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.

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.

Beobachtungen von Stapelfehlordnungen bei der Oxydation der zweiten zur ersten Stufe des Graphithydrogensulfats / Observation of stacking disorder during the oxidation of second stage to first stage graphite hydrogensulfate

1984 ◽  
Vol 39 (8) ◽  
pp. 768-777 ◽  
Author(s):  
Ko Young Shin ◽  
Hanns-Peter Boehm
Keyword(s):  
Interlayer Spacing ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Second Stage ◽  
Intermediate Phases ◽  
Degree Of Oxidation ◽  
Stage 1 ◽  
Kinetics Of ◽  
Stacking Disorder

Graphite has been oxidized to graphite hydrogensulfate with (NH4)2S2Og in concentrated H2SO4. The stage 2 compound formed very rapidly, but further oxidation to stage 1 could be followed conveniently. X-ray diffraction of the intermediate phases showed nonintegral (00l)-reflections indicative of partial interstratification disorder. The interlayer spacing of the stage 1 compound increased with continued oxidation. The degree of oxidation as function of oxidation time has been determined from the position of the minima in the reflectance spectra. The density of the compounds and the ratio of acid molecules to anions in the intercalated layers has been estimated using these data and those of buoyancy measurements. There is a minimum in packing density early in the formation of the first stage. The kinetics of intercalation seems to be first order with respect to the free interlayer spaces.

Thermal and Mechanical Stability of Polycrystalline Nanowires

2007 ◽  
Vol 264 ◽  
pp. 133-140
Author(s):  
Leonid Klinger ◽  
Eugen Rabkin
Keyword(s):  
Plastic Deformation ◽  
Applied Load ◽  
Mechanical Stability ◽  
Deformation Behaviour ◽  
High Yield ◽  
Morphological Stability ◽  
Diffusion Controlled ◽  
Kinetics Of ◽  
And Diffusion ◽  
Shape Changes

We considered a polycrystalline cylindrical nanowire with bamboo microstructure strained uniaxially by an external load. Our molecular dynamic computer simulations demonstrated that grain boundary grooving plays an important role in determining the morphological stability of nanowires. Also, an exceptionally high yield stress of nanowires emphasizes the importance of diffusion in their plastic deformation under applied load. We formulated a phenomenological diffusion-based model describing morphological stability and diffusion-controlled deformation behaviour of polycrystalline nanowires. The kinetics of the shape changes was calculated numerically.

Current transient study of the kinetics of nucleation and diffusion-controlled growth of bimetallic phases

2012 ◽  
Vol 17 (2) ◽  
pp. 345-351 ◽  
Author(s):  
Oscar Díaz-Morales ◽  
Jorge Mostany ◽  
Carlos Borrás ◽  
Benjamin R. Scharifker
Keyword(s):  
Current Transient ◽  
Controlled Growth ◽  
Diffusion Controlled ◽  
Transient Study ◽  
Kinetics Of ◽  
And Diffusion

scholarly journals ISOTHERMAL CURING KINETICS OF POLYMETHACRYLIMIDE/NANO-SiO2 COMPOSITES BASED ON A DYNAMIC THERMOMECHANICAL ANALYSIS

2021 ◽  
Vol 55 (2) ◽  
pp. 293-304
Author(s):  
Jing Zhang ◽  
Yi-min Wu ◽  
Xu Ma ◽  
Bao-Yu Huang ◽  
Song Lv ◽  
...  
Keyword(s):  
Activation Energy ◽  
Integral Method ◽  
Model Fitting ◽  
Curing Kinetics ◽  
Thermomechanical Analysis ◽  
Avrami Model ◽  
Nano Sio2 ◽  
Friedman Method ◽  
Kinetics Of ◽  
Relative Conversion

The isothermal curing kinetics of polymethacrylimide/nano-SiO2 composites were investigated using a dynamic thermomechanical analysis. The relative conversion was defined with the storage modulus. The Avrami model-fitting method, Friedman method and integral method were applied to analyze the curing kinetics. The storage modulus and loss modulus increased appreciably, spanning three orders of magnitude throughout the curing. The frequency correlation of the relative conversion was noticeable at 180 °C because the glass transition took place when the curing degree was not high enough. The Avrami model-fitting analysis gave good fits for the experimental data. The activation energy calculated with the Avrami equation changed from 65.46 kJ/mol to 25.28 kJ/mol at 180–190 °C, while at 190–200 °C, the activation energy changed from 107.14 kJ/mol to 63.82 kJ/mol. The model-free analysis revealed the dependence of the activation energy on the relative conversion. The activation energy increased from 104.3 kJ/mol to 130.6 kJ/mol with the use of the Friedman method when the relative conversion ranged between 0.4–0.8. Similarly, the activation energy calculated with the integral method increased from 71.5 kJ/mol to 103.4 kJ/mol. When the relative conversion exceeded 0.8, the activation energy decreased gradually. The mobility of the reactive groups was hindered and the crosslinking density of the composite was much higher. The curing kinetics became diffusion controlled. The activation energy of the PMI/SiO2 composite was greater than that of PMI, which could be attributed to the hindrance effect caused by nano-SiO2.

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.

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