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Calculated Activation Energy (calculated + activation_energy)
Selected AbstractsStructural, electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman techniqueCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006H. Karaa Abstract Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X-Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 109 to 6.5 × 105 ,-cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as-grown, 36 and 472 meV for as-implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (IPC) and illumination intensity (,) was studied and it was observed that the relation obeys the power law, IPC ,,n with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as-grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge-implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A novel photochromic time,temperature indicator to support cold chain managementINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2010Judith Kreyenschmidt Summary A detailed investigation of the behaviour of a new printable photochromic time,temperature indicator (TTI) was conducted to characterise its properties under specific temperature conditions and to analyse the influence of ultra violet (UV) light irradiation (activation) on the discolouration process. The reproducibility of the charging process and the discolouration process of the TTI were analysed. For different charging times the calculated activation energies based on the Arrhenius model ranged from 23.2 to 25.3 kcal mol,1 depending on the UV light irradiation (charging time). A quality contour diagram was established to define the appropriate charging time for different kinds of products. Due to the possibility of defining the shelf life of a TTI by different charging times, this novel TTI constitutes a reliable tool to monitor the cold chains of a broad range of food products on their way from production to consumption. [source] Thermal, phase transition and spectral studies in erythromycin pseudopolymorphs: dihydrate and acetone solvateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006Zhanzhong Wang Abstract The thermal, phase transition and spectral studies of erythromycin A dihydrate and acetone solvate were performed by Differential Scanning calorimetry (DSC), Thermo Gravimetry (TG-DTA), X-Ray Powder Diffraction (XRPD) and Fourier Transform Infra-Red (FTIR) spectrum. The non-thermal kinetic analysis of erythromycin A dihydrate was carried out by DSC at different heating rates in dynamic nitrogen atmosphere. The result showed that heating rate has substantial influence on the thermal behavior of erythromycin dihydrate. The Arrhenius parameters were estimated according to the Kissinger method. Corresponding to dehydration of dihydrate, melting of dehydrated dihydrate, phase transition from dehydrated dihydrate to anhydrate, and melting of anhydrate, the calculated activation energy were 39.60, 269.85, 261.23, and 582.16 kJmol,1, the pre-exponential factors were 3.46 × 103, 8.06 × 1032, 9.23 × 1030, and 7.29 × 1063 s,1, respectively. Ozawa method was used to compare activation energy values calculated by Kissinger method. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transesterification for biodiesel production catalyzed by combined lipases: Optimization and kineticsAICHE JOURNAL, Issue 6 2010Yun Liu Abstract Preparation of biodiesel from waste cooking oil catalyzed by combined lipases in tert -butanol medium was investigated. Several crucial parameters affecting biodiesel yield were optimized by response surface methodology, such as dosage of combined lipases of Novozym 435 and Lipozyme TLIM, weight ratio of Novozym 435 to Lipozyme TLIM, amount of tert -butanol, reaction temperature, and molar ratio of oil to methanol. Under the optimized conditions, the highest biodiesel yield was up to 83.5% The proposed model on biodiesel yield had a satisfactory coefficient of R2 (= 94.02%), and was experimentally verified. The combined lipases exhibited high-operational stability. After 30 cycles (300 h) successively, the activity of combined lipases maintained 85% of its original activity. A reaction kinetic model was proposed to describe the system and deduced to be a pseudo-first-order reaction, and the calculated activation energy was 51.71 kJ/mol. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Analysis of Nanocrystalline and Microcrystalline ZnO Sintering Using Master Sintering CurvesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006Kevin G. Ewsuk Master sintering curves were constructed for dry-pressed compacts composed of either a nanocrystalline or a microcrystalline ZnO powder using constant heating rate dilatometry data and an experimentally determined apparent activation energy for densification of 268±25 and 296±21 kJ/mol, respectively. The calculated activation energies for densification are consistent with one another, and with values reported in the literature for ZnO densification by grain boundary diffusion. Grain boundary diffusion appears to be the single dominant mechanism controlling intermediate-stage densification in both the nanocrystalline and the microcrystalline ZnO during sintering from 65% to 90% of the theoretical density (TD). Based on both the consistency of the calculated activation energy as a function of density and the narrow dispersion of the sintering data about the master sintering curve (MSC) for the nanocrystalline ZnO, there is no evidence of either significantly enhanced surface diffusion or grain growth during sintering relative to the microcrystalline ZnO. The MSC constructed for the nanocrystalline ZnO was used to design time,temperature profiles to successfully achieve four different target sintered densities on the MSC, demonstrating the applicability of the MSC theory to nanocrystalline ceramic sintering. The most significant difference in sintering behavior between the two ZnO powders is the enhanced densification in the nanocrystalline ZnO powder at shorter times and lower temperatures. This difference is attributed to a scaling (i.e., particle size) effect. [source] | ||||||||||