Papers by Keyword: Activation Energy

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Authors: Xiao Yang Gong, Zhi Feng Gu, Tong Wei Li
Abstract: Studies of ion motion in crystalline and glassy materials, Jonscher power law, which was frequently referred to as the so-called universal dynamic response (UDR) is an effective method, but the power law exponents obtained from curve-fitting are sensitively affected by the frequency window employed in the analysis. So how to choose frequency window and which window can truly describe the nature of the materials, are important for every researcher. In this paper, through analyzing the experimental data of frequency dependence of ac conductivity in 50Li2O–50P2O5 glasses, a simple method to choose frequency window was found and further discussions indicated our choice was reasonable.
Authors: Vsevolod I. Razumovskiy, Pavel A. Korzhavyi, Andrei V. Ruban
Abstract: Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).
Authors: Hiroshi Yukawa, T. Nambu, Yoshihisa Matsumoto
Abstract: The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. It is found that the hydrogen solubility decreases by the addition of ruthenium, tungsten or molybdenum into niobium. The mobility for hydrogen diffusion during hydrogen permeation is estimated from the linear relationship between the normalized hydrogen flux, , and the product of the hydrogen concentration and the difference of hydrogen chemical potential, . It is found that the mobility for hydrogen diffusion during hydrogen permeation is larger for Nb-based alloys than pure niobium, especially at low temperature. The activation energy of the mobility for hydrogen diffusion decreases by the addition of ruthenium, tungsten or molybdenum into niobium.
Authors: Shahram Ahmadi, Ali Shokuhfar, M.R. Abotalebi, Arash Rezaei
Abstract: The precipitation of T1 phase during the ageing of an Al- Li- Cu -Zr alloy sheet was studied by DSC (Differential Scanning Calorimetric) technique. Results showed that precipitation of T1 phase occurred in temperature range of 250°C to 300°C whereas its dissolution occurred within the temperature of 450°C to 530°C. Furthermore, activation energies for precipitation and dissolution of T1 phase were determined 122.1 kJ/mol and 130.3 kJ/mol, respectively.
Authors: Seong Ho Son, Do Won Chung, Dae Chol Kwon, Hong Kee Lee
Abstract: The thin film resistors such as Ni-Cr alloy could be formed by the electrodeposition method for embedded passive device in printed circuit board. A kinetic study on the electrodeposition of nickel-chromium alloy on copper has been performed using a rotating disk geometry. Activation energies of nickel and chromium in the temperature range between 15°C and 35°C were 8.9kcal/mole and 3.5kcal/mole, respectively. The electrodeposition rate of nickel seems to be controlled partly by electrochemical reaction and partly by mass transport, namely mixed controlled. However, that of chromium seems to be controlled by mass transport. As the amount of chromium in deposit increased, the electric resistance of deposit surface increased. The maximum electric resistance of nickel-chromium alloy deposit was 78.6Ω /□.
Authors: Tian Bo Yu, Niels Hansen
Abstract: A model is suggested to analyze recovery kinetics of heavily deformed aluminum. The model is based on the hardness of isothermal annealed samples before recrystallization takes place, and it can be extrapolated to longer annealing times to factor out the recrystallization component of the hardness for conditions where recovery and recrystallization overlap. The model is applied to the isothermal recovery at temperatures between 140 and 220°C of commercial purity aluminum deformed to true strain 5.5. EBSD measurements have been carried out to detect the onset of discontinuous recrystallization. Furthermore, comparison between the present model and a similar recently developed recovery model is made, and the result is discussed.
Authors: Chen Dong
Abstract: The diffusion behaviors of Fe adatom on Fe nanoparticles with three different sizes have been explored by molecular dynamics (MD) simulation. The activation energies and pre-exponential factors are extracted from the Arrhenius relation. The MD simulation shows that the hopping, exchange and direct/indirect crossing mechanisms contribute to the diffusion of Fe adatom on Fe nanoparticles and the diffusion behaviors do not show a significant nanosize effect.
Authors: Yan Huang
Abstract: Solute drag theory is critically revisited and an alternative approach is presented to account for the effect of solute elements on grain boundary migration during annealing. A fundamental new concept is introduced in the model that, in the linear range of irreversible thermodynamics, solute atoms segregated in a grain boundary will not lag behind when the boundary migrates. While lagging behind is the very essential assumption for the solute drag theory. Instead of blaming the lagging behind, the mobility drop due to solute addition is attributed to the decrease in boundary energy as a result of boundary segregation. According to this model, grain boundary mobility is dependent on solute concentration rather than migration rate. The predictions of the model are compared with experimental results, with a good agreement.
Authors: Fu Gao Wei, Kaneaki Tsuzaki, Toru Hara
Abstract: A new method has been developed to determine the activation energy for hydrogen desorption from steels by means of thermal desorption spectrometry (TDS). This method directly fits the Kissinger’s reaction kinetic formula dX/dt=A(1-X)exp(-Ed/RT) to experimentally measured thermal desorption spectrum and best fit yields the activation energy (Ed) and the value of constant A. It has been proven that this new method is applicable to precise measurement of the activation energy for hydrogen desorption from incoherent TiC particle, coherent TiC precipitate, grain boundary and dislocation in 0.05C-0.20Ti-2.0Ni and 0.42C-0.30Ti steels.
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