Search Results
Thermal analysis techniques, DSC and TG can advantageously be used in quality control of drug products.
Abstract
DSC measurements were carried out for [Ni(H2O)6](ClO4)2 (sampleH) and [Ni(D2O)6](ClO4)2 (sampleD) in the temperature range 300–380 K. For both compounds two anomalies on the DSC curves were detected. The results for sampleH are compared to those previously obtained using adiabatic calorimetry method. For both compounds studied in this work the high-temperature transition appears at the same temperature while the low-temperature one is shifted towards higher temperatures in sampleD. Disorder connected with H2O or D2O groups is suggested in the intermediate phase between the low- and high-temperature transitions.
Abstract
Vermiculite was prepared to react with aliphatic diamines (ethylene-, trimethylene-, tetramethylene- and hexamethylene-) diamine. The products were characterized by elemental analysis, infrared spectroscopy and X-ray diffraction. The amounts of diamines adsorbed were 0.89, 0.86, 0.79 and 0.68 mmol g–1, respectively for NH2(CH2)⋅nNH2 where n=2, 3, 4, 6. The basal spacings of the intercalated vermiculites varied between 1300 and 1470 pm. Thermogravimetry and DSC data confirmed intercalation of diamines in gallery space of vermiculite.
Abstract
Human serum albumin unfolding in ethanol/water mixtures was studied by use of differential scanning calorimetry. Ethanol-induced changes in DSC curves of defatted and non-defatted albumin were markedly different. In the presence of ethanol, bimodal denaturation transition for fatty acid free albumin was observed while that for albumin containing endogenous fatty acids was single and more sharpen than in aqueous solution. Ethanol was found to decrease the thermal stability of albumin due to the binding to the unfolded state to a higher degree than to the native state, thus favouring unfolding. The binding with different affinities has been suggested depending on ethanol concentration range.
Abstract
Differential scanning calorimetry (DSC) was used to construct phase diagrams of binary mixtures of alkylcyclohexanes and to characterize metastable phases formed in the binary mixtures. The experimentally measured liquidus curves were compared to the liquidus curves calculated using ideal solution theory. The measured phase diagrams of pentadecylcyclohexane/nonadecylcyclohexane and octadecylcyclohexane/nonadecylcyclohexane binary mixtures are consistent with theoretical phase diagrams constructed based on the assumption that these mixtures form eutectic systems. It was also observed that a metastable phase formed in some binary mixtures of pentadecylcyclohexane/nonadecylcyclohexane under fast cooling conditions. It is hypothesized that this metastable phase recrystallizes into the eutectic phase upon heating.
Summary
The potential of DSC in suggesting modifications of thermal treatments of Al alloys to increase mechanical properties is described. Significant results can be obtained from calorimetric evolution after a series of annealings, even without a direct observation of the microstructure. The role of a reference baseline is discussed. The Guinier-Preston (GP) zones formation, dissolution or transformation is followed, and their relevance for the microhardness increase is shown, for an AlZnMg alloy of technical interest. Multi-stage thermal treatments have been confirmed to be beneficial. A secondary precipitation occurs at room temperature after annealing at temperatures at which primary precipitation is almost complete.
Abstract
The mechanism and kinetics of curing reaction of tetrafunctional epoxy resin (Ag-80)/novel diamines curing (SED) system were studied by non-isothermal and isothermal DSC. Different equivalent ratios of amine-epoxide give rise to different curing mechanisms. The main condensation reaction can be attributed to the reactions between the primary amine and epoxide and between the hydroxyl and epoxide when temperature is below 200°C, and to the reaction between the second-ary amine and epoxide when temperature is above 200°C. The corresponding apparent activation energies are 58.3 kJ·mol−1 and 99.3 kJ·mol−1 respectively. Apparent activation energies of condensation reactions between primary amine and epoxide and between hydroxyl and epoxide are just the same, which are 47.3 kJ·mol−1.
Abstract
The use of modulated temperature differential scanning calorimetry (TMDSC) and differential scanning calorimetry (DSC) in the measurement of the glass transition temperature (T g) in polymer-water systems presents several important problems. These include the presence of water evaporation endotherms, partial water evaporation during scanning, changes in pan integrity due to vapour pressure developing in the pan headspace during analysis, and possible interaction between water and polymer at high temperatures. As a result, in most of the cases, only apparent T g values can be obtained. In this study, TMDSC and DSC were used to determinate the thermal behaviour of methylmethacrylate copolymer-water systems. The samples were previously equilibrated at different relative humidities (RH) from 0 to 97% RH. Three different pan arrangements were used. In addition, thermogravimetric analysis (TG) was carried out to determine the initial amount of water in the sample. None of the pan arrangements was entirely suitable for the study of these systems. When sealed pans were used, the plastification effect of water was observed. Some evidence of degradation was also observed in which water and methylmethacrylate appeared to play roles.
The freezable water contents of samples obtained from previously chilled semimembranous muscle of middle-aged beef carcasses after a 24 h cooling period a room at in 5±1‡C were determined by differential scanning calorimetry (DSC) at −5, −10, −15, −20, −30, −40, −50 and −65‡C. This was accomplished by freezing the samples at the above-mentioned temperatures, followed by thawing to 35‡C, and measuring the melting peaks of freezable water. The areas of these peaks were determined by using the peak integration method programs through a computer linked to the DSC, and they were then used to determine the latent heat of melting (δH m) in kJ kg−1 at each freezing temperature. The resultant latent heat of melting per sample was divided by the latent heat for pure water to determine the amount of freezable water present in these samples. This amount of freezable water was divided by the total water content of the meat sample to determine the percentage of freezable water in the sample. The percentage of freezable water was subtracted from 100 to determine the percentage of bound water present in the sample.
Summary Emulsifiers are often used in the food industry to stabilize interfaces in emulsions and foams, for example. When added to an aqueous phase, emulsifiers form spontaneously self-assembly structures. Such structured fluids can be used for active ingredients encapsulation or as micro-reactors for flavour formation. In the present paper we describe the potentialities of DSC, mainly micro-DSC, to study phase transitions of emulsifiers alone and with addition of water. The main role of the calorimetric techniques will probably be to precisely determine melting and crystallization zones, to inform about polymorphism and hysteresis due to undercooling, and especially to follow the effects of guest molecules on the weak liquid crystal transitions. Micro-DSC, when compared to other techniques, generally allows measurements over an extended temperature range.
