Search Results
Abstract
The effect of sterilisation by irradiation has been studied for the seven most often used in medicine derivatives of 1,4-dihydropyridine (nifedipine, nisoldipine, nicardipine, nitrendipine, nimodipine, felodipine and amlodipine). The sterilisation was performed for the compounds in the solid phase with an electron beam of the energy 10 MeV, at room temperature, using the irradiation doses from 20 to 400 kGy. The effects of the irradiation were studied by the methods SEM, DSC, XRD and TLC. The sterilisation with doses 20-100 kGy was found to cause no changes in the physico-chemical properties of the compounds, while the irradiation with higher doses (200-400 kGy) was found to induce changes in the colour, DSC spectrum and TLC picture. As follows from the TLC results, the main product of radiolysis of the compounds studied was a pyridine nitrozoderivative, which indicates the same mechanism of decomposition as in the process of photodegradation. The results prove that the 1,4-dihydropyridine derivatives being highly sensitive to visible and UV radiation are generally resistant to ionising radiation and thus can be subjected to sterilisation by irradiation.
Abstract
The rate of pyrolysis and oxidation of 8 different samples of oil shale kerogen concentrate (KC) were investigated using DSC analysis. Recently performed thermogravimetric studies (TG and DTG) with the same samples of KC indicated that the activation energy of the pyrolysis of specific KCs increases with increasing paraffinic structure in the KC. An opposite effect, i.e. a decrease of the activation energy with an increase of paraffinic structure was determined in the case of KC oxidation. In this study, using the standard ASTM E-698 method based on the determined temperature at which the maximum heat effect could be observed (exo in the case of oxidation and endo in the case of pyrolysis), an activation energy for the pyrolysis, as well as for the oxidation process was determined and also successfully correlated with the content of paraffinic structure of KC. Thus, the higher content of paraffinic structure in KCs indicates that higher values of the activation energy could be determined either in the case of pyrolysis or oxidation followed by DSC analysis.
Abstract
A review is made about the different kinds of water in surfactant-based microstructures (liquid crystals, microemulsions and micelles) and their study by DSC.
Abstract
This research was aimed to investigate the combustion and kinetics of oil shale samples (Mengen and Himmetoğlu) by differential scanning calorimetry (DSC). Experiments were performed in air atmosphere up to 600�C at five different heating rates. The DSC curves clearly demonstrate distinct reaction regions in the oil shale samples studied. Reaction intervals, peak and burn-out temperatures of the oil shale samples are also determined. Arrhenius kinetic method was used to analyze the DSC data and it was observed that the activation energies of the samples are varied in the range of 22.4–127.3 kJ mol−1 depending on the oil shale type and heating rate.
Abstract
Results of high thermal resolution microcalorimetric and dilatometric measurements performed on reducer — polytetrafluoroethylene (M-PTFE) pyrotechnic compositions have been discussed. The materials were selected for the study because of their behaviour in combustion tests. Two complementary thermal properties, i.e. the specific heat and coefficient of linear thermal expansion (CLTE), have been analysed in detail. The specific heat was obtained from DSC measurements performed from −20 to 375C. Measurements of CLTE and linear expansion were carried out from −40 to 270C. In both cases the measurements were performed on thermocycling with the high thermal resolution preserved. A special attention has been paid to a two-stage phase transition occurring just below the room temperature.
Abstract
In the present study, the effect of primary processing route on the dissolution and precipitation reactions in a commercial Al−Si alloy (designated as A390) is investigated using differential scanning calorimetry (DSC). The Al−Si alloy selected for the present investigation was processed using conventional casting and spray atomization and deposition routes. The results of differential scanning calorimetry conducted on the as-processed samples indicated no significant dissolution reaction for the as-cast A390 alloy when compared to the similar results obtained for as-spray atomized and deposited samples. However, the thermal analysis conducted on the solutionized cast and spray deposited samples exhibited no significant difference in the kinetics of precipitation reactions. The results of the differential thermal analyses were finally rationalized in terms of observed microstructural features.
Abstract
A DSC study has been carried out on isomalt, a commercial sugar alcohol derived from sucrose and widely used as a sweetener in the food industry. Isomalt is a mixture of two isomers:α-D-glucopyranosyl–1-6-mannitol (GPM) and α-D-glucopyranosyl–1-6-sorbitol (GPS). Release of the water of crystallisation (around 100C)and melting (around 150C) have been phenomenologically characterised using different scanning rates and heat treatments. The effect of dehydration/re-hydration on the melting has been investigated. The isomalt glass transition, at about 60C, was studied on samples cooled after melting. The dynamic aspect of structural relaxation of isomalt has been quantified by its fragility parameter. Glassy state stability has been evaluated by performing ageing experiments at sub-T g temperatures. During ageing, apart from the expected enthalpy relaxation effects, isomalt showed a peculiar behaviour, due to its isomeric composition. These preliminary and phenomenological results have been interpreted in terms of isomer structure and of carbohydrate-water interactions in the mixture.
Abstract
Tert-butyl peroxybenzoate (TBPB) is one of the sensitive and hazardous chemicals which have been popularly employed in petrifaction industries in the past. This study attempted to elucidate its unsafe characteristics and thermally sensitive structure so as to help prevent runaway reactions, fires or explosions in the process environment. We employed differential scanning calorimetry (DSC) to assess the kinetic parameters (such as exothermic onset temperature (T 0), heat of reaction (ΔH), frequency factor (A)), and the other safety parameters using four different scanning rates (1, 2, 4 and 10°C min−1) combined with curve-fitting method. The results indicated that TBPB becomes very dangerous during decomposition reactions; the onset temperature and reaction heat were about 100°C and 1300 J g−1, respectively. Through this study, TBPB accidents could be reduced to an accepted level with safety parameters under control. According to the findings in the study and the concept of inherent safety, TBPB runaway reactions could be thoroughly prevented in the relevant plants.
Abstract
The effect of the deformation temperature on the energy stored in post-yield deformed poly(butylene terephthalate) PBT, was studied by means of DSC tests. Deformed specimens were rapidly cooled after unloading, in order to avoid the energy relaxation processes occurring before the DSC measurements. Cooling revealed to have a significant contribution on the whole stored energy, as shown by DSC tests conducted on undeformed PBT specimens conditioned at various temperatures. This work is aimed at separating the effects due to cooling and those ascribed to deformation on the energy storage and release processes, permitting to better understand previous findings on post-yield compressed PBT.
Abstract
PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition is studied by MDSC which allows to access the glass transition temperature T g and the variations of ΔC p=C p1−C pg (difference between thermal capacity in the liquid-like and glassy states at T=T g). Variations of T g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed with regard to the structure engaged in these materials. The increments of ΔC p at T g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’ of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase.
