Differential Scanning Calorimetric Measurements Research Articles

Magnetic Field-Induced Reverse Martensitic Transformation and Thermal Transformation Arrest Phenomenon of Ni41Co9Mn39Sb11 Alloy

In order to investigate behavior of magnetic field-induced reverse martensitic transformation for Ni-Co-Mn-Sb, magnetization experiments up to a static magnetic field of 18 T and a pulsed magnetic field of 40 T were carried out. In the thermomagnetization curves for Ni41Co9Mn39Sb11 alloy, the equilibrium transformation temperature T0 was observed to decrease with increasing applied magnetic field, μ0H, at a rate of dT0/dμ0H = 4.6 K/T. The estimated value of entropy change evaluated from the Clausius-Clapeyron relation was about 14.1 J/(K·kg), which was in good agreement with the value obtained by differential scanning calorimetric measurements. For the isothermal magnetization curves, metamagnetic behavior associated with the magnetic field-induced martensitic transformation was observed. The equilibrium magnetic field, μ0H0 = (μ0HAf + μ0HMs)/2, of the martensitic transformation tended to be saturated at lower temperature; that is, transformation arrest phenomenon was confirmed for the Ni-Co-Mn-Sb system, analogous with the Ni(Co)-Mn-Z (Z = In, Sn, Ga, Al) alloys. Temperature dependence of the magnetic field hysteresis, μ0Hhys = μ0HAf − μ0HMs, was analyzed based on the model for the plastic deformation introduced by the dislocations. The behavior can be explained by the model and the difference of the sweeping rate of the applied magnetic field was well reflected by the experimental results.

Effect of barley β-glucan concentrate on oscillatory and creep behavior of composite wheat flour dough

Soluble dietary fibers can be used as valuable functional ingredients in food products because of their ability to influence the structural properties of the matrix in which they are embedded. The influence of barley β-glucan concentrate (BGC) addition (up to 10%) into standard wheat flour dough was evaluated through small and large deformation rheological measurements at selected temperatures (25–85°C). Upon addition of BGC (⩽5%), significant increase in mixing time, dough stability and water absorption, and decrease in extensibility were recorded. The mechanical strength of the composite doughs lowered with increasing water content but it improved with BGC incorporation at constant moisture content within the studied frequency range (0.1–10Hz). Both the elastic modulus (G′) and the complex viscosity (η∗) of doughs showed the temperature dependency within the frequency range tested. Time–temperature superposition of η∗–ω curves fitted well for up to 5% BGC incorporation when G′–ω failed at similar condition. Creep–recovery tests for BGC incorporated doughs recorded greater resistance to deformation. Differential scanning calorimetric measurement showed the protein denaturation temperature was influenced by both levels of wheat flour substitution by BGC and moisture content in the dough. Scanning electron microscopy used to study microstructure of doughs.

Crosslinking of gelatin membranes with ferulic acid or glutaraldehyde: Relationship between gas permeability and renaturation level of gelatin triple helices

ABSTRACTThis study investigated the gas separation membranes made with gelatin, crosslinked with ferulic acid (FA) and blended with polyethylene glycol (PEG) 200, by using a solvent‐free procedure. Gas permeation properties (He, N2, O2, and CO2) of these “green membranes” were studied and discussed in relation with their structure. Differential scanning calorimetric measurements were carried out to determine the gelatin triple helical renaturation level. The lowest permeability values [He and CO2 permeability (4.5 × 10−2 Barrer) with CO2/O2 selectivity of 14.5] were reached with gelatin/PEG 200 uncrosslinked membranes showing the highest renaturation level (40%). Crosslinking with FA lead to less rigid and brittle materials than GTA and to 10 times more permeable membranes compared with uncrosslinked membranes. Membranes crosslinked with glutaraldehyde broke during gas permeation measurements. Results demonstrated that higher gas permeability values were closely related to lower renaturation level of gelatin. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 280–287

Thermal and Tensile Behavior of HD-PE Films Containing Iron (III) Acetylacetonate after UV Irradiation

Abstract The thermal, tensile and other properties of high density polyethylene films containing iron (III) acetylacetonate as pro-oxidant additive have been studied after exposure to UV irradiation for up to 300 h. The effect of photooxidation on polyethylene films with and without pro-oxidant was estimated by Fourier transform infrared spectroscopy, X-ray diffraction analysis, Differential scanning calorimeter measurements and the tensile properties. It was observed that UV irradiation had almost no effect on the melting temperature of the different samples. After exposure, the degree of crystallinity increased from 69% to 72% for the initial polyethylene samples without pro-oxidant additive and by 3% for the samples containing iron (III) acetylacetonate. It was found that the increase in the carbonyl index of initial HDPE was not significant even after 60 h exposure to UV irradiation while samples with pro-oxidant suffered substantial degradation still for 35 h. It was observed that the decrease of the tensile strength is more pronounced for the samples with pro-oxidant under irradiation for 60 to 70 h. The films containing pro-oxidant lose ∼90% of its initial elongation at break after 35 h exposure.

Complexation (cucurbit[6]uril-pyrene): Thermodynamic and spectroscopic properties

The influence of the macrocyclic compound cucurbit[6]uril (CB6) on the photophysical properties of the fluorophore pyrene (PYR) has been studied. Guest–host interaction was observed by UV–visible spectroscopy and spectrofluorimetry. The fluorescence of PYR was significantly increased in the presence of CB6. The binding equilibrium constants for the complex with 1:1 stoichiometry were determined in HCOOH 55% w/v. The values of the association constants, KA, and the fluorescence quantum yield ratios between complexed and free substrate, ϕPYR–CB6/ϕPYR, at different temperatures were (3.1±0.9)×102M−1 and (5.1±0.2), (3.6±0.5)×102M−1 and (5.9±0.1), (4.8±0.7)×102M−1 and (5.5±0.1) at 15.0°C, 25.0°C and 40.0°C, respectively.The enthalpic and entropic contributions to the complexation process were determined, yielding ΔS=(92±3) Jmol−1K−1 and ΔH=(13±1) kJmol−1. From these results it can be concluded that the complex formation is mainly driven by the entropic term. The forces involved in the complexation are interpreted from the sign and magnitude of the thermodynamic parameters obtained.The partial inclusion of PYR or the formation of a suspended complex is proposed in base of all the data. The interaction is also demonstrated in the solid state by differential scanning calorimetric (DSC) measurements.

Study of thermo-oxidative chemical pre-treatment of isotactic polypropylene

A thermo-oxidative pre-treatment with chemical solutions is required in order to provide the adherence of inorganic semiconductor to the isotactic polypropylene (iPP) surface. A few thin films of iPP were treated with oxidizing solution at 90 °C. The crystalline properties were analyzed using XRD, and it had shown the presence of the α-monoclinic phases. The ATR-FTIR spectra had indicated that characteristic iPP peaks after thermo-oxidative chemical pre-treatment diminished sharply. Moreover, the new carbonyl groups (C = O) were observed, which signified oxidation. The UV–Vis spectra had showed a blue shift in the absorption edge, which corresponded to decrease in the optical band gap. The non-isothermal decomposition and crystallization kinetics of iPP films were studied and compared by means of thermogravimetric analysis and differential scanning calorimetric measurement. The values of the melting temperature T m and the crystallization temperature T c were found to be iPP surface structure and heating/cooling rate dependent. The activation energy of crystallization E c was determined.

Improved thermal stability and intense blue upconversion in Yb3+/Nd3+/Tm3+ tri-doped tellurite glasses

New Yb3+/Nd3+/Tm3+ tri-doped tellurite glasses (TeO2–Bi2O3–ZnO–Na2O) with improved thermal stability and intense blue upconversion emission were prepared by melt-quenching technique. The thermal stability and blue upconversion of glass samples were investigated by means of differential scanning calorimeter (DSC) and fluorescent spectrophotometer measurements. DSC results show that the prepared tellurite glasses have favorable thermal stability for fiber drawing and the difference (ΔT) between the estimated crystallization onset temperature (Tx) and the transition temperature (Tg) reaches about 186°C, which is larger than that of some other tellurite glass hosts. Under the excitation of 980nm laser diode (LD), the tri-doped glass samples exhibit an intense blue (~474, 485nm) upconversion emission, which is attributed to the simultaneous contributions from Tm3+:1G4→3H6 and Nd3+:2G9/2→4I9/2 transitions, and the possible upconversion luminescent mechanism based on the energy transfers from Yb3+ is presented. The above results indicate that the new synthesized Yb3+/Nd3+/Tm3+ tri-doped tellurite glass is a promising candidate applied for the blue solid-state lasers.

Synthesis of polyethylene/polyester copolymers through main chain exchange reactions via olefin metathesis

The synthesis and characterization of linear polyethylene/polyester copolymers produced by olefin cross metathesis and subsequent catalytic hydrogenation are described. The success of the scrambling reaction between 1,4-polybutadiene and unsaturated polyester via olefin cross metathesis was confirmed by 1H NMR. Differential scanning calorimetric (DSC) measurements indicated that the size of the copolymer blocks varied gradually with the exchange ratio. Catalytic hydrogenation of the unsaturated copolymers with different exchange ratios was carried out using Pd–Al2O3. The crystallinity of the resulting hydrogenated polymers depended on the exchange ratios achieved during olefin cross metathesis. This suggests that the unique sequential structure imparted to the unsaturated polymers during metathesis was retained during the hydrogenation process.

Mechanical, thermal, and flame-retardant performance of polyamide 11–halloysite nanotube nanocomposites

This study focused on the influence of different filler loadings on the elongation at break and flammability properties of the PA11/FR/HNTs nanocomposites. Polyamide 11 (PA11)/flame-retardant (FR) additives/halloysite nanotubes (HNTs) nanocomposites were melt compounded via twin-screw extrusion for all the compositions. Three FR additive loadings (15, 20, and 25 wt%) and three HNTs loadings (2.5, 5, and 10 wt%) were selected. The formula with 25 % FR and 2.5 % HNT had the lowest additives content and the highest elongation at break of 10.22 % among all UL-94 V-0 rated formulas. A homogeneous dispersion of HNTs in PA11 matrix was observed by transmission electron microscopy. Differential scanning calorimeter measurements indicated that HNTs behaved as nucleating agents by accelerating the rate of crystallization, thus increasing crystallization temperature. The young’s modulus of the PA11 nanocomposites was enhanced with the addition of HNTs. Micro-scale combustion calorimeter results demonstrated that the addition of HNTs also decreased the peak heat release rate of the nanocomposites. These results indicate the effectiveness of HNTs on the mechanical, thermal, and flame-retardant performance of PA11/FR/HNTs nanocomposites.

Determination of the PCM melting temperature range using DSC

The melting temperature range is one of the most important parameters for phase change material (PCM), it affects the PCM application areas and the performance of the system integrated with PCM. The melting temperature range of PCM is usually measured by a differential scanning calorimeter (DSC) with the dynamic measurement method. Unfortunately, the measurement results with this method are dependent of the heating rate. Determination of the melting temperature range of PCM means to find the starting melting temperature at which PCM starts melting and the ending melting temperature at which the melting process is finished. In this paper, a new DSC measurement method, which is the partially-melted DSC measurement method, was proposed to determine the ending melting temperature of PCM. With this method, the actual ending melting temperature of the sample PCM was found out and it was independent of the heating rate. Because there was no clear boundary between the non-melted state and the partially-melted state, the actual starting melting temperature of PCM was not able to be determined accurately.

Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior

Reactive air brazing (RAB) is a promising and economic method for joining ceramic to metal as well as ceramic to ceramic. Hybrid joints gain importance in the field of challenging applications such as gas separation or solid oxide fuel cells. While the ceramic partner is often directly chosen due to its functionality, the metallic partner needs to be chosen carefully in order to avoid high residual stresses due to the differences in the thermal expansion coefficients. This leads to the restriction of the usage of a significant number of potential joining partners. Ceramic/metals components with unadapted thermal expansion behavior (Ba0.5Sr0.5Co0.8Fe0.2O3–δ/Crofer 22 H and 3YSZ/AISI 314) were joined by RAB. Cu‐containing as well as Cu‐free Ag‐based filler metals were used. Analysis of the cross‐section of brazed samples showed that the microstructure of the samples depends especially on the used filler metal. The melting process as well as the exothermic reactions leading to a distinct reaction zone could be observed in the differential scanning calorimetric measurements. While the microstructure of the joints is not significantly influenced by the base material, the strength of the BSCF/Crofer 22 H specimens is nearly four times lower than the strength of the specimens with the adapted thermal expansion coefficients (BSCF/AISI 314 and 3YSZ/Crofer 22 H). The reasons are residual stresses caused by the different thermal expansion coefficients. Finite element simulations assuming a visco‐plastic material model show that an amount of stress can be reduced by relaxation within the silver based braze. But the volume of the high residual stresses is still larger in the BSCF/Crofer 22 H joints than that of the BSCF/AISI 314 joint resulting in a lower fracture strength.

High tensile strength fiber of poly[(R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyhexanoate] processed by two‐step drawing with intermediate annealing

ABSTRACTHigh tensile strength fibers of poly[(R)‐3‐hydroxybutyrate‐co‐(R)‐3‐hydroxyhexanoate] [P(3HB‐co‐3HH)], a type of microbial polyesters, were processed by one‐step and two‐step cold‐drawn method with intermediate annealing. Thermal degradation behaviors were characterized by differential scanning calorimeter and gel permeation chromatography measurements. Thermal analyses were revealed that molecular weights decreased drastically within melting time at a few minute. One‐step cold‐drawn fiber with drawing ratio of 10 showed tensile strength of 281 MPa, while tensile strength of as‐spun fiber was 78 MPa. When two‐step drawing was applied for P(3HB‐co‐3HH) fibers, the tensile strength was led to 420 MPa. Furthermore, the optimization of intermediate annealing condition leads to enhance the tensile strength at 552 MPa of P(3HB‐co‐3HH) fiber. Wide‐angel X‐ray diffraction measurements of these fibers suggest that the fibers with high tensile strength include much amount of the planer‐zigzag conformation (β‐form) as molecular conformation together with 21 helix conformation (α‐form). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41258.

Lanthanum doping effect in barium strontium titanate glass ceramics

Lanthanum doping effect in barium strontium titanate (Ba,Sr)TiO3 (BST) glass ceramics has been investigated by differential scanning calorimeter (DSC), X-ray diffractometry and Raman spectroscopy. Studies were performed on specimens with lanthanum oxide (La2O3) concentrations between 0 and 1.0mol% for BaO–SrO–TiO2–SiO2–Al2O3 glass system. The analysis of the dependence of DSC measurements on La2O3 concentration has shown that the increase of La2O3 concentration promotes the formation of the barium strontium titanate crystalline phase. The X-ray diffractometry results have demonstrated that the amount of barium strontium titanate crystalline phase increases and then decreases with the increase of the La2O3 concentration. The Raman spectrum results, which coincide with the X-ray diffractometry patterns, confirmed that lanthanum ions diffused into the lattice structure and modified the tetragonality of the barium strontium titanate phase. However, the additive of 1.0mol% La2O3 may go beyond the solid solubility limit of lanthanum in the BST lattice.

Tetrakis(phthalocyaninato) terbium–cadmium quadruple-decker liquid crystals with good semiconducting properties

Neutral and mono-oxidized states of novel sandwich-type tetrakis[2,3,9,10,16,17,23,24-octa(dodecanoyloxy)phthalocyaninato] terbium–cadmium quadruple-decker complex {[Pc(OC12H25)8]Tb[Pc(OC12H25)8]Cd[Pc(OC12H25)8]Tb[Pc(OC12H25)8]} (1) and {[Pc(OC12H25)8]Tb[Pc(OC12H25)8]Cd[Pc(OC12H25)8]Tb[Pc(OC12H25)8]}·SbCl6 (2) were synthesized and spectroscopically characterized. Polarized optical microscope (POM) together with differential scanning calorimeter (DSC) measurement revealed their similar two rectangular columnar mesophases over a relatively lower temperature range and higher temperature range, respectively, within their wide liquid crystal temperature range of 19–266°C for 1 and 4–249°C for 2. Temperature-dependent X-ray diffraction (XRD) analysis result disclosed the slight difference in terms of the neighboring quadruple-decker π–π stacking between these two mesophases, which in turn accounts for their electric conducting behavior along with the change in temperature. In addition, due to the ionic conductive nature, the mono-oxidized liquid crystals of 2 display more than 2 order of magnitude higher electric conductivity than that for 1, with the highest value 4.1×10−4Scm−1 achieved at 140°C.

Hydrogen storage properties and thermal stability of V35Ti20Cr45 alloy by heat treatment

The crystal structure, microstructure, hydrogen storage properties and thermal stability of the as-cast and annealed V35Ti20Cr45 alloys prepared by arc-melting were studied in this work. It was confirmed that the as-cast alloy is a body-centered cubic (bcc) single phase, while it consists of bcc main phase and C14-typed Laves secondary phase after annealed at 973 K for 72 h. As a result of the microstructure change, the activation performance and kinetic properties of the annealed alloy are improved greatly due to the catalysis of C14-typed Laves secondary phase in the annealed alloy. The kinetic mechanism of hydrogen absorption/desorption processes in the as-cast and annealed alloys was discussed using the Johnson-Mehl-Avrami (JMA) equation. Based on the plateau pressure data from pressure-composition-temperature (PCT) measurements with the Van't Hoff equation, the calculated formation enthalpies of the hydride formed in the as-cast and annealed alloys indicate that heat treatment results in lower thermal stability of the hydride in the as-cast alloy. Furthermore, using the Kissinger method with the peak temperatures from differential scanning calorimeter (DSC) measurements at different heating rates, the calculated activation energies of the dehydrogenation in the as-cast and annealed alloys suggest that heat treatment is very beneficial to improve hydrogen absorption/desorption capacities in the alloy.

Study on the Properties of Multi-Extruded Recycled PE and PP

This paper mainly describes the changes of properties of low density polyethylene and polypropylene after multiple processing. Melt flow index (MFI) analysis, thermal gravimetric analysis (TGA) ,differential scanning calorimeter (DSC) and mechanical properties measurements were used to characterize the thermal stabilities, processability, mechanical properties of virgin and recycled PE and PP. The results indicated that MFI of PE decreased with increasing the number of processing cycles whereas the opposite trend applies to PP. The thermal degradation temperature of the 6th extrudates decreased slightly in comparison with virgin ones. An amorphous region of recycled PE was observed by DSC. The mechanical properties of extruded materials were also affected due to the thermal mechanical degradation.

Synthesis, Characterization, and Thermal Properties of Organic–Inorganic Hybrids Based on Gelatin and Organomodified Silicones

ABSTRACTThe synthesis of organic–inorganic hybrids is an interesting approach as it offers the possibility of combining the advantages of organic polymer (elasticity, formability) and inorganic material (hardness, strength, high chemical resistance, and thermal stability). Gelatin–siloxane hybrid materials were prepared in the reaction of gelatin and organomodified silicones containing epoxy‐ and both epoxy‐ as well as fluoroalkyl groups. The hybrids obtained were characterized using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, and scanning electron microscopic analysis. Thermal properties of the samples were evaluated by means of thermogravimetric analysis and differential scanning calorimetric measurements, showing the influence of type and amount of organosilicon compound on thermal properties of the hybrid materials. The samples obtained with siloxane containing fluoroalkyl groups as well as with mixed siloxanes revealed higher thermal stability than unmodified gelatin. Glass transition temperatures of the hybrids occurred at lower values than for gelatin, exhibiting the plasticizing effect of the applied siloxanes. Enthalpy values of the hybrids decreased, indicating the changes in the helical structure of gelatin caused by the introduction of siloxane.

Preparation and characterization of the AP/Al/Fe2O3 ternary nano-thermites

A novel ammonium perchlorate (AP)/aluminum (Al)/iron oxide (Fe2O3) nano-thermites was prepared by orderly using sol–gel, wet impregnation, and solvent-anti-solvent processes. Samples prepared in this work were characterized by scanning electron microscope (SEM), nitrogen adsorption–desorption tests, X-ray diffraction (XRD), and differential scanning calorimetric (DSC) measurements. The results showed that AP and nano-aluminum were dispersed in the pores of the iron oxide gel, resulting in a large specific surface area (84.7 m2 g−1). The XRD results showed that AP dispersed homogeneously in the energetic composites at nano-scale. DSC analyses indicate that the Al/Fe2O3 nano-thermites played a catalytic role in the thermal decomposition of AP, thus the interaction of thermite reaction was greatly enhanced by accelerated decomposition of AP. The experimental results showed that the as-prepared AP/Al/Fe2O3 nano-thermites were of high energy, making it a competitive candidate material in the field of micro-propellants.

L‐carvone‐loaded nanofibrous membrane as a fragrance delivery system: fabrication, characterization and in vitro study

ABSTRACTThe present work reports the fabrication of a fragrance delivery system using nanofibres by an electrospinning method. Fragrant oils are volatile essential oils that easily undergo degradation and evaporation. Nanostructured fibres of poly(vinyl alcohol) (PVA) and poly(ε‐caprolactone) (PCL) were prepared by an electrospinning process. In this study, l‐carvone was used as a model fragrant oil, and it can be used as an air‐freshening agent. l‐carvone (5 wt%) loaded PVA solution (10 wt%) (C‐PVA) and PCL solution (13 wt%) (C‐PCL) were electrospun into nanofibres. The scanning electron microscopy (SEM) images showed that the incorporation of essential oil l‐carvone in PVA and PCL solution caused the resulting as‐spun fibre to be non‐uniform, and the average diameter was found to increase from 100–190 nm to 230–400 nm for the PVA mat and from 300–500 nm to 390–800 nm for the PCL mat. The functional group, crystallinity and thermal stability of prepared electrospun nanofibres were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) measurements. The degree of crystallinity of electrospun PVA, C‐PVA, PCL and C‐PCL was found to be 10.46%, 7.4%, 56.16% and 53.41% respectively. The in vitro release of l‐carvone from the prepared electrospun fibres was conducted at 30 ± 0.2°C for 24 h by both the encapsulation and imbibition methods. The maximum release of l‐carvone (5 wt%) was observed to be 61% and 64.1% from PVA nanofibres and 36% and 48.4% from PCL nanofibres by the encapsulation and imbibition methods respectively. These results show the potential of the prepared electrospun l‐carvone‐loaded PVA and PCL nanofibrous membrane in the fragrance delivery system. Copyright © 2014 John Wiley & Sons, Ltd.

A polymer-based MEMS differential scanning calorimeter

We present a flexible, polymer-based MEMS differential scanning calorimetric (DSC) device integrating highly sensitive thermoelectric sensing, real-time temperature monitoring and microfluidic sample and reagent handling for the thermodynamic characterization of biomolecules with minimized sample consumption. The device, based on an inexpensive, commercially available polymer substrate, consists of a pair of calorimetric microchannels that are integrated with resistive temperature sensors and heaters as well as an antimony–bismuth (Sb–Bi) thermopile. For DSC measurements, the two channels are filled respectively with a biomolecular sample and a reference solution, whose temperatures, measured in situ using the resistive temperature sensors, are varied at a constant rate using closed-loop temperature control. The difference in the thermal power between the sample and reference induces a temperature difference, which is measured using the thermopile for thermodynamic characterization of the biomolecules. We demonstrate the utility of this MEMS DSC device by measuring the unfolding of lysozyme in a small volume (1μL), and at practically useful protein concentrations (5mg/mL). Thermodynamic properties of lysozyme, such as the molar enthalpy change and melting temperature at different lysozyme concentrations, have been obtained and found to agree with published data.