltetrahydrofuran

1965 ◽  
Vol 285 (1402) ◽  
pp. 319-338 ◽  
Keyword(s):  
Glassy Phase ◽  
Kcal Mole ◽  
Radical Species ◽  
Molecule Reaction ◽  
Positive Ions ◽  
Primary Products ◽  
Diffusion Controlled ◽  
Thermal Bleaching ◽  
The Matrix ◽  
Kinetics Of

From a study of the u. v., visible, near i. r. and e. s. r. spectra induced by γ -irradiation at 77°K in glassy MTHF and in glassy MTHF containing various additives and from a study of controlled temperature increases on these spectra, the following conclusions are drawn. (1) The primary products of the radiolysis are electrons ( e - ) and positive ions ( MTHF + ) which undergo a rapid ion-molecule reaction to give O CH 3 radicals ( R ⋅). (2) e - can either be trapped in the glassy MTHF matrix or can be captured by either napththalene, ferric chloride, carbon tetrachloride, nitrous oxide or trans -stilbene if these substances are present. (3) The e - T are bleachable by light or heat and disappear independently of the radicals R⋅ without either augmentation of R⋅ or the production of any new radical species. (4) e - T and R⋅ disappear thermally and independently by second-order reactions, the rate constants being K e - + e - (M -1 S -1 ) = 10 12⋅4±1⋅1 exp ─ [0⋅85 ± 0⋅10 kcal/mole/ R ( T ─ 75)] and K R˙ + R˙ (M -1 S -1 ) = 10 13⋅3±1⋅4 exp ─ [1⋅20 ± 0⋅15 kcal/mole/ R ( T ─ 75)]. These rate expressions suggest that both reactions are diffusion controlled at low temperatures in the glassy phase. (5) The kinetics of the thermal bleaching of e - T indicate that the electrons migrate distances of about 150 Å from their parent positive ions before being trapped in the matrix. (6) The effect of FeCl 3 in reducing the formation of e - T at 77°K and its lack of effect on the thermal bleaching of e - T suggests that the reaction e - + FeCl 3 → FeCl 2 + Cl - only occurs before the electron is thermalized.

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.

Effect of Excess PbO on the Kinetics of the Growth of PMNT Polycrystals by Templated Grain Growth Method

2005 ◽  
Vol 475-479 ◽  
pp. 1137-1140
Author(s):  
Lili Zhao ◽  
Feng Gao ◽  
Wei Min Wang ◽  
Chang Sheng Tian
Keyword(s):  
Grain Growth ◽  
Templated Grain Growth ◽  
Experimental Conditions ◽  
Precipitation Mechanism ◽  
Oriented Structure ◽  
Diffusion Controlled ◽  
The Matrix ◽  
Growth Method ◽  
Final Composition ◽  
Kinetics Of

The oriented 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3 (PMNT) polycrystals were prepared by the conventional ceramic technique and the templated grain growth method adding excess PbO in the matrix. Kinetics of the development of oriented structure was investigated systemically. In the presence of PbO liquid phase, the oriented PMNT polycrystals mainly grow by the dissolution-precipitation mechanism. The diffusion is determined by the sintering temperature and the PbO-excess content in the matrix. The thickness of oriented PMNT polycrystals displays a t1/3 dependence, which is characteristic of diffusion-controlled growth. For the thicker oriented structure, 20% excess PbO in the PMNT matrix and 1150oC for 10h are the proper experimental conditions. Moreover, the addition of PbO in the matrix hardly affects the final composition of ceramic matrix.

omparisons of Silicide Formation by Rapid Thermal Annealing and Conventional Furnace Annealing

1987 ◽  
Vol 92 ◽  
Author(s):  
E. Ma ◽  
M. Natan ◽  
B.S. Lim ◽  
M-A. Nicolet
Keyword(s):  
Thermal Annealing ◽  
Rapid Thermal Annealing ◽  
Silicide Formation ◽  
X Ray Diffraction ◽  
Furnace Annealing ◽  
Cross Sectional ◽  
Conventional Furnace ◽  
Diffusion Controlled ◽  
Conventional Furnace Annealing ◽  
Kinetics Of

ABSTRACTSilicide formation induced by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) in bilayers of sequentially deposited films of amorphous silicon and polycrystalline Co or Ni is studied with RBS, X-ray diffraction and TEM. Particular attention is paid to the reliability of the RTA temperature measurements in the study of the growth kinetics of the first interfacial compound, Co2Si and Ni2Si, for both RTA and CFA. It is found that the same diffusion-controlled kinetics applies for the silicide formation by RTA in argon and CFA in vacuum with a common activation energy of 2.1+0.2eV for Co2Si and 1.3+0.2eV for Ni Si. Co and Ni atoms are the dominant diffusing species; during silicide formation by both RTA and CFA. The microstructures of the Ni-silicide formed by the two annealing techniques, however, differs considerably from each other, as revealed by cross-sectional TEM studies.

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 Study on indium leaching from mechanically activated hard zinc residue

2011 ◽  
Vol 47 (1) ◽  
pp. 63-72 ◽  
Author(s):  
J.H. Yao ◽  
X.H. Li ◽  
Y.W. Li
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Planetary Mill ◽  
Leaching Rate ◽  
Obvious Effect ◽  
Diffusion Controlled ◽  
Leaching Reaction ◽  
Kinetics Of ◽  
Positive Effect ◽  
Solution Kinetics

In this study, changes in physicochemical properties and leachability of indium from mechanically activated hard zinc residue by planetary mill were investigated. The results showed that mechanical activation increased specific surface area, reaction activity of hard zinc residue, and decreased its particle size, which had a positive effect on indium extraction from hard zinc residue in hydrochloric acid solution. Kinetics of indium leaching from unmilled and activated hard zinc residue were also investigated, respectively. It was found that temperature had an obvious effect on indium leaching rate. Two different kinetic models corresponding to reactions which are diffusion controlled, [1-(1- x)1/3]2=kt and (1-2x/3)-(1-x)2/3=kt were used to describe the kinetics of indium leaching from unmilled sample and activated sample, respectively. Their activation energies were determined to be 17.89 kJ/mol (umilled) and 11.65 kJ/mol (activated) within the temperature range of 30?C to 90?C, which is characteristic for a diffusion controlled process. The values of activation energy demonstrated that the leaching reaction of indium became less sensitive to temperature after hard zinc residue mechanically activated by planetary mill.

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