Theory and Practice of Modulated Temperature Differential Scanning Calorimetry

Lacey, A. A.; Price, Duncan M.; Reading, M.

doi:10.1007/1-4020-3750-3_1

Cited by 33 publications

(56 citation statements)

References 35 publications

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“…AC calorimetry is well known as a sensitive technique for measuring thermo-physical properties of materials in the presence of heat loss [17][18][19][20]. In AC calorimetry, an oscillating heat input is supplied to the sample and the resulting temperature oscillation is measured [20].…”

Section: Ac Calorimetrymentioning

confidence: 99%

“…This effect is negligible if the separation is much smaller than K, but it increases rapidly as the separation exceeds K. If the frequency used in a measurement is sufficiently small, thermal effects do not affect the measurement; otherwise a thermal model of the calorimeter is needed to interpret the results. In a typical measurement on a bulk material [17], the frequency is kept below 1 Hz to prevent any thermal gradients. Because T 0 (t) should not change significantly during a single temperature oscillation, the low frequency also sets an upper limit of approximately one Kelvin per second on the scanning rate.…”

Section: Ac Calorimetrymentioning

confidence: 99%

“…It is useful to deconvolve the voltage response into the four frequency components, V 0 , VZ, V 2Z , and V 3Z , whose sum is equal to the full voltage response (Eq. 17) while the harmonic components are …”

Section: Scanning Ac Calorimetrymentioning

confidence: 99%

“…When AC calorimetry is applied to bulk materials, the relevant frequency range is quite low (~1 Hz), because of the finite size of the sample and the thermal resistance between the sample, heater, and thermometer [17]. Indeed, the low frequency increases the thermal diffusion length and ensures that the entire sample is subjected to the maximum temperature oscillation, essential to obtaining accurate heat capacity measurement.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, the low frequency increases the thermal diffusion length and ensures that the entire sample is subjected to the maximum temperature oscillation, essential to obtaining accurate heat capacity measurement. The low frequency also sets an upper limit on the scanning rate to ensure that the mean temperature of the sample does not change significantly during a single temperature oscillation [17].…”

Section: Introductionmentioning

confidence: 99%

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Scanning AC Nanocalorimetry and Its Applications

Xiao

Vlassak

2016

Fast Scanning Calorimetry

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This thesis presents an AC nanocalorimetry technique that enables calorimetry measurements on very small quantities of materials over a wide range of scanning rates (from isothermal to 3×10^3 K/s), temperatures (up to 1200 K), and environments. Such working range bridges the gap between traditional scanning calorimetry of bulk materials and nanocalorimetry. The method relies on a micromachined nanocalorimeter with negligible thermal lags between heater, thermometer, and sample. The ability to perform calorimetry measurements over such a broad range of scanning rates makes it an ideal tool to characterize the kinetics of phase transformations, reactions at elevated temperatures or to explore the behavior of materials far from equilibrium. We By combining scanning DC and AC nano-calorimetry techniques, we study the nucleation behavior of undercooled liquid Bi at cooling rates ranging from 10^1 to 10^4 K/s. Upon initial melting, the Bi thin-film sample breaks up into isolated islands. The number of islands in a typical sample is sufficiently large that highly repeatable nucleation behavior is observed, despite the stochastic nature of the nucleation process.We establish a data reduction technique to evaluate the nucleation rate from DC and AC calorimetry results. The results show that the driving force for the nucleation of melted Bi is well described by classical nucleation theory over a wide range of cooling rates. The proposed technique provides a unique and efficient way to examine nucleation kinetics v with cooling rates over several orders of magnitude. The technique is quite general and can be used to evaluate reaction kinetics in other materials.Lastly, we apply the scanning AC nanocalorimetry technique to study solid-gas phase reactions by measuring the change in heat capacity of a sample during reaction. We apply this approach to evaluate the oxidation kinetics of thin-film samples of zirconium in air. The results confirm parabolic oxidation kinetics with an activation energy of 0.59±0.03 eV. The nano-calorimetry measurements were performed using a device that contains an array of micromachined nano-calorimeter sensors in an architecture designed for combinatorial studies. We demonstrate that the oxidation kinetics can be quantified using a single sample, thus enabling high-throughput mapping of the composition-dependence of the reaction rate.vi

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Section: Ac Calorimetrymentioning

confidence: 99%

Section: Ac Calorimetrymentioning

confidence: 99%

Section: Scanning Ac Calorimetrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Scanning AC Nanocalorimetry and Its Applications

Xiao

Vlassak

2016

Fast Scanning Calorimetry

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Estimating the reversing and non‐reversing heat flow from standard DSC curves in the glass transition region

Artiaga

López-Beceiro

Tarrío-Saavedra

et al. 2011

Journal of Chemometrics

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A mathematical model for the total heat flow obtained in differential scanning calorimetry (DSC) experiments from polymers with enthalpic relaxation is proposed. It is limited to the glass transition and enthalpic relaxation range of temperature and to the cases where the enthalpic relaxation is the only non-reversing process taking place. The model consists of a mixture of functions representing the heat capacity heat flow of the glassy and non-glassy fractions, the glass transition progress and the enthalpic relaxation heat flow.Optimal fittings of the model were performed on the experimental total heat flow data, obtained from two thermoplastics with different aging times. Considering which functions of the mixture represent reversing and non-reversing processes, the reversing and non-reversing heat flows were also estimated. The estimated reversing and non-reversing signals were compared with the ones obtained by modulation. On the whole a good match was found, which was even better considering that the estimates are not affected by the frequency effect of the modulated temperature DSC (MTDSC) measurements. The model assumes linear trends for the heat capacity heat flow of the glassy and non-glassy structures. The glass transition progress is represented by a generalized logistic function and the enthalpic relaxation heat flow by the first derivative of another generalized logistic. It brings about a new approach to these phenomena, where the parameters of these functions represent the temperature at which each event is centered, the change of heat capacity (C p ) at the glass transition and the energy involved in the enthalpic recovery.

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Segmental Relaxation Dynamics in Amorphous Polylactide Exposed to UV Light

Araujo

Sainlaud

Delpouve

et al. 2022

Macro Chemistry & Physics

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The degradation of polylactide (PLA) under UV exposure is investigated in terms of cooperativity and kinetic fragility at the glass transition. In the first part, possibly coexisting degradation mechanisms are evoked from the interpretation of the infrared spectroscopy analyses. Furthermore, the reduction of PLA chain length, owing to photolytic scissions predominant over local crosslinks, is assessed from chromatography, and confirmed by the shift of the glass transition temperature toward lower temperature. Modulated temperature thermogravimetric analysis (MT-TGA) also shows that the activation energy needed to initiate thermal degradation falls after UV exposure. In the second part, the impact of UV-induced degradation on the cooperative rearranging region (CRR) size and the kinetic fragility, respectively, calculated thanks to calorimetric and dielectric measurements, is discussed. Despite the assumed concomitance of several degradation mechanisms, it is observed that the glass transition, the kinetic fragility, and the CRR size decrease together with the exposure time. Moreover, it is found that the data align well on another trend depicting the change in the relaxation properties caused by plasticization of PLA. Thus, the variations of segmental relaxation properties caused by UV may be related to the increase of free volume linked to the damaging of the PLA structure.

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Theory and Practice of Modulated Temperature Differential Scanning Calorimetry

Cited by 33 publications

References 35 publications

Scanning AC Nanocalorimetry and Its Applications

Scanning AC Nanocalorimetry and Its Applications

Estimating the reversing and non‐reversing heat flow from standard DSC curves in the glass transition region

Segmental Relaxation Dynamics in Amorphous Polylactide Exposed to UV Light

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