Low activation energies for interstitial oxygen conduction in the layered perovskites La1+xSr1−xInO4+δ

In the present work the results of theoretical analysis of the process of diffusion of covalently bonded atoms (interstitial oxygen atoms) in Si1-xGex alloys are presented. The diffusion coefficient (activation energy and pre-exponential factor) was calculated by means of quantum-chemical simulations (Hartree–Fock, NDDO, PM5) and the dependences of the activation energy and pre-exponential factor on Ge atoms concentration (x) were analyzed with the use of the percolation theory. The study has revealed that the diffusivity of impurities (defects) in alloys can decrease considerably at low concentration (x<0.05) of a minor alloy component and this variation results from the fact that the pre-exponential factor depends on the concentration of component elements of the alloy. The alloy-induced decrease in the pre-exponential factor is associated with removal of the degeneracy of the number of equivalent diffusion paths. It is found that a sharp decrease in the pre-exponential factor causes experimentally observed decreases in the coefficient of diffusion of interstitial oxygen atoms and in the rate of formation of oxygen thermal donors in Si1‑xGex crystals at x~0.01.

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Understanding Reactivity at Very Low Temperatures: The Reactions of Oxygen Atoms with Alkenes

Science ◽

10.1126/science.1142373 ◽

2007 ◽

Vol 317 (5834) ◽

pp. 102-105 ◽

Cited By ~ 105

Author(s):

H. Sabbah ◽

L. Biennier ◽

I. R. Sims ◽

Y. Georgievskii ◽

S. J. Klippenstein ◽

...

Keyword(s):

Low Temperatures ◽

Oxygen Atoms

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High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽

10.3390/met11040581 ◽

2021 ◽

Vol 11 (4) ◽

pp. 581

Author(s):

Abdulhakim A. Almajid

Keyword(s):

Activation Energy ◽

Aluminum Alloy ◽

High Temperature ◽

Threshold Stress ◽

Activation Energies ◽

Temperature Deformation ◽

High Temperature Range ◽

Temperature Range ◽

True Activation Energy ◽

Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

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Effect of CaO on catalytic combustion of semi-coke

Green Processing and Synthesis ◽

10.1515/gps-2021-0002 ◽

2021 ◽

Vol 10 (1) ◽

pp. 011-020

Author(s):

Luyao Kou ◽

Junjing Tang ◽

Tu Hu ◽

Baocheng Zhou ◽

Li Yang

Keyword(s):

Activation Energy ◽

Apparent Activation Energy ◽

Combustion Rate ◽

Activation Energies ◽

Combustion Reaction ◽

Tg Analysis ◽

Conversion Rates ◽

Apparent Activation Energies ◽

Ozawa Integral Method ◽

Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

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The Effect of α-Al(MnCr)Si Dispersoids on Activation Energy and Workability of Al-Mg-Si-Cu Alloys during Hot Deformation

Advances in Materials Science and Engineering ◽

10.1155/2020/3471410 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12

Author(s):

Xiaoguo Wang ◽

Jian Qin ◽

Hiromi Nagaumi ◽

Ruirui Wu ◽

Qiushu Li

Keyword(s):

Activation Energy ◽

Aluminum Alloys ◽

Constitutive Equation ◽

Hot Deformation ◽

Flow Instability ◽

Void Formation ◽

Activation Energies ◽

Compression Tests ◽

Softening Mechanism ◽

Dynamic Softening

The hot deformation behaviors of homogenized direct-chill (DC) casting 6061 aluminum alloys and Mn/Cr-containing aluminum alloys denoted as WQ1 were studied systematically by uniaxial compression tests at various deformation temperatures and strain rates. Hot deformation behavior of WQ1 alloy was remarkably changed compared to that of 6061 alloy with the presence of α-Al(MnCr)Si dispersoids. The hyperbolic-sine constitutive equation was employed to determine the materials constants and activation energies of both studied alloys. The evolution of the activation energies of two alloys was investigated on a revised Sellars’ constitutive equation. The processing maps and activation energy maps of both alloys were also constructed to reveal deformation stable domains and optimize deformation parameters, respectively. Under the influence of α dispersoids, WQ1 alloy presented a higher activation energy, around 40 kJ/mol greater than 6061 alloy’s at the same deformation conditions. Dynamic recrystallization (DRX) is main dynamic softening mechanism in safe processing domain of 6061 alloy, while dynamic recovery (DRV) was main dynamic softening mechanism in WQ1 alloy due to pinning effect of α-Al(MnCr)Si dispersoids. α dispersoids can not only resist DRX but also increase power required for deformation of WQ1 alloy. The microstructure analysis revealed that the flow instability was attributed to the void formation and intermetallic cracking during hot deformation of both alloys.

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New experiments on the relationship between light-induced defects and photoconductivity degradation

MRS Proceedings ◽

10.1557/proc-664-a12.2 ◽

2001 ◽

Vol 664 ◽

Cited By ~ 2

Author(s):

Stephan Heck ◽

Howard M. Branz

Keyword(s):

Activation Energy ◽

Defect Density ◽

Activation Energies ◽

Dangling Bond ◽

Fast Recovery ◽

Slow Recovery ◽

Degradation Model ◽

Induced Defects ◽

The Relationship ◽

Hydrogenated Amorphous

ABSTRACTWe report experimental results that help settle apparent inconsistencies in earlier work on photoconductivity and light-induced defects in hydrogenated amorphous silicon (a-Si:H) and point toward a new understanding of this subject. After observing that light-induced photoconductivity degradation anneals out at much lower T than the light-induced increase in deep defect density, Han and Fritzsche[1] suggested that two kinds of defects are created during illumination of a-Si:H. In this view, one kind of defect degrades the photoconductivity and the other increases defect sub-bandgap optical absorption. However, the light-induced degradation model of Stutzmann et al.[2] assumes that photoconductivity is inversely proportional to the dangling-bond defect density. We observe two kinds of defects that are distinguished by their annealing activation energies, but because their densities remain in strict linear proportion during their creation, the two kinds of defects cannot be completely independent.In our measurements of photoconductivity and defect absorption (constant photocurrent method) during 25°C light soaking and during a series of isochronal anneals between 25 < T < 190°C, we find that the absorption measured with E ≤1.1 eV, first increases during annealing, then exhibits the usual absorption decrease found for deeper defects. The maximum in this absorption at E ≤1.1eV occurs simultaneously with a transition from fast to slow recovery of photoconductivity. The absorption for E ≤1.1eV shows two distinct annealing activation energies: the signal rises with about 0.87 eV and falls with about 1.15 eV. The 0.87 eV activation energy roughly equals the activation energy for the dominant, fast, recovery of photoconductivity. The 1.15 eV activation energy roughly equals the single activation energy for annealing of the light-induced dangling bond absorption.

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On the catalytic dehydrogenation of naphthenes II. Competition experiments and energies of C-H bonds

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1947.0078 ◽

1947 ◽

Vol 190 (1022) ◽

pp. 309-328 ◽

Cited By ~ 2

Keyword(s):

Activation Energy ◽

Active Sites ◽

Catalyst Surface ◽

Resonance Energy ◽

Activation Energies ◽

Theoretical Treatment ◽

Catalytic Dehydrogenation ◽

Simple Relationship ◽

Hydrogen Atoms ◽

Methyl Cyclohexane

The rates of dehydrogenation in competition experiments using mixtures of two naphthenes, or a naphthene and a cyclic mono-olefine or two cyclic mono-olefines, have been examined theoretically and experimentally for the stationary state conditions. Provided the two reactants can occupy the same sites on the catalyst surface, then the ratio of the rates should be directly proportional to the ratio of the partial pressures at any instant. Theory suggests that a constant which can be derived from these competition experiments should be independent of the overall pressures, or of the initial ratio of concentrations or of the overall extent of dehydrogenation. Further, the ratio of the rates in competition should bear no simple relationship to the ratio of the individual rates alone, but should be related to the slopes of the 1/rate against 1/pressure plot for the two components considered separately. Moreover, the constant should be a ratio of two functions each of which is characteristic of one of the naphthenes. The theoretical conclusions have been confirmed experimentally which proves either that the groups of active sites on the catalyst surface are widely separated or that any set of sites is available for the reaction of any molecular species, and no interference takes place between naphthene molecules adsorbed on adjacent sites. Proof that a naphthene and cyclohexene are dehydrogenated on the same sites is supplied by the observation that a constant is obtained when different mixtures of cyclohexene and trans -1:4-dimethyl cyclohexane are allowed to compete for the surface. The ratios for methyl, ethyl, the three dimethyl and the three trimethyl cyclohexanes in competition with cyclohexane have been accurately determined at temperatures of 400 and 450° C. From the constants so derived the activation energy differences for the removal of the first pair of hydrogen atoms has been obtained. These values are discussed in terms of the possible transition complexes, and it is shown that the reaction proceeds by the loss of a pair of hydrogen atoms simultaneously and not by a half-hydrogenated state mechanism. Using these activation energies and the experimentally found overall activation energy of 36 kcal./g. mol., the resonance energy per resonating structure was determined as 1-73 kcal. This is in good agreement with the energies of C-H bonds in alkyl radicals (2-2 kcal./g.mol./ resonating structure). The theoretical treatment suggests that the weakest C-H link in methyl cyclohexane should be in the three position to the methyl group. A study of the activation energies involved shows that the methyl cyclohexene produced from methyl cyclohexane is not 1-methyl-1-cyclohexene, thus confirming the theoretical deduction.

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Improvement in Carbonization Efficiency of Cellulosic Fibres Using Silylated Acetylene and Alkoxysilanes

Fibers ◽

10.3390/fib7100084 ◽

2019 ◽

Vol 7 (10) ◽

pp. 84

Author(s):

Maria Mironova ◽

Igor Makarov ◽

Lyudmila Golova ◽

Markel Vinogradov ◽

Georgy Shandryuk ◽

...

Keyword(s):

Activation Energy ◽

Thermal Decomposition ◽

Thermal Behavior ◽

Comparative Studies ◽

Decomposition Reaction ◽

Activation Energies ◽

Composite Fibers ◽

Carbon Yield ◽

Pyrolysis Reaction ◽

Cellulosic Fibres

Comparative studies of the structure and thermal behavior of cellulose and composite precursors with additives of silyl-substituted acetylene and alkoxysilanes were carried out. It is shown that the introduction of silicon-containing additives into the cellulose matrix influenced the thermal behavior of the composite fibers and the carbon yield after carbonization. Comparison of the activation energies of the thermal decomposition reaction renders it possible to determine the type of additive and its concentration, which reduces the energy necessary for pyrolysis. It is shown that the C/O ratio in the additive and the presence of the Si–C bond affected the activation energy and the temperature of the beginning and the end of the pyrolysis reaction.

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Oxygen diffusion in amorphous and partially crystalline gallium oxide

Physical Chemistry Chemical Physics ◽

10.1039/c8cp06439c ◽

2019 ◽

Vol 21 (8) ◽

pp. 4268-4275 ◽

Cited By ~ 2

Author(s):

Alexandra von der Heiden ◽

Manuel Bornhöfft ◽

Joachim Mayer ◽

Manfred Martin

Keyword(s):

Activation Energy ◽

Diffusion Coefficients ◽

Low Temperatures ◽

Oxygen Diffusion ◽

Gallium Oxide ◽

Tracer Diffusion ◽

Tof Sims ◽

Tracer Diffusion Coefficients ◽

Oxygen Tracer

We established a TTT diagram of crystallisation of gallium oxide. Determination of oxygen tracer diffusion coefficients by IEDP/ToF-SIMS allowed us to access the activation energy for amorphous GaO1.5 at low temperatures.

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INFLUENCE OF THE CROSSLINK STRUCTURE ON THE ACTIVATION ENERGY CALCULATED UNDER THERMO-OXIDATIVE CONDITIONS

Rubber Chemistry and Technology ◽

10.5254/rct-17-83714 ◽

2018 ◽

Vol 91 (1) ◽

pp. 205-224 ◽

Cited By ~ 1

Author(s):

Richard J. Pazur ◽

T. Mengistu

Keyword(s):

Activation Energy ◽

Zinc Oxide ◽

High Temperature ◽

Oxidation Process ◽

Activation Energies ◽

Structure Stability ◽

Temperature Oxidation ◽

Network Chain ◽

Temperature Activation ◽

Sulfur Donor

ABSTRACT A series of six carbon black reinforced brominated poly(isobutylene-co-isoprene) (BIIR) compounds has been developed varying only in cure system type: sulfur, sulfur donor, zinc oxide, peroxide, phenolic resin, and ionic. Compounds were aged from room temperature up to 115 °C, and hardness, mechanical properties, and network chain density were measured. Non-Arrhenius behavior was observed due to data curvature from 70 to 85 °C. The oxidation process was adequately described by assigning low (23–85 °C) and high (85–115 °C) temperature regimes. Heterogeneous aging due to diffusion limited oxygen (DLO) occurred for heat aging above 85 °C, and all measured responses except tensile strength were strongly affected, causing lower activation energies. The activation energy for the high temperature oxidation process is in the range of 107 to 133 kJ/mol in the following ascending order: zinc oxide, ionic, sulfur donor, sulfur, peroxide, and resin. The midpoint of the high temperature activation energies is of the same order as the BIIR and poly(isobutylene) elastomers. The low temperature activation energy is in the range of 55–60 kJ/mol and is likely due to a combination of oxidative chain scission (crosslink density loss) and crosslinking recombination (network building) reactions. Apart from the crosslink structure stability, the presence of unsaturation along the polymer chain after vulcanization affects the high temperature activation energy.

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