Differential Scanning Calorimetry Heating Curves Research Articles

Dynamic Cyclic Fatigue and Differential Scanning Calorimetry Analysis of R-Motion

The aim of this study was to assess the dynamic cyclic fatigue resistance of an R-Motion file at simulated body temperature and document corresponding phase transformations compared to OneCurve and HyFlex EDM (HFEDM). R-Motion (25/.06), OneCurve (25/.06), and HFEDM (25/.06) files were selected and divided into 3 groups (n=9) according to the file type. Dynamic cyclic fatigue testing was done with a custom-made artificial stainless-steel canal that had a 90° angle of curvature and a 5-mm radius of curvature. Files were operated continuously at body temperature until fracture in the artificial canal. The time to fracture was calculated. Statistical analysis was performed, and significance was set at 5%. Phase transformation temperatures for 2 instruments of each group were analysed by differential scanning calorimetry (DSC) analysis. The highest mean time to fracture value was measured in the HFEDM group (277.84 ± 2.51), followed by the R-Motion group (115.09 ± 0.01), whilst the lowest value was found in the OneCurve group (44.28 ± 3.63). Post hoc pairwise comparisons were all statistically significant (P < .001). DSC heating curves show austinite start temperatures to be 33.94 °C and 43.32 °C and austinite finish temperatures to be 35.09 °C and 50 °C for R-Motion and HFEDM, respectively. DSC cooling curves show martensite start temperatures to be 27.54 °C and 44.52 °C and martensite finish temperatures to be 29.13 °C and 37.68 °C for R-Motion and HFEDM, respectively. DSC curves of OneCurve failed to demonstrate transformation temperatures within the tested heat range. Crystalline arrangement of Ni and Ti atoms within the NiTi alloys greatly affects the dynamic cyclic fatigue resistance of the file.

Structural Changes due to Heating and Stress Loading of Metastable Quenched Martensite Structures in Ti–(10–20) mass% Nb Alloys

The metastable-phase characteristics of Ti–Nb alloys can be exploited to improve their functional properties such as damping. In this study, we investigated the structural changes in the metastable quenched martensite structure of Ti–Nb alloys subjected to heating and tensile strain. We examined the differential scanning calorimetry (DSC) heating curves in the reduction state, X-ray diffraction (XRD) profiles under loading/unloading, and material properties such as Young’s modulus and internal friction upon heating. In the DSC heating curve of the 10%-cold-rolled Ti15Nb specimen, an exothermic peak was observed, and for Ti18Nb and Ti20Nb, the exothermic peak exhibited broadening. We speculate that the underlying reason is the biphasic formation resulting from specimen deformation. From the XRD measurements, we found that the lattice tended to shrink upon stress application and recover upon unloading. Significant changes in Young’s modulus and internal friction were observed in the α′′ structures of Ti18Nb and Ti20Nb during initial heating up to 373 K. We posit that the material properties changed owing to structural changes, such as lattice-constant changes, biphasic formation, and crystal orientation changes, resulting from heating or plastic deformation.

Fabrication and Properties of Self-crimp Side-by-Side Bicomponent Filaments Composed of Polyethylene Terephthalates with Different Intrinsic Viscosity

Abstract Self-crimp side-by-side bicomponent filaments (SBSBFs) were prepared via melt spinning using two kinds of polyethylene terephthalate (PET) with great disparity of intrinsic viscosity. The influence of the volume ratio on the surface morphology, crystallinity, crimping properties, mechanical properties and shrinkage properties of the bicomponent filaments was investigated using wide-angle X-ray diffraction, a differential scanning calorimetry (DSC), scanning electron microscope, etc. As the proportion of the low-viscosity component increases, the shrinkage in boiling water or hot air, as well as the shrinkage force and the sonic orientation factor of the bicomponent filaments decrease, and the DSC heating curves change from double peaks to a single peak. These phenomena should be ascribed to the high orientation and low crystallinity of the high-viscosity PET component and low orientation and high crystallinity of the low-viscosity PET component. Moreover, the crimp property of the bicomponent filament with a volume ratio of 50:50 is superior to those with other volume ratios.

Thermal and microstructural analysis of the low-melting Bi-In-Pb alloy

Low-melting alloys, based on bismuth and indium, have found commercial use in soldering, safety devices, coatings, and bonding applications. In this respect, the accurate knowledge of their thermal properties such as melting and solidification temperatures, latent heat of melting, supercooling tendency, etc. is of large importance. In the present research, low-melting alloy with nominal composition Bi40In40Pb20 (at. %) was investigated by means of scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS) and by differential scanning calorimetry (DSC). Microstructural and chemical (SEM-EDS) analysis has revealed the existence of two coexisting phases in the prepared alloy, which was identified as BiIn and (Pb). Melting and solidification temperatures and the related heat effects were measured by the DSC technique. The solidus temperature obtained from the DSC heating curves was 76.3 °C and the solidus temperature obtained from the corresponding DSC cooling runs was 61.2 °C. The experimentally obtained results were compared with the results of thermodynamic calculation according to CALPHAD (calculation of phase diagram) approach, and a close agreement was noticed.

High-Performance n -Hexane Purification by Nonporous Adaptive Crystals of Leaning Pillar[6]arene

The production of high-purity n-hexane under mild conditions is of great significance in both the petrochemical industry and synthetic chemistry. Here, we report an easy-to-operate and energy-effic...

Interpretation of Double-Peak Endotherm on DSC Heating Curves of Bitumen

Since the late 1960s, differential scanning calorimetry (DSC) has been used to characterize petroleum bitumen, in particular, for the determination of the crystallized fraction (CF) content. This p...

Thermal properties of lignin-based polycaprolactones

Lignin-based polycaprolactone (PCL) graft copolymers with various graft ratios were prepared by ring-opening reaction in order to design new lignin derivatives. Molecular length of PCL side chain was varied in a wide range, i.e. caprolactone/hydroxyl group (CL/OH) ratio was varied from 3 to 100 mol mol−1. The effect of lignin on thermal properties of PCL was examined by differential scanning calorimetry (DSC) and thermogravimetry. In DSC heating curves of lignin-based PCL, glass transition, pre-melt crystallization and melting were observed. From DSC results, the phase diagram of lignin-based PCL was established. It was found that glass transition temperature (Tg) decreased until CL/OH ratio reached 20, and then, Tg was maintained at around 200 K. Tg slightly increased when CL/OH ratio became higher than 20. The above facts suggest that the random structure of lignin affects the molecular motion of copolymers in a limited length of PCL chains, and that with increasing PCL chain length, free molecular motion is restricted by crystallization. The amorphous region of lignin–PCL was reorganized at pre-melt crystallization, and crystallinity increased. When CL/OH ratio increased more than 20, two melting peaks were observed; the low-temperature side is PCL crystallite affected by lignin and the high-temperature side melting peak is attributed to melting PCL crystal. The effect of lignin on thermal decomposition is apparently observed for lignin-based PCL when CL/OH ratio is smaller than 20. The above results suggest that lignin-based PCL graft copolymers have the potential of an applicant of novel nature-friendly polymers.

Biobased odd–odd poly(propylene dicarboxylate)s

Biobased odd–odd poly(propylene dicarboxylate)s, based on 1,3-propanediol and three odd diacids [i.e., glutaric acid (C5), pimelic acid (C7) or azelaic acid (C9)], have been synthesized and analyzed, in order to study the effect of chain length of aliphatic diacids on thermal properties. Crystallization and melting behaviors were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), temperature-modulated differential scanning calorimetry (TMDSC) and polarized optical microscope (POM). DSC results suggested that the crystallization ability increases with the increasing chain length. WAXD patterns of the three polyesters showed a similar crystal structure. In DSC heating curves after isothermal crystallization of the samples, three endothermic peaks for the polyesters at shorter chain length (C5, C7) and at most four endothermic peaks for longer-chain-length polyester (C9) were displayed, and the mechanism of the multiple melting phenomenon was discussed. One or two exothermic peaks can be seen for shorter (C7) or longer (C9) polyester in the non-reversible heat flows of TMDSC, respectively, which evidenced once or twice melting–recrystallization–remelting processes occurring during melting heating. Finally, POM observation indicated that the spherulitic growth rate increases with the increasing chain length. Besides, ring-banded structures were observed in short-chain-length (C5, C7) samples, but C9 aliphatic polyester.

Variation of the Structure-and-Phase Condition and Physical and Mechanical Properties of Cold-Deformed Leaded Brass Under Heating

The methods of optical and scanning electron microscopy, microhardness measurement, differential scanning calorimetry (DSC), dilatometry, dynamic mechanical analysis, and hydrostatic weighing are used to study the structure and the physical and mechanical properties (density, microhardness, modulus of elasticity, coefficient of linear thermal expansion) of cold-deformed brass LS59-1 in the initial condition and after heating to 800°C. The DSC heating curve exhibits exo- and endothermic effects due to stress relaxation and retrogression (the exothermic effect at 115 – 235°C), melting of lead segregations (the endothermic effect at about 328°C), transition of the β′-phase into a disordered β -condition (the endothermic effect with minimum at 458°C), and transition of the brass into a single-phase β -condition (the endothermic effect at 642 – 747°C with minimum at 721°C).

Thixoformability and Microstructural Evolution of Al-Si-Cu Alloys

Abstract Commercial aluminium casting alloys such as those from Al-Si-Cu family are widely used in the automotive industry because of their combinations of good fluidity and mechanical strength. Semisolid metal processing utilizing these alloys thus far has given products with better mechanical properties over those produced via traditional metal forming processes. However, there is still demand to widen the range of suitable alloys for the semisolid processing. One way of achieving this is by modifying the alloy compositions. Hence, modified alloys under this family were formulated and assessed. This paper reports results of the thermodynamics evaluation and microstructural evolution for one of these modified alloys, and comparing them with that of the commercially available A319 alloy. Data from Differential Scanning Calorimetry heating curves along the semi-solid range of the alloys were analysed and used as an approximation in determining their thixoformability. The work had demonstrated that the selected modified alloy is suitable for semisolid processing by having wider working window temperature, lower temperature sensitivity of liquid fraction and adequate solidification range. Both alloys, the modified and the commercial A319 alloys, were also successfully thixoformed and their microstructural features and quantitative measures obtained and compared. They both had given the shape factor and solid globule size within the acceptable values for the semisolid processing, i.e. of around 0.7-0.8 and 50-60 µm, respectively. However, in short, the modified alloy has shown better thixoformability characteristics than the commercial alloy.

The DSC Investigation on Phase Transformations of Directionally Solidified (DS) and Powder Metallurgy (PM) Ni-Base Superalloys

The phase transformations of the directionally solidified (DS) and powder metallurgy (PM) Ni-base superalloys were investigated by JMatPro, synchrotron XRD (SXRD) and differential scanning calorimetry (DSC). The minor phases, such as MC, eutectic γ′ and Ni5Hf, and γ matrix with secondary γ′ existed in as-cast microstructure of DS DZ22. However, only γ matrix was found in PM625 alloy powders. The phase change in both heating (melting) and cooling (solidification) process was investigated by DSC on DZ22 test bar and PM625 alloy powders respectively. The DSC experiment with different heating/cooling rates (5-40°C/min) was performed on DS superalloy DZ22. The results indicated that the heating/cooling rate had obvious effect on the DSC results of the phase transformation temperatures of liquidus, MC carbides, solidus, eutectic (γ+γ′) and secondary γ′. The heating and cooling DSC curves shifted to high and low temperature direction respectively, accompanied by the heating/cooling rate increased. However, the average values of specific peaks of heating and cooling curves are relatively consistent which is close to the equilibrium phase change temperatures of the alloy and makes the results comparable. Besides the average value method, the liquidus temperature of the alloy (0°C/min) can also be obtained by method of linear-fit/extrapolating from 5-40°C/min heating/cooling rates or inflection point deviate from the baseline of DSC cooling curves which could minimize the heating/cooling rate effects. The DSC experiment was carried out on PM625 superalloy powders with different particle size range (0-355μm), the results indicated that the particle size had minor effect on liquidus and solidus temperatures of DSC heating curves, the differences were less than 2°C. The change in phase transformation temperatures under different heating/cooling rate should be considered for selecting the process parameter (heat treatment, HIP or casting) for manufacturing Ni-base superalloy components.

Modelling of differential scanning calorimetry heating curves for precipitation and dissolution in an Al-Mg-Si

A detailed understanding of precipitation is essential to alloy and process design in age hardened metals, but experimental observation of the underlying processes is challenging. To accelerate such investigations, we introduce a model to simulate Differential Scanning Calorimetry (DSC) curves. The precipitation behavior of an AA6016 aluminum alloy was simulated by a classical nucleation and growth model, coupled with a thermodynamic database containing Al, Mg, Si, Fe, Cu and Mn and their corresponding stable and metastable phases. The focus was laid on the evolution of the phases β″, β′, β (Mg2Si) and Si under isothermal and non-isothermal conditions. DSC tests with rates of 5 and 10 K/min were conducted in the temperature range of 100–500 °C. The simulations were compared to these experiments. Transmission Electron Microscopy (TEM) was used to verify the precipitate phases and their sizes. The simulation results agree well with the experimental DSC curves and particle sizes.

Extraction of soursop oil (Annona muricata L.) by ultrasonic technique

The soursop, Annona muricata L., Annonaceae family is a fruit mostly found in the northern and northeastern of Brazil, the Caribbean, and Central America. Extraction of the soursop seed oil was carried out in an ultrasound bath, yelling a 20% w/w yield, and fatty acids profile analyzed by gas chromatography indicated a predominance of stearic, oleic, and palmitic acid, in a relative percentage of 40.47%, 31.87%, and 19.82%, respectively. Thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) were used to characterize the thermal behavior of this oil. The phase transition of this oil was evaluated by DSC analysis, on heating and cooling modes. Additionally, the thermal behavior analysis evaluated by TG and DTG was carried out with two different sample masses and three heating rates (5, 10, and 20 °C min−1) under oxidant and inert purge gases. The cooling and heating DSC curves indicate the influence of saturated and unsaturated fatty acids in the thermal behavior. The activation energy (Ea) was obtained with the isoconversional methods proposed by Capela and Ribeiro, Ozawa and Friedman, and the resultant data lead to a dependence on the sample mass and purge gases, which show several kinetic patterns.

Structure and properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/poly(L-lactic acid) quasi core/sheath melt-electrospun microfibers

A facile route was proposed to fabricate core–sheath microfibers, and the relationships among processing parameters, crystalline structures and the mechanical properties were investigated. The compression molded poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH)/poly(L-lactic acid) (PLLA) strip enhanced the spinnability of PHBH and the mechanical properties of PLLA as well. The core–sheath ratio of the fibers was determined by the prefab strip, while the PLLA sheath component did not completely cover the PHBH core component due to the weak interfacial tension between the melts of PHBH and PLLA. A rotational target was applied to collect aligned fibers, which were further drawn in a water bath. The tensile strength and the modulus of as-spun and drawn fibers increased with increasing the take-up velocities. When the take-up velocity was above 500 m/min, the jet became unstable and started to break up at the tip of the Taylor cone, decreasing the mechanical properties of the fibers. The drawing process facilitated the crystallization of PLLA and PHBH, and the tensile strength and the modulus increased linearly with the increasing the draw ratio. The crystal information displayed from wide-angle X-ray diffraction patterns and differential scanning calorimetry heating curves supported the results of the tensile tests.

Thermal properties of freezing bound water restrained by sodium lignosulfonate-based polyurethane hydrogels

In order to develop a new functional product from lignin, sodium lignosulfonate (LS)-based polyurethane (LSPU) hydrogels were prepared from LS and hexamethylene diisocyanate (HDI) derivatives in water. Isocyanate/hydroxyl group ratio (NCO/OH ratio) was varied from 0.05 to 0.8 mol mol−1, and water content (Wc = mass of water/mass of dry sample) of the obtained LSPU hydrogels was varied from 0 to 3.0 g g−1. Phase transition behavior of hydrogels with various Wc’s was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). In DSC heating curve of LSPU hydrogels, glass transition, cold crystallization, melting and liquid crystallization were observed. Cold crystallization, two melting peaks and variation of melting enthalpy indicate that three kinds of water, i.e., non-freezing water, freezing bound water and free water, exist in LSPU hydrogel. Glass transition temperature (Tg) decreased from 230 to 190 K in a Wc range where non-freezing water was formed in the hydrogel. Tg increased when freezing bound water was formed in the system. Tg leveled off in a Wc range where normal ice was formed. The effect of NCO/OH ratio on molecular motion of LSPU hydrogel is examined based on Tg and heat capacity difference at Tg (ΔCp). Water vaporization curve measured by TG also indicates the presence of bound water which evaporates at a temperature higher than ca. 410 K. By atomic force microscopic observation, the size of molecular bundle of LSPU hydrogel is calculated and compared with that of LS-water system. By cross-linking, the height of molecular bundle decreased from ca. 3–1 nm and lignin molecules extend in a flat structure.

Phase transition of poly(vinyl alcohol) hydrogel filled with micro-fibrillated cellulose

Aqueous solution of poly(vinyl alcohol) (PVA) forms hydrogels by freezing and thawing. In this study, micro-fibrillated cellulose (MFC) was mixed with PVA aqueous solution. Thermal properties of PVA–MFC composite hydrogels were investigated in a wide range of water content by differential scanning calorimetry (DSC). On DSC heating curves, glass transition, exothermic peak due to cold crystallization and endothermic peak attributed to melting of water were observed. Phase diagrams of PVA–MFC composite hydrogels were established based on transition temperatures. The amount of non-freezing water increased when MFC is introduced into hydrogels. Glass transition temperature of amorphous ice restrained by PVA–MFC composite hydrogel is restricted by the presence of MFC. Results obtained by DSC suggest that gelation occurs in adjacent PVA molecules due to compartmentalization in the presence of MFC molecules.

Mixed metal carbonates/hydroxides for concentrating solar power analyzed with DSC and XRD

Li2CO3–Na2CO3–K2CO3 molten salt mixtures are potentially suitable for high temperature thermal energy storage in the concentrating solar power. We investigated the LiNaK carbonate salt with hydroxides of lithium (LiOH), potassium (KOH), or calcium (Ca(OH)2) by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). From the repeated heating DSC curves, lower melting points with excellent reproducibility were found when 10wt% LiOH or KOH was added into 40wt%Li2CO3–20wt%Na2CO3–40wt%K2CO3. Based on the characterization of XRD patterns, the molten eutectic mixtures consisted of LiKCO3, LiNaCO3, and residual Li2CO3 when the ternary carbonate salt was heated at the temperature above the melting point and cooled rapidly. In the system of LiNaK carbonate salt with additives of LiOH or KOH, more LiKCO3 and LiNaCO3 with lower melting point can be formed by substitution reaction. Thus, optimal molar ratio for the mixed molten salts with low melting point could be quickly obtained by studying the composition of the resulting eutectic mixtures.

Shape‐Memory Polymer Networks Prepared from Star‐Shaped Poly[(L‐lactide)‐co‐glycolide] Precursors

SummaryAmorphous degradable copolymer networks such as poly[(L‐lactide)‐co‐glycolide] (PLGA) are promising multifunctional polymers with tailorable degradation profiles and capable of a thermally‐induced shape‐memory effect. Currently, the shape‐memory performance for covalently crosslinked networks based on linear PLGA dimethacrylate precursors (cPLGA) is limited. In this study we explored the shape‐memory properties of cPLGA networks prepared from three‐armed 2‐isocyanatoethyl methacrylate functionalized precursors via photopolymerization. cPLGA exhibited excellent dual‐shape properties characterized by an almost complete fixation of the temporary shape as well as an almost perfect recovery of the original shape. In the dry state cPLGA exhibited a switching temperature (Tsw) of 60 °C with a narrow recovery temperature interval of ΔTrec = 5 °C, while a significant lower Tsw of 40 °C with a ΔTrec = 15 °C was obtained when the polymer network was investigated in an aqueous environment. A concomitant decrease in the glass transition temperature could be observed in differential scanning calorimetry heating curves for copolymer networks after storage in aqueous buffer solution at 37 °C for 7 days, which can be attributed to the up‐take of water molecules (1.5 wt%). The shape‐memory properties achieved for cPLGA, in particular the shape recovery ratio and ΔTrec were superior to those of analogous polymer networks based on linear PLGA dimethacrylates.

Studies on Diels–Alder thermoresponsive networks based on ether–urethane bismaleimide functionalized poly(vinyl alcohol)

Thermoreversible networks obtained by the Diels–Alder cycloaddition reaction of poly(vinyl furfural) with urethane bismaleimides containing polyether chain were synthesized. The formation of the networks was confirmed by attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR–FTIR). The materials thermal properties were investigated using differential scanning calorimetry (DSC) and a coupling of dynamic thermogravimetry with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS) for pyrolysis behaviour under nitrogen atmosphere. A thermal decomposition mechanism of the networks and poly(vinyl furfural) was discussed via evolved gas analysis. The thermoreversibility of the networks was demonstrated by the presence of the endothermic peak characteristic to the retrodienic process on the DSC heating curves and also the appearance of the exothermic peak, due to the dienic process, on the DSC cooling curve. The dynamic contact angle and free surface energy values of the networks were determined. Measures of the heterogeneity and roughness of the surfaces suggested that the surfaces of the networks’ films are more homogenous than the initial poly(vinyl furfural) surface. Dynamic water vapour sorption studies were conducted.

Radiopaque iodinated poly(ester-urethane)s based on poly(butylene succinate): Retarded crystallization and dual recrystallization behaviour

A series of biodegradable radiopaque iodinated poly(ester-urethane)s (IPEUs) were synthesized by chain-extension of dihydroxylated poly(butylene succinate) (PBS–OH) and isophorone diisocyanate (IPDI) with iodinated bisphenol-A (IBPA). The effects of IBPA on the crystallization and melting behaviour of IPEUs were investigated by wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC). WAXD results suggest that the PBS soft segments form only one crystal modification, and that the crystallinity of the samples decreases with increasing the amorphous hard segments. POM observation indicates that the ring-bands of spherulites disappear and then the spherulitic texture is disturbed with increasing the IBPA content. The analysis of isothermal crystallization kinetics shows that the crystallization of IPEUs is retarded by the introduction of IBPA chain extender with bulky pendent groups. In the DSC heating curves, at most four endothermic peaks were observed and their origins were examined. Two recrystallization exothermic peaks were observed for IPEUs in the nonreversible signals of TMDSC. The twice sequential melting–recrystallization–remelting model could be used to explain the multiple melting behaviour of IPEUs.