Alternating Differential Scanning Calorimetry Research Articles

A composition-dependent thermal behavior of Si20Te80−xSnx glasses: Observation of Boolchand intermediate phase

Thermal properties have been investigated using alternating differential scanning calorimetry (ADSC) for determining the phase transitions of Si20Te80−xSnx glass samples (1 ≤ x ≤ 6). Experiments are performed to assess the variations of thermal characteristics such as glass transition temperature (Tg) and crystallization temperature (Tc) etc. as a function of Sn variation. The glass-forming ability (GFA) and thermal stability (ΔT) are analyzed for understanding the suitability of as-prepared material in terms of network connectivity and rigidity. The studies have revealed minimum non-reversing enthalpy (ΔHNR) value between compositions (2 ≤ x ≤ 5) of Si20Te80−xSnx glasses, which serve as a basis of the existence of Boolchand's intermediate phase (BIP). It is observed that an increase in Sn dopant resulted in an increase in the density and decrease in the molecular volume of Si20Te80−xSnx samples. These studies reveal the correlation with the memory switching behavior displayed by Si20Te80−xSnx glasses.

Manifestation of intermediate phase in Cu doped Si-Te glasses

Alternating differential scanning calorimetry (ADSC) analysis has been carried out on bulk Si15Te85-xCux (1 ≤ x ≤ 10) glasses to examine the thermal properties of the glassy samples in detail. The investigations on the compositional dependence of ΔHNR (non- reversing enthalpy) manifests a trough between the composition 2 ≤ x ≤ 6 which stands as the basis of the presence of Boolchand's Intermediate phase in that range. Additionally, anomalous behavior has been observed at the compositional dependence of various thermal parameters at x = 9, which stipulates the appearance of chemical threshold at the stated composition. Annealed bulk samples have been exposed to XRD studies to discern the type of formed crystalline phases. The study has reported the manifestation of Te, Si1Te2, Si2Te3, Cu3Te2 phases.

Thermal cure kinetics of epoxidized linseed oil with anhydride hardener

The thermal cure kinetics of an epoxidized linseed oil with methyl nadic anhydride as curing agent and 1-methyl imidazole as catalyst was studied by differential scanning calorimetry (DSC). The curing process was evaluated by non-isothermal DSC measurements; three iso-conversional methods for kinetic analysis of the original thermo-chemical data were applied to calculate the changes in apparent activation energy in dependence of conversion during the cross-linking reaction. All three iso-conversional methods provided consistent activation energy versus time profiles for the complex curing process. The accuracy and predictive power of the kinetic methods were evaluated by isothermal DSC measurements performed at temperatures above the glass transition temperature of the completely cured mixture (T g∞ ). It was found that the predictions obtained from the iso-conversional method by Vyazovkin yielded the best agreement with the experimental values. The corresponding activation energy (E a) regime showed an increase in E a at the beginning of the curing which was followed by a continuous decrease as the cross-linking proceeded. This decrease in E a is explained by a diffusion controlled reaction kinetics which is caused by two phenomena, gelation and vitrification. Gelation during curing of the epoxidized linseed/methyl nadic anhydride system was characterized by rheological measurements using a plate/plate rheometer and vitrification of the system was confirmed experimentally by detecting a significant decrease in complex heat capacity using alternating differential scanning calorimetry (ADSC) measurements.

Evidence of an intermediate phase in ternary Ge7Se93-xSbx glasses

The compositional dependence of thermal properties, such as glass transition temperature (T-g), non-reversing enthalpy change (Delta H-NR) and the specific heat capacity change (Delta C-p) of melt quenched Ge7Se93-xSbx (21 a parts per thousand currency sign x a parts per thousand currency sign 31) glasses, has been studied using alternating differential scanning calorimetry (ADSC) which is analogous to modulated differential scanning calorimetry (MDSC). The glass transition temperature, T-g, which is a measure of global connectivity of the glass, has been found to increase with the addition of Sb. In addition, a change in slope has been observed in the composition dependence of T-g at an average coordination aOE (c) r > = 2.40. The experimentally observed compositional variation of glass transition temperature, has been compared with the theoretical predictions from the stochastic agglomeration theory (SAT) and has been found to be consistent. Further, a narrow thermally reversing window is seen in the compositional variation of the relaxation enthalpy (Delta H-NR), which is centered around aOE (c) r > = 2.40. The change in specific heat capacity (Delta C-p) at T-g is also found to exhibit a distinct minima at aOE (c) r > = 2.40, suggesting that the structural rearrangements for the liquid in the glass transition region are minimized around aOE (c) r > = 2.4.

A sharp thermally reversing window in As 45Te 55−xI x chalcohalide glasses revealed by alternating differential scanning calorimetry and photo thermal deflection studies

The composition dependence of different thermal parameters such as glass transition temperature, non-reversing enthalpy, thermal diffusivity etc., of bulk As 45Te 55− x I x chalcohalide glasses (3 ⩽ x ⩽ 10), has been evaluated using the temperature modulated Alternating Differential Scanning Calorimetry (ADSC) and Photo Thermal Deflection (PTD) studies. It is found that there is not much variation in the glass transition temperature of As 45Te 55− x I x glasses, even though there is a wide variation in the average coordination number ( r ¯ ) . This observation has been understood on the basis that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than r ¯ . Further, it is found that both the non-reversing enthalpy (Δ H nr) and the thermal diffusivity ( α) exhibit a sharp minimum at a composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 ⩽ x ⩽ 7. The results obtained clearly indicate a sharp thermally reversing window in As 45Te 55− x I x chalcohalide glasses around the composition x = 6.

Evidence for a thermally reversing window in bulk Ge–Te–Si glasses revealed by alternating differential scanning calorimetry

Experiments on Ge15Te85− x Si x glasses (2 ≤ x ≤ 12) using alternating differential scanning calorimetry (ADSC) indicate that these glasses exhibit one glass transition and two crystallization reactions upon heating. The glass transition temperature has been found to increase almost linearly with silicon content, in the entire composition tie-line. The first crystallization temperature (T c1) exhibits an increase with silicon content for x < 5; T c1 remains almost a constant in the composition range 5 < x ≤ 10 and it increases comparatively more sharply with silicon content thereafter. The specific heat change (ΔC p) is found to decrease with an increase in silicon content, exhibiting a minimum at x = 5 (average coordination number, ⟨r⟩ = 2.4); a continuous increase is seen in ΔC p with silicon concentration above x = 5. The effects seen in the variation with composition of T c1 and ΔC p at x = 5, are the specific signatures of the mean-field stiffness threshold at ⟨r⟩ = 2.4. Furthermore, a broad trough is seen in the enthalpy change (ΔH NR), which is indicative of a thermally reversing window in Ge15Te85− x Si x glasses in the composition range 2 ≤ x ≤ 6 (2.34 ≤ ⟨r⟩ ≤ 2.42).

Kinetics and modeling of the diffusion‐controlled diallyl terephthalate polymerization

AbstractFree radical polymerization kinetics of diallyl terephthalate in bulk was investigated in a wide temperature range from 50°C to 150°C with four different peroxide initiators. Conversion points were measured using Fourier Transform Infrared (FTIR) measurements. The initiator efficiencies and the initiator decomposition rate constants were evaluated from special experiments, applying the theory of dead end polymerization. In addition, the ratios between the degradative and the effective kinetic rate constants to propagation rate constants were obtained from molecular weight measurements at various initiator concentrations. The ratio of chemically controlled termination and propagation rate constant k/ktc of the polymerization system was obtained using the initial rates of polymerization and the number average molecular weight data between 0.25 · 10−3 and 15.7 · 10−3 L mol−1 s−1. The glass transition temperature of the polymer, 191°C, was measured by the Alternating Differential Scanning Calorimetry (ADSC) technique. Computed conversions from the developed kinetic model were in good agreement with the conversion and molecular weight measured data. The values of diffusion controlled propagation and termination rate constants ktd0 and kpd0 with clear and physical meaning were the only two parameters obtained from the developed kinetic model fitting. Polym. Eng. Sci. 44:2005–2018, 2004. © 2004 Society of Plastics Engineers.

Aging Behavior of a Novel kind of Poly(ether ether ketone)

In this paper, aging behaviors of a novel kind of poly(ether ether ketone) were studied by alternating differential scanning calorimetry(ADSC). Samples were annealed at 129°C, about 20°C below its glass transition temperature, for different periods, then scanned in the ADSC. The effect of aging time on these parameters is illustrated. We found that the total heat flow closely corresponded to conventional DSC in respect of peak endotherm temperature. The phase angle became sharper on aging and the peak moved towards higher temperatures.

Effects of Cold Drawing and Annealing on the ADSC Response and Microhardness of Amorphous and Crystalline Poly(ethylene naphthalate)

The tensile loading – induced necking in notched specimens of amorphous poly(ethylene naphthalate) (PEN) was studied by conventional (DSC) and alternating differential scanning calorimetry (ADSC) and microhardness measurements. It was shown that in this PEN, similarly to amorphous copolyesters, necking occurred via cold drawing and not via true plastic deformation. The variation of the microhardness along the height and width of the necked region of the specimen reflects the specific orientation of the material during tensile loading. It was observed that the tensile loading provokes a drastic (jump-like) orientation of the macromolecules in draw direction, which even increases in the vicinity of the tip of the necked zone.

Measurement of the wax appearance temperatures of crude oils by temperature modulated differential scanning calorimetry

Temperature modulated differential scanning calorimetry (TMDSC) is used for the first time to measure the wax appearance temperature (WAT) of crude oil samples. The commercial implementation of TMDSC chosen for this study is alternating differential scanning calorimetry (ADSC) marketed by Mettler-Toledo. We show that changes in the ADSC signals exhibit excellent correlations with WATs measured using conventional differential scanning calorimetry, DSC. For oil samples having low wax contents, ADSC is a more sensitive technique for identifying the onset of wax crystallisation and, specifically, the phase angle between the heating rate and heat flow modulations is extremely sensitive to this process.

Measuring the Glass Transition of Thermosets by Alternating Differential Scanning Calorimetry

The glass transition temperature of thermosets is determined by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The different values of the glass transition obtained from heat flow measurements (total and reversible) and heat capacity (modulus of the complex heat capacity) are analysed and compared with the values obtained by conventional DSC. The effect of the sample mass on the values of Tg, heat capacity and phase angle has been analysed. The effect of the thermal contact between sample and pan has been studied using samples cured directly inside the pan and disc-shaped samples of different thickness. The results obtained for the thermal properties and the phase angle are compared and analysed. The modulus of the complex heat capacity enables the determination of the dynamic glass transition, Tgα, which is frequency dependent. The apparent activation energy ofthe relaxation process associated with the glass transition has been evaluated from the dependence of Tgα on the period of the modulation.

Enthalpy relaxation of an epoxy-anhydride resin by temperature-modulated differential scanning calorimetry

The enthalpy relaxation of an epoxy–anhydride resin was studied by physical aging and frequency-dependence experiments with alternating differential scanning calorimetry (ADSC), which is a temperature-modulated differential scanning calorimetry technique. The samples were aged at 80 °C, about 26 K below the glass-transition temperature, for periods up to 3800 h and then scanned under the following modulation conditions: underlying heating rate of 1 K min−1, amplitude of 0.5 K, and period of 1 min. The enthalpy loss was calculated by the total heat-flow signal, and its variation with the log (aging time) gives a relaxation rate (per decade), this value being in good agreement with that calculated by conventional DSC. The enthalpy loss was also analyzed in terms of the nonreversing heat flow, revealing that this property is not suitable for calculating enthalpy loss. The effect of aging on the modulus of the complex heat capacity, |Cp*|, is shown by a sharper variation on the low side of the glass transition and an increase in the inflexional slope of |Cp*|. Likewise, the phase angle also becomes sharper in the low-temperature side of the relaxation. The area under the corrected out-phase heat capacity remains fairly constant with aging. The dependence of the dynamic glass transition, measured at the midpoint of the variation of |Cp*|, on ln(frequency) allows one to determine an apparent activation energy, Δh*, which gives information about the temperature dependence of the relaxation times in equilibrium over a range close to the glass transition. The values of Δh*, determined from ADSC experiments in a range of frequencies between 4.2 and 33 mHz and at an amplitude of 0.5 K, and an underlying heating rate of 1 K min−1, were analyzed and compared with that obtained by conventional DSC from the dependence of the fictive temperature on the cooling rate. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2272–2284, 2000

Aging of polycarbonate studied by temperature modulated differential scanning calorimetry

The enthalpy relaxation behaviour of polycarbonate has been studied by alternating differential scanning calorimetry (ADSC). Samples have been annealed at 125°C, about 20°C below their glass transition temperature, for periods up to 2000 h, and then scanned in the ADSC using the modulation conditions: heating rate=1 K min −1; temperature amplitude=1 K; period=1 min. The data have been analysed in terms of total, reversing and non-reversing heat flows, and also in terms of complex, in-phase and out-of-phase specific heat capacities and a phase angle. The effect of aging time on each of these parameters is illustrated and compared with the predictions of an earlier theoretical model. It is shown that there is very good agreement between the experimental results and the theoretical predictions, the most important aspects being the following. The total heat flow closely corresponds to conventional DSC in respect of both peak endotherm temperature and enthalpy loss (derived from the area under the peak). In contrast, the non-reversing heat flow peak area does not provide a good measure of the enthalpy loss because the reversing heat flow (and complex specific heat capacity) depends significantly on aging, the transition region becoming much sharper as the aging time increases. Likewise, the phase angle (when appropriately corrected for the problem of heat transfer) also becomes sharper on aging, and the (negative) peak moves towards higher temperatures. The out-of-phase specific heat capacity is calculated using the corrected phase angle, and it is shown that the area under this peak is essentially independent of aging time, confirming another prediction from the earlier theoretical model that this area provides no information about the enthalpy loss that occurs during the aging process.

Isothermal curing of an epoxy resin by alternating differential scanning calorimetry

The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxypropylene was studied by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements allows to analyse the vitrification process at curing temperatures ( T c) below the maximum glass transition of the fully cured epoxy ( T g ∞ =85.8°C). Initially, the modulus of the complex heat capacity, |C ∗ p| , increases until a maximum (conversion between 0.42 and 0.56) and then decreases. This step is followed by an abrupt decay of |C ∗ p| , due to the vitrification of the system, which allows the determination of the vitrification time. This value agrees well with that determined by the partial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in |C ∗ p| at vitrification decreases with the increase of T c becoming zero at temperature T g ∞ . This epoxy-triamine system shows a delay of the vitrification process respect to other model epoxy systems probably due to the presence of polyoxypropylene chains in the network. The decay of |C ∗ p| during vitrification may be normalised between unity and zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the mobility factor.

Temperature modulated differential scanning calorimetry. Part I:: Effects of heat transfer on the phase angle in dynamic ADSC in the glass transition region

The relatively new technique of alternating differential scanning calorimetry (ADSC) relies upon the measurement of a phase angle between the heating rate and heat flow in order to separate the real and imaginary parts of the complex heat capacity. A significant problem in this context is the separation of an `instrumental' phase angle, arising from the heat transfer between instrument and sample, from any `sample' phase angle which may result from a transition. In this work, the theoretically anticipated dependence of phase angle on the frequency of modulation has been investigated experimentally for polycarbonate in dynamic scans through the glass transition region using the Mettler–Toledo ADSC. There is a good agreement between the experimental results and the predictions of simple models for both heat transfer and relaxation in the transition region. This provides support for the procedure originally suggested by Schick and co-workers for the correction of the phase angle to allow for the instrumental effects.