Note: Color development rate in dulce de leche

1995 ◽  
Vol 1 (2-3) ◽  
pp. 137-140 ◽  
Author(s):  
M.S. Pauletti ◽  
E. Castelao ◽  
N. Sabbag ◽  
Y S. Costa
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Formation Process ◽  
Arrhenius Equation ◽  
Development Rate ◽  
Sensorial Analysis ◽  
Color Formation ◽  
Color Development ◽  
Global Rate ◽  
Different Temperatures

The time necessary to obtain the characteristic dulce de leche color at different temperatures was studied. Samples were held at constant temperature until they reached a standard prescribed color. Sensorial analysis of the final color of the samples was performed in order to detect any difference. Results showed that color among samples was not significantly different (p = 0.95). Arrhenius equation was used to correlate the kinetics results. Variance analysis showed a very good correlation of experimental data (r2 = 0.98). The apparent activation energy values for both studied systems were similar (13.88–14.45 kcal mol–1) but somewhat smaller than those given by other authors for similar systems. The global rate constant value of color formation process at any temperature was slightly larger when the protein/carbohydrate ratio was higher.

scholarly journals Kinetics and thermodynamic properties related to the drying of 'Cabacinha' pepper fruits

2016 ◽  
Vol 20 (2) ◽  
pp. 174-180 ◽  
Author(s):  
Hellismar W. da Silva ◽  
Renato S. Rodovalho ◽  
Marya F. Velasco ◽  
Camila F. Silva ◽  
Luís S. R. Vale
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Free Energy ◽  
Thermodynamic Properties ◽  
Gibbs Free Energy ◽  
Removal Rate ◽  
Effective Diffusion ◽  
Drying Time ◽  
Three Samples ◽  
Different Temperatures

ABSTRACT The objective of this study was to determine and model the drying kinetics of 'Cabacinha' pepper fruits at different temperatures of the drying air, as well as obtain the thermodynamic properties involved in the drying process of the product. Drying was carried out under controlled conductions of temperature (60, 70, 80, 90 and 100 °C) using three samples of 130 g of fruit, which were weighed periodically until constant mass. The experimental data were adjusted to different mathematical models often used in the representation of fruit drying. Effective diffusion coefficients, calculated from the mathematical model of liquid diffusion, were used to obtain activation energy, enthalpy, entropy and Gibbs free energy. The Midilli model showed the best fit to the experimental data of drying of 'Cabacinha' pepper fruits. The increase in drying temperature promoted an increase in water removal rate, effective diffusion coefficient and Gibbs free energy, besides a reduction in fruit drying time and in the values of entropy and enthalpy. The activation energy for the drying of pepper fruits was 36.09 kJ mol-1.

Diffusion Coefficients of Interest for the Simulation of Heat Treatment in Rare-Earth Transition Metal Magnets

2012 ◽  
Vol 727-728 ◽  
pp. 163-168 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Experimental Data ◽  
Heat Treatment ◽  
Activation Energy ◽  
Rare Earth ◽  
Transition Metal ◽  
Impurity Atom ◽  
Diffusion Coefficients ◽  
Arrhenius Equation ◽  
Atom Diffusion ◽  
Essential Input

In the case of the modeling of sintering and heat treatments, the diffusion coefficients are an essential input. However, experimental data in the literature about diffusion coefficients for rare-earth transition metal intermetallics is scarce. In this study, the available data concerning diffusion coefficients relevant for rare-earth transition metal magnets are reviewed and commented. Some empirical rules are discussed, for example the activation energy is affected by the size of the diffusing impurity atom. Diffusion coefficients for Dy, Nd and Fe into Nd2Fe14B are given according an Arrhenius equation D=D0exp (-Q/RT). For Dy diffusion into Nd2Fe14B, Q 315 kJ/mol and D08 . 10-4m2/s.

scholarly journals Drying kinetics of baru flours as function of temperature

2018 ◽  
Vol 22 (10) ◽  
pp. 713-719 ◽  
Author(s):  
Douglas R. Reis ◽  
Fabrício B. Brum ◽  
Eduardo J. O. Soares ◽  
Jessiana R. Magalhães ◽  
Fabrício S. Silva ◽  
...  
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Food Industry ◽  
Nutritional Value ◽  
Effective Diffusivity ◽  
Drying Kinetics ◽  
Statistical Parameters ◽  
Noticeable Effect ◽  
Different Temperatures ◽  
Kinetics Of

ABSTRACT Several types of seeds have been initially used in the food industry due to the great potential that vegetable proteins have. Baru is a fruit commonly found in the Cerrado biome, having a high nutritional value. This paper aimed to determine and analyze the drying kinetics of whole and defatted baru almond flours at different temperatures. The flour resulting from almond milling was defatted using petroleum ether. The drying processes were performed at temperatures of 40, 50 and 60 ºC. The mathematical models of Page, Henderson and Pabis, Midilli & Kucuk, Thompson and Approximation of Diffusion were fitted to the experimental data. The results showed a noticeable effect of air temperature on the drying kinetics of whole and defatted baru almond flours. According to the statistical parameters of analysis, the models Midilli & Kucuk and Page were the ones with the best fits to the experimental data. The effective diffusivity values found ranged from 8.02 × 10–10 to 19.90 × 10–10 m2 s-1 and for the activation energy were 22.39 and 39.37 KJ mol-1 for whole and defatted almonds, respectively.

The Meyer–Neldel Rule in Conduction Mechanism of the Electrospun ZnO Nanofibers

NANO ◽  
2016 ◽  
Vol 11 (03) ◽  
pp. 1650025 ◽  
Author(s):  
Andrzej Stafiniak ◽  
Marek Tłaczała
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Conduction Mechanism ◽  
Deep Level ◽  
Electrical Measurements ◽  
Thermally Activated ◽  
Theoretical Assumptions ◽  
Different Temperatures ◽  
Zno Nanofibers ◽  
Improved Model

An analytical model describing the conductivity of ZnO nanofibers depending on the grains size is proposed. The research is based on the thermal dc electrical measurements of a single electrospun ZnO nanofiber calcined at different temperatures. In the our previous research, we showed that electrical conduction of ZnO nanofibers is mainly thermally activated. The activation energy of conductivity was strongly dependent on the grain size, which in turn depended on the calcination temperature. This could be due to migration of a point defect in the grain of ZnO and could change the carrier concentration. Our recent studies have shown that ZnO nanofibers behavior is consistent with the Meyer–Neldel rule. This indicates an exponential energy distribution of deep level traps in the material. Based on the theoretical assumptions and experimental data, the improved model of conductivity in a single ZnO nanofiber calcined at different temperatures was proposed.

scholarly journals Instantaneous activation energy of alkali activated materials

2019 ◽  
Vol 3 ◽  
pp. 121-123
Author(s):  
Shiju Joseph ◽  
Siva Uppalapati ◽  
Ozlem Cizer
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Reaction Rate ◽  
Arrhenius Equation ◽  
Isothermal Calorimetry ◽  
Traditional Methods ◽  
Cement Based Materials ◽  
Different Temperatures ◽  
Higher Temperature ◽  
Alkali Activated

Alkali activated materials (AAM) are generally cured at high temperatures to compensate for the low reaction rate. Higher temperature accelerates the reaction of AAM as in cement-based materials and this effect is generally predicted using Arrhenius equation based on the activation energy. While apparent activation energy is calculated from parallel isothermal calorimetry measurements at different temperatures, instantaneous activation energy is typically measured using a differential scanning calorimeter. Compared to the apparent activation energy, instantaneous activation energy has minimal effects on the microstructural changes due to the variation in temperature. In this work, the evolution of activation energy was determined by traditional methods and was compared with the instantaneous activation energy. It was found that while the activation energy changed with the progress of reaction over traditional methods, the instantaneous activation energy did not show any changes / or remained the same. The instantaneous activation energy was also found to be higher compared to the apparent activation energy determined with traditional methods.

Influence of the Temperature on the Diffusion Coefficient Value during the Cobalt Electrodeposition on Different Substrates

2014 ◽  
Vol 976 ◽  
pp. 144-147
Author(s):  
Nancy Ramos Lora ◽  
Luis Humberto Mendoza Huizar ◽  
Clara Hilda-Rios-Reyes ◽  
Carlos Andrés Galán-Vidal
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Temperature Effect ◽  
Glassy Carbon ◽  
Arrhenius Equation ◽  
Voltammetric Techniques ◽  
Different Temperatures ◽  
Cobalt Electrodeposition

Cobalt electrodeposition on palladium and glassy carbon was studied at different temperatures by using voltammetric techniques. Temperature effect on the diffusion coefficient value was analyzed. The results clearly showed that cobalt electrodeposition is a diffusioncontrolled process. The temperature effect on the values of the diffusion coefficient was analyzed through the Arrhenius equation. The value of the activation energy was calculated as 21.56 kJ mol-1and 25.73 kJ mol1for palladium and glassy carbon respectively.

Kinetics of Hydrothermal Decomposition of Potassium Feldspar with Calcium Hydroxide

2012 ◽  
Vol 549 ◽  
pp. 65-69 ◽  
Author(s):  
Yu Qin Liu ◽  
Hong Tu Xia ◽  
Hong Wen Ma
Keyword(s):  
Activation Energy ◽  
Kinetic Equation ◽  
Calcium Hydroxide ◽  
Arrhenius Equation ◽  
Hydrothermal Reaction ◽  
Potassium Feldspar ◽  
Different Temperatures ◽  
Temperature Ranges ◽  
Dissolution Ratio ◽  
Kinetics Of

The aegirine-augite syenite potash ore, taken from Changling, Luonan in Shannxi province, were hydrothermally decomposed over the temperature ranges of 533 K to 563 K using calcium hydroxide as additive. The dissolution ratio of the K2O at different reaction temperature and time was determined. Analysis of the experimental results revealed that the dissolution rate of potash ore satisfies the chemical reaction controlled kinetic equation. The rate constant of hydrothermal reaction at different temperatures was obtained. The activation energy was calculated using the Arrhenius equation. The hydrothermal decomposition mechanism of microcline was proposed.

scholarly journals Research of high-speed HFC-boriding kinetics

2021 ◽  
Vol 285 ◽  
pp. 07038
Author(s):  
Vladimir Malikov ◽  
Alexander Shegolev ◽  
Alexey Ishkov
Keyword(s):  
Activation Energy ◽  
Chemical Reactions ◽  
High Frequency ◽  
High Speed ◽  
Arrhenius Equation ◽  
Main Element ◽  
Kinetic Curves ◽  
Boride Coatings ◽  
Different Temperatures ◽  
Boriding Process

The paper presents studies boride coatings, which were created using high-frequency treatment with currents. Chemical reactions characterized the boriding procedure at various temperatures are show. The choice of the main element, of the reaction-boriding scheme is characterize, their role is revealed, and the probable processes leading to the realization of topochemical boriding initiated by HFC-heating are established. The kinetic curves received during the test at different temperatures are showed. Anamorphoses of the kinetic curves are showed, and the values of activation energy and parameters of the boriding process using HFC-heating are calculated on the basis of linearization of the Arrhenius equation.

Effect Of Elevated Temperatures On Complete Concrete Deformation Diagrams

2019 ◽  
pp. 9-14
Keyword(s):  
Experimental Data ◽  
Elastic Modulus ◽  
Elevated Temperatures ◽  
Peak Load ◽  
Relative Deformation ◽  
Deformation Characteristics ◽  
Compression Tests ◽  
Strain Behavior ◽  
Different Temperatures ◽  
Deformation Diagrams

The analysis of the previous results of the study on concrete stress-strain behavior at elevated temperatures has been carried out. Based on the analysis, the main reasons for strength retrogression and elastic modulus reduction of concrete have been identified. Despite a significant amount of research in this area, there is a large spread in experimental data received, both as a result of compression and tension. In addition, the deformation characteristics of concrete are insufficiently studied: the coefficient of transverse deformation, the limiting relative compression deformation corresponding to the peak load and the almost complete absence of studies of complete deformation diagrams at elevated temperatures. The two testing chambers provided creating the necessary temperature conditions for conducting studies under bending compression and tension have been developed. On the basis of the obtained experimental data of physical and mechanical characteristics of concrete at different temperatures under conditions of axial compression and tensile bending, conclusions about the nature of changes in strength and deformation characteristics have been drawn. Compression tests conducted following the method of concrete deformation complete curves provided obtaining diagrams not only at normal temperature, but also at elevated temperature. Based on the experimental results, dependences of changes in prism strength and elastic modulus as well as an equation for determining the relative deformation and stresses at elevated temperatures at all stages of concrete deterioration have been suggested.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

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