Papers by Keyword: DSC

Abstract: Identification of critical temperatures is paramount for semisolid processing. Application of the principles of differential calculus to identify these temperatures on semisolid transformation curves allows the semisolid metal (SSM) processing window to be determined. This paper synthesizes and organizes a methodology that can be used to this end, namely the differentiation method (DM). Examples are given of the application of the method to 356, 355, and 319 aluminum alloys, which are commonly used in SSM processing, and the results are compared with those of numerical simulations performed with Thermo-Calc^® (under the Scheil condition). The DM is applied to experimental differential scanning calorimetry (DSC) heat-flow data for cooling and heating cycles under different kinetic conditions (5, 10, 15, 20, and 25 °C/min). The findings indicate that the DM is an efficient tool for identifying critical points such as the solidus, liquidus, and knee as well as tertiary transformations. The results obtained using the method agree well with those obtained using traditional techniques. The method is operator-independent as it uses well-defined mathematical/graphical criteria to identify critical points. Furthermore, the DM identifies an SSM processing window defined in terms of a higher and lower temperature for rheocasting or thixoforming operations (T_SSML and T_SSMH) between which the sensitivity is less than 0.03 °C^-1 and, consequently, the process is highly controllable. This DM has already been published in a partial and dispersed way in different works in the past and the aim here is to present it in a more cohesive and didactic way, synthesizing the presented data and comparing them.

Abstract: Compatibility investigation was performed between stearate lubricants (sodium stearate and magnesium stearate) and acidic pharmaceutical compounds (ibuprofen, indomethacin and valproic acid) and citric acid as acidic pharmaceutical excipient using differential scanning calorimetry (DSC). Alteration in DSC thermogram was found in all mixtures. There was a presence of melting endothermic peak of stearic acid in all mixtures (except that of stearate lubricants and indomethacin) indicating breakage of salt form of stearate lubricants depended on the physicochemical properties of drug compounds and pharmaceutical excipient. Therefore, the avoidance for using stearate lubricants with acidic pharmaceutical compounds and excipient should be concerned in development of pharmaceutical formulations.

Abstract: Elements of high purity (99.999) ,were used to prepare the alloy , Bi ,Sn,Zn and Cu .Two types alloy Bi – Sn – Zn and Bi – Sn – Cu were prepared by mechanical alloying technique (MA) .Annealing at 100 °Cfor 8 hours was applied for the resulting alloys . X-ray diffraction and differential scanning colorimetriy were tested for the two types of alloy before and after annealing. The best results was noticed in the ternary alloythat prepared at 4 hours milling time ,and annelid at 100 °C, for 8 hours ,under static air.

Abstract: Micro-fibrillated celluloses (MFCs) are made from oil palm empty fruit bunches (EFB). EFB is processed through several stages of the process, including washing, alkalization, and bleaching to remove impurities, lignin, and hemicellulose. Each treatment stage was characterized by differential scanning calorimeter (DSC) and thermogravimetric (TGA) analysis. Morphological analysis was characterized using Scanning Electron Microscope (SEM). The process results show that MFC has an average length and thickness of 450 and 80 microns for coarse fibers respectively, averaging 50 and 5 microns for fine fibers, respectively. Fibrillation fibers appear on the surface of fibers which are treated using alkalization and bleaching processes. The TGA results showed a decrease in weight occurred at a temperature of 40 to 109 °C for the first stage of the heating process and at a temperature of 247 to 382 °C for the second stage. The decrease in fiber weight is caused by evaporation of water content and degradation of cellulose compounds at each stage. The glass transition temperature of MFC was obtained at 236 °C. The thermal stability of cellulose from fibers treated using alkalization and bleaching processes proved the formation of cellulose crystals. Removal of lignin and hemicellulose is shown by the absorption of O-H and C-C bonds in FTIR spectroscopy. From these results, it is stated that micro-fibrillation cellulose is formed well through a series of processes given.

Abstract: Differential scanning calorimetry (DSC) was used to study non-isothermal kinetics of α→β transformation of Zr-0.5wt%Sn-0.15wt%Nb-0.5wt%Fe-0.25wt%V alloy. The DSC curves were measured from room temperature to 1030 °C at the heating rate of 15, 20, 30, 50°C /min respectively. The Flynn-Wall-Ozawa (FWO) method was used to get the activation energy (E) of α→β transformation at different conversion ratios. Then the values of activation energy obtained were modified by Ozawa iterative equation. The kinetic mechanism functions of α→β transformation were investigated by Criado-Ortega methods. The results show that the activation energy is related to conversion ratios. It means α→β transformation is not a simple one-step reaction but a complex multi-step reaction. The most probable kinetic mechanism functions are different in different temperature ranges, which are -ln(1-x) for ≤830 °C, [-ln(1-x)]^1/2 for 834~848 °C, [-ln(1-x)]^2/5for 850~856 °C and [-ln(1-x)]^1/3 for 858~868 °C respectively.

Abstract: The positive effect of Sc,Zr-addition on mechanical properties in Al-based alloys preferred for automotive manufacture to produce lightweight vehicles is generally known. Microstructure, mechanical, electrical and thermal properties of the conventionally cast and homogenized (475 °C/60 min) Al-5.4wt.%Zn-3.1wt.%Mg-1.5wt.%Cu (7075) and Al-5.2wt.%Zn-3.0wt.%Mg-1.4wt.%Cu-0.2wt.%Sc-0.1wt.%Zr (7075-ScZr) alloys during isochronal annealing were characterized. Precipitation reactions were studied by microhardness, electrical resistivity and conductivity measurements, differential scanning calorimetry and positron annihilation spectroscopy. Microstructure observation by scanning and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries in the alloys. The melting of this eutectic phase was observed at ~ 481 °C for the both alloys. The distinct changes in microhardness and electrical resistivity isochronal curves as well as in heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and by formation of the metastable phase particles of the Al–Zn–Mg–Cu system. Clusters/GP zones were formed during the cooling and/or in the course of the storage at room temperature. These clusters/GP zones were formed predominantly by Mg and Zn alloying elements. Hardening effect after isochronal annealing at temperatures above ~ 300 °C reflects the Sc,Zr-addition in both states of the 7075-ScZr alloy. Probably precipitation of the T-phase (Al₂Zn₃Mg₃) and S-phase (Al₂CuMg) particles took place during the annealing. The Sc,Zr-addition does not significantly influence precipitation of the particles formed in the Al–Zn–Mg–Cu system.

Abstract: Poly (diethylene glycol) adipate diol, tolylene-2,4-diisocyanate, 1,3-bis (3',4-dicarboxylphenoxy) benzene and 1,4-bis (4'-aminophenoxy) biphenyl were used as monomers to form statistical copoly (urethane-imide) s with variable content of imide blocks (from 37 to 65% (wt)). The copolymers imide blocks on the T_g and T_m values relative content increasing effect was traced, which is associated with the phase separation of hard imide and flexible polyester blocks in the systems studied.

Abstract: The precipitation of two 6xxx (Al-Mg-Si) alloys with and without copper (Cu) and excess silicon (Si) has been investigated by using the differential scanning calorimetry (DSC), transmission electron microscopic (TEM) and X ray diffraction (XRD) analysis. The analysis of the DSC curves found that the excess Si accelerate the precipitation. The values of activation energies for each peak of DSC curves were determined by using Kissinger–Akahira–Sunose (KAS) and Boswell isoconversional methods. The alloy which has an excess Si and copper require larger activation energy for precipitation despite the acceleration of the precipitation by the excess Si. TEM observation result shows there is smaller size and higher density of precipitate in excess Si alloy than those of excess-free.

Abstract: The rolling operation consists of deforming the material by passing it between two rolls whose spacing is smaller than the initial thickness of the sample, the reduction in thickness is obtained discontinuously by successive passes in the rolling mill whose spacing between the cylinders gradually decreases. This operation can influence on the mechanical and microstructural properties of the deformed materials The effect of cold rolled on microstructural evolution and precipitation sequence in Al-Mg-Si alloy has been investigated by using optical microscopy and Differential Scanning Calorimetry (DSC) in this study. The results revealed that the distribution of the grains are elongated along the rolling direction. We also noted that insoluble coarse particles that originated during the manufacturing process of the alloy have become visible after the rolling processes. The dislocations generated by the plastic deformation during cooled rolling constitute preferential sites for the germination and the growth of the phases, which accelerates the kinetics of the precipitation.

Abstract: The n-type semiconductor SnO₂ nanoparticles were synthesised using standard route and the effect of this nanoparticle doping on structural, morphological and thermal properties of PVA-PVP polymer blend has been investigated. Pure and PVA-PVP/SnO₂ Nanocomposite films were prepared using solution casting technique. The powder X-ray diffraction result shows that the crystalline nature of the blend increases with doping level. FESEM study shows that the surface morphology of the polymer nanocomposite varies with doping level. AFM study reveals that in the nanocomposite films, the average roughness changes with dopant concentration. The DSC studies on the samples were performed from 40°C to 400°C under nitrogen atmosphere and it shows that the thermal properties of the blend changes with doping concentration.