Enthalpy relaxation of selenium observed by fast scanning calorimetry

Pilař, Radim; Honcová, Pavla; Schulz, Gunnar; Schick, Christoph; Málek, Jiřı́

doi:10.1016/j.tca.2014.09.026

Cited by 16 publications

(40 citation statements)

References 40 publications

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“…In the following paragraphs, we will demonstrate that the distortion produced by the above-described incorrect normalization ( Fig. 1; [13]) is not negligible, especially in case of the FSC data, where the relaxation undershoots are rather flat and wide.…”

Section: Correct Data Preparationmentioning

confidence: 79%

“…A very short isothermal step (0.01 s) had to be inserted between the cooling and consequent heating due to the temperature regulation of the calorimeter; nonetheless, it was shown by means of theoretical simulations that this short isotherm did not influence the overall relaxation response of the material at all. For further experimental details see [13].…”

Section: Methodsmentioning

confidence: 99%

“…The curve-fitting and simulations performed in [13] and within this article are based on the phenomenological Tool-Narayanaswamy-Moynihan (TNM) model [18][19][20]:…”

Section: Methodsmentioning

confidence: 99%

“…1 the FSC heating scans of amorphous selenium are depicted (the data are reproduced from [13]). Normalized heat capacity C N p is used to display the FSC signal [13]; data in this format are needed for evaluation of the structural relaxation parameters. Each curve corresponds to one heating scan performed after the preceding cooling at a defined cooling rate-see ''Experimental'' section for details.…”

Section: Correct Data Preparationmentioning

confidence: 99%

“…The recent very interesting enthalpy relaxation measurements of amorphous selenium (a-Se) [13] obtained within the joint collaboration of our laboratory and University of Rostock will be used as the model data.…”

Section: Introductionmentioning

confidence: 99%

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Glass transition kinetics measured by fast scanning calorimetry

Svoboda

2015

J Therm Anal Calorim

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Enthalpy relaxation data obtained for amorphous selenium by means of fast scanning calorimetry were described in terms of Tool-Narayanaswamy-Moynihan model. The effect of thermal gradients formed within the measured sample was found to explain the marked difference between the FSC and conventional DSC data obtained for a-Se. If the influence of thermal gradients is accounted for, the similar set of TNM parameters as obtained for a-Se from conventional DSC can be used to describe the FSC data. Temperature profiles of the thermal gradients as well as sources of additional uncertainties occurring within the introduced conception are discussed in detail. In addition, a normalization procedure accounting for the difference between the slopes of heat capacity in the glass and undercooled liquid regions was introduced. Correct data preparation was found to have a critical influence on the applied enthalpy relaxation evaluation procedures. Due to the unresolved issue of the prediction of manifesting thermal gradients found in case of the recent study on amorphous selenium, the FSC technique appears, for the time being, to have limited usage for enthalpy relaxation studies.

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Section: Correct Data Preparationmentioning

confidence: 79%

Section: Methodsmentioning

confidence: 99%

“…The curve-fitting and simulations performed in [13] and within this article are based on the phenomenological Tool-Narayanaswamy-Moynihan (TNM) model [18][19][20]:…”

Section: Methodsmentioning

confidence: 99%

Section: Correct Data Preparationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Glass transition kinetics measured by fast scanning calorimetry

Svoboda

2015

J Therm Anal Calorim

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Accelerated aging of 18 years rejuvenated polylactide bottles by fast scanning calorimetry

et al. 2022

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This study focuses on the accelerated physical aging kinetics of rejuvenated polylactide (PLA) that has previously been processed and stored during 18 years under ambient conditions. The finish of a conditioned PLA bottle is subjected to structural relaxation for times varying between 0.001 and 1000.0 min at 45°C, that is, 15°C below its calorimetric glass transition temperature. The recovery of in‐situ aged PLA is monitored by fast scanning calorimetry and it is observed that the thermodynamic equilibrium is reached within the experimental aging time. Moreover, the time evolution of the enthalpy of recovery finds consistency with results obtained for PLA granules which did not undergo additional processing neither prolonged storage nor service life conditions. Thus, it is deduced that both processing and storage do not induce major degradation reactions that could affect the aging kinetics. Therefore, the behavior of a structurally rejuvenated amorphous PLA is depicted through the one of an unaged PLA.

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Post‐curing and structural relaxation of epoxy networks during early stages of aging for civil engineering applications

et al. 2023

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In this work, epoxy networks used for civil engineering constructions are aged at ambient temperature, and the impact of the early stages of aging on mechanical properties is analyzed. It is observed that Young's modulus and the yield stress increase with the aging time whereas the strain at break and the toughness decrease. The structural causes for these variations are investigated by swelling experiments, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. By combining experimental results, it is deduced that the aging process occurs in two stages. During the first 7 days of aging, the change in mechanical properties should essentially be attributed to the postcuring, which results in additional crosslinking reactions. When increasing the aging time to 21 days, the crosslinking density reaches a plateau, but a second stage emerges, in which the mechanical properties continue evolving in the same way, with variations of the mechanical parameters being of comparable amplitude. This second stage is attributed to the evolution of the thermodynamic state of the glass, leading to a densification of the epoxy network through minimization of the free volume, and favoring the creation of physical interactions between polymer segments. Therefore, structural relaxation is shown to have a significant impact on the mechanical properties.

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Enthalpy relaxation of selenium observed by fast scanning calorimetry

Cited by 16 publications

References 40 publications

Glass transition kinetics measured by fast scanning calorimetry

Glass transition kinetics measured by fast scanning calorimetry

Accelerated aging of 18 years rejuvenated polylactide bottles by fast scanning calorimetry

Post‐curing and structural relaxation of epoxy networks during early stages of aging for civil engineering applications

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