Differential Scanning Calorimetric Scans Research Articles

Glass transition temperature studies of planetary ball milled glasses: Accessing the rapidly cooled glassy state in Na4P2S7-xOx, 0 ≤ x ≤ 7, Oxy-thio phosphate glasses

This report details the very first in-depth study of the glass transition temperature (Tg) for planetary balled milled (PBM) Na4P2S7-xOx (NaPSO), where 0 ≤ x ≤ 7, glasses. For 0 ≤ x ≤ 5, fully amorphous, homogeneous, and chemically reacted compositions can be prepared. For samples with 5 < x ≤ 7, partially amorphous but fully chemically reacted glass-ceramics can be produced. The reproducible, thermally cyclable onset Tg and the onset crystallization temperature, Tc, were investigated as a function of the composition and of the short-range order (SRO) structures of the glasses. Additionally, we examined the extreme sub-Tg exothermic relaxations present due to the high energy milling processing and correspondingly high effective quenching rate. Using a differential scanning calorimeter (DSC) and scanning from well below the onset Tg, the glasses are observed to relax exothermally below Tg. The integrated relaxation enthalpy, ΔHrel, is ~ 0 for the x = 2 glass, but is significantly exothermic for lower and higher values of x. Once the high fictive state of these glasses has been erased by scanning to above the Tg, but below the Tc of the glass, the DSC scans of the glasses recover normal behavior for a normally cooled glass without any relaxation exotherm. The Tgs of these glasses remain relatively constant for 0 ≤ x ≤ 3, but for glasses with 3 < x ≤ 5, Tg increases sharply following the combined effects of the phosphate chain length increasing caused by the formation of bridging oxygens and the increasing concentration of more charge dense non-bridging oxygens (NBOs). For x > 5, both Tg and Tc decrease sharply, becoming nearly identical at x = 7 where glass formation essentially ceases. For smaller values of x, Tc increases with both chain length and the structural complexity of the composition but decreases sharply for glass-ceramics of x > 5.

Influence of cooling rate and annealing on the DSC Tg of an epoxy resin

Glass transition temperature (Tg) is a key epoxy property and often being monitored in the production by the differential scanning calorimeter (DSC) method in the printed circuit board (PCB) industry. The dual-effect of cooling rate and annealing on the endothermic peak in the DSC scan of CE-688 epoxy resin plays a big role in the DSC Tg evaluation. An improved DSC program was developed in order to minimize/eliminate the influence of endothermic peak. Meanwhile, the curing pressure also shows distinct effect on the Tg of the epoxy resin.

Sub-T g enthalpy relaxation in a milling-derived chalcogenide glass

In this work we succeeded in synthesizing a chalcogenide glass, that is, the Ag3PS4 glass, by milling the mixture of the crystalline Ag2S and P2S5 powder. In terms of potential energy, the glass was excited by the milling process. The evidence for the energy excitation was the occurrence of the sub-Tg relaxation recorded by a differential scanning calorimeter (DSC). The relaxation behavior in the milling-derived Ag3PS4 glass was found to significantly differ from that of a hyperquenched oxide glass. We observed two decoupled peaks of the energy release during a DSC scan, which are in contrast to the single asymmetric peak of the hyperquenched glass. The low-temperature peak could be attributed to the β-relaxation of the Ag–S ionic bonds, whereas the high-temperature peak could arise from the α-relaxation of the distorted rigid [PS4] units involving covalent bonds. The decoupling between the two peaks implies the fragile nature of the Ag3PS4 glass. Upon the dynamic heating and the sub-Tg annealing we found that the relaxation of the Ag3PS4 glass is of high nonexponentiallity, and hence, of high structural heterogeneity.

Phase Transitions of Samani Date Palm (Phoenix dactylifera L.) Fruit Using Differential Scanning Calorimeter (DSC)

The aim of the present study was to investigate the effect of heating rate, annealing condition, and moisture content on the glass transition temperatures (Tg), onset of melting point (Tm), initial freezing point (TF), and enthalpy change during melting (Hm) of Samani dates using Differential Scanning Calorimeter (DSC). Three different heating rates; 1, 5, and 10 °C/min were employed during DSC scan to study its effect on the thermal properties of dates. In addition, Samani samples were annealed for 30 min at -30 °C to study the effect of annealing on the same properties. Different levels of moisture content were also used to study its impact on the same properties. The results showed that as the heating rate increases, the Tg increases significantly (p<0.05). Also, annealing has a significant (p<0.05) effect on Tg and Hm and has no significant effect on Tm and TF values. Tg was decreased with the increase of moisture content, while Tm, TF, and Hm increased significantly (p<0.05) with increasing moisture content. The obtained results can be used to enhance stability of stored dates, maintain quality, and extend shelf life. The procedures developed can establish a protocol to yield phase transitions information for dates using DSC.

Simulated Isothermal Crystallization Kinetics from Non-Isothermal Experimental Data

In the present work, a new simple and robust approach, named ‘simulated isothermal’ technique, is proposed for getting isothermal transformation behavior of crystallization of glassy alloys at temperatures well above the normal crystallization temperatures (Tx) from a set of non-isothermal differential scanning calorimetric (DSC) scans performed at different heating rates. The isothermal and simulated isothermal kinetic data for the crystallization of glassy alloys compare well. The problem of finding small heat change on crystallization during isothermal DSC scans below Tx is avoided in the present approach, since it uses non-isothermal DSC scans, which is associated with large heat change on crystallization. It also enables to get complete understanding of the mechanism of crystallization of glassy alloys.

Microstructure evolution, hardening and thermal behavior of commercially pure copper subjected to torsion deformation

Commercial pure copper was torsion-deformed under equivalent strains from 1 to 5 at ambient temperature. Microstructure evolution of torsion samples was characterized using metallographic observation on the longitudinal section parallel to the torsion axis and transverse section perpendicular to the torsion axis. Elongated ultrafine grained structure was observed on the edge area of the bar samples. The grain size decreased with increasing shear strain. While no obvious refinement was significantly improved on the central area. Transmission electron microscopy (TEM) observation showed that microstructure refinement correlated with the accumulation and rearrangement of dislocations. The results of Vickers hardness measurement indicated that the inhomogeneous hardness distribution on the transverse section of samples was similar to the counterpart of microstructure. The variations of hardness and microstructure both depended on the value of torsional simple shear depending on the radial positions of the samples. The hardening of torsional samples was mainly attributed to dislocation strengthening. Differential scanning calorimeter (DSC) results revealed that an exothermic peak occurs in the temperature range ~250–300°C during the DSC scan of torsion samples.

Effects of amylose chain length and heat treatment on amylose–glycerol monocaprate complex formation

Aqueous mixtures of amylose with different chain lengths (DP 23–849), which had been enzymatically synthesized or isolated from potato and maize starches, and glycerol monocaprate (GMC, 5:1 weight ratio) were analyzed by using a differential scanning calorimeter (DSC). The mixtures were thermally treated (first DSC scan: 20–140°C, 5°C/min and prolonged heat treatment: 100°C for 24h) and its effect on the amylose–GMC complex formation was analyzed by DSC and X-ray diffractometer. The amylose, especially short ones, readily associated in the dispersion forming the amylose–amylose crystals but the presence of GMC inhibited the crystal formation. The longer amylose had the greater possibility for the complex formation with GMC, and the prolonged heat treatment facilitated the amylose–GMC complex formation. Both type I and type II complexes were formed during quenching after the initial DSC heating. However, only the type II complexes were formed after the prolonged heat treatment with improved crystallinity and thermostability.

Properties of a Model Aryl Boronic Acid and Its Boroxine

Many boronic acid-containing molecules are currently under investigation as possible therapeutics. An increase in the knowledge of the physical and chemical properties of these compounds will lead to their improved formulation into usable dosage forms. The current study describes the formation and characterization of a boronic acid anhydride, called a boroxine. The model boronic acid, 4-methoxybenzeneboronic acid is used. The current study demonstrates the utility of thermal (differential scanning calorimetry and thermogravimetric analysis) and spectral (solid-state nuclear magnetic resonance and ultraviolet spectroscopy) methods to quantitate and characterize the boronic acid and its boroxine, validated against definitive structures solved by single-crystal X-ray diffraction. The present work also demonstrates that the hydrolysis of the boroxine in the presence of water is very rapid in a time scale relative to drug substance manufacture and product formulation.

Effect of nanoclay and carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) rubber on the reaction induced phase separation and cure kinetics of an epoxy/cyclic anhydride system

The effects of nano clay, carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) liquid rubber and the combination of both on the cure kinetics of diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin/nadic methyl anhydride were studied. Cure kinetics studies were carried out by performing dynamic and isothermal differential scanning calorimetric (DSC) experiments. The dynamic DSC experiments were carried out at four different heating rates. Dynamic kinetic modeling was performed using Kissinger and Ozawa approaches. Since these methods are based exclusively on the maximum rate of cure, which occurs approximately at the beginning of the cure reaction, the activation energy calculated using these methods is valid only for the initial stage of the cure. The clay (3 phr) filled epoxy system has an activation energy 24 % lower than the unfilled system. The role of the surfactant chemistry on the initial stage of the cure reaction was also studied. A plausible reaction mechanism which involves the effect of the nanoclay surfactant as an accelerator of the cure reaction was proposed. The phase separated CTBN rubber hindered the cure reaction and has 3 % higher activation energy for epoxy/CTBN system than the unfilled system. In the ternary epoxy/3 phr clay/15 phr CTBN system, the accelerating effect of clay on cure was highlighted. The cure activation observed in the presence of clay overshadows the hindrance created by the phase separated CTBN. Isothermal DSC scans were carried out at five different temperatures. The experimental datas showed an autocatalytic behavior of the reaction, and the isothermal modeling was carried out by Kamal autocatalytic model. The results showed a very good agreement within the whole conversion range for the unfilled and all the filled systems. The evolution of the morphology and phase separation was also studied using optical and scanning electron microscope. Faster cure reaction resulted in smaller phase-separated CTBN particles in epoxy/clay/CTBN ternary system as compared with those observed in epoxy/CTBN binary blend.

Investigation of Crystallization Kinetics in Glassy Se and Binary Se&amp;lt;sub&amp;gt;98&amp;lt;/sub&amp;gt;M&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; (M=Ag, Cd, Zn) Alloys Using DSC Technique in Non-Isothermal Mode

The crystallization kinetics of glassy Se and binary Se98M2 (M=Ag, Cd, Zn) alloys have been studied at different heating rates (5, 10, 15, 20 Kmin-1) using Differential Scanning Calorimetric (DSC) technique. The crystallization temperature (Tc) is determined from exothermic peak obtained in DSC scans of present samples. The variation in peak crystallization temperature (Tc) with the heating rate (β) has been used to investigate the growth kinetics using Kissinger, Augis-Bennet and Matusita-Sakka models. The activation energy of crystallization (Ec) has been found to increase with Ag additive and to decrease with Zn and Cd additive. The value of various kinetic parameters such as rate constant (Kp), Avrami index (n), thermal stability (S) and Hruby number (Hr) have been calculated under non-isothermal mode. The maximum change in different kinetic parameters has been found after the incorporation of Ag additive.

Precipitation kinetics in Al-Si-Mg/TiB2 in-situ composites

Al-7Si-0.3Mg-TiB 2 in-situ composites were made by the salt-metal reaction i.e., the reaction of K 2 TiF 6 and KBF 4 salts with the molten alloy. The kinetics of the formation of intermediate metastable precipitates in the process of Mg 2 Si formation in Al-7Si-0.3Mg-TiB 2 in-situ composites with three different amounts of TiB 2 particles (2.5, 5 and 10 wt.%) were studied using differential scanning calorimeter (DSC) and also compared with the Al-7Si-0.3Mg base alloy. Kissinger analysis of non-isothermal DSC scans at various heating rates was carried out to evaluate the activation energies associated with the precipitation processes. The metastable precipitates were characterized by taking the solutionized samples to their respective DSC peak temperatures at a particular heating rate and the samples were then observed under a transmission electron microscopy. It was found that there is a decrease in the activation energies of the GP zones with increase in TiB 2 content.

Observation of phase separation in some Se–Te–Sn chalcogenide glasses

Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) techniques were employed here to investigate the glass transition behavior and crystallization kinetics of Se 80− x Te 20Sn x ( x=0.0, 2.5 and 5) alloys, which were prepared by the conventional melt quenching method. Two exothermic peaks have been observed in the DSC scans for the samples that contain Sn. Three crystalline phases (Se 7.68Te 0.32, SnSe and SnTe) were classified after heat treating the Se 77.5 Te 20Sn 2.5 glass at temperature corresponding to the second crystallization peaks for 3 h. All the characteristic temperatures such as glass transition temperature ( T g ), crystallization temperature ( T c ) and crystallization peak temperatures ( T p ) were found to depend on both the heating rate and the composition. This dependence has been used to deduce the activation energy of the glass transition ( E g ), the activation energy of crystallization ( E c ), the Avrami exponent ( n), thermal stability and the fragility index ( F i ).

Ionic liquids: Determination of their aqueous content using differential scanning calorimeter equipment, chaotic parameters and a radial basis network model

A new computerized approach to the determination of water in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium hexafluorophosfate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ionic liquids (ILs) using the differential scanning calorimeter (DSC) scans of their mixtures with water is presented here. This approach consists of a combination of chaotic algorithms and a radial basis network (RBN). The data collected (heat flow signal) from DSC scans of ILs and water mixtures are used to calculate six chaotic parameters (two Liapunov exponents, two correlation parameters and two fractal dimensions), and then, these values are transferred into an RBN trained computer for modeling and estimating output. The predicted results using the RBN were compared with the measurements of water content carried out by the Karl Fischer technique and the difference between the real and predicted values was less than 0.05 and 4.9% in the internal and external validation, respectively. Such an integrated chaotic parameters (CPs)/RBN system is capable of detecting and quantifying water content in the aforementioned ILs, based on the created models and patterns, without any previous knowledge of this thermal process.

Modified Cyclohexanone-Formaldehyde Resin as an Epoxy Resin Curing Agent

Cyclohexanone-formaldehyde (CHF) resin was brominated and the brominated CHF (BCHF) was then reacted with excess aromatic diamines. The aminated CHF resins designated as ACHFs (modified ketone resin) were characterized and then applied as epoxy resin curing agents. Thus, the curing of the commercial epoxy resin diglycidil ether of bisphenol-A (DGEBA) by ACHFs was monitored by differential scanning calorimetric (DSC), based on the the DSC scans, the glass fiber-reinforced composites of DGEBA-ACHF systems were prepared and characterized by chemical resistivity and mechanical properties.

Polylactide/nano‐ and micro‐scale silica composite films. II. Melting behavior and cold crystallization

AbstractNonisothermal crystallization of polylactide (PLA)/silica composites prepared by (i) directly blending the PLA with nanoscale colloidal silica sol and by (ii) a sol–gel process are studied by differential scanning calorimeter (DSC) at various heating rates. Samples quenched from the molten state exhibited two melting endotherms (Tml and Tmh) due to melt‐recrystallization during the DSC scans. Lower heating rate and the presence of silica particles generate a lower peak intensity ratio of Tml /Tmh. The nonisothermal crystallization kinetics is analyzed by modified Avrami model, Ozawa model, and Liu‐Mo models. The modified Avrami and Liu‐Mo models successfully described the nonisothermal cold crystallization processes, but Ozawa is inapplicable. The nucleation constant (Kg) is calculated by modified Lauritzen‐Hoffman equation and the activation energy by Augis‐Bennett, Kissinger, and Takhor models. These calculated parameters indicate consistently that the nanoscale silica particles seem to form more heterogeneous nucleation to increase crystallization, but microscale one form hindrance to retard crystallization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

An Investigation on Wetting Characteristics of Solder Particle for Solderable Electrically Conductive Adhesives (ECAs)

A novel electrically conductive adhesives (ECAs) with solder particle have been developed. The kinetics of the curing reaction were investigated using isothermal differential scanning calorimeter (DSC). The dynamic DSC scans were also conducted to investigate the temperature dependant curing degree. The temperature dependant viscosity characteristic of polymer was investigated using rheometer. The wetting characteristic of two solders on two kinds of metals were investigated using an optical microscope. It was found that developed resin material showed good fluxing capacity against Sn-Bi solder on Ni/Au and the wetting angles was about 24º.

Effect of aerosil dispersions on the photoinduced nematic–isotropic transition

We report differential scanning calorimetric (DSC) and dielectric measurements on thenematic–isotropic transition in the bulk and aerosil composites of a liquid-crystal mixturehaving a photoactive guest azobenzene compound in a non-photoactive host, 4-n-heptylcyanobiphenyl (7CB). The DSC scans taken at different cooling rates show that, at slowerrates, the bulk displays a single peak across the transition, whereas the composites in thesoft gel regime exhibit a double-peak profile. Such a double-peak profile, although seen inhigh-resolution ac calorimetric studies, has been observed for the first time inDSC experiments. The temperature range of the region between the two peaks iscomparable to that seen in ac calorimetric experiments and has similar features.This observation is significant since the appearance of the low-temperature peakin ac calorimetric data has been explained to be due to a crossover from therandom-dilution to the random-field limits. This work also constitutes the firstexperiments on the photoisomerization driven isothermal phase transitions inliquid-crystal–aerosil composites. The studies carried out in the absence and presence of alow-magnitude UV radiation not only bring out the standard features now establishedfor such photostimulated phase transitions, but display a few surprises. Notableamong them are that (i) the photoinduced shift in the transition temperature is anon-monotonic function of the aerosil composition and appears qualitatively similar to thedependence of the transition temperature itself, and (ii) the thermal anomaly mentionedabove characterizing the crossover is also seen in the temperature-dependentas well as the temporal variation of the sample capacitance for a composite inthe soft gel regime. We have also evaluated, using the temporal variation of thecapacitance, the different response times associated with the UV-on photochemicalprocess as well as the UV-off thermal back-relaxation process; the response timesappear to have a similar dependence on the aerosil concentration as the transitiontemperature.

Free Volume Micro Probe Study of Silver Ions Implanted in Polycarbonate

Positron lifetime, UV-VIS absorption and differential scanning calorimetric (DSC) measurements were performed on pristine polycarbonate (PC) and Ag2+-ion-implanted polycarbonate before and after isochronal annealing treatment. UV absorption results indicated the formation of silver clusters in the polymer matrix. The cluster sizes and number of atoms in these clusters were evaluated from UV results. DSC scans for the sample before and after implantation revealed the diffusion of silver ions in the matrix. Further, these results reveal that the Tg of the implanted PC decreased from its pristine value before annealing whereas it increased after annealing. This was inferred to be due to the formation of cross-links by Ag2+ ions when implanted but after annealing, the cross-link seemed to decrease, which resulted in increased diffusion. Positron results as a function of annealing temperature revealed that small size clusters may have been formed in the available free volume and there was migration of silver atoms in the polymer matrix due the rearrangement of the polymer chains. From the positron results the activation energy for the diffusion of silver atoms was determined to be 0.6 eV.

Melting behaviors, crystallization kinetics, and spherulitic morphologies of poly(butylene succinate) and its copolyester modified with rosin maleopimaric acid anhydride

AbstractThis article investigated the melting behaviors, crystallization kinetics, and spherulitic morphologies of poly(butylene succinate) (PBS) and its copolyester (PBSR) modified with rosin maleopimaric acid anhydride, using wide‐angle X‐ray diffraction, differential scanning calorimeter (DSC), and polarized optical microscope. Subsequent DSC scans of isothermally crystallized PBS and PBSR exhibited two melting endotherms, respectively, which was due to the melt‐recrystallization process occurring during the DSC scans. The equilibrium melting point of PBSR (125.9 °C) was lower than that of PBS (139 °C). The commonly used Avrami equation was used to describe the isothermal crystallization kinetics. For nonisothermal crystallization studies, the model combining Avrami equation and Ozawa equation was employed. The result showed a consistent trend in the crystallization process. The crystallization rate was decreased, the perfection of crystals was decreased, the recrystallization was reduced, and the spherulitic morphologies were changed when the huge hydrogenated phenanthrene ring was added into the chain of PBS. The activation energy (ΔE) for the isothermal crystallization process determined by Arrhenius method was 255.9 kJ/mol for PBS and 345.7 kJ/mol for PBSR. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 900–913, 2006

Observation of phase separation in some Se–Te–Ag chalcogenide glasses

Differential scanning calorimetric (DSC) measurements have been made in glassy Se 70Te 30− x Ag x alloys. At low concentration of Ag ( x = 2, 4, 6), only one endothermic and one exothermic peaks are observed at glass transition and crystallization temperatures. However, at higher concentration of Ag ( x = 8, 10), two endothermic and two exothermic peaks have been observed in DSC scans. The double stage crystallization at higher concentration of Ag has also been reported in various other glassy systems by other workers. The activation energy of crystallization ( E c) has been determined for each stage.