Papers by Keyword: Differential Scanning Calorimetry (DSC)

Abstract: The Mg-Zn-Y system attracts interest of researchers due to the formation of quasicrystalline particles which are believed to improve mechanical properties of Mg-based alloys. In the Mg-Zn-Y-Nd-Zr alloy (WE43 modified by addition of Zn) studied here the formation of icosahedral phase (I-phase) with quasicrystalline structure competes with cubic W-phase. Grain boundary phases in Mg-Zn-Y-Nd-Zr alloys subjected to various heat treatments were characterized. It was found that the portion of the I-phase in Mg-Zn-Y-Nd-Zr alloy can be increased by a suitable heat treatment. Moreover, the solidification process is influenced by the cooling rate resulting in a striking difference in the morphology of grain boundary phases.

Abstract: Nowadays, polymeric composites reinforced with natural fibers are being considered in the civil engineering area. The use of polymeric composites to reinforce degraded timber structures can improve its behavior. Fibers with larger structural applications are glass and carbon but the use of natural fibers is an economical alternative and posses many advantages such as biodegradability, low cost and is derived from natural and renewable sources. Epoxy composite reinforced with sisal fabric was processed by resin transfer molding (RTM) at room temperature and this work studies thermal behavior and its respective mechanism of thermal decomposition. Samples of sisal fiber, epoxy resin and sisal/epoxy composite were characterized by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Thermogravimetric curves showed that sisal fibers can be used in manufacturing process where the processing temperature does not exceed 177°C and shown that the epoxy resin has the greatest stability material followed by sisal/epoxy composite.

Abstract: The 6xxx series alloys are well known for desirable combinations of high strength, weldability, corrosion resistance and formability. This paper investigates the influence of chemical composition on the solution heat treatment parameters of rheo-high pressure die cast (R-HPDC) 6xxx series aluminium alloys. The presence of copper in the 6xxx series aluminium alloys affects the solution heat treatment by promoting incipient melting. The incidence of incipient melting is investigated for the R-HPDC alloys using Differential Scanning Calorimetry (DSC) and optical microscopy. R-HPDC is known to produce surface liquid segregation and centre-line liquid segregation when processing the alloys and these areas are the most susceptible to incipient melting. The applicability of single and multiple step solution heat treatments are investigated. The alloys used for this study include the Cu-free alloy 6082, as well as the Cu-containing alloys 6013 and 6111.

Abstract: PVC insulation has extensively been used for insulating low voltage electrical cables. They offer superior insulating properties but how ageing and exposure could affect their insulation properties is a matter of concern. Chemical exposure related failure modes are known but have received only limited study. The traditional testing methods like insulation testing could only test whether the present properties are satisfactory. The application of thermal analysis methods like differential scanning calorimetry could identify the variation in thermal characteristics with respect to ageing and chemical exposure. Polluted environments may cause a direct attack upon a polymer. It has been concluded that significant changes in the behavior of insulation occurs in acidic environment that may lead to insulation failures.

Abstract: Thermally reactive materials have caused many serious accidents involving storage and transportation, due to being thermally reactive. The safe storage and management of these materials still is a critical problem in many countries. We studied the thermal hazard of thermal reactive materials, such as a propellant, by employing differential scanning calorimetry (DSC) non-isothermal tests and isothermal tests, and then comparing the kinetic parameters by isothermal and non-isothermal of kinetics, avoiding the mistaken results of the single thermal analysis model. The chosen approach was to obtain reliable kinetics of thermal decomposition by safety and effective technology by modelling method, which acquired the safety parameters of storage condition that could be applied as thermal reactive materials safer design during storage safety conditions and relevant operations.

Abstract: The effect of the presence of fillers on the thermal properties of a high performance elastomer was investigated in this work. The characterization of the specific heat capacity (C_p), the specific heat flow and the glass transition temperature of a polyurea elastomer reinforced with two different classes of fillers, i.e. short glass fibers and alumina nanoparticles, was conducted by using a differential scanning calorimeter (DSC). We present and discuss the results of the experimental characterization carried out on the reinforced material. The results are compared to those obtained by testing the pure polymer.

Abstract: Abstract.In this paper, the nonisothermal crystallization kinetics was investigated by differential scanning calorimetry for the poly(m-xylylene adipamide) (MXD6) which were prepared by polymerization in reactor. The Avrami theory modified by Jeziorny and Z.S. Mo equation were used to describe the nonisothermal crystallization kinetics. The analysis based on the Avrami theory modified by Jeziorny shows that the Avrami exponent n of MXD6 ranges from 2.3 to 3.3, Moreover, both Avrami exponent (n) were around 3.0, which probably suggests a thermal nucleation and a three-dimensional crystal growth. The good linearity of the plots indicates the successful application of Z.S. Mo method in this case.

Abstract: Free cutting alloys of Al-Cu (AA2011 and AA2111B) in T6 temper and Al-Mg-Si system (AA6023 and AA6262) in tempers T6 and T8 were subjected to Charpy U - notch impact testing at the temperatures ranging from 20°C to 350°C. The microstructure of the materials was characterized by light metallography, fracture surfaces were observed using scanning electron microscope (SEM). The alloys showed a significant decrease in the impact energy KU at temperatures ~125°C (AA2011, AA2111B), ~170°C (AA6023), and ~250°C (AA6262), respectively. This decrease of KU was caused by melting of disperse phases containing low-melting point metals (Pb, Sn, Bi), which was confirmed by differential scanning calorimetry. Additional annealing of the AA6262-T8 alloy for 2h at 400°C followed by slow cooling led to the transformation of Pb + Bi particles accompanied by the shift of the melting temperature from ~250 to ~310 °C. Higher temperature solution annealing of the AA6023 alloy for 30 min at 540°C (as a replacement of common 30 min at 520°C) resulted in a partial transformation of Sn + Bi particles accompanied by melting point shift from ~170 to ~200°C. Chemical composition of the corresponding phases was monitored by energy dispersive X-ray spectroscopy in SEM.

Abstract: The transition temperatures of small amounts of eutectic particles contained in free-cutting aluminum alloys (namely AA6262 and AA6023) are investigated in this paper. Detection of the transition temperatures by conventional differential scanning calorimetry (DSC) measurements is difficult because of the small volume fraction (~ 1wt.%) of the eutectic. On the other hand, the melting of the particles induces small changes of elastic moduli of the alloy, which can be sensitively measured by resonant acoustic methods, for example by resonant ultrasound spectroscopy (RUS). It is shown that the phase transitions of the particles correspond to well-detectable changes of the resonant spectrum, which enables a more detailed characterization of the transition process. A significant thermal hysteresis is observed between the cooling and the heating runs, and also the widths of the temperature ranges in which the transitions occur exhibit a strong melting/freezing asymmetry.

Abstract: Isothermal time-temperature-precipitation (TTP) diagrams deliver important material data like temperature and time ranges critical for precipitation. During the last years an in-situ calorimetric method to record continuous cooling precipitation diagrams has been developed to application level by our group. However, isothermal TTP-diagrams were still determined by ex-situ analyses only. In this work in-situ measurements of precipitation reactions were carried out during isothermal soaking. Therefore the whole heat treatment cycle was performed in a differential scanning calorimeter (DSC). Al-Mg-Si-alloys 6063 and 6005A were analysed. Solution annealing and overcritical quenching to several temperatures between 450 °C and 250 °C was followed by isothermal soaking. Based on the heat flow curves during isothermal soaking TTP-diagrams were determined. Further microstructure investigations by scanning electron microscopy and hardness tests after artificial ageing were performed. Both alloys show similar results. In the TTP-diagramms three so-called ”C-curves” could be observed. Every C-curve is expected to represent precipitation of a different phase. Hardness and microstructure investigations correspond with the data of the TTP-diagramms.