Activation energy approach for alkali-activated glass inorganic binders in different aging conditions

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.

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Differential Activation Energy and NBO Interaction Approaches to Torquoselectivity and Its Dependence on the Conformational Profile of the Substituent

10.26434/chemrxiv.13502571.v2 ◽

2021 ◽

Author(s):

Veejendra Yadav

Keyword(s):

Activation Energy ◽

Ring Opening ◽

Energy Approach ◽

Differential Activation ◽

Distinct Level ◽

Lower Activation ◽

Secondary Reactions ◽

The Subject ◽

Interaction Approach ◽

Lower Activation Energy

The torquoselectivity of ring opening of 3-CF3-cyclobutene, 3-CHF2-cyclobutene, 3-CH2F-cyclobutene, 3-CF3-oxetene and perfluoro-3-CH3-cyclobutene have been studied at the MP2/cc-pVTZ level of theory and the results analysed by using the differential activation energy approach and also differential NBO interactions of the breaking ring bond with the substituent bonds. The outward or inward ring opening that has lower activation energy in the differential activation energy approach or larger interaction in the differential NBO interaction approach constitutes the preferred mode. The predictions from the two approaches are largely found to be contradicting each other, specifically when the substituent is electron-deficient. The CHF2 and CH2F substituents on cyclobutene and oxetene can adopt three distinct conformations with respect to the cleaving ring bond. It has been discovered that each conformer exhibits a distinct level of torquoselectivity and some may even contribute to the overall selectivity substantially. The conformational profile of the substituent, therefore, is recommended to be taken into account in any serious treatment of the subject. The experimental torquoselectivity, if otherwise, is a likely consequence of secondary reactions, specifically equilibration through reaction reversal while honouring the relative thermodynamic stabilities of the ring opened products.

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Stereochemical Effect of the Small Ring Unit in 7-R-3,4-Cyclopropano- and 7-R-3,4-Epoxy-bicyclo[4.2.0]octan-1,5-Dienes on Conrotatory Ring Opening Torquoselectivity

10.26434/chemrxiv.14387495 ◽

2021 ◽

Author(s):

Veejendra Yadav

Keyword(s):

Activation Energy ◽

Ring Opening ◽

Energy Approach ◽

The Other ◽

Small Ring ◽

Formyl Group ◽

Differential Activation ◽

Interaction Approach ◽

Relationship Of

Application of the differential activation energy approach suggests that the strong inward opening tendency of the formyl group in 3,4-cyclopropano-7-formyl-bicyclo[4.2.0]octan-1,5-diene and also 3,4-epoxy-7-formyl-bicyclo[4.2.0]octan-1,5-diene is either counter balanced to a level that the reaction turns torquo-neutral or it rotates outward, depending upon the stereo-relationship of the small ring unit with the formyl substituent. The NBO interaction approach, however, predicts inward selectivity throughout. These molecules, therefore, can be used as excellent test examples to judge the validity of one approach over the other.

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Differential Activation Energy and NBO Interaction Approaches to Torquoselectivity and Its Dependence on the Conformational Profile of the Substituent

10.26434/chemrxiv.13502571.v1 ◽

2020 ◽

Author(s):

Veejendra Yadav

Keyword(s):

Activation Energy ◽

Ring Opening ◽

Energy Approach ◽

Differential Activation ◽

Distinct Level ◽

Lower Activation ◽

Secondary Reactions ◽

The Subject ◽

Interaction Approach ◽

Lower Activation Energy

The torquoselectivity of ring opening of 3-CF3-cyclobutene, 3-CHF2-cyclobutene, 3-CH2F-cyclobutene, 3-CF3-oxetene and perfluoro-3-CH3-cyclobutene have been studied at the MP2/cc-pVTZ level of theory and the results analysed by using the differential activation energy approach and also differential NBO interactions of the breaking ring bond with the substituent bonds. The outward or inward ring opening that has lower activation energy in the differential activation energy approach or larger interaction in the differential NBO interaction approach constitutes the preferred mode. The predictions from the two approaches are largely found to be contradicting each other, specifically when the substituent is electron-deficient. The CHF2 and CH2F substituents on cyclobutene and oxetene can adopt three distinct conformations with respect to the cleaving ring bond. It has been discovered that each conformer exhibits a distinct level of torquoselectivity and some may even contribute to the overall selectivity substantially. The conformational profile of the substituent, therefore, is recommended to be taken into account in any serious treatment of the subject. The experimental torquoselectivity, if otherwise, is a likely consequence of secondary reactions, specifically equilibration through reaction reversal while honouring the relative thermodynamic stabilities of the ring opened products.

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Activation Energy and NBO Interaction Approaches to Torquoselectivity and its Dependence on the Conformational Profile of the Substituent

10.26434/chemrxiv.13502571.v3 ◽

2021 ◽

Author(s):

Veejendra Yadav

Keyword(s):

Activation Energy ◽

Ring Opening ◽

Energy Approach ◽

Distinct Level ◽

Lower Activation ◽

Secondary Reactions ◽

The Subject ◽

Lower Activation Energy

The torquoselectivity of ring opening of 3-fluoromethylcyclobutenes, 2-fluoromethyl-3-oxetenes and perfluoro-3-methyl-cyclobutene have been studied at the MP2/cc-pVTZ level of theory and the results analysed by using the activation energy approach and also the NBO interactions of the breaking ring bond with the substituent bond. The outward or inward opening that has lower activation energy in the activation energy approach or larger interaction in the NBO approach constitutes the preferred mode. The CHF2 and CH2F substituents on cyclobutene and oxetene can adopt three distinct conformations with respect to the cleaving ring bond. It has been discovered that each conformer exhibits a distinct level of torquoselectivity and some higher lying conformer may even significantly contribute to the overall selectivity. The conformational profile of the substituent, therefore, is recommended for taking into consideration in any serious treatment of the subject. The experimental selectivity, if otherwise, is likely to be a consequence of secondary reactions such as the reaction equilibration, which honours the relative thermodynamic stabilities of the ring opened products.

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The influence of alkaline activator concentration on the apparent activation energy of alkali-activated materials

MATEC Web of Conferences ◽

10.1051/matecconf/202032201008 ◽

2020 ◽

Vol 322 ◽

pp. 01008

Author(s):

Dariusz Mierzwiński ◽

Janusz Walter ◽

Piotr Olkiewicz

Keyword(s):

Mechanical Properties ◽

Activation Energy ◽

Apparent Activation Energy ◽

Alkaline Solution ◽

Concrete Strength ◽

Physical And Mechanical Properties ◽

Solidification Process ◽

Negative Temperature ◽

Activation Temperature ◽

Alkali Activated

The aim of this article is to analyse the changes of apparent activation energy (Ea) of alkali-activated materials (AAM) at temperatures up to 100°C. Apparent activation energy (Ea) refers to the minimum amount of energy is required for the occurrence of reaction. The existing AAM research is based on assumptions about Portland cement (OPC). A number of studies have been conducted on the development of concrete strength depending on, inter alia, the duration of seasoning and the liquid to solid ratio (L/S). Based on the apparent activation energy and taking into account the effect of time and temperature at the same time, the physical and mechanical properties of OPC can also be predicted. The influence of the activator on the solidification process should also be taken into account for alkali-activated materials. This article shows the effect of changes in the concentration of the alkaline solution used in the AAM process on activation energy. The synthesized AAM material uses a solution based on water glass, sodium hydroxide, sand and volatile ash from the ‘Skawina’ coal-fired power plant (located in Skawina, Lesser Poland). The chemical composition of the material used is classified as class F ash. The concentration of the alkaline solution was 8M, 10M, 12M and 14M. The described research method was based on the use of thermistors with a negative temperature factor. It enabled prediction of the physical and mechanical properties of the materials tested. The results clearly indicate that this method can be used to determine the activation energy of the AAM. However, when determining apparent activation energy (Ea), the time and activation temperature of the binding processes of these types of materials should be taken into consideration.

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Differential Activation Energy and NBO Interaction Approaches to Torquoselectivity and Its Dependence on the Conformational Profile of the Substituent

10.26434/chemrxiv.13502571 ◽

2020 ◽

Author(s):

Veejendra Yadav

Keyword(s):

Activation Energy ◽

Ring Opening ◽

Energy Approach ◽

Differential Activation ◽

Distinct Level ◽

Lower Activation ◽

Secondary Reactions ◽

The Subject ◽

Interaction Approach ◽

Lower Activation Energy

The torquoselectivity of ring opening of 3-CF3-cyclobutene, 3-CHF2-cyclobutene, 3-CH2F-cyclobutene, 3-CF3-oxetene and perfluoro-3-CH3-cyclobutene have been studied at the MP2/cc-pVTZ level of theory and the results analysed by using the differential activation energy approach and also differential NBO interactions of the breaking ring bond with the substituent bonds. The outward or inward ring opening that has lower activation energy in the differential activation energy approach or larger interaction in the differential NBO interaction approach constitutes the preferred mode. The predictions from the two approaches are largely found to be contradicting each other, specifically when the substituent is electron-deficient. The CHF2 and CH2F substituents on cyclobutene and oxetene can adopt three distinct conformations with respect to the cleaving ring bond. It has been discovered that each conformer exhibits a distinct level of torquoselectivity and some may even contribute to the overall selectivity substantially. The conformational profile of the substituent, therefore, is recommended to be taken into account in any serious treatment of the subject. The experimental torquoselectivity, if otherwise, is a likely consequence of secondary reactions, specifically equilibration through reaction reversal while honouring the relative thermodynamic stabilities of the ring opened products.

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

Advances in Materials Science and Engineering ◽

10.1155/2019/3531543 ◽

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.

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