Chemistry of the Transition Metals. II. Reaction of Branched Alkyl Chlorides with Titanium

1972 ◽  
Vol 50 (14) ◽  
pp. 2167-2174 ◽  
Author(s):  
W. R. Summers ◽  
J. F. Harrod
Keyword(s):  
Activation Energy ◽  
Elevated Temperatures ◽  
Halogen Bond ◽  
Heterogeneous Reaction ◽  
Butyl Chloride ◽  
Dissociative Chemisorption ◽  
Ambient Temperatures ◽  
Catalytic Dehydrochlorination ◽  
Titanium Surfaces ◽  
Kinetics Of

Except for t-butyl chloride, the 1- and 2-methyl substituted ethyl chlorides reacted at ambient temperatures with clean titanium surfaces to produce mixtures of the corresponding alkanes and alkenes; t-butyl chloride gave only isobutene. At elevated temperatures (80–150 °C depending on reactant) the branched alkyl chlorides underwent clean, catalytic dehydrochlorination on hydrochlorinated titanium films to give gaseous olefin and hydrogen chloride, in contrast to the previously observed dehydrohalogenation of n-alkyl halides, where metal was consumed continuously in a non-catalytic fashion.The kinetics of the dehydrochlorination were exceptionally simple and reproducible for a heterogeneous reaction and all reactions were first order in reactant. The reactivity order was t-butyl > i-propyl > neopentyl > i-butyl (ca. 106:6:3:1). Although a slight dependence of activation energy on reactant pressure was observed, all reactants gave a limiting activation energy of 15.5 ± 0.5 kcal/mol and the large variation in activity is attributed to differences in the Arrhenius pre-exponential factor.It is proposed that the non-catalytic and catalytic dehydrohalogenation reactions proceed by different mechanisms, the former via a dissociative chemisorption of the carbon–halogen bond and the latter via a concerted, surface-assisted HCl elimination.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

scholarly journals Thermogravimetric Study of the Kinetics of the Reaction C + CO2 under Pore-Diffusion Control

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1886
Author(s):  
Igor Donskoy ◽  
Aleksandr Kozlov
Keyword(s):  
Activation Energy ◽  
Heterogeneous Reaction ◽  
Experimental Studies ◽  
Pore Diffusion ◽  
Diffusion Control ◽  
Diffusion Resistance ◽  
Problem Solution ◽  
Heating Rates ◽  
Carbon Gasification ◽  
Kinetics Of

This study presents experimental studies of charcoal gasification with CO2 at different heating rates (1, 5, 10, 20, and 50 K min−1). The kinetics of the reaction C + CO2 under pore-diffusion control is studied. We propose a new method for the proper determination of activation energy during the processing of thermogravimetric curves of porous carbon gasification under conditions of pore-diffusion resistance. The results of the inverse kinetic problem solution are compared with different hypotheses about the regime of the investigated heterogeneous reaction process (kinetic, diffusion, pore-diffusion). The change of reaction regimes from kinetic to diffusion is detected during charcoal gasification at different heating rates. At heating rates of 5–20 K min−1, the values of activation energy of carbon gasification reaction in the carbon dioxide atmosphere, obtained by the proposed method, closely match the data found in the previous studies. The use of diffusion models in the processing of thermogravimetric curves determines the conditions under which conventional kinetic models fail to provide adequate information about the temperature dependence of the heterogeneous reaction rate.

Kinetic Study of the Pyrolysis of Formaldehyde

1972 ◽  
Vol 50 (7) ◽  
pp. 992-998 ◽  
Author(s):  
C. J. Chen ◽  
D. J. McKenney
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Kinetic Study ◽  
Pressure Range ◽  
Heterogeneous Reaction ◽  
Experimental Results ◽  
Arrhenius Parameters ◽  
Rate Laws ◽  
Kinetics Of

Kinetics of the thermal decomposition of pure formaldehyde were studied over a temperature range of 466–516 °C and a pressure range of ~ 50–160 Torr. Arrhenius parameters and rate laws were determined for carbon monoxide, hydrogen and methanol as follows:[Formula: see text]A mechanism is postulated which is qualitatively consistent with the experimental results but the activation energy for reaction 1[Formula: see text]is ~15 kcal/mol lower than predicted from recent thermochemical data, suggesting the possibility of a heterogeneous reaction.

Annealing the Defects in a-Si:H Under Illumination

1993 ◽  
Vol 297 ◽  
Author(s):  
Helena Gleskova ◽  
P.A. Morin ◽  
S. Wagner
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Deep Level ◽  
Hydrogenated Amorphous Silicon ◽  
Electron Hole ◽  
Single Carrier ◽  
Hydrogenated Amorphous ◽  
Kinetics Of ◽  
Hole Recombination

The results of a study of the kinetics of the light-induced annealing of the deep-level defects in hydrogenated amorphous silicon (a-Si:H) are presented. They show that at elevated temperatures illumination increases the rate of annealing compared to annealing in the dark. We also detected light-induced annealing at room temperature. On the basis of a model in which the defects are generated by electron-hole recombination and annealing occurs through the action of a single carrier, we found values of 0.86 eV for the activation energy of the light-induced generation coefficient γ-1, and 1.23 eV for the light-induced annealing prefactor λ

Effects of salts on the kinetics of oxidation of alkenes by thallic salts in aqueous solutions

1981 ◽  
Vol 46 (3) ◽  
pp. 693-700 ◽  
Author(s):  
Milan Strašák ◽  
Jaroslav Majer
Keyword(s):  
Aqueous Solutions ◽  
Phase Transfer ◽  
Heterogeneous Reaction ◽  
Qualitative Model ◽  
Kinetic Effect ◽  
Tetraalkylammonium Salts ◽  
Reaction Conditions ◽  
Kinetics Of Oxidation ◽  
Kinetics Of ◽  
Heterogeneous Reaction Conditions

The kinetics of oxidation of alkenes by thallic sulphate in aqueous solutions, involving the two reaction steps-the hydroxythallation and the dethallation - was studied, and the effect of salts on the kinetics was examined; this made it possible to specify more precisely the reaction mechanism and to suggest a qualitative model of the reaction coordinate. It was found that in homogeneous as well as in heterogeneous reaction conditions, the reaction can be accelerated appreciably by adding tetraalkylammonium salts. These salts not only operate as catalysts of the phase transfer, but also exert a significant kinetic effect, which can be explained with a simplification in terms of a stabilization of the transition state of the reaction.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

scholarly journals Fluoride Leaching of Titanium from Ti-Bearing Electric Furnace Slag in [NH4+]-[F−] Solution

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1176
Author(s):  
Fuqiang Zheng ◽  
Yufeng Guo ◽  
Feng Chen ◽  
Shuai Wang ◽  
Jinlai Zhang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Electric Furnace ◽  
Kinetic Equations ◽  
Surface Chemical ◽  
Leaching Rate ◽  
Surface Chemical Reaction ◽  
Mechanism And Kinetics ◽  
Semi Empirical ◽  
Kinetics Of ◽  
Furnace Slag

The effects of F− concentration, leaching temperature, and time on the Ti leaching from Ti-bearing electric furnace slag (TEFS) by [NH4+]-[F−] solution leaching process was investigated to reveal the leaching mechanism and kinetics of titanium. The results indicated that the Ti leaching rate obviously increased with the increase of leaching temperature and F− concentration. The kinetic equation of Ti leaching was obtained, and the activation energy was 52.30 kJ/mol. The fitting results of kinetic equations and calculated values of activation energy both indicated that the leaching rate of TEFS was controlled by surface chemical reaction. The semi-empirical kinetics equation was consistent with the real experimental results, with a correlation coefficient (R2) of 0.996. The Ti leaching rate reached 92.83% after leaching at 90 °C for 20 min with F− concentration of 14 mol/L and [NH4+]/[F−] ratio of 0.4. The leaching rates of Si, Fe, V, Mn, and Cr were 94.03%, 7.24%, 5.36%, 4.54%, and 1.73%, respectively. The Ca, Mg, and Al elements were converted to (NH4)3AlF6 and CaMg2Al2F12 in the residue, which can transform into stable oxides and fluorides after pyro-hydrolyzing and calcinating.

scholarly journals A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 331-363
Author(s):  
Eugeniy Lantcev ◽  
Aleksey Nokhrin ◽  
Nataliya Malekhonova ◽  
Maksim Boldin ◽  
Vladimir Chuvil'deev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Phase ◽  
Continuous Heating ◽  
Diffusion Creep ◽  
Hard Alloys ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact ◽  
Kinetics Of

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

scholarly journals Influence of Heterointerfaces on the Kinetics of Oxygen Surface Exchange on Epitaxial La1.85Sr0.15CuO4 Thin Films

2021 ◽  
Vol 11 (9) ◽  
pp. 3778
Author(s):  
Gene Yang ◽  
So-Yeun Kim ◽  
Changhee Sohn ◽  
Jong K. Keum ◽  
Dongkyu Lee
Keyword(s):  
Thin Films ◽  
Oxygen Vacancies ◽  
Elevated Temperatures ◽  
Surface Exchange ◽  
Electrical Conductivity Relaxation ◽  
Exchange Kinetics ◽  
Relaxation Curves ◽  
Kinetics Of ◽  
Oxygen Surface Exchange ◽  
Oxygen Surface

Considerable attention has been directed to understanding the influence of heterointerfaces between Ruddlesden–Popper (RP) phases and ABO3 perovskites on the kinetics of oxygen electrocatalysis at elevated temperatures. Here, we report the effect of heterointerfaces on the oxygen surface exchange kinetics by employing heteroepitaxial oxide thin films formed by decorating LaNiO3 (LNO) on La1.85Sr0.15CuO4 (LSCO) thin films. Regardless of LNO decoration, tensile in-plane strain on LSCO films does not change. The oxygen surface exchange coefficients (kchem) of LSCO films extracted from electrical conductivity relaxation curves significantly increase with partial decorations of LNO, whereas full LNO coverage leads to the reduction in the kchem of LSCO films. The activation energy for oxygen exchange in LSCO films significantly decreases with partial LNO decorations in contrast with the full coverage of LNO. Optical spectroscopy reveals the increased oxygen vacancies in the partially covered LSCO films relative to the undecorated LSCO film. We attribute the enhanced oxygen surface exchange kinetics of LSCO to the increased oxygen vacancies by creating the heterointerface between LSCO and LNO.

Atomically Smooth Ultrathin Oxide Layers on SI(113)

1999 ◽  
Vol 567 ◽  
Author(s):  
H.-J. Müssig ◽  
J. Dabrowski ◽  
S. Hinrich
Keyword(s):  
Elevated Temperatures ◽  
Oxidation Mechanism ◽  
Dissociative Chemisorption ◽  
Initial Oxidation ◽  
Precursor State ◽  
Oxide Layers ◽  
Adsorption Sites ◽  
Molecular Precursor ◽  
Diffusion Paths ◽  
Ultrathin Oxide

ABSTRACTWe report the first direct observation of dissociative chemisorption of oxygen molecules on a silicon surface at room temperature via a molecular precursor state. We link this to the fact that smooth oxide layers can be grown easily on Si(113). The process of initial oxidation is discussed in terms of surface diffusion paths and surface stress. First ab initiocalculations help elucidate the favored adsorption sites and the oxidation mechanism. Experimental evidence was found for bond geometries resulting in the quasi-epitaxial growth of a chemisorption layer on the substrate at elevated temperatures (600°C). In contrast to the first stages of Si(001) oxidation, neither defects nor the ejection of Si atoms plays a significant role during the initial oxidation of Si(113).

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