Non-isothermal DSC Measurements Research Articles

A Novel Approach to Analysis of Complex Crystallization Behavior in Zr-Based Bulk Metallic Glass by Non-isothermal Kinetics Studies

The complex crystallization behavior of the Zr40Ti15Cu10Ni10Be25 bulk metallic glass (BMG) produced by suction-casting method was studied with the non-isothermal DSC measurements with the heating rate from 5 to 40 K/min. Three exothermic phenomena were observed for the investigated material. The novel evaluation procedure for qualitative and quantitative analysis of intricate crystallization kinetics for Zr-based BMGs is proposed. The unusual deconvolution of the DSC curves based on a Gaussian function and a two-phase exponential decay function allowed for separate, detailed analysis of overlapped peaks. The activation energies for each crystallization stage were studied based on overall (Kissinger) and local (Kissinger–Akahira–Sunose) procedures. The KAS method applied separately for both low and high heating rates showed a significant difference in local activation energies. Finally, the local Avrami exponent evaluation revealed that the first two stages of crystallization are diffusion-controlled with mainly increasing nucleation rate, whereas the third crystallization is more growth-dominated.

Effect of curing pressure on the curing behavior of an epoxy system: Curing kinetics and simulation verification

Most composites require a certain amount of pressure to cure, therefore, it is crucial to comprehend the effect of pressure on the curing reaction. Nonetheless, the majority of studies on curing reaction focus on isothermal or non-isothermal DSC measurements at ambient pressure. Using a high-pressure differential calorimetry scanner (Netzsch DSC 204HP), the curing process of a bisphenol A diglycidyl ether system is studied in order to evaluate the influence of curing pressure. The results indicate a competitive relationship between the effect of heating rate and pressure on the reaction rate, with the influence of heating rate being stronger. The reaction follows the autocatalytic model, and the average activation energy EP and pre-exponential factor AP decrease as the pressure increases. The obtained kinetics are used to simulate the process of forming composite laminates. When the thickness of laminates exceeds 18 mm, the maximum difference of the temperature and curing degree between ambient pressure and 2 MPa pressure is 20.65 °C and 0.161, respectively, indicating that the simulation results of thick composites are affected by whether the curing pressure is considered in kinetics.

A study of 2,3-dichloro-[formula omitted]-xylylene polymerization kinetics using high-vacuum in situ differential scanning calorimetry

The polymerization kinetics of 2,3-dichloro-p-xylylene was studied by in situ non-isothermal DSC measurements with a custom-made heat-flux calorimeter integrated into a vacuum vapor deposition polymerization reactor. The total exothermal effect of polymerization reaction (ΔH=57±6kJmol−1) and its temperature range (−155 to −80 °C) were evaluated. In contrast to polymerization of unsubstituted p-xylylene, DSC reveals a complex shape of the polymerization peak for 2,3-dichloro-p-xylylene, consisting of two overlapping individual peaks. It was suggested that the first peak is associated with polymerization reaction starting from active radical centers formed during the deposition stage, whereas the second peak is connected with polymerization starting from active centers initiated during heating of the monomer condensate. The Fraser-Suzuki deconvolution procedure was used to separate these two processes. The differential isoconversional method by Friedman was applied for the kinetic analysis. It was found that for both of the processes the effective activation energy drops at high conversion degrees from about 25–27kJmol−1 to about 14kJmol−1. Such behavior can be explained by transition to diffusion-controlled regime of the reaction due to vitrification of the polymer-monomer reaction mixture.

Bio-based furan coatings: adhesion, mechanical and thermal properties

In this study, preparation of polyfurfuryl alcohol (PFA) as a renewable binder resin with an origin in biomass conversion is reported for developing a heat-resistant coating. PFA resin was synthesized in the presence of maleic anhydride as a catalyst. Various techniques were used to characterize the synthesized PFA resin. In the second step, different coating samples were prepared using PFA resin. Flexibility, adhesion strength and thermal/curing behavior of the coating samples were investigated as a function of their compositions such as the resin, plasticizers and titanium dioxide (TiO2) contents. The coatings were cured optimally at 150 °C according to isothermal and non-isothermal DSC measurements. Leveling property of the coatings was significantly improved in the presence of TiO2 due to a corresponding increased viscosity of the compound. The adhesion strength of the coating was low due to the aromaticity of PFA chains, high cross-linking degree of the binder resin and the difference existing between thermal expansion coefficient of the coating and steel substrate. In the presence of dioctyl phthalate and long-oil alkyd resin as plasticizers, flexibility and adhesion strength of the coatings were significantly improved up to 15 mm and 2.7 MPa, respectively. High thermal stability of the coatings was supported by TGA findings but it was deteriorated in the presence of alkyd resin. Alkyd resin, a plasticizer, increased the extent of cross-linking due to the chain flexibility enhancement according to DSC and DMTA findings. Finally, a heat-resistant coating formulation containing 9.3 wt% long-oil alkyd resin and 9.3 wt% TiO2 was selected as a good candidate for heat-resistant coating development due to the highest thermal and mechanical properties shown.

Non-isothermal Primary Crystallization Kinetics of the Amorphous Fe85.3B11P3Cu0.7 Alloy

In the present research, the primary crystallization kinetics of the amorphous Fe85.3B11P3Cu0.7 alloy was analyzed using non-isothermal DSC measurements. The average and local activation energies, Ea, were determined by different isokinetic and isoconversional methods. The results obtained for activation energy in this research, show that due to the complexity of the primary crystallization process in this alloy, isoconversional methods are more suitable than the isokinetic ones. The Avrami exponents lie between about 1 and 2 in a wide temperature range of 370˂T≤410˚C. This indicates that one dimensional growth of nuclei with a decreasing rate of nucleation is the main mechanism during non-isothermal primary crystallization process of the amorphous Fe85.3B11P3Cu0.7 alloy which is a new finding for this alloy. Study of magnetic properties in the amorphous and nanocrystalline states revealed that annealing the amorphous ribbons at 440˚C for 10 minutes gives rise to a significant increase in saturation magnetization, Ms, i.e. from 144 in as-spun to 201 emu/g in annealed states. This amount of Ms makes this material a good candidate for different applications, especially in transformer cores.

Effect of ionic liquids on the thermal decomposition process of tert-butyl peroxybenzoate (TBPB) by DSC

Tert-butyl peroxybenzoate (TBPB) is thermally unstable organic peroxide, which may cause disasters such as fire or explosion when excessive heat released due to thermal decomposition. Ionic liquid is often used as a catalyst and inhibitor in engineering applications recently. This study investigated the thermal decomposition characteristics of TBPB when added two different ionic liquids which are 1-Propyl-3-methylimidazolium iodide ([PMIM][I]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) respectively with different mass ratio under DSC tests. Characteristic parameters such as the onset exothermic temperature (T0) and heat of decomposition (ΔHd) of samples were compared. Kinetic parameters such as activation energy Ea were computed using two isoconversional methods which were Ozawa method and Friedman method respectively. The model based (zeroth order reaction) estimation method was used to estimate TMRad at T0 from non-isothermal DSC measurements to assess the thermal hazard of five samples. The paper aims to study the effect of ionic liquids (ILs) on the thermal decomposition of TBPB and analysis the influence of two ionic liquids on the decomposition mechanism of TBPB.

Influence of gamma radiation and temperature on the ageing of EVA cable insulation studied by DSC

Effect of gamma radiation and temperature on the stability of ethylene vinyl-acetate copolymer (EVA) cable insulation was studied by non-isothermal DSC measurements. From the dependences of oxidation onset temperatures on heating rates, the kinetic parameters describing the temperature dependence of induction period have been obtained. The kinetic parameters enabled to calculate the length of induction period for a chosen temperature and to evaluate the residual stability of EVA cable insulation after an artificial ageing stress. It has been shown that the extinction of residual stability with radiation dose obeys a first-order kinetics for all studied temperatures and the extinction constants of residual stabilities have been calculated. Their values indicate, that the radiation ageing has a more significant effect on the residual stability of EVA cable insulation than the temperature ageing at 90 °C.

A study of chloro-p-xylylene polymerization kinetics using high-vacuum in situ differential scanning calorimetry

The polymerization kinetics of chloro-p-xylylene in condensed state was studied by in situ non-isothermal DSC measurements conducted at different heating rates in the range from 1.1 to 6.3 °C min−1, using a custom-made heat-flux calorimeter integrated into a vacuum vapor deposition polymerization reactor. The total exothermal effect of polymerization reaction (Q = 71 ± 9 kJ mol−1) and its temperature range (−140 to −80 °C) were determined. The differential isoconversional method by Friedman was applied for the kinetics analysis. The effective activation energy increases monotonically with the degree of conversion from about 36 to 55 kJ mol−1. Such behavior was associated with transition to diffusion-limited regime of the polymerization reaction. The reaction model f(α) was evaluated using a model-free method based on the use of the compensation effect. The calculated f(α) values were independent on the heating rate and correspond to the second-order reaction model f(α) = (1 − α)2 in the conversion degrees interval of 30–90%.

A study of p-xylylene polymerization kinetics using high-vacuum in situ differential scanning calorimetry

The polymerization kinetics of p-xylylene in condensed state was studied by in situ non-isothermal DSC measurements, using a custom-made heat-flux calorimeter integrated into a vacuum vapor deposition polymerization reactor. The temperature range (−110 to −75°C) and the total heat effect (Q=86±8kJmol−1) of the polymerization reaction were found to be almost identical to the values previously measured ex situ with a commercial Perkin Elmer DSC7 calorimeter. The differential isoconversional method by Friedman was applied for the kinetics analysis. The effective activation energy exhibits variation with the degree of conversion in the range from 30kJmol−1 to 50kJmol−1 indicating the complexity of the reaction mechanism. To evaluate the reaction model f(α) a model-free method based on the use of the compensation effect has been employed. The calculated f(α) values are adequately fitted to the Avrami–Erofeev A2 model in the conversion degrees interval of 20–80%. The discrepancy observed at the end of the reaction is probably due to diffusion control of the reaction, whereas the complexity of the reaction mechanism can be a reason of the discrepancy at low degrees of conversion.

X-ray micro computed tomography, segmental relaxation and crystallization kinetics in interfacial stabilized co-continuous immiscible PVDF/ABS blends

Abstract A model immiscible blend system (PVDF/ABS, 50/50 wt/wt) was studied here and an attempt was made to stabilize the co-continuous structures using either a mutually soluble homopolymer (PMMA) or by introducing particles like graphene oxide sheets (GO) which preferentially localizes in PVDF or a combination of both i.e. PMMA wrapped GO, synthesized by in situ polymerization of MMA in presence of GO sheets (PMMA-GO). The improvement in structural properties couldn't be realized with GO alone or when added along with PMMA separately however, with PMMA-GO significant improvement in structural properties was realized. The coarsening of co-continuous microstructure during annealing was monitored here using both scanning electron microscopy and micro tomography. 2D SEM micrographs and the X-ray tomography reveal that the PVDF/ABS blends containing only PMMA coarsened upon annealing however, in presence of PMMA-GO although the phase dimension of the initial morphology was larger than the blends with only PMMA but the coarsening was suppressed as observed from micro-CT scans. The crystallization kinetics using modified Avrami model was assessed through non-isothermal DSC measurements to study the effect of PMMA, GO and PMMA-GO on the crystallization behaviour of the blends. Taken together, our results uncover an important observation wherein PMMA-GO effectively compatibilizes and stabilizes the morphology against post-processing operations like annealing in PVDF/ABS blends and also significantly improves the structural properties.

Characterization and crystallization kinetics of Er-doped Li2O–Y2O3–P2O5 glass studied by non-isothermal DSC analysis

This work deals with preparation and characterization of Er-doped lithium–yttrium phosphate glass and study of the influence of the particle size in samples on the crystallization process and its kinetics. Two types of prepared samples were used—powder with particle size fractions 90–106 and 200–212 µm and the bulk one. These glassy samples were studied by non-isothermal DSC measurements at heating rates from 2 to 40 K min−1 under nitrogen atmosphere. Obtained data were used for evaluation of the influence of the particle size on the activation energies of the crystallization process by seven the most widely used methods. Activation energies for both powder and bulk samples calculated by model-free methods (Kissinger, Augis–Bennett, and Matusita–Sakka) were similar and independent on the particle size. On the contrary, the influence of the particle size on the activation energy was well described by isoconversional methods (Kissinger–Akahira–Sunose, Starink, Tang, and Flynn–Wall–Ozawa). Moreover, the prepared glassy samples were calcined at temperature over the crystallization temperature and characterized by powder X-ray diffraction analysis.

Synthesis and characterization of nano-structured Se77Sb15Ge8 thin films

Amorphous nano-structured thin films have made great attention because of its enormous importance for the development of nano-technology. The present research paper describes the synthesis and characterization of Se77Sb15Ge8 nano-structured thin films. By melt quench techniques, bulk Se77Sb15Ge8 material was put in order whose amorphous nature was confirmed by XRD and non-isothermal DSC measurements. Thin films (nano-structured) of amorphous Se77Sb15Ge8 material were made by physical vapor condensation technique. To examine the surface morphology of thin films, scanning electron microscope was employed. The average particle size lies in the range 30–60nm. The detailed examination of the data of optical absorption points out that the optical transition is indirect in nature. The optical band gap is viewed around 1.53eV. The dark conductivity of nano-structured Se77Sb15Ge8 thin films was also studied at various temperatures in the range 313–463K in the steps of 5K. It is noticed that the dark conductivity tends to increase with increasing temperature. Our experimentation data advocates that the conduction is owing to thermally supported channeling of the charge carriers in the confined states close to the band edges. The dc activation energy in nano-structured Se77Sb15Ge8 thin films is found to be 1.23eV. A good agreement has been obtained between the estimates of activation energy and optical band gap.

Impact of particle morphology on structure, crystallization kinetics, and properties of PCL composites with TiO2-based particles

Crystallization kinetics of polycaprolactone (PCL) filled with TiO2-based particles (TiX) was shown to depend on the TiX particle type and concentration, which were associated with a slight polymer matrix degradation. The partially degraded, shorter, and more mobile polymer chains increased the overall crystallization rate at the initial stage of crystallization, while at the later stages, the non-nucleating TiX particles acted as a sterical hindrance, slowing down the crystallization process. The PCL/TiX composites were prepared by melt-mixing and contained 2.5 and 5 wt% of the filler. The investigated TiX particles included isometric anatase microparticles (mTiO2) and titanate nanotubes with high-aspect ratio (TiNT). Light and electron microscopy showed very homogeneous dispersion of the mTiO2 particles in the PCL matrix, while the TiNT formed large agglomerates. In situ polarized light microscopy displayed faster isothermal crystallization of all PCL/TiX composites, but the micrographs indicated that the TiX particles did not act as nucleation centres. Isothermal DSC experiments, evaluated in terms of Avrami theory, confirmed the PLM results and showed that the overall rate of isothermal crystallization increased in the following order: PCL <PCL/TiNT <PCL/mTiO2. Non-isothermal DSC and rheological measurements revealed the correlation between the crystallization rate and the polymer matrix degradation—the well-dispersed mTiO2 particles with high specific surface caused the highest PCL degradation and, consequently, the earliest start of non-isothermal crystallization as well as the fastest isothermal crystallization. Microindentation hardness measurements confirmed that the partial degradation of the polymer matrix did not have a significant impact on the mechanical performance of PCL/mTiO2 composites.

Isothermal and non-isothermal crystallization kinetics of polyamide 12 used in laser sintering

Laser sintering of polymers is a steadily improving additive manufacturing method. Mainly used materials are semicrystalline thermoplastics, and as part of those, polyamide 12 has established most. When semicrystalline polymers cool down from the melt, they exhibit volume shrinkage due to crystallization. This crystallization occurs non-uniformly within the produced parts and thus is responsible for part warpage. Aim of this study was to investigate the crystallization kinetics of an, in laser sintering widely used, polyamide 12-based polymer available by supplier EOS with appellation PA2200. For that purpose, several isothermal and non-isothermal DSC measurements were taken. The isothermal measurements were analyzed according to the theory of Avrami. Furthermore, the parameters of the crystallization model by Nakamura were calibrated, and both conditions were simulated. It was found that the isothermal data are very well describable by the theory of Avrami as well as the model by Nakamura can be used to model both conditions.

Applicability of Augis–Bennett relation for determination of activation energy of glass transition in some Se rich chalcogenide glasses

The present work reports the results of non-isothermal DSC measurements on some Se-based ternary glasses for evaluation of activation of glass transition. The activation energy of glass transition (Eg) is determined using Augis–Bennett's relation, which is basically derived for amorphous to crystalline phase transition. Moynihan's relation which is derived on the concept of thermal relaxation and is basically used for glass transition is also used for determination of Eg values. We have observed that Eg values obtained from Augis–Bennett's relation are in admirable agreement with the Eg values which are obtained using Moynihan's relation.

Nucleation parameter and size distribution of critical nuclei for nonisothermal polymer crystallization: The influence of the cooling rate and filler

ABSTRACTThe nucleation parameter Kg of filled PP, HDPE, and PA6 is determined through nonisothermal DSC measurements. A novel method is proposed for the determination of the size distribution of critical nuclei, where the most commonly found fraction was obtained as a peak value. The models are tested at different cooling rates and different filler loadings. Kg varies up to a certain cooling rate and afterwards remains constant. The introduction of talc in PP and HDPE facilitates nucleation and thus reduces Kg. An opposite trend occurs upon the addition of bentonite in PA6. The changes of Kg and are reflected on sample morphology, as confirmed with SAXS. The ratio between the final crystal thickness and amounts to approx. 2 and thus agrees well with the one listed in literature. The simple linear correlations of the obtained Kg are established with Young's modulus and yield stress. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41433.

Validation of the estimation of oxidation induction time from non-isothermal DSC measurements

In this paper, correctness of the method for estimation of the oxidation induction time (OIT) from a set of non-isothermal DSC measurements is verified for two samples of sunflower oil in the temperature range of 110–160 °C. It can be concluded on the basis of root-mean-square deviations between the experimental and predicted values of OIT in the high-temperature region (above 110 °C) that both the Arrhenius and non-Arrhenian models lead to a very good agreement of the calculated values of OIT with the experimental ones without any statistically significant bias. Moreover, the uncertainties in the predicted values of OIT are practically identical for all three models applied.

Thermooxidative stability of poppy seeds studied by non-isothermal DSC measurements

Papaver somniferum L. is an important crop cultivated mostly for seed production. Poppy seeds have a high nutritive value and are used as a food and as a source of edible oil. This oil is a rich source of polyunsaturated fatty acids. It is well known that the unsaturated fatty acids easily undergo oxidation reactions, which lead to the reduction of shelf life, nutritional quality, development of unpleasant tastes and odors. The goal of this study was to develop the methodology for testing the stability of poppy seeds using non-isothermal DSC. For the treatment of the experimental data a method based on non-Arrhenian temperature function has been applied and the values the kinetic parameters have been obtained. In order to assess the durability of the commercial poppy seeds, the lengths of induction periods have been calculated.

A study of p-xylylene polymerization kinetics by isoconversional analysis

The polymerization kinetics of p-xylylene in condensed state was studied by non-isothermal DSC measurements conducted at different heating rates. The total exothermal effect of polymerization reaction (Q=86±3kJmol−1) is found to be almost independent from the heating rate. The polymerization temperature spans from −115°C to −80°C at a heating rate of 1°Cmin−1 and from −85°C to −30°C at a heating rate of 200°Cmin−1. The integral isoconversional method by Vyazovkin and differential isoconversional method by Friedman were applied for the kinetics analysis. Two polymerization regimes have been identified, depending on the heating rate. The effective activation energy exhibits variation with the degree of conversion; it varies from 40 to 65kJmol−1 at low heating rates (1–10°Cmin−1) and from 40 to 24kJmol−1 at high heating rates (20–200°Cmin−1). We suggest that at the low heating rates the polymerization proceeds in the solid state, whereas at the high heating rates it occurs in the liquid state. Atomic force microscopy measurements reveal the effect of polymerization conditions on the surface morphology of the resulting poly(p-xylylene) films.

Study of phase separation in Ga25Se75−xTex chalcogenide thin films

The effects of composition and thermal annealing in between glass transition and crystallization temperature on the optical and structural properties of Ga25Se75−xTex were investigated. The glass transition and crystallization temperature of the synthesized samples was measured by non-isothermal DSC measurements. Amorphous thin films of Ga25Se75−xTex glasses were grown onto ultra clean glass/Si wafer (100) substrates using the vacuum evaporation technique. The effect of thermal annealing on the optical gap (Eg) for Ga25Se75−xTex thin films in the temperature range 358–388K is studied. As-prepared and annealed thin films were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and optical absorption. Thermal annealing was found to be accompanied by structural effects, which in turn, lead to changes in the optical constants. The optical absorption coefficient (α) for as-deposited and thermally annealed films was calculated from the absorbance data. From the knowledge of absorption coefficient at different wavelengths, the optical band gap (Eg) was calculated for all compositions of Ga25Se75−xTex thin films before and after thermal annealing. Results indicate that allowed indirect optical transition is predominated in as-deposited and thermally annealed thin films. The influence of Te incorporation and thermal annealing in Ga25Se75−xTex thin films results in a gradual decrease in the indirect optical gap, this behavior can be explained as increased tailing. The decrease in optical band gap and an increase in absorption coefficient and extinction coefficient with thermal annealing can be attributed to transformation from amorphous to crystalline phase.