Papers by Keyword: Activation Energy

Abstract: One of the potential applications of TiO₂ is its use in gas sensor technology. The aim of this work was to study the gas sensing properties of TiO₂ thin films in combination with the effect of post-deposition annealing treatment. Titanium dioxide thin films with thickness 100 nm were prepared by the reactive dc magnetron sputtering. The thin films were deposited on sapphire substrate from a titanium target in an oxygen atmosphere. The samples were then post-annealed in air in the temperature range 600 °C 1000 °C. Crystal structure, surface topography and absorption edge of the thin films have been studied by X-ray Diffraction technique, Atomic Force Microscopy and UV-VIS Spectroscopy. It was found that the phase gradually changed from anatase to rutile, the grain size and roughness tended to increase with increasing post-annealing temperature. The effect of these factors on gas sensing properties was discussed. For electrical measurements comb-like Pt electrodes were prepared by standard photolithography and the films were exposed to different concentrations of H₂ gas up to 10000 ppm in synthetic air at various operating temperatures from 200 °C to 350 °C.

Abstract: A quaternary Ni₈₆Cr₇Si₄Fe₃ amorphous alloy was synthesized by melt spinning technique. Surface modification was done by electron beam melting (EBM), neutron irradiation and γ-rays. Microstructure of as cast, annealed and modified samples was examined by scanning electron microscope. Crystallization behavior was studied by annealing the samples in vacuum at different temperatures in the range 773-1073 K. Techniques of X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for characterization. Differential scanning calorimetry (DSC) was conducted at various heating rates in the range 10-40 K/min. Thermal parameters like glass transition temperature T_g, crystallization temperature T_x, supercooled liquid region ΔT_x and reduced glass transition temperature T_rg were measured. The Ni₈₆Cr₇Si₄Fe₃ alloy exhibits wide supercooled liquid region of 60 K indicating good thermal stability. The activation energy was calculated to be 160±4 kJ/mol using Kissinger and Ozawa equations respectively which indicates high resistance against crystallization. The XRD results of the samples annealed at 773 K, 923 K, 973 K and 1073 K/20 min show nucleation of Ni₂Cr₃ and NiCrFe crystalline phases. Vickers microhardness of the as cast ribbon was measured to be 680.. About 30-50 % increase in hardness was achieved by applying EBM technique.

Abstract: Due to the depletion of high-quality iron ore, it is becoming ever more urgent to involve the ores which, for some reason or other, could not be used in metallurgy, or were used in limited quantities. For example, the siderite ores of Bakalsk deposit (Chelyabinsk region, Russia, stocks of more than 1 billion tons) are of very limited use in the blast-furnace practice because of the relatively low iron content (29% on average) and high magnesium oxide content (11-15%). At present, the technology of obtaining calcined siderite concentrate (CSC) from the ores of Bakalsk deposit includes raw ore roasting (fractions 10 - 60 mm) in blast furnaces at temperatures above 1000⁰С, and dry magnetic separation.

Abstract: Hydrolysis of sodium borohydride is regarded as a promising technology to produce pure hydrogen in portable fuel cell fields. In this paper, Ce is examined to be a better co-catalyst than Ni and Fe for the attapulgite clay (AT)-supported cobalt-boride (Co-B) catalyst. Factors, such as solution temperature, NaBH4 concentration and NaOH concentration on performance of these catalysts in hydrolysis of sodium borohydride are investigated. Furthermore, characteristics of these AT-supported catalysts are studied using SEM and XRD. Activation energy of hydrogen generation using such catalysts is estimated to be 37.02 kJ/mol.

Abstract: New in-situ 3DXRD results obtained since the last Rex&GG conference are presented and discussed. This includes: Documentation of the formation of nuclei with new orientations, determination of apparent activation energies for individual bulk grains during recrystallization and evolution in the 3D microstructure during grain growth.

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.

Abstract: In this paper, modelling and plotting of recrystallization curves of copper-titanium powder materials with titanium content of 0.5%, porosity 5% and 10%. The mathematical model that describes an influence of temperature, degree of deformation, strain rate, initial grain size and porosity to grain size after deformation has developed. The interconnection of deforming parameters and structure has presented by function of several variables with analytical expression obtained by method of undetermined coefficients based on experimental data. Theoretical recrystallization curves for copper-titanium powder materials with different porosity have plotted. It has established that porosity decelerates the kinetics of structure formation during dynamical softening of porous powder materials.

Abstract: In recent past, a linear regression model to predict the activation energy (Qrex) and kinetics of static recrystallisation for hot-deformed austenite was developed based on stress relaxation test results of over 40 different carbon steels. The model is able to predict satisfactorily the static recrystallisation (SRX) kinetics of common carbon steel grades (including microalloyed steels) and also several special steel grades. In this study, the main effects of seven alloying elements, viz., C, Mn, Cr, Ni, Mo, Nb and V, on the activation energy of recrystallisation were further examined by using eight experimental steels based on an orthogonal Taguchi L8 matrix. All steels contained constant additions of B, Ti and Si. Even though originally intended for studies on phase transformation characteristics and hardenability under direct quenching conditions, the L8 matrix steels were suitably employed for further validation of the SRX regression model. In addition, the SRX characteristics and kinetics of a set of new steel compositions including C-Mn, C-Mn-Nb and C-Mn-Nb-Ti types were examined in the light of model equations, which further confirm the suitability of the regression model.

Abstract: The influence of aluminum doping on the ionic conductivities and phase transition in the La2Mo2–xAlxO9-δ(x = 0.1, 0.2, 0.3) oxide-ion conductors has been investigated by XRD, DSC and dielectric relaxation measurements. The results indicate that the solubility of Al3+ in La2Mo2O9 sample is about 10mol%, Al3+ can not suppress the α/β phase transition in the La2Mo2O9, and the aluminum substituted La2Mo2O9 has a higher conductivity in whole temperature than that of pure La2Mo2O9.

Abstract: High-temperature creep experiments were performed on a Cu-2.8 ат.% Co solid solution. Cylindrical foils of 18 micrometers thickness were used for this purpose. Creep tests were performed in a hydrogen atmosphere in the temperature range of about from 1233 K to 1343 K and at stresses lower than 0.25 MPa. For comparison, a foil of pure copper and Cu-20 at.% Ni solid solution were investigated on high temperature creep. Measurements on the Cu foil showed classical diffusional creep behavior. The activation energy of creep was defined and turned out to be equal 203 kJ/mol, which is close to the activation energy of bulk self-diffusion of copper. There was a significant increase in activation energy for the Cu-20 at.% Ni solid solution. Its activation energy was about 273 kJ/mol. The creep behavior of Cu-Co solid solution was more complicated. There were two stages of diffusional creep at different temperatures. The extremely large activation energy (about 480 kJ/mol) was determined at relatively low temperature and a small activation energy (about 105 kJ/mol) was found at high temperatures. The creep rate of Cu-Co solid solution was lower than that of pure copper at all temperatures. In addition, the free surface tension of Cu-2.8 ат.% Co was measured at different temperatures from 1242 K to 1352 K. The surface tension increases in this temperature range from 1.6 N/m to 1.75 N/m. There were no features on the temperature dependence of the surface tension.