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Arrhenius Law (Arrheniu + law)
Selected AbstractsCorrosion of Borosilicate Sealing Glasses for Molten Carbonate Fuel CellsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2003Maria J. Pascual The development of a new sealant for molten carbonate fuel cells (MCFC) requires a study of the attack of molten carbonates on selected materials. Silica and Pyrex® glasses have better corrosion resistance against molten carbonates than other glasses, but they have unsuitable thermal expansion coefficients. Comparisons have also been made between borosilicate glasses of suitable thermal expansion for sealants for MCFC and silica and Pyrex® glasses. The corrosion kinetics in molten carbonates follows two limiting relations and involves two corrosion mechanisms. The weight loss varied linearly with time, indicating a dissolution of the glass network at short times. Longer times show corrosion, depending on the square root of time, typical of a diffusion mechanism and indicating formation of a protective layer on the surface of the glass. The main crystalline corrosion product is lithium methasilicate. The glass-corrosion rate follows the well-known Arrhenius law. These studies used scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical analysis. A general corrosion mechanism of borosilicate glasses in molten carbonates is proposed. [source] Environmental dew point and skin and lip weatheringJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 5 2010C Devillers Abstract Xerosis represents a physiological response of the stratum corneum (SC) to environmental threats. The influence of the environmental dew point (DP) is not fully understood. This parameter is the air temperature at which the relative humidity is maximum. This study aimed to assess the relationship between the environmental DP and the water-holding capacity of the skin and lower lip vermilion. For comparison, SC property was evaluated after occlusive application of cooled and uncooled hydrogel pads. Electrometric measurements using a dermal phase meter (DPM) device were performed on the back of the hands, the cheeks and the lower lip of 40 healthy menopausal women. Assessments were performed in the outdoor conditions during winter and spring. The same measurements were recorded after hydrogel pads, at room temperature or cooled to 4 °C, were placed for 15 min on the test sites. The environmental DP was recorded at each evaluation time. The SC water-holding capacity was discretely influenced by the DP. In the open-air environmental conditions, a positive linear relationship was found on the cheeks between the DP and DPM values. The relationship was weaker on the lips. Conversely, a consistent increase in DPM values was recorded immediately after removal of the cooled and uncooled hydrogel pads. The observations made in the open-air testing conditions are consistent with the predicted events following the Arrhenius law. By contrast, the combination of cooling and occlusion by the hydrogel pads is responsible for the reverse effect on the SC. [source] Ascorbic acid destruction in aqueous model systems: an additional discussionJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2001Ana M Rojas Abstract The influence of different non-electrolytes (fructose, xylitol, glucose/mannitol mixture) and electrolytes (NaCl, KCl) on anaerobic L -ascorbic acid (AA) degradation in an aqueous model system (pH 3.5, aw 0.94) was studied to assess the effect on that reaction of substances commonly used to diminish the water activity of fruit or vegetable juices, as well as its relation with non-enzymatic browning (NEB) development, at processing (70, 80, 90,°C) and storage (24, 33, 45,°C) temperatures. AA degraded as a function of time with a behaviour that could be described by first-order kinetics at all temperatures studied, and activation energies could be calculated using the Arrhenius law. The presence of humectants enhanced AA destruction, with D -fructose promoting the fastest L -ascorbic acid destruction and browning development at processing temperatures. The influence of humectants on NEB seemed to determine differences between their influence on AA degradation. Water activity decrease by humectant addition produced higher AA stability in solution at storage temperatures. The differential effect of each humectant used to decrease the water activity seemed to be related to its influence on solvent structure. © 2001 Society of Chemical Industry [source] Hopping magnetoresistance in two-dimensional arrays of Ge/Si quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2006A. I. Yakimov Abstract The temperature and magnetic field dependences of the conductivity associated with hopping transport of holes over 2D arrays of Ge/Si quantum dots with various filling factors are studied experimentally. A transition from the Efros-Shklovskii law for the temperature dependence of hopping conductivity to the Arrhenius law with an activation energy equal to 1.0-1.2 meV is observed upon a decrease in temperature. The activation energy for the low-temperature conductivity increases with the magnetic field and attains saturation in fields exceeding 4 T. It is found that the magnetoresistance in layers of quantum dots is essentially anisotropic: the conductivity decreases in magnetic fields oriented perpendicular to a dot layer and increases in a field whose vector lies in the plane of the sample. The absolute values of magnetoresistance for transverse and longitudinal field orientations differ by two orders of magnitude. Effect of spin correlations on the hopping magnetoresistance is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Purely electronic transport and localization in the Bose glassANNALEN DER PHYSIK, Issue 12 2009M. Müller Abstract We discuss transport and localization properties on the insulating side of the disorder dominated superconductor-insulator transition, described in terms of the dirty boson model. Analyzing the spectral properties of the interacting bosons in the absence of phonons, we argue that the Bose glass phase admits three distinct regimes. For strongest disorder the boson system is a fully localized, perfect insulator at any temperature. At smaller disorder, only the low temperature phase exhibits perfect insulation while delocalization takes place above a finite temperature. We argue that a third phase must intervene between these perfect insulators and the superconductor. This conducting Bose glass phase is characterized by a mobility edge in the many body spectrum, located at finite energy above the ground state. In this insulating regime purely electronically activated transport occurs, with a conductivity following an Arrhenius law at asymptotically low temperatures, while a tendency to superactivation is predicted at higher T. These predictions are in good agreement with recent transport experiments in highly disordered films of superconducting materials. [source] An Improved Non-Isothermal Kinetic Model for Prediction of Extent of Transesterification Reaction and Degree of Randomness in PET/PEN BlendsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4-5 2008Mahdi Golriz Abstract An improved non-isothermal kinetic model was developed based on mass balance and Arrhenius laws using a second-order reversible reaction capable of predicting the extent of transesterification reaction (X) and the degree of randomness (RD) in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) blends prepared by a twin screw micro-compounder over a full composition range under different processing conditions. The experimental values of X and RD were determined by 1H-NMR and a direct relationship between them developed. The model constants were tuned by an optimization method using half of the experimental data, with the other half used for verification. Good agreement was found between the experimental and theoretical data in the verification stage and, therefore, it was concluded that the model is capable of predicting the extent of transesterification reaction with a high level of confidence for a wide range of processing conditions. Similarly to the experimental results, the model showed that, among all parameters affecting the extent of transesterification reaction, the time and temperature play the major role, whereas the blend composition does not have a significant role. [source] Effect of supercritical deposition synthesis on dibenzothiophene hydrodesulfurization over NiMo/Al2O3 nanocatalystAICHE JOURNAL, Issue 10 2009Mehrdad Alibouri Abstract The synthesis of two NiMo/Al2O3 catalysts by the supercritical carbon dioxide/methanol deposition (NiMo-SCF) and the conventional method of wet coimpregnation (NiMo-IMP) were conducted. The results of the physical and chemical characterization techniques (adsorption,desorption of nitrogen, oxygen chemisorption, XRD, TPR, TEM, and EDAX) for the NiMo-SCF and NiMo-IMP demonstrated high and uniform dispersed deposition of Ni and Mo on the Al2O3 support for the newly developed catalyst. The hydrodesulfurization (HDS) of fuel model compound, dibenzothiophene, was used in the evaluation of the NiMo-SCF catalyst vs. the commercial catalyst (NiMo-COM). Higher conversion for the NiMo-SCF catalyst was obtained. The kinetic analysis of the reaction data was carried out to calculate the reaction rate constant of the synthesized and commercial catalysts in the temperature rang of 543,603 K. Analysis of the experimental data using Arrhenius' law resulted in the calculation of frequency factor and activation energy of the HDS for the two catalysts. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | ||||||||||||||||