Adiabatic Reaction Kinetics of Buna-S Vulcanization

1949 ◽  
Vol 22 (2) ◽  
pp. 386-391
Author(s):  
M. Gordon
Keyword(s):  
Reaction Kinetics ◽  
Published Data ◽  
Heat Of Reaction ◽  
Present Communication ◽  
Kinetic Measurements ◽  
Sulfur Vulcanization ◽  
Temperature Constant ◽  
Kinetics Of ◽  
Insight Into ◽  
Butadiene Styrene

Abstract In a previous paper a technique for making kinetic measurements adiabatically instead of isothermally was discussed, and the possible advantages of this technique in reactions involving polymers was indicated. In the present communication, the theory is supported by an analysis of published data relating to the vulcanization of butadiene-styrene copolymer. There are considerable gaps in our knowledge of the overall chemical changes concerned in the vulcanization of various rubbers, quite apart from the kinetic interpretation of rate measurements and the postulation of elementary steps. Because of the difficulties involved, isothermal rate measurements have not yet given much insight into the kinetics or the chemistry of the time-honored sulfur vulcanization discovered over a hundred years ago. The difficulty of maintaining the temperature constant against the considerable heat of reaction is only one of the obstacles ; that of finding a convenient and accurate measure of the progress of vulcanization considered as a chemical reaction is perhaps even greater. The difficulties of the adiabatic technique are essentially different in nature.

Hydrogen Passivation Kinetics of Si Nanocrystals in SiO2

2003 ◽  
Vol 770 ◽  
Author(s):  
Andrew R. Wilkinson ◽  
Robert G. Elliman
Keyword(s):  
Reaction Kinetics ◽  
Activation Energies ◽  
Hydrogen Passivation ◽  
Time Resolved ◽  
Luminescence Efficiency ◽  
Si Nanocrystals ◽  
Preliminary Study ◽  
Kinetics Of ◽  
Insight Into

AbstractHydrogen passivation of non-radiative defects increases the luminescence intensity from silicon nanocrystals. In this study, photoluminescence (PL) and time-resolved PL were used to investigate the chemical kinetics of the hydrogen passivation process. Isochronal and isothermal annealing sequences were used to determine the reaction kinetics for the absorption and desorption of hydrogen, using the generalised consistent simple thermal (GST) model proposed by Stesmans for Pb defects at planar Si/SiO2 interfaces. This included determination of the activation energies and rate constants for the forward and reverse reactions as well as the associated spread in activation energies. The reaction kinetics determined from such measurements were found to be in excellent agreement with those for the passivation of Pb defects at planar Si/SiO2 interfaces, suggesting the nanocrystal emission process is also limited by such defects. These results provide useful model data as well as insight into the processing conditions needed to achieve optimum passivation in H2. As an extension to the work, a preliminary study into passivation by atomic hydrogen was pursued via a post-metallization Al anneal (alneal). A considerable gain in luminescence efficiency was achieved over the previously optimised passivation in H2.

Insight into structural aspects and study of reaction kinetics of model [oxo(salen)iron(IV)] complexes with dipeptides

Polyhedron ◽  
2021 ◽  
Vol 196 ◽  
pp. 114952
Author(s):  
Periyakaruppan Karuppasamy ◽  
Dharmaraj Thiruppathi ◽  
Jeyaraj Vijaya Sundar ◽  
Muniyandi Ganesan ◽  
Thangamuthu Rajendran ◽  
...  
Keyword(s):  
Reaction Kinetics ◽  
Kinetics Of ◽  
Insight Into ◽  
Structural Aspects

Isothermal DSC study of the curing kinetics of an epoxy/silica composite for microelectronics

2016 ◽  
Vol 2016 (1) ◽  
pp. 000415-000420 ◽  
Author(s):  
Lérys Granado ◽  
Stefan Kempa ◽  
Stefanie Bremmert ◽  
Laurence J. Gregoriades ◽  
Frank Brüning ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Kinetic Method ◽  
Base Material ◽  
Curing Kinetics ◽  
Degree Of Conversion ◽  
Circuit Board ◽  
Heat Of Reaction ◽  
Kinetic Measurements ◽  
Model Free ◽  
Kinetics Of

Abstract Curing kinetics of an industrially important printed-circuit board (PCB) base material (epoxy-phenol/glass fillers) were studied from isothermal differential scanning calorimetry (DSC) measurements between 150 and 190 °C. The extent of cure was calculated by integration of the exothermic peak and normalization by the total heat of reaction (obtained by non-isothermal DSC). The kinetic profiles show two regimes: one fast, and one slower. The completion was reached above 180 °C. The kinetic parameters have been elucidated using an isoconversional model-free kinetic method. The linearity of Arrhenius plots was satisfactory. The apparent activation energy of curing reaction has been found to increase with the degree of conversion. The elucidation of the kinetic parameters allows us to propose an accurate and predictive description of the curing kinetics of the composite until a degree of conversion of 50%. Finally, we discuss how these kinetic measurements and models can be completed and optimized.

New Theoretical Insight into the Reaction Kinetics of Toluene and Hydroxyl Radicals

2020 ◽  
Author(s):  
Xiaoqing Wu ◽  
Can Huang ◽  
Shiyao Niu ◽  
Feng Zhang
Keyword(s):  
Reaction Kinetics ◽  
Quantum Chemical ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Total Rate ◽  
Barrier Heights ◽  
Reaction Channels ◽  
High Level ◽  
Kinetics Of ◽  
Insight Into

<p><a></a><a>Toluene’s removal mechanism in the atmosphere is mainly attributed to OH radical, which includes major OH-addition and minor H-abstraction reactions. The cresols and RO2 derived from OHadducts reacting to O2 have significant impacts on the generation of secondary organic aerosols (SOA) and O3. However, computed branching ratios of various OH-adducts at various theoretical levels are largely inconsistent, mainly because previously reported barrier heights of OH-addition reaction showed a strong method dependence. In the present study, we demonstrate that this reaction involves a nonnegligible anharmonic effect (during the process of OH moving to the benzene ring), which has been overlooked by previous studies. The reaction kinetics of toluene + OH was systematically studied by a high-level quantum chemical method (CCSD(T)-F12/cc-pVQZ-F12//B2PLYP-D3/6-311++G(d,p)) combined with RRKM/master equation simulations. The particle-in-a-box approximation was used to treat the anharmonicity in this system. The final total rate coefficient is calculated to be 2.60 × 10−12 cm3 molecule−1 s−1 at 300 K and 1 atm. The main products for toluene + OH are computed as ortho-adducts (50.8%), benzyl radical + H2O (21.1%), ipso-adduct (16.3%), para-adduct (6.1%), and meta-adduct (4.6%). Our results indicate that both high level quantum chemical calculations for the crucial barrier heights and appropriate treatments for the anharmonicity determine the accuracy of the final computed total rate coefficients and branching ratios. Further analysis on the branching ratios of various reaction channels provides insight into the atmosphere-initiated oxidation of toluene. </a></p>

New Theoretical Insight into the Reaction Kinetics of Toluene and Hydroxyl Radicals

2020 ◽  
Author(s):  
Xiaoqing Wu ◽  
Can Huang ◽  
Shiyao Niu ◽  
Feng Zhang
Keyword(s):  
Reaction Kinetics ◽  
Quantum Chemical ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Total Rate ◽  
Barrier Heights ◽  
Reaction Channels ◽  
High Level ◽  
Kinetics Of ◽  
Insight Into

<p><a></a><a>Toluene’s removal mechanism in the atmosphere is mainly attributed to OH radical, which includes major OH-addition and minor H-abstraction reactions. The cresols and RO2 derived from OHadducts reacting to O2 have significant impacts on the generation of secondary organic aerosols (SOA) and O3. However, computed branching ratios of various OH-adducts at various theoretical levels are largely inconsistent, mainly because previously reported barrier heights of OH-addition reaction showed a strong method dependence. In the present study, we demonstrate that this reaction involves a nonnegligible anharmonic effect (during the process of OH moving to the benzene ring), which has been overlooked by previous studies. The reaction kinetics of toluene + OH was systematically studied by a high-level quantum chemical method (CCSD(T)-F12/cc-pVQZ-F12//B2PLYP-D3/6-311++G(d,p)) combined with RRKM/master equation simulations. The particle-in-a-box approximation was used to treat the anharmonicity in this system. The final total rate coefficient is calculated to be 2.60 × 10−12 cm3 molecule−1 s−1 at 300 K and 1 atm. The main products for toluene + OH are computed as ortho-adducts (50.8%), benzyl radical + H2O (21.1%), ipso-adduct (16.3%), para-adduct (6.1%), and meta-adduct (4.6%). Our results indicate that both high level quantum chemical calculations for the crucial barrier heights and appropriate treatments for the anharmonicity determine the accuracy of the final computed total rate coefficients and branching ratios. Further analysis on the branching ratios of various reaction channels provides insight into the atmosphere-initiated oxidation of toluene. </a></p>

A chemiluminescence study of the kinetics of reactions of Cr(III) with carboxylate ligands: oxalate, salicylate, and humic acid

1990 ◽  
Vol 68 (6) ◽  
pp. 881-885 ◽  
Author(s):  
Douglas L. Huizenga ◽  
Howard H. Patterson
Keyword(s):  
Humic Acid ◽  
Reaction Kinetics ◽  
Rate Constants ◽  
Natural Waters ◽  
Ligand Concentration ◽  
Reaction Pathways ◽  
Carboxylate Ligands ◽  
Kinetics Of ◽  
Insight Into

The reaction of Cr(III) with chelate-forming carboxylate ligands can be monitored at the low ligand concentrations typical of natural waters by chemiluminescence analysis of unreacted Cr(III). This technique is utilized here for the measurement of Cr(III) reaction kinetics with oxalate, salicylate, and humic acid over a wider ligand concentration range than previously reported. Variation of the pH and ligand concentrations allowd the determination of rates of reaction by three pathways with different pH dependencies. The magnitude of rate constants of these pathways for Cr(III) with inorganic (Cl−, SCN−) and carboxylate ligands gives insight into the reaction pathways for the environmentally important ligand humic acid. Keywords: Cr(III), oxalate, salicylate, humic acid.

Isothermal DSC Study of the Curing Kinetics of an Epoxy/Silica Composite for Microelectronics

2017 ◽  
Vol 14 (2) ◽  
pp. 45-50 ◽  
Author(s):  
Lérys Granado ◽  
Stefan Kempa ◽  
Stefanie Bremmert ◽  
Laurence J. Gregoriades ◽  
Frank Brüning ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Kinetic Method ◽  
Base Material ◽  
Curing Kinetics ◽  
Circuit Board ◽  
Heat Of Reaction ◽  
Scanning Calorimetry ◽  
Kinetic Measurements ◽  
Model Free ◽  
Kinetics Of

Abstract Curing kinetics of an industrially important printed-circuit board (PCB) base material (epoxy–phenol/glass fillers) were studied by isothermal differential scanning calorimetry (DSC) measurements between 150 and 190°C, as relevant curing temperatures for the PCB industry. The extent of cure was calculated by integration of the exothermic peak and normalization by the total heat of reaction (obtained by nonisothermal DSC). Although the cross-linking was completed above 180°C, the kinetic profiles show two regimes: one fast and one slow. The kinetic parameters have been elucidated using an isoconversional model-free kinetic method, with the exact method of Friedman, to give to the PCB manufacturers a road map to predict curing behavior of base material. The linearity of Arrhenius plots was satisfactory. The apparent activation energy of curing reaction has been found to increase with the degree of conversion. The elucidation of the kinetic parameters allows us to propose an accurate and predictive description of the curing kinetics within the fast regimen of reaction (i.e., without vitrification). Finally, we discuss how these kinetic measurements and models can be completed and optimized.

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