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.

scholarly journals Effect of Temperature and pH on Early Hydration Rate and Apparent Activation Energy of Alkali-Activated Slag

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Ping Li ◽  
Jianhui Tang ◽  
Xudong Chen ◽  
Yin Bai ◽  
Qiyao Li
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Effect Of Temperature ◽  
Early Hydration ◽  
Alkali Activated Slag ◽  
Hydration Rate ◽  
Different Temperatures ◽  
Shell Forming ◽  
Activated Slag ◽  
Alkali Activated

In order to investigate the effect of temperature and pH on the early hydration rate of alkali-activated slag (AAS), NaOH was used as alkali activator, and the nonevaporable water (NEW) content of the slag paste at different temperatures (5, 20 and 35°C) and pH (12.10, 12.55, 13.02, and 13.58) was measured. On the basis of the Arrhenius formula, the hydration rate of slag was characterized by the content of nonevaporative water, and the apparent activation energy of slag hydration at different pH was also obtained. The early hydration rate of slag was significantly affected by temperature and pH of activator solution. The apparent activation energy Ea of slag decreased with the increase of pH, and there was a good linear relationship between them. When pH was less than 13.02, increasing the temperature can accelerate the hydration rate of slag. However, under the condition of high pH (pH = 13.58), the hydration rate of slag was negatively correlated with temperature, which was related to the “shell forming” phenomenon of slag hydration.

scholarly journals CORRELATION BETWEEN PREEXPONENTIAL FACTOR AND ACTIVATION ENERGY OF ISOAMYLALCOHOL HYDROGENOLYSIS ON PLATINUM CATALYSTS

2010 ◽  
Vol 4 (1) ◽  
pp. 1-5 ◽  
Author(s):  
Triyono Triyono
Keyword(s):  
Activation Energy ◽  
Rate Constant ◽  
Reaction Rate ◽  
Arrhenius Equation ◽  
Preexponential Factor ◽  
Active Centers ◽  
Exponential Term ◽  
Lower Activation ◽  
Higher Temperature ◽  
Lower Activation Energy

Arrhenius equation stated that reaction will proceed faster at higher temperature and with lower activation energy (Ea). Many literatures reported that preexponential factor (A) is constant for certain reaction and there is no relation between A and Ea. Experiment on the reaction of isoamylalcohol hydrogenolysis showed that logarithm of A increased linearly with Ea. The result of this investigation suggests that the rate of a process is affected by the number of active centers on the surface of a catalysts, which influences the value of the pre-exponential term in the expression for the rate constant of a reaction. An increase in the number of active centers corresponds to a higher value of A, the active centers would be less effective and is attended by a growth in the value of Ea. Therefore, reaction with lower activation energy will not always has higher reaction rate due to decreasing of Ea.   Keywords: isoamylalcohol hydrogenolysis, preexponential factor, activation  energy.

scholarly journals The Apparent Activation Energy of a Novel Low-Calcium Silicate Hydraulic Binder

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5347
Author(s):  
Mónica Antunes ◽  
Rodrigo Lino Santos ◽  
João Pereira ◽  
Ricardo Bayão Horta ◽  
Patrizia Paradiso ◽  
...  
Keyword(s):  
Activation Energy ◽  
Compressive Strength ◽  
Apparent Activation Energy ◽  
Isothermal Calorimetry ◽  
Hydration Product ◽  
Specific Rate ◽  
Initial Development ◽  
Low Calcium ◽  
Acceleration Period ◽  
Different Temperatures

In this work, the apparent activation energy (Ea) of a novel low-calcium binder was, for the first time, experimentally determined, using a calorimetric approach. Additionally, a correlation between the Ea, measured at the acceleration period with the C/S ratio of the hydration product is proposed. The Ea of the prepared pastes was determined through isothermal calorimetry tests by calculating the specific rate of reaction at different temperatures, using two different approaches. When comparing the Ea, at the acceleration period of this novel binder with the one published for alite and belite, we observed that its value is higher, which may be a result of a different hydration product formed with a distinct C/S ratio. Finally, to study the temperature effect on the compressive strength at early ages, a set of experiments with mortars was performed. The results showed that the longer the curing time at 35 °C, the higher the compressive strength after 2 days of hydration, which suggests a higher initial development of hydration products. This study also indicated that the novel binder has a higher sensitivity to temperature when compared with ordinary Portland cement (OPC).

Nitridation Isothermal Kinetics of In Situ β-Sialon Bonded Al2O3-C Refractories

2016 ◽  
Vol 697 ◽  
pp. 572-575
Author(s):  
Xue Qing Yang ◽  
Nai Peng ◽  
Cheng Ji Deng
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Isothermal Kinetics ◽  
Nitridation Reaction ◽  
Result Show ◽  
Different Temperatures ◽  
Two Stages ◽  
Kinetics Of ◽  
And Diffusion

The kinetics of in-situ β- Sialon bonded Al2O3-C (SAC) refractories were investigated by TGA techniques via isothermal nitridation experiments at different temperatures. The result show that the nitridation process of in-situ β-Sialon bonded Al2O3-C refractories can be divided into two stages: the nitridation reaction rate controlling stage in the first 10 min, and the apparent activation energy of nitridation reaction is 370 kJ/mol ; then the reaction is controlled by both chemical reaction and diffusion rate in the following 110 min, the apparent activation energy of nitridation reaction is 410 kJ/mol.

scholarly journals Thermal Properties of Calcium Sulphoaluminate Cement as an Alternative to Ordinary Portland Cement

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7011
Author(s):  
Małgorzata Gołaszewska ◽  
Barbara Klemczak ◽  
Jacek Gołaszewski
Keyword(s):  
Activation Energy ◽  
Portland Cement ◽  
Apparent Activation Energy ◽  
Thermal Behaviour ◽  
Ordinary Portland Cement ◽  
Isothermal Calorimetry ◽  
Heat Of Hydration ◽  
Curing Temperature ◽  
Cement Pastes ◽  
Calcium Sulphoaluminate

This paper presents the results of research into the heat of hydration and activation energy of calcium sulphoaluminate (CSA) cement in terms of the dependence on curing temperature and water/cement ratio. Cement pastes with water/cement ratios in the range of 0.3–0.6 were tested by isothermal calorimetry at 20 °C, 35 °C and 50 °C, with the evolved hydration heat and its rate monitored for 168 h from mixing water with cement. Reference pastes with ordinary Portland cement (OPC) were also tested in the same range. The apparent activation energy of CSA and OPC was determined based on the results of the measurements. CSA pastes exhibited complex thermal behaviour that differed significantly from the thermal behaviour of ordinary Portland cement. The results show that both the w/c ratio and elevated temperature have a meaningful effect on the heat emission and the hydration process of CSA cement pastes. The determined apparent activation energy of CSA revealed its substantial variability and dependence, both on the w/c ratio and the curing temperature.

Base-catalysed reduction of pyruvic acid in near-critical water

2013 ◽  
Vol 67 (5) ◽  
Author(s):  
Li Luo ◽  
Zhi Hou ◽  
Yuan Wang ◽  
Li Dai
Keyword(s):  
Activation Energy ◽  
Formic Acid ◽  
Pyruvic Acid ◽  
Sodium Acetate ◽  
Reaction Rate ◽  
Arrhenius Equation ◽  
Base Catalyst ◽  
Acid Yield ◽  
Exponential Factor ◽  
Reaction Rate Constants

AbstractThe reduction of pyruvic acid in near-critical water has successfully been conducted under conditions of various temperatures, pressures, reaction time and the presence of formic acid as the reducing agent. In this work, additives (K2CO3, KHCO3, and sodium acetate) used in the reduction of pyruvic acid were also investigated. The results showed that by adding K2CO3 (25 mole %) a markedly higher lactic acid yield (70.7 %) was obtained than without additives (31.3 %) at 573.15 K, pressure of 8.59 MPa, 60 min, and in the presence of 2 mol L−1 formic acid. As a base catalyst, K2CO3 definitely accelerated the reduction of pyruvic acid. The reaction rate constants, average apparent activation energy and pre-exponential factor were evaluated in accordance with the Arrhenius equation. The reaction mechanism of the reduction was proposed on the basis of the experimental results.

Wet And Dry Oxidation of Polycrystalline SixGe1-x Films

1998 ◽  
Vol 533 ◽  
Author(s):  
P.-E. Hellberg ◽  
S.-L. Zhang ◽  
F. M. d'Heurle ◽  
C. S. Petersson
Keyword(s):  
Activation Energy ◽  
Reaction Rate ◽  
Quantitative Description ◽  
Reaction Rate Constant ◽  
Enhancement Effect ◽  
Wet Oxidation ◽  
Simultaneous Oxidation ◽  
Dry Oxidation ◽  
Different Temperatures ◽  
Si Films

AbstractWet and dry oxidations of polycrystalline SixGe1-x, with various compositions have been studied at different temperatures. The growth rate of SiO2 is found to be enhanced by Ge, and the enhancement effect is more pronounced in H2O than in O2. A mathematical model, which assumes simultaneous oxidation of Si and Ge and reduction of GeO2 by free Si available at the growing-oxide/SixGe1-x interface, is found to give a quantitative description of the SiO2 growth during thermal oxidation of SixGe1-x. Kinetic parameters are extracted by comparing the model with experiments. The linear and parabolic rate constants for Si oxidation are determined on control Si (100) wafers and polycrystalline Si films. Simple expressions are used for the interdiffusion of Si and Ge in SixGe1-x. For wet oxidation, the activation energy for the reaction rate constant of Ge oxidation is found to be smaller than that of Si oxidation.

scholarly journals Stability of vitamin C in broccoli at different storage conditions

2019 ◽  
Vol 8 (1) ◽  
Author(s):  
Nasser Al-Habsi ◽  
Sithara Suresh ◽  
Amani Al-Yhmedi ◽  
Marwa Al-Shoryani ◽  
Mostafa I. Waly ◽  
...  
Keyword(s):  
Activation Energy ◽  
Vitamin C ◽  
Reaction Rate ◽  
Storage Conditions ◽  
Order Reaction ◽  
Titration Method ◽  
First Order ◽  
Reaction Rate Constants ◽  
Different Temperatures ◽  
Thermal Stability Of

In this study, the retention of vitamin C in fresh broccoli stored at different temperatures (i.e. chiller, room, cooking, and roasting or baking; 5-120°C) was investigated. The thermal stability of vitamin C in broccoli was analysed at 5, 20, 45, 60, 70, 80, 110, and 120°C. The vitamin C content was measured by the indophenol titration method. Vitamin C was affected negatively at all stored temperatures. The degradation of vitamin C was modelled by first-order reaction kinetics and the reaction rate constants were observed as 9.03×10-8 and 5.65×10-3 s-1 when stored at 5°C and 120°C, respectively. The activation energy was estimated as 74.2 kJ/mol within the temperature range used in this study. The lowest decay of vitamin C was observed during the chilling condition. The data on retention of vitamin C in broccoli could be used to determine their stability, when stored as raw, and when heated at different temperatures.

Reduction Kinetics of Bayan Obo Coexisted Iron and Niobium Ore by Carbon-Bearing Pellet

2011 ◽  
Vol 418-420 ◽  
pp. 346-352 ◽  
Author(s):  
Fu Shun Zhang ◽  
Zeng Wu Zhao ◽  
Yan Li ◽  
Nai Xiang Feng
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Reaction Rate ◽  
Mass Loss Rate ◽  
Reduction Process ◽  
Inert Atmosphere ◽  
Reaction Rate Constant ◽  
Carbon Gasification ◽  
Reaction Rate Constants ◽  
Two Stages

The mass loss rate of carbon-bearing pellet of coexisted iron and niobium ore during reduction process was investigated between 900 and 1050°C in inert atmosphere. The reduction mechanism was studied by analyzing reaction rate constant, apparent activation energy，and the controlling step. The results show that temperature has the significant effect on the reduction of carbon-bearing pellet. The reduction processes include the faster reaction stage and the slower reduction stage, and respective reaction rate constants in two stages are k1=exp (21.025-40484/(RT)) and k2= exp (21.060-42516/(RT))，while respective apparent activation energy are 337 and 353 KJ/mol. Both steps are controlled by carbon gasification.

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