DSC Peak Research Articles

Thermally induced crystallization of amorphous Fe40Ni40P14B6 alloy

The crystallization mechanism and kinetics of Fe40Ni40P14B6 amorphous alloy were studied under non-isothermal conditions. Thermal stabilization of this alloy manifests in DSC through two complex peaks, corresponding to crystallization and recrystallization, respectively. The complex crystallization DSC peak was deconvoluted into individual steps corresponding to crystallization of individual phases, where the results using both Gaussian–Lorentzian cross-product and Fraser–Suzuki function were compared. It was determined that the values of kinetic triplets of the individual steps did not exhibit any significant difference, depending on the deconvolution function. Anisotropic growth was indicated to be the prevailing type of impingement for all crystallization steps. Using the calculated values of the respective kinetic triplets and the mechanisms determined from the value of Avrami exponent, distinct values of activation energies for nucleation and crystal growth for crystallization of each individual phase were calculated, showing significantly higher values for nucleation than those for crystal growth. Alloy samples treated non-isothermally in the DSC cell exhibit inhomogeneous surface morphology with highly granulated structure dependent on heating rate.

Thermal Analysis Goes With Mass Spectrometry to Evaluate the Molecular Weight of a Fluorinated Plasma Polymer

A combination of thermal analysis (differential scanning calorimetry DSC) and mass spectrometry (MS) has been proposed to estimate the molecular weight (MW) of fluorinated plasma polymers, not reachable by MS only owing to their high dispersity. A noticeable crystalline index has been previously reported for these plasma polymers leading to a detectable melting peak in DSC, itself not sensitive to dispersity. Relying on the variation of the melting temperature as a function of MW, a set of standards of various MW have been synthesized by atom transfer radical polymerization (ATRP). MW (from MS) plotted as a function of melting temperatures (from DSC) provided a calibration curve further used to estimate the MW of plasma polymers based on their own melting temperature. The comparison of the DSC thermograms of plasma polymer and another reference made by free radical polymerization (FRP) finally offered an original insight into the contributions from insoluble and soluble parts, mimicked by a FRP (branched, low MW) and a ATRP (linear, high MW) polymer respectively.

Formulation studies on ibuprofen sodium–cationic dextran conjugate: effect on tableting and dissolution characteristics of ibuprofen

The effect of electrostatic interaction between ibuprofen sodium (IbS) and cationic diethylaminoethyl dextran (Ddex), on the tableting properties and ibuprofen release from the conjugate tablet was investigated. Ibuprofen exhibits poor flow, compaction (tableting) and dissolution behavior due to its hydrophobic structure, high cohesive, adhesive and viscoelastic properties therefore it was granulated with cationic Ddex to improve its compression and dissolution characteristics. Electrostatic interaction and hydrogen bonding between IbS and Ddex was confirmed with FT-IR and DSC results showed a stepwise endothermic solid–solid structural transformation from racemic to anhydrous forms between 120 and 175 °C which melted into liquid form at 208.15 °C. The broad and diffused DSC peaks of the conjugate granules as well as the disappearance of ibuprofen melting peak provided evidence for their highly amorphous state. It was evident that Ddex improved the flowability and densification of the granules and increased the mechanical and tensile strengths of the resulting tablets as the tensile strength increased from 0.67 ± 0.0172 to 1.90 ± 0.0038 MPa with increasing Ddex concentration. Both tapping and compression processes showed that the most prominent mechanism of densification were particle slippage, rearrangement and plastic deformation while fragmentation was minimized. Ddex retarded the extent of dissolution in general, indicating potentials for controlled release formulations. Multiple release mechanisms including diffusion; anomalous transport and super case II transport were noted. It was concluded that interaction between ibuprofen sodium and Ddex produced a novel formulation with improved flowability, tableting and dissolution characteristics with potential controlled drug release characteristics dictated by Ddex concentration.

Determination of the eutectic concentration between Mn(NO3)2·6H2O and NaNO3 using the DSC peak sharpness method

While inorganic eutectic phase change materials (PCM) present the advantage of a high volumetric melting enthalpy and a high thermal stability under repeated heating/cooling cycles, there is a lack of known materials in the temperature range of 20–24 °C, interesting for building applications. The DSC peak sharpness method is employed to determine the eutectic concentration between Mn(NO3)2·6H2O and NaNO3, which is 96.5 mass% Mn(NO3)2·6H2O and 3.5 mass% NaNO3. Thereby, the DSC peak sharpness method is demonstrated to yield the same result independently of the two chosen heating/cooling rates of 0.5 and 2 K min−1. The eutectic PCM has an onset temperature of 22.1 °C and a melting enthalpy of (126 ± 6) J g−1. Even though the same eutectic concentration is obtained for both heating/cooling rates, the heating/cooling rate of 0.5 K min−1 reveals that the melting peak of Mn(NO3)2·6H2O is composed of two overlapping melting peaks. The second melting peak supposedly corresponds to the eutectic between Mn(NO3)2·6H2O and Mn(NO3)2·4H2O, which melts at a slightly lower temperature than Mn(NO3)2·6H2O (difference of −0.6 °C). This assumption is in accordance with the water content of the purchased Mn(NO3)2·6H2O measured via Karl Fischer titration being (0.66 ± 0.2) mass% too low.

Controlled Electrostatic Self-Assembly of Ibuprofen-Cationic Dextran Nanoconjugates Prepared by low Energy Green Process - a Novel Delivery Tool for Poorly Soluble Drugs.

The direct effect of electrostatic interaction between ibuprofen and cationic dextran on the system-specific physicochemical parameters and intrinsic dissolution characteristics of ibuprofen was evaluated in order to develop drug-polymer nanoconjugate as a delivery strategy for poorly soluble drugs. Amorphous ibuprofen-DEAE dextran (Ddex) nanoconjugate was prepared using a low energy, controlled amphiphile-polyelectrolyte electrostatic self-assembly technique optimized by ibuprofen critical solubility and Ddex charge screening. Physicochemical characteristics of the nanoconjugates were evaluated using FTIR, DSC, TGA, NMR and SEM relative to pure ibuprofen. The in vitro release profiles and mechanism of ibuprofen release were determined using mathematical models including zero and first order kinetics; Higuchi; Hixson-Crowell and Korsmeyer-Peppas. Electrostatic interaction between ibuprofen and Ddex was confirmed with FT-IR, (1)H NMR and (13)C NMR spectroscopy. The broad and diffused DSC peaks of the nanoconjugate as well as the disappearance of ibuprofen melting peak provided evidence for their highly amorphous state. Low concentrations of Ddex up to 1.0 × 10(-6)g/dm(3) enhanced dissolution of ibuprofen to a maximum of 81.32% beyond which retardation occurred steadily. Multiple release mechanisms including diffusion; discrete drug dissolution; anomalous transport and super case II transport were noted. Controlled assembly of ibuprofen and Ddex produced a novel formulation with potential extended drug release dictated by Ddex concentration.

Thermally induced structural transformations of a series of palladium(II) complexes with N-heteroaromatic bidentate hydrazone ligands

Thermal stability of a series of palladium(II) complexes with N-heteroaromatic bidentate hydrazone ligands was investigated using a combination of experimental measurements and DFT calculations. All complexes exhibit a reversible second-order transition around 333 K, which can be attributed to structural reorganization of the ligand molecules. Thermal degradation begins in 570–610 K temperature region, with an endothermic peak, followed by exothermic peaks in DSC. TG measurements show a well-defined mass loss corresponding to the initial degradation, while subsequent processes are poorly separated. DFT calculations suggest that the initial degradation step occurs with release of Cl, which then reacts with remaining part of the complex molecule in an exothermic process. This leads to decomposition of the ligand molecule into four fragments corresponding to ethyl chloride, carbon dioxide, methyl amine, and the fragment with the aromatic group. Mass spectrum suggests that creation of these fragments most likely corresponds to the initial degradation, after which some of these coordinate to Pd center, whose coordination sphere is left incomplete by release of Cl. TG measurement to 1123 K indicates that the final degradation product at this temperature is palladium.

Kinetics of non-isothermal decomposition of cinnamic acid

The thermal stability and kinetics of decomposition of cinnamic acid were investigated by thermogravimetry and differential scanning calorimetry at four heating rates. The activation energies of this process were calculated from analysis of TG curves by methods of Flynn-Wall-Ozawa, Doyle, Distributed Activation Energy Model, Satava-Sestak and Kissinger, respectively. There are only one stage of thermal decomposition process in TG and two endothermic peaks in DSC. For this decomposition process of cinnamic acid, E and logA[s−1] were determined to be 81.74 kJ mol−1 and 8.67, respectively. The mechanism was Mampel Power law (the reaction order, n = 1), with integral form G(α) = α (α = 0.1–0.9). Moreover, thermodynamic properties of ΔH ≠, ΔS ≠, ΔG ≠ were 77.96 kJ mol−1, −90.71 J mol−1 K−1, 119.41 kJ mol−1.

Temperature Triggered Shape Memory Effect of Transpolyisoprene-based Polymer

IntroductionPure gutta-percha (trans-1, 4-polyisoprene [TPI]) has been used extensively as a main component of gutta-percha for root canal filling. TPI has the interesting shape memory property by cross-linking, and this polymer was commercialized under the product name of SMP-2 (Kuraray Corp, Kashima, Japan). Therefore, the purpose of this study was to examine the thermal properties and the mechanism of the shape memory function of cross-linked SMP-2. MethodsThe crystalline of the TPI was observed by x-ray diffraction. The effects of temperature on shape recovery, recovery stress, and relaxation modulus (Er[5]) were measured in cross-linked cylindrical specimens of SMP-2. Differential scanning calorimetry was used to monitor thermal events. ResultsOn heating, a pronounced increase in recovery stress, a marked decrease in Er(5), and endothermic DSC peaks were observed over the same temperature range (38°–51°C) with shape recovery. On the other hand, on cooling, a pronounced decrease in recovery stress, a marked increase in Er(5), and an exothermic DSC peak were observed over the same temperature range (27°–33°C). ConclusionsThe shape memory property of TPI is derived from its crystallinity and cross-linking ability. Fixing the deformed shape and shape recovery from the deformed shape to the original shape is relatively easy to achieve by changing the temperature of SMP-2. The shape memory function of the cross-linked SMP-2 was expected to be very useful as a root canal filling material by the modification of its some thermal properties.

Kinetics of the decomposition reaction of phosphorite concentrate

Apatite is the raw material, which is mainly used in phosphate fertilizer, and part are used in yellow phosphorus, red phosphorus, and phosphoric acid in the industry. With the decrease of the high grade phosphorite lump, the agglomeration process is necessary for the phosphorite concentrate after beneficiation process. The decomposition behavior and the phase transformation are of vital importance for the agglomeration process of phosphorite. In this study, the thermal kinetic analysis method was used to study the kinetics of the decomposition of phosphorite concentrate. The phosphorite concentrate was heated under various heating rate, and the phases in the sample heated were examined by the X-ray diffraction method. It was found that the main phases in the phosphorite are fluorapatiteCa5(PO4)3F, quartz SiO2,and dolomite CaMg(CO3)2.The endothermic DSC peak corresponding to the mass loss caused by the decomposition of dolomite covers from 600?C to 850?C. The activation energy of the decomposition of dolomite, which increases with the increase in the extent of conversion, is about 71.6~123.6kJ/mol. The mechanism equation for the decomposition of dolomite agrees with the Valensi equation and G-B equation.

Mechanism for thermite reactions of aluminum/iron-oxide nanocomposites based on residue analysis

Sol-gel method was employed to combine Al and iron-oxide to form nanocomposites (nano-Al/xero-Fe2O3 and micro-Al/xero-Fe2O3). SEM, EDS and XRD analyses were used to characterize the nanocomposites and the results indicated that nano-Al and micro-Al were compactly wrapped by amorphous iron-oxide nanoparticles (about 20 nm), respectively. The iron-oxide showed the mass ratio of Fe to O as similar as that in Fe2O3. Thermal analyses were performed on two nanocomposites, and four simple mixtures (nano-Al+xero-Fe2O3, nano-Al+micro-Fe2O3, micro-Al+xero-Fe2O3, and micro-Al+micro-Fe2O3) were also analyzed. There were not apparent distinctions in the reactions of thermites fueled by nano-Al. For thermites fueled by micro-Al, the DSC peak temperatures of micro-Al/Xero-Fe2O3 were advanced by 68.1 °C and 76.8 °C compared with micro-Al+xero-Fe2O3 and micro-Al+micro-Fe2O3, respectively. Four thermites, namely, nano-Al/xero-Fe2O3, nano-Al+micro-Fe2O3, micro-Al/xero-Fe2O3, and micro-Al+micro-Fe2O3, were heated from ambient temperature to 1020 °C, during which the products at 660 °C and 1020 °C were collected and analyzed by XRD. Crystals of Fe, FeAl2O4, Fe3O4, α-Fe2O3, Al, γ-Fe2O3, Al2.667O4, FeO and α-Al2O3 were indexed in XRD patterns. For each thermite, according to the specific products, the possible equations were given. Based on the principle of the minimum free energy, the most reasonable equations were inferred from the possible reactions.

Effect of 1-substituted imidazole derivatives for the curing process of epoxy- -isocyanate composition

Abstract The kinetics of the curing process of isocyanate-epoxy materials hardened in the presence of 1- substituted imidazole derivatives was studied by the Coast-Redfern method. The extent of a conversion parameter of the curing process in two ways was calculated: DSC (peak area integration) and rheology (viscosity changes). The activation energy values were determined for epoxy-isocyanate cured in the presence of 0.5; 1.0 and 2.0 phr 1-substituted imidazole derivatives respectively. Increasing of accelerators amount results in decreasing the activation energy and other kinetic parameters.

Thermo-mechanical behavior of electrospun thermoplastic polyurethane nanofibers

Analysis of the thermo-mechanical behavior of electrospun thermoplastic polyurethane (TPU) block co-polymer nanofibers (glass transition temperature∼−50°C) is presented. Upon heating, nanofibers began to massively contract, at ∼70°C, whereas TPU cast films started to expand. Radial wide-angle X-ray scattering (WAXS) profiles of the nanofibers and the films showed no diffraction peaks related to crystals, whereas their amorphous halo had an asymmetric shape, which can be approximated by two components, associated with hard and soft segments. During heating, noticeable changes in the contribution of these components were only observed in nanofibers. These changes, which were accompanied with an endothermic DSC peak, coinciding with the start of the nanofibers contraction, can be attributed to relaxation of an oriented stretched amorphous phase created during electrospinning. Such structure relaxation becomes possible when a portion of the hard segment clusters, forming an effective physical network, is destroyed upon heating.

Non-isothermal decomposition behavior of Fluorel bonded explosives containing attractive cyclic nitramines

The thermal behavior and decomposition kinetics of Fluorel-bonded PBXs based on some attractive cyclic nitramines were explored by means of non-isothermal TG and DSC techniques. The exothermic onset temperatures on DSC curves of RDX-FL, BCHMX-FL, HMX-FL and CL-20-FL were noticed at 208.7, 235.6, 277.2 and 239.2°C with the peak maximum of 233.8, 237.4, 278.8 and 239.5°C, respectively. The corresponding heat releases are 1758, 1393, 1546 and 1893Jg−1, which are much lower than that of the pure cyclic nitramines. According to DSC peak shift, similar to Viton A, Fluorel polymer is probably not chemically compatible with BCHMX resulting in much lower thermal stability and heat of decomposition compared with pure BCHMX. It is also proved that Both Fluorel and Viton A could decrease or inhibit the autocatalytic effect occurring during liquid-state decomposition of RDX. However, opposite to Viton A, the Fluorel polymer could enhance the autocatalytic effect of BCHMX due to bad chemical compatibility. The activation energies for thermolysis of RDX-FL and CL-20-FL are found almost independent on the conversion rate (0.3<α<0.7) with the mean values of 170±3, and 206±3kJmol−1, while those of BCHMX-FL and HMX-FL are largely dependent on the conversion rate with average values of 189±4 and 117±5kJmol−1.

A New Synthesis of BaHPO&lt;sub&gt;4&lt;/sub&gt; Precipitated by BaCO&lt;sub&gt;3&lt;/sub&gt;-H&lt;sub&gt;3&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;-NaOH System at Room Temperature

Barium hydrogenphosphate, BaHPO4 was synthesized for the first time through simple and rapid method using BaCO3-H3PO4-NaOH, pH =9.0 at room temperature for 30 min. The studied BaHPO4 decomposed in a single well-defined stage via deprotonated hydrogenphosphate reactions, revealed by TG/DTG and DSC techniques. The calculated wavenumbers based on DSC peak were comparable with FTIR results, which support the breaking bonds of P-OH (HPO42-) in the deprotonated hydrogenphosphate reactions. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) for the deprotonated hydrogenphosphate reactions calculated from DSC data indicate that the deprotonated HPO42- reaction occur a lower-energy pathway and spontaneous process. The FTIR, XRD and SEM data of the studied BaHPO4 and its decomposed product Ba2P2O7 are also reported.

Depositing of Amorphous Ferri-Oxide Nanoparticles on Surfaces of Submicron Aluminum Powder

Nanoparticles with about 20nm diameter were densely coated on the surface of submicron Al via a sol-gel processing in ethanol, wherein 1,2-epoxypropane acted as a weak base to consume proton in solution. After the medium gelled, uniform network formed and aluminum particles imbedded in it. The core-shell structure and the nanoparticles were observed in SEM analysis. The EDS spectrum and the XRD pattern revealed that the cores consisted of amorphous ferri-oxide of which the mass ratio is closed to that of crystal Fe2O3. Thermal analysis was performed and the results indicated that the DSC peak point of ferri-oxide/Al nanocomposite showed 53 °C lower than that of [ferri-oxide+A simple mixture.

Properties of biodegradable poly(butylene carbonate) (PBC) composites with fumed silica nanoparticles

Biodegradable poly(butylene carbonate)/fumed silica (PBC/SiO2) nanocomposites were prepared by melt compounding. The PBC/SiO2 nanocomposites exhibited a good dispersion of aggregates of SiO2 in the PBC matrix, and an improvement in mechanical properties. Nanoparticles affect, also, the thermal properties of PBC and especially the crystallization rate, which in all nanocomposites is faster than that of pure PBC. Due to ongoing crystallization and the crystal perfection during heating process, the melting peak of PBC shifted to higher temperature when heating from amorphous state with decreasing heating rate. With increasing cooling rate, the non-isothermal crystallization exotherms became wider and shifted to lower temperature. At a given cooling rate, the crystallization peak temperature of neat PBC was lower than that of its nanocomposite. Non-isothermal crystallization kinetic procedure, the method of Ozawa, was applied to the first deconvoluted DSC peak only by processing the data related to DSC peak. The average value of Ozawa exponent m of pure PBC is 3.04, while the one of its nanocomposite is about 2.98. Moreover, the thermal stability of the nanocomposites was increased. The Td enhancement of the nanocomposite was remarkable.

Non-isothermal crystallization kinetics of polypropylene/MAP-POSS nanocomposites

Non-isothermal crystallization kinetics of polypropylene (PP)/methylacryloypropy polyhedral oligomeric silsesquioxanes (MAP-POSS) nanocomposites (PP/MAP-POSS) were investigated by DSC at various cooling rates. Jeziorny and Mo method were used to study the non-isothermal crystallization kinetics. The results show that the Jeziorny and Mo method are all successful in describing the non-isothermal crystallization kinetics of PP/MAP-POSS nanocomposites. The MAP-POSS can act a role of heterogeneous nucleation and increase the crystallization rate constant Z c and decrease crystallization half time t 1/2, and the spherulite crystal size decreases, the inter-spherulitic action or crosslinking structure each other appear at the appropriate content. The DSC peak temperature T p increase about 5 °C, t 1/2 reduce 0.21 min at 6 % content of MAP-POSS and heating rate of 10 °C/min. The MAP-POSS can also increase the mechanical property of PP/MAP-POSS nanocomposites, the tensile strength and impact strength increase from 12.97 to 19.93 MPa and from 33.2 to 52.6 kJ/m2, respectively, at 4 % content of MAP-POSS. But the spherulitic crystal becomes larger and boundaries become clearer again; the macrophase separation will occur and mechanical properties decrease when more and more MAP-POSS was added. The nanocomposite has the best mechanical property at 4 % content of MAP-POSS.

Polymorphic effects at the eutectic melting in the H2O–glycine system

Solid mixtures of ice with three glycine polymorphs were heated up to the eutectic melting and the DSC has detected the eutectic temperatures of −2.8 °C for α-, −3.6 °C for β-, and −2.8 °C for γ-glycine. DSC peaks of the eutectic melting are rather strange in shape, indicating unclear processes in the solutions. Accurate DSC measurements of extremely small samples can probably provide us with the physicochemical tool for the investigation of polymorphic differences among different solutions. This may be important in relation to different bioavailability of solutions prepared from different polymorphs. Eutectic temperature of −4.7 °C in water–glycine system allows us to suggest that the unknown polymorph of glycine exists.

Control of the properties of xanthan/glucomannan mixed gels by varying xanthan fine structure

The interaction of native xanthan gum, deacetylated xanthan gum and depyruvated xanthan gum with konjac glucomannan has been studied using DSC and controlled stress rheometry. In the absence of electrolyte the DSC cooling curves for native xanthan and deacetylated xanthan showed a single peak and there was a corresponding sharp increase in the storage modulus indicating gel formation. It is apparent that on cooling, association of the konjac glucomannan with the native xanthan molecules is triggered by the xanthan coil–helix transition. In the presence of electrolyte, there were two DSC peaks observed. The higher temperature DSC peak was attributed to the xanthan coil–helix transition while the lower temperature DSC peak was attributed to konjac glucomannan–xanthan association as noted by an increase in the storage modulus. The gels formed were much weaker than those in the absence of electrolyte. The DSC cooling curves for depyruvated xanthan in the absence of electrolyte showed two peaks. The higher temperature peak was attributed to the coil–helix transition while the lower temperature peak corresponded to gelation as noted by an increase in the storage modulus. The gels were very much weaker than for native xanthan gum and deacetylated xanthan gum.

An investigation on solid-state pyrolytic decomposition of barium trihemiaquatris(oxalato)lanthanate(III)decahydrate using TG–DTA in air and DSC in nitrogen

A heterobimetallic oxalate coordination compound, barium(II)trihemiaquatris(oxalato)lanthanate(III)decahydrate, has been synthesized and characterized by elemental analysis, IR and electronic spectral studies. Crystalline nature of the compound with orthorhombic symmetry is corroborated from powder X-ray diffraction studies. The solid-state pyrolytic decomposition studies (TG, DTG and DTA) in air showed that the compound decomposed mainly to BaO, La2O3 and BaLa2O4 along with carbides of both the metal at ca. 1,000 °C through a number of intermediate steps. The DSC studies in nitrogen up to 670 °C found that the compound crumbled through several endothermic and one exothermic processes. The kinetic parameters, E*, lnk o, ΔH # and ΔS # of dehydration and decomposition steps in nitrogen are evaluated from DSC peaks and discussed.