Papers by Keyword: Differential Scanning Calorimetry (DSC)

Abstract: In order to probe CO₂-coal interactions, differential scanning calorimetry (DSC) experiment was carried out in the atmosphere of He and CO₂ with coals from Huozhou, Changzhi and Jincheng areas in Shanxi Province (classified as high-volatile bituminous coal, low-volatile bituminous coal and anthracite, respectively). It was found that, in a He atmosphere, all the three curves show no enthalpy and are almost reversible, indicating no adsorption occurs. However, in a CO₂ atmosphere, all the three curves show exothermic peaks and endothermic peaks and are irreversible, indicating, except for physical reactions, chemical reactions may also occur. It was proposed that the C atom of CO₂ accepted electrons from coal molecular, and formed an electron donor-acceptor complex (i.e., an EDA complex), in other words, chemical reactions occured, hence exothermic peaks occured. The interconnections of the active sites to other groups in coal molecular are weakened due to the formation of EDA complexes, so easily to be broken during heating, hence endothermic peaks occured. The irreversibility of the curves indicate structure change of coal, which may be influenced by two factors: a) during slow cooling, the ordering of side chains, which were expanded in high temperature, leads to a less associated structure; b) in heating process, the breakage of side chains enhances the associations of coal macromolecular, and leads to a more highly associated structure.

Abstract: As a hydrophilic polysaccharide, Mesona Blumes gum (MBG) -enables to improve the quality and retard the staling of breads. The purpose of this work was to evaluate the effect of MBG on the enhancement of the quality and the staling of wheat breads. The bakery samples were stored in a polyethylene bag for 1, 2, 3, and 4 days at 25oC. Our findings indicated that MBG can improve the parameters such as width/height ratio, specific volume and moisture content of wheat breads. The texture profiles (hardness, cohesiveness, springing, chewiness) were measured through texture profile analysis (TPA). The results of differential scanning calorimetry (DSC) and TPA revealed that MBG can retard bread staling, further prolonging its shelf life. The microstructure of bread was analyzed by the scanning electron microscopy (SEM), illustrating that MBG have the ability to enhance the gelatinization of starch with a dense, uniform and small size pore texture.

Abstract: Ti6Al4V samples were isothermally compressed using a Gleeble^(TM) 1500D thermo-mechanical simulator. Differential scanning calorimetry (DSC), microstructural analyses, and thermodynamic calculations were used to investigate the sequence of transformation of β into α or vice-versa and the presence of different phases in the compressed Ti6Al4V sample. Globular alpha phase was revealed in the isothermally compressed sample in addition to martensitic and lamellar α/β structures. The transition temperature range of β into α-phase was determined using the DSC thermograms and thermodynamic calculated diagrams. The fraction of α-phase globulized increased as the strain rate decreased from 0.01s^-1 to 10^-3s^-1, and the spheroidization of the α-phase is only possible in a specific range of deformation temperatures.

Abstract: The Ni₂FeGa Heusler alloy is synthesized by arc melting in argon atmosphere. It shows two phase microstructure, γ-phase ( disordered fcc ) and Austenite ( ordered bcc, L₂₁ ). Phase identification and microstructural characterization were carried out using XRD, SEM and TEM. Solidification at various undercoolings upto 215 °C was performed using flux undercooling technique. B₂O₃ was used as the flux that provides an inert atmosphere and isolates the molten pool from the quartz tube. The solidified microstructure of the undercooled samples were analyzed and the result indicates γ-phase to be the primary phase to form. The samples are also textured. XRD patterns indicate different texture at different undercoolings. Possible mechanisms for such changes will be discussed. The competitive nucleation mechanism can not also be ruled out as the SEM micrographs show the globular morphology of γ-phase likely due to defragmentation of primary dendrites. Thermal analysis by DSC shows incongruent melting of Ni₂FeGa Heusler alloy which strengthen the argument of poor nucleation ability of L₂₁ ordered intermetallic austenite phase as compared to primary γ-phase. Up to achieved undercooling limits, γ-phase forms as the primary phase competitively with the L₂₁ ordered phase. Studies indicate that competitive nucleation mechanism is a likely mechanism to explain the phase selection.

Abstract: The effect of copper contents on the microstructure and mechanical properties of A319 aluminium alloy in thixoformed conditions was investigated. The results showed that the addition of 1 wt. % and 2 wt. % copper to A319 alloy reduced the fraction liquid sensitivity and enlarged the working window temperature. Based on the differential scanning calorimetry (DSC) data, the curve of the fraction liquid versus temperature was constructed for each alloy, indicated the temperatures corresponded to the fraction liquid of 30% and 50%. It was found that the working window temperature for A319 alloy of 7 oC increased to 12 °C when 2 wt. % copper was added, while the sensitivity decreased from 0.027 °C^-1 to 0.016 °C^-1.The alloy feedstocks produced by cooling slope casting were thixoformed successfully at 40% fraction liquid. The thixoformed A319 alloys attained a hardness level as high as 118.2 ± 2.5 HV when 2 wt. % copper was added.

Abstract: In order to produce good functional Laser Sintering (LS) parts, it is important that the powder on the part bed surface receives a sufficient amount of power energy through the laser sintering process. The reason is that sufficient energy density is produced when the energy input increases and is applied to the part bed surface, which causes a higher temperature, and thus better melt flow. The objective of this research is to investigate the thermal properties of polymer materials used in Selective Laser Sintering (SLS) processes. In this experiment, there were five different thermoplastics powders known as polyamide 12 (PA2200), Glass Fill Polyamide (GF3200), Alumide, Duraflex and CastForm were tested using Differential Scanning Calorimetry (DSC). This outcome of this research would assist the SLS users to improve the sintering process and quality of the part surface finish.

Abstract: In situ aluminum matrix composites were fabricated through exothermic dispersive (XD) reaction from a powder mixture of Al and Cr₂O₃. The reaction mechanism was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC) analysis. When the temperature increases to around 1050K, Al can react with Cr₂O₃ to form the reinforcments Al₂O₃ particles and CrAl₄ blocks. With the increase of heating rate, DSC analysis shows that the reaction peak shifts to a higher temperature and the corresponding ignition temperature also increases. Based on DSC curves with different heating rates, the activation energy can be calculated and its value is 191.8 kJ/mol.

Abstract: The microstructure development in cold rolled electrical steel under dynamic heat treatments was subjected to investigation. Significantly distinguish types of microstructures were obtained in the investigated steels confirming the different character of grain boundary motion. Application of annealing temperature within two phase region (austenite+ferrite) leads to abnormal grain growth in silicon steels. Moreover, in the optimum temperature range, there was a particular temperature leading to the most optimal microstructure and texture[1]. The effect of Si content on the phase transition temperature of the electrical steel (0.6, 1, 2.5, 2.9 % Si) was studied by using differential scanning calorimetry (DSC) analysis. The result indicated that DSC analysis could be used to detect the shift temperature of phase transformation in the electrical steel with different Si addition. DSC have been used in thermochemical studies and as complementary to the study of phase transformation. It can be used as a compliment to optical and electron microscopy.

Abstract: Magnetic nanoparticles used in biomedicine require surface modification ensuring formation of non-toxic, biocompatible nanoparticles. Among the great variety of available biocompatible polymers, a hydrophilic polymer polyethylene glycol (PEG) that has the ability to prevent protein adsorption was chosen for coating prepared magnetite nanoparticles. The aim of this work was to use differential scanning calorimetry (DSC) for studying the adsorption of PEG of different average molecular weights and different feed weights on magnetite nanoparticles and to estimate the maximal amount of PEG adsorbed on the magnetite nanoparticles. The increasing PEG molecular weight has a tendency to the decrease in the maximal feed weight ratio of PEG to magnetite in the studied complex systems. The morphology observed by scanning electron microscopy showed that all studied systems of magnetic particles coated with PEG had almost spherical shape.

Abstract: The wide damping maximum which is reported to appear in bones, involving both cortical and cancellous parts, between around 280 K and 420 K; has been determined to be a composition of different processes taking place at different temperatures in cancellous and cortical parts. In fact, in the present work the mechanical response of cow ribs bones has been analysed by coupling mechanical spectroscopy, differential scanning calorimetry, thermogravimetry and scanning electron microscopy studies. Cancellous part develops two damping maxima at around 320 K and 350 K. Cortical part exhibits a wide maximum in damping between around 310 K and 410 K and another damping relaxation between 390 K and 410 K. The physical-chemical driving force giving rise to the above relaxation processes are discussed.